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THE MRC HYDROPOWER MITIGATION GUIDELINES

Guidelines for Hydropower Environmental Impact Mitigation and Risk Management in the Lower Mekong Mainstream and Tributaries

MRC TECHNICAL GUIDELINE SERIES Vol. 2 January 2019

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2ISSN: 2706-8439

Mekong River Commission SecretariatP.O. Box 6101, 184 Fa Ngoum Road

Unit 18, Ban Sithane Neua, Sikhottabong District, Vientiane 01000, Lao PDRTel: +856 21 263 263. Fax: +856 21 263 264

www.mrcmekong.org

© Mekong River Commission

The MRC is funded by contribution from its member countries and development partners including Australia, Belgium, European Union, Finland, France, Switzerland, Germany, Japan, Luxembourg, the Netherlands, Sweden, Switzerland, the United States and the World Bank.

The MRC Hydropower Mitigation Guidelines

MRC Technical Guideline Series Vol. 2

Guidelines for Hydropower Environmental Impact Mitigation and Risk Management in the Lower Mekong Mainstream

and Tributaries

January 2019

Copyright © Mekong River Commission 2019

First published (2019)

Some rights reserved

This work is an approved product of the Mekong River Commission and reflect the collective views of the Commission and its

member countries. While all efforts are made to present accurate information, the Mekong River Commission does not guarantee

the accuracy of the data included in this work. The boundaries, colours, denomination, and other information shown on any map

in this work do not imply any judgement on the part of the Mekong River Commission concerning the legal status of any territory

or the endorsement or acceptance of such boundaries.

Nothing herein shall constitute or be considered to be a limitation upon or waiver of the privileges and immunities of the Mekong

River Commission, all of which are specifically reserved.

This publication may be reproduced in whole or in part and in any form for educational or non-profit purposes without special

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Mekong River Commission would appreciate receiving a copy of any publication that uses this publication as a source. This

publication cannot be used for sale or for any other commercial purpose whatsoever without permission in writing from the

Mekong River Commission

The MRC Hydropower Mitigation Guidelines (Volume 2)

ISSN: 2706-8439 (Print)


Biological diversity/aquatic ecology

For bibliographic purposes, this volume may be cited as:

The MRC Hydropower Mitigation Guidelines / The Mekong River Commission/Vientiane/Lao PDR (2019)

Information on the MRC publications and digital products can be found at http://www.mrcmekong.org/publications/

Cover and insider photos: Sayan Chuenudomsavad

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Documentation and Learning Centre

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Telephone: +856-21 263 263 | E-mail: [email protected] | www.mrcmekong.org

Contents1 Description, Purpose and How to Use the Manual ........................................... 12 Hydrology and Downstream Flows – Status, Risks and Mitigation ................. 5

2.1 Basin Context – Status and Overview ........................................................................52.1.1 Introduction ....................................................................................................... 52.1.2 Stream Flows ................................................................................................... 52.1.3 Water Use and Abstraction ............................................................................... 92.1.4 Floods and Droughts ........................................................................................ 9

2.2 Risks, Impacts and Vulnerabilities..............................................................................102.3 Hydrology and Downstream Flows Mitigation Measures ..........................................192.4 Indicators and Monitoring ..........................................................................................20

3 Geomorphology and Sediments – Status, Risks and Mitigation ..................... 23

3.1 Basin Context - Status and Overview ........................................................................233.1.1 Importance of sediments and sediment transport in river systems ................. 233.1.2 Catchment geomorphology ............................................................................. 243.1.3 Sediment transport in the LMB ........................................................................ 293.1.4 Recent changes to sediment transport in the LMB ......................................... 313.1.5Otheractivitiesaffectingsedimenttransport ................................................... 333.1.6 Observed geomorphic Changes associated with Altered Sediment Delivery . 36

3.2 Risks, Impacts and Vulnerabilities .............................................................................373.2.1Annualandinter-annualflowchanges ............................................................ 383.2.2Short-termflowfluctuations ............................................................................. 393.2.3 Loss of river connectivity and creation of impoundments ................................ 403.2.4 Intra or inter-basin transfers ............................................................................ 41

3.3 IdentificationofLMBspecificgeomorphicrisksassociatedwithHPdevelopments .413.3.1 Zone 1: Chiang Saen to upstream of Vientiane .............................................. 413.3.2 Zone 2: Upstream Vientiane to Kong Chiam ................................................... 423.3.3 Zone 3: Kong Chiam to Kratie ......................................................................... 443.3.4 Zone 4: Kratie to Chaktomuk and Tonle Sap .................................................. 453.3.5 Zone 5: Delta ................................................................................................... 473.3.6 Interaction between HP impacts and other catchment developments ............ 483.3.7LMBSpecificchallengesassociatedwithsedimentmanagement .................. 48

3.4 Geomorphology and Sediments Mitigation Measures ..............................................493.4.1 Background information from the MRC Preliminary Design Guidance .......... 503.4.2 General approaches to geomorphology and sediment mitigation .................. 503.4.3 Master Plan & Feasibility ................................................................................ 533.4.4 Detailed design ............................................................................................... 593.4.5 Construction phase ......................................................................................... 733.4.6 Operational phase .......................................................................................... 74

3.5 Indicators and monitoring ..........................................................................................77

4 Water Quality – Status, Risks and Mitigation ..................................................... 81

4.1 Basin Context - Status and Overview ........................................................................814.1.1 Introduction and importance of water quality in river system .......................... 814.1.2 Water quality trends in the LMB ...................................................................... 814.1.3Changestosedimentandflowandimpactsonwaterquality ......................... 90

4.2 Risks, Impacts and Vulnerabilities .............................................................................924.2.1Annual/inter-annualflowchanges ................................................................. 934.2.2Dailyorshort-timeperiodflowchanges .......................................................... 944.2.3 Loss of river connectivity ................................................................................ 954.2.4 Conversion of river to lake ............................................................................... 964.2.6 Other risks associated with hydropower developments .................................. 98

4.3 Water Quality Mitigation Measures ...........................................................................994.3.1 General ............................................................................................................ 994.3.2 Background information from the MRC Preliminary Design Guidance .......... 994.3.3 Master Plans and feasibility ............................................................................ 1004.3.4 Detailed design ............................................................................................... 1034.3.5 Construction .................................................................................................. 1084.3.6 Operational Stage ......................................................................................... 109

4.4 Water quality indicators and monitoring ...................................................................109

5 Fisheries and Aquatic Ecology – Status, Risks and Mitigation ......................115

5.1 Basin Context – Status and Overview .......................................................................1155.1.1 Importance ological cycle .............................................................................. 1165.1.2 Importance of natural sediment transport ....................................................... 1185.1.3 Importance of connectivity / migration systems .............................................. 1195.1.4 Importance of habitats .................................................................................... 1265.1.5 Fisheries ......................................................................................................... 1305.1.6 Recent changes to species diversity and abundance .................................... 134

5.2 Risks, Impacts and Vulnerabilities ............................................................................1345.2.1Annual/interannualflowchanges .................................................................1375.2.2Short-termflowfluctuations/hydropeaking .................................................... 1385.2.3 Loss of river connectivity/ fragmentation ........................................................ 141

5.2.3.1 Blocked migration .............................................................................. 1425.2.3.2 Delay in migration .............................................................................. 1465.2.3.3 Turbine passage ................................................................................ 1475.2.3.4Spillflowpassage ............................................................................... 1475.2.3.5 Impoundments & reservoirs ............................................................... 1475.2.3.6 Sedimentation & river bed incision .................................................... 1515.2.3.7Reservoirflushing .............................................................................. 152

5.2.4 Water abstraction .......................................................................................... 1545.2.5 Water quality alterations ................................................................................. 154

5.3 Fisheries and Aquatic Ecology Mitigation Measures ................................................1585.3.1 General ........................................................................................................... 158

5.3.2 Master Plan and Feasibility ............................................................................ 1585.3.2.1 Dam siting .......................................................................................... 1585.3.2.2 Adaptation of hydropower scheme/ operation .................................. 1625.3.2.3Developmentofenvironmentalflowrules .......................................... 1635.3.2.4 Development of Water quality standards and turbidity thresholds ..... 1675.3.2.5Ecologicalconsiderationsforreservoirflushingoperations ............... 168

5.3.3 Detailed design ............................................................................................... 1695.3.3.1 Restoration of connectivity................................................................. 1695.3.3.2 Compensation of habitat loss ............................................................ 177

5.3.4 Construction ................................................................................................... 1775.3.5 Operation ........................................................................................................ 178

5.4 Indicators and Monitoring .........................................................................................178

6 Biodiversity, Wetlands and Natural Resources – Status, Risks and Mitigation ...............................................................................................................................183

6.1 Basin Context - Status and Overview .......................................................................1836.1.1 Biodiversity and Flagship Species .................................................................. 1836.1.2 Wetlands and Natural Resources ................................................................... 188

6.2 Risks, Impacts and Vulnerabilities ............................................................................1976.3 Biodiversity, Wetlands and Natural Resources Mitigation Measures ........................199

6.3.1 Overarching principles ................................................................................... 1996.3.2 Master Plan and Feasibility ............................................................................ 2006.3.3 Detailed Design .............................................................................................. 2006.3.4 Construction and Operation ........................................................................... 202

6.4 Indicators and Monitoring .........................................................................................202

7 Engineering Response to Environmental Risks ..............................................205

7.1 Overview ...................................................................................................................2057.2 MasterPlans .............................................................................................................205

7.2.1 River basin planning ....................................................................................... 2057.2.2 Project locations and layouts .......................................................................... 206

7.3 Feasibility and Detailed Design .................................................................................2087.3.1 Annual / Inter Annual Changes to Flow .......................................................... 2087.3.2Daily/short-timescalechangestoflowandwaterlevel ................................ 208

7.3.2.1 Hydropeaking..................................................................................... 2087.3.2.2 Cascades ........................................................................................... 2097.3.2.3 Re-regulating Dams ........................................................................... 2097.3.2.4 Re-regulating Ponds .......................................................................... 212

7.3.3 Loss of River Connectivity .............................................................................. 2137.3.3.1 Sediment Management...................................................................... 2137.3.3.2 Fish passage ..................................................................................... 2167.3.3.3 Low head barrages ............................................................................ 2187.3.3.4 Very low head technologies ............................................................... 222

7.3.3.5 Partial barrages ................................................................................. 2237.3.4 Impoundments ................................................................................................ 223

7.3.4.1 Water quality ...................................................................................... 2237.3.4.2 Outlet Structures ................................................................................ 2257.3.4.3 Aeration Weirs ................................................................................... 227

7.3.5 Diversion / Intra Basin Transfers ................................................................... 227

7.4 Construction .............................................................................................................2297.4.1 Site controls .................................................................................................... 2297.4.2 Construction access & material sources ........................................................ 2297.4.3 Erosion protection .......................................................................................... 2307.4.4 Re-vegetation ................................................................................................ 2307.4.5 Access restriction ........................................................................................... 231

7.5 Operation ..................................................................................................................2327.5.1 Annual / Inter Annual Changes to Flow .......................................................... 232

7.5.1.1Changestoseasonalflowpatterns.................................................... 2327.5.1.2 Cascade operations ........................................................................... 2337.5.1.3Changestofloodfrequencyandmagnitude ...................................... 235

7.5.2 Inter basin transfers ........................................................................................ 2367.5.2.1 Flood management ............................................................................ 2367.5.2.2 Hydropeaking..................................................................................... 2367.5.2.3 Impact compensation......................................................................... 236

7.5.3 Adaptive management ................................................................................... 237

7.6 Dam Safety Guidelines and Recommendations ......................................................2387.6.1 General Considerations .................................................................................. 2387.6.2 Gated Spillways .............................................................................................. 2397.6.3 Safety Plans ................................................................................................... 2407.6.4 Expert Review ................................................................................................ 241

8 Ecosystem Services – Status, Risks and Mitigation .........................................245

8.1 StatusandOverview-Conceptandclassificationofecosystemservices ...............2458.2 Valuation of Ecosystem Services at Risk in LMB ......................................................2478.3 Suggestions for improved valuation of ecosystem services for in the LMB ..............2508.4 Mitigation Recommendations and Options for Ecosystem Services .........................251

8.4.1 ESIA Mitigation versus Ecosystem Services Mitigation.................................. 2518.4.2 Mitigating impacts on ecosystem services ..................................................... 2548.4.3 Managing dependencies of development projects on ecosystem services .... 255

References for Guidelines and Manual ..............................................................................261Acknowledgement ..............................................................................................................301

List of TablesTable2.1: Hydrologyanddownstreamflows–Keyrisks,impactsandvulnerabilities. ............. 19

Table 2.2: Hydrology and Flows indicators. ................................................................................ 20

Table 3.1: Geomorphic attributes of the 5 general geomorphic zones recognised in the LMB. . 26

Table3.2. Geomorphology&sediments–Keyrisks,impactsandvulnerabilities ...................... 37

Table3.3: BypasstunnelcharacteristicsinJapanandEurope(KantoshandSumi,2010). ...... 61

Table3.4: Planning,designandmanagementconsiderationsofsedimentbypasstunnels(Sumi,2015). ......................................................................................................................... 61

Table3.5: Summary of sediment transport and geomorphic indicators as identified by ISH11(2013). ........................................................................................................................ 78

Table4.1: Presentwaterqualitytrendsthatarerelevanttohydropowerplanningandoperations. ....................................................................................................................................92

Table4.2: WaterQuality–Keyrisks,impactsandvulnerabilities................................................93

Table4.3: Full energy chain greenhouse gas emission factors in gCO2 equiv / kWh(e) h-1(modifiedfromIAEA,1996,Tremblayet al.,2009). ................................................. 102

Table 4.4: Water quality parameters and indicators applicable to Hydropower operations. ......110

Table4.5: WaterqualitymonitoringrequirementsasafunctionofPrincipalWateruse(Thornton,et al.,1996). ..............................................................................................................111

Table5.1: Mekongfishguilds,associatednumberofspeciesandtheirtotalandrelativecontributionto the total catch recorded by the AMCF survey, Nov 2003 – Dec 2004 (from Halls & Kshatriya,2009). ...................................................................................................... 122

Table 5.2: Summary of deep pool characteristics including substrate type, max. depth, area, estimatedfishdensityandbiomassandnumberoffishspecies(Hallset al.,2013). .... ..................................................................................................................................127

Table5.3: Estimatedfisheriesyieldofselectedfloodplains(Hortle&Bamrungrach,2015). .... 131

Table5.4: EstimatedLMByields(kt/year)percountryandhabitat(basedonHortle&Bamrungrach,2015). ....................................................................................................................... 132

Table5.5: Selectedendangeredspecies(fishbase.organdiucnredlist.org). ........................... 134

Table5.6: Aquaticecologyandfisheries–Keyrisks,impactsandvulnerabilities. .................. 136

Table 5.7: Natural flow variations in m/hour (based on daily means of historic water levelchanges). ................................................................................................................. 140

Table 5.8: Mekong guilds vulnerable to mainstream dam development (Baran, 2010; adapted fromHalls&Kshatriya,2009). ................................................................................. 144

Table5.9: Estimatesofexistingandexpectedfisheriesyieldsfromreservoirsincludingretentionrate,areaandmeandepth(diversesources). ......................................................... 149

Table 5.10: Comparison of water quality data of the Mekong River between 1985-2010 and 2011 (MRC,2013)(yellowvalueshighlightvaluesoutsideoftheguidelinesfortheprotectionofhumanhealthand/oraquaticlife). ....................................................................... 156

Table5.11:Comparisonoftotaldissolvedgas(TDG)saturationlevelsbelowlargeChinesedams(Qu et al.2011). ....................................................................................................... 157

Table5.12:ParametersandthresholdsusedtoclassifythewaterqualityintheMekong(Baran&Guerin,2012;basedonMRC,2007). ...................................................................... 167

Table5.13:Comparison/applicabilityofupstreamfishpasssolutionsintheLMBincludingexamplesfromotherrivers(Schmutz&Mielach,2015). .......................................................... 173

Table 5.14: Selection of possible indicators for monitoring the impact on aquatic organisms. ... 179

Table6.1: ImportantwetlandtypesintheLowerMekongBasinbycountry(SOB,2011). ....... 189

Table 6.2: Valuable wetland ecosystems/habitats in the Mekong river basin. .......................... 190

Table 6.4: Examples of important wetland sites in Cambodia .................................................. 193

Table6.5: ExamplesofimportantwetlandsitesinLaoPDR. .................................................. 194

Table 6.6: Examples of important wetland sites in Thailand. .................................................... 195

Table 6.7: Examples of important wetland sites in Viet Nam. .................................................. 196

Table6.8: Locationandstatusoftheidentifiedenvironmentalhotspots. ................................. 197

Table6.9: Biodiversity, natural resources and ecosystem services- Key risks, impacts andvulnerabilities. .......................................................................................................... 199

Table6.10:ConservationareaswithintheprojectareaofLHWP(Source:MonyakeandLillehammer,2011).

Table8.1: SummaryofecosystemservicesvaluesinLMB(USD/ha/year). ............................ 250

FiquresFigure1.1: MRCGenericPracticalProcessforRiskandImpactMitigation-ProjectLifeCycle.

................................................................................................................................ 2

Figure2.1: FlowregimeofthemainMekongRiver(MRC,2006). ............................................ 6

Figure2.2; Timingofthetransitionbetweenwetanddryseason-VientianeandKratie(MRC,2006). ...................................................................................................................... 6

Figure2.3: SpecificyieldandpercentageaverageflowcontributionintheMekongbasin. ...... 7

Figure2.4: Contributionofthevarioustributariesontheflowduringwetanddryseason. ....... 8

Figure 2.5: Average contribution of the various tributaries to the main Mekong over the year. . 8

Figure2.6: ChangesinflowoftheSesanRiverduetohydropowerandirrigation.................... 9

Figure2.7: Percentagedeviationfromaverageflow(VientianeandKratie)1960–2005(MRC,2006). .................................................................................................................... 10

Figure 2.8: Expected changes in discharge due to implementation of Lancang reservoirs (Räsänen,2014). ....................................................................................................11

Figure 2.9: Overall changes in hydrograph shape due to reservoir implementation. .............. 12

Figure2.10: Expectedchangesinflowduetoclimate,hydropowerdevelopmentandirrigation ..(Räsänen,2014). ................................................................................................... 13

Figure 2.11: Daily discharge values at Chiang Saen (average values before 2008 and the year 2014). .................................................................................................................... 15

Figure2.12: Annual daily discharge hydrograph at Pak Beng dam site (baseline &Yunnan /Yunnan+Laostributarydams). ............................................................................ 16

Figure2.13: PatternofinflowandoutflowfromTonleSap. ...................................................... 17

Figure 2.14: Expected changes in inundation pattern at Tonle Sap (Arias, et al,2014). ........... 18

Figure2.15: Expected changes in inundation area atTonleSap in km2 (Kummu&Sarkkula,2008). .................................................................................................................... 18

Figure3.1: Blockdiagramshowingthe4dimensionsofsedimentdelivery:downstream(length),intoandoutofthefloodplains(width),depositionorerosioninthechannel(vertical),andvariabilitythroughtime(temporal).(FISRWG,1998). ................................... 23

Figure3.3: (left)DistributionofrapidsintheMekongshowingdistributionofbedrockcontrolledchannelsintheLMB;(right)DistributionofdeeppoolsshowinghighestdensityanddepthsbetweenMukdahanandPakse. ................................................................ 27

Figure3.4: Distributionof areas subject to flood risks (floodplains) in theLMB. Mainstreamfloodplainsshowninpink,tributaryfloodplainsindicatedinyellow.Areaspronetoflashfloodingareshownintan.Aroundthedelta,theareassusceptibletostorm

surgesandtsunamisarehighlightedinblue(MRC2010). ................................... 28

Figure3.5: (left)SchematicshowingdistributionofsedimentinputtotheLMBbasedonWUP-FINmodelling;(right)GrainsizedistributionofsuspendedsedimentsintheMekongmainstream in theLMB. CS=ChiangSaen,LP=LuangPrabang,NK=NongKhai,PK=Pakse,KT=KratieandTC=TanChau(Koehnken,2015). ............................ 30

Figure3.6: Theoretical sediment trapping efficiencies of the Lancang cascade (Kummu andVaris,2007). .......................................................................................................... 31

Figure3.7: (left) Comparison of historic (coloured bars) and recent (blue bars) suspendedsediment loads at monitoring sites on the Mekong mainstream. Historic loads based on results from MRC Master catalogues and recent results based on sediment monitoringcompletedbytheMRCMemberCountries(Koehnken,2014). .......... 32

Figure 3.8: Timing of sediment delivery in the LMB 2009 - 2013. Graphs show percentage of total sediment load transported eachmonth atChiangSaenandKratie (fromKoehnken,2014). .................................................................................................. 33

Figure 3.9: Map of aggregate extraction in the LMB based on surveys of operators (Bravard, et al,2014). ............................................................................................................... 34

Figure3.10: (Top 4 photos) time-series of progressive infilling of the floodplain between theMekongmainstream and Tonle Sap Rivers; (left) map showing route of historicoverland from Mekong mainstream to Tonle Sap. Exchange has been limited by roadconstructionandfloodplaininfilling. .............................................................. 35

Figure 3.11: Map of Mekong Delta in Vietnam indicating the density and extent of the excavated canalsystem.Blueareaindicatesextentoffloodingin2000.(MRC,2005). ....... 36

Figure 3.12: Example of hydrograph showing Baseload power generation over a 1-month period. .................................................................................................................. 39

Figure 3.13: Example of vegetation and soil loss from the riparian zone due to extended inundation associated with baseload power generation in Western Tasmania, Australia. ...... 39

Figure3.14: Hydrographshowingeffectofhydropeakingonwater levels in theupperSrePokRiver, Vietnam. ...................................................................................................... 40

Figure 3.15: Seepage erosion on a sandy alluvial bank downstream of a hydropower scheme in Tasmania, Australia. .............................................................................................. 40

Figure 3.16: Low-angle bank slope developed on an alluvial bank downstream of a hydro-peaking hydropower project in Western Tasmania, Australia. ............................................ 40

Figure3.17: (topleft)GoogleEarthviewofareachinzone1,showingstrongbedrockcontrolandlocalisedsandydeposits;(topright)photooferodingsandbankshowinglinesassociatedwithextendedperiodsoffixedwaterlevelsanderodingsoilsandtrees;(middle left) hydrograph showing increase in dry seasonwater levels at ChiangSaen;(middleright)Lossofvegetationinriparianzoneduetoextendedinundation;(bottomleft)bankflatteninganderosionbetweentreeswhicharestabilisinglocalbank. ...................................................................................................................... 42

Figure3.18: (topleft)MekongRiverupstreamofKongChiamshowingbroadvalleyandbedrockconstrainedchannelandbedrock islands; (top right)Alluvial riverbankandfloodplainalongtheMekongRiverupstreamofKongChiam;(bottomleft)alluvialriverbank in tributary in North eastern Lao PDR showing lateritic characteristics andsusceptibilitytoerosion;(bottomRight),GraphofTotalSuspendedSolidsatPakseshowing reduction in suspended sediment over time............................................ 44

Figure3.19: (topleft)ObliqueGoogleEarthimageshowingmulti-channelledbedrockcontrolledareadownstreamofPakse,andentranceofthe3SRiversystem;(topright)ViewofMekongupstreamofKongChiamshowingbroadchannelandbedrockconstrainedchannel; (middle left) multi-island area upstream of Kratie; (middle right) sanddepositsonislandsupstreamofKratie;(bottomleft)floodedforestnearLaoPDRCambodian border. ................................................................................................ 45

Figure3.20: (topleft)GoogleearthimageshowingMekong,CambodianfloodplainandTonleSapsystem;(topright)Fine-grainedriverbankdownstreamofKampongCham,(Middleleft)ViewofMekongdownstreamofKampongChamshowingbankprotectionworks,broadriverchannelandfloodplain;(middleright)Claymaterialdredgedtocreatechannel inTonleSap; (bottom left)grain-sizedistributionofsuspendedsedimentatKratie in2012-2013showingdominanceofsilt insuspended load (Koehnken,2014) ..................................................................................................................... 46

Figure3.21: (top left) Oblique Google Earth image showing the Chaktomuk bifurcation nearPhnomPenhtothedeltashoreline;(topright)Canalandfloodplainindeltaarea;(middle left) Bassac River near Chau Doc showing development; (middle right)River bank near Leuk Daek on Mekong River showing evidence of erosion ;(bottom left)grain-sizedistributionofsuspendedmaterialatTanChauontheMekongRiver,2012-2013(Koehnken,2014)................................................................................ 48

Figure3.22: ElevatedflowduringthedryseasonatChiangSaen(left)andPakse(right).Purplelineindicates2014–2015dryseasonflows,darkbluelinedenotesthelongtermaverage,orangelineshowspreviousyear’s(2013-2014)flowpattern. ................ 49

Figure 3.23: Schematic showing the range of sediment mitigation approaches used in Japan (Sumi et al.,2015). ................................................................................................ 52

Figure3.24: Classificationofsedimentcontrolmeasures(Sumi,T.andKantoush,S.A.,2011). . .............................................................................................................................. 52

Figure3.25: ExampleofhowsitingofanHPcanaffectenvironmental impactsandmitigationoptions. The diagram at left shows a hypothetical river with two tributaries. The downstream disruption of sediment supply and sediment management within the impoundmentwilldifferdependingonwhetheradamisconstructedatsites‘A’,‘B’,or‘C’.Adamat‘A’willhaveasmallerimpactondownstreamflowsandsedimentsupplyascomparedto‘B’or‘C’.Adevelopmentlocatedat‘C’willneedtoincludesediment mitigation strategy to avoid sedimentation near power station intakes.. 53

Figure3.26: LocationsofNationalProtectedAreas inLaoPDR,manyofwhichare located incatchments where hydropower has been, or is in the process of being developed. . .............................................................................................................................. 55

Figure 3.27: Sediment management at dams in Japan (Sumi, 2008 in Sumi et al.,2015). ...... 57

Figure3.28: Potentially sustainable and non-sustainable sediment mitigation measures as afunctionofreservoircapacity(CAP)andmeanannualwater(MAF)andsediment(MAS)inflows(Annondale,2013).......................................................................... 58

Figure3.29: MekongHPprojectsplottedonaBassonandRooseboom(1997)diagram.Projectsshown in legend: NT2 = Nam Theun 2, ULC=Upper Lao PDR Cascade usingsediment loads post-Lancang cascade. ................................................................ 58

Figure3.30: Examplesofoff-streamimpoundments,fromtheReservoirSedimentationHandbook(MorrisandFan,1998). ......................................................................................... 59

Figure 3.31: Example of a river course being used as a bypass channel for sediment management (MorrisandFan,1998). ......................................................................................... 60

Figure 3.32: Schematic of bypass system and sediment budget at Miwa Dam, Japan (Sakurai andKobayashi,2015). .......................................................................................... 62

Figure 3.33: Slit check dam designed to promote sediment deposition when concentrations are high(Sumi,2008). ................................................................................................. 63

Figure3.34: Gravelmining intheupperendof theThreeRiverGorgesproject in theYangtze(Wang,undated). ................................................................................................... 63

Figure 3.35: Sediment replenishment methods according to sediment placement or injection types(a)in-channelbedstockpile(b)High-flowstockpile(c)Pointbarstockpile,and(d)highflowdirectinjection(Ocket al.,2013,inMorris,2015). ........................... 64

Figure 3.36: Gravel replenishment into Isar at the Oberfohringer Wehr: Excavated material is transportedbytruckanddepositedinriver(left)andnaturallydistributedbyminorfloodevents(right)(KantoshandSumi,2010). ..................................................... 64

Figure3.37: SedimentsluicingregimeatThreeGorgesDam,China(topleft):Annualoperatingcurve for the TGD reservoir showing Normal Pool Level (NPL), Dry SeasonControlLevel(DCL)andFloodseasoncontrolLevel(FCL,fromZhou,2004);(topright) generalised annual water level curve compared to suspended sedimentconcentrationsofinflowingwater(Wang,undated);(bottomleft)Modelledvolumeof accumulated sediment under the Dry Flood operating rule shown above, and under‘basic’operationswithoutthesedimentsluicingoperatingrules. ................ 67

Figure 3.38: Example of turbidity venting through a low-level gate to move sediment through an impoundment(MorrisandFan,1998). .................................................................. 68

Figure3.39: AGoogleEarthimageofthePleiKrongHPontheupperSesanRivershowingthereleaseofhighsedimentbearingwaterthroughlowleveloutlets(orpowerhouse)accompanied by the discharge of low-sediment bearing water from the surface of the impoundment. .................................................................................................. 69

Figure3.40: Turbidity current venting through low-level sluice in Shihmen reservoir (Taiwan),seen from the spillway from which clear water from the upper layers is released to dilutetheturbidoutflow(PhotofromPaulHsu,International). ............................. 69

Figure3.44: GoogleEarthimageoftheKamchayHydropowerProjectinsouthwesternCambodia,showing the main dam and downstream re-regulation weir. ................................ 73

Figure 3.45: Slope protection measures at Nam Ngiep designed to minimise sediment erosion. ...............................................................................................................................74

Figure 3.46: Adaptive management approach to hydropower during the operational phase of the project. ................................................................................................................... 75

Figure3.47: BardepositionintheColoradohigh-flowreleasein2013,atCarbonCanyon(RM65.1R).(Left)situationbeforehighflow,(right)situationafterhighflow................ 77

Figure4.1: WaterQualityclassofMekongmainstreamstations for ‘Human ImpactonWaterQuality’ 2000 – 2008 based on WQMN results. ND= No results available. ........ 82

Figure4.2: Boxandwhiskerplotsofammonia(topleft)totalphosphorus(topright)andChemicalOxygen Demand (bottom right) for the period 1995 or 2000 to 2013 showingcatchment trends (Ly et al.,2015). ........................................................................ 83

Figure4.3: WQMNresultsfrom2005–2012comparedwith2013resultsforammonia(topleft),totalphosphorus(topright)andChemicalOxygenDemand(bottomleft)forPakseand Stung Treng. ................................................................................................... 84

Figure 4.4: Median monthly values for Temperature between 1985 and 2008 at Chiang Saen, NakhonPhanom,Pakse,Kratie,PrekKdam(TonleSap),TanChauandMyThuanbased on monthly WQMN results. ......................................................................... 85

Figure4.5: Medianmonthlyvaluesforelectricalconductivity(EC)between1985and2008atChiangSaen,NakhonPhanom,Pakse,Kratie,PrekKdam(TonleSap),TanChauand My Thuan based on monthly WQMN results. ................................................. 85

Figure4.6: Medianmonthly values forTotalPhosphorusbetween1985and2008atChiangSaen,NakhonPhanom,Pakse,Kratie,PrekKdam(TonleSap)TanChauandMyThuan based on monthly WQMN results. ............................................................. 86

Figure4.7: MedianmonthlyvaluesforNitrite+Nitrate(NO2+NO3)Phosphorusbetween1985and2008atChiangSaen,NakhonPhanom,Pakse,Kratie,PrekKdam(TonleSap)Tan Chau and My Thuan based on WQMN results. .............................................. 86

Figure4.8: WQMN Total phosphorus results for Chiang Saen, Nakhon Phanom, KampongCham and Tan Chau, 1985 – 2012. ...................................................................... 88

Figure4.9: WQMNTotalNitrogenresultsforChiangSaen,NakhonPhanom,KampongChamand Tan Chau, 1985 – 2012. ................................................................................. 88

Figure4.10: WQMNammoniaresultsforChiangSaen,NakhonPhanom,KampongChamandTan Chau, 1985 – 2012. ........................................................................................ 89

Figure4.11: WQMNNitrite+NitrateresultsforChiangSaen,NakhonPhanom,KampongChamand Tan Chau, 1985 – 2012. ................................................................................. 89

Figure4.12: WQMNChemicalOxygenDemand(COD)resultsforChiangSaen,NakhonPhanom,

KampongChamandTanChau,1985–2012. ...................................................... 90

Figure4.13: TSScomparedtoTotalPhosphorusatChiangSaenfortheperiods1985–2003and2004 – 2008. ......................................................................................................... 91

Figure 4.14: Comparison of suspended sediment concentrations at Chiang Sean during the dry season for the period 1968 – 1992 (left) and 2009 – 2013 (right) showing largereduction. ............................................................................................................... 91

Figure4.15: ComparisonofflowatChiangSaenin1985and2013demonstratingthedelayedonsetofhighflows,reducedpeakflowsandhigherlowseasonflowsin2013relativeto the historic record. ............................................................................................. 91

Figure 4.16: Comparison of water temperature in the release from a power station and an unregulated tributary, showing warmer autumn temperatures and cooler spring temperatures in the power station release. ........................................................... 94

Figure 4.17: Comparison of water temperature downstream of a hydropeaking power station (JohnButtersPowerStationontheKingRiver,Tasmania,Australia)andinanearbyunregulated tributary. ........................................................................................... 95

Figure4.20: Dissolvedoxygen(mg.L-1)profilesintheNamTheun2Reservoir(RES1andRES9)between 2008 and 2013 (WD: warm dry season, WW: warm wet season, CD: cool dryseason).(Chanudetet al.,2015). .................................................................... 97

Figure4.21: Schematicshowingmercurycyclingwithinan impoundment. (MercuryPollution:IntegrationandSynthesis.(CopyrightLewisPublishers,animprintofCRCPress.inUSGS,1995). ........................................................................................................ 98

Figure4.22: JohnButtersPowerStationontheKingRiverinTasmania,Australia.SitingoftheHPwasguidedbypresenceof tributarycontaminatedbyacidicdischarges fromhistoric mine sites. ............................................................................................... 101

Figure4.23: Estimates of lifecycle GHG emissions (gCO2eq.kWh-1) for broad categories ofelectricitygeneration technologies (IPCC,2012).The redstar indicates theGHGemissionsfactorforthefirst2yearsafterimpoundmentoftheNT2Reservoir(whichisnotthelifecycleGHGemissions). .................................................................... 102

Figure4.24: Multipleleveloutletsinadamallowingdischargeofwaterofdifferingcharacteristics.(Thornton et al.1996,afterColeandHannan,1990).......................................... 103

Figure4.25: Examplesofpassiveaerationstructures.(topleft)flow‘splitting’featuresonthetopofthegatesatPakMundam,Thailand;(topright)aerationweiratNamTheun2,LaoPDR,(bottomleft)designoflabyrinthfloodmanagementspillwayatNamNgiep1(Kansai,2013),(bottomright)InfusionweiratChatugeDam,NorthCarolina. 104

Figure4.26: Water temperature (°C) and dissolved oxygen (mg.L-1) profiles in the regulatingpond (REG1) between 2009 and 2013. (WD:warmdry season,WW:warmwetseason,CD:cooldryseason).Chanudetet al., 2015 ........................................ 105

Figure4.27: (top) Auto-venting turbine aeration methods, showing Central, Distributed andPeripheralAir intakes, (bottom)Auto-venting hub baffleon a turbine (Tennessee

ValleyAuthoritywebsite). .................................................................................... 105

Figure4.29: (left)Spillwayflowattimeoffishmortalityevent;(right)Flowoverspillwayfollowinginstallationofdeflectors. ...................................................................................... 107

Figure 4.30: Longitudinal zonation of water quality conditions in reservoirs (Thornton et al., 1996, modifiedfromKimmelandGroeger,1984). ........................................................ 107

Figure 4.31: Solar powered mixer to reduce the growth of noxious algae in reservoirs. ......... 108

Figure 4.32: Macrophyte harvester used to remove plant growth around infrastructure. ........ 108

Figure4.33: LandfillatNamNgiep1forthedisposalofnon-recyclablewaste. ...................... 109

Figure5.1: Giantpangasius(Pangasiussanitwongsei(MRC,2007). ....................................115

Figure5.2: The flow regime and its importance for aquatic organisms, discharge at LuangPrabanginyear1988(basedonMRC,2009)......................................................116

Figure5.3: Importantfactorsoftheflowregime(Karr1991). .................................................117

Figure5.4: Importantprinciplesofnaturalflow(Bunn&Arthington,2002). ...........................118

Figure5.5: Number of percentage ofMekong fish species feeding on various food sources(Valbo-Jorgensen et al.,2009). ............................................................................119

Figure5.6: EstimatedhourlybiomasspassagerateatXayaburi(FishtekConsulting,2015). .... ............................................................................................................................ 120

Figure5.7: Schematicdescriptionofguildsandtheirdistribution(MRC,2009). ................... 121

Figure 5.8: Lower, middle and upper migration systems with major migration routes in the LMB; black arrows indicate migrations at the beginning of the wet season and brown arrows indicate migrations at the beginning of the dry season (Schmutz & Mielach 2015,basedonPoulsenet al.,2002).................................................................. 123

Figure 5.9: Migratory species occurrences on the basis of the Mekong Fish Database (Grill et al., 2014; based on Visser et al.,2003). .............................................................. 124

Figure 5.10: DCIStrahler and DCIMigr: Weighting factors (i.e. number of migratory species and Strahler)andcurrentsituation(i.e.BDP2030scenario)withconnectedriversectionsingreenanddisconnectedriversectionsinred). ................................................ 125

Figure5.11: Larvalfishcaughtwithconicalplanktonnetsandseinenets(Cowxet al.,2015). ... ............................................................................................................................ 126

Figure 5.12: Longitudinal schematization of deep pools with their depths in Mekong mainstream betweenChiangSaenandPhnomPenhareas(Hallset al.,2013). ................... 127

Figure5.13: Ecologicalregionsandrivertypes(with/withoutfloodplains)(Grillet al.,2014). 128

Figure5.14: LocationofrapidswithintheLMB(MRC,2011). ................................................. 129

Figure5.15: The left graph shows the flood inundation of the year 2000 (major flood zone)

and reservoirs, while the right graph shows a map of wetlands and environmental hotspots(MRC2011). ......................................................................................... 130

Figure5.16: ConsumptionbasedyielddatadividedintofishguildsandOAAspercountry. ... 133

Figure5.17: Potential1st,2ndand3rdorderhydropowerimpacts. ........................................ 135

Figure5.18: Schematicrepresentationofimpactsofdamsonfloodplainflooding(Baran,2010). .............................................................................................................................138

Figure5.19a: Larvaldriftobservationsduringincreasing,peakanddecreasingflow(comparisonbetweennopeaking(controlgroup)andpeaking);Figure5.19b.Strandingatdifferentdownrampingrates(i.e.2.9/0.5/0.32/0.2cm/min)(adaptedfromSchmutzet al. 2014). .................................................................................................................. 140

Figure5.20: NumberofannualwaterlevelfluctuationsatCS(ChianSaen),LP(LuangPrabang),VT(Vientiane)andMH(Mukdahan)(solidlinesindicatea5-yearmovingaverageforeachstation)(Cochraneet al.,2014). ................................................................. 141

Figure5.21: Exampleforecosystemwithhigh(left)andlow(right)degreeofconnectivity(FromLoucksandvanBeek,2005). .............................................................................. 142

Figure 5.23: Fragmentation history of selected large river basins and predictions for the Mekong (Grill et al.,2014). ................................................................................................ 143

Figure5.24: Migratory species range in theLMB:a) recordedmigratory species, b) recordedlocationsandmigratory rangeofPangasiusgigas,c) rangeofmigratoryspecies(Grill et al,.2014). ................................................................................................ 144

Figure 5.25: Main migration corridors and their relative importance based on 18 migratory fish species:Black arrows formainstreammigrations, brownarrows for tributarymigrations(Baran,2010). .................................................................................... 145

Figure 5.26: Comparison of egg/larvae density upstream and downstream of the Santa Clara damand the related flows in theMucuriRiver (October2002 toFebruary2003;Pompeuet al.2011). ........................................................................................... 150

Figure 5.27: Location and proposed normal operating water levels of proposed hydropower dams inrelationtothelongitudinalprofileoftheLowerMekongriverbedanddryseasonwater surface (Operating water level of dams are according to CNR 2009 and ICEM 2010, yellow shading indicates alluvial reaches of the river, the remaining sections are bedrock-controlled (Halls et al.2013). .......................................................... 152

Figure5.28: Relational trendsof freshwater fishactivity to turbidityand time (basedonwww.lakesuperiorstreams.org/understanding/param_turbidity.html; Newcombe & Jensen, 1996). .................................................................................................................. 153

Figure5.29: Oxygenneed(a)andoxygensaturation(b)independenceofthewatertemperature(Kieckhäfer,1973). .............................................................................................. 155

Figure 5.30: Visible gas bubbles in vasculature of operculum and in eye as observed in acute gas bubbledisease.(www.adfg.alaska.gov) .............................................................. 156

Figure5.31: Relationbetweenspillwayflowandtotaldissolvedgassaturation(Quet al.,2011). .............................................................................................................................157

Figure5.32: ProposedintactriversinVuGiaThuBonbasin(ICEM2008). ........................... 160

Figure5.33: Hydropower capacity and river kilometres affected by fragmentation for differentscenarios in theCoatzacoalcosBasin (reddots: scenarios shown in next figure;Opperman et al.,2015). ...................................................................................... 160

Figure5.34: Twoscenarioswithsimilarhydropowercapacitybutconsiderablydifferentlevelsofconnectivity (Opperman et al.,2015). ................................................................. 161

Figure5.35: Maximumamountofconnectedriverchannelfordifferentlevelsofsystemcapacityexploitation (Opperman et al.2017). ................................................................... 161

Figure5.36: StrategicHPplanningapproach–national/regionalandproject-specificassessments(ICPDR2013). ..................................................................................................... 162

Figure5.37: Exampleofflowregimebuiltupusingbuildingblocks(fromAcremanandDunbar,2004basedonTharme&King,1998). ............................................................... 165

Figure5.38: Actualandtotaldissolvedgaslevelsexperiencedbyfishatvariousdepths(Weitkampet al.,2003). ........................................................................................................ 168

Figure5.39: Schematicsketchoftheattractionflowpump(Schmutz&Mielach,2015;adaptedfromHassinger2008). ......................................................................................... 171

Figure5.40: Attractionflowpumpinoperation(UniversitätKassels.a.). ................................ 172

Figure5.41: Recommendedfishpasstypes(1:GeesthachtatElbeRiver(GeesthachtElbes.a.);2:Nature-likefishpassatDanubeRiver;3:PlannedbypasssystemfortheDanubeRiver.ThefigureshowstheintegrationofthebypasssystemintothemainstemoftheDanubebelowthedam(Mühlbauer&Zauner2010,unpublishedreport). ... 174

Figure5.42: Examplesforinnovativesolutions(basedonAufleger&Brinkmeier,2015). ...... 176

Figure6.1: TheFishingCat(Source:SoB,2010). ................................................................ 183

Figure6.2: TheGiantIbis(Source:SoB,2010). ................................................................... 184

Figure6.3: SiameseCrocodile(Source:SoB,2010)............................................................. 185

Figure6.4: Sustainabilityofflagshipspecies(Source:MRCBDP,2011). ............................. 187

Figure6.5: TheKatsedamintheLesothoHighlandsWaterProject(Photo:AstridJanssen,WLDelftHydraulics). ................................................................................................ 201

Figure 7.1: Alternative dam locations at Sambor, Cambodia (Source: Ian G Cowx, Hull Fisheries Institute). .............................................................................................................. 207

Figure7.2.DordogneHydropowerCascade,France(Source:EdF). ........................................ 209

Figure7.3.NamTheun2regulatingdam,LaoPDR(Source:Multiconsult). ............................. 210

Figure7.4.NamNgiep1dischargeprofile,LaoPDR(Source:NamNgiep1PCLtd). ..............211

Figure7.5: NamNgiep1regulatingdam,LaoPDR(Source:NamNgiep1PCLtd). ........... 212

Figure7.6: PergauRe-regulatingPond,Malaysia(Source:InstitutionofCivilEngineers-UK). ............................................................................................................................ 213

Figure7.7: Sectionsthroughtheoverflow(top)andunderflow(bottom)baysatDalHydropowerProject,Sudan(Source:Multiconsult). ................................................................ 214

Figure7.8: Section through sediment sluices at Dal Hydropower Project, Sudan, (Source:Multiconsult). ....................................................................................................... 215

Figure7.9: SedimentsluicemodelstudyforDalHydropowerProject,Sudan,(Source:TUM&Multiconsult). ....................................................................................................... 215

Figure7.10: ReservoirareaatKindarumaHydropowerProject,Kenya(Source:Multiconsult). ... ............................................................................................................................ 216

Figure7.12: Xayaburi Fish Migration System, Lao PDR (Source: Xayaburi Power CompanyLtd). ........................................................................................................................... .............................................................................................................................217

Figure7.13: MerseyLowHeadTidalBarrage,LiverpoolUK(Source:PeelEnergyLtd). ....... 221

Figure7.14: Merseyturbineandgatecaissons(Source:PeelEnergyLtd). ........................... 221

Figure7.15: Verylowheadbarrage(Source:VNFFrance). ................................................... 222

Figure7.15: NgonyeFallspartialbarrage-Zambia(Source:Multiconsult). ........................... 223

Figure7.16: Nakayreservoirstratification–LaoPDR(Source:NamTheun2PowerCompanyLtd). ..................................................................................................................... 224

Figure7.17: NakayreservoirCO2emissions–LaoPDR(Source:NamTheun2PowerCompanyLtd). ..................................................................................................................... 225

Figure7.18: Nakayreservoirriparianrelease–LaoPDR(Source:Multiconsult). .................. 226

Figure7.19: NamTheun2powerintakeapproachchannel–LaoPDR(Source:NamTheun2PCLtd). ..................................................................................................................... 226

Figure7.20: NamTheun2downstreamaerationweir–LaoPDR(Source:Multiconsult). ..... 227

Figure7.21: NamTheun2downstreamchannel–LaoPDR(Source:NamTheunPowerCompanyLtd). ..................................................................................................................... 228

Figure7.22: NamNgiep1regulatingpowerhouseworksarea,LaoPDR(Source:NamNgiep1PCLtd). ............................................................................................................... 230

Figure7.23: SoilstabilisationonRoad13North,LaoPDR(Source:Multiconsult). ................ 231

Figure7.24: AccessbridgeacrossthedownstreamchannelofNamTheun2HydropowerProject,LaoPDR(Source:Multiconsult). ......................................................................... 232

Figure7.25: Nakayreservoirwaterlevels,LaoPDR(Source:NamTheunPowerCompanyLtd). .............................................................................................................................233

Figure7.26: Reservoircascadeoperation(Source:Multiconsult). .......................................... 234

Figure7.27: NamNgiep1PMFattenuation,LaoPDR(Source:NamNgiep1PowerCompanyLtd). ..................................................................................................................... 235

Figure7.28: NamTheun2downstreamchannelconfluence,LaoPDR(Source:Multiconsult). ... ............................................................................................................................ 237

Figure7.29: UpstreamfaceoftheNamOu6dam,LaoPDR(Source:Multiconsult). ............ 239

Figure7.30: GeneralviewoftheBujagaliHydropowerProject,Uganda(Source:Multiconsult)... ............................................................................................................................ 240

Figure 8.1: Linkage between ecosystem services and constituents of human well-being (Source: Emerton2006,citedin;WWF-GreaterMekong2013). ....................................... 246

Figure8.2: Typesandclassificationofecosystemservices(Source:USIADMekongAdaptationandResiliencetoClimateChange2015). ........................................................... 246

Figure8.3: Thedifferentactivitiesinvolvedinecosystemandecosystemservicesassessmentsas of MRC (Source: Discussion Note on MRC Ecosystem and Ecosystem Services Activities,18thAugust2015). ............................................................................. 247

Figure8.4: ComparisonoforiginalandrevisedNPVsfor thethreescenariosassuming10%,3%and1%discountrates(Source:Costanzaet al.2011). ................................ 249

Figure 8.5: A step-by-step method for ecosystem service assessment in the six-step standard ESIA.Source:(WorldResourcesInstitute2013a). ............................................. 253

Figure8.6: Mitigatingandenhancingproject impactsonecosystemservicebenefits(Source:WorldResourcesInstitute2013a). ....................................................................... 254

Figure 8.7: Managing project dependencies on ecosystem services to ensure planned operational performance. .................................................................................... 256

Figure8.8: Thelogicofpaymentsforecosystemservices(Source:Engel,Pagiola,andWunder2008). .................................................................................................................. 257

Abbreviations and acronymsADB Asian Development Bank

AEP Annualexceedanceprobability

BDP BasinDevelopmentPlan

BOD Biochemical Oxygen Demand

BOKU UniversityofNaturalSciencesandLifeSciences/Universitätfür Bodenkultur, Wien

BP BankProcedure(WorldBank)

CIA Cumulative Impact Assessment

COD Chemical Oxygen Demand

CPUE Catchperuniteffort

DF Design Flood

DHI Danish Hydraulic Institute

DIN Dissolved Inorganic Nitrogen

DIP DissolvedInorganicPhosphorus

DO Dissolved Oxygen

DRIFT Downstream Response to Imposed Flow Transformation

DSF Decision Support Framework

DSHPP DonSahongHydropowerProject

DTM Digital Terrain Model

DSF Decision Support Framework

EAMP EnvironmentalAssessmentandManagementPlan

EF Environmental Flow

EFA Environment Flow Assessment

EGAT Electricity Generating Authority of Thailand

EIA Environmental Impact Assessment

ELOHA Ecological Limits of Hydrologic Alteration

EP EnvironmentProgramme

EPP EmergencyPreparednessPlan

ESIA Environmental and Social Impact Assessment

FP FisheriesProgramme

GBD Gas Bubble Disease

GFL Great Fault Line

GIS Geographical Information System

GIZ GesellschaftfürInternationaleZusammenarbeit

GMS Greater Mekong Sub-Region

HPP HydropowerProject

IAIA International Association for Impact Assessment

IBFM Integrated Basin Flow Management

ICCS International Cooperation & Communication Section

ICOLD International Commission on Large Dams

IEA International Energy Agency

IEC International Electrotechnical Commission

IFIM Instream Flow Incremental Methodology

IHA International Hydropower Association

IKMP InformationandKnowledgeManagementProgramme

IR Inception Report

IRBM Integrated River Basin Management

ISH Initiative on Sustainable Hydropower

IUCN International Union for Conservation of Nature

IWRM Integrated Water Resources Management

JOR Joint Operation Rules

LAPTS LaoElectricPowerTechnicalStandard

LMB Lower Mekong Basin

MRC Mekong River Commission

MRCS Mekong River Commission Secretariat

MSL Mean Sea Level

MW Mega Watt

NFPA-(US) NationalFireProtectionAssociation

NGO Non Governmental Organization

NMC National Mekong Committee

OP OperationalPolicy(WorldBank)

OSP OfficeoftheSecretariatinPhnomPenh(MRC)

OSV OfficeoftheSecretariatinVientiane(MRC)

PAH PolycyclicAromaticHydrocarbon

PCB PolychlorinatedBiphenyl

PDG PreliminaryDesignGuidance

PDIES ProceduresforDataandInformationExchangeandSharing

PMF ProbableMaximumFlood

PMFM ProceduresforMaintenanceFlowsontheMainstream

PNPCA ProceduresforNotification,PriorConsultationandAgreement

PWQ ProceduresforWaterQuality

PWUM ProceduresforWaterUseMonitoring

R&D Research & Development

RSAT Rapid Basin Wide Hydropower Sustainability Assessment Tool

RVA Range of Variability Approach

SEA Strategic Environmental Assessment

SEG Sediment Expert Group

SoB State of the Basin

ToR Terms of References

TP TotalPhosphorus

TSS Total Suspended Solids

UMB Upper Mekong Basin

USACE United States Army Corps of Engineers

VEC Valued Ecosystem Components

WB World Bank

WQMN Water Quality Monitoring Network

WUA Weighted Usable Area

WUP WaterUtilizationProject

WWF World Wildlife Foundation

xxviii | Chapter 1. Description,PurposeandHowtoUsetheManual


xxix

1 Introduction

1 | Chapter 1. Description,PurposeandHowtoUsetheManual


1 Description, Purpose and How to Use the Manual This Manual on hydropower risks and impact Mitigation intends to support the MRC Hydropower Mitigation Guidelines (MRC, 2018). Both documents are outputs of the study “Guidelines forHydropower Environmental Impact Mitigation and Risk Management in the Lower Mekong Mainstream and Tributaries” that MRC carried out during 2012-2017 under its Initiative on SustainableHydropower(ISH).ThisManualgoesmuchmoreindetailrelatedtodescribingrisks,impacts and vulnerabilities as well as in describing mitigation options. In the Guideline document these are summarized in Chapter 5.3 in the tables 5.1 to 5.5. In this Manual there is also a wide array of examples of good industrial practise mitigation options internationally, from the Greater MekongSub-Region (GMS) and the LowerMekongBasin (LMB).TheGuidelines andManualare further supported by a Knowledge Base (http://www.mrcmekong.org/about-mrc/completion-of-strategic-cycle-2011-2015/initiative-on-sustainable-hydropower/guidelines-for-hydropower-environmental-impact-mitigation-and-risk-management-in-the-lower-mekong-mainstream-and-tributaries-ish0306/).FinallytheGuidelinesandtheManualaresupportedbyaCaseStudyReport(http://www.mrcmekong.org/news-and-events/newsletters/catch_and_culture), where promisingmitigation options has been modelled and analysed for all mainstream dams. At conceptual level some alternative schemes layout assessments both for mainstream dams and those of the Mekong tributaries were also made.

The Mitigation Guidelines identified hydropower risks, impacts, vulnerabilities and associatedmitigation options under 5 major themes, namely:

1. Hydrologyanddownstreamflows2. Geomorphology and sediments3. Water quality4. Fisheries and aquatic ecology; and5. Biodiversity, natural resources and ecosystem services

In this Manual the structure is basically the same where these issues are separated into Chapters 2 to 6. However Ecosystem Services has been separated out as a stand-alone Chapter 8, and a Chapter 7 on Engineering Response to Environmental Risks, with good industrial practice example has also been included. Multicriteria Evaluation of Mitigation Recommendation and Dam Safety Guidelines is only addressed in the Guideline document.

In consistency with the Guidelines, for the thematic areas above a set of 5 key common overarching changesrelatedtohydropowerdevelopmenthasbeenidentified,whichare;

I. Annual/inter-annualchangestoflow

II. Daily/short-timescalechangestoflowandwaterlevel

III. Loss of river connectivity

IV. Impoundments

V. Diversion and intra basin transfers

2

Risks,impactsandvulnerabilitieswithineachtheme(1to5)forthechanges(ItoV)arethenlisted.The risks, impact and vulnerabilities is then the basis for the detailed mitigation options proposed withineachtheme(Chapters2to8)atthevariousphasesduringtheprojectlifecycleinlinewiththemitigationherarchyasshowninfigure1.1(seeChapter1oftheMitigationGuidelinesformoredetail).

Overall, reference to the relevant sections in the Mitigation Guidelines, to find supportingdocumentation, is made where appropriate.

Once projects are approved to go to the feasibility stage, avoidance of impacts remains a priority and mitigation and minimisation options become more relevant. At the feasibility stage of projects it is also critical to optimise the design for maximum economic efficiency together with concurrent minimisation of environmental and social impacts. The full and detailed environmental and social impact assessment (ESIA) may indicate that certain impacts are not able to be mitigated. In which case, during the project design and operations phase, compensation measures must be considered. The operational phase of a project may last 50 years or more. It is therefore important that ongoing monitoring of the effectiveness of mitigation measures is put in place. If agreed performance targets are not being met, adaptive management and revised operating rules may be devised to further mitigate the impacts.

ProjectDevelopment

Energy and HydropowerMaster Plan

Project and Cascade

Feasibility Study

HP ProjectDesign

Construction and Operation

MitigationDuidelineProcess

MitigationHierarchy

Avoidance

Understand the BasinContext, Risks and Impacts

SEA, CIA, ESIA

Select, research and designappropriate mitigation

options

Impliement Monitoringand Adptive

Management

Mitidate (incl minimise)

Compensate

Figure 1.1. MRC Generic Practical Process for Risk and Impact Mitigation - Project Life Cycle.

3 | Chapter 1. Description,PurposeandHowtoUsetheManual


4

2 Hydrology and Downstream Flows – Status, Risks and

Mitigation

5 | Chapter 2. Hydrology and Downstream Flows – Status, Risks and Mitigation


2.1 Basin Context – Status and Overview

2.1.1 Introduction

The hydrology and water resources form the basis for the study of the potential impact of hydropower development in the Mekong region and therefor it is important to sketch the overall regime of the river.Particularly the ‘layout’of theflowregimeover theentirebasin is important toassesstheexpectedimpactofhydropowerdevelopmentonaregionalandlocalscale.Forthispurpose,firstan overview is provided with regard to the most salient features of the hydrology of the Mekong, mostly based on existing studies published either by MRC or available in the international literature. Thefirststudiesoftheexpectedand,recently,observedimpactofhydropowerdevelopmentarepresented and discussed. The changes in hydrology are evidently intimately linked to the various topics that are discussed in the subsequent Chapters in this report, particularly the sediment transportandthefishery,butdirectlinksalsoexistbetweenthe(expected)changeindischargeand the navigation and salt intrusion in the Mekong delta. In this chapter, only the expected impacts ofhydropowerontheflowregimearediscussed,whileinthesubsequentchaptersthelinktothevarioussectorsisanalysed.Inasimilarway,thelocalmitigationoptionsfortheaffectedsectorsare discussed in the corresponding chapters. Here only remarks are made on the possible large-scale measures that might be taken, but it should be realized that possibilities to compensate for thechangesintheoverallflowregimeoftheMekongduetohydropowerdevelopmentarelimited.

2.1.2 Stream Flows

The hydrological regime of the Mekong River and its tributaries form the basis for the present situation with regards to sediment transport, ecology, water quality, etc. Although there are many rivers with a seasonal cycle in the monsoon-driven river systems in Asia, the Mekong has a very specialflowpatternthatisthereasonforanumberofuniquefeaturesthatareintimatelylinkedtoaverywell-definedseasonalcycle.ThiscycleisshowninFigure2.1.InFigure2.2,thetimingofthetransitionbetweenthewetanddryseasonisgivenforVientianeandKratie.Inbothfigures,themost important feature is the small deviation in time of the transition zones, the start varying only a few weeks in time over the years.

6

Figure 2.1. Flow regime of the main Mekong River (MRC, 2006).

Week of occurrence Week of occurrence

Annual calendar variable averageStandard deviation (weeks)

Annual calendar variable averageStandard deviation (weeks)

Minimum Discharge 14 2.1 Minimum Discharge 14 2.0

Dry season end 21 1.9 Dry season end 20 1.7

Flood season start 25 2.2 Flood season start 25 1.9

Flood season end 45 2.1 Flood season end 44 1.7

Dry season start 47 2.4 Dry season start 47 2.3

Figure 2.2. Timing of the transition between wet and dry season - Vientiane and Kratie (MRC, 2006).

Particularlythestrongdependencyoftheriverecologyonthetimingofthetransitionimpliesthatany(man-made)changestothetimingwill immediatelysorteffect.Evidently,theintroductionofmajor(over-yearstorage)reservoirsonboththemainriverandthetributarieswilleasilyleadtoashiftinthetimingofthetransitionzones,apartfromchangesintheflowmagnitudeitself.



Figure2.3.SpecificyieldandpercentageaverageflowcontributionintheMekongbasin.

Theactualimpactofpossiblechangesintheriversystemontheflowregimedependsverymuchon the location. In thefirstplace, it is important tovisualize theprinciplesourcesofflow in theriverbasin(Figure2.3).Thespecificyield,i.e.theyearlyamountofrunoffinmm,isshownintheleftfigureandshowsthatingeneraltheyieldincreasesfromWesttoEast.However,thereareanumberof‘hotspot’tributarybasins,shownintherightpicture,thatonaveragehaveaverylargecontribution,expressedinpercentagesoftotalflowoftheMekong.InthispictureitisshownthattheaveragecontributionfromtheUpperMekong(Lancang)basinisabout16%,whiletwomajortributaryregions,inLaosandthe‘3S’inCambodia/Vietnam,contributeevenmore,respectively19%and23%.Ontheotherhand,thelargetributarybasininthewesternpart,inThailand,contributesonly6%oftotalflowduetoamuchlowerrainfallinthisregion.Itshouldberemarked,though,thatnot only are these average yearly values, on a volume basis, but they give the percentages of the totalflowoftheMekong.Thelocalimportanceofacertaintributarycanbemuchhigher,e.g.theimpact of Lancang on the stretch of the Mekong between the Chinese border and Vientiane, or the impactofthe‘3S’riversontheflowatKratie,areverysignificant.ThisisexpressedinFigure2.4,whereadistinctionisalsomadebetweenthewetanddryseasoncontribution.FromthisfigureitisclearthatthecontributionofflowfromLancangisabout65%inthedryseasonatVientiane,butdiminishestoabout40%duringthewetseason,stillmuchlargerthantheaverage16%forthetotalflowovertheyearintheMekong.Herealsothedominantroleofthelocal(Lao)tributariesisshown, which play a major role in the total discharge at Vientiane both in the wet and dry season. AtKratietheimpactofLancanghasevidentlydiminished,butparticularlyinthedryseasonitisstillintheorderof35%.Here,thecontributionoftheLaoand3Stributariesisdominant.

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Figure2.4.Contributionofthevarioustributariesontheflowduringwetanddryseason.

In Figure 2.5 the average contribution of the flow from the various tributaries to themain Mekong River over the year is shown in a hydrograph. Here the large impact of the Lao tributaries (Nam Ngum, Nam Theun and Nam Hinboun) is clear as wellas the impact of the ‘3S’ (Se Kong, Se San and Sre Pok) between Pakse and Kratie.

Figure 2.5. Average contribution of the various tributaries to the main Mekong over the year.



2.1.3 Water Use and Abstraction

Although there are many locations of water use and abstraction along the Mekong River and its tributaries, the total impact of these abstractions, both at present and in the future, are considered to be much lower than the impact of the existing and planned hydropower reservoirs. Only in the Mekong Delta does the water demand from irrigation play a major role in the hydrology.

AninterestingstudyontheimpactofirrigationontheflowregimeintheMekongbasinisgivenbyRäsänen(2014),usingoneofthe‘3S’rivers,theSesan,asanexample.Thestudylookedatboththe impacts of hydropower development and irrigated rice. The conclusion was that the impact of the abstractions for irrigation were minor compared to the impact of the hydropower development, withthetotalabstractionbeingintheorderof1.9-2.1%ofthetotalflowoftheSeSan(Figure2.6).Irrigated agriculture without hydropower development did, however, have a major impact on the dry seasonflowswithvaluesof32%(February)to70%(earlyMay)ofriverdepletion.Thisshowsthatthe impact of water consumption by irrigated agriculture may easily be obscured by the impact of large dams and should be taken into account.

Figure2.6.ChangesinflowoftheSesanRiverduetohydropowerandirrigation.

In the present study, the water use is included in the modelling as the boundary conditions for the simulation of the Lao cascade will be based on the simulations with the DSF modelling suite, particularlytheIQQM(noweWater)modellingresults.

2.1.4 Floods and Droughts

It is expected that the introduction of large reservoirs will also have a major impact on the extremes ontheMekong.Inordertojudgethechanges,itisimportanttoassessfirstthepossiblenaturalchanges in theoccurrenceoffloodsanddroughts.Theformeraremoredifficult toestablishastheyareshort-durationevents,intheorderofseveraldaystoafewweeks,butlowfloweventsnormally last much longer, in the order of several weeks to an entire season or even years. In Figure2.7 theoccurrenceofdeviations fromtheaverageflowon theMekongatVientianeandKratie is shown that gives an impressionof possible changes in theextremes, particularly thelow-flowevents.Fromthisfigurenoparticulartrendcanbefound,althoughsomevariationwithlong-termeffects(intheorderofdecades)canbeseen,particularlyforthelocationofVientiane,

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wheretheflowseemstobeaboveaverageintheperiod1960–1985andbelowaverageintheperiod1985–1993,withaboveaverageflowsagainafter1993.ThispatternisalsodiscernibleatKratie,but lesspronounced. Ingeneral,no long-term trendcanbeobserved for thisperiod.

Figure2.7.Percentagedeviationfromaverageflow(VientianeandKratie)1960–2005(MRC,2006).

A thorough study is available on the occurrence of floods and droughts in theMekong basin(Räsänen,2014),withthegaugingstationofStungTrenginCambodiaasmajorpointofreference.In this study, the correlation between large scale weather phenomena, like ENSO (El Niño Southern Oscillation)wasstudied.Thiswasfoundtoexplainmostofthefloodsanddroughtswerecorrelatedwith ENSO events. A distinction should be made between El Niño and La Niña, respectively leading tobelowandaboveaverage rainfall. Itwas found thatatStungTreng theannual flowvolumedecreasedonaverageabout19.9%duringElNiñoand increasedabout13.2%duringLaNiñaevents. In addition, theENSOmodulated also the timing of the annual floodpulse,where thestartofthefloodperiodwasdelayedandthefloodperiodwasshorterduringanElNiño,whiletheopposite happened during a La Niña year. It was observed that the activity of ENSO has increased during the past decades with more extreme events as a result. Not all the extreme events are due thoughtoENSO,about50%oftheeventscanbecorrelatedtoENSO,whiletherestareduetoothercircumstancesliketropicalcyclones.MoredetailsaregiveninRäsänen(2014).ThestrongvariabilityandtheongoingincreaseintheENSOmakeitmoredifficulttodistinguishthecauseforchanges in the occurrence of extreme events, either coming from natural sources or by the impact ofman-madechangesinthebasin.However,changesintheextremes,particularlythelowflows,can definitely be expected due to the implementation ofmajor reservoirs, especially the damson Lancang, but also the larger reservoirs on the main tributaries. A discussion of the expected changes will be given in the next paragraph.

2.2 Risks, Impacts and Vulnerabilities

Severalstudiesexistontheexpectedimpactoftheimplementationofreservoirsontheflowregimeof the Mekong River, both for the Lancang as for the main river further downstream, and for the tributaries.AnoverviewofthepotentialimpactsisgiveninRäsänen(2014).Accordingtothisstudy,thesixlargereservoirsplannedintheLancangwillhavearegulatingcapacityofabout28%oftheannualflowatChianSaenandabout5%ofthetotalyearlyflowoftheMekong.Theoverallexpectedchangeof discharge due to the Lancang cascade along the main river over the year is shown in Figure 2.8.



Figure 2.8. Expected changes in discharge due to implementation of Lancang reservoirs (Räsänen, 2014).

InthisfigureitisclearthattherewillbeamajorimpactoftheLancangreservoirsontheflowregimeinthemainMekong.Evidentlytheimpactdiminishesdownstream,butevenatKratie,particularlyin thedryseason, there isstillachangeofabout40%in thedischarge.Thesmallestchangesoccurinthewetseason(October&November)whentheflowfromothertributariesdominatethecontributiontothetotalflow,assumingthatnochangeswouldoccurinthosetributaries.Withtheon-going, and planned, implementation of reservoirs in the tributaries, particularly in Laos, but also inthe3S,thisassumptionisnotvalidandthemajorshiftinflowregimecanbeexpectedallalongthe Mekong river. The overall changes in the hydrographs of both the tributaries and the main river anywhere where reservoir development is on-going or planned, is shown in Figure 2.9.

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Figure 2.9. Overall changes in hydrograph shape due to reservoir implementation.

Inthisfigure,themostimportantexpectedchangesareshown.Thosechangesare:

• Decreasingofpeakflowsanddecreaseinannualfloodvolume

• Increaseindryseasonflow

• Smoothingofthehydrographduetothedampingeffectofthereservoirs

• Diminishingofearlyfloodseasonflowsandincreasingoflaterfloodseasonflows

• Laterstartandendofthefloodseason

• Meanannualflowwillremainmoreorlessthesame.

The last point often leads to the erroneous assumption that the reservoirs do not have an important impact;nowater(apartfromsomeevaporationandseepagelosses)islostduetothereservoirs.

Thesechangesarealreadyapparent inthemainMekong,althoughdefiniteconclusionscannotbedrawnyetuntilsufficientyearsofdataareavailableandcomparisonsaremadewiththerainfalldatatoavoidmixingupthesourcesoftheobservedchangesintheflowregime.

ItisimportanttoquotetheconclusionsfromthestudybyRäsänen(2014)onthecombinedeffectsofthedevelopmentofhydropower,annualmeteorologicalcycles(ENSO)andirrigatedagriculture(Figure2.10).



Figure2.10.Expectedchangesinflowduetoclimate,hydropowerdevelopmentandirrigation(Räsänen, 2014).

Inmanycases,theeffectsarecumulativeanditisdifficulttodistinguishtheactualsourceofanobservedanomalyintheflowregime.Thisisimportanttorealizewhenconclusionsaredrawnfromthe observations of recent discharge series.

Theexpectedresultsofthechangesintheflowregimearemanifold,butherethemostimportantchanges at basin level on other issues are:

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1. Changeintimingofthetransitionzoneaffectsfishery

2. Changeinflowvelocitiesaffectbothfisheryandsedimenttransport/erosion

3. Changeinfloodseasondurationandmagnitudeaffectsparticularlythesediment/erosionandwill have a major impact on the Tonle Sap system

4. ChangeindryseasonflowwillaffectsaltintrusionintheMekongdelta

Thedetailedchangesinthegeomorphology/sedimenttransportandfisheriesarefurtherdiscussedin Chapters 3 and 5.

There is still limited quantitative information available on the expected impact of the existing and planned hydropower development. However, in a recent draft report of the study by CAR consultants3forthefeasibilityofthePakBengrun-of-riverhydropowerdam,theexpectedimpactoftheLancangandthelocalhydropowerdevelopment(NamPha1andNamTha1)inLaosonthehydrology at the dam site were studied. Although the results are still preliminary, they make a useful distinctionbetweentheimpactoftheLancangstretch(Yunnaninthereport)andthereservoirsonthe Laos tributaries.

In Figure 2.11 the impact of the Lancang stretch at Chian Saen is shown, together with observed daily discharges in the year 2014. Although such data should be combined with rainfall to distinguish between natural variability and reservoir-induced changes, it is likely that the observed dailydischargehydrographfor2014reflectstheoperationofthereservoirsontheLancangstretch.Clearlythechangesinflowregimeinthewetanddryseasonareshown,aswellasthelaterstartofthewetseasonflowincreaseduetothedamoperation.

3 CarEngineering(2015):PakBeng&SanakhamFeasibilityStudyReview.DraftReportBook1:PakBeng.



Figure 2.11. Daily discharge values at Chiang Saen (average values before 2008 and the year 2014).

In Figure 2.12 the expected impact of both the Lancang reservoirs and the combined Lancang / Laos tributary dams is shown. As can be expected, given the size of the Chinese dams, the dominantimpactiscausedbythechangesinflowregimeintheLancangstretch.Theimpactoftheplanned reservoirs on the tributaries has the same tendency, but much smaller.

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Figure 2.12. Annual daily discharge hydrograph at Pak Beng dam site (baseline & Yunnan / Yunnan + Laos tributary dams).

The relative impact regime show above has been supported by the results of the hydrology and flows modelling in the Case Study Report (http://www.mrcmekong.org/news-and-events/newsletters/catch_and_culture), where the impacts of the 5 mainstream cascade dams north of Vientianewasassessedagainsthistoric (nodams)BDP2030 (Lancangcascadeand tributarydams included) conditions, quote; “The impacts of the development of the Lao cascade, bothindividualandcumulativeforthefivereservoirs,islimitedduetothesmallvolumeofthereservoirs.In most cases, the residence time of the reservoirs is in the order of days, and even at the onset of thewetseason,withthereservoirsfillingup,therewillbenomajorchangeintheriverregime.Inthe overall context of the Lao cascade with the major reservoirs in the Lancang River, the impact of the Lao cascade on the hydrology is minor”. For further details reference is made to Chapters 3.3 and 5.3 of the Case Study report.

AccordingtotheCARconsultantsstudymentionedearlier,theexpectedchangeinflowregimeatthePakbengdamsiteare:

Lancang stretch:

• Dischargeincreaseduringthelowflowseason:+52%onaveragefromDecembertoMay;

• Dischargedecreaseduringthehighflowseason:-14%onaveragefromJunetoNovember.

Lancangpluslocal(Laos)tributaries:

• Dischargeincreaseduringthelowflowseason:+60%onaveragefromDecembertoMay;



• Dischargedecreaseduringthehighflowseason:-17%onaveragefromJunetoNovember

Forthelowflowseason,importantforthefeasibilityofthehydropowerdevelopment,theimpactisevenmoresignificant.Theannualminimummonthlydischargeshighlightthatthe5-yearreturnperioddischargeincreasesby95%and106%,underregulationrespectivelyofLancangcascadeand planned hydropower projects in Lao PDR.During the flood season, there is an expecteddecrease in flow of respectively 13% and 15%.This shows also the impact of the (two) localreservoirs is minor compared to the Lancang stretch.

TherecentstudyonthePakbengrun-of-riverhydropowerdevelopmentisagoodexampleoftheimportance of the study of the ongoing and planned activities upstream is on the local hydrology. Althoughstudiesdoexistontheoverallchanges,liketheonecitedearlierbyRäsänen(2014),itis urgently required to arrive at a more comprehensive picture of the expected changes using a Masterplan approach for the entire river system.

Aspecial case thatneedsattention is theTonleSap lakesystem.TheTonleSap reverseflowsystemisverysensitivetothechangesinthedurationandmagnitudeofthefloodseason.InFigure2.13theyearlycycleisshownwiththeaverageflowsinandoutofthelakeplusthevariationsinthe pattern.

Figure2.13.PatternofinflowandoutflowfromTonleSap.

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A study was made of the impact of the implementation of reservoirs on the Mekong river, including developments in the 3S tributaries. The results are shown in Figure 2.14 and Figure 2.15.

Figure 2.14. Expected changes in inundation pattern at Tonle Sap (Arias, et al, 2014).

Figure 2.15. Expected changes in inundation area at Tonle Sap in km2 (Kummu & Sarkkula, 2008).

The results of the study show that there will be a shift in the timing of the inundation period and extensioninTonleSapduetothechangesintheflowconditionsintheMekongasresponsetotheimplementationofreservoirsonboththemainriverandinthetributaries(particularlyinthe‘3S’).Ingeneral the inundation extent will decrease, while the duration of the inundation period will become longer. As a result, it can be expected that a change will occur in the ecology of the wetlands and coastal zones of the lake.



The key risks, impacts and vulnerabilities to hydrology and water resources are summarised and aggregated as follows and are also presented in the Mitigation Guidelines.

Table2.1.Hydrologyanddownstreamflows–Keyrisks,impactsandvulnerabilities.

Change Key Risks, Impacts & VulnerabilitiesAnnual / inter-annual changes to flowChanges in seasonality & continuous uniform release

Changeoftiming&durationoffloodsandlowflows,changesinflowsTonleSapandchangesin salt intrusion in the delta

Modification of flood intervals: Reduction inoccurrence of minor floods & no change inlarge events

Peaksinfloodandlowflowchange,smootherhydrograph

Daily / short-time period changes in flowHydro-peaking Safety and navigation related changes caused

by sudden rise or drop of water levels

2.3 Hydrology and Downstream Flows Mitigation Measures

As mentioned already in the introduction, there are not many options for mitigation of hydrological impact of the implementation of major reservoirs on the Mekong River (however joint releases of flowsfromdamsintributarysystemsisdiscussedintheCaseStudy).Forthesmaller(run-of-river)reservoirs, liketheonesplannedaspartoftheLaoCascade,theflowchangesthemselvesareminor and the high-frequency changes due to hydro¬peaking can in principle easily be mitigated by limitations on ramping rates and/or the introduction of Sanakam as a re-regulation dam as analysed in theCaseStudy(MRC,2018c). It isverydifferentsituationfor themajorreservoirs,particularly with inter-annual storage, where the possibilities for mitigation of the impact on the flowregimecanonlybefoundwithinthesystemitself.Intheory,itwouldbepossibletointroduceasystemofoperationalrulesthattriestomimicasfaraspossiblethenaturalflowregime,butthiswill most often be limited by the hydropower requirements.

Mitigationof thecumulative impactsof thetributaryandmainstream(includingLancang)dams,notonlyforhydrologyanddownstreamflowsbutallthemes,wouldrequirefurthertransboundarydialogue on options to adapt and coordinate the operation of these respective large storage schemes (for example joint flow releasesasmentionedabove).Hence, integratedhydropowerplanningatthesystemscale(basin,catchment)–usingthefullmitigationhierarchy(avoidance,minimization,compensation)shouldbetheNewFrontierfortheLMBcountries(seeMRC,2018c–the Case Study Report and also Schmidt et al. 2017, as well as Oppermann et al. 2013 and 2017 fordiscussiononthebenefitsofsystemscalehydropower(portfolio)planning).Loucks(2003)alsoneatlylinksthistomaximizationofbenefitsbystating–“theinterdependenceofsystemcomponentsand decisions strongly argues for managing them in an integrated holistic and sustainable manner ifmaximumbenefitsaretobeobtainedfromthem”.

Related to the above, currently the hydropower development in the Mekong has various degrees of coordination, i.e. there seems to be a lack of proper connection between the various studies and the overall integrated approach is lacking. This integrated plan could be essential though, as

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isolatedstudiesnecessarilylackaproperassessmentoftheexpectedchangesintheflowregimebyongoingorplannedactivitiesupstreamthatwilllikelyaffecttheplanninganddesignoffuturehydropower developments. The Mitigation Guidelines and Manual could be a useful tool within this context.

2.4 Indicators and Monitoring

Regarding the issue of monitoring, it should be mentioned that there is an urgent need to improve the coordination of the operation of the various reservoirs on the Mekong River. At present, there is little information on real-time operation is available along the course of the river, i.e. on the daily operation of the Chinese dams in the Lancang stretch. It is recognised that it would not be easy to make adjustments to the operation rules of the existing reservoirs, which are hardly known now, but at least information on the operation would be an option. Given the major impact of these reservoirsontheflowregimeoftheMekong,particularlyinthedryseason,suchamonitoringandearly-warningsystemwouldbeverybeneficialforthedownstreamwaterusers,bothhydropowerand other sectors.

SomeindicatorsformonitoringofhydrologyandflowsareoutlinedinTable2.2below.IndicatorsonhydrologyandflowshasalsobeenfurtherdevelopedandutilizedintheCaseStudy(seeMRC,2018cforfurtherdetails).TheseindicatorsarealsoportrayedintheMitigationGuidelines.

Table 2.2. Hydrology and Flows indicators.

System components LMB level National/ local level

Hydrology

And Flow

• Flow (sub-daily/ every hour or minute)

• Water level (sub-daily/ every hourorminute)

• Onset of wet season

• Duration of wet season

• Minimumflows

• average wet season peakdailyflow

• averageflowvolumeentering Tonle Sap

• monthly average dry seasonflow(i.e.flowinmarch)

• totalwetseasonflowvolume

21 | Chapter 3. Geomorphology and Sediments – Status, Risks and Mitigation


22

3 Geomorphology and Sediments – Status, Risks

and Mitigation



3.1 Basin Context - Status and Overview

3.1.1 Importance of sediments and sediment transport in river systems

Sediments and sediment transport are linked to the physical, chemical and biological attributes of riversystems,estuaries,andcoastalenvironments.Physically,themagnitudeandcharacteristics(grain-size,composition,surfacearea,etc.)ofsedimentmovingthroughariverdictatesthenatureandmorphologyofriverbeds,banksandfloodplainsbothspatiallyandtemporally.Thetransport,deposition, storage and erosion of sediment govern habitat distribution and quality within river channelsandfloodplainswhichunderpinsbiologicalsystemsandbiodiversity.

The seasonal timing and magnitude of sediment transport in a river is fundamental to ecological functioning, with food and nutrient delivery, migratory cues, breeding habitats, and riparian and floodplainecologicalcyclesalldependantonsedimenttransportatspecifictimesoftheyear(seealsoChapter5onFisheriesandAquaticEcology).Itisalsoimportanttorecognisethedependenceof sediment transport on riverine hydrology, and how generally sediment delivery or removal is linkedtospecifichydrologicconditionsorcycles.AsdepictedinFigure3.1,sedimenttransportneeds to be considered in four-dimensions: (i) the downstreammovement of sediment (ii) thelateral transportofsedimentbetweenthechannelandfloodplain(iii) theverticaldepositionandre-suspensionofsedimentwithintheriverchannelorfloodplainand(iv)theseasonalpatternandvariable over time.

Figure 3.1. Block diagram showing the 4 dimensions of sediment delivery: downstream (length), intoandoutofthefloodplains(width),depositionorerosioninthechannel(vertical),andvariability through time (temporal). (FISRWG, 1998).

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Sediments also play an important role in many aspects of water quality in rivers, inter alia;

• Sediment concentration and grain-size determines light penetration which controls algal or other plant growth;

• The composition of sediments determines the availability of naturally occurring nutrients, and affectstheavailabilityofoxygen(e.g.organicrichsedimentscanreduceoxygenlevels);

• The geochemical reactions between sediments and river water control fundamental water quality parameters such as pH, alkalinity and acidity (e.g. carbonates, pyritic sediments, organicrichsediment);

• The grain-size and surface area of sediments is critical for the transport of nutrients and other parameters which are transported through adsorption on the sediments. Fine-grained sediment serve as the link between solid and dissolved in the aquatic environment;

Sediments and sediment transport are also important for social reasons. In alluvial reaches, the stability of river channels and banks is dependent on continued sediment availability and delivery. Physicalchangestoriverbanksandchannelscanincreaseriskstoinfrastructurelocatedonriverbanks,affectnavigationandleadtotheredistributionofland.Physicalchangestoriverchannelscanaffectlocalhydraulics,navigation,riverbankandfloodplainagriculture,andriverineandcoastalfisheries,allofwhichcanhavesocialimpacts.Sedimentsalsoprovideareadysourceofbuildingmaterials,andchangestosedimenttransportcanaffecttheavailabilityofmaterialforextractionand / or lead to increased impacts due to the extractions.

In addition to sediment supply and transport, rivers require variability in sediment delivery to maintain the dynamic equilibrium present in natural river systems. Inter-annual variability combined with episodic extreme events is necessary for maintaining diversity within riparian zones and in-channel habitats.

3.1.2 Catchment geomorphology

TheMekongRiveroriginatesinthehighmountainsofChinaandflowsthrougharangeofgeologicand geomorphic settings which control the supply and delivery of sediment to the mainstream Mekongandultimately thefloodplainsofCambodiaandVietnam.Reviewsof thegeologyandgeomorphologyoftheriverareavailableinotherMRCreports(Carling,2005,2009;MRC,2010)and this brief overview is limited to attributes of direct relevance to hydropower development and mitigation with respect to sediment transport.

TheMekongRiverintheUMBisconfinedtoanarrow,steep,bedrockvalleyoverthefirst1800kmofitscourse,withgradientsreducingsubstantiallyintheLMB(Figure3.2).IntheLMB,thecourseof therivercontinues tobestronglybedrockcontrolled innorthernLaoPDR,beforeenteringapredominantly alluvial zone upstream of Vientiane, which extends downstream to Savannakhet (LaoPDR)/Mukdahan(Thailand).Downstreamofthispoint, theriver isstructurallycontrolledtovaryingdegreesuntil itenters thealluvial reachesof thefloodplainnearKratie. Thefloodplainreaches, which include the Tonle Sap River, Tonle Sap Great Lake and Vietnamese Delta, are considered sediment sinks in the context of the Mekong, although sediment is also derived from the tributaries feeding the Tonle Sap Great Lake.

Thedelineationoftheserecognisedgeomorphic‘zones’areshownonthemapandlong-sectionin Figure 3.2 and the general geomorphic characteristics of the mainstream are summarised in



Table3.1.Recognisingtheinherentdifferencesbetweenthegeomorphiczonesandthevariabilitywithin zones is fundamental to understanding potential changes associated with hydropower developments and identifying appropriate mitigation measures. These characteristics also have a stronginfluenceonthedistributionofhydropowerprojectswithintheLMBasthesteepersloped,bedrockcontrolledreachesinnorthernLaoPDRareconduciveforthedevelopmentofhydropoweron the mainstream. The steep slopes of the upper catchment, which also experience high rainfall runoff,arealsomajorsourcesofsedimenttotheriversystem.

1 4 3 2 5

& T

onle

Sap

R

& G

reat

Lak

e

Figure 3.2. (top left) Long-section of the Mekong River showing elevation and national boundaries (MRC, 2005). (top right) Generalised hydro-geomorphic zones of the Mekong River (MRC, 2005); (bottom) Long-section of the LMB showing depth of thalwag and extent of geomorphic zones.

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Table 3.1. Geomorphic attributes of the 5 general geomorphic zones recognised in the LMB.

Zone Reach Description Approximate River km Geomorphology

1 China Border to upstream Vientiane ~750 Single bedrock channel

2 UpstreamVientianetoKongChiam ~800 Alluvial-braided with bars; sediment storage & reworking with high sediment input from tributaries;

3 KongChiamtoKratie ~350 Anastomosed bedrock channels, storage & reworking

4 KratietoChaktoumuk,TonleSapRiverandGreat Lake

~230 Meandering alluvial channels, floodplain&TonleSapsystem

5 PhnomPenhtodeltafront ~350 Deltaic alluvial channels & distributaries

As indicated in the descriptions of the geomorphic zones, there are two areas within the mainstream which are dominated by bedrock controlled channels, namely, the zone 1, extending from the Chinese border to upstream of Vientiane, and zone 3, the anastomosing river reach between KongChiamandKratie.Theexposureofbedrockinthesereachesisextensive,asshownbythedistributionofrapids(Figure3.3).Thesebedrockcontrolledreachesarealsocharacterisedbythepresenceof‘deeppools’whichprovideaquatichabitatandrefugesduringthedryseason.ThedeepestpoolsinthemainstreamLMBoccurbetweenMukdahanandPakse,andaremaintainedby a combination of high shear stress, and the annual pattern of sediment delivery (MRC, 2005, Halls et al.,2013).



Figure 3.3. (left) Distribution of rapids in the Mekong showing distribution of bedrock controlled channels in the LMB; (right) Distribution of deep pools showing highest density and depths between Mukdahan and Pakse.

All geomorphic zones contain floodplains, ranging from discrete floodplain pockets typicallyconcentratednear tributaryconfluences, to theextensiveCambodianfloodplainandTonleSapsystem, and Vietnamese delta (Figure 3.4). These alluvial reaches are directly linked to anddependant on the sediment transport regime of the Mekong for maintenance. Alterations to the flowandsedimentregimeoftheriverwilltranslatetoadjustmentsinthesealluvialenvironments.

Thesegeomorphicreachesarediscussedinmoredetail inChapter3.3,whereMekongspecificrisks associated with hydropower development are discussed in more detail.

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Figure3.4.Distributionofareassubjecttofloodrisks(floodplains)intheLMB.Mainstreamfloodplainsshowninpink,tributaryfloodplainsindicatedinyellow.Areaspronetoflashfloodingare shown in tan. Around the delta, the areas susceptible to storm surges and tsunamis are highlighted in blue (MRC 2010).



3.1.3 Sediment transport in the LMB

SedimentdeliverytotheMekongmainstreamiscloselylinkedtotheflood-pulseoftheriver,withthehighestsedimentloadstransportedduringtherisinglimbandflood-peaksofthewetseason.Sediment investigations have found that bedload also moves as a pulse over the duration of the wet season as well, with pulses observed moving into, through and out of deep holes in the channel over the course of one year (Conlan et al.,2008).

Alterationstothequantityorcharacteristics(e.g.grain-size)ofsedimentstransportedthroughariverwill translateintogeomorphicchangestothebedand/orbanksandfloodplainsofariversystem,astherivermovestowardsanewdynamicequilibrium.Thesephysicalchangescanaffectchannelmorphology,bankstabilityandfloodplaincharacteristics.

PriortothedevelopmentofhydropoweronthemainstreamoftheMekong,thegeneralconsensuson the sediment budget of the LMB was that approximately 160 Mt/yr of sediment was transported bytheriverinsuspensionatthedownstreamsiteofPakse.Ofthistotal,approximately60%wasderived from upstream theChinese border, 10% from the 3S river system, and the remaining30%contributedbytherestofthetributaries.Noestimatesofbedloadtransportareavailableforhistorical conditions.

The suspended sediment load of the Mekong River has historically been described as silt. Recent investigationshowever (which reflect conditionsafter implementationof theChinese cascade),and monitoring by the MRC Countries, has documented both silt and sands in the suspended load.Sandispredominatingintheuppercatchment(upto80%)andgradingtosiltdownstream,wheresandcomprisesabout10%ofthesuspendedload(Bravardet al.2013,Koehnken,2014).Bedload and bed textures in the LMB have been found to vary over distance and time in the river bed.Coarsergravelsandsandspredominateintheuppercatchmentduringperiodsofhighflow,gradingtofinersandinthelowerriver.Duringthedryseason,finermaterialisdepositedontheriver bed, leading to an increase in the proportion of silt in the bed materials.

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Figure 3.5. (left) Schematic showing distribution of sediment input to the LMB based on WUP-FIN modelling; (right) Grain size distribution of suspended sediments in the Mekong mainstream in the LMB. CS=Chiang Saen, LP=Luang Prabang, NK=Nong Khai, PK= Pakse, KT= Kratie and TC=Tan Chau (Koehnken, 2015).



3.1.4 Recent changes to sediment transport in the LMB

The development of the Lancang cascade in the UMB, damming of tributaries for hydropower and irrigation,andothercatchmentdevelopmentshavealtered theflow regimeof the riverand thesediment dynamics of the mainstream Mekong.

Sediment trapping by reservoirs is well recognised, with the extent to which sediments are trappeddependentonthemorphologyoftheimpoundment,thecharacteristics(grain-size)oftheinflowingsediments,thehydrodynamicswithintheimpoundmentandtheoperatingregimeoftheproject.SedimenttrappingefficienciesderivedfortheLancangcascade(Figure3.19)showthatthe smaller impoundments, such as Manwan and Jinghong have lower rates as compared to the larger impoundments, such as Gonguoqiao and Nuozhadu. Sediment trapping is cumulative, but as coarser material is trapped in upstream impoundments, the actual trapping rates in downstream impoundmentsmayreduce,duetothefiner-natureoftheinfluentsedimentload.Thispreferentialtrappingcanalsoleadtonutrientsbeingtrappedindifferentproportionsascomparedtosediments,duetonutrients’affinityforthefiner-grainedsediments.

Understanding the distribution of nutrients with respect to sediment grain-size is a knowledge gap in the Mekong. Integrated water quality and suspended sediment monitoring and investigations are required to provide this important information.

Figure3.6.TheoreticalsedimenttrappingefficienciesoftheLancangcascade(KummuandVaris, 2007).

Consistent with predicted sediment trapping, the sediment load in the LMB has decreased as dams in the UMB and LMB tributaries have been completed, leading to a large reduction in the suspended load of the river. Recent MRC monitoring results suggest that suspended sediment loads in the LMB are now in the range of ~70 Mt/yr, compared with the historic values of ~160 Mt/yr

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(Koehnken,2014).Largereductionhavebeenrecordedatallmonitoringlocations,withthelargestreduction occurring at the upstream site closest to the cascade, Chiang Saen, where suspended sediment loads are now estimated to be ~10-12 Mt/yr as compared to historic values of 60-100 Mt/yr(Figure3.7).Nohistoricinformationisavailableregardingthegrain-sizedistributionoftheload entering the LMB from the UMB, but it is likely that the reduction in sediment loads has been accompanied by a reduction in grain-size distribution due to the coarser sediment being more efficientlyretainedintheimpoundments.

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Figure 3.7. (left) Comparison of historic (coloured bars) and recent (blue bars) suspended sediment loads at monitoring sites on the Mekong mainstream. Historic loads based on results from MRC Master catalogues and recent results based on sediment monitoring completed by the MRC Member Countries (Koehnken, 2014).

(right) Box and whisker plot summarising of suspended sediment concentrations at ChiangSaen between 1994 and 2013 based on historic results and recent monitoring results. The box encompassesthe25thto75thpercentilevalues,whilstthe‘whiskers’indicatetheminimumandmaximum values. The median is shown as a line in the box.

In addition to a reduction in the magnitude of sediment delivery from the UMB, there have also beenrecentchangestothetimingofsedimentdelivery.TheMekongisa‘sediment’pulsesystemaswellasahydrologicalfloodpulsesystem,with60%ofthesedimentloadtransportedwithina2monthperiod,and80%withina4monthwindowundernaturalconditions.AsshowninFigure3.8,thispatternremainsintactatKratiethroughoutthe2009–2013period,howeveratChiangSaen,the timing of sediment delivery is being altered, as evident by the 2013 results. The downstream sites(suchasKratie)arelesssusceptibletothechangesrelatedtotheLancangCascade,butasmore tributary dams are commissioned and operate, similar changes to sediment delivery patterns may occur in the lower LMB as well.



Figure 3.8. Timing of sediment delivery in the LMB 2009 - 2013. Graphs show percentage of total sediment load transported each month at Chiang Saen and Kratie (from Koehnken, 2014).

3.1.5 Otheractivitiesaffectingsedimenttransport

In addition to sediment trapping in dams, other activities in thebasin affect thehydrologyandsedimenttransportoftheLMB.Relevantactivitiesincludesandmining,theinfillingoffloodplains,andthedevelopmentofinfrastructurefloodplains.

Sand and gravel extraction from the LMB has been cited as altering the sediment budget of the mainstream Mekong, with extracted quantities conservatively estimated at >35 Mm3 in 2011, equivalent to ~50 Mt/yr (Bravard, et al.,2014).ExtractiveindustriesarepredominantlyremovingsandfromtheriverbedandtheseactivitiesareconcentratedinthelowerLMB,with~80%ofthedocumented extractions occurring in Cambodia and Viet Nam. Large volume extractions can lead to bed incision and channel instability due to over-steepening of banks.

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Figure 3.9. Map of aggregate extraction in the LMB based on surveys of operators (Bravard, et al, 2014).



Muchofthesandextractedfromtheriverisusedforfloodplainfillingwhichaffectsthehydrologyandgeomorphologyof theriver in twoways: (i) Infilling reduces thevolumeavailable forwaterstorageon thefloodplain, thus reducing thebufferingcapacityof thesystem,and reducing theconnectivitybetweentheriverandfloodplain;and(ii)becausethereisreducedstorageavailabilityonthefloodplainwaterremainsinchannelswhichincreasesflowvelocitiesandpromoteschannelincision. Channel incision will lead to deepening and increase channel capacity, which in turn will reducetheconnectivitybetweentheriverandthefloodplain.

In addition to the direct filling of floodplains, the construction of roads and other infrastructurecan alter the local hydrology and hydraulics of an area, leading to hydrologic and geomorphic change. The photos shown in Figure 3.10 are a time series of the divide between the mainstream MekongandtheTonleSap.Overlandflowbetweenthesewaterwayshasbeendisruptedbytheconstructionofanelevatedroadway,andthesubsequentinfillingofthefloodplain.

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Figure 3.10 . (Top 4 photos) time-series of progressiveinfillingofthefloodplainbetweenthe Mekong mainstream and Tonle Sap Rivers; (left) map showing route of historic overland from Mekong mainstream to Tonle Sap. Exchange has been limited by road constructionandfloodplaininfilling.

In the Mekong Delta, investigations have been completed examining the relationship between sediment delivery to the floodplain and the canals and otherwatermanagement infrastructure

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present in thedelta (Figure3.11). Apelet al., (2012) found that thehighest concentrationsofsedimentand thehighest rateofsedimentdepositiononundevelopedfloodplainsoccurduringtheonsetoffloods. Theresearchers found that thevastnetworkofcanals in thedelta restrictthe sedimentpulse reaching thefloodplain,withgatesandpumpsalsoaltering the timingandextentoffloodplaininundation.Insteadoffloodpeakscontrollingsedimentdispersal,theheightofcontrol structures and timing of operations controls sediment distribution. Smaller, but numerous built structures such as embankments, channels and dykes, have more localised effects onfloodplains,butmostprobably lead tosignificantcumulative impacts (WorldFishCenter,2007).

Figure 3.11. Map of Mekong Delta in Vietnam indicating the density and extent of the excavated canalsystem.Blueareaindicatesextentoffloodingin2000.(MRC,2005).

3.1.6 Observed geomorphic Changes associated with Altered Sediment Delivery

A reduction in suspended and bedload sediment transport has the potential to alter the distribution andquantityofsedimentdepositedinthefloodplain,deliveredtothedelta,orstoredinthechannel.Reductionsinsedimentloadcanalsoaffectwaterqualityandecologicalprocessesthroughthelossofavailablenutrients,oraltereddeliverypatterns.Impactsfromareductioninfine-grainedsedimenttransportaremorelikelytooccurinareaswherefinesedimentswerepreviouslydeposited.Thesecan be at long distances from the site of sediment retention. The impacts may be evident over relatively short-time scales due to the immediate reduction in transported material. Conversely, changes in the transport of coarser material which is predominately transported as bedload, may be delayed relative to the reduction in sediment loads due to the availability of sediment resident in the channel for downstream transport.

In recent investigations, sand extraction in the delta has been linked to changes in the morphology of the Mekong and Bassac River channels (Brunier, et al.,2014).AlinkhasalsobeensuggestedbetweenthereductioninthesuspendedsedimentloadintheMekongandalterationstotheflowregime toerosionof thedelta front (Anthony,2015).Basedonananalysisof satellite imagerybetween 2003 and 2011, annualised average retreat rates of the delta front – range from ~3 m to ~12mindifferentsectorsofthedelta.



Recent research has also shown that the attributes of the coastal plume of the river have altered over the 2003 – 2011 period, with changes consistent with a reduction in sediment delivery to the SouthSea(Loisel,2014).Itisacknowledgedthatthesystemsarecomplexandotherfactorsarealso cited as potentially contributing to the observed changes, such as changes to the morphology ofthedeltachannels,flowchanges,climatechange,seallevelriseandcoastaldynamics.

One of the hindrances in the LMB to understanding or recognising geomorphic change is a lack of understanding regarding the natural or present rates of change in the river. Rates of erosion or deposition or large scale long term changes such as channel migration or alterations have not been documented.

A better understanding of the present and past rates of geomorphic change in the rives is required in order to better predict, manage and mitigate changes associated with hydropower or other water resource developments.


HPprojectscanaffectsedimenttransportthroughtwomechanisms:

• Alterationoftheflowregimewhichaffectssedimenttransport;and,

• AlterationofthequantityofsedimentavailabledownstreamoftheHPproject.

Typicalflowandsedimentchangesandcommongeomorphicresponsestotheseflowchangesaredescribedintheflowingsections,andsummarisedinTable3.2.

Table3.2.Geomorphology&sediments–Keyrisks,impactsandvulnerabilities

Change Key Risks, Impacts & Vulnerabilities

Annual / inter-annual changes to flow

Changes in seasonality & continuous uniform release

Water logging & loss of vegetation leading to increased bank erosion Increased erosionduetoincreasedscour(bedincision,bankerosion)

Winnowing of smaller sediment leading to bed armouring & reduction in downstream sediment supply

Bank scour focussed over limited range leading to increased bank erosion

Modificationoffloodintervals: Reduction in occurrenceofminorfloods&no change in large events

Channel narrowing through encroachment of vegetation Increased risk in upstream offloodingandfloodplainstrippingduringlarge(>1:10ARI)floodevents

Change in relationship of flow&sedimenttransport

Decouplingoftributary&mainstreamflowsErosionand/ordepositionduetotributary rejuvenation

Daily / short-time period changes in flow

Hydro-peakingRapid wetting & drying of banks increases susceptibility to bank erosion and seepage processes

Increaseinshearstressduringflowchangesincreaseserosionandbedincision

Loss of river connectivity

Disconnectbetweenflowand sediment delivery

Sediment availability not timed with periods of recession leading to decreased deposition

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Lossofsediment‘pulse’

Creation of impoundments

Trapping of sedimentsReduction in sediment availability downstream of dam leading to increased erosion

Changes to the grain-size distribution of sediment downstream contributing to channel armouring and alteration of habitats

Water level changes within impoundment Lake bank erosion, increased risk of landslips

Diversions or intra basin transfers

Decreasedflowindonorbasin

Channel narrowing due to vegetation encroachment

Armouring of beds and bars due to reduced sediment transport

Decreaseinfrequencyofhighfloweventsincreasesimpactsofextremeevents(upstreamflooding,floodplainstripping)

Increasedflowinreceivingbasin Increasedbankerosionandbedincisiontoaccommodateincreasedflow

3.2.1 Annualandinter-annualflowchanges

Continuous uniform flow release: Uniformflowreleasesaretypicallyassociatedwithbaseloadpowergeneration,withlowornovariabilityofflowinthereleasefordaysorweeksatatime.Thesetypes of discharges can affect banks by increasing and concentrating scour at discrete levelsalong a bank face. Unregulated rivers generally induce scour at a range of bank levels owing to thevariabilityofflows.Ifthevariabilityisremoved,thenscourcanbefocussedwithinanarrowrangeofbankheights, inducingbankinstability.Theextendeddischargeofauniformflowlevelcan also result in the removal of vegetation from river banks, through inundation and water logging. The loss of vegetation will increase bank instability due to a reduction in the physical protection and buttressing of the bank associated with the loss of roots and foliage, and a decrease in bank roughnesswhichwillincreasethesusceptibilityofthebanktoerosion.Extendedcontinuousflowswill also prevent the deposition of organic matter on bank faces, thus diminishing plant recruitment, and ultimately leading to denuded bank faces, which are more susceptible to erosion.

Inthebedoftheriver,sedimentswhichcanbetransportedbytheuniformflowwillbewinnowedand moved downstream, reducing the variability of bed sediment grain-sizes, and increasing the riskoftheremainingmaterialbecomingimmobileand‘locked’.

Inaddition,prolongedelevatedflowlevelswillincreasebanksaturation,andincreasetheriskofseepage failure following power station shutdown. Seepage failure occurs when the river level drops rapidly, and saturated banks are unsupported, and unstable. As water drains from the banks along steep groundwater slopes, sediment can be entrained and transported out of the bank, leading to bank failure.



Figure 3.12. Example of hydrograph showing Baseload power generation over a 1-month period.

Figure 3.13. Example of vegetation and soil loss from the riparian zone due to extended inundation associated with baseload power generation in Western Tasmania, Australia.

Reduction in medium flood flows:Alteringthefloodfrequencywith inarivercanchangethe‘mosaic’ of erosion and deposition occurring within unregulated rivers. High flows periodicallydeliversedimentstofloodplains,soreducingthefrequencyofhighflowscanreducedepositiononfloodplains.Highflowsexerthighratesoferosionforshortperiodsoftimeinriparianzones,whichdrivesdiversitywithintheriparianenvironment.Reducingthefrequencyofhighfloweventcanleadto a reduction in the extent of the riparian zone due to terrestrial vegetation moving downslope. Whereflowvariability isgreatlyreduced,theriparianzonemaydisappear.Thesechangesmayactually increase bank stability, but also lead to channel narrowing due to the encroachment of vegetation.Wherethisoccurs,thereisahighriskoffloodingstrippingandfloodingwhenahighflowdoesoccur,owingtothereducedcapacityofthechannel.

Reduction in large flood events: Large storage impoundments that have the capacity to retain ordampenverylargefloodscanaffectthegeomorphologyofthedownstreamchannelthroughthedecouplingofmainstreamandtributaryinflows.Thechangesintherelativemagnitudeandtimingofflowinthemainstreamandtributarieswillleadtoadjustmentsoftherivermorphologyattributaryconfluences.Confluencesmayexperienceincreasederosion,leadingtochannelwideningofthetributary,orincreaseddepositionleadingtothecreationof‘rejuvenation’bars.

Similartoareductioninmediumflowevents,areductioninverylargefloweventsovertimewilllead to channel constriction due to increased vegetation growth on banks and bars, such that when alargeflooddoesoccur,thereisreducedchannelcapacityleadingtoahigherriskoffloodplainstrippingandassociatedflooding.

3.2.2 Short-termflowfluctuations

Hydro-peakingoperations:Totargetperiodsofhighvalueelectricitytariffs,hydropowerplantsareoftenoperatedina‘peaking’modewheredischargeislimitedtocertainperiodsoftheday,andthestation is either shut-down or discharging very low volumes of water during the remaining hours. Therapiditywithwhichhydropowercanbestartedorstoppedmakesitsuitedtotargeting‘peak’power periods, but the rapidly changing water levels can increase bank erosion through seepage processes, as described in the previous section. Hydropeaking can also lead to bank scour owing

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to the high shear stresses associated with changing water levels (shear stress is proportional to thewatersurfaceslope).Combined,theerosionalprocessofseepageandscourcanleadtobankretreat, through the mobilisation and deposition of bank material onto bank toes following power station shut-down due to seepage processes, and then the subsequent removal of the material byscourduringthefollowingoperational‘peak’.Erosionwillcontinueuntilalong,low-anglebankslopeiscreatedwhichisstableunder‘seepageconditions(Figure3.16).

Figure3.14.Hydrographshowingeffectofhydropeaking on water levels in the upper SrePok River, Vietnam.

Figure 3.15. Seepage erosion on a sandy alluvial bank downstream of a hydropower scheme in Tasmania, Australia.

Figure 3.16. Low-angle bank slope developed on an alluvial bank downstream of a hydro-peaking hydropower project in Western Tasmania, Australia.

3.2.3 Loss of river connectivity and creation of impoundments

The trapping of sediment within a hydropower impoundment alters the timing and magnitude of sediment delivery downstream of the dam. Trapping of sediment will also alter the grain-size distributionofsedimentwhichpassesthroughthereservoir,andusuallyresultsinafiningofthesuspended sediment load downstream. Bedload, generally composed of coarser sediments, is very efficientlytrappedwithinimpoundments,whereastheretentionoffinersedimentsisdependentonthe retention time and water velocity within the lake. A reduction in sediment discharge downstream of the dam frequently results in one or more of the following geomorphic changes:

• Erosion of alluvial banks or in stream bars downstream of the power station;

• Armouring(winnowingoffine-sedimentsand‘locking’ofcoarsersediments)oftheriverbed;

• Alteration to the level of the river bed;



• Changes to the extent and magnitude of sediment deposition, and changes to the composition of the deposited sediments;

• Changestothevegetationonriverbanksandfloodplainswhichaffectsbankstability;

• Increased flooding upstream due to deposition of sediments at the upstream end of thereservoir.

Inadditiontogeomorphicchanges,theretentionofsedimentwithinreservoirscanaffecthydropoweroperations through the loss of storage (notably the active storage by the deltaic deposits at the headoftheimpoundment),cloggingofoutlets,andabrasionofturbinesorotherinfrastructure.

3.2.4 Intra or inter-basin transfers

Divertingwaterfromonecatchmenttoanother,willaffectthegeomorphicprocessesinboththedonor and recipient waterways. The geomorphic changes typically associated with the donor catchmentduetoreducedflowincludechannelnarrowingthroughtheencroachmentofvegetation,and a reduction in sediment transport of material delivered by tributaries. These changes can lead to increasedimpactsduringlargefloodsasthechannel isnolongercapableoftransferringthesame volume of water.

Conversely, the receiving catchment is generally characterised by an increase in channel depth and/orwidthduetotheincreasedflowvolumes.Increasederosionandassociatedbankinstabilityarecommonimpactsassociatedwiththeseflowchanges.

3.3 Identification of LMB specific geomorphic risks associated with HP de-velopments

HowhydropowerdevelopmentintheMekongmainstreamortributarieswillaffectthegeomorphologyof the rivers will vary depending on the attributes of the area, and the operation of the hydropower scheme. The following sections highlight potential changes associated with each of the fivegeomorphic zones in the LMB.

3.3.1 Zone1:ChiangSaentoupstreamofVientiane

The characteristics of the Mekong in this zone include steep slope, a single channel, strong bed-rock control, with bedload consisting of a high proportion of gravels. The area is also characterized by extensive, transitory sand deposits, which are concentrated near the mouths of tributaries and at local slope breaks. The reach has recently experienced a large decrease in sediment supply and alterations to water levels due to development of the Lancang Cascade, and geomorphic changes arealreadyoccurringwithinthereach.ThecommissioningoftheXayabouriHPandtributarydamsinthenearfuturewillfurtheralterflowsandsedimenttransportthroughthereach.

Althoughthemorphologyofthechanneliscontrolledbybedrockatthelargescale,modificationstothesandyinsets(bedmaterial,bankdeposits,sandbarsandislands)arelikelytoincludethefollowing:

• Reduction in the presence of gravels and sands in the bed of the river due to reduced supply. This could lead to channel deepening in some areas, but will be limited by the depth of bedrock;

• Erosion of sandy banks and islands leading to the potential loss of habitat and river side

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gardens or other land;

• Loss of riparian vegetation due to increased inundation during the dry season;

• Reductionintheheightoftheriparianzoneduetoareductioninfloodflows;

• Increased exposure of bedrock;

• Conversion of a 100 km of river environment to a lake environment following closure of the Xayabouri dam.

Recent observations suggest that geomorphic changes associated with changes to water level in the dry season are already occurring, with the loss of vegetation, and erosion of banks. Bank protection measures have been, and are being implemented at a large number of locations in the zone,whichmayreflectincreasedbankerosioninthearea.

Figure 3.17. (top left) Google Earth view of a reach in zone 1, showing strong bedrock control and localised sandy deposits; (top right) photo of eroding sand bank showing lines associated withextendedperiodsoffixedwaterlevelsanderodingsoilsandtrees;(middleleft)hydrographshowing increase in dry season water levels at Chiang Saen; (middle right) Loss of vegetation in riparianzoneduetoextendedinundation;(bottomleft)bankflatteninganderosionbetweentreeswhich are stabilising local bank.



3.3.2 Zone2–UpstreamVientianetoKongChiam

ThegeomorphiczonethatextendsfromupstreamofVientianetoKongChiamischaracterizedbylowerslopesascomparedtotheupstreamzone,andlongalluvialreachesborderedbyfloodplainsofvaryingwidth.Themainstreamchannel is incisedthroughfine-grainedfloodplaindeposits inmanyareas,resultinginsteepfine-grained,lateriticbanksthroughoutthezone.Lozengeshapedislands are similar in characteristic to the lateritic banks, with more mobile sand deposits creating barsadjacenttotheislands.Thefloodplainsborderingthechannelareunderlainbythicklateriticdeposits,which yield fine-grainedsedimentswhendisturbed. Within thezone there isa largeincrease in flowand sediment load in the river owing to the inflowof the ‘left bank’ tributariesfromLaoPDR,whichhavesomeofthehighestrunoffratesinthecatchment.Severalofthesetributarieshavealreadybeendevelopedforhydropower(NamTheun,NamHinboun),andmanyotherHPprojectsareunderdevelopmentinthiszone.

Theinfluenceofbedrockincreasesinthedownstreamendofthezone,withthereachbetweenMukdahan and Kong Chiam characterized by very deep pools, which are likely controlled bybedrock at depth. In this reach the channel is also constrained by bedrock and rapids become more common.

ThiszoneisalreadyexperiencingflowchangesassociatedwiththeLancangCascadeandtributarydevelopments. There are no mainstream dams planned for this zone of the river, but in the future theflowandsedimentregimeofthezonewillcontinuetobemodifiedduetotheestablishmentofthecascadeinupperLaoPDR,andthecontinueddevelopmentofhydro-resourceswithinthetributaries.

PotentialgeomorphicchangesrelatedtothiszoneassociatedwithHPdevelopment includethefollowing. Many of these processes are likely already occurring due to the existing hydropower development in the Lancang and tributaries.

• Channel widening in alluvial reaches due to a large reduction in sediment load such that erosion is not balanced by deposition;

• Channel incision leading to a reduction in the connectivity between the river channel and the floodplain;

• Lossofvegetationduetotheincreasedindryseasonflowsleadingtoinundationandwaterlogging. Vegetation may also increase above the regulated high water level owing to a reductioninfloodevents;

• Tributaryrejuvenationduetothedecouplingofflowsbetweenthemainstreamandtributaries.This impact will be compounded in this reach due to the large number of tributary Hydro projectswhichwilleventuallyoperate,andbecausethealluvialnatureofconfluencesinthezone.Relativechangesinflowsbetweenthemainstreamandtributariesarelikelytoinducechangestothemouthsoftributaries,potentiallyextendinguptothelevelofMekonginfluenceonthefloodplain,

• Potentiallossormodificationofdeeppools.Deeppoolsaredependentonmaintainingthetiming of the sediment pulse in the river, and the high shear stress of the river during peak flows.Asthecumulativeimpactofmainstreamandtributarydamsaltersflowmagnitudesand sediment timing, the risk of change to the deep pools will increase.

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Figure 3.18. (top left) Mekong River upstream of Kong Chiam showing broad valley and bedrock constrainedchannelandbedrockislands;(topright)Alluvialriverbankandfloodplainalongthe Mekong River upstream of Kong Chiam; (bottom left) alluvial river bank in tributary in North eastern Lao PDR showing lateritic characteristics and susceptibility to erosion; (bottom Right), Graph of Total Suspended Solids at Pakse showing reduction in suspended sediment over time.

3.3.3 Zone3KongChiamtoKratie

ThezoneencompassingKongChiamtoKratieishighlyvariable,andincludesalluvialandbedrockcontrolled channel reaches. Slope within the zone varies, and is locally steep in the bedrock sections. An interesting characteristic of the reach, is the development of anastomosing channels within bedrock in several sections. These sections also contain a wide range of alluvial deposits and islands. Lozenge shaped islands similar to those occurring upstream are also present, as are thethicklateriticriverbanks.Thezoneisalsocharacterizedbytheinflowofthe3SRiversystem(SrePok,SeSan,SeKong)whichcontributesalargepercentageofwaterandsedimenttothesystem. Floodplains are generally concentrated in the upper and lower reaches of the zone, with highflowaccommodatedwithinthebroad,multi-channeledreachinthemid-zone.

Geomorphic risks associated with the development of hydropower in the LMB include:

• Bank erosion and channel incision within the alluvial reaches;• A loss of the sandy insets and islands in the bedrock controlled reaches leading to an

increased exposure of bedrock;• Lossofvegetationduetoinundation,withthe‘flooded’forestscharacteristicofthisreachat

riskduetotheincreaseindryseasonflows;• The conversion of a river environment to a lake in areas upstream of future dam construction.



Figure 3.19. (top left) Oblique Google Earth image showing multi-channelled bedrock controlled area downstream of Pakse, and entrance of the 3S River system; (top right) View of Mekong upstream of Kong Chiam showing broad channel and bedrock constrained channel; (middle left) multi-island area upstream of Kratie; (middle right) sand deposits on islands upstream of Kratie; (bottomleft)floodedforestnearLaoPDRCambodian border.

3.3.4 Zone4:KratietoChaktomukandTonleSap

ThezoneextendingfromKratietotheChaktomukconfluence,andtheTonleSapRiverandGreatLakeischaracterizedbyalluvialreachesflowingthroughextensivefloodplaindeposits.Thereachhas lowriverslopes,andthick lateriticfloodplains.Little ‘new’sedimententers thisreach(e.g.minor tributariesandthetributariesof theGreatLake)andsediment transportedbytheriver isderivedfromupstream,orreworkingofthefloodplaindeposits.Thelowerslopeoftheriverresultsinthesuspendedloadoftheriverbeingcharacterizedbyfinergrainsizesascomparedtoupstream.

ThetimingandmagnitudeofflowandsedimentmovingintoandoutoftheTonleSapRiverandintotheGreatLakearestronglyinfluencedbywaterlevelintheMekongmainstream(seeChapter2),andthesystemprovideswaterandsediment‘buffering’tothedownstreamdelta.

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Hydropower associated geomorphic risks associate with this zone include:

• A potential increase in bank erosion, channel incision and channel migration associated with thereducedsedimentloadsandalteredflowregime;

• Anincreasingdisconnectionbetweentheriverchannelandfloodplainduetodeeperchannelsandreducedpeakfloodflows;

• Lossofvegetationduetoinundationassociatedwithincreaseddryseasonflowlevels;

• A reduction in the magnitude and change in the timing of the sediment pulse entering the Great Lake.

Figure 3.20. (top left) Google earth image showingMekong,CambodianfloodplainandTonle Sap system; (top right) Fine-grained river bank downstream of Kampong Cham, (Middle left) View of Mekong downstream of Kampong Cham showing bank protection works,broadriverchannelandfloodplain;(middle right) Clay material dredged to create channel in Tonle Sap; (bottom left) grain-size distribution of suspended sediment at Kratie in 2012-2013 showing dominance of silt in suspended load (Koehnken, 2014)



3.3.5 Zone5Delta

FromtheChaktomukconfluencetothesea,theMekongischaracterizedasabroad,flatalluvialdeltasystem.Thezonehasaverylowslope,andflowandsedimentmovementisaffectedbytidalinfluences.No‘new’sedimententersthezone,withallmaterialderivedfromupstreamorfromre-working within the deltaic environment. The suspended sediment load is characterized by a higher proportionofclaysandfinesiltsascomparedtoupstream,withsandpredominantlytransportedasbedload.Flowandsedimentdispersioninthedeltahasbeenmodifiedthroughthedevelopmentof an extensive canal system and other water management infrastructure.

Risks associated with the development of hydropower upstream include:

• Bank erosion and channel incision and channel migration;

• Anincreasingdisconnectbetweentheriverchannelandfloodplainduetodeeperchannelsandreducedpeakfloodflows;

• Loss of riparian vegetation due to increased inundation during the dry season;

• AlterationoftheseasonalrelationshipbetweentidalforcesandtheflowandsedimentpulseintheMekong,potentiallyleadingtoamodificationofsaltintrusionintheestuarybranchesand the estuarine turbidity maximum;

• Decreasing floodplain availability for water storage through infilling and infrastructuredevelopment can induce channel incision by forcing water to remain within a restricted area. This can exert a similar pressure on the channel as hydropower projects;

• Reductioninthesupplyoffinesediment(washload)totheinundatedareasinthedelta,dueto sediment trapping by upstream reservoirs and changes to the magnitude and duration of flooddischarges.

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Figure 3.21. (top left) Oblique Google Earth image showing the Chaktomuk bifurcation near Phnom Penh to the delta shoreline; (top right) Canal and floodplainindeltaarea;(middleleft)BassacRivernear Chau Doc showing development; (middle right) River bank near Leuk Daek on Mekong River showing evidence of erosion ;(bottom left) grain-size distribution of suspended material at Tan Chau on the Mekong River, 2012-2013 (Koehnken, 2014).

3.3.6 InteractionbetweenHPimpactsandothercatchmentdevelopments

HydropowerisnottheonlydevelopmentintheLMB(orUMB)affectingtherivergeomorphology.As discussed in 3.1.5, activities such as sand mining, and infrastructure developed to control flow,channelalterationstoimprovenavigation,ordevelopmentsonfloodplainscanalsoinducegeomorphic change in the river.

Recognising the potential relationship and linkages between these various development activities is necessary in order to identify cumulative impacts. Some important feedback mechanisms and linkages include:

• Channel incision and floodplain isolation; both hydropower and sand mining have thepotential to induce river bed incision and bank erosion through a reduction in the availability of sediment. The extraction of sand and gravels downstream of hydropower projects has the potentialtoexacerbatetheimpactsofsedimenttrappingbytheHP;

• TheextractionofsandcombinedwiththetrappingofsedimentinHPprojectswilldecreasethe sediment available to the downstream environment for maintenance of depositional environments,suchasthefloodplainanddelta;

• Pump and storage irrigation projects have the same potential to alter flow regimes andsediment balances as hydropower developments.

3.3.7 LMBSpecificchallengesassociatedwithsedimentmanagement

The present status of the Mekong River needs to be considered when identifying potential mitigation measures. The LMB is in a state of change due to developments and activities in the UMB and within the LMB. These changes are likely to be inducing geomorphic changes to the river channel andfloodplainatpresent,andneedtoberecognisedwhenconsidering‘baselines’andpotentialfuture changes.

Lancang Cascade & tributary dams: The implementation of the Lancang Cascade has altered the timingofwaterandsedimentdelivery.Changesincludeincreaseddryseasonflows,adelayintheonsetofthewetseason,andalesspronouncedrelationshipbetweenflowandsediment.SomeoftheseflowchangesareshowninFigure3.22.Thelossofstrong,consistentseasonalitywithintheflowandsedimentregimeoftheriverwillmakeitchallengingtoidentifyperiodswhensedimentsluicingorflushingmightbeapplicable.Thevariabilityofflowscouldalsomakeenergyplanningmore challenging.



Theflowandsediment regime in theLMBwill continue tochange into the futureasadditionalhydropower projects come on line, and other water resource development projects are implemented. In particular, the larger, inter-annual storage schemes that have been and continue to be developed in some tributaries will increase the water discharged during the dry seasons, and decrease wet seasonflows.Theseongoingchangeswillpresentchallengesformanagingdownstreamdams,and highlights the need for flexibility with respect tomitigation, and operations. Coordinatingoperationswithinandbetweencatchmentsislikelytoleadtothemostefficientoperationsandbestenvironmentaloutcomes,forexamplethroughjointflowreleasesandflushing/sluicing(seeCaseStudyreport).

Geomorphic impact of sediment extractions: Large volumes of sand, pebbles and gravels are extracted from theMekongeachyear foruse in floodplain in-fillingandconstructionmaterials.Recent estimates (Bravard et al., 2014)basedonsurveysofextractiveoperationswereof theorder of ~35 Mm3/yr, with most of the extractions occurring in the lower alluvial reaches of the Mekong. The geomorphic impacts of extractions of this magnitude are unknown, although anecdotal observations suggest increased bank failure near extractive sites. However, the present degree or ratesofchangetothebanksandbedoftheriverareunquantified,soquantifyingtheseimpactsisnot possible based on present available information.

Unknownfuturewaterresourcedevelopments:Predictingfuturechangestoriverfloworsedimentinputisdifficult,ascatchmentdevelopmentsoverperiodsofdecadestocenturiesareunknown.ThedevelopmentofHPprojectsalsoincreasesdevelopmentopportunitiesthroughtheestablishmentof access roads, lakes and other infrastructure. These developments in turn promote other opportunities, such as forestry, irrigation, aquaculture, tourism and other recreation which in turn canaffectinflowstoHPprojects,orrequireadditionalregulationofoutflowstomeetdownstreamneeds or values. As it is not possible to predict the future, planning and designing for operational flexibilityisthebestapproachtominimisingthisrisk.

Figure3.22.ElevatedflowduringthedryseasonatChiangSaen(left)andPakse(right).Purplelineindicates2014–2015dryseasonflows,darkbluelinedenotesthelongtermaverage,orangelineshowspreviousyear’s(2013-2014)flowpattern.

3.4 Geomorphology and Sediments Mitigation Measures

This section provides an overview of mitigation approaches relevant to hydropower developments and includes general descriptions of approaches and the underlying theory behind mitigation measures.

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3.4.1 BackgroundinformationfromtheMRCPreliminaryDesignGuidance

TheMRCPreliminaryDesignGuidance forMainstreamDams (2009) provides an overview ofpotential sediment related impacts associated with the development of hydropower projects and approaches for mitigation and management. These impacts include reservoir deposition, changes tosedimenttransportfrominflowingtributaries(bothinthereservoiranddownstream),downstreamchannel adjustments related to changes in hydrology and sediment loads and associated impacts on habitat distribution and quality. A summary of guiding principles for considering sediment related issues during the planning phase is provided for developers, which highlight the importance of:

• Understanding the relationships between hydraulics, river morphology and ecology;

• Assessing whether dam developments should be avoided in reaches susceptible to severe morphological change;

• Making dams transparent to sediment transport as much as possible;

• Considering sediment transport issues associated with tributary inputs.

ThePDG(MRC,2009)discussesarangeofsedimentmanagementoptions,includingsedimentrouting,sedimentbypass,sedimentflushing,mechanicalremoval,sedimenttrapsandsedimentaugmentation downstream of reservoirs. General guidance is provided with respect to site selection, modelling and monitoring of sediments into, within and downstream of the impoundment, and the inclusion of gates to enable sediment management options. Operational and ecological issues associated with the timing of sediment management are also highlighted, with an emphasis on continued monitoring over the life-cycle of the project to guide management strategies. Reactive measures, such as physical bank protection are indicated as a means of mitigating impacts which cannot be avoided through management of the project.

The following sections provide a more in-depth description and consideration of the issues addressedinthePDGandMitigationGuidelines.

3.4.2 General approaches to geomorphology and sediment mitigation

As previously discussed, mitigation measures to address sediment transport and geomorphic aspectsofhydropowerdevelopmentsneedtobeconsideredateverystageoftheHPlife-cycle(seealsoChapter5and6intheMitigationGuidelines).Mitigationneedstobeanintegralpartofthe planning, development, construction and operational periods of a project, and not something that is considered reactively, in response toa ‘problem’. Theenvironmental challenges facingHPschangeover time,as impoundmentsdevelopandcatchmentactivitiesevolve. Frequentlythechallengesfacinganewoperationaredifferentascomparedtothosefacingthesameprojectafterdecadesofoperation,andlong-termflexibilityneedstobeakeycomponentofallmitigationstrategies.

Mitigation measures need to be based on an accurate and detailed understanding of the river system, with ongoing and long-term monitoring at a variety of spatial and temporal scales required for the identificationand implementationofeffectivemitigationstrategies. InformationandmonitoringneedsassociatedwithhydropowerprojectswereidentifiedandsummarisedintheISH11Project,whichshouldbeconsultedformoredetail.Indicatorsrelevantforidentifyingandevaluating mitigation measures are discussed in Section 3.5.



Whilst mitigation strategies are generally aimed at ameliorating an impact or stress resulting from hydropower operations, mitigation strategies should also be considered with respect to the potential forincreasingtheoperationalflexibilityofahydropowerproject.Forexample,are-regulationweircanhelpmitigatedownstreamgeomorphicimpactsassociatedwithwidelyfluctuatingwaterlevels,thusprovidingoperationalflexibilitytotheoperatorsofthescheme.Similarly,aerationweirswhichincreasetheoxygencontentofwaterdischargedfromahydropowerprojectenablemoreflexibilitywith respect to operations as releasing low DO water does not pose an environmental risk to the downstream ecosystem.

An overview of the risks posed by HP development on geomorphic and sediment transportprocesses and mitigation options to address these risks are summarised in Table 3.2. The following sectionspresentanoverviewoftherangeofmitigationmeasuresandhowtheyfitwithinthelife-cycle of hydropower projects.

Range of mitigation strategiesSedimentmitigationcanbedivided into(1)minimising inputsor(2)maximisingthroughput inareservoir,or(3)physicalremovalofdepositedsediment,withacombinationofapproachesmostlikely to provide the best results. These approaches are summarised schematically in Figure 3.23 and Figure 3.24 based on experience in Japan (Sumi et al, 2015). As shownunder the‘Methodsanddetailsofsedimentcontrolmeasures’columninFigure3.24,thereareawiderangeof infrastructure options / requirements for sediment management, with the selection of sediment managementapproachdependantonthesite-specificcharacteristicsoftheproject.

A range of sediment mitigation approaches have been developed overtime because there is no single approach that is applicable to all reservoirs, catchments and scenarios. A sound, site specificunderstandingofthehydrology,sedimentloads,sedimenttiming,sedimentcharacteristics,reservoircharacteristicsanddownstreamenvironmentareall required for the identificationandsuccessful implementation of mitigation measures.

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Figure 3.23. Schematic showing the range of sediment mitigation approaches used in Japan (Sumi et al., 2015).

Figure3.24.Classificationofsedimentcontrolmeasures(Sumi,T.andKantoush,S.A.,2011).



3.4.3 MasterPlan&Feasibility

Sediment and geomorphic mitigation needs to be considered and incorporated at the earliest stages ofHPplanninganddesign.Theseconsiderationsneedtobebasedonasolidunderstandingofthe water way and sediment characteristics of the catchment. During the planning and feasibility stages,site-specificinvestigationsshouldbeinitiatedtoprovideagreaterlevelofdetailregardingsediment movement and the geomorphic characteristics of the impoundment area, and downstream river as compared to what might be available from larger scale catchment assessments.

Siting and designThe siting and design of anHP project will determine its potential impact on the downstreamenvironment, and guide the selection of mitigation approaches. Evaluating and minimizing potential impacts associated with siting is considered a fundamental mitigation strategy, as indicated in Tables 5.1-5.5 in The Mitigation Guidelines where siting options are listed under Avoidance for eachoftheflowalterationcategories.

The location of the development with respect to upstream and downstream tributaries will govern the amountofpowerwhichcanbegeneratedbyanHP,andwilldeterminewhichmitigationmeasuresmay or may not be applicable. The geometry of reservoirs and the physical location of tributaries enteringtheimpoundmentwillalsoaffecttheviabilityofmitigationmeasures.

At a local scale, the siting of hydropower projects within extended bedrock controlled reaches can limit channel widening and bed incision immediately downstream of the project, and assist with the management of dissolved oxygen concentrations in the discharge (discussed in water quality section).

The process of siting of hydropower projects also needs to consider sedimentation issues, including managing and mitigating reservoir sedimentation processes and associated storage losses, potentialdamagetohydropowerinfrastructureduetosedimentsandsedimentationeffects,anddownstream geomorphic impacts associated with changes to the sediment regime in the river.

Developments which have large, unregulated tributaries entering short-distances downstream of thedamwall(orpowerstationdischargepoint)generallyhaveareducedimpactonthedownstreamriver systemowing to theunregulated flowand sediment inflowsprovidedby the tributaries.Aschematic example of how mitigation strategies and downstream impacts may vary depending on the siting of a project is shown in Figure 3.25.

A

B

C

A

B

C

Figure3.25.ExampleofhowsitingofanHPcanaffectenvironmentalimpacts and mitigation options. The diagram at left shows a hypothetical river with two tributaries. The downstream disruption of sediment supply andsedimentmanagementwithintheimpoundmentwilldifferdependingon whether a dam is constructed at sites ‘A’, ‘B’, or ‘C’. A dam at ‘A’ will haveasmallerimpactondownstreamflowsandsedimentsupplyascompared to ‘B’ or ‘C’. A development located at ‘C’ will need to include sediment mitigation strategy to avoid sedimentation near power station intakes

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During the siting of hydropower projects consideration needs to be given to the larger catchment, including present and future developments (future hydropower, irrigation projects, possible land use changes, etc.). Project designsneed to be flexible to accommodate potential changes toupstreamwaterandsedimentinflows,anddownstreamvaluesandwaterdemands.Theconstraintson project operations may vary over time depending on the number and location of upstream or downstreamHPprojects,andmitigationresponsesneed tobeable toadapt to futurechangesand demands. For example, Xayabouri will be the most downstream dam when commissioned, and will therefore need to provide discharge patterns conducive to the downstream transboundary water needs. In the future, the power project may be upstream of other developments, and the demands for downstream releases may change.

A catchment approach is required during the planning phase if minimizing sediment input is identifiedasanappropriatemitigationoption.Coordinatedcatchmentmanagementinvolvingallstakeholders should be initiated at the earliest possible stage of the project to ensure successful implementationofcatchmentmanagementplansandstrategies.InLaoPDR,theestablishmentofNationalProtectedAreassurroundingimpoundmentshasbeenadoptedasasedimentmitigationapproach which also serves to protect local biodiversity including fauna displaced by development oftheimpoundment(Figure3.26).Longtermmanagementoftheprotectedareawithrespecttodisturbanceisrequiredforthisstrategytobeeffective.



Figure 3.26. Locations of National Protected Areas in Lao PDR, many of which are located in catchments where hydropower has been, or is in the process of being developed.

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Impoundment size and characteristics (refer to IV.1.2 in Table 6.4, the Mitigation Guidelines): The size and morphology of hydro impoundments relative to the quantity of water and sediment inflows will be a determinant factor in governing which sediment mitigation strategies can beadopted at the site.

Instreamdamswhichcreateimpoundmentswillhavealargereffectonriverflowsandthedownstreamenvironmentascomparedtooffstreamdams,orthosewhichonlypartiallyobstructriverflows.In general, small, shallow reservoirs with low residence times have lower downstream impacts on flowand retain less sediment as compared to large inter-annual storageprojects. Smallerimpoundments are also generally more amenable to sediment sluicing or flushing strategies,howevereachsiteisdifferentandadetailedunderstandingofthemorphologyofimpoundmentsisrequired to guide mitigation.

Some general guidance relating the size, water inflows and sediment inflows and applicablemitigationmeasures was developed by Basson and and Rooseboom (1997), who identified arelationshipbetweenthecapacityofreservoirsandthemeanannualwaterandsedimentinflowsand appropriate mitigation measures. This approach has been expanded upon by others, with examples shown in Figures 3.27 and 3.28.

Developmentswhicharecharacterisedbylowstoragetoinflowratios,andlowstoragetosedimentinflow ratios are most amenable for sediment flushing, whereas sediment sluicing has beensuccessful in storages with slightly higher ratios of these parameters. Mitigation strategies for developments with very large storages relative to water and sediment inflow aremore limitedin sediment mitigation options, with long term storage and density current venting being most common.

These parameters have been plotted on a similar graph for the existing Lancang Cascade, XayabouritheLowerSesan2proposeddevelopmentandtheNamTheun2(NT2)scheme,basedonfiguresavailableintheliteratureandEIAs(Figure3.29).ThetwolargeChinesdams(XiawanandDachaoshan)andNT2plotsquarelyinthe‘storage’areaofthegraph,whereasalloftheotherprojectsfallwithintherealmofsedimentsluicingorflushing.Xayabouriisplottedtwice,onceusingthe ‘historic’sediment loadestimateof80Mt/yr,and theotherbasedon thereducedsedimentloadmeasuredatthesitefollowingestablishmentoftheLancangCascade(~20Mt/yr).NT2andXayabouri post-Lancang Cascade have relatively low sediment loads compared to the envelope of‘mostworlddams’.ThisisattributabletotheforestednatureofthecatchmentupstreamoftheNT2 impoundment, and the sediment trapping occurring in the Lancang Cascade upstream of Xayabouri.

These types of graphs should be considered as a guide only, as other factors, such as the morphologyoftheimpoundment,andpatternofwaterandsedimentinflowswillalsodeterminetheapplicability of sediment management strategies. For example, in an assessment of the feasibility offlushingsedimentfromreservoirs,Atkinson(1996)foundthatreservoirswheresedimentflushingwassuccessfultendedtobe<5kminlength,whereasflushinginlongerimpoundmentsresultedinfar less removal of material. Sediment sluicing is more applicable to larger and especially longer impoundments, where the technique has been successful in reservoirs in excess of 50 km.

Also of consideration is the relative location of inflowing tributaries in relation to power stationintakes. Sedimentation in the reservoir in Rangit dam in India experienced uneven sediment deposition and damage to turbines due to the entrance of a high sediment-bearing river close to



the power station intakes. Mitigation measures developed to address the issue included operating rulesgoverningtheseasonaluseofintakesandlowlevelgatestomanagesedimentinflowandprotect,andthereinforcementofinfrastructurewithhighperformanceconcrete(Sen,2014).

Thelessonprovidedbythesegraphsandexperiencesatdifferentsitesisthatthetypesofmitigationapproachesadoptedforanyprojectneedtobebasedonthesitespecificphysical,environmentaland economic characteristics of the site and river system.

Figure 3.27. Sediment management at dams in Japan (Sumi, 2008 in Sumi et al., 2015).

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Figure 3.28. Potentially sustainable and non-sustainable sediment mitigation measures as a functionofreservoircapacity(CAP)andmeanannualwater(MAF)andsediment(MAS)inflows(Annondale, 2013).

Figure 3.29. Mekong HP projects plotted on a Basson and Rooseboom (1997) diagram. Projects shown in legend: NT2 = Nam Theun 2, ULC=Upper Lao PDR Cascade using sediment loads post-Lancang cascade.



3.4.4 Detailed design

During the design stage, the infrastructure required for implementation of the mitigation options identifiedduringtheplanningandfeasibilityphaseneedtobeengineered.Includinginfrastructurein the initial design isgenerally lessexpensiveandmoreefficient than retro-fittinghydropowerstation or dams with mitigation infrastructure after commissioning. The range of potential mitigation approaches is summarized in Figure 3.24 and sediment mitigation infrastructure related to these approaches include:

• Offstreamimpoundments(referIII-IV.2.1inTable6.3and6.4,TheMitigationGuidelines):Offstreamimpoundmentscanbeusedtoreducesedimentaccumulationinareservoir,bytargeting low sediment bearing water for capture, and allowing periods with high sediment concentrationstoflowunimpededdownstream.Examplesofseveralgeometriesofoff-streamimpoundments are shown in Figure 3.30 and Figure 3.31.

Figure3.30.Examplesofoff-streamimpoundments,fromtheReservoirSedimentationHandbook (Morris and Fan, 1998).

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Figure 3.31. Example of a river course being used as a bypass channel for sediment management (Morris and Fan, 1998).

• Bypasscanalsorchannels(referI.2.4,III-IV.2.1inTable6.1and6.3,theMitigationGuidelines):Bypass structures, whether they are tunnels, constructed canals or existing river channels can be used to pass high sediment bearing water and bedload around an impoundment, thus decreasingthetrappingofsediment.Anadvantageofthis(andtheoff-streamimpoundment)approach, is that the seasonality of sediment delivery to the downstream river is maintained.

Sediment bypass channels have been successfully used in Japan and Switzerland for decades, with construction of relatively steep channels or tunnels which maintain sediment movement. Table 3.3 show the characteristics of sediment bypass tunnels in use in Japan and Europe, which Table 3.4 lists the planning, design and management considerations required for successful implementation of sediment bypass structures.

Operations of bypass structures are typically linked to the seasonal hydrology of the catchment. An exampleistheMiwaDamontheMibuRiverinJapanwherethesedimentladenflowsassociatedwiththerisinglimbofhydrographsaredivertedintothetunnel.The‘clear’water,whichisgenerallyassociatedwiththefallinglimbisstored(Kondolf,et al.,2014).Bypassinfrastructurecanbeaddedafter the development of a project, as evidenced by the Wushe dam in Taiwan, where an accelerated loss of storage within the impoundment due to earthquake induced sediment inputs has led to the investigationofretro-fittingabypassstructuretotheproject(Laiet al.,2015).Sedimentbypassstructures as a mitigation approach for hydropower is gaining favour internationally, and the First International Conference on Bypass was held in 2015 in Switzerland.



Table3.3.BypasstunnelcharacteristicsinJapanandEurope(KantoshandSumi,2010).

Table3.4.Planning,designandmanagementconsiderationsofsedimentbypasstunnels(Sumi,2015).

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• Upstream sedimentation ponds or check dams (refer III.2.1,III.2.2 in Table 6.3, Mitigation Guidelines): Reducing the volume of sediment entering an impoundment can also be accomplishedusingupstreamsedimentationponds,orupstream‘check-dams’whichpromotethedepositionofsedimenteitheroffstreamor intheupstreamofthemainimpoundment.Maintenance of the ponds involves periodic clearing of the ponds, which is typically done duringperiodsof lowsediment inflow.Recoveryofmaterialdepositedeitherupstreamof‘check-dams’ or deposited naturally at the upstream end of reservoirs can be accessedandexcavatedduringperiodsof lowflow. The recoveredmaterial canbeused for localconstruction or at additional expense, could be transported to a neighbouring tributary or downstream of the dam site and discharged back into the river system (Figure 3.32, Figure 3.33).

Figure 3.32. Schematic of bypass system and sediment budget at Miwa Dam, Japan (Sakurai and Kobayashi, 2015).



Figure 3.33. Slit check dam designed to promote sediment deposition when concentrations are high (Sumi, 2008).

• Re-introductionofdredgedmaterial(referIII.2inTable6.3,MitigationGuidelines):Approachesfor re-introducing excavated or recovered material back into the downstream channel vary, depending on the nature of the material, and the downstream mitigation goal. Material can be placed into the base of the downstream channel where low and high water levels will transportdifferentsize fractionsdownstream,or it canbeplaced in thechannelat levelswhereonlyhighflowswillmobilisethematerial,orsomecombinationofthetwo,asshowninFigure 3.34 to Figure 3.36.

Figure 3.34 Gravel mining in the upper end of the Three River Gorges project in the Yangtze (Wang, undated).

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Figure 3.35 . Sediment replenishment methods according to sediment placement or injection types(a)in-channelbedstockpile(b)High-flowstockpile(c)Pointbarstockpile,and(d)highflowdirect injection (Ock et al., 2013, in Morris, 2015).

Figure 3.36. Gravel replenishment into Isar at the Oberfohringer Wehr: Excavated material is transportedbytruckanddepositedinriver(left)andnaturallydistributedbyminorfloodevents(right) (Kantosh and Sumi, 2010).

• Infrastructure to promote warping. Warping involves the discharge, diversion or retention of sedimentladenwateronfloodplainsupstreamofreservoirssuchthatthesedimentsdepositprior to the water returning to the channel and entering a reservoir. Warping has the added benefit of depositing nutrient rich sediments on a floodplain, where they can be used inagriculture, rather than trapping them in a reservoir where they can fuel algal growth and contribute towaterquality issues.Sedimentwarping is implemented in themiddleYellowRiverwhere there hasbeenextensiveerosionon theLoessPlateau.Warpingdamsareconstructed across incised channels and trap coarse sediments prior to entering the main riverchannel (YRCC,2012).Warpinghasalsobeuseddownstreamof impoundments in



associationwith sediment flushing and sluicing so that the heavily sediment ladenwaterentersthefloodplainratherthantheriverineenvironment(ShaozuandJinze.,1989).

The following sediment mitigation approaches require infrastructure to be incorporated into the dam wall to allow the passage of sediment through the impoundment. Generally low level and highlevelgatesareincludedinhydropowerdesignstoprovideflexibilityinimplementingmitigationstrategies. Common approaches include:

• Sedimentsluicing(referI.2.3,II2.2,IV.2.2inTables6.1,6.2,and6.4,MitigationGuidelines).The aim of sediment sluicing is to maintain sediment in suspension and move it through the impoundment prior to deposition. Sediment sluicing is applicable to operations which are located in catchment characterised by distinct wet and dry seasons. Sediment sluicing typically involves a reduction in the water level in the impoundment prior to the onset of periods when sediment concentrations are anticipated to be elevated. As sediment concentrations in theinflowincrease,lowlevel(andhighlevelifapplicable)gatesareopenedwhichincreasethe velocity of water through the impoundment, and the sediment rich water is discharged downstream. Once suspended sediment concentrations have decreased, the low level gates are closed, and low-sediment bearing water is retained in the impoundment. This approach has been used for decades as hydropower projects around the world.

Sediment Sluicing typically consists of the following operational steps:

• The water level of the reservoir is drawn down at the end of the dry season in anticipation ofthefirstmajorfloodpulses,whichusuallycontainthehighestconcentrationsofsediment;

• Water levels are maintained at these reduced levels throughout the initial flood pulsepromotinganincreaseinthewatersurfaceslope(andvelocity)ofthewatermovingthroughthe reservoir, so a greater percentage of sediment is retained in suspension as compared to ‘normal’operations;

• The low level gates at the dam are opened during the pulse, and the high-sediment water is allowed to pass through the dam into the downstream environment;

• Followingareductioninthesuspendedsedimentoftheinflowingwater,thegatesareclosedand water levels are increased for the duration of the wet season, and into the next dry season.

Successfulsedimentsluicingrequirestheavailabilityof‘excess’watertotransportthesedimentthrough the impoundment, and relatively large capacity outlets, and is generally more successful innarrowreservoirswherehigherflowvelocitiescanbemaintainedacrosstheimpoundment.AnexampleofhowsedimentsluicingismanagedattheThreeGorgesProjectinChinaisshowninFigure 3.37.

Sediment sluicing was investigated for applicability to the Upper Laos Cascade as part of the coordinatedflushingregime(cf.CaseStudyreport).Asimpoundmentsweresequentiallyflushed,the downstream impoundment maintained water level at MOL to increase water surface slopes withinthereservoirandpromotethe‘sluicing’ofsedimentsthroughthedownstreamimpoundment.The aim was to promote as much sediment movement into the next impoundment downstream as possible, as well as promote deposition in the lower reaches of the reservoirs such that the sedimentwouldbereadilymobilisedduringthenextflushingevent.Thisapproachwasfoundtobe applicable to the cascade but required coordinated operations of the Hydro projects.

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Figure 3.37. Sediment sluicing regime at Three Gorges Dam, China (top left): Annual operating curve for the TGD reservoir showing Normal Pool Level (NPL), Dry Season Control Level (DCL) and Flood season control Level (FCL, from Zhou, 2004); (top right) generalised annual water levelcurvecomparedtosuspendedsedimentconcentrationsofinflowingwater(Wang,undated);(bottom left) Modelled volume of accumulated sediment under the Dry Flood operating rule shown above, and under ‘basic’ operations without the sediment sluicing operating rules.

Another example where sediment sluicing is employed is in Africa, where hydropower stations on several major rivers have been designed to promote downstream migration of sediment to avoid loss of live storage and to mitigate river channel erosion caused by sediment denuded river discharge. The proposed 650 MW Dal hydropower project on the Main Nile in Sudan has been designedsuch that riverdischargesduring thehighflowseasoncanbeconveyed through thebarrage by a combination of generating plant and sluice gates with the reservoir level drawn down to Minimum Operating Level. This strategy was originally established at Roseires upstream on the Blue Nile and has subsequently been adopted by the hydropower plants on the system including MeroweandtheplannedKajbarproject. AtRoseiresdrawdownduringthe lowflowseason isprimarily determined by the need for irrigation but the result is that the reservoir level is low at the onsetofthehighriverflowperiodandsedimentdepositionislargelyavoidedinthelivestoragezone. Downstream sediment migration can be brought into natural equilibrium after a few years of operation.Asimilarapproachwasadoptedbythe128MWKapichiraprojectontheLowerShirein Malawi.

• Turbidity current venting (refer I.2.3, II2.2, IV.2.2 in Tables 6.1, 6.2 and 6.4, Mitigation Guidelines):Turbidityventingissimilartosedimentsluicingbutwaterlevelsremainhigherin

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the reservoir as compared to sluicing. Venting can be achieved when sediment laden water enteringanimpoundmentissufficientlydenseto‘flow’alongthebottomofthereservoirtothetoeofthedamwall(Figure3.38).Forthisreason,densityventingismostsuitabletoimpoundmentswithsteeplyslopinglongitudinalprofiles.

• Lowlevelgatesordeepsluicescanbeusedto‘vent’thissedimenttothedownstreamriver.During sediment sluicing or turbidity venting, clean water is frequently released from high level gates or spillways to dilute the concentration of sediment in the downstream river (Figure3.38).SuccessfulturbiditycurrentventingoperationshavebeenperformedintheShihmen reservoir in Taiwan. The turbidity currents usually occur during typhoons, when largeamountsoffinesedimentsareoriginatingfromlandslidesinthecatchment,coincidingwithsevererainfall.Theuseof3-dimensionalmodels(a.o.Delft3D)andadvancedmonitoringtechniques allow the dam operators to optimise the release of the turbidity currents and the amountofclearwatertosufficientlydilutetheflowforenvironmentalconstraints(Figure3.40andFigure3.41).

• Turbidity venting is also adopted in the Mapragg hydropower project in Switzerland, with low-level outlets opened once the suspended sediment concentration in the bottom water behind thedamwallexceeds2g/L (Figure3.42). Venting involves thegradual increaseinflowtomimicamediumsizedfloodevent.Ventingcontinuesuntilsuspendedsedimentconcentrationsdecreasetobelow2g/L,andthenflowisgraduallydecreasedtoalsomimicamediumfloodevent.Maximumsedimentconcentrationsduringflushingareprojectedtobeupto14g/L(BoesandHagmann,2015).

Figure 3.38. Example of turbidity venting through a low-level gate to move sediment through an impoundment (Morris and Fan, 1998).



Figure 3.39. A Google Earth image of the Plei Krong HP on the upper Sesan River showing the release of high sediment bearing water through low level outlets (or power house) accompanied by the discharge of low-sediment bearing water from the surface of the impoundment.

Figure 3.40 . Turbidity current venting through low-level sluice in Shihmen reservoir (Taiwan), seen from the spillway from which clear water from the upper layers is released to dilute the turbidoutflow(PhotofromPaulHsu,International).

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Figure 3.41. Turbidity current in Shihmen reservoir simulated with Delft3D (Commandeur, 2015).

Figure 3.42. Water discharge and suspended sediment concentrations during density current venting at the Mapragg hydropower project in Switzerland.

• Sedimentflushing(referI.2.3,II2.2,IV.2.2inTables6.1,6.2and6.4,MitigationGuidelines)involves a similar approach as sediment sluicing however lake levels are reduced to pre-impoundment levels,enabling the ‘river’ toerodedepositedsediments. Thisapproach isefficientatremobilisingsedimentsdepositedinthepre-existingriverchannel,butmaynotbeeffectiveaterodingdepositslocatedonhistoricfloodplains.

Theuseofsedimentflushingiswidespreadinternationally.Whiteet al.(1999)andWhite(2000)have reviewed the efficacy of sediment flushing based on an analysis of 50 case studies andidentifiedthefollowingfactorswhichinfluencetheviabilityandefficiencyofsedimentflushing:

• Riverineconditionsmustbecreatedinthereservoirforasignificantlengthoftime,withfulldrawdownandemptyflushingbeingmoreeffectivethanpartialdrawdown;

• Thehydrauliccapacityoftheoutletsmustbesufficienttomaintainthereservoirataconstantlevelduringtheflushingperiod:



- Flushingdischargesofatleasttwicethemeanannualflowarerequired;

- Flushingvolumesofatleast10%ofthemeanannualrunoffshouldbeanticipated;

- There must be enough water available to transport the required volume of sediment;

- Aregularannualcycleofflowsandadefinedfloodseasonprovideoptimumconditionsforsedimentflushing,includingmonsoonconditions.

• The deployment of lateral and longitudinal diversion channels has been successful in promotingflushinginreservoirswhicharehydrologicallargeorcontainsignificantproportionsofdepositioninareasremotefromthemainflushingchannel;

• Sediment sizes are an important factor in determining whether the quantity of water available forflushingwillbeadequatetoremovethedesiredquantityofsedimentfromthereservoir;

• Depositedcoarsesedimentsaremoredifficulttoremovethanfinesediments;

• Understanding the size range of incoming sediment is important;

• Deltadepositsoffinesandandcoarsesiltarethemostlikelytoproducesuccessinflushinga reservoir;

• Themost suitable conditions for flushing are to be found in reservoirswhich are similarin shape to the incised channel which develops during flushing. Long, relatively narrowreservoirsarebettersuitedtoflushingthanshort,wide,shallowreservoirs;

• Operationalconsiderations,suchaswaterandpowerdemandcanlimittheabilitytoflushsuccessfully.

• Theapplicabilityofsedimentflushing to theupperLaosCascadewas investigated in theCase Study (MRC 2018c). Flushing was found to be a viablemitigationmeasure overthelongterm.Duetothelowsediment loadsenteringtheimpoundments, theefficacyofflushingislikelytoincreaseovertimeasmoresedimentisdepositedinthelowerreservoirs.Sequentialandcoordinatedflushingwasfoundtobethemostefficientmethodforsedimentmanagement,withflushingconductedinanupstreamdirection(SankhamfollowedbyPakLay,Xayabouri,etc)suchthatthesedimentconcentrationsdischargedtothedownstreamriverremainedwithinacceptablelimits(e.g.withinhistoricbackgroundconcentrations).

• Pressure flushing differs from other mitigation approaches, as the water level of theimpoundmentisnotdecreased.Duringpressureflushing,lowlevelgatesareopenedandthesedimentnearthetoeofthedamwallismobilisedanddischargedfromthedam.PressureflushingisonlyeffectiveintheimmediatevicinityofthedamasindicateinFigure3.43whichshowstheextentofflushingasafunctionofwaterdepthandoutflowvolume.

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Figure 3.43. Approximate limit of scour upstream from low level outlets in static water (from White and Bettess, 1984, in Atkinson, 1996).

A final type of infrastructure applicable to hydropower projects includes re-regulation weirs orponds. The aim of these structures is to reduce downstream bank erosion by reducing water levelfluctuationsinthedownstreamenvironment.Re-regulationweirsareespeciallyrelevanttooperationswhichintendtooperateinapeakingmore,andorwherewaterlevelfluctuationsareundesirable, for social or ecological reasons. At Nam Ngiep 1 in the LMB, a re-regulation weir has been included in thedesignof theprojectwhich includesasmall turbine. In thisconfiguration,energy is also generated by the re-regulation weir. An example of a re-regulation weir in Cambodia is shown in Figure 3.44.



Figure 3.44. Google Earth image of the Kamchay Hydropower Project in southwestern Cambodia, showing the main dam and downstream re-regulation weir.

3.4.5 Construction phase

Mitigating geomorphic and sediment transport issues during the construction phase of the development is highly dependent on the work completed during the design phase of the project. During site establishment and construction, large quantities of sediment can be generated through

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land disturbance and site preparation works. This especially relevant to areas in the LMB which are characterizedbythick,fine-grainedlateriticsoilswhicharesusceptibletoerosiononceexposed.Identifying and establishing environmentally sensitive access corridors and using construction methodswhichminimizelanddisturbancearetwoapproacheswhichcanminimizesedimentrunoffduring the construction phase.

Other approaches include concentrating earth works during the dry season so there is a lower risk ofsedimentrichrunoffenteringlocalrivers,wettingroadsduringthedryseasontosuppressdustgeneration and providing physical protection for exposed hillsides and banks which are at risk of erosion(Figure3.45). Duringconstruction,cut-offdrainsandsettlingpondsshouldbeused tocapture and settle material generated from the site. In the longer term, the rapid revegetation of hillslopes and disturbed areas is considered the best long-term solution to mitigating construction impacts.

Figure 3.45. Slope protection measures at Nam Ngiep designed to minimise sediment erosion.

Mitigation measures aimed at reducing impacts in the downstream river or in the impoundment area can also be initiated during the construction phase. For example, river banks near the discharge pointofthepowerstationwhichhavebeenidentifiedashavingahighriskoferosionandwhichcouldaffect infrastructureorcommunitiescouldbestabilizedandbuttressedduring thisphase.Similarly, areas in the impoundment which are likely to be at risk due to wave induced erosion, or the changes in water level could also be targeted for preventative stabilization if warranted.

3.4.6 Operational phase

The operational phase of a hydropower project is the longest period within the life cycle of the project. During this period, the impacts and challenges faced by the operator are likely to change



as conditions within the impoundment, and large catchment change and evolve. It is important thatoperationalflexibilitybeincorporatedintoprojectsatthefeasibilityanddesignstagessothatpower station managers have a range of mitigation approaches available over the long period ofoperations.Operational approaches tomitigationare relevant toeachof the fivemajor flowalterations as shown in Tables 6.1-6.5, Mitigation Guidelines.

Operation of a hydropower plant is ideally based on an adaptive management approach, with operations guided by operational opportunities, and mitigation needs. Figure 3.46 shows an example of an adaptive management approach for hydropower management. The system is based on monitoring appropriate indicators, and reporting results on a regular basis either internally or externally through publications such as State of the Basin reports. The monitoring results are used toevaluatetheeffectivenessofmitigationmeasures.Ifthemeasuresareachievingthedesiredoutcome, then monitoring continues through another cycle.

If indicators are not within desired ranges, then a series of investigations and models may be initiated to better understand what has changed in the system, and / or what the change in the value of the indicators signifies. If warranted,mitigationmeasures can be revised and trialedor implemented, followingwhichmonitoring isagainused togauge theefficacyof theactions.

Figure 3.46. Adaptive management approach to hydropower during the operational phase of the project.

Examples of monitoring linked to adaptive management responses include:

• Monitoringtheeffectivenessofsedimentmanagementstrategies,suchassedimentsluicingor flushing with respect to maintaining viable sand bars and banks in the downstreamenvironment and monitoring the deposition of sediment in the reservoir to assess the longevity of impoundment, and revising operating strategies as required (e.g., increase or decrease the

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durationofsedimentsluicing,implementsedimentflushinginadditiontosedimentsluicing,implementadditionalcatchmentmanagementstrategiestoreduceinputs,etc.);

• Monitoringthedownstreamimpactofwaterlevelfluctuationsonerosionratesofriverbanksandmodifying theconditionsunderwhichflowramp-downsare required,oradjusting theramp-down rate;

• Altering mitigation strategies due to additional hydropower projects coming on line either upstream, downstream or in tributaries. This might include developing joint operations to increaseefficiencieswithrespecttomitigationstrategiessuchassedimentsluicing.

During the operational phase it is also important to maintain good monitoring data bases, and to document changes and actions which have occurred. The operational phase of a project can last decades to centuries, so ensuring that the knowledge base acquired by one generation is available toguidefuturegenerationsiskeytoefficientlong-termoperations.

Operating Rules Operating rules are first defined during the feasibility stage, but implementation occurs duringthe operational stage. The success of sediment mitigation measures is largely dependent on the development and implementation of appropriate operating rules. Examples of the range of operating rules that are applicable to sediment and geomorphic mitigation include:

• Maintenanceof reservoir lake levelswithin specified ranges tominimisedisturbanceanddestabilisation of shoreline banks;

• Setting limits for the rate at which lake levels can change to reduce bank erosion;

• Schedules and triggers for operation of sediment bypass canals and tunnel;

• Establishingtheyearlylakeleveltargetstomaximiseefficacyofupstreamsedimentretentionbasins, including recovery of material;

• Identifying appropriate operating patterns associated with the re-introduction of sediment downstream of a dam;

• Establishing the annual sediment sluicing schedule and requirements, including identifying appropriate lake levels, dates or triggers for implementation, rates and duration of draw down and sluicing events, and release volumes from high-level and low-level outlets;

• Schedulesforsedimentventing,basedoninflowingwaterratesandsedimentconcentrations;

• Up ramping or down-ramping rules to minimise downstream bank erosion.

Operatingrulesaresite-specificandneedtobebasedonasolidunderstandingofthehydrologyand sediment characteristics of the project.

Example of Adaptive ManagementAn example of adaptive sediment management is the Glen Canyon Dam on the Colorado River (USA).Theretentionofsedimentinthereservoirafterthestartofoperationsatthedamin1962has caused a gradual decline of sand bars in the Grand Canyon. Similar to the upstream reaches of the LMB, the Colorado is a bed-rock dominated channel with sand bars in eddy zones below rapids andstagnantzones.Thisdeclinecausedseriouslossoffishhabitat,andthelossofcampingsitesforvisitorstotheNationalPark.Inresponse,theUSgovernmentinitiatedanoperationalstrategy



tomitigatetheseimpacts,andrestorethesandbars.Thisstrategyincludesartificialfloodreleasesfromthedamafterhightributaryflows(withhighsandloads)depositsandinthemainriverchannel.Theartificialfloodflowsallowsandtobepickedupfromthebed,anddepositedontheremainingsandbars.Presentlystudiesinthisriverfocusontheimpactofturbidityonthedistributionofinvasivefishspecies,andoneffectsofvegetationonbardevelopmentandstabilization.‘Lessonslearned’from this river, can contribute to a better understanding and appropriate sediment management in the Mekong bed-rock reaches.

Figure3.47.BardepositionintheColoradohigh-flowreleasein2013,atCarbonCanyon(RM65.1R).(Left)situationbeforehighflow,(right)situationafterhighflow.

3.5 Indicators and monitoring

The ISH11 project (Improved Environmental and Socio-Economic Baseline Information for HydropowerPlanning) identifiedinformationneedsforhydropowerprojectsovertheproject-life-cycle. Table 3.4 summarises parameters and information that are relevant to hydropower planning and operations. When considering sediments and geomorphology, it is important to implement monitoring regimes that will provide adequate information at the required scales. For example, short term sediment transport information is required to understand the timing, seasonality and variability of sediment inputs, whilst the same information over years and decades is needed to assesshowlong-termsedimentyieldsrespondtoupstreamflowalterations,catchmentlandusechanges or climate change.

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Table3.5.SummaryofsedimenttransportandgeomorphicindicatorsasidentifiedbyISH11(2013).

ParameterGroup Relevance for hydropower planning and operation

ParameterTypesandExamples

Sediments and Geomorphology

• Influxofsedimentstoimpoundments is critical for siting and design of hydro schemes

• Need to understand sediment and geomorphic processes to design appropriate mitigation measures

• Changes to sediment fluxesdownstreamofpower stations can affectgeomorphologicaland ecological processes and have social impacts

• Separating changes due to hydropower fromtheeffectsof other basin developments/actions at transboundary locations.

Sediment characteristics: suspended and bedload fluxes,seasonality,grain-size,organic content, mineralogy, lithology

Geomorphic characteristics and habitat quantity & quality: Channel cross-sections, longitudinal channel profiles,planformfeatures(e.g. channels, sinuosity, braiding),presenceofwoodydebris

Geomorphic rates: rate of channel migration, rates of channelinfillingorincision,bank stability

River dynamics: coefficientin variability of depth, heterogeneity of current velocitiesfloodplainconnectivity, Tonle Sap reversal

Tidal sediment dynamics: rates of change and locations for transport, deposition, erosion

79 | Chapter 4. Water Quality – Status, Risks and Mitigation


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4 Water Quality – Status, Risks and Mitigation




4.1.1 Introduction and importance of water quality in river system

Goodwaterqualityiscriticalforhumanandecologicalhealth.Riverinewaterqualityisaffectedbyinflowsandinputs,aswellasinstreamandgroundwaterprocesses.Inthecontextofsustainablehydropower planning, implementation andmanagement,water quality can have a direct effecton hydropower infrastructure and operations, and hydropower operations can affect waterquality, especially during storage in reservoirs and release to the downstream environment. The establishment of hydropower schemes can also lead to the parallel development of new water basedindustries(e.g.aquaculture,irrigation,industrial)orsocialbenefits(potablewatersupply)which have water quality requirements or impacts that need to be understood. Water quality is also a transboundary issue, with the potential for cumulative impacts.

ThePDG(MRC,2009)focusesonwaterqualityrisksassociatedwithaseriesoflow-headdamsas proposed for the mainstream Mekong in the LMB, emphasizing that larger deeper storages maypromotegreaterchanges.ThewaterqualityrisksidentifiedbythePDGincludechangestophysical and chemical water quality parameters which can impact on the downstream ecosystem, andgeomorphology(asrelatedtosedimentconcentrations).

The water quality parameters that are important to consider in hydropower developments include temperature, pH, dissolved oxygen, Biological Oxygen Demand, nutrients (total and dissolved phosphorusandnitrogenspecies)andcoliformbacteria.Theseparameterscanbealteredduringstoragewithinareservoirandespeciallyunderconditionswherethermalstratificationcanleadtothe development of stagnant water at depth.

Guidance for maintaining water quality includes the design and management of reservoirs which willachievethewaterqualityguidelinesassetoutintheMRCTechnicalGuidelinesforProceduresonWaterQuality.ThePDGstate thenecessityof site– specificwaterqualitymonitoring,withthe results to be interpreted within larger scale trends provided by the Water Quality Monitoring Network and Ecological Health Monitoring Network.

4.1.2 Water quality trends in the LMB

Water quality has been collaboratively monitored by the MRC Member Countries since 1985 (Cambodiabeganin1993)throughtheWaterQualityMonitoringNetwork(WQMN).Monthlyresultscollected through the WQMN are analysed annually using indicators related to protection of aquatic life, human impacts and agricultural uses. Water quality in the mainstream Mekong is generally considered acceptable, based on the results reported by the MRC Member Countries and water qualityIndicesreportedinannualWaterQualityReportCards(MRC,2008).

Resultsfortheperiod2000–2008aresummarisedinFigure4.1fortheindicator‘HumanImpactson Water Quality’ which is based on the water quality results for dissolved oxygen, ammonia, total phosphorus and Chemical Oxygen Demand (COD). The summary suggests that sinceapproximately 2004 there has been a catchment wide decline in water quality, with the poorest results recorded in theuppercatchmentand thedelta,withseveral sites reporting ‘D’ values .Tributaries generally have acceptable water quality.

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Figure 4.1. Water Quality class of Mekong mainstream stations for ‘Human Impact on Water Quality’2000–2008basedonWQMNresults.ND=Noresultsavailable.

Amoredetailedinvestigationofwaterqualitywascompletedin2003and2004undertheWUPProgramme(MRC,2007).Waterandsedimentsampleswereanalysedforarangeofcontaminants,including persistent and bio-accumulating organic pollutants such as pesticides, PAHs, PCBs,dioxins and furans. Concentrations were typically below detection levels or published guidelines, although several sediment samples gave a positive toxic response to the bioassay organisms. The information is considered to provide a baseline for future surveys.

MorerecentWQMNmainstreamresults(MRC,2015)alsoshowtrendsof increasingvaluesforthese water quality parameters. In Figure 4.2 the results from the mainstream sites have been grouped by year for the parameters ammonia, total phosphorus and COD showing sizeable increases in ammonia and total phosphorus in recent years.



Figure 4.2. Box and whisker plots of ammonia (top left) total phosphorus (top right) and Chemical Oxygen Demand (bottom right) for the period 1995 or 2000 to 2013 showing catchment trends (Ly et al., 2015).

SitespecificcomparisonsforPakseandStungTrengshowincreasesintotalphosphorusandCODatPakse,withincreasesinammoniaandtotalphosphorusatStungTreng.Thedifferenceintrendsatthesiteshighlighttheimportanceofthetributaryinputs,withPakseinfluencedbythePakMuninflow,andStungTrengreflectinginputsfromthe3S.

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Figure4.3.WQMNresultsfrom2005–2012compared with 2013 results for ammonia (top left), total phosphorus (top right) and Chemical Oxygen Demand (bottom left) for Pakse and Stung Treng.

Analysis of WQMN time-seriesThe WQMN monthly results also provide information about spatial and seasonal changes at the monthlytime-scale. Medianmonthlytemperature,electricalconductivity(EC), totalphosphorusanddissolvednitrogenspecies(Nitrate+Nitrite)arepresentedinFigure4.4through4.7fortheperiod 1985 to 2008. The Temperature results show a warming of water and reduction in seasonal differencesbetweenChiangSaenandthedownstreamsites.PrekDamhashigherdryseasonmedian temperature values, probably due to the broad shallow nature of the lake which promotes warming.ThedeltasitesshowadecreaseintemperaturerelativetoKratieduringthebeginningand end of the wet season.

ElectricalconductivityresultsshowsimilarseasonaltrendsatallsitesexceptPrekKdam.Inthemainstream sites EC decreases with distance downstream and is highest during the dry season, whichistypicalofrivers.ThehighervaluesrecordedatChiangSaenlikelyreflecttheinputsfromlimestoneareas in theuppercatchment. AtPrekKdamelectricalconductivity is lowduringthedryseason,andincreasesinJuneasflowfromtheMekongenterstheriverduringthepeakfloodperiods.

Monthlymediantotalphosphorusanddissolvednitrogenspecies(nitrite+nitrate)resultsprovidean overview of general nutrient trends in the LMB for the same period (1985 – 2008) (Figure4.6and4.7).NutrientvaluesinthemainstreamMekongtendtodecreasedownstreambetweenChiangSaenandKratie,andthenincreaseinthedeltasites.ThewaterqualityintheTonleSapissimilartothatofthemainstreamMekongduringtheperiodofinflowingwater,butdiffersduringtheoutflowingperiod,withelevatednitrogenconcentrationsoccurringlateinthedryseason.Thesehighervalueslikelyreflectthedrainingofthefloodplainasthelakecontractsandreflectsthehighproductivity of the system.



Figure 4.4. Median monthly values for Temperature between 1985 and 2008 at Chiang Saen, Nakhon Phanom, Pakse, Kratie, Prek Kdam (Tonle Sap), Tan Chau and My Thuan based on monthly WQMN results.

Figure 4.5. Median monthly values for electrical conductivity (EC) between 1985 and 2008 at Chiang Saen, Nakhon Phanom, Pakse, Kratie, Prek Kdam (Tonle Sap), Tan Chau and My Thuan based on monthly WQMN results.

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Figure 4.6. Median monthly values for Total Phosphorus between 1985 and 2008 at Chiang Saen, Nakhon Phanom, Pakse, Kratie, Prek Kdam (Tonle Sap) Tan Chau and My Thuan based on monthly WQMN results.

Figure 4.7. Median monthly values for Nitrite + Nitrate (NO2+NO3) Phosphorus between 1985 and 2008 at Chiang Saen, Nakhon Phanom, Pakse, Kratie, Prek Kdam (Tonle Sap) Tan Chau and My Thuan based on WQMN results.

Viewing the WQMN results as time-series provides insights into water quality events and trends overtime.Availableresultsfortheperiod1985to2012forTotalPhosphorus,TotalNitrogen,Nitrite+NitrateandCODareshownforChiangSaen,NakhonPhanom,KampongChamandTanChauin the following graphs. The results show the following:

• TP(Figure4.8)andTN(Figure4.9)showdistinctincreasesaround2002atthethreesitesin the river, with a gradual decrease in concentrations over the following few years. The 2012resultswereagainelevated.Theresultsfromtheupperdelta(TanChau)showoverallhigher values, and there is no distinct increase around 2002;

• Ammonia results (Figure4.10)showsmall increasesatabout thesame timeas the totalnutrientresultsatChiangSaenandNakhonPhanom,butnotatthedownstreamsites;



• Thenitrite+nitrateresults(Figure4.11)donotshowapunctuatedincreasearound2002,suggesting that the increase in TN is not attributable to these parameters;

• TheCODresults(Figure4.12)alsoshowincreasesintheriverinesitesataboutthesametime, and there is a trend of increasing values in the delta.

Collectively,thesewaterqualityresultsmaybereflectingtheestablishmentoftheLancangCascade,and other developments in the tributaries, and may be indicative of likely future water quality changes associated with the establishment of new hydropower projects in the LMB. Water quality results from the Lancang Cascade showed that water quality typically deteriorated in the years following impoundment with improvements noted after a period of about 7 years in the case of the ManwanHP(Wei,et al.,2009).Theincreaseandsubsequentdeclineintotalnutrients,ammoniaand COD at the WQMN monitoring sites is consistent with the decomposition of organic matter in recently inundated areas. Ammonia and COD commonly increase in the low-oxygen environments created by impoundments. The large increase in the total nutrients but lack of increase in nitrite +nitratecouldbereflectingthenutrientsoccurringpredominantlyasparticulateorganicPorN,which is also consistent with the establishment of reservoirs. Land use changes during this period may also be contributing to the water quality changes.

Some of the nutrient results may also be attributable to a change in the relative proportion of fine tocoarsesedimentsbeing transportedby the river followingestablishmentof theLancangCascade. Liu et al.,(2014)investigatedthedistributionof phosphorus species in the sediments of the Xiawan, Manwan and Dachoashan impoundments and found that total phosphorus was correlated with iron in the sediments, and exchangeable phosphorus was correlated with the silt/clay component of the sediment, suggesting the relationshipisassociatedwithsurfacearea.Differencesin the proportion of biologically available phosphorus presentintheimpoundmentswereattributedtodifferentrates of nutrient release from the sediments, with the two newerimpoundments(XiawanandDachoashan)havinghigherlevelsofbioavailableP,presumablyelatedtothedegradation of organic material following initial inundation. Iron results at Chiang Saen show a very large increase in the mid-2000s, but unfortunately the parameter was not included in the WQMN after 2005, so the long-term trend is unknown. Unfortunately dissolved phosphorus parameters are not included in the WQMN either so it is not possible to determine whether these trends were discernible in the downstream LMB.

The lack of dissolved phospho-rus results in the WQMN data base is a limitation to under-standing how available phos-phorus is changing over time in response to water resource developments in the LMB. It is recommended that this parame-ter be re-included in future mon-itoring;

The re-inclusion of iron in the WQMN parameter list would also increase the potential to un-derstand water quality changes associated with hydropower de-velopments.

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\

Figure 4.8. WQMN Total phosphorus results for Chiang Saen, Nakhon Phanom, Kampong Cham andTanChau,1985–2012.

Figure 4.9. WQMN Total Nitrogen results for Chiang Saen, Nakhon Phanom, Kampong Cham andTanChau,1985–2012.



Figure 4.10. WQMN ammonia results for Chiang Saen, Nakhon Phanom, Kampong Cham and TanChau,1985–2012.

Figure 4.11. WQMN Nitrite + Nitrate results for Chiang Saen, Nakhon Phanom, Kampong Cham andTanChau,1985–2012.

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Figure 4.12. WQMN Chemical Oxygen Demand (COD) results for Chiang Saen, Nakhon Phanom,KampongChamandTanChau,1985–2012.

4.1.3 Changestosedimentandflowandimpactsonwaterquality

AspreviouslydiscussedinSections3.1and3.2,therehavebeenconsiderablechangestotheflowand sediment regimes of the LMB owing to the development of the Lancang Cascade and tributary dams,andaggregatemining.Thesechangescanaffectwaterqualityinavarietyofways:

• Sediments provide a large surface area onto which nutrients and contaminants become bound. Alteration to the quantity and grain-size distribution of sediments entering the LMB could alter the transport patterns of nutrients in the Mekong. A possible example of this is showninFigure4.13,wheretherelationshipbetweenTSSandTotalPhosphorusshowsadistinctchangebeforeandafter~2003.The2004–2008datasetsshowahigherTP/TSSratiowhich is consistent with similar amounts of phosphorus being transported on less sediment. It islikelythatthesuspendedsedimentinthe2004–2008periodisfinerascomparedtopre-2004(duetopreferentialretentionofsedimentinthehydropowerimpoundments),soitispossiblethatthefateandtransportpathwaysofthenutrientsdifferbetweenthetwoperiods.Nutrientfluxesandbudgetsarebeingderivedfromthecatchmentandwillbecontainedinsubsequent reports.

• ThereductioninsuspendedsedimententeringtheLMBfromChinacanaffectwaterqualitybyincreasingthelightpenetrationtotheriver(orpotentiallyhydropower).Lightpenetrationis likely to increase when suspended sediment concentrations are below 100 mg/L. The comparison between historic and recent suspended sediment concentrations at Chiang Saen(Figure4.14)showsthatmediansedimentconcentrationswerebelowthisvalueforthree months of the dry season prior to development of the Lancang Cascade, whereas in the recent data set this occurs for six months. Much of this increase is attributable to the delayedonsetoffloodflowsrelativetounregulatedconditions(Figure4.15).Anincreasein



light penetration can promote algal growth, and increase water temperatures, which in turn canaffectparameterssuchasdissolvedoxygen.

Figure 4.13. TSS compared to Total Phosphorus at ChiangSaenfortheperiods1985–2003and2004–2008.

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Figure 4.14. Comparison of suspended sediment concentrations at Chiang Sean during the dry seasonfortheperiod1968–1992(left)and2009–2013(right)showinglargereduction.

Figure4.15.ComparisonofflowatChiangSaenin 1985 and 2013 demonstrating the delayed onsetofhighflows,reducedpeakflowsandhigherlowseasonflowsin2013relativetothehistoric record.

The existing trends and risks associated with water quality in the LMB are summarised in Table 4.1. Additional vulnerabilities and risks associated with hydropower development in the LMB are discussed in the following section.

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Table4.1.Presentwaterqualitytrendsthatarerelevanttohydropowerplanningandoperations.

Trend HP Risk

Increasing nutrient concentrations

Algal growth in impoundment with the potential to impact ecosystems & human health; Algal growth can reduce oxygen levelswhichcanaffectthequalityofdischargefromapowerstation;

Increasing COD

Consume oxygen in impoundments contributing to the creation of low DO conditions;

Increased risk of discharging low DO water from power station;

Increased risk in promoting the release of nutrients/contaminants from sediments;

Increasing light penetration Promotealgalgrowthinimpoundmentandindownstreamenvironment;

Delayed onset of wet seasonIncreased water temperature;

Prolongedgrowthofalgaeduringdryseason;

Change to sediment delivery Change to light penetration & nutrient transport.


This section reviews the potential impact that the development of hydropower projects can have onwaterquality,basedonthefivelarge-scalechangestypicallyassociatedwithhydropower.TherisksandassociatedwitheachoftheseflowchangesaresummariesinTable4.2.



Table4.2.WaterQuality–Keyrisks,impactsandvulnerabilities.


Annual / inter-annual changes to flow

Changes in seasonality & continuous uniform release

Changes / loss of seasonal temperature patterns downstream

Change in relationshipbetweenflowandsedimentdelivery

Increased water clarity increasing risk of algal growth Increased water clarity increasing water temperature

Daily / short-term changes in flow

Hydro-peakingorfluctuatingdischarge

Fluctuating water quality including increase in variability of temperature and nutrients

Altered concentrations of downstream discharges or inputs

Loss of river connectivity

Changes to nutrient transferTrapping of nutrients within impoundment leading to change in downstream delivery

Creation of impoundments

Conversion of river to lake

Lakestratificationleadingtolowdissolvedoxygenbearing water and release of nutrients, metals or pollutants from sediments

Increased water clarity in lake increases risk of algal blooms

Temperaturechangeinlake(warmerorcooler)

DOandtemperatureofdischargeaffectedbyimpoundment – Low DO or high gas supersaturation

Diversions or intra basin transfers

Diversion of water from one catchment to anotherChange in nutrient and other water quality parameters in both donor and receiving catchments

4.2.1 Annual/inter-annualflowchanges

The physical and chemical characteristics of water can be altered during impoundment through physical processes, such as the warming or cooling or water, or chemical processes, such as redox reactions associated with low dissolved oxygen conditions. These processes are discussed in more detail in Section 4.2.4.

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Inter-annual storage of water commonly leads to alterations in the temperature of water released fromthepowerstationrelativetothe‘natural’condition.Inareaswherethereisastrongseasonality,thisdifferencemaybeconsiderable,andaffecttheecologyofthedownstreamriversystem.Thedepth of the water intake is a factor in determining temperature changes to water; high-level intakes that draw water from at or near lake surfaces may be seasonally more adjusted as compared to water drawn from deep in impoundments where temperatures can remain constant throughout the year.

Theexample inFigure4.16 is fromthefinal impoundment inacascade inAustraliaandhasahighlevelintake.Medianwatertemperaturesduringsummer(Feb)andwinter(July)aresimilartovalues obtained from nearby unregulated tributaries, however, during autumn and spring there is a considerabledifferenceintemperatures.

Reductionstodissolvedoxygenduringsummerperiodswhenlakesarestratifiedisalsoacommonfeature of hydropower projects that store water over annual or inter-annual time scales.

Figure 4.16. Comparison of water temperature in the release from a power station and an unregulated tributary, showing warmer autumn temperatures and cooler spring temperatures in the power station release.

Long-duration storage such as that associated with the inter-annual storage schemes, can also promote increased algal growth within impoundments due to the generally slow velocity of the water, which enables algae to remain at the surface, and increased light penetration following the deposition of sediments. The risk of algal growth will increase if there are elevated nutrient concentrations within the water way, and if water and air temperatures are warm.

4.2.2 Dailyorshort-timeperiodflowchanges

Hydropeaking, or similar short duration releases from hydropower stations, can alter water quality inthedownstreamriversystembydischarge‘pulses’ofwatermodifiedduringstorageresultingin fluctuating temperature, electrical conductivity or other water quality characteristics in thedownstreamenvironment.Anexampleof‘thermo-peaking’associatedwithhydropeakingisshownin Figure 4.17 where power station operations can result in temperature changes of up to 15°C in short periods of time.



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Figure 4.17. Comparison of water temperature downstream of a hydropeaking power station (John Butters Power Station on the King River, Tasmania, Australia) and in a nearby unregulated tributary.

4.2.3 Loss of river connectivity

The loss of river connectivity is closely related to the establishment of an impoundment and the potential for sediment deposition and nutrient capture. A large proportion of nutrients are typically associated with sediments in a river, but the nutrients are not uniformly distributed within sediments. The preferential capture of certain size-classes of sediment will alter the delivery of nutrients downstream, but not in a uniform manner. An example of nutrient and sediment changes associated with hydropower impoundments is shown in Figure 4.18 for the Susquehanna River, USA.

Thebalanceshowsthatapproximately70%ofthesedimentsweretrappedintheimpoundments,butthisresultedinonlya2%decreaseinNitrogenand40%decreaseinPhosphorusexporttothedownstreamcatchment. Thesedifferencesareattributable to largersedimentsbeingmoreefficientlytrappedwithinimpoundments,butnutrientsbeingmorecommonlyassociatedwithfiner-grained materials.

Figure 4.18. Sediment and nutrient capture in the Susquehanna River, USA (USGS, 1998).

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4.2.4 Conversion of river to lake

The conversion of a river to a lake can lead to major changes in water quality, with the degree of change usually associated with the duration of impoundment. Typical changes include

• Temperature alterations: Temperatures can decrease in surface waters and decrease in sub-surface waters relative to the temperature of unregulated rivers. An example of this for the Nam Theun 2 Reservoir is shown in Figure 4.19;

• Thermalstratification:Temperaturedifferencesbetweensurfaceandsub-surfacewaterscanleadtostratificationofawaterbodywithcoldermoredensewateroverlainbylessdensewater;

• Reductionsinsub-surfaceoxygenconcentrations:Duringperiodsofthermalstratification,there is no contact between the bottom water and the atmosphere. As oxygen in the sub-surface water is consumed by normal biological processes, conditions of low or no dissolved oxygenmay result (Figure4.20). Following theexhaustionofoxygen,methanogensandsulphate reducing bacteria will become active, leading to the generation and potential release of methane and hydrogen sulphide from impoundments. This is a very common issueduringthefirst5 to10yearsfollowingestablishmentofan impoundment. Becausemethane is a potent greenhouse gas, consideration of the climate change impact associated with development of the impoundment is often assessed within the context of the renewable energy generated by the project in the EIA process. Hydrogen sulphide is a potentially highly toxic gas that can also cause irritation at low concentrations;

• Conditions of low dissolved oxygen can lead to the reduction and dissolution of iron and manganese oxy-hydroxides, increasing the dissolved concentrations of these parameters, and any other metals, nutrients or contaminants associated with the iron or manganese;

• Reductions in the dissolved oxygen content of the river downstream of the impoundment due to release of low DO from depth in the impoundment;

• Increases in iron, manganese or other metals, contaminants or nutrients associated with low dissolved oxygen conditions in the impoundment. Increased iron concentrations in the dischargefromtheNamTheun2HydropowerProjecthavebeenrecorded,andhavehadimpacts on hydropower infrastructure (Chanudet et al.,2015);

• The methylation of mercury has been found to occur within impoundments if the metal is present in the soils or bedrock underlying the area or there is a pathway through which it can enter the impoundment. The increased methylation is attributable to increased microbial activityinthewaterbody.MercuryhasbeenidentifiedasacontaminantofconcernintheUMB impoundments and waterways (He et al,2009);

• A reduction in suspended sediments in the impoundment can increase light penetration leading to increased algal and plant growth. This in turn can consume oxygen from the watercolumn.Noxiousplantgrowthcanalsoaffecthydropowerinfrastructure.ThegrowthofwaterhyacinthshasimpactedoperationsattheKafueGorgeprojectinZambiaandattheOwensFallsProjectinJinja,Ugandabycausingblockagesofhydropowerturbines(UNEP,2013).

• Very high dissolved oxygen concentrations associated with aeration of water during power station generation or subsequent aeration.



Figure 4.19. Water temperature (°C) profilesintheNamTheun 2 Reservoir (RES1 and RES9) between 2008 and 2013 (WD: warm dry season, WW: warm wet season, CD: cool dry season). (Chanudet et al., 2015).

Figure 4.20. Dissolved oxygen (mg.L-1)profilesin the Nam Theun 2 Reservoir (RES1 and RES9) between 2008 and 2013 (WD: warm dry season, WW: warm wet season, CD: cool dry season). (Chanudet et al., 2015).

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Figure 4.21. Schematic showing mercury cycling within an impoundment. (Mercury Pollution: Integration and Synthesis. (Copyright Lewis Publishers, an imprint of CRC Press.in USGS, 1995).

4.2.5 Inter intra-basin transfers Neighbouringcatchmentsorsub-catchmentscanhavequitedifferentwaterqualitycharacteristicsdepending on the underlying geology and land-uses, and diverting water between basins may change thephysical or chemical attributes in both catchments. The lower flows in the ‘donor’catchment may lead to increased water clarity due to a decrease in sediment concentrations or increasedwater temperature, due to slowermovingwater. The ‘receiving’ catchmentmay besubjectedtofluctuatingorcontinuouschangestowaterquality,dependingonthepatternofwaterrelease. An example of this has been documented through the Nam Theun 2 monitoring program where changes to the concentration of calcium in the water have been linked to small changes in the macroinvertebrate assemblage present downstream.

4.2.6 Other risks associated with hydropower developments

In addition to the water quality risks associated with present water quality trends in the catchment (Table 4.1) and risks associated with the establishment and operation of hydropower projects(Table4.2),therearesomeotherlong-termrisksthatneedtoberecognisedandconsideredinthecontext of hydropower mitigation and management.

Catchments and catchment uses change over time, and water quality usually reflects thesechanges. Land use changes such as the clearing and conversion of forests to agricultural lands, development of irrigation schemes and increasing the number of crops grown in a year are all possible future developments which have the potential to alter the quality of water entering the Mekong mainstream and tributaries.



The development of hydropower schemes can increase the availability of a reliable or potable water supply, which in turn may fuel growth and development in the area. More directly, aquaculture opportunities within impoundments, increased populations and increased access can all lead to increased pressure on water quality.

In the context of mitigation, these future potential changes are impossible to identify with a high degreeofconfidencepriortodevelopmentofthescheme,sofuturewaterqualityrisksneedtobeconsideredwhenmitigationoptionsarebeingidentifiedforahydropowerscheme.

An additional risk facing the LMB with respect to water quality is the timing and intensity of hydropowerdevelopmentinthecatchment.Itisrecognisedthatfollowingfillingofanimpoundmentandextendingintothefirstfewyearsofhydropoweroperationwaterqualitytendstobepoorestowingtothedegradationoforganicmatterintheinundatedarea.Thefillingandcommissioningofa large number of hydro-power projects in the tributaries of the LMB are scheduled to occur within a relatively short period of time. This situation could result in a cumulative degradation of water quality in the LMB, as reduced water quality enters from the tributaries.

4.3 Water Quality Mitigation Measures

4.3.1 General

Mitigation approaches for water quality need to be considered at all stages of the hydropower life cycle. Water quality needs to be considered within a catchment context to include the water entering of the impoundment, the processes occurring within the impoundment, and the potential downstream impacts associated with discharge from the power station and impoundment. Maintenance of good water quality entering into, and within the impoundment, is not only of environmentalandsocialbenefit,butgoodwaterqualityisalsorequiredforthemaintenanceandefficientoperationofhydropowerinfrastructure.

Water quality will change over the life-cycle of a hydropower project so mitigation and management needs to be based a good understanding of the catchment which requires monitoring at a range of temporal and spatial scales. In the LMB, the existence of the WQMN provides a sound basis atthecatchmentscaleforwaterqualitycharacteristicsandtrends,butadditionalsite-specificandmore frequent monitoring is required to underpin sustainable management of water quality issues. Water quality monitoring and indicators are discussed in more detail Section 4.4.

Changestowaterqualityovertimewill includecatchmentchangeswhichaffectinflowingwater,evolution of the impoundment which can alter the physical and chemical attributes of water during storage, and downstream needs and ecological values. These factors necessitate that hydropowerdevelopmentsbeflexiblewith respect tomitigationapproaches,andbeguidedbyadaptivemanagement.Waterqualitymanagementneedstobeintegratedwithflowandsedimentmanagement and mitigation, as these are inter-related.

4.3.2 BackgroundinformationfromtheMRCPreliminaryDesignGuidance

ThePDGfocusesonwaterqualityrisksassociatedwithaseriesoflow-headdamsasproposedforthe mainstream Mekong in the LMB, emphasizing that larger deeper storages may promote greater changes.ThewaterqualityrisksidentifiedbythePDGincludechangestophysicalandchemicalwater quality parameters which can impact on the downstream ecosystem, and geomorphology

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(asrelatedtosedimentconcentrations).

The water quality parameters that are important to consider in hydropower developments include temperature, pH, dissolved oxygen, Biological Oxygen Demand, total nitrogen, total phosphorus and coliform bacteria. These parameters can be altered during storage within a reservoir and especiallyunderconditionswherethermalstratificationcanleadtothedevelopmentofstagnantwater at depth.

Guidance for maintaining water quality includes the design and management of reservoirs which willachievethewaterqualityguidelinesassetoutintheMRCTechnicalGuidelinesforProceduresonWaterQuality.ThePDGstate thenecessityof site– specificwaterqualitymonitoring,withthe results to be interpreted within larger scale trends provided by the Water Quality Monitoring Network and Ecological Health Monitoring Network.

The following sections provide a more in-depth description and consideration of the issues addressedinthePDG.

4.3.3 MasterPlansandfeasibility

Waterqualityconsiderationsneedtobeincludedincatchmentlevel-MasterPlansandhydropowerfeasibility studies, as highlighted under sections I to IV in Tables 6.1 – 6.5, Mitigation Guidelines. Planning should be based on a sound knowledge of the catchment, and risk-assessments asto the quality of water entering the impoundment, and water quality needs and considerations downstream of the impoundment should be considered at the earliest stages of the project.

The siting and morphology of impoundments will have a direct impact on long-term water quality characteristics.Thesize,morphologyandthrough-flowofanimpoundmentwilldictatewhetherstratificationwilloccur,which inturnexertsastrongcontrolonwaterqualityoverthe lifeof theproject.Ingeneral,smallreservoirsinwhichtheinflowgreatlyexceedsthevolumeofstoragewillhave lower riskswith respect tostratificationdue toshortstorageperiods. However,even lowvolume, short storage duration impoundments can stratify if they are long, narrow and deep, with a largeproportionof‘dead’storage.Thelocationofthepowerstationintakewillalsoaffectmixingwithinthereservoir,astheintakewillgenerate‘currents’.

Small volume reservoirs also tend to exert less of an impact on downstream water quality, as retention time is low so physical characteristics such as temperature or dissolved oxygen have less time to change during storage, and the discharge is likely to retain its seasonality. Wind mixing maybesufficienttomaintainathermallymixedandwelloxygenatedreservoiriftheimpoundmentis shallow.

The siting of dams should consider the potential for the downstream reach to induce turbulence in thedischarge,whichisbeneficialforbothaerating,andde-gassingwaterandpromotingmixing.Mixingcanbe important ifwater isbeing released frommultiple levelswithin the lake. Projectdesignandsitingshouldalsoconsider theproximityofcommunitieswhichmaybeaffectedbynoxious odours associated with the release of hydrogen sulphide bearing water, especially during thefirstyearsofoperation.

Water quality impacts can also be ameliorated if unregulated tributaries enter immediately downstreamoftheimpoundment.Thesetributarieswilldecreasethepercentageofregulatedflowin the river, and provide seasonal cycles with respect to temperature and water quality parameters.



AnexampleofwherethesitingofahydropowerprojectwasinfluencedbywaterqualityissuesistheJohnButtersPowerSchemeontheKingRiverinTasmania,Australia.Thedamandpowerstation were intentionally situated upstream of a tributary which transports contaminated mining waste from an historic mine site. The low pH, high acidity water in the tributary, and associated high suspended solids content at times lead to concerns about the potential impact on hydropower infrastructure,andthepotentialwaterqualityoftheimpoundment(Figure4.22).

Figure 4.22. John Butters Power Station on the King River in Tasmania, Australia. Siting of the HP was guided by presence of tributary contaminated by acidic discharges from historic mine sites.

During the design and planning phase, clearing of the area of inundation needs to be considered. The clearing of reservoir areas is generally completed to reduce the amount of organic matter that will decompose following inundation. Recent investigations have indicated that a large proportion of the carbon is associated with soil organic matter that is not removed during clearing. Additional vegetationgrowthmayoccurbetweenthetimeofclearingandreservoirfillingwhichwillalsoaffectthenetvolumeofcarbonreduction.FishmonitoringinNamTheun2hasfoundthatfishpopulationin terms of biomass and abundance was enhanced in areas of structured habitat in the form of inundatedtreessuggestingthatleavingsomevegetationmaybebeneficialasfishhabitat(Cottetet al.,2015).

Eachreservoirneedstobeconsideredonasite-specificbasis,withissuessuchasaccessandcollateraldamageassessed.Providingaccessinundationareasmayproveharmful inthe longterm if deforestation extends beyond the area of inundation, or the access roads provide future access to areas which are desirable to protect.

Greenhouse gas emissions: As part of the water quality investigations associated with the establishment of an impoundment, the potential for methane release during the life cycle of the storage needs to be considered, and placed in a comparative context with the amount of greenhouse gases released through other electricity generating methods. Table 4.3 compared greenhouse gas emissions for various energy sources, and shows the large range associated withhydropoweroperations,withthedifferenceslargelyattributabletothelatitudeoftheproject.Tropical reservoirs have the potential to have higher GHG yields owing to the greater carbon stores within impoundments, and the potential for ongoing high carbon inputs to the impoundment. In temperate and boreal areas, the GHG emissions have been found to peak within 3 to 5 years of inundation, whereas the time periods associated with tropical reservoirs can be much longer (Tremblay, et al.,2009).

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Table4.3.FullenergychaingreenhousegasemissionfactorsingCO2equiv/kWh(e)h-1(modi-fiedfromIAEA,1996,Tremblayet al.,2009).

MeasurementsofGHGemissionsfromNamTheun2ineasternLaoPDRpriorto,andduringthefirst2yearsofoperationwascompletedbyDeshmukh(2013),andestimatesof310and300gCO2 eq/kWh were derived for the two years. These years likely represent some of the highest emissionsduringtheproject’slifecycle.Theinvestigationalsofoundthatupto25%oftheGHGemission could be attributed to exposed banks during reservoir drawdown. The GHG emission rate for Nam Thuen 2 is compared to the energy production technologies in Figure 4.23.

Figure 4.23. Estimates of lifecycle GHG emissions (gCO2eq.kWh-1) for broad categories of electricity generation technologies (IPCC, 2012). The red star indicates the GHG emissions factorforthefirst2yearsafterimpoundmentoftheNT2Reservoir(whichisnotthelifecycleGHGemissions).




The inclusion of infrastructure to allow mitigation and management of water quality issues needs to be considered and incorporated into the planning and design stage of the project. Management options for water quality issues considered as having a high risk of occurring (such as low dissolved oxygenlevelsforseveralyearsaftercreationofanimpoundment),needtobeaddressedaswellas including infrastructure thatwillprovide futureflexibilitywithrespect tooperationsandwaterquality issues. The long life span of hydropower projects it is not possible to predict all potential future water quality issues with any degree of certainty, and having infrastructure which can be used in an adaptive management approach is the best way to reduce future water quality risks. Examples of infrastructure associated with water quality mitigation are described in the following sections.

Multiple inlets / outlets, including high level (refer I.2.3, II.2.2, III.2.2, IV.2.3 in Tables 6.1 – 6.4, MitigationGuidelines):Thedepthfromwhichwaterisdrawnfromareservoirwillaffectthewaterquality entering the power station and released to the downstream environment. Figure 4.24 shows howdifferentoutletlevelscanbeusedtoreleaseanoxicbottommixedwithsediments,colddeepwaterorwarmerwelloxygenatedwaterfromabovethethermocline.Thesedifferentoutletlevelscanbeusedtomaximiseorminimisedischargesfromaspecificlevelofthelake,orbeusedtomixwaters. Multiple intakes are applicable for management of the release of seasonally appropriate water temperatures or minimising the release of anoxic water. These outlets are also applicable forsedimentmitigationapproaches,includingthesluicingorflushingfromlowlevelsandproviding‘clean’waterfromhigherleveloutlet.

Operating patterns of power stations can also be used to manage dissolved oxygen concentrations inreservoirs.Thedrawingofwaterfromdifferentlevelsinducescurrentswithintheimpoundmentswhichwilldraw‘newer’moreoxygenatedwaterintotheimpoundmentTurbine‘pulsing’throughlow-level outlets has been used to keep sub-surface waters from stagnating.

Figure 4.24. Multiple level outlets in a dam allowingdischargeofwaterofdifferingcharacteristics. (Thornton et al. 1996, after Cole and Hannan, 1990).

Passiveaerationapproachesandinfrastructure(referII.2.4,IV.2inTables6.2and6.4,MitigationGuidelines): Low dissolved oxygen in hydropower impoundments is a common issue, andnumerous passive mitigation measures have been developed to increase the dissolved oxygen concentrations of water downstream of dams and power stations. Most exploit gravity to induce turbulenceintheflowingwater,whichincreasesaeration.Figure4.25showsarangeofpassivetechniques which have been adopted at sites within the LMB, and internationally. The turbulence ofwatercanbeincreasedby‘flowsplitters’asitpassesoverspillwaygatesasemployedatPakMundam,inThailand.AtNamTheun2,anaerationweirprovidesaerationaswaterflowsoverthe structure within the discharge channel. Intermittent smaller weirs in the discharge channel also

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assist with aeration. The aeration provided by the weirs also induces the precipitation of iron from thewater,thusreducingdownstreamconcentrations.AtNamNgiep1,a‘Labyrinth’spillwaydesignincreases the aeration of water over the spillway and in the downstream river. The Tennessee Valley AuthorityintheUnitedStateshaveincorporatedan‘infusion’weirdownstreamofahydropowerproject which oxygenates the surface water discharge as it passes through the structure.

An example of the change in dissolved oxygen provided by the mitigation measures employed at Nam Theun 2 is provided by comparing the dissolved oxygen concentrations with those in Figure 4.26.

Figure4.25.Examplesofpassiveaerationstructures.(topleft)flow‘splitting’featuresonthetop of the gates at Pak Mun dam, Thailand; (top right) aeration weir at Nam Theun 2, Lao PDR, (bottomleft)designoflabyrinthfloodmanagementspillwayatNamNgiep1(Kansai,2013),(bottom right) Infusion weir at Chatuge Dam, North Carolina.



Figure 4.26. Water temperature (°C) and dissolved oxygen (mg.L-1)profilesintheregulatingpond(REG1) between 2009 and 2013. (WD: warm dry season, WW: warm wet season, CD: cool dry season). Chanudet et al., 2015

Auto-ventingturbines(referII.2.4,IV.2inTables6.2and6.4,MitigationGuidelines):Auto-ventingturbines vent low pressure areas within turbines to the surface to draw air into the turbine during power generation (Figure 4.27). Introducing air during power generation has been commonlyemployedsincetheearly1960s(March,1992)andisusedtooptimisepowergenerationaswellasimprove downstream environmental conditions. The introduction of air into the turbine can occur atdifferentpointswithintheturbine,anddifferentapproachesprovidethemostbenefitatdifferentturbine loads.

Figure 4.27. (top) Auto-venting turbine aeration methods, showing Central, Distributed and PeripheralAirintakes,(bottom)Auto-ventinghubbaffleonaturbine(TennesseeValleyAuthoritywebsite).

Activeaerationapproaches(refer II.2.4, IV.2 inTables6.2and6.4,MitigationGuidelines): Theactive pumping of air or injection of oxygen into reservoirs has been used to oxygenate water whilst still in storage in the impoundment. Examples of these systems as used by the Tennessee Valley Authority are shown in Figure 4.28.

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Figure 4.28. (left) Surface water pumps which oxygenate sub-surface water at the Douglas Dam in Tennessee, USA, (right) Oxygen injection system used to inject liquid oxygen through a diffuserhosedeepinareservoir(TennesseeValleyAuthoritywebsite).

Managing over oxygenated water. Water which contains high levels of dissolved gases is also potentially harmful to aquatic environments as elevated dissolved gas levels can induce gas-bubble disease, a potentially fatal disease which can harm fish, amphibians andmacroinvertebrates.Generallygassaturationinexcessof120%isassociatedwiththecondition,althoughthedepthofthewaterandtemperaturewillalsoaffectgassaturation.GasBubbleDisease(GBD)generallyoccursduringthereleaseofhighlyturbulentwater,suchas‘spills’duringlargefloodevents.GBDhas also been associated with the over-oxygenation of water as it passes through a power station. Gascanbeentrainedasthewaterflowsthroughtrash-rackspriortoenteringthestation,orifairisinjected to reduce cavitation or enhance environmental releases.

Mitigation approaches to reduce the risk of releasing water containing high levels of dissolved gases include:

• Continuous monitoring of dissolved oxygen in the tail water and adjustment of air injection or auto-venting turbines to maintain gas levels within acceptable limits;

• Installation of infrastructure to reduce turbulence associated with the discharge or spill of water;

• Siting of projects in areas where downstream turbulence will assist with de-gassing of the discharge.

AnexampleofgasbubblediseasemitigationisprovidedbytheYacyretaHydropowerprojectontheParanaRiverbetweenArgentinaandParaguay(IEA,2006).The3,000MWprojectwascompletedin1994andisoperatedbytheEntidadBinacionaldeYacyreta.Thepresenceofanislandintheriverat the dam site resulted in the construction of a split spillway system. Soon after construction of the dam,butpriortooperationofthepowerstation,amassfishmortalityeventoccurreddownstreamof the spillway, with the cause identified as gas bubble disease. Investigations identified thatsymmetric discharge through the partially opened gates was responsible for the event, with gas saturationlevelsreaching150%downstreamoftheimpoundment(comparedto100%withintheimpoundment).Itwasalsorevealedthatthehighgasbearingwaterwasveryslowtomixwiththeunderlying turbine discharge water, with elevated gas conditions persisting for 90 km downstream.

Operating procedures which restricted the use of partially opened spillway gates were implemented tomanage the situation in the short term. In the longer term, deflectorswere installed at the



downstreamslopeofthespillwaywhichsmoothedtheflowandgreatlyreducedtheentrainmentofgasinthedischargeenteringthestillingbasin(Figure4.29).Thedeflectors,incombinationwithoperating procedures that require symmetrical use of the spillways resolved the GBD issue.

Figure4.29.(left)Spillwayflowattimeoffishmortalityevent;(right)Flowoverspillwayfollowinginstallationofdeflectors.

Inreservoirmanagementofwaterquality(ReferIII.2inTable6.3,MitigationGuidelines):Waterquality trends and processes will vary depending within an impoundment, with most lakes characterisedbya‘riverine’,‘transitional’and‘lacustarine’zone(Thornton,et al,1996).Aschematicof these areas and their typcial characteristics are summarised in Figure 4.30. in situ strategies to mitigate water quality are typically related to maintenance of water circulation to reduce oxygen consumption(includingairinjection),ormixingofsurfacewaterstominimisealgalgrowth.Solarpoweredmixers (Figure4.31) can reducealgal growthbymixing surfacewaters and reducingconditions favourable for growth. These are typically used in scenarios where the impoundment is utilised for drinking water as mixing reducing the risk of blue-green algal growth.

Where aquatic plant growth interfers with hydropower or other infrastrucutre, or navigation, the physicalharvestingofplantsinlimitedareasmaybeutilised(Figure4.32).

Figure 4.30. Longitudinal zonation of water quality conditions in reservoirs (Thornton et al., 1996,modifiedfromKimmelandGroeger, 1984).

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Figure 4.31. Solar powered mixer to reduce the growth of noxious algae in reservoirs.

Figure 4.32. Macrophyte harvester used to remove plant growth around infrastructure.

4.3.5 Construction

Theconstructionphaseofahydropowerprojectisadiscretephasewhichrequiresspecificwaterquality mitigation approaches. Construction can involve large scale land disturbance, the use of large volumes of fuels, explosives, drilling reagents and other chemicals. Best practice construction andreagenthandlingtechniquesarerequiredtominimizetherunoffofsedimentandcontaminantsintowaterways.Theuseofcut-offdrains,sedimentorgreaseandoilcollectionandsettlementponds and the bunding of areas using hydrocarbons are all common approaches to water quality maintenance. The education of the workforce and implementing a site-wide awareness of best practice techniques is also critical to successful water quality management.

The construction phase of hydropower projects generally results in a large influx of people tothe area, which may continue after commissioning. A rapid increase in population necessitates that waste and waste water management systems be implemented prior to project construction, and high standards of sanitation be incorporated at work camps. Waste generated during the construction phase should not be disposed of in the future impoundment area, and a long-term waste management plan for the region should be developed which provides long-term protection ofwaterqualityinthecatchment.AtNamNgiep1inLaoPDR,wastemanagementhasincludedthedevelopmentofalandfillwellremovedfromtheriverforthedisposalofnon-recyclablewaste.



As catchment populations increase during and after the construction phase, the hydropower developer should work with the local and regional governments to ensure that adequate municipal and industrial water quality infrastructure be implemented and maintained. The local opportunities provided by the establishment of an impoundment need to be managed and regulated such that waste water discharges will not compromise water quality within the impoundment.

Figure4.33.LandfillatNamNgiep1forthedisposal of non-recyclable waste.

4.3.6 Operational Stage

Water quality management during the operational stage of the development needs to be based on monitoringandtheadoptionofadaptivemanagement(referthe‘OperationsColumn’inTables6.1-6.5,MitigationGuidelines).Waterqualityrisksandchallengeswillchangebetweenseasonsandoveryears,andaflexibleapproach,basedonsoundmonitoringisthebestmanagementstrategyfor maintaining acceptable water quality within and downstream of a hydropower project.

During the operational phase, operating rules related to dissolved oxygen within and downstream of the reservoir need to be developed and implemented utilising the range of management and infrastructure options incorporated during the planning and design stages.

Continuous monitoring and management of dissolved oxygen concentrations in the discharge from dams and power stations is required to minimise downstream impacts. Over longer time frames, the potential impacts of catchment developments and activities need to be considered within the context of water quality mitigation, and a cooperative catchment management approach is can usually provide the best outcomes.

4.4 Water quality indicators and monitoring

The ISH11 project (Improved Environmental and Socio-Economic Baseline Information for HydropowerPlanning) identifiedmonitoringandinformationneedsforhydropowerprojectsoverthe project-life-cycle. Table 4.4 contains a summary of the range of information requirements associated with water quality, and summarises indicators which can provide the required information. When considering water quality, it is important to implement monitoring regimes that will provide adequate information at the required scales. For example, continuous dissolved oxygen monitoring is required to ensure downstream impacts associated with power station discharge are minimised, whilst catchment information is required over scales of years to decades to assess how long-term

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catchmentdevelopmentmayaffectreservoirinflows.

Water quality indicators associated with managing hydropower operations within a catchment context aresummarisedinTable3.12,indicatorsassociatedwithspecificwaterusesaresummarized.

Table 4.4. Water quality parameters and indicators applicable to Hydropower operations.

Type of Parameter or Indicator

Relevance for hydropower planning and operation Indicator examples

Water quality

• Water quality can affecthydropowerinfrastructure

• Need to understand influentwaterqualityto predict and manage potential changes during storage, and to assess whetherinflowingwateris changing over time;

• Need to understand changes to water quality during storage socandifferentiatebetween hydropower development impacts and other impacts (such asaquaculture)

• Need to understand any downstream impact on water quality due to hydropower operations, and to distinguish between hydropower impacts and other land use impacts

Suspended sediment characteristics: size and composition of material

Physio-chemical water quality characteristics: temperature, pH, acidity, alkalinity, dissolved oxygen in surface and sub-surface water

Metals: total and dissolved iron, manganese, zinc, mercury, arsenic

Nutrients: concentration, speciation, seasonal variability, changes during storage



Table4.5.WaterqualitymonitoringrequirementsasafunctionofPrincipalWateruse(Thornton,et al.,1996).

113 | Chapter 5. Fisheries and Aquatic Ecology – Status, Risks and Mitigation


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5 Fisheries and Aquatic Ecology – Status, Risks and

Mitigation



ThefollowingchaptersfocusonthestatusofaquaticecologyandfisheriesintheLMBandhighlightrisks as well as mitigation options related to hydropower development in the mainstream and tributaries.

The status of aquatic organisms is strongly linked to the availability and accessibility of suitable habitats. Geology and tectonics, as well as climate and land cover are important factors which influence hydro-morphological conditions at smaller scales. They are responsible for channelcharacteristicsandthereforehighlyrelevantfortheformationofdifferenthabitats in longitudinaldirection and over time (e.g. seasons). As a consequence, any changes to the system (e.g.hydrology,geomorphology,waterquality)causechangestothehabitatandconsequentlyinfluenceaquatic organisms. Therefore, several aspects, which were already discussed in previous chapters, will be raised once again and addressed from the perspective of aquatic ecology.

5.1 Basin Context – Status and Overview

The physical diversity of the Mekong favours a high species diversity and productivity (Valbo-Jorgensen et al.,2009).Asaconsequence,theLMBrepresentsaregionalhotspotforbiodiversity(Termvidchakorn&Hortle,2013)supportingarichflora(e.g.non-cultivatedsubmergedorfloatingwater plants, phytoplankton) and fauna (e.g. invertebrates, fish, amphibians, reptiles, birds,mammals).

With a fish fauna of at least 1,000 fish species, theMekong has the second highest richnessof species in theworld after theAmazonRiver (Halls & Kshatriya, 2009; FishBase, Froese &Pauly,2010;Baran&Myschowoda,2009).Thenumberofspeciesiscontinuouslyincreasingastaxonomistsreclassifyexistingspeciesandidentifynewones(NCCV,2013).Fishspeciesdiversityincreasesfromheadwaterstothelowersections,asusualinrivers(Schmutz&Mielach,2015).

With approximately 220 endemic fish species (Lu & Siew, 2005), endemism is fairly high,especially in the upper catchments (Van Zalinge et al. 2003). Furthermore, theMekong has the highest number of giant freshwater fish in theworld (i.e. at leastseven species; Stone 2007). It includesthe critically endangered Mekong giant catfish (Pangasianodon gigas), giantpangasius(Pangasiussanitwongsei)andgiantbarb(Catlocarpiosiamensis)aswellas the endangered seven-striped barb (Probarbus jullieni) (Hortle, 2009,Hoganet al.,2004,Baird,2006).

Due to the large number of species and lack of ecological studies, many species are hardly explored. However, the Mekong FishDatabase(MFD,2003)providesdataon>500fishspecies.Furtherinformationisavailablefromfishbase(fishbase.org)orselectedliterature.Forinstance,Poulsenet al.(2004)describethedistributionandecologyofaround40importantriverinefishspeciesoftheMekongRiverBasin,feeding preferences, population structure and critical habitats. Furthermore, Cowx et al.(2015)andHortle et al.(2012)investigatedlarvalandjuvenilefishcommunitiesanddriftalongtheLMB.

Figure 5.1. Giant pangasius (Pangasius sanitwongsei (MRC, 2007).

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5.1.1 Importance ological cycle

AsdescribedinChapter2,theflowregimeoftheMekongischaracterizedbyadistincthydrologicalcycle of wet- and dry seasons. The Mekong’s rich ecosystem has evolved in accordance with the seasonal hydrological cycle. Furthermore, the four seasons, i.e. dry, wet and two transition seasons(seealsoFigure5.2),coincidewithdistinctiveecosystemfunctions(MRC,2009):

Figure5.2.Theflowregimeanditsimportanceforaquaticorganisms,dischargeatLuangPrabang in year 1988 (based on MRC, 2009).

1. ThedryseasonstartsbetweenNovember/December(Kratie)andJanuary(downstreamofTonleSap).Itisaperiodwhereaquaticorganismssufferfromlimitedhabitatavailabilityandpoorwaterquality.Themagnitude(Q)andduration(days)of the lowestdischargeof thisseason is a good indicator for the stress experienced by the ecosystem.

2. Thefirsttransitionseasonstartsattheonsetoftheflood(thefirsttimetheflowincreasestotwicetheminimumdischarge)andisusuallyconfinedtoafewweeksinMayandJune.Pre-floodspatesmaytriggerspawningmigrationsandhavepositiveimpactsonthewaterquality(e.g.oxygen).TheincreaseofflowislargerindownstreamsectionsoftheMekong.

3. ThefloodseasonstartsaroundJunewhen theflowexceeds the long-termmeanannualdischarge(MQ)forthefirsttime.Asthefloodvolumeisequallyimportantastheflooddischarge,bothcriteriaareusedforthedistinctionofflood-,normal-anddrought-years.Themagnitude,durationandtimingoftheannualflooddeterminetheavailability,sizeandproductivityofthefloodplainecosystem(e.g.TonleSap–GreatLakeSystem)andconsequentlytheyieldofcommerciallyimportantspecies.AnotherimportantphenomenonistheflowreversaloftheTonleSap,allowingfishandnutrientstoenterthefloodplainsystem.



4. ThesecondtransitionseasonstartswhentheflowdropsbelowMQ.Itisashortperiodintheupperreaches(twoweeksinearlytomid-November)buttendstobelongerandlaterfurtherdownstreamduetothedewateringoftheTonleSap.Theaveragedailyrateofflowrecession(m³/d)indicatestherateofpostflooddrainageofthefloodplainsandtriggersdownstreamfishmigrationaswellasvegetationchanges.

EspeciallyintheupperLMB,China’scatchmentcontributesahighshareoftheflow(i.e.60%inthedryand40%inthewetseasoninVientiane),however,astributariesenterthesystem,theimportancedecreases(i.e.35%inthedryand15%inthewetseasoninKratie;seealsoFigure2.4).As a consequence, dry season flows have approximately the samemagnitude along theMekongmainstream(i.e.dominatedbyChinesehydrograph)whilewetseasonflowsincreaseinmagnitudeindownstreamdirection(seealsoFigure2.5).

The ecological integrity of a river depends to a high degree on an intact hydrological cycle. The magnitude,duration,frequency,timingandrateofchangeoftheflowareresponsiblefortype-specificsedimentcompositions (e.g.preventionofclogging),waterqualityconditions (e.g. temperature,oxygen),availabilityofenergysources(e.g.nutrients)andbioticinteractions(e.g.spawning)(seealsoFigure5.3;Karr,1991;Bunn&Arthington,2002).Anaturalflowregimethereforeensuressite-specifichabitats,supports lifehistorypatterns (e.g. formationofspawninghabitats, recruitmentsuccess)andseasonalconnectivitytherebyprovidingsuitablehabitatsandconditionsforlocallyadaptedaquaticorganisms(seealsoFigure5.4).

Figure5.3.Importantfactorsoftheflowregime(Karr1991).

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Figure5.4.Importantprinciplesofnaturalflow(Bunn&Arthington,2002).

5.1.2 Importance of natural sediment transport

Sediment transport in the Mekong is closely linked to the hydrologic cycle. While dissolved nutrients are low, nutrients are often associated with sediments. Depending on the particle size and characteristics(e.g.gravel,sand,clayandsilt),theabsorptionandtransportationofnutrients(e.g.phosphorusandnitrogen)andorganicparticles isfacilitated.Thereby,thesedimenttransport iscloselyrelatedtotheproductivityoftropicalriverecosystemsastheMekong,includingfloodplains,estuariesandcoastalareas(Baran&Guerin,2012).

Thefollowingbiologicalprocessesrelyonnaturalsedimenttransport(Baran&Guerin,2012):

- Respiration: the decomposition of organic components transported by sediments requires oxygen and therefore has a direct negative impact on the dissolved oxygen concentration. Ontheotherhand,absorbednutrientsinfluenceplantphotosynthesisandconsequentlytheamount of dissolved oxygen.

- Nutrition: Sediments and their connected nutrients represent the basic input for the food web. On the one hand, turbidity reduces photosynthesis and decreases primary production. On the other hand, a reduction of suspended sediments might cause a decrease in primary production by reducing the nutrient load.

- Habitats:Sedimentsareimportantforthesite-specificinformationofhabitatsandspawninggrounds.

- Migration:Changesinturbidityareknowntotriggermigrationsforseveralfishspecies.

Any changes to the sediment transport (e.g. caused by dam development, the related impoundments orhydrologicalchanges)willeventuallyalsointerferewiththeabovedescribedprocesses(Baran&Guerin,2012).



Fishbiodiversityandfisheriesyielddependstoahighdegreeontheavailabilityandaccessibilityofimportant habitats and food sources, which are both linked to a natural sediment transport. Valbo-Jorgensen et al.(2009)assessedthefooditemsoftheMekongfishfaunaandconcludedthatmudfeedersconstituteonly1%ofallspecieswhile69specieswereclassifiedasdetritivores.

Figure5.5.NumberofpercentageofMekongfishspeciesfeedingonvariousfoodsources(Valbo-Jorgensen et al., 2009).

Manyfishspeciesfeedonthefirstlevelsofthetrophicpyramid.Sincezooplanktonandbenthicinvertebrates rely on carbon components of sediment and phytoplankton, algae and aquatic plants require nutrients absorbed on sediment, permanently reduced sediment loads alter the food webs andconsequentlymayreducefishdiversityandbiomass(Baran&Guerin,2012).

5.1.3 Importance of connectivity / migration systems

Connectivity is a measure of how spatially continuous a corridor or a matrix is (Forman & Gordon, 1986).Thus,healthyecosystemsalsodependontheconnectivitytowardsfloodplains.Astreamcorridor with connections among its natural communities promotes transport of materials and energyandmovementoffloraandfauna(Loucks&vanBeek2005).

The ecosystem productivity of large tropical river-floodplain systems like theMekong is highlydependentontheundisturbedconnectivitybetweenriverandfloodplainhabitats(Bayley,1995).Manyspeciesrelyonthosehabitatstofulfiltheirlifecycles(e.g.spawningandnurseryhabitats)(Kinget al., 2009; Louca et al., 2009; Tonkin et al.,2008)andperformmigrationsbetweenthem.

Northcote (1984)definesmigrationas “movements that result inanalternationbetween twoormore separate habitats, occur with a regular periodicity, and involve a large proportion of the population”.Mostfishspeciesareconsideredmigratorytosomedegree.Whilesomemoveonly100mfrommainstreamhabitatstofloodplainstobreed,othersmovehundredsofkilometrestoreachcriticalhabitats(NCCV,2013)andthereforehighlydependonintactconnectivitybetweenthese habitats. Fish migrations in the LMB involve shifts between marine and freshwater habitats, between upstream and downstream areas within the Mekong River, between the Mekong River and its tributaries, and between rivers and floodplains (Schmutz &Mielach, 2015).Migrationsmostlyoccurwithregardtothespatialseparationbetweendryseasonrefugehabitatsandfloodseasonspawning,nurseryandgrowthhabitats(Poulsenet al.,2004).Althoughmigrationsoccur

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throughout the year, there are migration peaks at the onset and during the wet season (Schmutz &Mielach,2015).

Fishmigrationsareusuallytriggeredbyseveralcomplexinteractingfactors(Pavlov,1989;Colgan,1993, Lucas & Baras, 2001).Although the knowledge with regard tomigration triggers is stillincomplete,itisassumedthatforthemajorityofspeciesitisassociatedwithchangesinriverflow(NCCV,2013).Themostimportanttriggersunderdiscussionintropicalfreshwaterfisharewaterlevel, current, discharge, precipitation, lunar cycle, water colour, turbidity and the apparition of insects(Baran,2006).

FishtekConsulting(2015)assessedthehourlyfishbiomasspassagerateatXayaburioveranentireyear(seeFigure5.6)withaDIDSONunderwatersonarvideosystemenablingfishobservationsinturbidwaters.Peakmigration(i.e.with1,200kg/hr)occurredwiththeonsetofthewetseason(May).Thehighestobservedvalueinthismonthwas5,000kg/hr.Ingeneral,thehighestmigrationrates were found between February and June, which corresponds to the dry season. These data are very valuable but should be interpreted with caution. Wet season estimates might be biased as a DIDSON camera covers only 20-30 m in range (Burwen et al.,2011)whichmakesitdifficulttogetaccuratedatainlargeriversand/orflows.Smallfishmighthavelowerdetectionratesandaccuratebiomassestimatesaredifficulttoachieve(Hateley&Gregory,2006.)

Figure 5.6. Estimated hourly biomass passage rate at Xayaburi (Fishtek Consulting, 2015).

While adults migrate actively up- and downstream, ichthyoplankton develops while drifting passively downstream(Termvidchakorn&Hortle,2013;Poulsen&Valbo-Jørgensen,2000;Hallset al., 2013;



Agostinho & Gomes, 1997a, Nakatani et al., 1997, Agostinho et al., 2000).Since reproductionoftencoincideswithfloods,therisingflowscarrytheeggsandlarvaetodownstreamriversectionsand/ or lateral floodplains which are important nursery habitats. The possibility to return to orrepopulatedownstreamreachesisimportantforlong-termreproductionsuccess(Poulsenet al., 2004; Agostinho et al.,2000).

Fishspeciescanbegroupedintodifferentguildswithregardtotheirmigratorybehaviour.WithintheLMB,speciesareusuallyclassifiedas“whitefish”whichmigratewithinthemainstreamandintothefloodplainsduringthewetseason,“blackfish”withrestrictedmigratorybehaviourand“greyfish”representinganintermediategroup(Poulsenet al.,2002;Schmutz&Mielach,2015).

However, there is also a more detailed classification provided by MRC (2009), which dividesspeciesintotenguilds(seeFigure5.7andTable5.1).

Figure 5.7. Schematic description of guilds and their distribution (MRC, 2009).

TheAMCF (AssessmentofMekongCaptureFisheries)survey reported233speciesbelongingto 55 familieswithin themain channel, floodplains and estuary (Table 5.1) shows the numberofspeciesperguildsandtheirrelevanceforfisheries(kgand%ofcatch).Guild10includes19marinespecies,22speciesareconsideredasnon-migratory(guild6,blackfish)and42specieswereonlyfoundintheestuary(guild7).Theremaining150species(belongingtotheguilds1-5,8,9)canbeconsideredasmigratory,withtheguilds2,3,8and9aslong-distancemigrators(Halls&Kshatriya,2009).Amoredetaileddescriptionofthesespeciesfollowsbelow.

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Table5.1.Mekongfishguilds,associatednumberofspeciesandtheirtotalandrelativecontribu-tiontothetotalcatchrecordedbytheAMCFsurvey,Nov2003–Dec2004(fromHalls&Kshatri-ya,2009).

• Guild 1 (rhithron) inhabits rapids and pools in rocky areas in the rhithron. They feed oninsects or algae, are small in size and are lithophilic or phytophilic with extended breeding seasons, however perform only limited migrations.

• Guild 2 (marine to rhithron) is represented by long distancemigrants (incl. anadromousspecies)whichspawninthemainchannel.Speciesmaybepelagophilic(withdriftingpelagiceggs),lithophilicorpsammophil.Adultsmaybepiscivorousbutdonotenterthefloodplain.

• Guild3(floodplainstorhithron)includesspeciesspawninginthemainchannelortributaries(pelagophilic,lithophilic,phytophilic,psammophilic)withpelagiceggorlarvalstages.Both,adultsandlarvaefeedinthefloodplainbutmigratetorefuges(pools)inthemainchannelduring the dry season.

• Guild4(floodplainstopotamon)differsfromguild3asspawningoccursonthefloodplain(phytophils)whilethemainchannelisusedasdryseasonrefuge.

• Guild5(floodplainsandpotamon)performslimitedmigrationsinthemainstream.Speciesaregeneralists(highlyadaptable,repeatbreeders,toleranttolowO2).Theyaresemi-migratorybutmightmigratetolateralfloodplainsduringfloodingtooccupysimilarhabitats.

• Guild 8 occurs in estuaries and the lower potamon and enters freshwater/ brackish areas for breeding.

• Guild 9 (marine to rhithron) reproduces in the sea, but juveniles or sub-adultmigrate tofreshwater habitats, often located far upstream in the catchment.

TheLMBisdividedintothreedistinctmigrationsystems(Baran,2006;Poulsen,et al.2002):

TheLowerLMBexpandsfromtheVietnamesecoastuptotheKhoneFallsinsouthernLaoPDR.It therefore includes the whole Cambodian and Vietnamese Mekong. Wet season feeding and



rearing habitats are spatially and temporally separated from the dry-season refuge habitats. During thedryperiod,migrationsoccuroutofthefloodplainsandtributaries(incl.TonleSap)towardsandupstream the mainstream of the Mekong River. Several species spawn with the onset of the wet season(Baran,2006).Theyeithermigratetowardthefloodplainstospawnorrelyontheflowtotransporttheiroffspringtothefloodplains(Poulsenet al.,2002).FortheDaifisheryintheTonleSapRiver,speciesofthegenusHenicorhynchusaccountfor40%ofthetotalcatch(Lienget al 1995; Pengbun&Chantoeun, 2001). However, also larger species (Catlocarpio siamensis, Cirrhinusmicrolepis,Cylocheilichthysenoplos,Robarbusjullieni)migratewithinthissystem(Poulsenet al., 2002).AccordingtoVanZalingeet al.(2000)whitefishaccountfor63%oftheyieldinthisarea.Although part of the Lower LMB, the Sesan tributary system also appears to contain its own sub-migration system.

The Middle LMB covers the area between the Khone Falls and Vientiane (Lao PDR) and ischaracterized by the presence of large tributaries (e.g. Mun River, Songkhram River, Xe Bang Fai River,HinbounRiverandothers)(Poulsenet al.,2002).Upstreammigrationsoftencoincidewiththewetseasonand risingwater levelswhenspeciesenter the tributariesand their floodplainsfor feeding and reproduction. During lower water levels, refuges downstream in the Mekong are inhabited(Poulsen,2003).TheMiddleLMBincludestheentireThaiMekongandaround80%ofthe Lao Mekong.

The Upper LMB is located in Lao PDR upstream of Vientiane (Poulsen et al., 2002) and ischaracterizedbyalackoffloodplainsandmajortributaries.Whilethewetseasontriggersupstreammigrations for spawning, dry season habitats can be found within the mainstream of the Mekong (VanZalingeet al.,2004).

Figure 5.8. Lower, middle and upper migration systems with major migration routes in the LMB; black arrows indicate migrations at the beginning of the wet season and brown arrows indicate migrations at the beginning of the dry season (Schmutz & Mielach 2015, based on Poulsen et al., 2002).

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Althoughthethreesystemsshowdifferentmigrationpatterns,theyarenotisolatedfromeachother(Barlow et al.,2008).Somespecies(e.g.CyclocheilichthysenoplosorCirrhinusmicrolepis)spendtheir juvenile stages in the Lower migration system but migrate upstream to the Middle system as adults(Poulsenet al.,2002).However,whiletheLowerandMiddlemigrationsystemsseemtobeconnected to a high degree, the Upper LMB is more isolated from them with only a few species covering all three systems. This might be caused by a section with rare pool habitats between PaksantotheLoeiRiver,whichmayactasanaturalbarrier(Poulsenet al.,2002).Inthisarea,observationsofmaturefisharerare.However,thesystemsmightbeconnectedbythedownstreamdrift of eggs and larvae.

The Mekong Fish Database (MFD; Visser et al.,2003)includescatchdata(speciespresence)of597 sampling sites along the Mekong mainstream and tributaries. Grill et al. (2014)usedthesedata toassess the rangeofmigratoryfishspecies in theLMB.Figure5.9ashows thenumberof migratory species per sample site. Figure 5.9b visualizes the minimum species range of the Mekonggiantcatfish(Pangasianodongigas)basedonrecordedoccurrences.Althoughitcoversonly12%oftherivernetworklength,itutilized72%oftheavailableflowvolume.Furthermore,Figure 5.9c combines the minimum species range of 25 migratory species into a migration heatmap (i.e. number of migratory species per river reach; Grill et al.,2014).

Figure 5.9. Migratory species occurrences on the basis of the Mekong Fish Database (Grill et al., 2014; based on Visser et al., 2003).

The DCI (Dendritic Connectivity Index; Cote et al., 2009), which was also applied by Grill et al. (2014) representsasuitable indicator forassessing theoverall connectivity inacatchment.Thereby, the DCI calculates the proportion of length of disconnected fragments in relation to the entire network (Cote et al.,2009).TheDCIcanbeextendedbydifferentweightingfactors(e.g.density ofmigratory species, flow volume,Strahler order) to reflect the importance for aquaticorganisms.WithintheCaseStudyReport(MRC,2018c),twodifferentDCIswerecalculated(i.e.DCIStrahlerandDCIMigr).WhiletheDCIMigrcoversarathersmallproportionofthecatchment(i.e.onlyMekongmainstreamand lowersectionsof larger tributaries) theDCIStrahlercoversalargerextent.WhilebothDCIsstartwithaconnectivityof100%,theyarealreadyreducedto37%



(DCIStrahler)and81%(DCIMigr)undercurrentconditions(i.e.BDP2030Scenario,withoutLMBmainstreamdams).

Figure 5.10. DCIStrahler and DCIMigr: Weighting factors (i.e. number of migratory species and Strahler) and current situation (i.e. BDP 2030 scenario) with connected river sections in green and disconnected river sections in red).

Whilemanyfishmigrateupstreamforspawning,theknowledgeaboutpost-spawningmigrationsisstillverysparse.Manyspeciesrelyonthepassivedownstreamdriftoflarvaeandeggsbyflow.Cowx et al.(2015)sampledelevensitesalongtheMekongtwiceamonthoverayearwithconicalplankton nets and seine nets. Although it is known, that many species migrate upstream with the onset of the wet season, Cowx et al.(2015)didnotobserveapeakseasonofichthyoplanktondrift.Larval drift could be observed throughout the year - also in the dry season. Overall, Cyprinids and Clupeidsmakeupahighshareofthecatch(seeFigure5.11).However,somespeciesweremoreprevalent in certain seasons and sampling sites.

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Figure5.11.Larvalfishcaughtwithconicalplanktonnetsandseinenets(Cowxetal.,2015).

5.1.4 Importance of habitats

The knowledge of important habitats is sparse in the LMB. However, some selected well documented habitatscanbeusedtoreflect theoverallhabitatavailabilityandquality.Alongwith theBDP,aplanningatlasoftheLMBwaselaborated(MRC,2011).Thisdocumentprovidesagoodoverviewof(1)protectedareas,(2)preliminarywetlandmapsandenvironmentalhotspots,(3),fishmigrationpatterns,(4)deeppools,(5)rapidsand(6)floodedareas(e.g.inundationoftheyear2000)(MRC,2011).

It is recognized that deep pools are critical for maintaining ecological integrity of the LMB, which is whytheyareoftenusedasfishconservationzones(FCZs;Hallset al.,2013).Deeppoolsarenotonlythoughttorepresentspawningareas(Poulsenet al.,2002),butalsoserveasshelterduringthedryseason.Manyspeciesleavethesedryseasonrefugesattheonsetofthefloodseasontomigratetotheirspawningandrearingareas(e.g.TonleSap,GreatLakeSystem)(Poulsenet al., 2004).Hallset al. (2013)preparedaMRCTechnicalPaper(No.31)ondeeppoolswheretheydiscusstheirfundamentalfunctionforsustainingthefisheriesoftheLMB.

Forexample, ithasbeenreported thatmorethan75%of theDaifisheriescatch inCambodiadependsuponfishpopulationsutilizingdeeppoolsbetweenKratieandtheKhoneFalls,andwithinthe Sesan river basin (Viravong et al.,2006).Whilemorethan200fishspecies(e.g.theMekonggiantcatfishandothercriticallyendangeredspecies)usedeeppoolsasdryseasonrefuges,somespeciesarebelievedtospawnthere(Boesemaniamicrolepis,Hypsibarbusmalcolmi)ortoinhabitthem throughout the year (Baird et al.,2001,Baird,2006;MRC,2005).OneofthosespeciesistheMekongRiverdolphin(Orcaellabrevirostris)whichspendsmostofitstimeindeeppoolsfromwhere it migrates to hunt (Halls et al.,2013).Furthermore,deeppoolsarealsobelievedtoprovideimportantshelterfrompredatorsandserveasthermalrefuges(Baird,2006).

AsshowninFigure5.12,thedeepestpoolsare(1)betweenHuayXayand20kmupstreamofVientiane,(2)betweenMukdahanandPakse(deepestpools)and(3)betweenStungTrengandKratie(Hallset al.,2013).



Figure 5.12. Longitudinal schematization of deep pools with their depths in Mekong mainstream between Chiang Saen and Phnom Penh areas (Halls et al., 2013).

Whilefishermenassumethatpooldepth is themost important factor (Baird,2006),Bairdet al. (1998)andBaird&Flaherty(1999)arguethatalsoflowvelocity,substratetype,slope,proximitytowetlandforestandtheoccurrenceofobjectswhichprovideshelterhaveahighinfluenceonthequalityofthedeeppools.Thefollowingtableprovidesanoverviewofdifferentcharacteristicsofselected pools.

Table 5.2. Summary of deep pool characteristics including substrate type, max. depth, area, esti-matedfishdensityandbiomassandnumberoffishspecies(Hallset al.,2013).

Country Province/name Sub-strateMaxdepth(m)

Area (ha)

Fishdensity(N/ha)

Fishbiomass(kg/ha)

Fishspecies

Citation

Cambodia/

LaoPDR

Stung Treng &

Champassak- 8 - 76 -

1.2-2.1

Mio

15,600-

328,00048 1

LaoPDR Campassak - 20 - - - 68 2

Cambodia Kratie/PrehTiet bedrock 30 1.5 5165 1151 121 3

CambodiaStung Treng/

Veoundocalluvial 70 29 340 48 116 3

Viet Nam An Gian/ Van Nao alluvial 30 31 2745 371 52 4

Viet Nam An Gian/ Tan Chau alluvial 40 28 9259 389 58 4

LaoPDRChampassak/ Ban

Boungalluvial 10 5 1327 61 34 5


Nabedrock 26 2 840 101 38 5


Hatbedrock 37 2 - - 59 5


Pymanponbedrock 7 3 - - 52 5

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1)Viravonget al.,2006;2)Baranet al.,2005;3)Chanet al.,2008;4)VuViAn (inprep.);5)Viravong (pers. comm to Halls et al.,2013)

Alsofloodplainsrepresentimportantspawningandrearinghabitats.Theextent,durationandtimingoftheannualflooddeterminethesizeandproductivityoftheecosystemandconsequentlytheyieldofcommerciallyimportantspecies(MRC,2009).However,alsootherfactorsase.g.thequalityofthewater(e.g.nutrientload)orthedepthplayamajorrole(Hortle&Bamrungrach,2015).Figure5.13showsthelocationofsmall,mediumandlargeriverswithorwithoutfloodplains.WhiletheupperLMBincludesonlysmallsectionswithfloodplains,floodplainsareprevailingintheMekongmainstream and larger tributaries of the lower LMB.

Figure5.13.Ecologicalregionsandrivertypes(with/withoutfloodplains)(Grilletal.,2014).

Rapids in theMekongmainstreamand its tributariessupportdiversefishassemblages.Rapidsoccurwherebedrockisexposedintheriverbed,forminganobstacletotheflow.TheyarequitecommonalongtheLMB(173recordedrapids)andevenoccurinpredominantlyalluvialreaches(e.g.betweenVientianeandSavannakhet).



Rapids provide important habitats for feeding and spawning. The rocky substrate supports diversefoodsourcesandthespecifichydraulicconditionsdistributenutrients,plantsandmacro-invertebratesinthewatercolumn,makingitavailableforfish(MRC,2011).Morethan200speciesrelyonthemashabitatforfeeding,breedingorspawning.Consequently,manyproductivefishinggrounds are located at or close to rapids (Poulsen et al., 2002, Valbo-Jørgensen & Poulsen,2000).AlsothecriticallyendangeredMekongGiantCatfishusesrapidsbetweenChiangKhongandChiangasspawningsites (MRC,2010).Due to thehigh turbulence,poolsareoften foundimmediatelydownstreamofrapids.(MRC,2011).

Figure 5.14. Location of rapids within the LMB (MRC, 2011).

Other hotspots are represented by protected or sensitive areas containing a rich biodiversity, important species at risk, areas important for migrating species or supporting key ecological processes(MRC,2011).Asanexample,MRC(2011)providesalistof39hotpotsincludingRamsarSites,BiosphereReserves,ProtectedareasandGreaterMekongSubregionHotspots.

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5.1.5 Fisheries

Due to the high species diversity and productivity, the Mekong supports the most productive inland fisheryoftheworld,comparedtootherinlandfisheries.About60millionpeopleinthefourmainLMBcountries relyon thesefisheries (Hortle,2007and2009).TheMekongfisherycontributesgreatly to socioeconomic development of theMekong countries. Furthermore, fishery providesthe main income for many riparian people and increases their food security and socioeconomic development.AccordingtoDugan(2008)thereareareas,asinSouthernLaos,thathaveahighdependenceonthesectorwhereupto80%ofthepopulationisinvolvedinfishing.

Fisheriesyieldcanbeestimateddirectly (yieldperarea)or indirectly (consumptionandmarketsales).Asmarketdataarenotwidelyavailable,approachesonthebasisofyieldperunitareaorhouseholdconsumptionareoftenusedtoestimatethesystem’syield(Campbell,2009).SeveralstudiesestimatedthetotalconsumptionoffishandotheraquaticorganismsintheLMB(Hortle,2007).

Hortle&Bamrungrach (2015)divided the totalareaoffisherieshabitats (i.e.194,364km²) intothreemainzonesandestimatedthefisheriesyield-per-unitareafromseveralsources:

1. Majorfloodzone:allareaswithinthemajorfloodin2000(majorriversandfloodplains,TonleSap-GreatLakeSystem,recessionricefields);

2. Rainfedzone:mainlyricefieldsbutalsoswamps,waterbodies,wetlandcropsandothers;30-50cmdeepwithnumerousbarriers,restrictedmigration,amphibiousspecies,blackfishes(snakeheads,walkingcatfish,swampeels,climbingperch)andOAA(frogs,sails,shrimps);

3. Permanentwater bodies outside zones 1&2: large reservoirs including rivers and canalsconnected to them.

Figure5.15.Theleftgraphshowsthefloodinundationoftheyear2000(majorfloodzone)andreservoirs, while the right graph shows a map of wetlands and environmental hotspots (MRC 2011).



Hortle&Bamrungrach(2015)includeestimatesofyieldfromfloodplainsonthebasisofseveralstudies.Theyieldofmajorfloodzonesisestimatedwith100-200kg/ha/year,wherebyhigheryieldsareassumedinmoreproductiveareas(CambodiaandVietNam)andloweryieldsinfloodplainsofshortdurationanddepth(LaosandThailand)(Hortle&Bamrungrach,2015).

Table5.3.Estimatedfisheriesyieldofselectedfloodplains(Hortle&Bamrungrach,2015).

Location Habitats Yield kg/ha/yr Composition Comment Source

Tonle Sap,

Cambodia

mostlyfloodplainwith

recession rice, rainfed

ricefields,permanent

waterbodiesbout5%of

area

243-532 fishandOAAs study area 8,252

ha,maxflooded

area 6,732 ha.

Basedonfisher

logbooks plus

commercial catches

whichwere4–9%

of total

Dubeau et al., 2001

Mekong Delta

Floodplain,

Viet Nam

ricefields,deepwater

floodplain,acidsoils

63 fish47%,OAAs

53%

intensive monitoring

at one site

De Graaf & Chinh,

2000

Mekong Delta

Floodplain,

Viet Nam

ricefields,deepwater

floodplain,non-acid&

acid soils

119 fish89%,OAAs

11%

intensive monitoring

at one site

De Graaf & Chinh,

2000

PreyVeng,

Cambodia

floodplain-ricefields,

single-crop, former forest

55 fish underestimated:

includes only

commercial large

and middle-scale

catchesinfishing

lots, does not

include artisanal

catch

Troeung et al.,

2003

PreyVeng,

Cambodia

floodplain-degraded

floodedforest31%cover

andricefields,singlecrop

92 fish Troeung et al.,

2003

Battambang,

Cambodia

floodplain-floodedforest 95 fish Troeung et al.,

2003

PreyNup,

Cambodia

(coastal)

artificialdeepfloodplains

behind polders

630 fish extensive

permanent

waterbodies

Lim et al., 2005

Tonle Sap

System

floodplain,total 230 fish? crude estimate Baran et al., 2001

Tonle Sap

Floodplain

foodplain, total for 1995-

99

139-190 fish? crude estimate Lieng & van

Zalinge,2001

The yield of the rainfed zone was estimated between 50-100 kg/ha/yr while permanent water bodies arebelievedtocontributewith100-300kg/ha/yr(seealsochapter5.2.3.5).

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Consideringthedistributionofhabitatswithineachcountry,Hortle&Bamrungrach(2015)estimatedthe total yield of the LMB. The calculated yield of 1.3 and 2.7 Mio. kt/year is similar to previous estimates(e.g.:0.7-2.9Mio.kt/yrbyHortle2007;2.23Mio.kt/yrbySverdrup-Jensen2002).Theapplicationof yield-ranges (i.e.max. andmin. yieldsper habitat) allowed theapproximation tothe“mostlikelyyield”onthebasisofconsumptiondata(i.e.2,304kt/year;Hortle&Bamrungrach2015).It isassumedthatthegapbetweenconsumptionandyieldinVietNam(i.e.349kt/yr) iscompensated by the surplus of the other countries, either by the migration of organisms or imports (seealsoTable5.4;Hortle&Bamrungrach,2015).

Table5.4.EstimatedLMByields(kt/year)percountryandhabitat(basedonHortle&Bamrun-grach,2015).

Habitat Cambodia Lao PDR ThailandViet Nam

Total LMBDelta Highlands

1Majorfloodzone

areainkm²total

yield in kt/yr

(assuming 100-200

kg/ha/yr most likely

yield kt/yr

28,262

283-565

565

4,617

46-92

92

7,795

78-156

117

17,343

173-347

260

-

-

-

58,017

580-1,160

1,035

2 Rainfed zone area

inkm²totalyieldin

kt/yr

(assuming 50-100

kg/ha/yr)mostlikely

yield kt/yr

17,605

88-176

176

8,962

45-90

90

93,119

466-931

698

8,573

43-86

64

1,576

8-16

16

129,835

650-1,299

1,044

3Permanentwater

bodiesareainkm²

total yield in kt/yr

(assuming 100-300

kg/ha/yr)

most likely yield

kt/yr

853

9-26

26

2,143

21-64

64

3,521

35-106

106

839

8-25

25

156

2-5

5

2,373

75-225

226

Total estimated

yield(kt/yr)767 246 921 349 20 2,304

Consumption

estimate

(foryear2000;kt/yr)

558 166 861 659 60 2,304

Surplus/deficit 209 80 61 -310 -39 0

(green:highyield;orange:middleyieldassumedtofit“mostlikelyyield”)



Inparticular,studiesbyVietNam,Cambodia,ThailandandLaoPDRfisheriesdepartmentsinco-operationwiththeMRC(Poulsenet al.,2002;Baran,2006)haveshownthattheGreatFaultLine(GFL),ageologicalfeatureformingtheKhoneFalls,representsaboundarybetweenthetwomostproductivefisheriessystemsintheMekongRiver(seealsomigrationsystemsinchapter5.1.3).ThelowerfisheriessystemisbasedontheMekongDelta,TonleSapLakeandtheinterconnectingmainstream Mekong channel upstream to the GFL. It includes all yields from Cambodia and Vietnam.ThemiddlefisheriessystemextendsfromtheGFLtoanareajustupstreamofVientianeand includes almost the entire catchment of Thailand (excl. small Thai tributaries upstream of Vientiane) and around 80% of the LaoMekong.The third system extends north upstream ofVientiane(Poulsenet al.,2004)andincludestheremaining20%oftheLaoMekongandsmallThaitributaries.Furthermore,thecatchoftheChinesepartoftheMekongRiver(Lancang)isabout25,000t(Xie&Li,2003),butisnotconsideredinthisreport.

On the basis of consumption based yield data and following the approach ofHalls (2010) thebiomasspercountrywasdividedintothe10mainfishguildsaswellasotheraquaticorganisms(OAAs).

Figure5.16.ConsumptionbasedyielddatadividedintofishguildsandOAAspercountry.

The productivity of these systems depends on many factors, but is greater in the lower systems which aremore favourable in terms of temperature, habitat availability, flow rate, and nutrientloads(Kanget al.,2009).Therelativeimportanceofthetributariesandfloodplainsassociatedwiththesemainstreamsystemsislesswellknown,butisassumedtoplayahighlysignificantroleinmaintainingthefisheriesproductionofthesystem(Poulsenet al.,2002).

Accordingtothefloodpulseconceptthehighproductivityismaintainedbytransferringnutrientsandorganicdetritusduringhighflows to thefloodplains.Total catchesarewell correlatedwiththeextent(floodheight,area,duration)ofannualflooding(Hallset al., 2008; Welcomme, 1985; De Graaf et al., 2001).Campbell (2009) andHortle&Bamrungrach (2015) indicate that river-

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floodplainsystemsyieldapproximate100-200kg/haannuallywithhighervaluesinmoreproductiveparts(Cambodia,VietNamDelta)andwithloweryieldswherefloodingislesspronounced(LaoDDR,Thailand).Theproductivityofreservoirsisdiscussedinchapter5.2.3.5–impoundments&reservoirs).

5.1.6 Recent changes to species diversity and abundance

SeveralfishspeciesoftheLMBarelistedontheIUCNRedListofthreatenedspecies.However,due to unknown migratory behaviour, indispensable habitats and life strategies, evaluations to detect the reasons for their decline are hard to perform. Main impacts are most likely associated to fishingpressureandhydro-morphologicalchangesconnectedtohydropowerdevelopmentintheLancangRiverandLMBtributaries.However,alsootherimpacts(e.g.irrigation,damming)mightbe responsible.

In general, some species are more sensitive than other species. With regard to fragmentation, the guilds, 2, 3, 8 and 9 can be considered as highly vulnerable. But also species outside these guilds might react due to changes in habitat availability or quality changes. Since all aspects and processes in the LMB are connected, impact pathways are not always easy to detect.

ThefollowingtableshowsselectedendangeredfishspecieswhichoccuralongtheLMBandareconsidered as migratory and therefore also threatened by mainstream hydropower development along the Mekong.

Table5.5.Selectedendangeredspecies(fishbase.organdiucnredlist.org).

English name Latin name IUCN list status Population status

Goonch Bagarius yarrelli near threatened decreasing

Two head carp Bangana behri vulnerable 30-50%decline

Boeseman croaker Boesemania microlepis near threatened decreasing, local extirpations

Giant barb Catlocarpio siamensis critially endangered 80-95%decline

Small scale mud carp Cirrhinus microlepis vulnerable 30-50%decline

Striped river barb Mekongina erythrospila* near threatened decreasing

GiantMekongcatfish Pangasianodongigas* critically endangered >80%decline

StripedcatfishPangasianodon

hypophthalmusendangered ~95%decline

Krempf’scatfish Pangasiuskrempfi vulnerable ~30%decline

Giant pangasius Pangasiussantiwongsei critically endangered ~99%decline

Jullien’s barb Probarbusjullieni endangered ~50%decline

Thicklip barb Probarbuslabeamajor* endangered ~50%decline

Laotian shad Tenualosa thibaudeaui* vulnerable ~30%decline

Giantsheatfish Wallago attu near threatened dereasing

* Endemic to the Mekong basin




Hydropowercanaffectaquaticorganismsandconsequentlyfisheriesinseveralways.Hydrologicalalterations(e.g.seasonalshifts,hydropeaking,diversionofflows)influencethesedimenttransportand the river morphology and may consequently change the accessibility, quality and quantity of habitats. Impoundmentsand reservoirs change the free-flowing river toamorestagnantwaterbody also causing impacts on sediment and water quality. Furthermore, dams act as a barrier blocking migrations and fragmenting habitats and populations. Finally, water quality alterations, caused by impoundments or hydrological alterations (e.g. thermopeaking) change the naturalhabitat conditions.

However,besidesdirecteffects,alsoindirectimpactsthroughthefoodwebhavetobeconsidered(seealsochapter5.1.2).Forinstance,hydropowermayalterthecompositionandabundanceofphytoplankton assemblages (Zhanget al., 2010;Perbiche-Neveset al., 2011),which serve asimportant primary producers in the aquatic ecosystem (Li et al.,2013a)(seeFigure5.17).

Figure 5.17. Potential 1st, 2nd and 3rd order hydropower impacts.

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Thefollowingtableprovidesanoverviewofthemostimportantchanges,theirpotentialeffectandrelated risks. The table follows the concept of the 5 key common overarching changes related to hydropower development. Furthermore, a chapter on water quality alterations was added to cover theimpactofwaterqualitychangescausedbyhydro-morphologicalalterations(e.g.impoundments)on aquatic organisms. A more detailed description of the table-content will be provide in the following sub-chapters.

Table5.6.Aquaticecologyandfisheries–Keyrisks,impactsandvulnerabilities.


(I) Annual / inter-annual changes to flowChangesinseasonality(e.g.delayedfloods,increaseofdryand

decreaseofwetseasonflows)

Habitat alteration/ loss related to increased erosion (river bed

incision,bedarmouring,bankerosionetc.;seealsoTable3.2)

Habitat alteration/ loss related to water quality changes (e.g.

temperature,waterclarity,salinity(relevantfortheDelta),nutrient

transport;seealsoTable3.3.)

Lossofecologicalfunctions(e.g.migration/spawningtriggers)

Loss of productivity due to reduced flood pulse (increase in

permanentlyfloodedareasanddecrease inseasonallyflooded

areas)

(II) Daily / short-time period changes in flow

FastincreaseofflowHigh drifting rate of fish and macroinvertebrates, loss of food

sources,offsetofmigrationtriggers,stressforaquaticorganisms

FastdecreaseofflowStranding/lossoffishandmacroinvertebrates,stressforaquatic

organisms

Morphological alterationsIncreased erosion and river bed incision causes habitat

degradation(seealsoTable3.3.)

ThermopeakingUnnatural(fastchanging)temperatureregime,stressforaquatic

organisms,offsetofmigrationtriggers

(III) Barriers/ loss of river connectivity

Disconnectbetweenflow,sedimentandnutrientdelivery

Habitat loss related to morphological alterations (see also Table

3.3.),offsetofmigrationtriggers,reducedproductivitywithregard

to nutrient trapping and limited delivery downstream

Habitat fragmentationBlocked/ reduced spawning and feeding migrations, potential

isolation of sub-populations

Turbine passage Stress,fishdamageandkills

Spillflowpassage Stress,fishdamageandkills

(IV) Creation of impoundments

Trapping of sediments

Morphological alteration and habitat loss. Upstream:

sedimentation,possiblyfillingupofdeeppools,reducedvertical

connectivity,changeofchoriotopes(fish,benthicinvertebrates),

degradation of shoreline habitats; Downstream: loss of habitat

structures(e.g.sandbars),reducedhabitatquality(e.g.change

of choriotopes, river bed armouring), reduced connectivity to

tributariesandfloodplains(relatedtoriverbedincision)

Lossoffreeflowingriversections Delay/ deposition of drifting eggs & larvae

Loss/reductionoffishspeciesadaptedtofreeflowingrivers



Lossoforientationforupstreammigratingfish

Increased visibility Algae growth and changes in temperature, oxygen

Stratification&temperaturechanges Stressduetowaterqualitychanges(temperature,oxygen)

Water level changes within impoundmentStranding of fish and macroinvertebrates, degradation of

shoreline habitats

ReservoirflushingFlushing of benthic organisms and fish, potentially high losses

related to high turbidity, destruction of habitats

(V) Diversions or intra basin transfers

Reduction of river dimension

Reduced productivity, species alteration (e.g. loss or large

species), reduceddepthmay impact connectivity,water quality

changes

HomogenisationofflowsArmouring of beds and bars due to reduced sediment transport,

habitat loss

IncreasedflowinreceivingbasinIncreased bank erosion and bed incision to accommodate

increasedflow

Water quality changes Stress

Combinedeffects(I-V)Reduction of biomass and diversity of fish and other aquatic

organisms

5.2.1 Annual/interannualflowchanges

As already discussed in Chapter 2, seasonal flow shifts (i.e. from the wet to the dry season)arealreadyvisibleintheMekongRiver.WithregardtotheLancangcascade,wetseasonflowsdecreasedbyapproximately5-35%anddryseasonflowsincreasedby45-150%(inKratieandChiangSaenrespectively;Räsänen,2014).Ofcourse,theimpactdeclinesindownstreamdirectionas tributaries enter the system. However, considering the realisation of storage hydropower plants in LMB tributaries, impacts will become more pronounced also in downstream areas of the mainstream. Together with the seasonal shifts, the hydrograph will become smoother. Furthermore, thefloodseasonwillstartandendlaterandwillshowlowerflowsatthebeginningandhigherflowsattheend,comparedtonaturalconditions(seealsoFigure2.9).

Sincehydrologyalso triggersecologicalprocesses(e.g.migrations),changesto the timingandmagnitudeoffloodsmighthavedrasticconsequences.However,littleisknownaboutthesensitivityoffishofthesemigrationtriggers.

Furthermore,theaccessibility,quantityandqualityoffloodplainhabitatsmaychange.Asshownin Figure 5.18, the floodplain represents a temporarily/ seasonally inundated area due to thechangesbetweenthedryandwetseasonwater levels.By increasingthedryseasonflowstheareapermanentlyfloodedincreases.Inaddition,reducedwetseasonflowslimittheareafloodedinthewetseasonresultinginlossoffloodpulsesanddecreasedproductivity.

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Figure5.18.Schematicrepresentationofimpactsofdamsonfloodplainflooding(Baran,2010).

Arias et al.(2014)comparedtheinundationoftheTonleSap(seealsoFigure2.14)betweenthebaselinescenarioandthedefinitefuturesscenarioincl.3Sdams.Marginallyinundatedareas(i.e.0.5-10%ofthetime)andareaspermanentlyinundated(i.e.90-100%ofthetime)willexpandby16%and9%respectively.Consequently,intermediateclasses(inundated20-90%ofthetime)will be reduced.

5.2.2 Short-termflowfluctuations/hydropeaking

Depending on the type of hydropower operation, energy production may be directly linked to the short-termenergydemand,leadingtorapidandfrequentchangesinflowscalled‘hydropeaking’.Ingeneral,hydropeakingcanoccurduetovariouscircumstancesandcanbegroupedinto(1)peakingflowsinasinglecycleorinseveralcyclesperdayalternatingwithminimalflows(Cushman,1985),(2)load-followingflows(inresponsetoimmediatesystemloaddemands;Geistet al.,2008),(3)flushingflows(discretionarybutmostlytimedwithpeaksinthenaturalhydrographwiththeaimofremovingaccumulatedsediments(Milhours,1990;Petts,1984),(4)spillflows(iftheregulatedcapacity is exceeded; Lundqvist et al.,2008),(5)recreationflows(Dauber&Young,1981)and(6)discretionaryoperationalflowsso thatdownstreamfacilitiescangenerateenergy(Younget al., 2011).



Although theeffectsofdamsand their role in fragmentationarewell documented, thespecificeffectsofhydropeakingonfisharenotyetassessedindetail.However,thisknowledgeiscrucialfor managers to predict andmitigate possible negative effects. Young et al. (2011) discussedthesehydropower-relatedpulsed-flowimpactsonstreamfishes,consideringconceptualmodels,knowledgegapsandresearchneeds.Impactswithregardtohydropeakingariseby(Younget al., 2011; Schmutz et al., 2014; Hunter, 1992; Anselmetti et al., 2007; Scruton et al., 2008; Smokorowski et al., 2011; Nagrodski et al., 2012; Harby & Noack, 2013; Bruno et al.,2013).

I. strandingoffishalongthechangingchannelmargins;

II. downstream displacement and drift;

III. red dewatering/ spawning interference;

IV. untimely or obstructed migration;

V. indirect impacts by e.g. loss of food, high turbidity, stress and increased predation as well as increased bank erosion.

Although most assessments focus on salmonid species (Nagrodski et al., 2012) also effectsonsomeotherspecieswereassessed(Younget al., 2011; Boavida et al.,2015).Therearenoanalyses in the LMB available, however, it is very likely that the known impacts are also valid for manyMekongfishspeciesifhydropeakingisappliedtoLMBdams.

In particular, the effects of stranding (also with regard to other pulsed flow effects) are welldocumented(e.g.Bauersfeld,1978;Hamilton&Buell,1976;Olson&Metzgar,1987).Althoughstrandingmayalsooccurnaturallythehighfrequencyofflowfluctuationscancausecumulativemortalitieswithsignificantfishlosses(Bauersfeld,1978;Hamilton&Buell,1976;Olson&Metzgar,1987).Strandingrateshighlydependonthelocalmorphology,substratetype,down-rampingrate,critical flow (i.e.minimumoperatingdischarge), frequencyof fluctuations, prior flowconditions,duration of stranding and timing of pulse, fish size and fish species (e.g. Young et al., 2011; Bauersfeld, 1978; Hunter, 1992; Parasiewicz et al., 1998; Schmutz et al., 2014; Olson, 1990; Hoffarth,2004).Alsotherampingrange(amplitude,magnitude)isanimportantindicatorwhichisrelevantfordownstreamdisplacement,reducedspawningoralteredmigration(Younget al.,2011).

The impact pathways are highly complex but the interaction of the season, frequency, magnitude, duration,photophase(day/night)aremostlikelytodeterminetheeffectsonspecificspeciesandageclasses(Younget al.,2011).Therearestillsubstantialknowledgegapswithregardto(1)pulsetypeandlifestage,(2)waterqualityandfishbehaviour(e.g.influenceofoxygenandtemperatureonmigration),(3)habitatcomplexity,(4)habitatchanges(e.g.changedmorphologycausedbyhydropeaking),(5)longterm,cumulativeeffectsand(6)mitigation(Younget al.,2011).Especiallyforthedevelopment of suitable mitigation measures, knowledge and clear understanding of mechanisms and relationships causing the impacts are necessary. Schmutz et al. (2014)usedanextensivefielddatasettoanalysetheimpactofdifferenttypesofhydrologicalandmorphologicalindicatorsincombinationwithfishcommunitydata.Theirresultsdemonstratedthatfishreacttoacombinationof peak frequency, ramping rate and habitat conditions, with an equal importance of habitat and flowcriteria.BasedonflumeexperimentsSchmutzet al.2014showedthatmostlarvalfishdriftduringtheincreaseandpeakflowduringhydropeakingevents(Figure5.19a).Theexperimentsalsorevealedthathighdownrampingratesresultinhighstrandingrates(Figure5.19b).Consequently,effectivemitigationmeasuresshouldconsider thecomplexityofhydro-morphologicalprocessesdeterminingthefunctional(hydraulic)habitatconditions(Schmutzet al.,2014).

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Figure5.19a.Larvaldriftobservationsduringincreasing,peakanddecreasingflow(comparisonbetweennopeaking(controlgroup)andpeaking);Figure5.19b.Strandingatdifferentdownramping rates (i.e. 2.9 / 0.5 / 0.32 / 0.2 cm/min) (adapted from Schmutz et al. 2014).

The most important aspect in this context is the deceleration of downramping after a peak period. These results of Schmutz et al.(2014)reflect,however,theconditioninsmallerriverswithinthetemperate zone. Comparisons with the natural hydrograph at several Mekong sites resulted in the followingvalues,whichindicatethatdownrampingusuallyoccursabout60%ofthetimeandwithaspeedof2-3cm/hourwhiletheuprisingoccursalittlefaster(i.e.3-4cm/hourandonly30%ofthetime).

Table5.7.Naturalflowvariationsinm/hour(basedondailymeansofhistoricwaterlevelchang-es).

decreasing water level (~60% of the time)

increasing water level (~30% of the time)

1%percentile 5%percentile 95%percentile 99%percentileLuangPrabang -0.030 -0.020 0.041 0.076Sanakham Dam -0.025 -0.015 0.028 0.051

Vientiane -0.022 -0.013 0.024 0.045

Paksane -0.020 -0.013 0.025 0.037

(Percentileswerecalculatedindependentlyfordecreasingandincreasingevents)

Within the LMB, hydropeaking caused by storage hydropower plants may occur mainly in the tributaries, however, detailed hydrological analyses are missing. With respect to the mainstream, Cochrane et al.(2014)analysedhistoricalwaterlevelsatsixstationsalongtheMekongandtheTonleSapRiverand concluded that there are already some alterations linked to the hydropower development in



theLancangRiver.EspeciallyinChiangSaen(mostupstreamstation),thenumberofwaterlevelfluctuations(cumulativeaveragedailyflows)increasedby75%withinthelastdecades.Effectsdecrease in downstream direction as tributaries enter the system. While these results are already very indicative,sub-dailyflowdatawouldberequiredtoassesstherealimpactontheaquaticecosystem.

Figure5.20.NumberofannualwaterlevelfluctuationsatCS(ChianSaen),LP(LuangPrabang),VT (Vientiane) and MH (Mukdahan) (solid lines indicate a 5-year moving average for each station) (Cochrane et al., 2014).

Alsorun-of-riverhydropowerplantswithintheMekongmainstreamareabletoperformsmallflowfluctuations,especially in thedryseason,whentheratiobetweenstoragevolumeand inflow ishigh.Oncethe inflowdropsbelowthe installedcapacity, itmightbecommercially interestingtoprocess theavailableflowduring timesofhigher revenueandrelease lessflowatother times.However,flowfluctuationsmightbelimitedbysafetyconcerns.Anyway,ithastobeinvestigated,if and to which degree mainstream dam will cause hydropeaking waves.

5.2.3 Loss of river connectivity/ fragmentation

HydropowerdevelopmentintheMekongmainstreamanditstributarieswillaffecttheconnectivityin the following ways:

- Blockedlongitudinalandlateralmigrationofadultspecies(sub-chapter5.2.3.1)

- Delayinmigration(sub-chapter5.2.3.2)

- Harmful downstreampassage through turbines and spillflows (sub-chapters 5.2.3.3and5.2.3.4)

- Reduction/ prohibition of passivedownstreamdrift of fisheggsand larvae (chapter5.2.3.5onimpoundments)

- Alteredaccessibilityofseasonalhabitatsduetoseasonalflowchanges(chapter5.2.1onseasonalflowchanges)

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The disruption of river continuity is considered the main cause of impact to aquatic organisms, especially migratory fish. Aquatic organisms rely on connectivity on four dimensions: lateral,longitudinal,verticalandseasonal(Stanford&Ward,2001;Ward,1989).Connectivityaffectsbothecosystems(functions,habitatsandcommunitystructures)andpopulationdynamics(migration,dispersal).AnexampleforanecosystemwithhighandlowdegreeofconnectivityisillustratedinFigure 5.21.

Figure 5.21. Example for ecosystem with high (left) and low (right) degree of connectivity (From Loucks and van Beek, 2005).

TheSerialDiscontinuityConcept,SDC,(Ward&Stanford,1983,revisedversion1995)isacentraltheory within river ecology, especially for regulated rivers. The SDC view dams as discontinuities withintherivercontinuum.Biophysicalresponsesarepredictedintermsof“discontinuitydistance”,the upstreamanddownstreamextent of impacts inducedby regulation, and by “intensity”, theextent of departure from thenatural reference condition (Stanford&Ward, 2001).TheoriginalSDC only considered longitudinal connectivity, whereas the revised version also included lateral andverticalconnectivity.Thisversionconsidersthatflowregulation,flowabstractionandchannelrevetmentalterexchangeofwaterandmaterialsbetweenriverchannelsandfloodplainsinrelationto natural or reference conditions.

Lengths of discontinuity impact have been measured for a variety of rivers and have been summed upinStanford&Ward(2001).Thediscontinuityimpactmayrangefromafewkilometres(Caning,Australia)toseveralhundredkilometres(ColoradoRiver,USA).FortheMekongmainstreamthediscontinuity might extend over thousand kilometres especially impacting long distance migrants.

Both the Mekong mainstream and tributary dams alter all four dimensions of connectivity. Nevertheless, impacts on the longitudinal connectivity are the most critical. Effects on lateralconnectivity,e.g.causedbychangedflowregimeisdiscussedinchapter5.2.1.

5.2.3.1 Blocked migration

Longitudinal fragmentation can be assessed by several methods. Simplistic methods assess the number of dams per river kilometre or the proportion of river inaccessible from the sea (Anderson et al., 2008; Lassalle et al., 2009, Vörösmarty et al., 2010, Grill et al.,2014).Thedendriticconnectivityindex(DCI)calculatestheproportionoflengthofdisconnectedfragmentsinrelationtotheentire



network (Cote et al., 2009).Thismethod, however, neglects the locationof the individual damwithin the river network. Thereby, a barrier upstream in a tributary results in the same DCI as barrier close to the river mouth, although the latter would cause much higher impacts. To overcome this methodologicaldisadvantage,theDCIcanbeextendedbydifferentweightingfactors(e.g.theflowvolume,riverclassesormigrationcorridors)(Grillet al.,2014;seealsochapter5.1.3).

Atthemoment,theLMBcanbeconsideredaswidelyfree-flowing,as there are no operating dams in the Mekong mainstream. In 2011,65% (DCI)of theentireMekongcatchmentareawereconnected with the largest disconnected parts being located in China and in the Nam Mun catchment (Grill et al.,2014).

However,with theXayaburidam, thefirstmainstreamdam isunderconstruction.Althoughfishpassfacilitiesareconsidered,itis most likely that the dam will contribute to the isolation of upper and lower sections, at least for certain species. If all planned damsarebuilt (i.e.additional81damsby2022), theMekongRiverwouldbecomehighlyfragmented,withaDCIof11%(Grillet al.,2014).ThismeansthattheMekongwillbecomeoneofthehighestfragmentedlargeriversoftheworld(seeFigure5.23).

Figure 5.23. Fragmentation history of selected large river basins and predictions for the Mekong (Grill et al., 2014).

144

Especially long-distance migrants are vulnerable to mainstream dam development. As already mentioned in chapter 5.1.3, the guilds 2, 3 and 9 can be considered as highly vulnerable. Guild 8 (semi-anadromousguild)isalsovulnerablebutonlytodamslocatedintherivermouthorinthelowerpotamon(Table5.8).

Table 5.8. Mekong guilds vulnerable to mainstream dam development (Baran, 2010; adapted fromHalls&Kshatriya,2009).

Also Grill et al.(2014)highlighted,thattheMekongmainstreamandmajortributarieshostthe highest number of migratory species, which makes these areas especially vulnerable to fragmentation.

Figure 5.24. Migratory species range in the LMB: a) recorded migratory species, b) recorded locations and migratory range of Pangasius gigas, c) range of migratory species (Grill et al,. 2014).



Baran(2010)useddataofseveralstudies(Poulsenet al., 2002 and 2004; MRC, 2001, MFD, 2003; Starr,2008,Halls&Kshatriya,2009)todescribethemigrationpatternsof23migratoryspecies.He developed a map of the main migration corridors of 18 migratory species where data on both distribution and importance in catches were available. In Figure 5.25 the arrow width indicates the relativeimportance(i.e.biomassinvolved)ofmigrationcorridorsinthemainstream(black)andthetributaries(brown).TheareabetweenPhnomPenhandStungTrengfeaturesthehighestnumberofconsideredspecies.Forthetributaries,the3Ssystem(12/18species)andtheTonleSap(11/18)seem to represent the most important migration corridors.

Figure5.25.Mainmigrationcorridorsandtheirrelativeimportancebasedon18migratoryfishspecies: Black arrows for mainstream migrations, brown arrows for tributary migrations (Baran, 2010).

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Asa resultof fragmentation,fisharenotable toperform theirmigrations. Ifcrucialhabitats forspawningorfeedingcannotbereached,fisharenotbeabletocompletetheirlifecycleorinteractwithothersub-population.Theresultingstockdeclineswillalsocauselossesforfisheries.

5.2.3.2 Delay in migration

Eveniffishpassesareavailable,migrationsmightbedelayedbymultipledampassage(Caudillet al., 2007)ordue to reducedorientation in the reservoir.Thiscancausehighenergy lossesthat impede the fish from completing spawning (Geistet al., 2000).Delayswere observed forAtlantic salmon (Salmo salar, Karppinen et al., 2002), barbel (Barbus barbus, Lucas & Frear1997),Americanshad(Alosasapidissima,Moseret al.,2000),sealamprey(Petromyzonmarinus,Haro&Kynard1997),paddlefish (Polyodonspathula,Zigleret al.,2004)andPacificsalmonids(Oncorhynchusspp.)oftheColumbiaRiverBasin(Williams,1998;Keeferet al.,2004).

Caudill et al. (2007)monitored themigrations of 18,286 adult salmonids over sevenmigrationseasons (1996 -2003) in theColumbiaRiver system.Althoughmostadultspassedeachdamwithintwodaysafterenteringthetailraceoftherespectivedam(Keeferet al.2004,2005)manyspecimens(1.4-13.7%ineachrun)neededmorethanfivedays(anduptoweeks)topassasingledam. Fish with long passing times were often unable to reproduce successfully.

When fish migrate upstream in dammed rivers, they have to face several challenges. Theyhavetopassthetailrace(1–2kmbeforethedam)withturbulentflowscomingfromtheturbinesandspillways.Afterthat,theyhavetofindtheentrancetotheFPwhichgreatlydependsonthecharacteristicsoftheattractionflowandthelocationoftheFP.Iffishcannotfindtheentranceatthefirstgo,theylosevaluabletimesearchingforalternativemigrationroutes.Oncetheyfoundtheentrance,theystillhavetopasstheFPs.Thetimespent inthetailraceandfishpassdepends,besideshydraulicsattheentrance,onflowlevels(turbinesandspillflow,Caudillet al.,2006a),fallback behaviour (Boggs et al.,2004)andwater temperature(Caudillet al., 2006b, Goniea et al., 2006, High et al.,2006).Iftheymanagetheascent,itmightbethatthepreviousdelayscanbe compensated by low-velocity conditionswithin the reservoirs upstream of the dam (Keeferet al., 2004, Naughton et al.,2005).However, ifmightalsobe that the lowflowvelocity in theimpoundmentcausesdisorientationandfurtherdelays.Therefore,onlyifspeciesrapidlyfindingtheentranceoftheFP,successfullypassingitandfindingsuitablereproductionhabitatsmaynotexperience a delay compared to undisturbed conditions.

Also in downstream direction, dams can cause a delay in migrations between spawning and rearing habitats(Muir&Williams,2012).Raymond(1979)discoveredattheColumbiaRiverthatsurvivalratesofChinooksalmonsmoltspassingdamswasverylow(averageof22%from1966-1980)andevenworseduringdryyears(e.g.1973,1977),therefore,mitigationmeasuresforimproveddownstreampassagewereintroduced(Williams&Matthews,1995).Theinstallationofscreenedbypass systems at most of the mainstream dams, spill management (Williams et al.,2005)andsurface-passage structures (Johnson&Dauble, 2006) restored survival rates to historic levels(Muir & Williams, 2012; Welch et al.,2008).Nevertheless,thetimerequiredfordownstreamtravelstill exceeds historic values and cause delayed entry into the ocean (Muir et al., 2006, Scheuerell et al.,2009)andanegativeenergybalance(Muir&Williams,2012).



5.2.3.3 Turbine passage

Fish migrating in downstream direction have to pass the turbines, if no other migration corridor is available. Turbines can cause damage or mortality due to (Agostinho et al.2002):

• Contactwithfixed/mobileequipment,

• Suddenpressurechanges(incl.exposuretolowpressureconditions),

• Extremeturbulence(e.g.amputation),and/or

• Cavitation

Forhighpressuresplants,themortalitycanreachupto100%.Ingeneral,severalfactorsinfluencethe damage of turbines, as e.g. diameter of the rotor, distance between the rotor blades rotation speed,pressuredifferences.Turbinepassagecancauselossesof10–40%ofjuvenilesandupto100%forlargefish,especiallyiftheyarepassingseveralconsecutivedams(Turnpenny1998,Holzner2000).

Halls&Kshatriya(2009)identified58highlymigratoryspeciesthreatenedbyMekongmainstreamdamswhichcontribute38.5% to the totalweightofall recordedspecies in thecatchsurveys.On the basis of passage success and mortality rates of 10 selected species, they modelled the cumulativebarrierandpassageeffectformigratoryspeciesattheLMBwithadetailedprojectionmatrix.Whilesmall species (up to40cm in length)wereassumed toshowamortalityof2-15%,largerspeciesmightbeconfrontedwithmortalitiesofupto80%overdam.Consideringthecumulativeeffectofseveraldams,especiallylargespecieswillsufferfromthispressure,whichiswhyfacilitiespreventingfishfromharmfulpassageroutesandintroducingthemtoasafebypasssystem are required.

5.2.3.4Spillflowpassage

Ingeneral,spillflowsrepresenthighdischargesexceedingthecapacityoftheturbines.However,spill flows are sometimes also intentionally used to bypass downstream-migrating fish. Whilespillwaypassage is considered themosteffectivepassage route for selectedspeciesandageclasses (e.g. juvenilesalmonids),disadvantagessuchas increasedmortality (Schilt,2007)andsupersaturationofdissolvedgas(seechapter5.2.5)havetobetakenintoconsideration.

Spillwaymortality varies from0.2 - 99%dependingon theheight anddesignof the spillways.TheColumbiaRiver (Bonneville-,McNary-andJohnDayDam)withspillwaysof~30mheightpresentedmortalityratesbetween0–4%.However,highermortalityrates(i.e.8–37%)wereestimatedfordamsattheElwhaRiver(GlinesandLowerElwhaDam,60and30minheight)(Bell&Delacy,1972;Ruggles&Murray,1983).Injuriesandmortalityarecausedbyabrasionagainstthesurface,suddenpressurechanges,rapidcurrentchanges(shearingeffects)orsupersaturation(Backmann et al.,2002).Spillwaypassagecanreducefitnessandswimmingperformance,causesdisorientation and consequently favour predation (Schilt, 2007; Larinier & Travade, 2002; Schmutz &Mielach,2015).

5.2.3.5 Impoundments & reservoirs

Hydropowerandtherelateddamscauseinundationofpreviouslyfreeflowingriversections.Theriverchangestoatotallydifferentenvironmentwithreducedflowvelocity,increasedsedimentation,increasedvisibility,higherdepths(andwidths)andalteredwaterquality(e.g.temperature,oxygen).

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Themainimpactsonaquaticorganismsareconnectedtothereductioninflowvelocity:

- Lossoforientation(ifflowvelocity<0.3m/s)

- Lossofspeciesadaptedtofree-flowingconditions(i.e.rheophilicguild)

- Sedimentationprocesses(alterationofhabitats;seealsoChapter3.2)

- Deposition of drifting larvae/ eggs

- Reduced turbidity/ increased visibility (with possible impacts on algal bloom and connectedwaterqualitychanges)

- Stratificationofthewaterbody(incl.waterqualitychanges)

Ingeneral, twomaintypeshavetobedistinguishedsincetheydifferwithregardtotheir impactontheaquaticecosystem:impoundmentswhichareusuallyassociatedwithrun-of-riverHPandreservoirswhichareassociatedwithstorageHP.

HPintheMekongmainstream(LMB)aremostlyrun-of-riverHPPs,whichutilisetheavailableflowfor electricity production. Although they might be capable of a short-term storage on an hourly or dailybasis, thegenerationhighlydependson thenatural riverflow.The impoundmentsusuallyhavealowretentiontime(i.e.highturnover)and,therefore,representa“hybrid”typeofwaterbodyneitherbeingalakenorariver.Duringlow-flowconditions,impoundmentsaremorelake-likeandmayevenstratify.Incontrast,duringfloods,theymightresumetypicalcharacteristicsofrunningwaters(Schmutz&Mielach,2015).

StorageHPPsbenefitfromthepossibilityofstoringwaterinareservoir.SuchHPPsaredesignedforflexibleenergyproductiontocoverpeakdemandsortimeswithhighrevenuepotential.Largereservoirs can storemonthsor even yearsof inflows.Retention timeof thewater dependsontheflowpassingthroughthereservoir.Largereservoirswithhighwater-retentiontimeresemblelakesand,deeperreservoirsarelikelytobeverticallystratified.SuchHPPscanbefoundinlargetributariesof theMekongor in theLancangRiver inChina.Pumped-storageHPPsrepresentaspecial type which pumps water from a lower reservoir or river into an upper reservoir in times of energysurplusandproducesenergywhenenergyisrequired(overallefficiencyof70-85%)(IEA,2015).Iftheyhaveanadditionalnaturalinflow,theycanbeconsideredasstorageHPwithpumpingpotential(Schmutz&Mielach,2015).

Althoughthereisnocleardefinitionordifferentiationbetweenimpoundmentsandreservoirs,theydifferwithregardtothespecificconditionswithinthewaterbodywhichhighlydependontheshape(e.g.depth)andwaterexchangerate(i.e.relationoffullsupplyvolumetotheinflow).Run-of-riverHPPsusuallyhavearelativelyhighinflowinrelationtotheirstorageandthereforehighexchangerates.Furthermore,withregardtoseasonalflowvariations,thetypicalimpoundment-characterisonlygiveninthedryseason,whilethewaterbodyisalmostfreeflowingduringthewetseason.Reservoirs,ontheotherhand,havealargestoragecomparedtotherelativelylowinflow(takesseveralmonths/yearstofillup)andhavemoreorlessconstantwaterlevels.

Thetransformationoffreeflowingriversectionsintoimpoundmentsorreservoirsmaycausesaloss or reduction of species adapted to river ecosystems and an increase of generalist species (e.g. plankton or algae bloom and eutrophication; Nogueira et al.,2010).Liet al.(2013a)assessedchanges in the cascade of Manwan and Xiaowan and observed that the abundance of phytoplankton sharplyincreasedintheimpoundedareas(inthedryandrainyseason),withdecreasingsharesof



Bacillariophytoa(whichdominatedinfreeflowingconditions)andincreasingsharesofChlorophytaandCyanophyceae.Thechangesinthespeciesassemblagewereconnectedtosignificantlyrisingwater temperatures, prolonged water retention times and increased transparency after damming. Other factors, as total nitrogen and total phosphorus, however, were not considered as key factors impacting the phytoplankton assemblage (Li et al., 2013a). Furthermore, the transformation oflotictolentichabitats,causedasignificantdeclineoffishspecies.Especiallyendemicfish(mostlyinsectivorous and herbivorous species) were replaced by non-native (mostly omnivorous andplanktivorous)species(Lieet al.,2013b).

While clams and shrimp can be abundant in reservoirs (Suwannapeng, 2007), it is usuallyassumedthatthefisheriesyieldincreasesforsomeyearsafterthefloodingduetonutrientreleaseofthefloodedareasandthendecreasesagain.However,adecreasemightbeoffsetasfarmingintensifiesandnutrientdeliverysustains(Hortleet al.,2015).Ingeneral,smallerreservoirs(withalongshorelinecomparedtothevolume)mightbringmoreyield,especially if theyarestocked(Hortle et al.,2015).Alsoaregulardrawdownofreservoirsmightre-mobilizenutrientsandthereforeincreasethefisheriesyield(Nissanka,2001).

WhileHortle&Bamrungrach(2015)estimatedthefisheriesyieldinreservoirsbetween100-300kg/ha/year, it has to be considered that such high rates can only be achieved by stocking which ismaybeonlyfeasibleinreservoirsbutnotinmainstreamimpoundmentswithlargeannualflowvolumesandchanginghabitatconditions(Baran,2010).Formainstreamimpoundments(ase.g.Xayaburi),Baran(2010)estimatesaproductivitybetween20kg/ha/yr(if<20%are<2mdeep)and200kg/ha/yr(impoundmentswith>50%are<2mdeep).Thefollowingtableprovidesselectedcharacteristicsandyield-estimatesforselectedrun-of-river-andstorageHP.Itshowsthatreservoirsonly yield >200 kg/ha/yr if they are stocked. With self-recruiting stocks, yields between 60 and 180 kg/ha/yr seem more reasonable.

Table5.9.Estimatesofexistingandexpectedfisheriesyieldsfromreservoirsincludingretentionrate,areaandmeandepth(diversesources).

CountryReservoir name

Water retention (days)

Area (km²)

Mean depth (m)

Bernacsek 1997 kg/ha/yr

Baran 2010 kg/ha/yr

Hortle et al. 2015 kg/ha/yr

Self-recruiting (%)

LaoPDR PakBeng* 0.8 88 3.1 50

LaoPDRLuang

Prabang*2.3 62 12.9 20

LaoPDR Xayaburi* 2.1 50 7.4 20LaoPDR PakLay* 1.1 77 5.1 20LaoPDR Sanakham* 11.1 71 53.7 20

LaoPDRNam Ngum

1**189.7 370 18.9 19 185 1 all, native

Thailand Nam Un** 501.5 85 6.1 19 121 2 most

Thailand Ubolratana** 369.1 410 16 31 59 397%,native

Viet Nam YangRe** 0.56 32.2 575 4 13Viet Nam EaKar** 1.41 54.7 388 4 2Viet Nam EaKao** 2.1 123.5 324 588 4 23

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Viet Nam Ea Soup** 2.4 51.4 214 4 98Viet Nam Lak Lake** 6.58 84.2 128 4 97

1 Mattson et al. 2001; 2 Nachaipherm et al.2003,3Pholprasith&Sirimongkonthaworn1999;4Tranet al. 2001

*Run-of-riverHP;**StorageHP;

Furthermore,thereducedflowvelocityinimpoundments/reservoirshasabarrier-effectforup-anddownstreamfishmigrations.Inupstreamdirection,fishmightnotbeabletoorientthemselvesifminimumflowvelocitiesarenotensured.Fishshowasocalled“positiverheotaxis”,whichmeansthattheydetectflowvelocity,useitfororientationandswimtowardsit(Lucas&Baras,2001).Iftheflowvelocityfallsbelowaspecies-andage-specificthreshold(usuallybetween0.15-0.3m/s)fishlosetheirorientation(Adam&Schwevers,1997;Seifert,2012;ICPDR,2013)andmightnotbeable to continue their migrations.

In downstream direction, the impoundment might prevent eggs and larvae, which highly depend on thepassivedownstreamdriftbynaturalflow,toreachtheirnursinghabitats(Agostinho&Zalewski,1995; Lowe-McConnell, 1999). If the flowvelocity is reduced, their transportmight bedelayedor, even worse, their deposition in the impoundment will cause high mortality rates (Agostinho & Gomes,1997b).Pompeuet al.(2011)assessedthelarvaedrift throughtheSantaClaraPowerPlantintheMucuriRiver.Thedamis60mhighand240mwide,causingareservoirof7.5km²(150Mio.m³).Larvaeabundance,bothup-anddownstreamofthereservoir,washighlyrelatedtohighflowrates(Figure5.26).Duringhigherflows(i.e.awaterresidenceof~4days),thedensityofeggsandlarvaewassimilarup-anddownstreamofthereservoir.Forlowerflows(e.g.waterresidencetimeof~19days),only8%ofeggs/larvaewerefounddownstreamofthedam(Pompeuet al.,2011).

Figure 5.26. Comparison of egg/larvae density upstream and downstream of the Santa Clara damandtherelatedflowsintheMucuriRiver(October2002toFebruary2003;Pompeuetal.2011).



Also in theTocantinsRiver, theLageadodam (residence timeof24days)hinders larvae frompassing the reservoir (Agostinho et al.,2007).Furthermore, thepassage through thedammayalsocauseinjuriesandlosses(Clay,1995;seealsochapters5.2.3.3and5.2.3.4).Withregardtothe Mekong, it is most likely that tributary reservoirs with high water retention times do not support larvae drift. In mainstream impoundments, it has to be investigated if passive drift might still be supportedduringdryand/orfloodseason.

Also with regard to water quality changes in the reservoir, it has to be considered that increased temperaturesandreducedoxygenlevelsmayhaveadrasticimpactonfish,especiallyonthemoresensitivelifestages,i.e.eggsandlarvae(seealsoChapters4.2and4.2.6).

5.2.3.6 Sedimentation & river bed incision

The ecological integrity of a river depends to a high degree on a natural sediment transport (as alreadydescribedinChapter3).AccordingtoKoehnken(2014)monitoringdatarevealedthatthesuspended sediment load in the LMB is already highly impacted by sedimentation processes. Compared to the historic values of 160 Mt/yr, the Mekong nowadays only transports ~70 Mt/yr. Although reductions have been recorded in all monitoring locations, the highest shortage was observedatChiangSaen(i.e.closestsitetotheChinesecascade),wheresuspendedsedimentloadsdecreasedfrom60-100MT/yrto10-12Mt/yr(Koehnken,2014).Suchsedimentdeficitscanhave a high impact on aquatic habitats, as the still high transport capacity might cause river bed incision.

Up- and downstream of the dams, the following impacts might occur:

-Sedimentation(upstream)causing

o fillingupofimportanthabitatstructures(e.g.deeppools)

o depositionoffinersediments,reductionofverticalconnectivity(cloggingofinterstitial)

o lossofsite-specificgrainsizes(lossofspeciesrelyingonthosesubstrates,e.g. lithophilicfish)

-Sedimentlack(downstream)causing

o lossofcertainhabitatstructures(e.g.sandbars)

o riverbedincision(deepeningoftheriver)

o reducedconnectivitytothefloodplainsandconsequentlylossoffloodplainhabitats

-Reservoirflushing(althoughitisamitigationmeasure,itisalsoconnectedwithnegative impacts on the aquatic ecosystem, therefore listed here for the sake of completeness; moredetailsfollowinchapter5.2.3.7).

Dams may not only block access routes to important habitats, they also cause massive habitat alterationsduetosedimentationupstreamandsedimentdeficitdownstreamofthedam.Duetosedimentation processes, species depending on a site-specific (natural) substrate compositionmight lose theirhabitat (e.g.species feedingonbenthic invertebrates inhabiting the interstitial).Furthermore,sedimentationprocessesmightcauseafillingupofdeeppoolsupstreamofthedam.

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As already discussed in chapter 5.1.4, deep pools are critical habitats for maintaining ecological integrity, as many species rely on them as habitat, especially during the dry season.

The cascade of planned mainstream dams will totally alter the geomorphology of the Mekong River andmostlikelyreducethequantityandqualityofdeeppools(seeFigure5.27).

Figure 5.27. Location and proposed normal operating water levels of proposed hydropower dams inrelationtothelongitudinalprofileoftheLowerMekongriverbedanddryseasonwatersurface(Operating water level of dams are according to CNR 2009 and ICEM 2010, yellow shading indicates alluvial reaches of the river, the remaining sections are bedrock-controlled (Halls et al. 2013).

The lack of sediment downstream might cause river bed incision (Thompson et al.,1998),therebyreducing the connectivity to floodplain habitats.Togetherwith reduced flood flows (e.g. due tostorage)thedimensionandqualityoffloodplainhabitatswillbereduced,affectingtheproductivityof the entire LMB. Also further downstream in the Delta, the lack of sediment might cause salt intrusion, thereby making this area unsuitable for freshwater species not able to sustain in brackish water.

5.2.3.7Reservoirflushing

Reservoir flushing is an important mitigation measure for sediment re-mobilisation and, thus,the restoration of natural sediment dynamics including the formation of type-specific habitats.Nevertheless, it is also associated with negative effects on physio-chemical conditions (e.g.turbidity,oxygendeficiency,hydropeaking)impactingfishdirectly(e.g.increaseddrift,gillandskininjuries,stress,fishkills)andindirectly(e.g.reducedfoodsupplycausedbyincreaseddriftandlossofbenthicinvertebrates,reducedgrowth,losthabitatsduetosedimentation)(Kempet al., 2011; Jones et al., 2012; Crosa et al., 2009; Henley et al.,2000).

Newcombe&Jensen(1996)classifiedtheeffectsofreservoirflushingas(1)lethaleffect(hightolowmortality,hightomediumhabitatdegradation,(2)lethalandpara-lethaleffects(highpredatorypressure, prolongedhatchingof larvae), (3) sub-lethal effects (reduction of growth, fitness andfeeding,disturbedhomingeffect,physiologicstress,elevatedbreathfrequency)and(4)behaviouraleffects(emigration,active/passivedrift).Whilebehaviouraleffectsaremainlyreversibleandlimitedtothedurationofexposure(Newcombe,1994),physiologicchangeshaveamorechroniccharacter.



For example, changes of the habitat availability due to sedimentation of flushed sediments inimportanthabitatsdownstreamthedam(Scullion&Milner,1979;LisleandLewis,1992)mayalsoinduce a loss of ecosystem productivity (Bjornn et al., 1977; Saunders & Smith, 1965; Alexander & Hanse1986).Geo-morphologicalchangescanalsonegativelyimpactfishmigrations(Alabaster&Lloyd,1982).Therefore,flushingisapotentialthreattoentirefishpopulations(Garricet al., 1990; Eberstaller et al.,2001;Schmutz,1999and2001).However,comprehensiveimpactassessmentsarechallengingandcomplex,astheassessmentofreservoirflushingshouldincludedelayedlong-termeffectsandindirectimpacts.

The intensity of impacts depends mainly on the concentration and duration of exposure, but also the size and texture of particles, water temperature, chemical and physical conditions (Stone & Droppo, 1994). Furthermore, toxic substances, acclimatisation as well as other stressors andtheirinteractionarerelevant(Waters,1995).Forexample,thereleaseoforganicmatterandtheconsecutiveoxygendepletionmayleadtosuffocationoffishandbenthicinvertebrates(Garricet al.,1990).

The“rankedeffectsmodel” isatoolforquantifyingnegativeeffectsofsuspendedsolidsonfish(Newcombe & Mac Donald, 1991; Newcombe & Jensen, 1996). The model compiled resultsof more than 80 investigations on the negative impact of total (inorganic) suspended solids(TSS) on freshwater fish (mainly salmonids but also for cyprinids) and benthic invertebrates.On the basis of duration (h) and concentration of exposure (mg/l), a so called “severity of illindex” (SEV) is calculated whereby several models are used depending on the species andage class. The results range from 0 (no changes in behaviour) to 14 (80-100 % mortality).

Figure5.28.Relationaltrendsoffreshwaterfishactivitytoturbidityandtime(basedonwww.lakesuperiorstreams.org/

understanding/param_turbidity.html; Newcombe & Jensen, 1996).

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Anothercomparablemodel (Newcombe,2003)allowsassessments in thefieldon thebasisofturbidity and visibility. However, it is only applicable to clear water streams. Since the above-mentioned models only consider direct impacts neglecting indirect effects caused by habitatchanges, Anderson et al.(1996)developedamodeltoassessthenegativeimpactsonfishhabitats,which also used rankings between 0 and 14.

In comparison to other rivers, the Mekong features naturally high turbidity thresholds (i.e. 1,400 mg/latChiangSaeninJune)which iswhy,comparedtootherrivers,higherthresholdscanbeconsideredastolerable.However,detailedassessmentsonspecies-andage-specificreactiontodifferentturbiditylevelsarestillmissing.

5.2.4 Water abstraction

Usually water is diverted for hydropower production from the main river channel to the hydropower plant and then reintroduced. Another possibility is the transfer of water from one catchment into another.Insuchacase,theriverisimpactedbywaterabstractionuntiltheeffectisoffsetbymajortributaries. Water abstractions may not only occur due to hydropower production but also with regard to other uses as e.g. irrigation.

In general, the impact depends on the quantity and quality of the water remaining in the main channel.Lossofhabitatisassociatedwithlossinfishproductivity.Usually,thereductionofflowgoeshandinhandwithareductionofflowdynamics.Thismightconsequentlychangethesubstratepatterns(e.g.siltingupoftheinterstitial).Furthermore,withregardtoflowreduction,theriverintheresidualflowsectionbecomessmaller(reduceddepthandwidth),whichmighthavenegativeimpactsontheconnectivity(totributariesandadjacentfloodplains),butalsoonthewaterquality.Thereducedbuffercapacityofthewaterbodymightinduceatemperatureincreaseand,togetherwith a reduction of water quality due to reduced dilution, increases the chance of eutrophication.

The importance of a natural flow regime (Karr, 1991; Bunn &Arthington, 2002) was alreadydiscussedinpreviousChapter2.1and5.1.1).Anydeviationfromthenaturalhydrologymayalterinstream habitats and affect natural processes which consequently reduces fish biodiversity,density and biomass.

5.2.5 Water quality alterations

Risks, impacts and vulnerabilities with regard to water quality alterations were already discussed in Chapter 4.2. This chapter will, therefore, focus on the impact of water quality alterations on aquatic organisms, as e.g.:

- Seasonaltemperatureincrease/decrease(mayoffsetmigrationtriggers;decreaseofstenothermspecies;fishkills)

- Thermopeaking(seechapter5.2.2)

- Oxygendeficiency(e.g.instratifiedreservoirsorduetotemperatureincrease)

- Oxygensupersaturation(maycausegasbubbledisease)

- pHchanges(ascertainpHvaluesfavourtheexistenceoftoxicsubstances)

- increased/decreasednutrientload(increaseBOD;algaebloom,eutrophication)

- increased/decreasedturbidity(harmfulconcentrations;increasedvisibility)



As shown in Figure 4.16, the LMB water temperatures are between 18-32°C. Natural temperature regimes are related to the hydrological cycle, with lower temperatures and higher temperature rangesinupstreamareas(~18-26°CinChiangSaen),comparedtodownstreamsections(~27-30°CinKratie).

Any changes to the seasonal temperature regime may impact aquatic organisms. As water temperature is also assumed to trigger migrations, any changes to the seasonal temperature regimemay also effect migrations. Furthermore, temperature changes might cause stress foraquaticorganisms.Whilesomespecies tolerateawide rangeof temperatures (i.e.eurytherm),otherspecies(i.e.stenotherm)areadapted to the local temperatureregimeandare, therefore,veryvulnerabletosmalltemperaturechanges.Furthermore,temperaturehasahighinfluenceonthe gonad development and maturation time of eggs. A reduction in temperature may postpone the hatching of eggs and, therefore, reduce the time available for feeding. Lower temperatures may - in general - result in lower productivity due to reduced metabolism. Furthermore, if lethal temperaturesarereached,massivefishkillsmightbetheconsequence.Especiallyeggsandlarvaereact sensitive to higher temperatures which is why impacts might level down the reproduction success.

Figure 5.29 depicts the relation between oxygen saturation and demand in dependence of the water temperature(Kieckhäfer,1973).BasedontheVan‘tHoffequation,anincreaseof10°Cenhancesmetabolic processes by 2-3 times and consequently also the oxygen demand. However, at the sametime,theabsoluteoxygensaturationinthewater(mg/L)decreasesathighertemperaturescausing an increasing discrepancy between demand and availability.

Figure 5.29. Oxygen need (a) and oxygen saturation (b) in dependence of the water temperature (Kieckhäfer, 1973).

In turbulent andnutrient-poorwater bodies, theoxygen saturationmight be close to 100%. Iftheorganic load increases,dailyoxygenfluctuationsmightoccur(duetoproductionatdaytimeand respiration at night time). The dissolved oxygen concentration in the free-flowingMekongmainstream ranges between 5.5-8.5 mg/l. Although lower concentrations can be observed in stagnantwatersduringthedryseason,anoxicconditionsonlyoccurifthewaterstratifies(e.g.indeepimpoundments)(MRC,2009).

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Lefecre et al.(2011)assessedtheswimmingdepthofPangasianodonhypophthalmusinrelationtothe oxygen level in a pond in the Mekong Delta and observed, that the species only used the upper-most25%ofthewatercolumn.Especiallyatnightandincreasingdepths(i.e.>1m),specieswereconfronted with hypoxia and anoxia. Furthermore, deeper areas might also host toxic compounds (e.g.ammonia,nitrite,hydrogensulphide)makingthemunsuitableforfish(Lefcreet al.,2011).

Table 5.10 provides several water quality parameters between 1985-2010 and 2011 compared to water quality guidelines with regard to human health and aquatic life.

Table 5.10. Comparison of water quality data of the Mekong River between 1985-2010 and 2011 (MRC,2013)(yellowvalueshighlightvaluesoutsideoftheguidelinesfortheprotectionofhumanhealthand/oraquaticlife).

Table 5.10. Comparison of water quality data of the Mekong River between 1985-2010 and 2011 (MRC,2013)(yellowvalueshighlightvaluesoutsideoftheguidelinesfortheprotectionofhumanhealthand/oraquaticlife).

Not only too low but also too high oxygen levels might cause problems to aquatic organisms. Supersaturatedlevelsoftotaldissolvedgasinthewatercancausegasbubbledisease(GBD).Thereby,gasbubblesaccumulateinthebloodvasculatureandtissues,causinglesionsinthefish.Both, supersaturation of oxygen and nitrogen can cause GDB, however, the total dissolved gas (TDG)ismoreimportantthanthelevelsthegasesindividually.

Figure 5.30. Visible gas bubbles in vasculature of operculum and in eye as observed in acute gas bubble disease. (www.adfg.alaska.gov)



Supersaturation means, that the water contains more dissolved gas than it can normally hold in solution at a given temperature and atmospheric pressure. This can occur in plunge pools from dams, where the gravity head forces gas into solution. Thereby, energy dissipation structures, spill rates(seealsoFigure5.31)andoperationpatternsarethemainfactorstobeconsidered(Quet al.,2011).

Figure5.31.Relationbetweenspillwayflowandtotaldissolvedgassaturation(Quetal.,2011).

The following table provides a comparison of large Chinese dams and their TDG saturations which arebetween115and143%.

Table5.11.Comparisonoftotaldissolvedgas(TDG)saturationlevelsbelowlargeChinesedams(Qu et al.2011).

Case No.

ProjectLocation of the observed section

Energy dissipationSpill rate (m3/s)

Power flow (m3/s)

TDG level (%)

1 Three Gorges4000 m downstream the dam

Ski-jump energy dissipation

20200 15600 138.0

2 Ertan3000 m downstream the dam


3706 1809 140.0

3 ZipingpuRainbow Bridge downstream the dam


340 0 114.9

4 ManwanDownstream stilling basin export


1810 1927 124.0

5 DachaoshanBridge downstream the dam


830 2120 116.0

6 GongzuiGongdian Bridge downstream the dam

Surfaceflowenergydissipation

2642 1580 142.5

7 Tongjiezi Stilling basin exportUnderflowenergydissipation

317 1920 138.7

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Labexperimentson theeffectsofgassupersaturationon lethalityandavoidance responses injuvenilerockcarp(Procyprisrabaudi)showthatthesefishcansurviveinwaterwithasupersaturatedlevelofupto115%ofTDG.Especiallyjuvenileindividualsavoidanddieinwaterwithhigherlevels(Huang et al.,2010).However,fieldstudiesrevealedthatcriticallevelsmightbeevenlower.Ryan

.(2000)collecteddatafromtheSnakeandColumbiaRivers.OnthebasisofGBDobservationsin large samples of non-salmonids and invertebrates, they developed a model for the prediction of GBD signs. TDG saturation, duration and level of exposure strongly correlated with the prevalence ofGBDsigns(r2=0.79).WhilesignswererarewhenTDGremainedbelow120%ofsaturation,externalGBDsignswereobservedforTDGlevels>120%.Weitkamp(2008)indicatesthatTDGsupersaturationalsooccursintheCanaldaPiracema.

Withregardtototalsuspendedsolids(TSS;reflectingturbidity/visibility)aquaticorganismshaveevolved and are therefore adapted to local and seasonal dynamics of TSS. The natural level of TSS highly depends on the geo-hydromorphological conditions in the catchment and can be highly variableover theyear.ThehighestnaturalTSSpeaksoccurduring largerfloodsandmayalsoaffectfish.However,healthyecosystemsareusuallyabletocompensatetheseeffectsinthelongrun.ReservoirflushingcancauseTSSconcentrationsmuchhigherthanthenaturalbackgroundconcentration. Depending on the concentration and duration, is can result in stress or complete eliminationoffishstocks.

5.3 Fisheries and Aquatic Ecology Mitigation Measures

This chapter builds on mitigation measures introduced in Chapters 2.3, 3.4 and 4.3 (related to hydro-morphologicalandwaterqualityalterations)andcomplementsaspectsrelevantforaquaticorganismswhichwerenotdiscussed(e.g.therestorationofconnectivityforfish).

5.3.1 General

Hydropower planning has to start at an early stage and on a large scale and under involvement of all relevant disciplines to allow the application of the full mitigation hierarchy, from avoidance through minimization, mitigation and compensation (Hartmann et al.2013;Poffet al.,2015).

The MRC Preliminary Design Guidance for Mainstream Dams (MRC, 2009) highlights, thatavoidance should be preferred over mitigation, and that compensation measures should only be considered for unmitigated impacts. To take full consideration of avoidance options, large scale assessmentsunderconsiderationofdifferenthydropowerlocationshavetobeperformed.Thereby,vulnerable locations can be avoided at an early stage. Furthermore, although general guidelines on selected mitigation measures exist, the incorporation of local characteristics and vulnerabilities is necessary, to ensure their functionality. Therefore, the collection and assessment of basin-wide characteristics (e.g.with regard tofishmigration, sediment transport,hydrology)constitutesanimportant mitigation measure itself. Furthermore, as many mitigation measures were not tested for large tropical rivers and the systemmay change due to additional HPs, a high degree ofadaptability/flexibilityshouldbeensured,allowingmodificationsonthebasisofknowledgegainedduring monitoring operations. Especially with regard to aquatic ecology, compensatory measures shouldonlybeconsidered, ifavoidanceandmitigationmeasuresareproven tobe insufficient.Even then, compensation measures have to be planned and implemented with great caution, since e.g. the stocking with alien species might cause additional pressure on native species.



5.3.2 MasterPlanandFeasibility

5.3.2.1 Dam siting

Dam siting refers to Tables 6.1 to 6.4 under I.1 to IV.1 in the Mitigation Guidelines. The siting and scale of hydropower projects are critical factors in determining the long-term impacts of developments. The development of master plans for sustainable hydropower development relies to a high degree on the collection and assessment of catchment-wide data. These data can then be used to identify basin-wide vulnerabilities and to develop guidelines or requirements which have to be aimed for.

Withregardtoaquaticecologyandfisheries,thefollowinginformationshouldbecollected

- Distribution of migratory and vulnerable species and assessment of their life-cycle requirements, e.g.

o migration purpose

o migration period

o life cycle

o migratorybehaviour(distance,swimmingcapabilities,migrationcorridor)

o location of spawning habitats

o environmental conditions triggering migrations

o roleoffloodplainmigrationsforsub-adultindividuals

o role of passive drift for eggs & larvae

- Distributionandrelevanceofhabitatstructures(e.g.deeppools,rapids)

- Vulnerabilitytocertainhabitatalterations(e.g.hydropeaking,seasonalshifts,impoundments)

As already discussed in previous chapters, certain reaches of the Mekong are more vulnerable than others.Withregardtofishmigration,thisappliestotheMekongmainstreamandlargertributaries.Consequently, hydropower plants further upstream in the Mekong mainstream (close to the Chines cascade)causeslessimpactsthanhydropowerplantsfurtherdownstream.Thesameappliesfortributary dams, where a dam at the mouth of the tributary would disconnect the entire upstream catchment. Also important habitats should be considered for the siting of dams. Furthermore, theremightbesiteswithtopologicalconstraints(e.g.spatialrestrictions)possiblypreventingtherealisationofthebestsuitablefishpass.

Large scale assessments should also incorporate the location of other existing and planned dams, since the realisation of a project in an already fragmented section most likely causes less impacts.TheInternationalCentreforEnvironmentalManagement(ICEM)performedaStrategicEnvironmental Assessment of existing hydropower plants (i.e. eight plants > 30 MW and 50 plants <50MW)fortheVuGiaThuBonRiverbasininVietnam(ICEM,2008),toassessexistingplansfor further hydropower development (Hartmann et al.,2013).Thecost-benefitanalysisof theseprojects included 15 themes for economic, social and environmental values and resources and concluded that the pace and scale of the proposed development cannot be sustained. However, by excluding some small hydropower plants from the development plan, the basin would retain the connectivityoftwofullsub-catchments(i.e.fromheadwaterstothesea;Figure5.32).

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Figure 5.32. Proposed intact rivers in Vu Gia Thu Bon basin (ICEM 2008).

Furthermore, Opperman et al. (2015)performedmultipledambuildingscenarios for threecasestudiesandcomparedthemonthebasisofhydropowercapacityandimpactonconnectivity(definedaslongestconnectednetworkinthecatchment).Inoneofthecasestudies,theCoatzacoalcosRiver Basin, hydropower was not yet developed. On the basis of 28 potential hydropower plants withacapacityof495MW,25differentscenarioswerecalculated.Upto40%ofthehydropowercapacitycouldbedevelopedwithrelativelylittleimpactsonconnectivity(i.e.~90%ofconnectivitypreserved).Furthermore,theimpactsonconnectivityvariedconsiderablybetweenscenarioswiththesameenergyoutput(Figure5.33).

Figure 5.33. Hydropower capacity and river kilometresaffectedbyfragmentationfordifferentscenariosintheCoatzacoalcosBasin (red dots: scenarios shown in next figure;Oppermanetal.,2015).



Figure5.34.Twoscenarioswithsimilarhydropowercapacitybutconsiderablydifferentlevelsofconnectivity (Opperman et al., 2015).

While the other two case studies (Magdalena River Basin in Colombia; Tapajós River Basin in Brazil)alreadyhadsomeexistinghydropowerplants,theresultsagainhighlightedthatlarge-scaleassessmentandstrategicportfolioplanningcanmakeasignificantdifferenceonoverallimpacts(Opperman et al.,2015).

Opperman et al. (2017) also highlight the importance considering systemplanning at an earlystage, since individual dams can may cause disproportionate high impacts (see example of Lower Sesan2inFigure5.35).Theconsiderationofdifferentoptionswouldhaverevealedscenarioswithsimilar exploitation but reduced environmental impacts. Once a site was chosen, optimization is constrained but can still take place at the design- and operation level (Opperman et al.2017).

Figure5.35.Maximumamountofconnectedriverchannelfordifferentlevelsofsystemcapacityexploitation (Opperman et al. 2017).

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TheInternationalCommissionfortheProtectionoftheDanubeRiver(ICPDR,2013)providesanexampleontheregionalscale.ItpromotesguidingprinciplesforsustainableHPdevelopmentintheDanubecatchmentincludingatwolevelsapproach(Figure5.36)undertheconsiderationofseveral criteria.

Figure5.36.StrategicHPplanningapproach–national/regionalandproject-specificassessments(ICPDR 2013).

To answer the questions of “where” to build a new hydropower plant, all rivers sections areevaluated in this approach with regard to their hydroelectric potential and environmental values. Ecologicalcriteriainclude(1)naturalness(hydromorphologicalstatus),(2)rarity,ecologicalvalueand sensitivity, (3) specific ecological structures and functions (e.g. habitats of sensitive fishspecies) and (4) conservationareas (e.g.Ramsar sites).After selecting siteswithhighenergypotentialandlowvulnerability,individualprojectsandtheirsite-specificmitigationmeasurescanbeplanned. Given the plans of further hydropower development on the Mekong and its tributaries (see forexampletheTributarySignificanceStudy–Hydropower;Muir,2010)theconceptofretainingsome intact river routes should be considered as an overarching mitigation option.

From the perspective of aquatic ecology, changes to the sediment transport processes should be kept to a minimum. In this context, also the minimisation of impoundments (i.e. locating them offsite or reducing their length) should be considered.Possible sedimentmanagement optionswere already discussed in Chapter 3.4. When applying these measures ecological requirements should be considered.

5.3.2.2 Adaptation of hydropower scheme/ operation

This refers to Tables 6.1 to 6.5 measures to implement under operation in the Mitigation Guidelines. Adaptive hydropower schemes or operations represent an important measure to avoid and mitigate impacts. For instance, the opening of gates during migration periods can represent a suitable measure for restoring connectivity when it is most important. However, if this option is not already taken into account in the planning phase, it might not be possible to provide a suitable migration corridor(i.e.suitableflowvelocitieswithroughbottomsubstrate).



Surfacespillflowcanserveasamigratorypathwayifthewaterdepthis¼ofthefallheightandatleast0.9m(DWA,2005).Fishcouldbeinjuredifthevelocityexceeds15-16m/s(Bell&Delacy,1972).Thiscriticalvelocitydependsonthefishlengthandisreachedafterafreefallof30-40mfor15-16cmlongfishor13mfor>60cmlongfish.Fishthatarelessthan10–13cmlongare not harmed if their velocity remains below the critical thresholds of 15 -16 m/s. However, accordingtoBAFU(2012)thefreefallshouldnotexceed2.5m.Areleasebelowthesurfaceisnotrecommendedsincefishmightbeharmed.

ThePakMunhydropowerplantopensthefloodgatesforfourmonthsoftheyeartofacilitatefishpassage.While thismeasure isalsosuitable toallowpassageof largefishpeaks,experiencesofspillwaypassageforlargefisharescarce.Parsleyet al.(2007)reportsuccessfulpassageofsturgeonsviabottomgatesattheDallesDam(ColumbiaRiver).However,noinformationhasbeenfoundifthismeasureiseffectiveinfacilitatingfishpassageintheLMB.Therefore,furtherresearchisnecessarytotestitsefficiencyandtoformulaterecommendationsfortheMekongRiver.

Furthermore, new innovative hydropower schemes can be considered or existing principles can be adapted to cause less impact. The reduction of the dam height may reduce impacts related to reservoirsand impoundments.Furthermore,a largenumberofdifferent fishpass typesandalternativeturbinedesigns(seealsochapter5.3.3.1)canbeconsideredtorestoreconnectivityinup- and downstream direction.

5.3.2.3Developmentofenvironmentalflowrules

This refers to I.2.1 and 1.2.5 in Table 6.1 and V.2.4 in Table 6.5 in the Mitigation Guidelines. The developmentandapplicationofenvironmentalflowrulesisimportantforavoidingandmitigatingalltypesofhydrologicalalterations,ase.g.hydropeaking,seasonalshiftofflowsandflowdiversion.

Gupta(2008)definesenvironmentalflow(EF)asdischargesofaparticularmagnitude,frequencyand timing, which are necessary to ensure that a river system remains environmentally, economically and socially healthy. In this context, EF can be considered as mitigation measures for all hydrological alterations(I.e.seasonalshifts,hydropeaking,waterabstraction).

Itiswidelyacceptedthatnotonlythequantityofdischargebutalso,flowdynamicsarekeyfactorsforsustainingnativespeciesdiversityandecologicalintegrityofrivers(e.g.Poffet al.,1997;Karr,1991;Bunn&Arthington,2002;Postel&Richter,2003;Annearet al., 2004; Biggs et al.,2005).AlsothePDG(MRC,2009)statesthatminimumflowreleasesaswellasrestrictionsonchangestonaturalvariabilityneedtobeassessedonthebasisofappropriateenvironmentalflortechniques.Sincewaterqualitychangesareusuallycausedbyalteringthefloworsedimenttransport,alsomitigation measures focusing on hydro-morphology may improve the water quality.

Several reviewsondifferentEFapproachesexist (e.g.Dysonet al., 2003; Acreman & Dunbar, 2004; Gupta, 2008; Tharme, 2003; Arthington et al., 2006). In general, their requirements andcomplexityincreasesfrom(1)hydrological,(2)hydraulicratingmethodsto(3)habitatratingto(4)holisticapproaches(Kinget al.,1999).

Hydrological analyses (also called desktop analyses) aremostly used to defineminimum flowthresholds(e.g.Q95%)(Barker&Kirmond,1998).Forexample,theTennantorMontanaMethod(Tennant,1976)definesEFvaluesaspercentageoftheaveragedailydischargeormeanannualflow(MQ)with10%MQconsideredasminimumflow,and60-100%MQforprovidingoptimalhabitatconditions. However, since these methods lack ecological relevance and sensitivity to individual

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rivers they are considered as inadequate to sustain ecological integrity. Therefore, hydraulic rating methods try to incorporate channel-discharge relationships. The Range of Variability Approach (RVA by Richter et al.,1997)uses32hydrologicalparameters(theirrangeandvariation)asindicatorsof hydrological alteration (IHA; Richter et al.,1996)tocharacterizeecologicallyrelevantattributesofthelocalflowregimeandtotranslatethemintodefinedflow-basedmanagementtargets.Themethodsuggestsanaturalflowparadigmincludingthefullrangeofnaturalintraandinter-annualvariation of hydrological regimes and associated characteristics of timing, duration, frequency and rate of change as critical factors to sustain the integrity of the riverine ecosystem (Richter et al., 1997).Althoughconsideringflowdynamics,thesemethodsstillneglecttherequirementsofaquaticbiota.TheFlowEventsMethod (FEM;Stewardson&Gippel,2003)evaluates the frequencyofhydraulically relevantflow indices (selectedbyexperts)underalternateflowregimes (Acreman&Dunbar,2004). Itconsistsoffivesteps:Afterpreparinga listofecological factorsaffectedbyflow variation, different flow events and their distribution in time are analyzed. Then hydraulicparameters(e.g.wettedperimeter)atthesedifferentfloweventsaremodelled.Acomparisonandevaluationofdifferentflowmanagementscenarioswithregardtoecologicalconsequencesleadstothespecificationofcertainflowrules(Stewardson&Gippel2003).

Furthermore,methodsassessingdifferentflowsincombinationwithhabitatavailabilityforcertainspeciesweredeveloped.Waters (1976) invented theconceptofweightedusablearea (WUA),whichwasusedbytheUSFishandWildlifeService(Bovee,1982)todevelopthecomputermodelPHABSIM(physicalhabitatsimulation).Itinvestigatestheusablehabitatforcertainspeciesunderdifferentflowscenarios(Acreman&Dunbar,2004).AsimilarmodelisMesoHABSIM(MesohabitatSimulationModel)wherethecomputermodelSimStreamisusedtopredictthehabitatavailabilityofaquaticcommunitiesfordifferentdischargescenarios(Parasiewicz,2001).AlsotheInstreamFlowIncremental Methodology (IFIM; Bovee & Milhous, 1978, Reiser et al., 1989a, b; Stalnaker et al., 1995)isusedfortheapproximationofasuitableEFonthebasisofbiologicalhabitatpreferencesandhydraulicmodelling(Poffet al.,1997).However,evenIFIMwascriticizedtobeconfusingandincompleteasthewholeassessmentmoduleremainslargelyatatheoreticallevel(King&Tharme,1994).Thisleadtothedevelopmentofholisticapproaches,ase.g.theBuildingBlockMethodology(BBM;Tharme&King, 1998)which states that aquatic organisms rely on basic elements (i.e.buildingblocks)oftheflowregime(e.g.lowflows,mediumflowsandfloods).InthismethodEFisassessedbyanexpert-basedcombinationofbuildingblocks.TheExpertPanelAssessmentMethod(Swales&Harris,1995),theScientificPanelApproach(Thomset al.,1996)ortheBenchmarkingMethodology (Brizga et al.,2002)trytoevaluate,howmuchaflowregimecanbealteredbeforetheintegrityoftheaquaticecosystemisalteredorseriouslyaffected.AlsoELOHA(“ecologicallimitsofhydrologicalteration”;Poffet al.,2010)isbasedonthepremisethatincreasingdegreesofflowalteration enforce increasing ecological change. The evaluation of the relationship is further based on the testing of plausible hypotheses stated by experts. Ecological response variables are most suitableiftheyreacttoflowalterations,allowvalidationusingmonitoringdataandareesteemedbysociety(e.g.forfishery)(Poffet al.,2010).



Figure5.37.Exampleofflowregimebuiltupusingbuildingblocks(fromAcremanandDunbar,2004 based on Tharme & King, 1998).

However, since (1) current EF determinations are often prescriptive and not negotiable (i.e.consequences of non-compliance are not discussed) and (2) socio-economic impacts are notadequately considered (costs-benefits of water-resource developments), the DRIFT method(DownstreamResponsetoImposedFlowTransformation;Kinget al.,2003)wasdeveloped.DRIFTutilizes knowledge of experienced scientists from biophysical disciplines as hydrology, hydraulics, fluvial geomorphology, sedimentology, chemistry, botany and zoology. Each specialist usesdiscipline-specificmethodstoderivethelinksbetweenriverflowandrivercondition.Furthermore,experts from socio-economic disciplines can be included. DRIFT aims at combining data and knowledgefromallrelevantdisciplinesinfourmodules(Kinget al., 2003; MRC, 2014; Acreman & Dunbar,2004):

• The biophysical module for evaluating changes of the ecosystem (e.g. hydrology, hydraulics, geomorphology,waterquality,riparianvegetation,aquaticplants,organismsetc.)inresponsetoalteredflow.

• The socio-economic module for covering all relevant river resources.

• The scenario-building module for impact assessment.

• The economic module for considering compensation-/ mitigation-costs of each scenario.

Allassumptionsandinterrelations, i.e.ecosystem’sresponsetocertainflowaspectsoftheflowregime, are recorded within the data management tool and can be viewed and changed if required. Therefore,ahighleveloftransparencyisensured.Basedondifferentscenariosandtheconnectedflowregimechanges,DRIFTcalculatestheresponsesoftheriverineecosystem(MRC,2014).

IntheLMB,theMRCproposedtheIntegratedBasinFlowManagement(IBFM)approachtobalanceeconomic, social and ecological requirements (Sarkkula et al., 2005). The IBFM incorporatesanalytical tools as e.g. hydrological, hydrodynamic or water quality models which are then linked to social, economic and policy issues. Sarkkula et al.(2005)used(1)floodcharacteristics(duration,area,arrivaltime,depth),(2)dissolvedoxygen,(3)TSSandnetsedimentationand(4)dryseasonwater quality as scenario indicators for the application of IBFM.

Althoughmanydifferentmethodologiesexist, it isstillachallengetotranslatetheknowledgeofhydrologic-ecologicalprinciplesintospecificmanagementrules(Poffet al.,2003).Forapplications

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intheLMB,(1)relationshipsbetweenhydrologicalalterationandhabitatchangesand(2)habitatrequirements of key species have to be assessed. Since the knowledge on habitat requirements is limited, the dimension of known important habitats as e.g. deep pools or rapids could be used as surrogate parameters for the overall habitat quality.

With regard to the Mekong, environmental flow assessments will be relevant for diversionhydropower plants, but also for storage- and selected run-of-river hydropower plants with irregular productioncharacteristics.Mitigationmeasureshavetofocusonsufficientflow(minimumflow)andtheconsiderationofnaturalflowdynamics:

o Sufficientflowfor

• Fishpassability(minimumdepthandminimumflowvelocity)

• Triggering spawning migrations

• Supportingspawningmigrations(includingmigrationpeaks)

o Incorporationofflowdynamicsfollowingthenaturalvariabilitytoensure

• That migration triggers remain functional

• Theseasonalityandnatural reallocationofsediment (mobilizationoffinesediments topreventsoilclogging)

• Theseasonalityanddiversityoftype-specifichabitats(e.g.floodplainhabitats)

• Suitableincrease-anddownrampingvelocities(forhydropeaking)

• Suitable conditions of oxygen and temperature

The selection of the appropriate methodology depends on available resources (e.g. time, money, anddata)andthequestionstated.Environmentalflowassessmentsshouldbeincorporatedintotheplanning phase of hydropower plants. Finally, it has to be kept in mind that each EF assessment, be it calculated by a simple rule of thumb or a holistic method, has to be evaluated with regard to its biologicalrelevanceandeffectivenessforthespecificrivertobeassessed.Therefore,theselectedEFhastobemonitoredand,ifnecessary,adaptedaccordingly(seealsochapter5.3.5).

Inthecaseofhydropeaking,environmentalflowsalsohavetoincorporatethefollowingpoints:

• Avoidance of hydro-peaking operations

• Adaptation of the operation mode of hydropower plants

• Interposition of re-regulation weirs or compensation basins

• Reduction or coordination of electricity demand peaks to reduce the peak demands

• Reductionoftheamplitude(increaseofthebaseflowand/ordecreaseofthehydropowercapacity)

• Decelerationoftheriseandfallofthedischarge(i.e.rampingrates)

• Improvement of river morphology

Withregardtohydropeaking,therearestillsubstantialknowledgegaps(Younget al.,2011)withregard to (1) pulse type and life stage, (2) water quality and fish behaviour (e.g. influence ofoxygenandtemperatureonmigration),(3)habitatcomplexity,(4)habitatchanges(e.g.changed



morphology caused by hydro peaking), (5) long term, cumulative effects and (6) mitigationpossibilities. Especially for the Mekong, suitable increase- and downramping rates have to be developed for the entire LMB.

5.3.2.4 Development of Water quality standards and turbidity thresholds

Measures for water quality maintenance were already discussed in Chapter 4.3. In general, mitigation measures have to aim for minimizing alterations on water quality upstream, within and downstream of impoundments under consideration of seasonal quality cycles (see reference to theMitigationGuidelines,underthewaterqualitychapter).Therefore,mitigationmeasureshavetoaimforadequatelevelsofdissolvedoxygenandsufficientlylowlevelsofphosphorus,nitrogenand biological oxygen demand. However, with regard to the Mekong, further assessments have to reveal suitable thresholds for these parameters.

According to Dao et al.(2008)referencesitesintheMRCbiomonitoringprogrammehavetomeetrequirements including a pH between 6.5-8.5, electrical conductivity <70 mS/m, dissolved oxygen concentration >5 mg/L and average SDS between 1.00-1.67. These values are also used as a baseline to measure environmental changes.

Asthephysiologicalprocessofoxygenuptakebydiffusionacrossthegillsreliesonthedifferencesin oxygen saturation between the blood and the surrounding water, DO should be measured in percent. However, most data are expressed in mg/l and therefore require the related temperature tocalculatetheprecentralconcentration.Ingeneral,levelsof>90%areconsideredassuitableforaquaticlife(Ongley,2009).Thesensitivitytolowoxygenlevelsisspecies-andagespecific,withmost species experiencing stress at levels below 2-4 mg/l, while mortality occurs at concentrations <2mg/l(http://edis.ifas.ufl.edu).

Assuming an average temperature of 27.2 °C for the Mekong system, this correspond to 7 mg/l. Since several Mekong species are adapted to low oxygen levels and capable of breathing surface air,also lower levelsmightbesufficient.Tsadik&Kutty (1997) indicated thatTilapiashowedameasurabledeclineinfishgrowthatoxygensaturations<90%.MRCtechnicalgroupsproposedavalueof5mg/lassuitableforaquaticlife(Ongley,2009).However,forimpactassessmentitisimportant to consider both, the oxygen level and the duration of exposure and to compare it to natural/ undisturbed conditions.

Table5.12.ParametersandthresholdsusedtoclassifythewaterqualityintheMekong(Baran&Guerin,2012;basedonMRC,2007).

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Withregard to thegasbubbledisease, therecent literature indicates thatfishcancompensatesupersaturated gas levels by occupying deeper areas with a higher hydrostatic pressures. Consequently,TotalDissolvedGas(TDG)supersaturationresultsinlittleornogasbubbledisease(GBD)atlevelsupto120%ofsaturationwhencompensatingdepthsof2mormoreareavailable(Weitkamp,2008).

TherelevanceoftheTSS-levelwillbediscussedinchapter5.2.3.7onreservoirflushing.

Figure5.38.Actualandtotaldissolvedgaslevelsexperiencedbyfishatvariousdepths(Weitkamp et al., 2003).

5.3.2.5Ecologicalconsiderationsforreservoirflushingoperations

ThisreferstoIV.2.2inTable6.4intheMitigationGuidelines.Ingeneral,thedefinitionofcertainturbidity thresholds is relevant to mitigate negative impacts. While a high protection level can be assuredwith25mg/lTSS,80mg/lisconsideredasmoderateand400mg/laslow(EIFAC,1965)protection level. However, these thresholds are only valid for temperate rivers. In comparison, Table5.11states thresholdsof≤35mg/lTSSfor fairand≤50mg/l forbadwaterqualityand istherefore stricter than the recommendations fromEIFAC (1965).However,TSSconcentrationsalways have to be assessed with regard to natural conditions including seasonal variations. For the Mekong,turbiditylevelsofupto1,400mg/l(inJuneatChiangSaen)occurnaturally,whichiswhyMekong-specificthresholdshavetobeestablished(ideallybythe incorporationofspecies-andage-specificreactionstodifferentturbiditylevels).

Thefollowingopenquestionshavetobeansweredtobetterunderstandandmanagetheeffectsofflushingoperations:



• Identificationofspeciesorageclassessensitivetoincreasedturbidity.

• Identificationofmigrationtriggersconnectedtoturbidity.

• Definitionofturbiditythresholdsonthebasisofnaturalevents(floodseason).

• Modellingandassessmentofdifferentreservoir-flushingoperationruleswithregardtotheirinducedconditions(e.g.flowvelocity,turbidity).

• Measurementsofturbidityduringflushingoperationsandinvestigationsontheactualeffectonthelocalfishfauna.

• Development of guidelines to reduce possible impacts.


5.3.3.1 Restoration of connectivity

This relates to III.2.1 to 2.5 in Table 6.3 in the Mitigation Guidelines. The disruption of river connectivity is considered the main cause of impact to aquatic organisms and especially migratory fish.Inordertomitigatetheeffectofhydropowerplantsonaquaticorganisms,fishpassesshouldbe considered for all existing and planned hydropower plants as referenced in the Mekong River Commission’sPreliminaryDesignGuidance(MRC,2009).Thisdoes,however,requireasoundunderstandingoftheecosystem,fishpassagetypesaswellastheirefficiencyandeffectivenessunder certain aquatic, ecological and biological conditions.

TheMRCPreliminaryDesignGuidanceforMainstreamDams(2009)definesthefollowinggoalsfor continuity restoration

• Fishpassesforbothup-anddownstreammigration(i.e.providingsafepassagefor95%ofthetargetspeciesandallflowconditions).

• Thereby, covering the most important species (i.e. broad selection including all ecological guilds,commerciallyimportant&threatenedspecies)inperiodswhentheymigrate.

• Establishment of preferences, tolerances and biological attributes of those target species (i.e.migrationperiodsandcorridors,swimmingcapabilities;biomasspeaks).

• Considerationofmultiplefacilitiesandentrancestocoverdifferentflowregimesandspeciesrequirements and biomass peaks.

• Damandfishpassagedesignwhichseekstominimisefishinjury,mortalityandentrapment(considerationoffishfriendlyturbines,iffeasible).

• Monitoringfacilities(up-anddownstreamofthedamandinthefishpass).

• Adjustablefacilities(andconsiderationofacontingencyfundformodificationatalaterstage,covering20%oftheinitialcostsofthefishpass).

• Development of compensation programs, if fish passage is too low to sustain viablepopulationsandfisheryresources.

Facilities for up- and downstream migration and fish protectionOnceaspecificsitewasselected,theplanningoffishpassesshouldoccurparalleltotheplanningofthehydropowerplant(andnotsubsequently!).Whilestandardsforfishpassdesignarealready

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availablefortemperaterivers(e.g.USA,Europe),examplesoffunctionalfishpassesintropicalrivers are sparse which makes it even more important to investigate the following points and to adapt existing guidelines accordingly:

- Detailed understanding of the hydro-morphological and hydraulic conditions at the site

- Basic knowledge on migratory species (should already be collected and available at the MasterPlan-stage)

- Assessmentofsuitabilityofdifferentfishpasstypesorotheradditionalsolutions(e.g.adaptedoperationmode;shouldbeconsideredatfeasibility-stage)

- Designofanadaptiveapproachincludingmonitoring(i.e.planningofanadjustablefishpasswhichallowstheconsiderationofmonitoringresultsduringconstructionandoperation)

Withregardtofishpasses,threemainaspectshavetobeconsidered,whichwillbeaddressedinsuccession in the following paragraphs:

- Facilitiesforupstreamfishmigration

- Facilitiesforfishprotectionanddownstreamfishmigration

Technologies for upstream fish migration vary with regard to the conceptual design, spatialdemandsandapplicabilityforsingleormultiple-species.Whilemostfishpassesarestillbuiltforsmallormedium-sizeddams(<15minheight),fishpassesatlargeriversliketheMekongremainachallenge.Overall,informationandexperiencesfromfishpassesintheMekongareextremelylimited. Data and information for tropical rivers are available largely for South American rivers (whichareofparticularinterestduetotheirdiverseandhighlyproductivefishfauna–similarlytotheMekongRiver),andfortemperateriversforNorthAmericaandEurope.Forlargedams,manychallenges remain, in particular for those constructed in multi-species tropical rivers. Therefore, theMRCperformeda reviewofexisting researchonfishpassage through largedamsand itsapplicability to theMekongmainstream river (Schmutz&Mielach,2015).The report aimed forsummarizing current knowledge and research on fish pass solutions for both upstream anddownstream migration. International examples are discussed and assessed with regard to their applicability to the Mekong River.

Ingeneral,afishpassshouldbefunctional>300daysperyear(DWA,2010),consideringextremehydrologicalconditions(highflows, lowflows)whichmightpreventtheoperationofafishpass.Furthermore,fishpassesshouldsupport themigrationsofamajorityoffish,enablingall typesofspecies,lifestagesandfishsizestopassthebarrier.Theefficiencyofanupstreamfishpassdepends on both its perceptibility and passability.

Perceptibility refers tofishfinding theentranceofafishpass,which isakeychallenge for theeffectivenessoffishpasses.Ingeneral,thefishpassentranceshouldbelocatedinthemigrationcorridorofrelevantspecies.InlargeriversastheMekong,severalfishpassesandentrancesarerequiredtoensuretheperceptibilityforallfishspeciesduringdifferentflowsituations(Larinieret al., 2002).Unfavourably locatedfishpassentrancescanmakeafishpass inefficientor causetime delays in migration (especially for several consecutive barriers) which in turn can causereproduction losses or even extinction of the species (Agostinho et al.,2002;DWA,2010).

Theperceptibilityofthefishpasscanbeincreasedbyattractionflow,whichdependsontheflowvelocity,flowvolumeandpositionoftheentry.Attractionflowscantakebetween1-10%ofthetotal



discharge (Williams et al.,2012),andthereforecancausehighenergylossestothehydropowerplant.Furthermore, if theentry isnot inan idealposition,evenhigherattractionflowsmightberequired(Calles&Greenberg,2005;Larinier,2002).Theintroductionofattractionflowturbinesisrecommendedtokeepenergylossestoaminimum(Schmutz&Mielach,2015).

SincetheoperationaldischargeoftheFPservesmainlythepassabilityoftheFP,itmightnotbesufficienttoactasattractionflowandadditionalflowmightberequiredatthefishpassentrytoattractfish.Therearetwopossibilitiestoincreasetheattractionflowatlargerivers:

1. Installationof a small hydropowerplant to increaseattraction flow,whichalsoproducesadditionalenergy(seeexampleofFPinIffezheimatriverRhine).

2. Installation of special pumps that use water coming directly from the forebay together with waterfromthetailracetoreinforcetheattractionflow(seeFigure5.39).AnexampleofsuchanattractionflowpumpwasdevelopedandpatentedbytheUniversityofKassel(Germany,Hassingers.a.).

Figure5.39.Schematicsketchoftheattractionflowpump(Schmutz&Mielach,2015;adaptedfrom Hassinger 2008).

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Figure5.40.Attractionflowpumpinoperation(UniversitätKassels.a.).

ThepumpisbasedontheVenturiprinciple.Itutilizesasmall,butenergy-richflowfromtheforebaytosetalargerflowintomotion.Thewatercomingfromtheforebayisacceleratedduetotheleveldifference,exitsatseveraljetsandtakesadditionalwaterfromthetailwater.Thepumpisdesignedtopreventfishentry.Only25%(forlowheaddams)to10%(head>8m)ofthedifferencebetweentheoperationaldischargeandtherequiredattractionflowareneededfromtheforebaywater(jet)whilealargeproportionentersfromthetailrace(Hassinger,2008and2011).

Such an attraction flow pumpwas installed in theRiverDrau at Villach (Austria) and showedpromising results.Thesystemhasnotbeen testedyet for large rivers (Hassinger2008,2011).However, it is likely that this principle also applies for large rivers such as the Mekong though additionaltestsareneeded(Schmutz&Mielach,2015).

With regard topassability, thefishpasshas tooffersuitablemigrationcorridors forall relevantspecies and age classes, which is the case if:

• hydraulic conditions allow the weakest species and age classes to pass,

• continuousroughsubstratetoensurelowerflowvelocitiestowardsthebottom,supportingbottom-dwelling and weaker species,

• continuousminimumflowvelocityof0.2-0.3m/s(rheoactivevelocity)allowsorientation,and

• spatialdimensionsandgeometry(depth,width,length)allowthelargestspeciesandbiomasspeakstopasstheFP.

However, for theMekong River the required fish pass designs and dimensions are yet to beestablished and more detailed knowledge on the local species is required (Schmutz & Mielach, 2015).



Ingeneral,verticalslotfishpassesandnature-likebypasschannelscanbeconsideredasstate-of-the-artforlargemulti-speciesrivers,whileotherfishpasstypesmayfavourspecieswithhighswimmingabilities.Trap-and-trucksolutions,fishliftsandfishlocksmightbesuitableforselectedspecies,butarenotconsideredasstand-alonesolutions(Schmutz&Mielach,2015).Table5.13providesacomparisonofupstreamfishpasssolutionsandtheirapplicabilitytotheLMB.

Table5.13.Comparison/applicabilityofupstreamfishpasssolutionsintheLMBincludingexam-plesfromotherrivers(Schmutz&Mielach,2015).

UpstreamFPtypes Case studies Advantages Disadvantages Applicability for the Mekong

Vertical-slotFP

FPIffezheim(Rhine),

FPGambsheim(Rhine),FPGeesthacht(Elbe);

Comparable low spatial demands, possibility to construct an optimally located entry under spatial restrictions; suitable for a diverse fishcommunity;hydraulic parameters can be easily calculated

More expensive than nature-like constructions; higher maintenanceeffort;no suitable habitat; no experiences available for large, high dams in tropical rivers

Suitable if morphometric values and hydraulic parameters are designed with regard to the local characteristics and fishcommunity

Nature-like bypass channel

CanaldaPiracema(Paraná),

FPFreudenau&elk(Danube),

Marchfeld channel (Rußbach,Danube)

Adequate for multiple species;effectiveif large enough, suitable habitat

Sensitive to upstream level variations; high spatial demands

Case studies for large rivers are rare but this type should be applicable if designed large enoughandsufficientspace is available

Bypass system Danube(planned)

High transfer capacity; suitable habitat; partial substitute of lost fluvialhabitat;canbe used to overcome several barriers concurrently; high cost-benefitratio

Sensitive to upstream level variations; optimal position of entry(nearthedam)difficultwithregardto low slope and high length of the FP;highdischargerequired; high spatial demands, no experiences available

Should be applicable for the Mekong if sufficientspaceisavailable.

Fish locks Salto Grande Dam (UruguayRiver)

Flexible design allows construction at differentdamtypes;suitable passage for selected species; potential for tropical rivers with low biomass

Capacity depends on cycle time and volume; no permanent attraction flow/passage;moresuitable for selected/indifferentspecies;inefficientifnotoperated regularly

Suitable if designed and operated properly; risk of selectivity remains. Therefore, only recommended in addition to other types

Trap & Truck Santa Clara Dam (MucuriRiver)

Can be used everywhere, especially when other systems fail; can be used to overcome several barriers; functionality can be easilyverified

Not suitable for high biomass; high operation costs; fishmightloseorientation; highly relies on present infrastructure

Only suitable as an interim solution for specificcasesorspecies; not suitable as a permanent solution

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Fish lifts/ Elevators Used for high heights

High costs for construction, operation and maintenance;fishmight be stressed and lose orientation; capacity depends on cycle time and volume; usually no permanent attraction flowandoperation

Only suitable in combination with otherFPsystems

Shipping locks No or low additional effort/costs

Usually at locations withlowflowvelocityand therefore no/limited attraction flow;nocontinuousoperation

Not suitable if they are not planned to attractfishinthefirstplace

Figure5.41.Recommendedfishpasstypes(1:GeesthachtatElbeRiver(GeesthachtElbes.a.);2:Nature-likefishpassatDanubeRiver;3:PlannedbypasssystemfortheDanubeRiver.ThefigureshowstheintegrationofthebypasssystemintothemainstemoftheDanubebelowthedam (Mühlbauer & Zauner 2010, unpublished report).

Facilities for fish protection and downstream migration are largely lacking, especially for large, multi-species rivers. However, unidirectional connectivity restoration can transform reservoirs to ecological traps (Pelicice &Agostinho, 2008). Downstream fish passes, fish-friendly turbines,adaptationsoftheoperationalmodeofspillflow(Ĉadaet al.,1997;Holzner,2000)ormodificationsof the hydropower plant management are methods to enable downstream migration (AG-FAH, 2011).

Forexample,attheItaipúDam(ParanàRiver,Brazil/Paraguay),larvaeareabletodriftthroughthe



reservoir and reach the dam. However, their migration through turbines or spillways leads to high mortality and reduces the number of larvae downstream of the dam (Agostinho et al.,2002).

Withregardtofishprotection,behaviouralorphysicalbarriersandadaptedturbinedesignsshouldbeconsidered.Anywayscreensshouldbepositioned inaway thatguidesfishtowardsbypasssystems.Behaviouralbarriersarefacilitiesproducingastimuluswhichrepelsfishfromenteringtheturbines(e.g.guidewalls,Louverscreens).FortheMekong,knowledgeonthebehaviouroffishfacingsuchbarriersismissing.AccordingtoWilliamset al.(2012),physicalbarriersactingasamechanicfiltershouldbepreferred.However,topreventevensmallfish,suchscreenswouldrequirecleardistances(barspacing)of<20mm(Dumont,2005;Larinier&Travade,2002;DWA,2005),whichwouldcauseveryhighlossestoenergyproduction.Thus,largerbardistancesareusuallyapplied.Asitisnotpossibletopreventallfishfromenteringtheturbinesandsolutionsforpassivedriftingjuvenilesarecurrentlyunavailable,“fish-friendly”turbinesshouldbeconsideredasastandard-equipmentforhydropowerplants.Althoughturbinesmightneverbefish-friendly,theycanat leastbedesignedinawaythat is lessharmfulforfishpassage.Nielsenet al.(inpress)prepareda“ReviewofExistingKnowledgeontheEffectivenessandEconomicsofFish-FriendlyTurbines” for the MRC giving more details on this topic.

While turbine passage represent only one possible corridor, additional facilities for downstream migrationshouldbeincluded.Forinstance,physicalbarriersshouldguidefishintoabypasssystemor intoafishpassforupstreammigration.SomeinnovativehydropowersolutionsareshowninFigure 5.42.

Horizontalrake(veryflat,comparable to a shaft power plant)

Guidingfishtotheoverflow(orabypasssystem)

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Fish-friendly turbine with includedfish-andturbineprotection(verylowhead(VLH)turbine)

Pivotingturbinewithincludedfish-andturbineprotection

Screw turbine for downstream migration

(new hydroconnect turbine, where up- and downstream migration is possible:www.hydroconnect.at)

Figure5.42.Examplesforinnovativesolutions(basedonAufleger&Brinkmeier,2015).

FortheXayaburidam,theturbineswereadapted,andconsistofverticalKaplanturbineswithadiameter of 8.6 m, 5 blades, 83 rpm, a minimal gap runner and an adapted guide vane design (FishtekConsulting,2015b).Monitoringofmortalityratesisrequiredtoassesseffectsofadaptations.



Floodplain rehabilitation (lateral connectivity)Therearevery fewexamplesoffloodplain rehabilitationprojects in theLMB,e.g. reconnectingfloodplainchannelsandhabitats.AlsotheBDP(andSEAsofindividualprojects)didnotconsiderfloodplainrestorationmeasuresintheirscenarioassessment.

Floodplain restoration and rehabilitation measures rehabilitating the hydrological connectivity betweenthemainstreamriverandthetributary/floodplainsystemareofhighimportance.Enhancedconnectivitycanbere-establishedbytheconstructionoffloodplainfishpassesorbymanipulationoftheriverhydrograph(Jones&Stuart,2008).Althoughthepotentialofreconnectingfloodplainhabitatstothemainstreamriverisnotyetinvestigatedindetail,firstattemptsareonthewayandseem to be very promising (Rhein NL, Baumgartner et al., 2010; Schmutz et al.,2013).Nowadays,many floodplainsof theMekongand tributary systemarealreadydisconnectedby leveesandwater-gates, interrupting the connectivity to the main river and therefore also require reconnection ortheinstallationoffishpassfacilities.

Mitigationmeasuresforfloodplainrehabilitationcanthereforebedefinedas:

• Removal of levees/ water-gates

• Constructionoffishpassestofloodplains/tributaries

• Reconnection of side-arms

• Reconstructionoffloodplains

• Definitionof suitableenvironmental flows toensure theseasonalavailability of floodplainhabitats(seechapter5.3.2.3)

5.3.3.2 Compensation of habitat loss

ThisreferstoI.3toV.3(compensationmeasures)inTables6.1to6.5intheMitigationGuidelines.As discussed in chapter 5.2.3.5 one of the main problems caused by run-of-river hydropower plants is the transformation of free flowing river sections into impoundments or reservoirs.Mitigation measures in relation to associated risks and impacts are mostly limited to morphological improvements at the head of the impoundment. In addition, significantmitigationmay only beachievable by changing the overall hydropower scheme layout (e.g. by implementing smaller hydropowerplantswithsmallerimpoundments).Withregardtoreservoirs(i.e.causedbystoragehydropowerplants),Meynell (2014) recommends the implementationof “designedwetlands” topromotethehabitatdiversityandincreasetheproductivityoffisheryresources.Theconstructionofearthdykesandspillwaysoverseasonalstreams(i.e.withaheightof~2-5mbelowthefloodedwaterlevelofthereservoir),allowswaterandfishtoenterduringthefloodseason,followedbyacontrolled drawdown mimicking a natural wetland’s hydrology. Energetic losses are assumed to be lowandcanmostlikelybeoffsetbythegaininfisheriesproduction.However,furtherinvestigationswill be needed to assess the functionality and applicability of such mitigation measures.

5.3.4 Construction

During construction, it is important to sustain suitable habitat conditions for all aquatic organisms. Consequently, all previously discussed parameters (e.g. water quality standards, environmental flowrules, turbidity thresholds,connectivity)havetobeensuredduringconstruction.Monitoring

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should already start at a very early stage, including construction to allow a quick response to deviationsofpreviouslydefinedstandards.

5.3.5 Operation

While some mitigation measures are already well developed for temperate regions in Europe or in theUSA,theirapplicabilityandefficiencyhastobetestedforlargetropicalriversastheMekongRiver. Therefore, suitable monitoring programmes are required to collect additional data on the efficiencyofplannedmitigationmeasures.

Suitablemethodsforfishpassesincludefishtraps(attheendofthefishpass),taggingmethods(e.g.PIT tag)or telemetrystudies.Telemetryandunderwatervideoobservationsmightalsobeuseful to assess, if species are able to continue their migrations, or if they show disorientated behaviour. Especially for the Mekong, fish-ecological investigations are of high importance toincreasetheknowledgeconcerningfishbehaviourandspeciesrequirements.

Ifmonitoringdatarevealthatpreviouslydefinedconditionsarenotmetorthatbiologicalindicators(e.g.speciesdiversity,biomass,anddensity)areimpactedinsomeway,developershavetorespondwith adaptive management until monitoring data show that the impacts are successfully mitigated. Only if the adaptation of mitigation measures are proven not to be successful, compensatory measures should be considered. However, in this case, compensatory measures should be performed in a cautious and sustainable manner to avoid further impacts on the aquatic ecosystem.


In spiteof thesubstantial global knowledgeonfishpasses,anumberof challengesandopenresearchquestionsremaintobeansweredinordertodevelopeffectivemitigationoptionsforfishpassage through dams on the Mekong mainstream and tributaries. These include the large size of fishpassesrequired,themigrationoflargespecies,migrationpeakswithhighbiomass,thehighdiversity of species and seasonal variations in the discharge and water level (for more details on knowledgegapsonfishpassesseeSchmutz&Mielach(2015).

Since it is impossible to monitor all habitat components and species, monitoring should focus on selected indicators covering a wide range of habitat characteristics and biotic requirements. Selected key species representing different guilds (e.g.with regard to vulnerability,migrations,feeding,habitatpreferences)shouldbeusedtoassesstheoverallimpactofHPPsandtheefficiencyof implemented mitigation measures. Examples are endangered species, endemic species, large species or economically important species.

Thefollowingtableprovidesalistofpossibleindicators(makingnoclaimtobeexhaustive):



Table 5.14. Selection of possible indicators for monitoring the impact on aquatic organisms.

System components

LMB level National/ local level

Hydrology

• Flow(sub-daily/everyhourorminute)

• Waterlevel(sub-daily/everyhourorminute)

• Onset of wet season

• Duration of wet season

• Minimumflows

• Average wet season peak daily flow

• AverageflowvolumeenteringTonle Sap

• Monthlyaveragedryseasonflow(i.e.flowinmarch)

• Totalwetseasonflowvolume

Morphology

• Bed elevation and habitat structures (deep pools, sand bars,rapids)

• Approximateflowvelocity

• Sediment load and transport rates (erosion vs. sedimentation)

• Substrate composition

• Nutrient transport

• Location and characteristics of important structures

• Quality of habitat structures (e.g. deeppools,sandbars,rapids)

• Bank erosion, landslips

• Sediment extractions

Connectivity

• Lateral connectivity

• Longitudinal connectivity

• Species assessment: which species rely on connectivity and what are their characteristics (sub-populations, spawning sites, migration period, migration corridor, migrationrange,swimmingcapabilities)

• Assessment of migration peaks

• More detailed assessment on national/local level: which species rely on connectivity and what are their characteristics (sub-populations, spawning sites, migration period, migration corridor, migration range, swimmingcapabilities)

• Assessment of migration peaks

• Important habitats (for reproductionandfeeding)

Water quality • General water quality

• Temperature

• pH

• Conductivity

• Dissolved oxygen

• BOD

• Totalsuspendedsediments(TSS)

• Totaldissolvednutrients(P,N)

• Salinity

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Floodplain

• Floodplaininundationpatterns(depth,duration)

• Inundationarea(extent)

• Qualityoffloodplainhabitats

• Type:floodedforest,marshes,inundatedricefields,inundatedgrasslands

• Riparian vegetation

• Off-riverwaterbodies

Aquatic

organisms

• Distribution of

• algae(e.g.diatom,blue-green)

• macrophytes(e.g.submerged,floating)

• macroinvertebrates(e.g.shrimps,mayflies)

• fish(e.g.differentguilds,endangered,commerciallyimportant)

• herpetofauna(e.g.reptiles,amphibians)

• birds(e.g.ground-nestingchannelsp.)

• mammals(e.g.dolphin,otter)

• vegetation (e.g. bank vegetation, riparian gardens, marshes)

• Biomass/ number/ relevance of

• algae(e.g.diatom,blue-green)

• macrophytes (e.g. submerged, floating)

• macroinvertebrates (e.g. shrimps, mayflies)

• fish(e.g.differentguilds,endangered, commercially important)

• herpetofauna (e.g. reptiles, amphibians)

• birds (e.g. ground-nesting channel sp.)

• mammals(e.g.dolphin,otter)

• vegetation (e.g. bank vegetation, ripariangardens,marshes)



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6 Biodiversity, Wetlands and Natural Resources

– Status, Risks and Mitigation

183 | Chapter 6. Biodiversity, Wetlands and Natural Resources – Status, Risks and Mitigation



6.1.1 Biodiversity and Flagship Species

Recent estimates of the biota of the greater Mekong region include 20,000 plant species, 430 mammal,1200bird,800reptileandamphibian(Thompson2008),and850fishspecies(Hortle2009).Newspeciescontinuetobedescribed,eventoday.Between1997and2007,atleast1068newspecieswerediscovered in theMekongBasin.Thisfiguredoesnot include invertebrates,whichcouldpossiblyaddthousandsmorenewspeciestothelist(Thompson2008).

Mammals

The wetlands of the Lower Mekong Basin are vitally important for many mammals. These mammal species fall into two groups: permanent wetland residents and seasonally wetland residents, particularly reliant on wetlands with permanent water in the dry season. These wetlands support 1 Globally Critically Endangered, 7 Globally Endangered, 4 Globally Vulnerable, and 1 Globally Near-threatened species of mammals. As many as 70 mammal species are endemic to the Mekong Basin(Thompson2008).

SpeciesofparticularconcernaretheCriticallyEndangeredIrrawaddyDolphin(Orcaellabrevirostris),GloballyEndangeredWildWaterBuffalo(Bubalusarnee),Hairy-nosedOtter(Lutrasumatrana),andFishingCat(Prionailurusviverrinus);GloballyVulnerableOrientalSmall-clawedOtter(Aonyxcinerea),EurasianOtter(Lutralutra);andtheEndangeredLowe’sOtterCivet(Cynogalelowei),

which is also endemic to the region. The Critically Endangered Irrawaddy Dolphin inhabits coastal and larger river systems in the Indo-Malayan realm. Today, the population is estimated to be less than 100 individuals (seealsosectiononFlagshipSpecies),whicharemainlyconfinedtoKratieandStungTrengProvincesinCambodiawith occasional wet season reports from theSeKong.TheGlobally EndangeredWildWater Buffalo (Bubalusarnee) was reported in southern Lao PDR earlier thiscentury. It is now believed to be close to extinction in the

Mekong River Basin as the result of disturbance and hunting.

Figure 6.1. The Fishing Cat (Source: SoB, 2010).

TheEndangeredLowe’sOtterCivetreportedaboveisreportedtobefoundinVietNam,Yunnanandnorth-easternThailandandmaystillbepresentinLaoPDRorCambodia.TheGloballyEndangeredHairy-nosed Otter and Globally Vulnerable Smooth-coated Otter (Lutrogale perspicillata) arereported from smaller rivers and relatively undisturbed habitats. Both species are believed to be in serious decline due to hunting. However, there are reports of viable populations in some localities in the Lower Mekong Basin. The Globally Vulnerable Oriental Small-clawed Otter is found in rivers and streams in forests and in adjacent degraded areas. The Globally Vulnerable Eurasian Otter isstillbelievedtooccurinanumberofdifferentwetlandhabitats;andTheGloballyEndangeredFishingCatisfoundinlowlandriverineanddeciduousforest(MRCTechnicalNote9,2010).Allotterspecies are under heavy threat by the local demand for skins and for use in traditional medicine (Campbell et al.2006).

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OthermammalsreportedinfloodedforestsnearTonleSapincludeflying-foxes(Pteropussp.)andthreespeciesofprimate; theslow loris (Nycticebuscoucang), the longtailedmacaque(Macacafascicularis) and the silvered leaf monkey (Semnopithecus cristatus) (Campbell et al. 2006).Furthermore, the Mekong stretches in northern Cambodia may be globally significant for theconservationofatleastthreemammalspecies;hogdeer(Axisporcinus),silveredleafmonkeyandotters (Bezuijen et al.2008).The most important habitat for large mammals is the mosaic of tall grass formations on floodplains (Bezuijen et al.2008).

Birds

Ofthe913birdspeciesintheLowerMekongBasin,220wereidentifiedasriparianspeciesfortheLowerMekongRiverandassociatedwetlandhabitats(forfeeding,nestingandresting).TheLMBwetlands are critically important for a number of globally-threatened water bird species. These wetlands support 6 Globally Critically Endangered species, 7 Globally Endangered species, 15 Globally Vulnerable species, and 15 Globally Near-threatened species, and at least 1 Endemic specieswhich is theGlobally Near-threatenedMekongWagtail (Motacilla samveasnae) (MRCTechnicalNote9,2010).

The Critically Endangered Giant Ibis (Pseudibisgigantean),longthoughttobeextinct,wasre-discoveredin 1993 along theSeKong floodplain in southern LaoPDR.SmallwaterbodiesalongtheSeKong inAttapeuProvinceinsouthernLaoPDRandneartheSeSanandSrepok Rivers in Stung Treng are vitally important for this species. The total world population may be less than 100 individuals.

Figure 6.2. The Giant Ibis (Source: SoB, 2010).

ThepopulationoftheGloballyEndangeredWhite-wingedDuck(Cairinascutulata)insouthernLaoPDRandnorthernCambodiaisoneofthelargestremainingworldwide.TheCriticallyEndangeredWhite-shoulderedIbis(Pseudibisdavisoni)andGloballyEndangeredGreaterAdjutant(Leptoptilosdubius)occurinthedipterocarpforestandwetlandmosaicofnorthernCambodianandsouthernLaoPDR.TheseareasarealsovitalfortheGloballyEndangeredGreenPeafowl(Pavomuticus).TheCriticallyEndangeredBengalFlorican(Houbaropsisbengalensis)isfoundinTramChimonthePlainofReedsandintheseasonallyfloodedgrasslandsofLakeTonleSap.SimilarhabitatsareimportantforGloballyVulnerableEasternSarusCrane(Grusantigonesharpie),whichinthewetseasonmigratestonorthernCambodiaandsouthernLaoPDRtoseekoutnon-floodedgrasslands.

Globally Vulnerable species relying on the riverine habitats of the Mekong and its larger tributaries includetheIndianSkimmer(Rynchopsalbicollis)andtheGloballyNear-threatenedBlack-belliedTern (Sternaacuticauda).OtherGloballyVulnerablespeciesdependingonavarietyofwetlandhabitats in theLowerMekongBasin include theMaskedFinfoot (Heliopaispersonata),Pallas’sFish-Eagle (Haliaeetusleucoryphus),GreaterSpottedEagle(Aquilaclanga),Spot-billedPelican(Pelecanus philippensis), Milky Stork (Mycteria cinerea) and the Lesser Adjutant (Leptoptilosjavanicus)(MRCTechnicalNote9,2010).

TheplainsofthelowerMekong,includingsouthernLaoPDR,stillretainsomeareasofnearprimaryhabitats for water birds, with mosaics of open deciduous dipterocarp forests, seasonally inundated



wetlands and grasslands and riverine habitats. Most notably, the plains of northern and eastern Cambodia are the last stronghold for giant ibis and breeding grounds for white-shouldered ibis and sarus crane (BirdLife International 2003; Bezuijen et. al. 2008; Wright et al.2009).Theareaalongthe Mekong River is probably also critical for the conservation of the Mekong wagtail (Motacilla samveasnae)andmaysupportthelargestIndochinesepopulationsofrivertern(Sternaaurantia),woolly-neckedstork (Ciconiaepiscopus)andpiedkingfisher (Ceryle rudis),aswellas theonlyknownbreedingcoloniesofPlainMartin(Ripariachinensis) inCambodia.The most important habitats for birds are the well-vegetated areas of the Mekong channel, particularly those areas forming a mosaic of seasonally exposed sand, grass, shrub and tree patches (Bezuijen et al.2008).

The Tonle Sap Great Lake is one of the most important areas for bird conservation in the region and has long been understood to be extremely important for gregarious large water birds, particularly storks, pelicans, ibises and cormorants. Seventeen globally threatened or near threatened species occur regularly around the Tonle Sap Great Lake (Campbell et al. 2006). The swamp forestsaround the lake support globally significant breeding populations of spot-billed pelican, lesseradjutant and greater adjutant. The seasonally inundated grasslands around the lake are probably alsotheglobalstrongholdforBengalflorican(Houbaropsisbengalensis).Theseecosystemsalsoharborimportantpopulationsofwhiterumped(Gypsbengalensis)andslender-billedvultures(Gypsindicus),bothcriticallyendangeredspecies.Oneoftheonlyknownslender-billedvulturenestingareas in the world was found in 2006 just east of the Mekong River in Cambodia’s Stung Treng province(ScienceDaily2007).

Reptiles

AccordingtotheMRCTechnicalNote9(2010)25speciesofreptilesfrom9familiesarerecordedfrom the Lower Mekong system of which, at least 5 of these are Globally Critically Endangered, 7 are Globally Endangered, 6 are Globally Vulnerable, and 2 are Globally Near-threatened. At least 1species,theTonleSapWaterSnake(Enhydrislongicauda)isendemictotheTonleSapLakeofCambodia.

The Siamese Crocodile (Crocodylus siamensis) is Critically Endangered, which was formerlywidespread throughout the Lower Mekong Basin, but has declined drastically due to excessive hunting and habitat destruction. This species is now very rare and believed to be extinct in the wild inVietNamandThailand.ThesmallnumbersconfinedtothesouthofLaoPDRandCambodiaare of high global importance as the last wild populations but they still face a number of threats. The most serious threats include hunting, habitat destruction and harvesting of the young for crocodile farms. The natural genetic stock is also under threat from cross-breeding with both the Cuban Crocodile(Crocodylusrhombifer)andtheSaltwaterCrocodile(Crocodylusporosus) encouraged by crocodile farms in the region (MRCTechnicalNote9,2010).

Figure 6.3. Siamese Crocodile (Source: SoB, 2010).

Over 20 species of turtles, tortoises and terrapins occur in the Lower Mekong Basin, 17 of which are listed in the Red Data Book. The River or MangroveTerrapin(Batagurbaska),South-eastAsianStripedSoftshellTurtle(Chitrachitra),andChineseThree-stripedBoxTurtle(Cuoratrifasciata)areCriticallyEndangered.Another6species

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are listed Globally Endangered, 6 species are listed Globally Vulnerable, and 1 species is listed GloballyNear-threatened(MRCTechnicalNote9,2010).TheMekongRiverinnorthernCambodiaisseenasgloballysignificantfortheCantor´sgiantsoftshellturtle(Pelochelyscantorii)andmaysupport the largest remaining breeding populations in the Mekong Basin (Bezuijen et al.2008).Anumber of aquatic or semi-aquatic turtles, snakes and lizards occur in the basin, many of which are hunted for subsistence or sold for food or medicine in local markets (Bezuijen et al.2008).

Two species of monitor are found associated with the wetlands of the Lower Mekong Basin. These are the Bengal monitor (Varanus bengalensis), and the water monitor (Varanus salva-tor) (MRC Technical Note 9, 2010). The reptiles utilize a wide range of habitats in the rivers and in the floodplains in the Mekong basin.

Amphibians

There have been few systematic studies of the amphibians of the Lower Mekong Basin. Over 100 speciesoffrogsarereportedfromLaoPDR.AccordingtotheIBFMReportNo.7,2005,atleast17species of amphibians in 5 families are present in the Lower Mekong System.

In Cambodia 30 species of frogs were documented (Stuart et al.2006)includingtwonewspeciesand11speciesreportedforthefirsttimeinthecountry.Bezuijenet al.(2009)reportatleast16frogand toad species from the Mekong River in northeastern Cambodia alone. The frog fauna of Lao PDRispoorlyknownrelativetothatofneighboringChina,Thailand,andVietNam,butscientistshavestillbeenabletoidentifyatleast46species(Stuart2005).

At least one species is listed Globally Endangered, 16 are listed Globally Vulnerable, and 1 is listed Globally Near-threatened.

Flagship species

AccordingtoMRCSEA(2010),WWF,andtheIUCNRedListatleast111speciesencounteredintheLower Mekong Basin have a Globally Threatened status. Of these 18 are Critically Endangered, 30 are Endangered, 43 are Vulnerable, and 20 are Near-threatened. At least 13 species are Mekong Endemicspecies,whereasmanyotherspeciesareofregionalandpublicconcern.(MRC,2010).

The Mekong Wetlands Biodiversity Conservation and Sustainable Use Programme selectedfour globally threatened species as so-called Flagship species, they are the Irrawaddy Dolphin (Orcaellabrevirostris),theSarusCrane(Grusantigonesharpii),theSiameseCrocodile(Crocodylussiamensis), and the Mekong Giant Catfish (Pangasianodon gigas). They are consideredrepresentative for the unique ecosystems and habitats of the Mekong River Basin. These four species have been selected as Flagship species because they meet one or more of the following criteria:

• They inhabit a broad diversity of important wetlands and therefore are representative of threatened wetland habitats and their associated fauna;

• They are regional in distribution and trans-boundary in nature; and

• They provide an opportunity for enhancing regional collaboration for conservation and management of biodiversity and ecosystems.



Below is a more detailed description of these species, under various risks due to development on theMekongasreportedintheBDPdevelopmentscenarios(SeeFigure6.4)

Figure6.4.Sustainabilityofflagshipspecies(Source:MRCBDP,2011).

Mekong River Dolphin, Irrawaddy Dolphin Orcaella brevirostris, IUCN Red List: Critically EndangeredThe Mekong Dolphin population is already listed as Critically Endangered and has an alarming mortalityrate.TheMekongpopulationisthoughttocontain66–86individuals(Dove2009).Theentire dolphin population is restricted to the southern Laotian and upper Cambodian Mekong River, inhabiting9deepwaterareas(preferably>8m)inthe190kmriversegmentfromKratietoKhoneFallsthatphysicallyobstructfurtherupstreammovement.Duringthefloodseason(June–October),the dolphins follow their prey through their habitat range on the Mekong and the lower reaches of tributaries, occasionally they ascend the Sekong River and its tributaries, Xepian to 50 km above the Sekongconfluence,althoughdeepdolphinpoolsremainareasofgreatestdolphinconcentration.There is limited movement between the northern most group at the transboundary pool on the Laos/Cambodia border and other groups that are linked to deep pools 65 – 190 km further south. The Mekong population of Irrawaddy dolphins has an annual mortality rate that greatly exceeds theacceptable1%,with19confirmedmortalitiesin2006(16calves)and13mortalities(11calves)inthefirsthalfof2007only(Doveet al.,2007).Withthisseriousdecline,theMekongdolphinissusceptible to extinction in the near future if mitigation measures are not properly implemented. AccordingtotheSEA(ICEM,2010)findings,mortalityofdolphinsinthebraidedchannelbetweenSiphandoneandKratiemayleadtolocalextinctionwithin10years.

Mekong Giant Catfish Pangasianodon gigas, IUCN Red List: Critically Endangered MekongGiantCatfishisthelargestfreshwatercatfishintheworldandisoneofthemostvulnerableendemic species in the Mekong River Basin, already listed as Critically Endangered and has an alarmingrateofdecline(90%decreaseinnumberinthepast2decades).Captivebreedingandre-introduction to the rivers and reservoirs has not resulted in any established populations. Only onespawningmigrationhasbeenfirmlyestablishedthroughoutthebasin(intheupperreachesnearBokeo–ChiangKhong).Thissuggeststhatonlyonepopulationexists.However,spawning

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mayalsooccurinnorthernCambodia(betweenKratieandStungTreng),wherethespecieshasbeensporadically reported (Poulsenet al., 2004).Presentdistribution is limited to theMekonganditstributariesinCambodia,LaoPDRThailandandVietNam.Currentspawnerabundanceisestimated to between 155 – 185 individuals.

Siamese Crocodile Crocodylus siamensis, IUCN Red List: Critically EndangeredThis freshwater crocodile, was thought to be extinct in the wild, until rediscovered again in southern LaoPDR,Savannakhet,in2005.Aroundonly200SiameseCrocodilesexistinthewild,confinedtothesouthofLaoPDR,CambodiaandVietNam.TheyarebeingfarmedextensivelyinCambodiaand Thailand.

Eastern Sarus Crane Grus antigone sharpii, IUCN Red List: VulnerableEasternSarusCraneisthetallestflyingbirdintheworld.Itoftenmakesshortseasonalmovementsbetween dry and wet season habitats. It formerly occurred throughout Indochina but over the last 50 years numbers has been decimated throughout the region. Its range has declined dramatically, butitstilloccursinlimitednumbers,(<1,000birds)in3countries:LaoPDR,Cambodia,andVietNam.Recordedpopulationsfromannualpopulationsurveysare:atPhuMygrassland/HaTienPlain–94cranesin2007;KienLuong–40cranesin2004-05.

6.1.2 Wetlands and Natural Resources

The LMB contains rich and extensive areas of wetlands, estimated to cover 6–12 million hectares oftheentirelowerbasin(Ringler2001).Theriveranditsnumeroustributaries,backwaters,lakes,and swamps support many unique ecosystems, such as deep river pools, plains of reeds and mangroveforests.AnumberofimportantwetlandtypeshavebeenidentifiedintheLMBcountriesas presented in Table 6.1.



Table6.1.ImportantwetlandtypesintheLowerMekongBasinbycountry(SOB,2011).

ThejointUNDP,IUCN,MRC,GEFfundedprogramonMekongWetlandsBiodiversityConservationand Sustainable Use, distinguished a number of wetland ecosystems/habitats in Mekong river basin,thatareparticularlyvaluable,eitherbecausetheysupporttheveryvaluableinlandfisheriesor other livelihoods of the people in the basin, or because they are very important for the sustenance oftherichbiodiversityofthearea.Table6.2brieflydescribesthesevaluableecosystems/habitats.

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Table 6.2. Valuable wetland ecosystems/habitats in the Mekong river basin.

Valuable ecosystems Description of their importance

1- River channels of the Mekong and its largest low gradient Tributariesz

Main river channels

Channels are vitally important for the seasonal longitudinalmigrationofwhitefishspeciesandforadistinctive guild of riverine bird species.

Thereareatleast17fishspeciesontheIUCNRedList of Threatened and Endangered species, 6 of which are highly migratory. The most well-known is theMekongGiantCatfishPangasianodongigas.

Mammals depending on the river channels are the Critically Endangered Irrawaddy Dolphin Orcaella brevirostris, the Globally Endangered Fishing Cat Prionailurusviverrina,andtheGloballyVulnerableSmooth-coated Otter Lutra perspicillata.

Deep pools

Deep pools are a vital dry season refuge for both residentandmigratoryfishspeciesandprobablycontain a diverse assemblage of undescribed invertebrates.

Rapids Rapidssupportadiverseassemblageoffish(andinvertebrate)species.

Small islands and riverine sandbars The smaller sand bars and islands provide safe breeding sites for many species of water birds, some of which are globally rare and endangered.

Seasonally inundated riverine forest

The biodiversity values of this habitat are not well known,buttheforestisprobablyimportantforfishbreedingandshelterduringpeakflow.Somefishspecies are known to feed on the fruit of the trees. The forest may also be important for monkeys and gibbons.

2- Permanent and seasonally-inundated floodplain wetlands (along the mainstream and major tributaries and in the Cambodian floodplain)

Seasonally-inundated riparian forest

One of the most important wetland habitats of the Lower Mekong Basin. Over 200 species of plants have been found in these inundated forests. Woody species of this forest are often laden with fruits and seeds at the time of inundation, providing food forthe34speciesoffruit-eatingfishoftheLowerMekongBasin.Over200speciesoffishusethishabitat as a feeding, breeding, and nursery ground and it is vitally important for breeding colonies of large water birds. The gallery and associated forest of Lake Tonle Sap is the best known and most productive example of this habitat.

Marshes, small pools and seasonal wetlands in the lowland plain

In the dry season, these wetlands are vital in maintainingbreedingstocksoffloodplainfish,including air-breathing species, while in the wet season they function as breeding and nursery groundsformanyfishspeciesThesewetlandsareimportant for almost all water birds in the Lower Mekong Basin.



- Inundated grasslands

These areas support a number of globally rare and endangered species (Sarus Crane, White-shouldered Ibis, Bengal Florican and Greater and LesserAdjutants).Although,intheLowerMekongBasin, these areas are greatly disturbed, they do hold more substantial grasslands that other parts of S.E. Asia and thus are a priority for conservation.

3- Deltaic Formations and the Plain of Reeds (Vietnamese floodplain)

Lowland forests

Melaleuca forests are encountered in areas of acid sulphate soils. A high proportion of them are of relatively recent origin, and many are within wood production reserves. Although today’s melaleuca forest is low in plant biodiversity, they act as one ofthefewsourcesoffish,amphibian,reptilianandbird biodiversity in the Delta. These melaleuca forests are of prime important for their breeding colonies of large water birds and are one of the few refuges in the Delta for freshwater species such as turtles.

Inundated grasslands

LikeintheCambodianfloodplains,theremaininggrasslands are important for water birds including the Sarus Crane, White-shouldered Ibis, Greater and Lesser Adjutants and the Bengal Florican.

Mangroves

This is an ecologically important area as a breeding groundformanyspeciesoffish,crabsandshrimps.Over300speciesoffishhavebeenrecordedintheDelta. The wildlife is diverse with mammals such asfishingcats,ottersandcrab-eatingmacaques.Manyfishandshrimpspeciesdependupontheestuaries of the Delta for their breeding and nursery areas.Somemarinespeciesoffishascendtherivers to spawn in the gradient or freshwater zone of the estuaries, while the larvae of many economically important shrimp species, spawning in the shallow coastal areas, are moved by tides into the brackish water zone where they stay as juveniles for 2-4 months amongst abundant food and safe from predators.

The Lower Mekong River Basin wetland ecosystems are exceptionally rich in biodiversity. They form habitats for a wide range of globally threatened and endemic species, by providing water and primary productivity upon which people and numerous species of plants and animals depend for survival and completion of their life cycle. Wetland ecosystems support high concentrations of birds,mammals,reptiles,amphibians,fishandinvertebratespecies.Manyofthesespeciescanonly live in wetlands and loss of wetlands will eliminate part of the wetland-dependent species.

The table below shows a rough indication of the number of species depending on the wetland types in the LMB. The table is based on sketchy available information from various sources.

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Table 6.3. LMB Wetland types and number of species dependent on them.

In the following important wetland sites by member countries is given.

Cambodia:

Cambodiamayhaveupto20separatewetlandsitesofregionaland/orinternationalsignificance–fiveexamplesarelistedinTable6.4.BoengChhmarandassociatedriversystemandfloodplainandStungTrengare internationallysignificantRamsarsitesandPrekToal,which ispartof theTonle Sap Lake system is the core zone of a Biosphere Reserve. The others have high biodiversity and other values and both would meet the criteria for Ramsar status in Cambodia.



Table 6.4. Examples of important wetland sites in Cambodia.

Lao PDR:

A total of30 regionally/internationally importantwetlandsiteshavebeen identified inLaoPDR(Calridge1996),mainlyinthecentralandsouthernpartsofthecountry.SiphandoninLaoPDRisnominated as a potential future Ramsar Site.

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Table.6.5.ExamplesofimportantwetlandsitesinLaoPDR.

Thailand:

Altogether, a total of 39 important wetland sites cover an area of 1,601,082 ha in the Mekong River Basin of Thailand (Scott 1989; Wolstencroft et al.1993;OEPP2002).Atleast15ofthesewetlandsare of international importance and 15 are of priority national importance, according to criteria of highfishandbirddiversity(OEPP2002).TheBungKongLong(Nongkhai)wetlandofInternationalImportance is located in Thailand.



Table 6.6. Examples of important wetland sites in Thailand.

Viet Nam:

TheMekongRiver Delta stretches fromKampongCham inCambodia through Viet Nam till itdischarges in the South China Sea. About 70 per cent of the Mekong Delta, formed by sediment deposition during the last 6000 years, lies within Viet Nam and is home to 17 million people, who dependuponitfortheirlivelihoods.Eachyearfloodwatersinundate3.9millionhectares.Thelowerreachesofthemainstream;estuariesandfloodplains(includingseasonallyinundatedgrasslands);aswell as themangrove andmelaleuca forests andmudflats are themost important wetlandecosystems. The fauna of the delta include 23 species of mammals, 386 species and subspecies ofbirds,35speciesofreptilesandsixspeciesofamphibians(Thinh2003).Atleast460speciesoffishareknownfromthedelta(Vidthayanon2008).TheMekongDeltacontainsabout20importantwetlands,fourofwhichareshowninTable6.7.Anotherfourorfiveimportantwetlandsitesarefound in the headwaters of the Sekong, Sesan and Srepok rivers in Viet Nam.

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Table 6.7. Examples of important wetland sites in Viet Nam.

Environmental Hotspots:

Within the Mekong basin a number of environmental ‘hotspots’ has been identified, that areconsidered to be of utmost importance for the functioning of the Mekong environmental system and havingtransboundarysignificanceinecological,socio-cultural,andeconomicaspects.Intotal32environmental‘Hotspots’thatarelikelytobeaffectedbythehydrologicalchangesunderdifferentdevelopmentscenarioshavebeenidentifiedwithintheLMB.Selectedashotspotswere:protected/sensitive areas with local/national/regional/global conservation management status, containing a richbiodiversity,alargenumberofimportantspeciesatrisk(threatenedorendemicspecies),aswell as areas important for migrating species, or supporting key ecological processes. Included are designatedRamsarSites,BiosphereReserves,ProtectedAreas,ImportantBirdAreas(IBA’s)andGreaterMekongSubregion(GMS)Hotspots(MRCTechnicalNote9,2010).



Table6.8.Locationandstatusoftheidentifiedenvironmentalhotspots.


The population increase, land use change and infrastructure developments in LMB, including development of mainstream and tributary dams, is and will impact the biodiversity, wetlands, and other important habitats, hence also local livelihoods of the Lower Mekong. Regarding dams and reservoirstheymayblocknaturalfishmigrationroutes;alterthehydrologyandtherivers’naturalpatterns of erosion and silt deposition, nutrient transport, as well as water temperature and water quality – all of which impacts on the aquatic life. The wetland ecosystems exist in a transition zone betweenaquaticandterrestrialenvironmentsandcanbeaffectedevenbyevenslightalterationstohydrology.Reduced‘floodpulse’transportofsedimentintothefloodplainscanalsoreducethenutrients available for aquatic plant growth – the primary engine driving much of the productivity ofthewetlandsandfloodplainhabitats.Belowarelistedsomemainissuesrelatedtoimpactsandvulnerabilities.Specificallythefollowingisatriskrelatedtoimpactsandvulnerabilities:

1. TheMekongIrrawadyDolphinandtheGiantCatfish,whicharealreadyunderthreatfrom other human activities, however they are both migratory and depend upon access to deep pools, hence they will be threatened especially by mainstream dams since these might be situated in their main migratory routes (see also Chapter 5.2.3, Fisheries andAquaticEcologywhichdiscussestheeffectofthisindetail).

2. It is likely that population of the Mekong Irrawaddy Dolphin is the most threatened ofalltheexistingpopulationsinSoutheastAsia(Dove2009).Theprincipalcauseofadultmortality has been drowning in fishnets,which from2001 to 2005 accountedforalmostone-thirdofdocumenteddeaths inCambodiaandLaoPDR(Bezuijenet al.2007).Causesofhighjuvenileandcalfmortalityarelargelyunknownbutarecentreportsuggeststhatpollutants,suchasmercury,DDTandPCB,mayhaveweakenedthe animals’ immune systems – especially in young individuals – making them more susceptible to disease (Dove 2009). This and other stresses, in combination withlimited genetic diversity due to inbreeding, may have made otherwise manageable bacterial diseases become deadly (SOBReport, 2011).As reported under point 1,especially mainstream dam development will exacerbate the stress upon this species. TheproposedDonSahongdamissituated<2kmnorthofthetransboundary‘DolphinPool’insouthernLaoPDR.Althoughallpermanentpopulationsoccurbelowthisdamsite, dolphins may visit Hoo Sahong channel and upstream areas for feeding in the wet season. Sambor dam is situated within the dolphin habitat range. (MRC Technical Note 9,2010).

3. Siamese Crocodile is currently under threat in the wild by other activities, and changes intheflowregimewillprobablycauseonlysmallchangetoitsnaturalhabitats.Breedingprograms may ensure the sustainability of this species.

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4. Sarus Crane, depends upon the availability of inundated grassland. This habitat is expectedtodiminishslightlyduetochangesinflowregime,butnottotheextentthatitwill threaten the sustainability of this bird.

5. Ofthe32identified‘environmentalhotspots’(seeTable6.8),9willbemoderatelyand1highlyaffectedundertheDefiniteFutureScenarioofBDP.

6. ChangesinFlowVolumesandFloodingPatterns(seealsoTable6.9,withreferencetoAnnualandInterAnnualChangestoFlow)-Constructionandoperationofhydropowerdams along the Mekong River and its tributaries could cause a decrease in wet season flowsandanincreaseindryseasonflows(ICEM2010,MRC2010a,Lauriet al.2012)throughouttheLMB.Changesinflowvolumescouldresultinchangesinwaterlevelsand inundation patterns, which could, over time, cause changes in LMB wetlands and floodplainhabitat.

7. Changes in Timing and Duration of Seasonal Flows (see also Table 6.9, with reference toAnnualandInterAnnualChangestoFlow)–Storageofwaterinupstreamdamsforhydropowerproductioncoulddelay theonsetoffloodflows(ICEM,2010andMRC,2016c)anddecreasethelengthofthetransitionseasonsbetweenhighandlowflows.Thesechanges inthetiminganddurationofhighflowscouldreducetheavailabilityofimportantwetlandandfloodplainhabitatsduringcriticallifehistorystagesofsomespecies.

8. Change in Sediment and Nutrient Transport (see also Table 6.9, with reference to Annualand InterAnnualChanges toFlow)–Constructionofdams in theUMBandlarge storage dams in the tributaries is predicted to cause a considerable reduction in coarse sediment transport throughout the river and a decrease in the supply of nutrients and sediment to the lower portions of the river including Tonle Sap Lake and the delta (seeChapters3.1.3to3.1.6).TheMainstreamdamsofLMBisgoingtoaddintothisdecrease(MRC,2016c).

9. Construction of planned LMB mainstream dams would reduce the remaining sediment supply, and would reduce nutrient deposition in the delta. A decrease in sediment transport would cause an increase in erosion throughout the system, leading to the loss of in-channel islands, sandbars, mangrove forests, and other riverine and coastal habitat. A decrease in nutrient transport and deposition would result in a decrease in primaryandsecondaryproductivitythroughoutaquaticandseasonallyfloodedareasin the delta.

10. Theglobally importantSiphandonewetlandsmightbedirectlyaffectedwithreducedseasonal variability and loss of wetland habitats due to the Don Sahong project.

11. Development of hydropower schemes on the Mekong River in countries upstream of Cambodia caneffect thewetlandecosystemsand fisheries of theTonleSapLake.Change in flow patternwill reduce the area of land subject to seasonal inundationaroundTonleSapLake(seealsoChapter2.2andFigures2.13-2.15).

12. AninternationallyRamsarsiteaboveStungTrengdamwouldbedirectlyaffected.

Based on the Status and Overview (Chapter 6.1) and the above specific risks, impacts andvulnerabilities, this has been transformed into more generic risks for LMB as a whole in the following table, that is also extracted into the Mitigation Guidelines, Chapter 3, to support the proposed mitigationguidelinesandrecommendations(Chapter5,ibd.).



Table6.9.Biodiversity,naturalresourcesandecosystemservices-Keyrisks,impactsandvulner-abilities.


Annual / inter-annual changes to flow 4

Changesinseasonalitytoflow Changesintimingofflowtowetlandsandfloodplainriparian habitats

Modificationoffloodrecurrenceintervals DispersalofspeciestoandbetweenfloodplainhabitatsChange in relationship between flow and sediment/nutrient delivery

Changes in wetlands functions, dynamics and ecosystem services due to timing of sediment and nutrient delivery

Change inundation/exposure of downstream floodplainsand wetlands Lossofwetland/floodplainhabitats

Daily / short-time period changes in flow 5

Fastincreaseanddecreaseofflowvelocity Degradation of function, dynamics and ecosystem ser-vices of wetland and riparian habitats

Loss of river connectivity 6

Changetosedimentandnutrienttransfer(amount)Changes in wetland functions, dynamics and ecosystem services due to decrease in transfer of sediments and nutrients

Impoundments

Change to/loss of riparian areas Loss of riparian- ecosystems, habitats and biodiversity

Diversion scheme / inter basin transfers

Alternation of flow regime of contributing and receiving(sub)catchments

Flowchangestowetlandandfloodplainareas(decreaseorincrease)leadingtochangesinecosystem-functions,dynamics and services as well as biodiversity

Most of the key risks, impacts and vulnerabilities are closely related to those outlined for Fisheries andAquaticEcologyinChapter5(andhencetheproposedmitigationmeasures),howeverpotentialloss of riparian- ecosystems, habitats and biodiversity stands out as a special case. These are residualimpactsthatarenotpossibletomitigate,socreatingoffsetsistheonlysolution.

6.3 Biodiversity, Wetlands and Natural Resources Mitigation Measures

The mitigation measures for biodiversity, wetlands and natural resources are closely related to those of Fisheries and will not be repeated in detail here, however extracted and commented on its relevance for this theme. This is listed below, for the relevant project phases.

6.3.1 Overarching principles

The proposed mitigation options and measures should align to international good industrial practice related to environmental mitigation policies, guidelines, standards and options (See the Mitigation Guidelines,Chapter6.5.1and&.5.2especially).Thiscould includeestablishmentofcatchmentscalemitigationtechniqueslikedamsitingandjointflowreleases,establishmentofcomprehensiveenvironmentalflowsrequirements,ecologicalcapacitybuildingandcontrolofadditionalecologicalstressor activities, as well as creation of compliance requirements for developers and operators.

4 ImpactsonfloodplainsandwetlandshasalsobeendiscussedunderChapter5.2.1ofFisheriesandAquaticEcology.

5 Impacts on habitat complexity and changes has also been discussed in Chapter 5.2.2, Fisheries and Aquatic Ecology.

6 Impacts on ecosystem function, habitats and community structures has also been discussed under Chapter 5.2.3, Fisheries and

Aquatic Ecology.

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6.3.2 MasterPlanandFeasibility

Dam siting and assessment alternative location for projects (see Chapter 5.3.2.1 in Fisheries and AquaticEcology, and its reference to theMitigationGuidelines) is also an importantmitigationmeasure for this theme to avoid direct impacts on sensitive biodiversity resources, wetland and floodplainhabitats,fragmentationofsensitivehabitatsorindirectimpactstotheseduetochangesinflowregime,sedimenttransportornutrientdelivery.Non-aquaticfaunaandflorawillalsobenefitifconnectivity is sustained as well as corridors for migration (see for example Figure 5.19 in Fisheries andAquaticEcology).

Developmentofenvironmentalflowrules(alsoincludingthoseofhydropeaking),detaileddiscussedunder Chapter 5.3.2.3 in Fisheries and Aquatic Ecology, will also help maintain wetland and floodplainfunctionsandbiodiversityvaluesatreasonablelevels.Forthelatteralsoplanningforprovisionofby-passflowsduringreservoirconstructionshouldbeincluded.

6.3.3 Detailed Design

ThisreferstoI.3toV.3(compensationmeasures)inTable6.1to6.5intheMitigationGuidelines.During this phase it is important to design plans for rehabilitation and restoration of impacted wetlands andfloodplains.ThisisthoroughlydiscussedinChapter5.3.3.1inFisheriesandAquaticEcology.Impoundments will however create residual impacts on riparian ecosystems. This loss can to some degreebecompensatedbycreatingbiodiversityandecosystemoffsetsareas,but forexampleby cascade developments on mainstream with several hundred kilometers of impoundments this can only be compensated partly. The general principle though should be to establish provision for equivalentorreasonablycomparableoffsetsforallcriticalhabitat lossordeterioration.Incasesof unavoidable harm to biodiversity, each project or groups of projects should take conservation actionstocompensate(e.g.regenerationofvegetationbyplanting,wetlandsrehabilitationetc.).

The Lesotho Highlands Water Project implemented during Phase 1B Feasibility and DetailedDesign an extensive biological program including also extensive studies on wildlife and plants, aquatic weeds, fisheries, aquatic communities, instream flow requirements, medical biology,limnologyandwaterquality.Thesespecialstudiesidentifiedkeyareasforoffsetsandenvironmentalreserves development. The conservation areas were developed and declared accordingly based on conservation status, and include two nature reserves, a conservation area and a botanical gardenthathousesrescuedplantsfromKatsevalleypriortoinundation(Table6.10,andFigure6.5theKatsedam).Trainingoflocalpeopleinnatureconservationhasbeentakingplaceaspartof the biological programme (Monyake and Lillehammer, 2011.



Table6.10.ConservationareaswithintheprojectareaofLHWP(Source:MonyakeandLilleham-mer,2011).

Name of conservation area Conservation objective Size (hectares)

Liphofung conservation area Heritage and cultural site 4.5

Bokong nature reserve Alpine reserve on highest elevation 1975

Muela nature reserve Fauna&floraoflowlandsandfoothills 45

Tsehlanyane Leucosidae woodland 5600

Katsebotanicalgardens RescuedplantsfromKatsedamvalley 3.62

In addition the National University of Lesotho herbarium was used to house all rare plants from all areas that were to be inundated.

Figure 6.5. The Katse dam in the Lesotho Highlands Water Project (Photo: Astrid Janssen, WL Delft Hydraulics).

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6.3.4 Construction and Operation

As for Fisheries and Aquatic Ecology During construction, it is important to sustain suitable habitat conditions for affected wetlands floodplains and riparian habitats. Consequently, all previouslydiscussed issues should bemonitored in an EnvironmentalMonitoring andManagement Plan(EMMP,seealsoChapter6.5.6intheMitigationGuidelines)duringconstructionaswellasduringoperation.ImplementationoftheEMMPshouldalsoconsistofanextensive,carefullytargeteddatacollection scheme on basic ecological data to also test the success of various mitigation measures.


For indicators and monitoring reference is made to table 5.18 in Chapter 5.4, in Fisheries and Aquatic Ecology. These will basically be the same for biodiversity, wetlands and natural resources and are not repeated here.

203 | Chapter 7. Engineering Response to Environmental Risks


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7 Engineering Response to Environmental Risks



7.1 Overview

Sections 2 to 6 of this Mitigation Manual present the Mitigation Guidelines, Recommendations and Mitigation Options for each of the following thematic areas:

• Hydrology and Water Resources

• Geomorphology and Sediments

• WaterQuality,Nutrients&ReservoirStratification

• Fisheries & Aquatic Ecology

• Biodiversity, Wetlands and Natural Resources

The Guidelines and Recommendations are presented in tables in each Section, sub-divided into fivekeycommonoverarchingchangesrelatedtohydropowerdevelopment.Theseare:

I. Annual/inter-annualchangestoflow

II. Daily/short-timescalechangestoflowandwaterlevel

III. Loss of river connectivity

IV. Impoundments

V. Diversion / intra basin transfers

This Section 7 presents selected engineering design and operational responses that have been adopted on hydropower projects in the region and internationally to mitigate the environmental risksidentifiedintheGuidelinestables.

7.2 Master Plans

Guideline table reference I.1, II.1, III.1, IV.1 & V.1.

7.2.1 River basin planning

Environmentalmanagement of hydropower schemes in the same river basin benefits from anintegrated approach and a common set of guidelines at a national and international level (this has alsobeendiscussedintheCaseStudyReport,MRC2018c).Thishasalreadybeenaccomplishedin other parts of the world. As an example, countries in the Danube Basin have devised a set of guidingprinciples(‘SustainableHydropowerDevelopmentintheDanubeBasin,GuidingPrinciples’,InternationalCommissionfortheProtectionoftheDanubeRiver,June2013)toaddresstheneedto increase renewable energy production and reduce greenhouse gas emissions by 2020 whilst maintaining riverine ecology and effectively achieving sustainability. Recommendations in theDanubeGuidingPrinciplesaresub-dividedintothefollowinggeneralprinciples:

• technical upgrading of existing hydropower plants;

• ecological restoration;

• strategic planning for new hydropower development; and

• mitigation measures.

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These guidelines are not legally binding but serve as guidance for national application.

Theconfigurationandsitingofthecurrentlyplannedmainstreamschemesgenerallyfollowstherecommendations given in the Mekong Mainstream Run-of-River Hydropower Report prepared in 1994 by Compagnie Nationale du Rhone (CNR), in collaboration with Acres InternationalLimited and the Mekong Secretariat Study Team. This report proposed several low head run of theriverhydropowerdevelopmentsbasedonlyonbenefitsduetoelectricitygeneration,althoughconsideration to social impacts was given at an initial screening stage. Suggested priorities also consideredfloodedareasandnumbersofpeopledisplacedinaqualitativemanner.Thereportfurtherrecommendedthatfisheriesandpublichealthconcernswereaddressedatlaterstages.

The 1994 study was updated in 2009 by CNR (Optimisation of Mekong Mainstream Hydropower – June2009).ThemainpurposeofthisupdatedstudywastodeterminethemaximumandminimumoperatingwaterlevelofeachoftheupstreamfivesitesinLaoPDR(PakBeng,LuangPrabang,Xayaburi,PakLayandSanakham)leadingtoaglobaloptimizationofthecascadeofdams.Thestudy seeks to assess an appropriate balance between hydroelectric production and social and environmental issues (albeit neither fish nor sediments are covered – these are the focus oftheMitigationGuideline study),without taking intoaccount construction costs. Thestudyalsoincludesapreliminaryreviewofenvironmentalandsocio-economicimpactsofthefivesites.TheXayaburi project has subsequently been re-optimised by the project developers and is currently underconstruction.ThePakBengprojecthasalsobeenthesubjectofafeasibilitystudyandre-optimisation.Inbothcasesthefinalprojectparametersaredifferenttothoseproposedinthe2009cascade study. This is largely because they are optimised on a project basis and not a cascade basis.

7.2.2 Projectlocationsandlayouts

The selection of future project locations and layouts should consider all environmental risks, mitigationoptionsandguidelinesatanearlystage,fromRiverBasinMasterPlanningtoFeasibilityStudy and Detailed Design.

Projectlocationsareusuallydeterminedbynon-environmentalfactorssuchaslocaltopography,availability of flows, economic viability, access, etc. As such, opportunities for fundamentalchanges may be limited, unless the river configuration lends itself to a more environmentallyfriendlysolution.Forexample,theprojectlocationmaybeadjustedtoallowfishmigrationfrom/totributaries and distributaries or through braided channels on the mainstream. At Sambor, on the MekonginCambodia,itwasidentifiedthatbymovingthedamupstreamfromitsoriginallocation,anaturallyoccurringbypasschannelcouldbeutilisedforfishpassage.ThisisshowninFigure7.1.



Figure 7.1. Alternative dam locations at Sambor, Cambodia (Source: Ian G Cowx, Hull Fisheries Institute).

More generally, the possibility of building lower head schemes at more frequent intervals along theMekongshouldbeconsidered.Thiswouldrequirefindingadditionallocationsforhydropowerdevelopment and would require a greater overall investment. However low head schemes have a reducedenvironmental footprintduringoperationandkeep the rivercloser to itsnaturalflowregime.Civilworksassociatedwiththeconveyanceofsedimentsandprovisionoffishpassagewouldbedesigned for lowerheadsandmaybemoreeffectiveasa result. Fishpassage inadownstream direction would be further aided by the use of low speed bulb turbines (typical of low headschemes)whichcanbedesignedtoachievelowerfishinjuryandmortality.

A concept for dividing the currently envisaged mainstream schemes into two lower head schemes is examined in the Case Study Report – Final Mainstream Dams Assessment Including Alternative Scheme Layouts. The concept comprises horizontal axis low speed bulb turbines and a rising sectorgatebarrage.Thisconfigurationoffersseveralenvironmentaladvantages:

• The reservoirs created by the low head barrages have considerably lower residence time than the full height alternative. This reduces impact on water temperature, water quality and sediment retention;

• Themaximumdepthof impoundmentwillbesimilartothefloodsurchargeduringthewetseason;

• The total energy generated is similar to the full height alternative;

• The capital cost is higher but the finance cost is lower and the overall cost of energy isprobably the same or lower than the full height scheme;

• The overshot configuration of the sector gates permits safe downstream fish passage intimesofflood;

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• Theentireschemecanbeshutdownandbecometransparentatcriticaltimesofyear,100%connectivityisrestoredandtheriverisreturnedtoitsnaturalregime.Naturalfishmigrationand sediment transport can occur.

Run of the river schemes typically benefit from well-defined design solutions and operationalrulestominimiseenvironmentalimpacts.Thesesolutionsshouldbeflexibletoallowforadaptivemanagement. In terms of design, it is good practice to provide blank openings, starter walls and other geometry to facilitate changes in design and operation in the future.

7.3 Feasibility and Detailed Design

7.3.1 Annual / Inter Annual Changes to Flow

Guideline table reference I.2.5, I.2.6

Changes to annual and inter annual discharge typically result from storage schemes designed to retain wet season discharge and release it during the dry months of the year to provide a uniform energy supply. A uniform power supply throughout the year is commercially valuable to thepowerofftakerbecauseitdisplacestherequirementforstandby(mostprobablythermal)dryseasonpowercapacityonthesystem.Thestorageofwetseasonflowsalsoreducesspillageandincreases annual energy output.

Projects designed as storage schemes typically have the potential to alter downstream floodhydrographsandattenuatefloodpeaks.

Basicdecisionsmadeat theMasterPlanandFeasibilityStudystagewill dictate thedesignofthe project and the quantity of seasonal storage to be provided. The commercial feasibility of the project will be assessed on this basis.

Ifitisdeterminedthatlossofseasonalityinthedownstreamdischargeandalteredfloodreleasehydrographs are environmentally unacceptable then these characteristics should not be incorporated in the design of the scheme. For storage schemes that are already in service, it will be possible in mostcasestochangetheoperationalregimetorestoreseasonalityandnaturalflooddischarges.There will however be a commercial cost arising from such changes.

The implications of these operational revisions are discussed in Section 7.5.

7.3.2 Daily/short-timescalechangestoflowandwaterlevel

Guideline table reference II.2.2, II.2.3, II.2.10

7.3.2.1 Hydropeaking

Hydropeakingiscommerciallyvaluablebecauseofthetypicalstructureofenergytariffs,wherebytariffsvaryaccordingtothetimeofdayanddayoftheweek.Thisformofoperationismostreadilyachieved on schemes with head ponds that can store water at certain times of the day and days of theweek,tolaterreleasethiswaterwhenthetariffishigher.

The introduction of daily discharge peaks in the river downstream of the power plant creates hydro safetyissues,riverbankdamageandtheriskoffishandboatstanding.Itistypicallyarequirementthat suitable flow ramp rates are introduced in the downstream discharge, and that the peak



discharge magnitude should be reduced and the minimum discharge should be increased. There are several engineering options for creating re-regulation of downstream discharges.

7.3.2.2 Cascades

On a cascade of schemes only the downstream scheme needs to be designed and operated for tail water control since the intermediate head ponds will have the capacity to absorb the de-regulatedflow.Thisapproachiscommonlyadoptedonhydropowercascadesaroundtheworld.For example on the Dordogne in France the cascade of hydroelectric dams between Bort and Chastang are used for daily peaking operations to augment base load power production from nuclear power stations. These schemes comprise high dams with large regulating storage. The downstreamschemeatSablierisanentirelydifferentdesigncomprisingalowheadbulbturbinegated barrage designed to deliver near constant daily discharge under a range of head pond levels andinflows.TheSablierschemewasinitiallyusedasatestfacilityforthebulbturbineseventuallyadopted for the tidal power facility at La Rance. The arrangement of the cascade is shown in Figure 7.2. The river reach between Argentat and Mauzac is returned to near natural conditions with this arrangement and the downstream schemes at Mauzac, Tuileres and Bergerac operate on a pure run of river basis. A similar arrangement has been discussed and modelled for the Lao hydropowercascadeintheCaseStudyReport(MRC,2018c),withSanakhamfunctioningwithasimilar purpose as the Sablier downstream scheme.

Figure 7.2. Dordogne Hydropower Cascade, France (Source: EdF).

7.3.2.3 Re-regulating Dams

ThemajorityofhydropowerschemesonthetributariesoftheMekonghaveasignificantstoragecapacity and operate on a peaking basis and provide seasonal regulation. If hydropeaking is

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adopted on the downstream scheme of a tributary development it is necessary to provide a re-regulating facility. The Nam Theun 2 project in Laos is an example of where a regulating dam was provided downstream of the power station to absorb rapid changes in generation output and impose acceptable ramp rates on the downstream discharge. The ramp rates were based on hydro safety and river bank stability considerations in the downstream channel and the receiving river, the Xe Bang Fai. The adopted water level ramp rates were 0.2 m/hr falling and 0.3 m/hr rising. The peak discharge was only required to be reduced from 330 m3/s at the power station to 315 m3/s at the Xe Bag Fai. The pond storage volume was dictated by the requirement to preserve a minimum downstream discharge of 30m3/s on a Sunday when the station is sometimes shut down.

The Nam Theun 2 regulating dam is shown in Figure 7.3. It is located on the natural river course of theNamKathang.Therearetwosetsofgates.OnesetregulatesdischargesbackintotheNamKathang.Thecurrentrequirementthatthedischargefromthesegatesshouldequalthenaturalinflow,includingfloods,butprovisionhasbeenmadeinthedesignforenhanceddischargestobemadeifthesearefoundtobeofbeneficialusetocommunitiesdownstream.Thesecondsetofgates regulates discharges from the power station into a 27 km long downstream channel leading to the receiving Xe Bang Fai. Additional outlets were incorporated into the design of the regulating dam when it was constructed. These outlets provide the potential for micro hydro and dry season irrigation. One of these outlets is currently being developed to provide water supply for dry season irrigated rice production.

Figure 7.3. Nam Theun 2 regulating dam, Lao PDR (Source: Multiconsult).



An alternative approach to re-regulation is being implemented at the Nam Ngiep 1 Hydroelectric ProjectinLaoPDR.Themain272MWpowerstationisdesignedtodeliverdailypeakenergytoThailandfor16hourseachday,sixdaysperweek.Thedischargeprofiledownstreamofthemainpower station is shown in Figure 7.4.

Figure7.4.NamNgiep1dischargeprofile,LaoPDR(Source:NamNgiep1PCLtd).

A regulating dam has been constructed across the river downstream of the main dam. This houses an 18 MW low head bulb turbine to provide base load energy to the Lao grid and release a more uniformdownstreamdischarge.TheoutflowprofileisalsoshownonFigure7.4andthegeneralarrangement of the Nam Ngiep 1 regulating dam is shown in Figure 7.5. A labyrinth weir is provided todischargefloodflows.Thisapproachavoidstherequirementforagatedspillwaybutimposesalargefloodsurchargeinthepondwaterlevel.

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Figure 7.5. Nam Ngiep 1 regulating dam, Lao PDR (Source: Nam Ngiep 1 PC Ltd).

7.3.2.4 Re-regulating Ponds

Both the Nam Theun 2 and Nam Ngiep 1 re-regulating facilities are created by constructing dams and re-regulating reservoirs in river valleys. This approach introduces additional environmental issuessuchaslossofsedimentandfishconnectivityintheriver,changestoriverineecologyandtherequirementtomanagefloodflows.Wherespaceisavailable,itispreferabletoprovidethere-regulating facilityoutside the riverchannelso that these issuesdonotarise. At thePergauHydroelectricProjectinMalaysiathere-regulatingpondwasplacedontherightbankoftheriverat the location of the tailrace outfall. The layout is shown in Figure 7.6. Discharges from the pond are commanded by a radial gate structure working on signals provided by the project Distributed ControlSystem.Anairregulatedsiphonspillwayisprovidedtoprotecttheconfiningembankmentfrom being over topped in the event of a logic failure or short notice changes in station dispatch. Designdetailsmaybefoundin(Grant-InstitutionofCivilEngineers–1999)anddesignguidanceforairregulatedsiphonsin(Hardwick&Grant–InstitutionofCivilEngineers–1997).



Figure 7.6. Pergau Re-regulating Pond, Malaysia (Source: Institution of Civil Engineers - UK).

7.3.3 Loss of River Connectivity

7.3.3.1 Sediment Management

Guideline table reference III.2.2, III.2.6

Efficientsedimentmanagementcanbeachievedthroughdifferentdesignsolutionsandoperationalapproaches. These approaches are well established in many parts of the world.

The Dal Hydropower Project, on the Nile River in Sudan, will achieve flood and sedimentmanagementwithfourgatedoverflowbaysandtengatedunderflowbays.Thegatedunderflowbayswillbeusedtodrawdownthereservoirtominimumoperatinglevelinordertopassthefloodflowsand accompanying suspended sediments by combination of the underflowbays and thegenerating plant throughout the wet season. As a consequence the maximum utilisation of the generating plant occurs with the reservoir drawn down to minimum operating level and the turbines havebeenselectedaccordingly.SectionsthroughtheunderflowandoverflowbaysareshowninFigure7.7.AverysimilarspillwayconfigurationhasbeenadoptedattheXayaburiHydroelectricProject on themainstreamMekong. Provisional operating rules have been developed for theXayaburiandPakBengprojectscomprisingreservoirdrawdownduringlowreturnperiodfloodstoflushsedimentfromthereservoirandprovideaseasonalsedimentpulsedownstream.

TheconvenienceofthissedimentmanagementstrategywasfirstobservedattheRoseiresreservoiron the Blue Nile, which has been in service for over 50 years and is progressively drawn down during the dry season to satisfy irrigation requirements. The reservoir is therefore fully drawn downwhenthesedimentladenearlywetseasonfloodflowsoccur.AsimilarstrategyiscurrentlyimplementedontheGreatNileattheMeroweHydroelectricProjectandwillbesimilarlyadoptedattheKajbarHydroelectricProject,bothofwhichareupstreamofDal.AfurtherexampleofwetseasondrawdowntolimitsedimentdepositionisadoptedattheKapichiraHydropowerProject,onthe Lower Shire River in Malawi.

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Theexceptionally high sediment load atDal (146Mt/year, 90%ofwhich is delivered betweenJulyandOctober)hasrequiredtheadditionalprovisionofdedicatedsedimentsluices,positionedbeneatheachpowerintaketomanagelocalbedloadnotremovedbyreservoirflushing.AsectionthroughasedimentflushingsluiceisshowninFigure7.8.Thisconfigurationhasbeentestedbyphysical and numerical modelling and is designed to keep the turbines free of course bed load and preserve the area in front of the power intakes.

Figure7.7.Sectionsthroughtheoverflow(top)andunderflow(bottom)baysatDalHydropowerProject, Sudan (Source: Multiconsult).



Figure 7.8. Section through sediment sluices at Dal Hydropower Project, Sudan, (Source: Multiconsult).

Figure 7.9. Sediment sluice model study for Dal Hydropower Project, Sudan, (Source: TUM & Multiconsult).

Incaseswheresedimentmanagement isnotefficient, theschememayremainoperationalandeconomically viable if a different operating strategy is adopted. The Kindaruma HydropowerProject,partof theTanaRiverCascadeinKenya,hasbeeninoperationforover50yearsandthe reservoir is largely filledwith sediments. However, thegeneratingplanthas recentlybeenrefurbished and the installed capacity of the station has been increased. It is now used for daily peaking which requires only limited storage capacity. The silted-up reservoir has proven to be an

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attractivehabitatforlocalfauna.Photographsofthereservoirareaandtherecentlyrefurbishedand expanded powerhouse are shown in Figures 7.10 and 7.11, respectively.

Figure 7.10. Reservoir area at Kindaruma Hydropower Project, Kenya (Source: Multiconsult).

Figure 7.11. Refurbished power station at Kindaruma Hydropower Project, Kenya (Source: Multiconsult).

7.3.3.2 Fish passage

Guideline table reference III.2.3

RecommendationsfortheconfigurationanddesignoffishpassagesforupstreamanddownstreammigrationarepresentedinSection5ofthisManual.Asignificantfeatureoffishpassagesystems



istherequirementtoprovideattractionflowsintheupstreamanddownstreamdirections.Theseattraction flows represent energy loss to the project and this loss can be significant onmajorschemes.

At the Xayaburi project, currently under construction on the mainstream Mekong, an elaborate system of upstream and downstream fish migration facilities is being incorporated.A generalschematic of the systems is shown in Figure 7.12.

Figure 7.12. Xayaburi Fish Migration System, Lao PDR (Source: Xayaburi Power Company Ltd).

The upstream system is represented by the red arrows and comprises a series of openings across the base of the power station above the draft tube outlets, with a further opening in the spillway bay on the right side of the intermediate block. These openings are linked by a collecting gallery thatconnectstothebaseofthefishladderontheleftabutment.Theladdercoversapproximatelyhalf theheightof thebarrage. Fromthe topof the ladder thefishareconveyed toheadpondlevelbyadoublefishlocksystem.Thecombinedupstreamsystemrequiresanattractionflowofapproximately5%ofthedesigngenerationflowofthestation.Feedingthissystemfromtheheadpondwouldthereforerepresent5%energylossfortheproject.Thesolutionhasbeentoprovidethe attraction flow in the connecting gallery and lower openings using a pumping station fromthe tail bay. The pumping head is very much less than the generating head on the project. The fishladderflowisdrawnfromtheheadpondthroughanauxiliaryhydropowerstationontheleftabutment,drivenbytheheaddifferencecommandedbythefishlocks.Thefishladderthereforebecomesasourceofenergygainandnotenergyloss.Dischargefromthefishladdercontributestotheattractionflowatthedownstreamentrancesandreducesthetailwaterpumpingrequirement.

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The downstream system is represented by the blue arrows in Figure 7.12. Openings are provided across theupstreamfaceof thepowerstationabove thepower intakes. Theattractionflowofapproximately2.5%ofpowergenerationdischargeisprovidedbyapumpingstationfromtheheadpond. Fish are collected in a pond at the right side of the power station and sluiced intermittently down the ramp in the intermediate block. This intermittent system limits the amount of water that by-passes the generating plant.

These provisions for energy management of the upstream and downstream attraction flowshave effectively avoided a loss of 7.5% of the overall scheme output. It is commercially andenvironmentally important that careful consideration is given to energy recovery onmajor fishpassage systems.

7.3.3.3 Low head barrages


Notwithstandingprovisionsforsedimentmanagementandfishpassage,mediumheadbarragesinthe range of 20 to 40 m head, still constitute a break in river connectivity. The spillway structures showninFigure7.7areabarriertofishmigration,evenwiththegatesfullyopenandthereservoirlevel drawn down. Similarly the vertical axis turbine configuration of the power station showninFigure7.8 isahazardfor largerfishspecies,evenwiththeselectionof lowspeedplantandimproved runner geometry.

An alternative approach is to adopt a greater number of low head barrages with a design that can completely restore river connectivity in either direction when required. A typical head range would be 5 to 15 m. An example of a barrage designed to have these characteristics is shown in Figure 7.13.ThelocationistheMerseyEstuaryinLiverpool,UK.Thereisalmostnofluvialdischargeintheestuarybutthetidalrangeissignificantandthebarrageindicatedwouldhaveaninstalledcapacity of 700 MW and be capable of delivering approximately 1,000 GWh/yr through ebb tide generation. The structure comprises low speed horizontal axis bulb turbines and sluices gates as shown in Figure 7.14. For the Mersey project these structures were designed as caissons that couldbe fabricatedoffsiteandfloated intoposition. Navigation locksareprovidedon the leftabutment.Thesillofthesluicegatesislevelwiththebedoftheestuaryandoffersnoobstructionwhenfullyopen.Verticalliftgatesareshownbecauseofthebi-directionalflow.Onariver,aradialgate would be a preferable solution.

With reference toFigure7.13, thestructureoffersno resistance to landwardflowon the rising(flood) tide. Thesluicegatesareopenand the turbinesareunloadedwith theblades rotated.Fishandsedimentcanpassundernaturalconditions.Onthefalling(ebb)tidethesluicegatesandturbinesarecloseduntilsufficientgeneratingheadhasbeendeveloped.Theebbtideisthenturbined at a head ranging from 10 to 5 m. Once the head drops below this range the sluice gates are re-opened to complete the ebb cycle and full connectivity is restored. Fish and sediment can passinaseawarddirection.(Grant&Libaux–2011)

Asimilarlydesignedstructurecouldbeconfiguredforasingledirectionfluvialcondition.Powergenerationcouldbesuspendedandfullconnectivityprovidedduringperiodsofpeakfishmigrationorsedimenttransport.Ahighdegreeofoperationalflexibilitywouldbeprovidedbyastructureofthis type.



Flood tide:

All sluice gates open and turbines unloaded.

Barrageoffersnoobstructiontoflowandfullfishandsedimentconnectivityisprovided

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Ebb tide (1st stage):

Gatesareclosedandaheaddifferencedevelops.Turbinesoperatedownto5mheaddifference



Ebb tide (2nd stage):

Onceheaddifferencehasdroppedbelow5mgatesareopenedandturbinesareunloaded.

Remainingpartoftheebbtidecycleissluiced,restoringfishandsedimentconnectivity.

Figure 7.13. Mersey Low Head Tidal Barrage, Liverpool UK (Source: Peel Energy Ltd).

Figure 7.14. Mersey turbine and gate caissons (Source: Peel Energy Ltd).

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7.3.3.4 Very low head technologies


Technologies are commercially available for power generation down to heads of approximately 2m. These installations are typically associatedwith zero fishmortality and require relativelylittle infrastructure. Examples include stream current devices, venturi energy converters, helical screwsandverylowheadreactionturbines.Poweroutputsare,bydefinition,verylow.Thesesolutions may be of interest on small water courses in isolated rural areas but not major generation facilities at a national scale.

An example of a high connectivity installation using commercially available very low head technology is shown in Figure 7.15. This barrage was one of many similar structures engineered for Voies Navigable de France for adoption on the Ainse and Meuse Rivers to maintain navigable water levels. The structure shown comprises a rubber dam in two sections and three MJ2 TechnologiesR turbines on the right abutment. The generating head is 2 m and the combined power output is 1.5 MW. The crest level of the rubber dams can be adjusted and full river connectivity can be provided bydeflatingthestructure.Theturbinehousingsarehingedandcanbeliftedoutofthewaterformaintenanceorwhenunobstructedriverflowisrequired.

It is noteworthy that a rubber dam was originally adopted for the diversion weir on the Theun HinbounprojectinLaoPDR.Thisstructurewasfoundtobevulnerabletodamagebyfloatingtrashandwasreplacedin2000byafixedconcreteweir.

Figure 7.15. Very low head barrage (Source: VNF France).



7.3.3.5Partialbarrages


An alternative approach to retain river connectivity is to construct a partial scheme that leaves much of the natural river channel unobstructed. There are many such schemes around the world, typicallyonmajorriverssuchastheZambezi(VictoriaFalls),theCongo(Inga)andtheMekong(DonSahong).Theopportunityforsuchschemesdependsonspecifictopographicfeaturessuchas central islands and major waterfalls with multiple channels. One such scheme that is currently underconsiderationistheNgonyeFallsprojectontheupperZambeziintheWesternProvinceofZambia.TheproposedlayoutisshowninFigure7.16.Theprojectleavesthevisualspectacleofthe Ngonye Falls unchanged and diverts water from the subsidiary left river channel into a canal andlowheadpowerscheme.Thereiseffectivelynobypassedreachwiththisarrangementandsedimenttransitisvirtuallyunaffected.Theimpactonfishmigrationiscurrentlybeingstudiedbutitis anticipated that the Ngonye Falls provide a natural barrier to upstream migration and the project willnotsignificantlychangethenaturalcondition.

Figure 7.15. Ngonye Falls partial barrage - Zambia (Source: Multiconsult).

7.3.4 Impoundments

Guideline table reference IV.2

7.3.4.1 Water quality

Impoundments created for storage schemes typically result in large residence times and thermal stratification.TheobservedstratificationcycleintheNamTheun2reservoirisshowninFigure

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7.16.StratificationisstrongestinthehotperiodfromApriltoJuly.ItthenweakensinthewetseasonfromAugusttoOctoberduerainfallandcatchmentinflows.Thereservoirbecomesmonomicticinthe cold season between November and March. The hypolimnion, when present, typically has low dissolved oxygen and high iron content.

Figure7.16.Nakayreservoirstratification–LaoPDR(Source:NamTheun2PowerCompanyLtd).

Water quality in the early years of operation is usually linked to clearance of biomass from the reservoir area. The Nakay Reservoir area was not generally cleared of forest cover prior to impounding. However selected areas near critical structures were cleared and commercially valuable timber was extracted. Considerations against general clearance at Nakay included:

• The environmental implications of clearing an area of 450 km2 of forest and burning the waste material;

• The recognition that a significant percentageof forest biomass is belowgroundat is notremoved by clearance;

• The potential for re-growth following primary clearance and during each recessional dry season period.

An examination of considerations regarding reservoir clearance is presented in the literature (Salignat et al–2011).

AnanalysisofCO2equivalentemissionsfromthereservoirundertakenbytheNamTheunPowerCompany is shown in Figure 7.17. In the early years of operation the CO2 release is assessed as approximatelyonethirdoftheamountreleasedperkWhbycoalfiredgeneration.Thelongtermfiguredropstoasmallfractionoftheequivalentemissionsforthermalpowergeneration.



Figure7.17.NakayreservoirCO2emissions–LaoPDR(Source:NamTheun2PowerCompanyLtd).

7.3.4.2 Outlet Structures

A key design consideration for the outlet structures from large reservoir impoundments should be to avoid or limit the release of low water quality into downstream rivers.

Forenvironmentalflowreleasestructuresthiscantypicallybeachievedbymultiplelevelintakesdesigned to take water only from the epilimnion. This is achieved at the Nam Theun 2 Nakay Dam by inserting and removing stop logs at the intake structure as the reservoir level varies, so that only the top 0.5 m of reservoir water is drawn into the intake. The release back into the river is commandedbya fixedconevalvedesigned todisperse the jet andpromoteaeration. Thearrangement is shown in Figure 7.18.

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Figure7.18.Nakayreservoirriparianrelease–LaoPDR(Source:Multiconsult).

Water abstractions from power intakes typically present a greater challenge because the intake must be set deeper in the hypolimnion so that it can command the full operating range of the reservoir. Multiple level intakes can be designed but are typically much less convenient to operate.

An alternative approach is to consider the siting of the intake structure. At Nam Theun 2 the power intake is set at the end of a long approach channel. Flow towards the intake in this approach channel causes re-mixing of the stratified layers and the net result is improved water qualitydownstream. A view of the intake and approach channel prior to impounding is shown in Figure 7.19.

Figure7.19.NamTheun2powerintakeapproachchannel–LaoPDR(Source:NamTheun2PCLtd).



7.3.4.3 Aeration Weirs

An aeration weir has been provided downstream of the power station at Nam Theun 2 to provide an additional system for improving water quality before the discharge is released into the receiving river. The aeration weir is shown in Figure 7.20. The weir dimensions are based on empirical data obtainedfromPetitSautinFrenchGuiana(Abrilet al–2008).Itwasfoundthatadispersedfallofapproximately2mwassufficienttorelease80%ofdissolvedmethaneandensureaminimumdissolvedoxygencontentof2mg/L.Thespecificdischargeontheweircrestatdesigndischargeis1m3/s/m.TheflowdispersionattheNamTheun2aerationweirisachievedbyatimberlatticeonthedownstreamsideoftheweircrest.Thislatticeisexpectedtodeteriorateoverthefirstfewyears of operation, after which it will no longer be required. The weir performs a long term function of maintaining a high water level in the downstream channel under a full range of discharges so that water can be abstracted by gravity for irrigation.

Figure7.20.NamTheun2downstreamaerationweir–LaoPDR(Source:Multiconsult).

7.3.5 Diversion / Intra Basin Transfers

Guideline table reference V.2.5

Asignificantengineeringconsiderationforintrabasintransfersistomakeprovisionforthereceivingriver to withstand a greatly increased discharge. In the case of the Nam Theun 2 project it was determinedthat itwasnotfeasiblefortheNamKathangatthepowerstationlocationtoacceptthe additional power generation discharge. An engineered downstream channel was therefore required to convey the power station discharge a distance of 27 km to the larger Xe bang Fai. The route(3)isindicatedonFigure7.21.Thefirst8kmofthedownstreamchannelislinedtopermithigherflowvelocitiesandasmallercrosssection.Thisapproachwasadoptedtominimiseland

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take through an area of productive rice paddy. The hydraulic grade line was kept above ground level by the aeration weir shown in Figure 7.20 to facilitate gravity fed dry season irrigation. The remainingsectionsofthedownstreamchannelareunlinedandreceiveinflowsfromlocalwatercourses. The downstream section of the channel was formed by enlarging the natural course oftheNamPhit.Controlweirsareprovidedatintervalsalongtheunlinedsectionstolimitwatervelocitiesduringde-wateringandre-fillingofthechannel.

Figure7.21.NamTheun2downstreamchannel–LaoPDR(Source:NamTheunPowerCompany Ltd).



7.4 Construction

7.4.1 Site controls

Environmental mitigation measures should be incorporated into the construction process by analysing the potential impacts of access, working areas, sources of materials, equipment and materials management and construction methodologies and defining actions to eliminate ormitigate these impacts. To this end, it is standard good industrial practice to require the contractor to prepare and submit an environmental monitoring and management plan for specialist review and approval.Thisplanshouldberequiredtoincludespecificsub-planswhichwouldtypicallycoverthe following:

• ErosionandSedimentControlPlan

• SpoilDisposalPlan

• QuarryManagementPlan

• WaterQualityMonitoringPlan

• Chemical Waste/Spillage Management Plan

• EmergencyPlanforHazardousMaterials

• EmissionsandDustControlPlan

• NoiseControlPlan

• PhysicalCulturalResources

• LandscapingandRevegetationPlan

• VegetationClearingPlan

• WasteManagementPlan

• Reservoir Impoundment Management Plan

• Environmental Training for Construction WorkersPlan

• On-siteTrafficandAccessManagementPlan

• Explosive Ordnance Survey and Disposal Plan

• Constructions Work Camps and SpontaneousSettlementAreasPlan

Inaddition,aManualofBestPracticeinSiteManagementofEnvironmentalMattersandaProjectStaffHealthProgramshouldbedraftedand reviewedbyan independentexpert.Toachieveaconsistent approach, such standards should be imposed by Government through the Concession Agreement.

In addressing the requirement for a high standard of environmental monitoring and management duringconstruction,mostmoderncontractorsrecognisethattherearecommercialbenefitstobegained from good site practice. Site maintenance costs can be reduced and waste construction materials frequently have commercial re-sale value if properly separated and managed.

7.4.2 Construction access & material sources

Major environmental impacts are sometimes caused by poor site planning and inadequate consideration of construction access. Temporary infrastructure and construction roads should be kept away from environmentally sensitive areas. In order to achieve this, it may be of value, for example, to consider the use of quarry locations that are not visually intrusive (e.g. in low lying areas)andthatareclosertotheconstructionsite,althoughtheymaynotprovidethebestmaterial.Consideration should also be given tominimising construction roads and specifically avoidingroads in steep terrain by adopting alternative routes. Alternative forms of access such as tunnels or constructinganaerialcablewaycanofferlessenvironmentallydamagingsolutions.Whereroads

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on cross slopes are required, excavated material should always be carried away and disposed of in designated and landscaped spoil areas and not dumped down valley slopes.

7.4.3 Erosion protection

During construction, open excavations and works areas require temporary protection to prevent erosion and contamination of water courses with sediment. Figure 7.22 shows good practice at theworksareafortheNamNgiep1regulatingdampowerhouse.Thecofferdamisarmouredontheouterfacewithrockfillandtheinternalslopesareprotectedwithgeo-fabrictopreventerosion.Waterpumpedfromexcavationsandsurfacerunofffromrainfallisdirectedtosettlementpondsbefore being returned to the river. Spoil areas have been landscaped and positioned away from theriver. Temporaryexcavationshavebeenprofiledtostableslopeswithestablisheddrainagepaths. A complex works area is maintained in a tidy and organised condition.

Figure 7.22. Nam Ngiep 1 regulating powerhouse works area, Lao PDR (Source: Nam Ngiep 1 PC Ltd).

7.4.4 Re-vegetation

Construction activities inevitably result in disturbance of vegetation and exposure of soil slopes. Re-establishment of indigenous vegetation should be the ultimate objective but can rarely be achieved insufficient timetopreventerosion,environmentalde-gradationandcontaminationofnatural water courses by sediment. A programme of soil stabilisation is typically required before revegetation is attempted. Indeed the most appropriate sequence in tropical climates is:

• soil stabilisation;

• followed by re-vegetation; and

• finally,re-forestation.



Areasthatareplantedduring thedryseasonareverydifficult tomaintainandareasplanted inthe wet season are likely to be damaged by erosion before root systems become established. There are a number of strategies for soil stabilisation that can be employed but some form of de-gradablefabricprotectionistypicallythebestapproach.OnRoad13NorthinLaoPDRrecentlycreated cut slopes are protected with coir matting. This protection is costly but provides shade and moisture retention during the dry season and protection from rainfall impact and erosion during the wet season. This allows indigenous vegetation to naturally colonise the slopes. The use of this approach is shown in Figure 7.23.

In other areas on Road 13 soil reinforcement has been provided by planting a sterile hybrid form of Vetiver grass along contour lines. This grass variety will rapidly establish a deep root system. Vetiverisunpalatabletobrowsinglivestockandthesterilevarietydiesoffafterapproximatelyfouryears, by which time natural vegetation has colonised the slope. In this manner soil stabilisation is achieved without introducing invasive alien species.

Figure 7.23. Soil stabilisation on Road 13 North, Lao PDR (Source: Multiconsult).

7.4.5 Access restriction

Consideration should be given at the construction stage to environmental problems that are likely to occur during the lifespan of the project. An example would be the de-commissioning of construction roads that might otherwise provide access for environmentally damaging activities such as timber extraction. This can be achieved at low cost by removing the drainage structures and preventing further use of unwanted roads. If access must be retained for social reasons, consideration should be given to restricting the type of vehicle that can use these roads. At Nam Theun 2 bridges with a

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limited width have been built to prevent large vehicles from accessing densely forested areas. An example is shown in Figure 7.24 where only small farm tractors and motorbikes can gain access to theoppositebankofthedownstreamchannel.Pedestrianrefugeshavebeenprovidedatlocationsalong the bridge.

Figure 7.24. Access bridge across the downstream channel of Nam Theun 2 Hydropower Project, Lao PDR (Source: Multiconsult).

7.5 Operation

7.5.1 Annual / Inter Annual Changes to Flow

7.5.1.1Changestoseasonalflowpatterns

Guideline table reference I.2.6

The provision of seasonal storage provides a valuable function to power system operators. Figure 7.25 shows the reservoir level trajectories for the Nakay Reservoir at Nam Theun 2 since commercial operation commenced in 2010. Other major storage schemes in the region follow similar patterns. The reservoir level is progressively lowered between December and the following June each year aswater is takenoutofstorage toaugment thedryseason inflow. FromJune toOctober theinflowexceedspowergenerationrequirementsandthereservoirre-fills.Thisapproachpermitstheproject to deliver a near constant power output throughout the year. However it also results in the downstream discharge being approximately constant throughout the year.

If it is preferable for environmental reasons to maintain seasonal patterns in downstream discharge then a decision can be made to change the operation of the project. Reservoir draw down and energy production during the dry months of the year could be reduced, and spilling during the wet months of the year would therefore increase. No engineering changes are required but the commercial consequences would be considerable.



Thedownstreamenvironmentalbenefitsofthisrevisedformofoperationwouldneedtobeassessedagainst the increased energy costs for the consumer and additional energy and installed capacity requirements from potentially less environmentally satisfactory forms of generation elsewhere.

Figure 7.25. Nakay reservoir water levels, Lao PDR (Source: Nam Theun Power Company Ltd).

7.5.1.2 Cascade operations


Cascadesofstorageschemesmayoffertheopportunitytodeliverlargelyuniformpowerthroughoutthe year whilst reintroducing some seasonality in the downstream discharge. The cascade shown inFigure7.26comprisesaredprojectwhichwasconstructedfirst,andanupstreamblueprojectwhich was constructed second.

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Figure 7.26. Reservoir cascade operation (Source: Multiconsult).

The optimum operating upper and lower rule curves for the red project are shown as chain dotted lines. Once the blue project is constructed seasonal regulation is introduced and the red project no longer needs to use all its operating storage. The red reservoir level therefore becomes more uniform and higher, thereby providing more generating head. The average water level becomes as shown by the solid red line in Figure 7.26.

Optimum operation of the blue project is within the rule curve envelope.

If a third project was added upstream of the blue project then the same change would occur and theaverageoperatingcurvesfortheblueandredprojectswouldbecomeflatterandhigher.Underthis condition it may be possible for the red project to turbine more water in the wet season than in the dry season, thereby re-introducing some seasonality in the downstream release.



7.5.1.3Changestofloodfrequencyandmagnitude


Peakfloodmagnitudesintheregionaretypicallyhighandmostprojectsrequiregatedspillwaystoprovidethenecessaryflooddischargecapacity.Gatedspillwayspermittheoperatorstocontrolspillwayreleases.Withtheexceptionofextremefloods,itwillbegenerallypossibleforschemeoperators to release floods inaccordancewith thenaturalmagnitudeor frequency. Therewillhowever be commercial consequences.

WithreferencetoFigure7.25lowreturnperiodfloodsaretypicallycapturedbythereservoiruntilfullsupplylevelisreached.Asaconsequence,manysmallerfloodeventsarenolongertransmitteddownstream. However this is an operational decision and not an engineering characteristic of the project.Naturalfloodeventscouldbereleasedduringreservoirfilling,ifrequiredforenvironmentalreasons.

Thereleaseoffloodeventsduringthereservoirfillingperiodincreasestheriskthatareservoirfullcondition may not be reached at the end of the wet season. It would also reduce the available head for power generation. The project owners would need to be compensated commercially if this form of operation was required.

Oncefullsupplylevel isreached,projectswithgatedspillwayswill typicallyreleasesuchfloodswithoutmodificationandanentirelynaturalfloodsequenceshouldbeachieved.Moreextremeeventswillbeattenuatedbyallowingthereservoirleveltoriseabovefullsupplylevel.ThePMFevent for the Nam Ngiep 1 project is shown in Figure 7.27.

Figure 7.27. Nam Ngiep 1 PMF attenuation, Lao PDR (Source: Nam Ngiep 1 Power Company Ltd).

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Attenuation of major flood events by using reservoir storage would normally be seen asenvironmentallybeneficial.

ForrunofriverMekongmainstreamschemestherequirementtopassfloodswithoutmodificationshould be automatic and be without commercial consequence.

The use of upstream hydrometric networks and cyclone forecasting systems is standard for most majorprojectsintheregionandfloodmanagementistypicallybasedonpredictedinflowssothatfloodfreeboardisnotusedunnecessarily.Thisdatawouldprovidethebasisforalternativefloodmanagement if required.

7.5.2 Inter basin transfers

Guideline table reference V.2.4, V.2.5

7.5.2.1 Flood management

Inter-basin transfers can require operational restrictions to avoid adverse impacts on the receiving river. The Nam Theun 2 project downstream channel joins the Xe Bang Fai at the location shown onFigure7.28.Thisareaispronetofloodingduringthewetseasonandadditionalinflowsfromthedownstreamchannelwouldworsen local flooding. TheConcessionAgreementandPowerPurchaseAgreement therefore impose a requirement that the output of the Nam Theun 2 isprogressivelyreducedandfinallystoppedatpre-definedgaugereadingsatMahaxaidownstream.Whilstthismeasuredoesnotpreventfloodinginthearea, itdoesensurethattheproject isnotresponsible.

7.5.2.2 Hydropeaking

Discharges into the Xe Bang Fai from the downstream channel retain the generation peaks resulting from the operation of the power station. In the wet season these variations are negligible comparedwiththenaturaldischargeintheXeBangFai.Inthedryseasonthesevariationsinflowcanrepresentinexcessofa200%changeindischargebutthiswasassessedtobeacceptable.The rates of change of discharge are however limited by the re-regulating pond as described in Section 7.3.2.3.

7.5.2.3 Impact compensation

DryseasonflowsintheXeBangFaiareconsiderablyincreaseddownstreamoftheconfluencewith thedownstreamchannel. There is also a backwater effect upstreamextendingpastBanSomsanouk shown on Figure 7.28. These changes have resulted in loss of river bank gardens and changedfishbreedingpatterns,allofwhichimpactlocallivelihoods.Anextensiveprogrammehasbeenimplementedtoassesstheseimpactsandprovidecompensationtoprojectaffectedpeople.



Figure7.28.NamTheun2downstreamchannelconfluence,LaoPDR(Source:Multiconsult).

7.5.3 Adaptive management

Guideline table reference I.4, II.4, III.4, IV.4, V.4

Monitoring and adaptive management during operation is an essential part of the environmental mitigation process. Some operational changes can be introduced without commercial consequence and adoption should therefore not present any particular problem. However changes that require capital expenditure or that impact energy generation and revenue cannot be imposed without compensationtotheprojectowners.Suchchangesmaybeverydifficulttoimplement.

Itisthereforemostimportantthatpotentialrequirementsforadaptivemanagementareidentifiedat the feasibility stage and incorporated in the design and commercial rationale of the project. The ESIA needs to be comprehensive and anticipate as many future requirements as possible. Design provisions for future changes should be incorporated into the works and provisions made in theConcessionAgreementandPowerPurchaseAgreementforchangestobeimplementedandcompensated.

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7.6 Dam Safety Guidelines and Recommendations

7.6.1 General Considerations

Dam safety is a subject of paramount importance in hydropower development, and as such all risk areasthatmayaffectsafetyduringdesign,constructionandoperationshouldbetakenintoaccount.It is generally desirable to avoid a risk altogether rather than manage the consequences. Standard proceduresaroundtheworld(e.g.TheConstruction(DesignandManagement)Regulations,UKGovernment,2015)requiredesignerstodemonstratethattheyhaveidentifiedpotentialrisksduringconstruction, operation and de-commissioning and have taken steps to either remove the risk from theirprojectlayout,mitigatetheriskbyreviseddesignoutlinesorprovidedeffectivewarningandsafety measures for residual risks. Where risks are unavoidable, suitable levels of risk for each projectcomponentshouldbedefined.Ifdefinedlevelscannotbeachieved,thenimplementationshould not proceed.

A consistent design approach is required following approved standards and guidelines, utilising safetyfactorsthataresufficientlyhighandprovidingsystemredundancies.Seismicstudiesshouldbeproject-specific,basedonconditionsofthelocalarea.Regionalstudiesshouldgenerallynotbeacceptedforfinaldesign.Theselectionofdesignfloodsstandards,althoughvaryingwidelyaround the world, should be undertaken using a common approach for all projects in the same river basin and should be in line with national legislation.

The design of hydropower projects should be undertaken bearing in mind future operation and maintenance of the schemes. As an example, isolating facilities should be considered in power tunnels and spillway bays for inspection and repairs, and provisions should be made for instrumentationfordammonitoringpurposes(e.g.leakagesandmovements).AttheNamOu6HydropowerProject,intheLuangPrabangprovinceofLaoPDR,ageo-membranerockfilldamhas been adopted which is considered to be one of the highest in the world of this type. In order that the upstream face may be inspected and repaired in the future a drawdown tunnel has been provided in order to lower the water levels in the reservoir during the dry season. In addition there isnobackfillorprotectionontheupstreamfacesothatitwillremainaccessible.Theupstreamface of the dam prior to impounding is shown in Figure 7.29.

239 | Chapter 8. Ecosystem Services – Status, Risks and Mitigation


Figure 7.29. Upstream face of the Nam Ou 6 dam, Lao PDR (Source: Multiconsult).

Consideration should always be given to alternative design solutions to reduce or eliminate safety risks during operation by simply changing the layout of the project elements, eliminating high risk elements or introducing new project elements.

7.6.2 Gated Spillways

In general, gated spillways should be avoided; thus eliminating the risk of gate failure and operator error. Where gated spillways are unavoidable, it is essential to provide multiple redundancies of power supplies and related systems, and ensure that adequate opening and closing rates can be achieved.Ifstandbydieselgeneratorsareprovidedthenspecificmeasuresarerequiredtoensurethat there is an adequate fuel supply and the engine can always be started.

It is unlikely that there will be any alternative to the adoption of gated spillways on the mainstream Mekongprojects.Aspecificissuethatrequiresconsiderationontheseprojectswillbeperformancefollowing a full load rejection by the generating units. For example, the Xayaburi project has a design generation discharge of 5,140 m3/s and this discharge must be immediately transferred to the spillway in the event of a station trip, otherwise there would be an unacceptable impact on discharge and tail water level downstream.

AttheBujagaliHydropowerProject,ontheVictoriaNile,theservicespillwayisanairregulatedsiphon with a capacity equal to the full station load. If a station load rejection occurs there is very little time to open the bottom outlet gates and the siphon replaces the discharge of the power station with minimal reservoir surcharge. This arrangement is passive and intrinsically safe. A generalviewoftheBujagaliProjectisshowninFigure7.30.

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Figure 7.30. General view of the Bujagali Hydropower Project, Uganda (Source: Multiconsult).

7.6.3 SafetyPlans

ItisessentialthataHydroSafetyPlan,anEmergencyPreparednessPlanandaFloodInstructionPlanareallinplacepriortoreservoirimpoundment.

AHydroSafetyPlanisrequiredtoprotectoperatingstaffandmembersofthepublic.Typicallythisplanincludesmeasuressuchassafetyfencing,securitylighting,floatingboomsneartheentrancesof power intakes, spillways and other water releasing structures, warning signs near bodies of water that may be subject to changes in level, manned guardhouses and procedures to restrict accesstoauthorisedpersonnelonlyandaudiblewarningswhereflowsaredischarged.Theplanshould also require the engagement of the local community with the implementation of awareness programmestoinformmajoroperationalevents(e.g.impoundment),safetyincidentsandprojectrisks to be avoided.

AnEmergencyPreparednessPlanshouldidentifyissuesduringnormaloperationandmaintenancethatmayleadtoanemergencyandrequireaspecificresponse.Flowchartsshouldbedevelopedto determine the responsibilities and actions to be taken as the problems develop, whether they can be resolved or not. These actions may include monitoring at more frequent intervals, internal communications,modifyingtheoperationalparameters,repairworksandnotificationtothepublicat risk. The plan should be developed in accordance with recognised international guidelines such astheFederalGuidelinesforDamSafety-EmergencyActionPlanningforDamOwners,publishedby the Federal Emergency Management Agency, US Department of Homeland Security. Sections within the plan should include as a minimum:



• Emergencyidentificationandevaluation

• Preventative Actions

• NotificationProceduresandFlowcharts

• Responsibilities under the Plan

• Preparedness

• Downstream Impacts

The appendices to the plan should typically include:

• Project Details

• Operators Instructions

• Reservoir Water Level Charts

• Inundation Maps and Predicted Water Levels

• Response during darkness and adverse weather

• Communication systems

• Emergency Supplies and Equipment Sources

• Emergency Power Supplies

• Access to Project Land and Structures

• Training

AFloodInstructionPlandefinestheproceduresandresponsesrequiredfortheoperationofgatedspillways and outlets, ensuring that the safety of the dam and appurtenant structures is maintained atalltimes.Theoperationalrulesundernormalconditionsandduringfloodeventsshouldproduceacceptable downstream releases for the community and the environment, avoiding releases larger than those prior to the construction of the project, sudden increases in water levels and out of bankdischarges,wherepossible.Inaddition,proceduresshouldbedefinedforthenotificationofdownstream population centres and dam owners when large releases are expected.

Operation & maintenance manuals should be drafted to provide guidance for the safe operation of the project, instruct monitoring procedures and prevent the deterioration of the project elements, sothattheprojectmayfulfilitslifecycle.

7.6.4 Expert Review

Design, construction and operational approaches and procedures should be reviewed by external experts from an early stage. It is frequently the case that external review is only commenced after Financial Close has been achieved. This always is too late since key design decisions will have beenmadebythisstagethatarecontractuallydifficulttochange.

TheWorldBank’sOperationalPolicy4.37requiresanindependentpanel,consistingofthreeormore experts, to review and advise on matters relative to dam safety and other critical aspects of

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the dam, its appurtenant structures, the catchment area, the area surrounding the reservoir and downstream areas. It is desirable to extend the terms of reference to cover other areas such as project layout, technical design, construction procedures and other project elements such as power facilities,riverdiversionduringconstruction,navigationbypassesandfishpassagearrangements.Alternatively, it may be preferable to appoint a consulting engineering company instead of an expert panel, as this could provide access to a broader range of expertise. In either case, it is essential that the recommendations given by the external party are taken into consideration.



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8 Ecosystem Services – Status, Risks and Mitigation



The ecosystem services spans issues covering all the previous thematic areas and is as such treated here in a separate Chapter. Ecosystem services has also close links to, and underpins, human livelihood for those living in and around LMB. Understanding mitigation of ecosystem services is still in its incubation period, however it should gradually be integrated into more traditional mitigation approaches and themes. An initiative in MRC to undertake this integration is described in Chapter 8.1.

8.1 Status and Overview - Concept and classification of ecosystem ser-vices

Ecosystem services are defined as “the benefits people obtain from ecosystems” (MillenniumEcosystemAssessment 2005). Ecosystem services have become an important research topicin sustainability science. A number of papers addressing ecosystem services has increased exponentially,especiallyafterthecompletionoftheMillenniumEcosystemAssessment(MA)in2005 (Carpenter et al.2009,Fisher,Turner,andMorling2009).Despitethis fastgrowing, thereis yet consensuson their concept and classification system.For instance, ecosystemserviceshave been interchangeably used with other terms such as ecological, landscape or environmental servicesduetodifferentunderstandingsoftheirconcept(Lamarque,Quetier,andLavorel2011).MAclassifiesecosystemservicesintofourcategories:provisioning,cultural,regulatingandsupportingservicesandmanysubcategoriesundereachcategory(MillenniumEcosystemAssessment2005).MA’sclassification(Figure8.1)isthemostwidelyadoptedsystem,butsomescholarshavearguedthat it is not appropriate for a practical valuation purpose as it leads to double counting the values of some ecosystem services in the aggregation of economic values of an ecosystem (the total economicvalueorTEVisthesumofdirectuse,indirectuse,optionuse,andnon-usevalues).Forinstance,itisarguedthatecosystemprocessesthatdonotdirectlyaffecthumanwell-beingarenotecosystemservices(Wallace2007);regulatingservicesshouldonlybeincludedinthevaluationifthey have an impact outside the direct ecosystem services to be valued (Hein et al.2006).

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valu

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va

lues

Exis

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Figure 8.1. Linkage between ecosystem services and constituents of human well-being (Source: Emerton 2006, cited in; WWF-Greater Mekong 2013).

A more recent classification system proposed by the European Environmental Agency (EEA)groupsthemanysubcategoriesproposedunderMA’sclassificationintothreesomewhatdifferentcategories: provisioning, regulating and maintenance, and cultural services (USIAD Mekong AdaptationandResiliencetoClimateChange2015).EEA’sclassificationhasbeenfurtherrefinedto provide a “so called” uniform, standardized and comprehensive system for the valuation ofecosystemservices(Figure8.2),butthepracticalityofthissystemremainstobeseen.

Figure8.2.Typesandclassificationofecosystemservices(Source:USIADMekongAdaptationand Resilience to Climate Change 2015).



Very recentMRC (2015)hasdeveloped theapproacheven further tobe tailored for theLMB,by combining the assessment of ecosystems components with that of ecosystem services assessment. Ecosystem assessment can involve an assessment of the ecosystem components and/or an assessment of the ecosystem services that are derived from the interaction of those componentsinsupportofhumanwell-being(Figure8.3).MRCusesthesameecosystemservicesclassificationasthatofMEA,e.g.;provisioning,cultural,regulatingandsupporting.

There is a direct link between the ecosystem components and services. Changes in the biophysical ecosystem components will have an impact on the ecosystem services that are produced. For example,significantdisturbanceofthehydrologicalregimeislikelytoimpactonthecapacityoftheecosystemtoproducefishforfoodprovision.Comprehensiveecosystemassessmentswilloftenconsider biophysical changes as well as the related changes in ecosystem services.

(Biophysical) Ecosystem Assessment

Ecosystem Services Assessment

More sensi�ve to impacts

More important for decisions

Biological

Hydrological Physico

chemical

Provisioning (e.g. food from fish)

Regula�ng (e.g. flood control)

Cultural (e.g. aesthe�c, spiritual)

Suppor�ng (e.g. habitat)

Monitoring

Provides data and informa�on to support assessment ac�vi�es

Modelling

Figure8.3.Thedifferentactivitiesinvolvedinecosystemandecosystemservicesassessmentsas of MRC (Source: Discussion Note on MRC Ecosystem and Ecosystem Services Activities, 18th August 2015).

8.2 Valuation of Ecosystem Services at Risk in LMB

A number of Mekong-related publications emphasises the importance of the concept of ecosystem services in understanding, valuing and managing our environmental assets and the necessity of these in basin development planning. Without valuation, economically important impacts of

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new infrastructure or development may be overlooked and accordingly decision-making tends to be biased towards new infrastructure or development. Among many publications reviewed, two (Costanza et al. 2011, WWF-Greater Mekong 2013) stand out to be most recently andcomprehensively analysing the values of Mekong ecosystem services. A more recent publication (USIADMekongAdaptationandResiliencetoClimateChange2015)genericallyhighlightspolicyvenuesintheLMBcountries(Cambodia,Laos,Thailand,andVietnam)whereecosystemservicesvaluation can play a role.

Costanza et al. (2011) focus their valuation of the services theMekongRiver provides to thepopulationoftheLMBthroughitsfisheriesandwetlands.AtvariousdiscountrateswithaspecifiedreplacementcostofUSD3.00/kg,thenetpresentvaluesofthelossincapturefisheries,thegaininreservoirfisheries(duetotheincreaseofdams),andthegaininaquacultureproduction(aprimarymitigationmeasureforlostcapturefisheries)wereestimated.Inaggregate,thevalueofincreasedreservoirfisheriesandaquacultureproductioncould replace the lostofcapturefisheriesvalue,under certain economic assumptions but not under others.

Theforgoneeconomicvalueduetothelossofthreetypesofwetlands(floodedforests,marshes,and inundatedgrasslands)under theestablishedscenarioswasestimatedatdifferentdiscountrates. The ecosystem services of wetlands in this case were claimed to embrace water supply, waterflowregulation,wastetreatment,floodprotection,foodproduction,rawmaterialproduction,habitat refuges, recreation, and aesthetics, but the estimation of the total economic value of the wetlands was not based on analyses of changes in values of these ecosystem services. A value transfer technique (Brander 2013) was instead used to transfer a unit value (USD/ha/year) ofeach type of the three wetlands from a recent Mississippi study. The results indicated a net loss inthetotalvaluesduetolostwetlandsintheLBMunderthe‘definitefuturescenario’and‘6damscenario’andanetgaininthetotalvaluesduetogainedwetlandsunderthe‘11damscenario’.Thelatterresultreflectstheprojectedincreaseinwetlandsfromdamreservoir inundationandincreased rainfall associated with climate change.

The recalculation of the values calculated in theBDP2 to reflect the changes in values of theecosystem services (fisheries and wetlands) under the established scenarios and at differentdiscountratesyieldedresultsasshowedinFigure8.4.Therevisedtotaleconomicvalueat1%discountrateturnsnegativeunderallscenarios.At3%discountrate,therevisedtotaleconomicvalue still turns negative under the 11 dam scenario or the revised economic gain under either thedefinitefutureor6damscenariodropstoaminimallevel.At10%discountrate,therevisedeconomic gains under all scenarios considerably drop, but are still positive. These values has been revisedandslightlyupdatedinarecentWorkingPaper(Intralawan,WoodandFrankel,2015),butconclusions remains largely the same.



Figure 8.4. Comparison of original and revised NPVs for the three scenarios assuming 10%, 3% and 1% discount rates (Source: Costanza et al. 2011).

ThepublicationofWWF–GreaterMekong(2013)providesananalysisofthevaluesofecosystemservices the population of the LMB obtains from four types of ecosystems (forests, freshwater wetlands,mangroves,andcoral reefs)under twodefinedscenarios (businessasusual–BAUandgreeneconomygrowth–GEG).Thevaluationonlycover theecosystemservicesofmostimportance, for which information is available, and for which real revenues can be attributed in ordertofocusoneconomicgainsontheground.Aunit-valuetransfertechnique(Brander2013)wasthebasisforthevaluation(noprimarydatawascollected).Table8.1summarisestheper-unitvalues of ecosystem services derived from various valuation studies in the Lower Mekong region (a database of previous estimates of ecosystem service values built for this study can be obtained fromWWF–GreaterMekong2013).Thevaluationoffreshwaterwetlandsinthiscasecoveredtwoecosystemservices: localuseofaquaticproductsandwaterqualityandflowservices.ThevaluesoftheseecosystemserviceswerederivedfromonestudyinCambodia(Chong2005),twostudies in Laos (Emerton et al.2002,Gerrard2004),onstudyinThailand(Pagdeeet al.2007),andonestudyinVietnam(DoandBennett2007).Theresults(Table8.1)suggestthatfreshwaterwetlands in the LMB have a total value of USD 1,634/ha/year, which is just about half of the mean valueof the three typesofwetlands (USD2997/ha/year) usedby (Costanzaet al. 2011).Thedifference in thevalueestimates isperhapsdue to factorssuchas thecoverageofecosystemservices included in the valuation, locations/countries and years of previous studies from which the transferred values are derived.

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Table8.1.SummaryofecosystemservicesvaluesinLMB(USD/ha/year).

Source:(WWF-GreaterMekong2013),p.16

It is anticipated that MRC own work on ecosystems and ecosystem services assessment described in Chapter 8.1 will give additional information to the Costanza and WWF report and be more practically oriented towards the activities and initiatives in MRC itself. MRC has also outlined its workinthisfieldfortheStrategicPeriodof2016-2020(MRC,2015).

8.3 Suggestions for improved valuation of ecosystem services for in the LMB

Given the importance of the values of ecosystem services as inputs for basin development planning and other initiatives in the LMB, improved valuation of changes in the ecosystem services under certain basin development scenarios is necessary. Below list some suggestions to improve such valuation:

• Identify and characterise ecosystem services to be valued: Maximizing the number of ecosystem services in the valuation is necessary in order to ensure the total economic value of an ecosystem is not underestimated, but caution needs to be paid to the problem of double counting. In addition to changes in values of fisheries/aquatic products and invalues of ecosystem services due to lost wetlands as studied by (WWF-Greater Mekong 2013, Costanza et al.2011), thevaluationshouldalsocover, forexample, forgonevaluesassociated with biodiversity loss and changes in values of ecosystem services provided by lost forests. Risks to aquatic species and loss of forests in expanded reservoirs (25,000 ha in total) present major public concerns and therefore including the values of thesemay substantially affect the total economic values of each scenario.Once identified, theecosystem services need to be characterized in a way that does not involve double counting



of certain values, resembles the potential outcomes of each scenario under consideration, and isreadilyvaluatedgivenavailabledata forvaluetransfer(Brander2013)oravailablemethods for primary valuation studies (see e.g., (Champ, Boyle, and Brown 2003, Garrod and Willis 1999)). For meaningful valuation, ecosystem services may be best identifiedand characterised through wide consultation with stakeholders and experts. The types and classificationofecosystemservicesproposedinFigure8.2and8.3maybeeitherconsideredin,orusedasinputsfor,suchidentificationandcharacterisation.

• Adjust value estimates if value transfer is used: There are three methods for value transfer: unitvaluetransfer,valuefunctiontransfer,andmeta-analyticfunctiontransfer(Brander2013).The firstmethod (unit value transfer) can be adjusted to reflect the differences betweenpreviousprimarystudyandpresentstudysites(e.g.,income,yearofvaluation).Valuationofecosystem services discussed above (WWF-Greater Mekong 2013, Costanza et al.2011)didnot make such adjustment, and many of the transferred values used were not from primary valuation studies either. The last two value transfer methods already take into account the characteristics of the site being studied.

• Analyse changes in values of ecosystem services to derive the total economic value of a changing ecosystem: The values of ecosystem services are not static; they depend both on the types, extent and quality of ecosystems, and on the level of reliance of the region’s human population on ecosystem services for their economic well- being. Quantifying changes in ecosystemservicesprovidedbyaparticulartypeofecosystems(e.g.,wetlands,forests)andestimating the values of the associated changes to derive the total value of an ecosystem can relatively reduce biased estimates, compared to directly estimating the total value of the ecosystem as done by (WWF-Greater Mekong 2013, Costanza et al.2011).

• Focus on marginal changes: Any new infrastructure or development involves trade-offsbetween the values of ecosystem services. Decision-makers are relatively more interested in the information about a net change in the values of changing ecosystem services induced by the new infrastructure or development than about the total value of the ecosystem services perse(TEEB--TheEconomicsofEcosystemandBiodiversityforLocalandRegionalPolicyMakers2010).

• Enhance primary valuation studies: There are a limited number of reliable primary valuation studiesintheLMBregion.Primaryvaluationstudiesarecostlyandtime-consuming,buttheyareessentiallyrequiredtoinformBDPdesignanddecision-making.Quantifyingchangesinecosystemservices (ecological processes that benefit humans) induced, for instance, bytheabovediscussedscenarios(definitefuture,6dams,and11dams)isaprerequisiteforvaluationthatrelatesdirectlytotheBDP.GivenbiologicalcomplexityoftheMekongwaterandwetlands,suchquantificationisdifficultandmightnotbecompletedinashort-term(3years).An alternative approach that uses a stated preference technique that describes the potential changes in ecosystem services under the discussed scenarios can be instead used to elicit public preferences and more quickly estimate the values of the changing ecosystem services (see;Chhun,Thorsnes,andMoller2013,McVittieandMoran2010)forexamplesofsuchanapproach).Resultsfromanappropriateprimaryvaluationusingsuchanapproachareatleastrelativelymorereliableanddefensiblethanthoseusingabenefittransfertechnique.

8.4 Mitigation Recommendations and Options for Ecosystem Services

8.4.1 ESIA Mitigation versus Ecosystem Services Mitigation

Weavingecosystemservicesintoimpactassessment(WorldResourcesInstitute2013a)offersapromising approach to eventually mitigating development impacts on ecosystem services provided

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by theMekongwater andwetlands.As of 2012, the International FinanceCorporation’s (IFC)performancestandardsrequireIFC-financedprojectstoassesstheirimpactsanddependenciesonecosystemservicesand takenecessarymeasures topreserve thebenefits fromecosystemservices.Yet,standardenvironmentalandsocialimpactassessments(ESIAs),whicharebroadlyapplied in theLMBcountries,donot specificallyaccount foraproject’s impactsonecosystemservices. For instance, none of the environmental impact assessment reports of dam construction projects approved in Cambodia (e.g., Lower San II, Kamchay, Kirirom III, Stung Atay I, andStungAktayII)specificallyaccounts for impactsonecosystemservices.Therecentlyapprovedenvironmental impactassessment reportofDonSahongHydropowerProject inLaos (NationalConsultingCompany 2013) does not either contain thewords “ecosystem service”.Assessingtheimpactsonecosystemsorenvironmentisdifferentfromassessingtheimpactsonecosystemservices; hence,mitigation options are also different. Box 8.1 contains some examples of thedifferences between both assessments. In relation to the impacts of dam construction in theMekong,fishingmightbe,forinstance,traditionallyembeddedinsomelocalcommunitiessothedegradationoflocalfisheriescouldalienatetheirculturalidentityinadditiontothelossofincomeandprotein intakes.Without specificallyaccounting forecosystemservices, thestandardESIAmight accordingly overlook stakeholders who are vulnerable to ecosystem change, or miss some oftheharmfulsocialconsequencesofaproject’senvironmentaleffects.

Box 8.1. Examples of the differences between standard Environmental and Social ImpactAssessment and Ecosystem Service Impact Assessment.

• Thegoalofstandardmitigationmeasuresforprojectimpactsonfisherieswouldbethemitigation of the impacts on fish populations. In contrast, when looking at ecosystemservices, the target of mitigation measures would be to maintain pre-project income levels andproteinintakesforfishingcommunities.

• In a standard ESIA, the assessment of project water abstraction looks at change in riverflows(e.g.,cubicmetersofwaterpersecond).Inthiscase,theindicatordoesnotcommunicate the implications of water abstraction for local women who fetch water from the river. When looking at ecosystem services, the ESIA team assesses the impact of water abstraction in terms of change in the quantity of water available to these women (e.g., cubicmeters ofwater per person).Change inwater availability can, in turn, belinked to a change in time spent by local women to fetch water.

• The impacts of a project on total wildlife populations may be considered low, and mitigation measures deemed unnecessary, in a standard ESIA. Addressing ecosystem services, however, focuses the assessment of project impacts on wildlife populations in hunting grounds,whichmightdifferfromtheassessmentofimpactoverthetotalpopulationandcanbedefinedintermsofpotentiallossinhealthandincomebyhuntingcommunities.

• InastandardESIA,habitatfragmentationcausedbyaprojectisassessedasinsignificantbecauseitwouldaffectonlyasmall,localizedarea.Incontrast,whenlookingatecosystemservices,theimpactmightbeassessedassignificantiflocalcommunitieshavecomplexand deep-rooted relationships to the habitat in its present condition.

Source:Extractedfrom(WorldResourcesInstitute2013a,b)

The Ecosystem Services Review for Impact Assessment (ESR for IA) provides guidance forintegrating ecosystem services into standard ESIA with two objectives: to mitigate project impacts onthebenefitsprovidedbyecosystemsandtoprovidemeasurestomanageoperationsdependenton ecosystems to achieve planned performance. The ESR for IA does not replace the standard



ESIA process; it instead considers ecosystem services in complement with what the ESIA process routinelyaddresses(seeFigure8.5,blueandblacktextrespectively).TheESRforIAprovidestheESIA team with a conceptual framework to link the project to ecosystems, ecosystem services, and benefits derived from ecosystem services. See (WorldResources Institute 2013a) for theintroduction to a step-by-step method of weaving ecosystem services into impact assessment or/andfor(WorldResourcesInstitute2013b)forESIApractitioners.Theearlyroad-testofthestep-by-stepmethodhasdemonstrateditspotentialtounveilunidentifiedsocio-economicdimensionsofenvironmental impacts and operational risks of ecosystem change and reveal additional mitigation measures for social impacts and management measures of operational risks.

Figure 8.5. A step-by-step method for ecosystem service assessment in the six-step standard ESIA. Source: (World Resources Institute 2013a).

254

8.4.2 Mitigating impacts on ecosystem services

Themain objective ofmitigating the impacts on ecosystem services is to ensure that affectedstakeholdersmaintainthebenefitstheyderivefromecosystemservices.LikeinstandardESIA,themitigationhierarchycanbeusedtoidentifymeasurestoavoid,minimize,restoreandoffsetlossesinthebenefitstheaffectedstakeholdersderivefromecosystemservicesandtoenhancegainsinsuchbenefits(Figure8.6).Ifacombinationofavoidanceandminimizationmeasuresisinsufficienttomitigatefortheloss,forexample,inculturalidentityassociatedwithfishing,restorationofnearbyfishinggroundsthatareaccessibletotheaffectedcommunitiescouldbeproposed.If,evenaftertheproposedrestoration,thereisstillananticipatedresiduallossinecosystemservicebenefits,theaffectedbeneficiariescouldbeengagedtodeterminewhethertheresiduallosswouldbeacceptableto them or monetary compensation is needed to achieve the no net loss. Valuation of ecosystem services discussed in the previous section provides a basis for determining a proxy amount of such compensation. If, even with monetary compensation, the residual loss in ecosystem service benefitsisdeemedunacceptablebytheaffectedstakeholders,alternativesfortheprojectshouldbe considered.

Figure8.6.Mitigatingandenhancingprojectimpactsonecosystemservicebenefits(Source:World ResourcesInstitute 2013a).

Monetarycompensationcanbeconsideredastheapplicationofthe“polluterspayprinciple”orasa way of internalizing residue impacts on ecosystem services. Such internalization can improve the efficiencyandintergenerationalequityintheuseofnaturalresources(Tietenberg2004);however,its application in the context of dam construction in the Mekong region needs to at least get through the following challenges:

• Intangiblebenefitsofecosystemservicesandlimitedknowledgeabouttheirvalues:Financialbenefitsandanticipatedeconomicboostasaresultofelectricitygeneratedfromhydropower



isoftengivenmoreweightthantheintangiblebenefitsofecosystemservices.Thisisevenexacerbated due to our limited knowledge about the values of ecosystem services to be impacted by dam construction. Recall that there are a quite limited number of publications about the values of ecosystem services in the LMB.

• Lack of operational mechanisms: Charging the loss of ecosystem service benefits fromdevelopers or forcing the developers to pay for compensation of the loss at an early stage of dam construction or operation might not be possible due to a wide range of uncertainty inherentintheassessmentofecosystems,ecosystemchanges,andvaluesofthebenefitsderived from changing ecosystem services. A recoverable assurance bond that is large enough to cover the worst case damages caused by dam construction is recommended as a method of shifting the burden of proof about impacts from the public to the developers (Costanza et al.2011).Anappropriateoperationalmechanism,whichisnotinplaceyet,isneededtoensureapaymentstreamofthelossofecosystemservicebenefitstotheaffectedstakeholders.

• Trans-boundaryimpacts:Thelossofecosystemservicebenefits,eventhoughamechanismfor monetary compensation is in place, cannot be fully compensated due to trans-boundary impacts. Getting each nation in the LMB responsible for the impacts of its development on other nations has been difficult; this is even exacerbated with the involvement of equityissues.Year2000wasusedas thebaseline for theassessmentof impactassessment inBDP2andestimationofthevaluesoftheimpactsdoneby(Costanzaet al.2011).Duetothe fact that some nations had more dams than others in that year, the assumed baseline is not equitable. The baseline for ecosystem services inclusive impact assessment needs to bedefinedinanequitablewayandgetconsensusesamongallnationsoftheLBMifsuchmonetary compensation is to be used as the last resort of the mitigation hierarchy to ensure thenonetlossofecosystemservicebenefits.

8.4.3 Managing dependencies of development projects on ecosystem services

The main objective of managing dependencies of development projects on ecosystem services is toensureplannedoperationalperformance(WorldResourcesInstitute2013a).Justastheprojectscanadverselyimpactthebenefitsderivedfromecosystemservices,changesinecosystemsandecosystemservicescan jeopardizeprojectoutcomes.ToabidebyIFCPerformanceStandards,projectdevelopersroutinelyhaveecosystemservicedependenceassessment(ESDA)conductedas part of the risk assessment process. The ESDA can alternatively be integrated into standard ESIA by using the step-by-step method developed by the ESR for IA. In this case, the ESIA team works inclosecollaborationwithprojectdeveloperstoidentifyalistofcost-effectivemeasurestomanagethe operational risks to project performance arising from ecosystem changes. As demonstrated in Figure8.7,themeasurescaneitherincreasethesupplyofanecosystemservice(bluearrow)and/or decrease the supply required by the project to achieve planned operational performance (orange arrow).Incaseofdamconstruction,theESIAteamcanproposeprotectionofupstreamwatershedtomaintainwatersupplyrequiredforhydropowerproduction.Alternatively(orincombination),theESIA team can propose lowering the height of a dam to reduce risks associated with shortage in water supply during a dry season.

256

Figure 8.7. Managing project dependencies on ecosystem services to ensure planned operational performance.

Paymentsforecosystemservices(PES)offerapromisingmechanismthatcantranslateexternal,non-market value of the ecosystems into real financial incentives for local actors to provideecosystemservices(Fripp2014).AsdemonstratedinFigure8.8,thepaymentstolocalactorsincombinationwiththebenefitsfromforestconservationneedtobegreaterthanoratleastequaltothebenefitsthatcouldbederivedfromalternativelandusesinordertoincentivizethoseactorsto protect the forest. Hydropower producers have been identified as potential payers of waterregulationandsoilconservationservicesoftheintactforestonupstreamwatershedforthebenefitsthey derive from the ecosystem services. For instance, one hectare of forest was valued at USD 69 per year for the two ecosystem services to the Da Nhim hydropower project in Vietnam (Winrock International2011).FaunaandFlora International (FFI)hasbeenexploringmarket-basedPESschemes at two hydroelectricity sites located within protected areas of the Cardamom Mountains landscapeinCambodia(WWF-GreaterMekong2013).



Figure 8.8. The logic of payments for ecosystem services (Source: Engel, Pagiola, and Wunder 2008).

PEScanbepromisingformanagingdependenciesofdevelopmentprojectsonecosystemservicestoensureplannedoperationalperformance;however,accordingto(WWF-GreaterMekong2013)all formsofPESareverymuchatanincipientstageintheLowerMekongcountries.PilotPESschemes exist, or are emerging, in all of the Lower Mekong countries, but only Vietnam has institutionalized PES and has it specifically covered by law. In Cambodia, Laos andThailand,thereisagreatdealofinterest(amongbothgovernmentandtheNGOcommunity)inscalingupsite-specific PES efforts and establishing some kind of national institutional, legal and fundingframeworkthatcouldguidethefurtherdevelopmentofPESacrossthecountry.

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260

References for Guidelines and Manual



Abril G, Boudou A, et al. Petit Saut Environmental Report after 12 Years Running. ComiteScientifiquedePetitSaut.2008.

Acreman, M., Dunbar, M.J., 2004, Defining environmental river flow requirements – a review,HydrologyandEarthSystemSciences8(5):861-867.

Adam B. & Schwevers U, 1997, Das Verhalten von Fischen in Fischaufstiegsanlagen, Österr. Fischerei 50: pp82-87.

AG-FAH, 2011, Grundlagen für einen Österreichischen Leitfanden zum Bau von Fischaufstiegshilfen, (FAHs), Im Auftrag des Bundesministeriums für Land- und Forstwirtschaft, Umwelt undWasserwirtschaft, Wien: 87 p.

Agostinho, A.A. & Gomes L.C, 1997, Reservatório de Segredo: bases ecológicas para o manejo. Maringá,EDUEM.

Agostinho,A.A.&M.Zalewski,1995,ThedependenceoffishcommunitystructureanddinamicsonfloodplainandriparianecotonezoneinParanáRiver,Brazil.Hydrobiologia303:141-148.

Agostinho A.A. & Gomes L.C, 1997, Manejo e monitoramento de recursos pesqueiros: perspectivas para o reservatório de Segredo, In Reservatório de Segredo: bases ecologicos para o manejo, AgostinhoAA,GomesLC(eds).Copel,Eduem,UEM-Nupelia:Maringa:pp319-364.

AgostinhoA.A.,ThomazS.M.,Minte-VeraC.V.&WinemillerK.O.,2000,BiodiversityinthehighParanáRiverfloodplain.InBiodiversitvinWetlands:Assessment,FunctionandConservation,vol.I,GopalB, JunkWJ,Davis JA (eds).BackhuysPublishers: Leiden: pp89-118.AgostinhoA.A.,Domingo L.C.G., FernandezR. & Suzuki H.I. (2002): Efficiency of fish ladders for neotropicalIchthyofauna. River Research and Applications 18: pp 299-306.

Agostinho, AA, Gomes, LC, Fernandez, DR, Suzuki, HI, 2002, Efficiency of fish ladders forneotropicalichthyofauna,RiverRes.Appl.18(3):299–306(doi:10.1002/rra.674.DWA,2010).

Agostinho, A.A., E.E. Marques; C.S. Agostinho, D.A. Almeida, R.J. Oliveira & J.R.B. Melo, 2007, FishladderofLajeadoDam:migrationsonone-wayroutes?NeotropicalIchthyology5(2):121-130. doi: 10.1590/S1679-62252007000200002

Alabaster,JS,Lloyd,R,1982,Finelydividedsolids.Pages1-20 InJ.S.AlabasterundR.Lloydeditors.Waterqualitycriteriaforfreshwaterfish,2ndedition.Butterworth,London.

Alexander, GR, Hansen, EA, 1986, Sand bed load in a brook trout stream. North American Journal of Fisheries Management 6: 9-23.

Amornsakchai,S.,Annez,P.,Vongvisessomjai,S.,Choowaew,S.,ThailandDevelopmentResearchInstitute(TDRI),Kunurat,P.,Nippanon,J.,Schouten,R.,Sripapatrprasite,P.,Vaddhanaphuti,C.,

262

Vidthayanon,C.,Wirojanagud,W.,Watana,E.2000.PakMunDam,MekongRiverBasin,Thailand.A WCD Case Study prepared as an input to the World Commission on Dams, Cape Town, www.dams.org

Anderson,PG,Taylor,BR,Balch,GC,1996,Quantifyingtheeffectsofsedimentreleaseonfishund their habitats. Canadian Manuscript Report of Fisheries und Aquatic Sciences No. 2346: 110 p.+3Append.

Anderson,E.P.,Pringle,C.M.,Freeman,M.C.,2008,Quantifyingtheextentofriverfragmentationby hydropower dams in the Sarapiquí River Basin, Costa Rica.Aquat. Conserv. Mar. Freshw. Ecosyst. 18, 408–417.

Annandale, G, 2013, Quenching the Thirst: Sustainable Water Supply and Climate Change, Createspace, ISBN-10: 1480265152.

Annear,T,Chisholm,I,Beecher,H,Locke,A,Aarestad,P,Coomer,C,Estes,C,Hunt,J,JacobsonR,Jobsis,G,Kauffman,J,Marshall,J,Mayes,K,Smith,G,Styalnaker,C,Wentworth,R,2004,Instream Flows for Riverine Resource Stewardship (revised edition), Instream Flow council,Cheyenne, Wyoming: 268 p.

Anselmetti,FS,Bühler,R,Finger,D,Girardclos,S,Lancini,A,RellstabC,Sturm,M,2007,Effectsof alpine hydropower dams on particle transport and lacustrine sedimentation, Aquatic Sciences 69: 179–198.

Anthony,E.J.,Brunier,G.,Besset,M.,Goichot,M.,Dussouillez,P.,andLapNguyen,V.,2015,Linking rapid erosionof theMekongRiver delta to humanactivities. ScientificReports, vol 5,Article number: 14745, doi:10.1038/srep14745

,H,NghiaHung,N,ThiLong,T,andKhac,V,2012,FloodhydraulicsandsuspendedsedimenttransportinthePlainofReeds,MekongDelta,inKuenzer,(eds.):Renaud,F.andC.Kuenzer2012:The Mekong Delta System – Interdisciplinary Analyses of a River Delta, Springer, ISBN 978-94-007-3961-1, DOI 10.1007/978-94-007-3962-8.

Arias, M.E., T. Piman, H. Lauri, T.A. Cochrane, andM. Kummu, 2014, Dams on theMekongtributaries as significant contributors of hydrological alterations to the Tonle Sap Floodplain inCambodia, Hydrol. Earth Syst. Sci., 18, 5303-5314.

Arthington,AH,Bunn,SE,Poff,NL,Naiman,RJ,2006,Thechallengeofprovidingenvironmentalflowrulestosustainriverecosystems,EcologicalApplications16(4):1311-1318.

AuflegerM.&BrinkmeierB.(2015):WasserkraftanlagenmitniedrigenFallhöhen–VerschiedeneKonzepte imkritischenVergleich.ÖsterrWasser-undAbfallw.67:281-291.DOI10.1007/s0506-015-0247-6.

Backman T.W.H., Evans A.F., Robertson M.S. & Hawbecker M.A., 2002, Gas bubble trauma



incidence in juvenile salmonids in the lower Columbia and Snake Rivers. N. Am. J. Fish. Manage. 22: pp 965–972.

BAFU, 2012, Wiederherstellung der Fischauf- und abwanderung bei Wasserkraftwerken. Checkliste Best practice. Bundesamt für Umwelt BAFU, Schweiz: 79 p.

Bain, M. S., Irving, J.S. and Olsen, R.D., 1986, Cumulative Impact Assessment: Evaluating the EnvironmentalEffectsofMultipleHumanDevelopments,ArgonneNationalLaboratory,EnergyandEnvironmental Systems Division, Argonne.

BairdI.,2006,ProbarbusjullieniandProbarbusLabeamajor:themanagementandconservationoftwoofthelargestfishspeciesintheMekongRiverinsouthernLaos.AquaticConservation:Marineand Freshwater Ecosystems 16: pp 517-532.

Baird, I. G., 1995, A Rapid Study of Fish and Fisheries; and livelihoods and natural resources along theSeSanRiver,Ratanakiri,Cambodia.OxfamUK,OxfamIreland&Novib.Dec.1995.

Baird,I.G.,P.Kisouvannalath,V.Inthaphaysi&B.Phylaivanh,1998,ThepotentialforecologicalclassificationasatoolforestablishingandmonitoringfishconservationzonesintheMekongRiver.TechnicalReportNo.2.EnvironmentalProtectionandCommunityDevelopmentintheSiphandoneWetland,ChampasakProvince,LaoPDR.

Baird, I. G. & M. S. Flaherty, 1999, Fish conservation zones and indigenous ecological knowledge in southern Laos: a first step in monitoring and assessing effectiveness. Technical Report.EnvironmentalProtectionandCommunityDevelopmentintheSiphandoneWetland,ChampasakProvince,LaoPDR.

Baird,I.G.,2006,Strengthindiversity:fishsanctuariesanddeepwaterpoolsinLaoPDR.FisheriesManagement and Ecology, 13: 1-8.

Baird,IG,2011,TheDonSahongDam:Potentialimpactsonregionalfishmigrations,livelihoods,andhumanhealth.CriticalAsianStudies43(2):211-235.

Baird,IG,Phylavanh,B,VongsenesoukB,Xayamanivong,K,2001,TheecologyandconservationofthesmallscalecroakerBoesemaniamicrolepis(Bleeker1858-59)inthemainstreamMekongRiver, southern Laos, natural History Bulletin of the Siam Society 49: 161-176.

BaranE.,vanZalingeN.,NgorP.B.,BairdI.G.&CoatesD,2001,FishresourceandhydrobiologicalmodellingapproachesintheMekongBasin.Penang:ICLARM.

Baran,E.;Zalinge,N.P.vanandNgor,P.B.,2001,Floods,floodplainsandfishproductionintheMekong Basin: present and past trends. In: The Asian Wetlands Symposium 2001, 27-30 Aug 2001,Penang,Malaysia.

264

Baran, E.; I.G. Baird andG. Cans, 2005, Fisheries Bioecology at the Khone Falls.WorldFishCenter,PhnomPenh,Cambodia,84pp.

Baran E., 2006, Fish migration triggers in the Lower Mekong Basin and other tropical freshwater systems, MRC Technical paper No. 14, Mekong River Commission, Vientiane: 56 p.

BaranE.&MyschowodaC.,2009,DamsandfisheriesintheMekongBasin,AquaticEcosystemHealthandManagement12(3):pp227-234.

BaranE.,2010,Mekongfisheriesandmainstreamdams,Fisheriessectionin:ICEM2010.MekongRiver commission Strategic Environmental Assessment of hydropower on the Mekong mainstream, International Centre for Environmental Management, Hanoi, Viet Nam: 145 pp.

BaranE.,GätkeP.,FontesJr.H.M.,MakrakisS.,MakrakisM.C.,RäsänenT.A.,SarayS,2014,Potentialforfishpassageandimplicationsforhydropower–thecaseoftheLowerSesan2DaminCambodia. Chapter 3.2 in ICEM, 2014. On optimizing the management of cascades or system of reservoirs at catchment level. ICEM. Hanoi, Vietnam [www.optimisingcascades.org].

Baran E. and Guerin E., 2012, Fish bioecology in relation to sediments in the Mekong and in tropical rivers.ReportfortheProject“AClimateResilientMekong:MaintainingtheFlowsthatNourishLife”ledbytheNaturalHeritageInstitute.WorldFishCenter,PhnomPenh,Cambodia.

Baran,E,Larinier,M,Ziv,G,Marmulla,G,2011,Reviewof thefishandfisheriesaspect in thefeasibility study and the environmental impact assessment of the proposed Xayaburi dam on the Mekong mainstream, Report prepared for the WWF Greater Mekong, 48p.

BarkerI.&KirmondA.,1998,Managingsurfacewaterabstraction.In:Hydyrologyinachangingenvironment,vol.1,H.WheaterandC.Kirby(Eds.),BritishHydrologicalSoiety,London,UK.249-258.

BarlowC.,BaranE.,HallsA.&KshatriyaM.(2008):HowmuchoftheMekongfishcatchisatriskfrommainstemdamdevelopment?CatchandCulture14:pp16-21.

Basson,G,2004,HydropowerDamsandFluvialMorphologicalImpacts–AnAfricanPerspective,United Nations Symposium on Hydropower and Sustainable Development, Beijing Internation ConventionCentre,Beijing,China,UnitedNationsDeptofEconomicsandSocialAffairs,p1-16.

BauersfeldK,1978,StrandingofjuvenilesalmonbyflowreductionsatMayfieldDamontheCowlitzRiver, 1976. Department of Fisheries, Olympia.

Baumgartner L., ThroncraftG.,MarsdenT., PhonekhampengO., SinghanouvongD., Stuart I.,SuntornratanaU., 2010,Development of fishpassage criteria for floodplain species ofCentralLaos. Australian Government. Australian Centre for International Agricultural Research.



Baumgartner,BL,Zampatti,B,Jonees,M,Stuart,I,Mallen-Cooper,M,2014,FishpassageintheMurray-Darling Basin, Australia: Not just an upstream battle, Ecological Management & Restoration Vol 15: 28-39.

Bayley,P.B.,1995.Understandinglargeriver–floodplainecosystems.BioScience45:153–158.

BellM.C.&DelacyA.C.,1972,Acompendiumonthesurvivaloffishpassingthroughspillwaysandconduits.Fish.EngineeringResearchProgram.CorpsofEngineering,NorthPacificDivision,Portland,Oregon:121p.

Bérubé,M,2007,CumulativeEffectsAssessmentatHydro-Quebec:WhatHaveWeLearned?,ImpactAssessmentandProjectAppraisal,25(2):101–109.

Bezuijen M.R., Timmins R. and Seng T. (eds), 2008, Biological surveys of the Mekong RiverbetweenKratieandStungTrengtowns,northeastCambodia,2006–2007.WWFGreaterMekong– Cambodia Country Programme, Cambodia FisheriesAdministration and Cambodia ForestryAdministration,PhnomPenh.

Bezuijen, M.R., Vinn, B. And Seng, L, 2009, A collection of amphibians and reptiles from the Mekong River, northeastern Cambodia. Hamadryad Vol.34, No.1, 2009

Biggs, BJF,Nikora, VI, Snelder,TH, 2005, Linking scales of flow variability to lotic ecosystemstructure and function, River Research and Applications 21: 283-298.

BirdLife International, 2003, Saving Asia’s threatened birds: a guide for government and civil society.BirdlifeInternational,Cambridge,UK.

Bjornn,TC,Brusven,MA,Molnau,MP,Milligan, JH,Klamt,RA,Chacho,E,Schaye,C, 1977,Transport of granitic sediment in streams and its effects on insects und fish. Office of WaterResearch and Technology, U.S. Department of the Interior. Washington, D.C. 20240. Research TechnicalCompletionReport,ProjectB-036-IDA:43p.

Boavida,I,Santos,JM,Ferreira,T,Pinheiro,A,2015,Barbelhabitatalterationsduetohydropeaking,Journal of Hydro-environment Research 2015: 1-11.

Boes, RM, and Hagmann, M, 2015, Sedimentation countermeasures – examples from Switzerland Proc.FirstInternationalWorksshoponSedimentBypassTunnels,VAW–Mitteilungen232(R.M.Does,ed.),LaboratoryofHydraulics,HydrologyandGlaciology(VAW),ETHZurich,Switzerland.

BoggsCT.,KeeferML.,PeeryCA.,BjornnTC.,StuehrenbergLC.,2004,Fallback,reascension,andadjustedfishwayescapementestimatesforadultChinooksalmonandsteelheadatColumbiaand Snake River dams. Transactions of the American Fisheries Society 133: 932-949.

266

Bovee, KD, 1982, A guide to stream habitat analysis using the instream flow incrementalmethodology,InstreamFlowInformationPaperno.12.FWS/OBSERVATION82/86.WashingtonD.C., USA.

Bovee,KD,Milhous,R,1978,Hydraulicsimulationininstreamflowstudies:theoryandtechniques,Ft.Collins(CO):OfficeofBiologicalServices,USFish&WildlifeService.InstreamFlowInformationPapernr.5,FWS/OBS-78/33.

Brander, L.M, 2013, Guidance manual on value transfer methods for ecosystem services. United NationsEnvironmentProgramme(UNEP).

Bravard, J-P, Goichot, M, Tronchère, 2013, An assessment of sediment processes in theLower Mekong River based on deposit grain-sizes, the CM technique, and flow-energy data,Geomorphology, http://dx.doi.org/10.1016/j.geomorph2013.11.004

Bravard,J-P,Goichot,M,Gaillot,S,2014,GeographyofSandandGravelMining in theLowerMekong River, EchoGéo [on line], v 26: http://echogeo.revues.org/13659 ; DOI : 10.4000/echogeo.13659

Brizga,SO,Arthington,AH,Choy,SC,Kennard,MJ,Mackay,SJ,Pusey,BJ,Werren,GL,2002,Benchmarking a top-downmethodology for assessing environmental flows inAustralian rivers,Proc.Int.Conf.EnvironmentalFlowsforRiverSystems,CapeTown,SouthAfrica,2002.

Brown,CA,Jourbert,A,2003,Usingmulticriteriaanalysistodevelopenvironmentalflowscenariosforriverstargetedforwaterresourcemanagement,WaterSA29(ISSN0378-4738).

Brunier,G,Anthony,EJ,Goichot,M,Provansal,M,Dussouillez,P,2014,Recentmorphologicalchanges in the Mekong and Bassac river channels, Mekong delta: The marked impact of river-bed mining and implications for delta destabilisation, Geomorphology, 224, 117-191.

Bruno, MC, Siviglia, A, Carolli, M, Maiolini, B, 2013, Multiple drift responses of benthic invertebrates to interacting hydropeaking and thermopeaking waves, Ecohydrology 6: 511–522.

Bunn,SE,Arthington,AH,2002,BasicPrinciplesandEcologicalConsequencesofAlteredFlowRegimesforAquaticBiodiversity.EnvironmentalManagement30(4):492-507.

Burwen,D.L.,S.J.Fleischman,&J.D.Miller,2011,AccuracyandPrecisionofSalmonLengthEstimates Taken from DIDSON Sonar Images. Transactions of the American Fisheries Society 139: 1306–1314.

ĈadaG.F.,CoutantC.C.&WhitneyR.R.,1997,Developmentofbiologicalcriteriaforthedesignofadvancedhydropowerturbines.DOE/ID-10578.PreparedforOfficeofGeothermalTechnologies,U.S. DOE, Idaho Falls, ID. 85 p.



CadaG.F.,2001,TheDevelopmentofAdvancedHydroelectricTurbinestoImproveFishPassageSurvival, Fisheries, vol 26, no. 9. pp 14-23.

CalridgeG.F,1996,AnInventoryofWetlandsofLaosPDR.IUCN,Bangkok.

Calles E.O. & Greenberg L.A., 2005, Evaluation of nature-like fishways for re-establishingconnectivity in fragmented salmonid populations in the river Emån. River Research and Applications 21: pp 951–960.

CampbellI.C.,PooleC.,GiesenW.andValbo-JorgensenJ,2006,Speciesdiversityandecologyof Tonle Sap Great Lake, Cambodia. Aquatic Sciences 68.

Campbell IC., 2009, The Mekong : biophysical environment of an international river basin / ed. byIanC.Campbell.-1.ed..-Amsterdam[u.a.]:Elsevier,AcademicPress,2009.-XIV,432S.ISBN:978-0-12-374026-7(hbk.)DuganP.(2008):Mainstreamdamsasbarrierstofishmigration:internationallearningandimplicationsfortheMekong,CatchandCulture,14(3):pp9-15.

Carpenter, Stephen R., HaroldA. Mooney, JohnAgard, andAnneWhyte, 2009, “Science formanagingecosystemservices:Beyond theMillenniumEcosystemAssessment.”PANSno.106(5):1305-1312.

CaudillC.C.,PeeryC.A.,DaigleW.R.,JepsonM.A.,BoggsC.T.,BjornnT.C.&JoostenD.,2006a,Adult Chinook salmon and steelhead dam passage behavior in response to manipulated discharge throughspillwaysatBonnevilleDam.ReportforUSArmyCorpsofEngineers,PortlandDistrict,Portland,Ore.

CaudillC.C.,ClaboughT.S.,NaughtonG.P.,PeeryC.A.&BurkeB.J.,2006b,Watertemperaturesinadult fishwaysatmainstemdamson theSnakeandColumbiaRivers.Phase2.Bi-ologicaleffects.ReportforUSArmyCorpsofEngineers,WallaWallaDistrict,WallaWalla,Wash.

CaudillC.C.,DaigleW.R.,KeeferM.L.,BoggsC.T.,JepsonM.A.,BurkeB.J.,ZabelR.W.,BjornnT.C.,PeeryC.A.,2007,Slowdampassage inadultColumbiaRiversalmonidsassociatedwithunsuccessfulmigration: delayed negative effects of passage obstacles or condition dependentmortality?CanadianJournalofFisheriesandAquaticSciences64:pp979–995.

Champ,PatriciaA.,KevinJ.Boyle,andThomasC.Brown,eds,2003,APrimeronNon-marketValuation.TheNetherlands:KluwerAcademicPublishers.

Chan, S.; S. Putrea and S. Lieng, 2008, Using local knowledge to inventory deep pools andimportantfishhabitatsinTonleSapandmainstreamaroundtheGreatLakeinCambodia.MRCConference Series,7: 43-63.

Chanudet, V., Guedant, P., Rode, W., Godon, A, Guerin, F., Serça, D., Deshmukh, C., andDescloux, S., 2015, Evolution of the pysico-chemical water quality in the Nam Theun 2 Reservoir anddownstreamriversforthefirst5yearsafterimpoundment,Hydroecol.Appl.EDF,2015;DOI:

268

10.1051/hydro/2015001.

Chhun,Sophal,PaulThorsnes,andHenrikMoller,2013,“Preferencesformanagementofnear-shoremarineecosystems:achoiceexperimentinNewZealand.”Resourcesno.2(3):406-438.

Chong, J, 2005, Valuing the Role of Wetlands in Livelihoods: Constraints and Opportunities for Community Fisheries and Wetland Management in Stoeng Treng Ramsar Site, Cambodia. In IUCN Water,NatureandEconomicsTechnicalPaperNo.3: IUCN—TheWorldConservationUnion,Ecosystems and Livelihoods Group Asia, Colombo.

Choowaew S, 2003, Classification and inventory of wetland/aquatic ecosystems in the LowerMekong River Basin of Thailand. MRCS consultancy report.

Clay,C.H,1995,DesignofFishwaysandOtherFishFacilities.BocaRaton,CRCPress,2nded.

Cochrane,T.A.,M.E.Arias,T.Piman,2014,Historicalimpactofwaterinfrastructureonwaterlevelsof the Mekong River and the Tonle Sap system, Hydrol. Earth Syst. Sci., 18, 4529-4541.

CNR, 2009, Optimization Study of MekongMainstreamHydropower. Prepared by CompagnieNationaleduRhône(CNR),Leon,France,fortheDepartmentofElectricity,MinistryofEnergyandMines,LaoPDR,106pp.

Coffen-Smout,S.,R.Halliday,G.Herbert,T.Potter,andN.With¬erspoon,2001,OceanActivitiesand Ecosystem Issues on the Eastern Scotian Shelf, Canadian Science Advisory Secretariat.

ColganP.,1993,Themotivationalbasisoffishbehaviour.In:BehaviourofTeleostFishes.PitcherT.J.(Ed.).ChapmanandHall,London,7:pp31-65.

Commandeur,A.S.(2015)TurbidityCurrentsinReservoirs.Thesis,DelftUniversityofTechnology(http://repository.tudelft.nl)

Conlan, IA, Rutherfurd ID, Finlayson BL, and Western AW, 2008, Sediment Transport through aForcedPoolontheMekongRiver:SandDunesSuperimposedonaLargerSedimentWave?MarineandRiverDuneDynamics,1-3April,2008,Leeds,UnitedKingdom.

Costanza, Robert, Ida Kubiszewski, Peter Paquet, Jeffrey King, Shpresa Halimi, HansaSanguanngoi, Nguyen Luong Bach, Richard Frankel, Jiragorn Ganaseni, and Apisom Intralawan, 2011,PlanningapproachesforwaterresourcesdevelopmentintheLowerMekongBasin.PortlandState University & Mae Fah Luang University.

Cote,D.,Kehler,D.G.,Bourne,C.,Wiersma,Y.F.,2009,Anewmeasureoflongitudinalconnectivityfor stream networks. Landscape Ecol. 24, 101–113.



Cowx,I.G;Kamonrat,W.;Sukumasavin,N.;Sirimongkolthawon,R.;Suksri,S.andPhila,N.,2015,LarvalandJuvenileFishCommunitiesoftheLowerMekongBasin.MRCTechnicalPaperNo.49.MekongRiverCommission,PhnomPenh,Cambodia.100pp.ISSN:1683-1489.

CroninR.(2009)MekongDamsandthePerilsofPeace,Survival:GlobalPoliticsandStrategy,51:6, 147-160, http://dx.doi.org/10.1080/00396330903461716

Crosa,G,Castelli,E,Gentili,G,Espa,P,2009,Effectsofsuspendedsediments fromreservoirflushing on fish and macroinvertebrates in an alpine stream.Aquatic Sciences, 72(1): 85–95(doi:10.1007/s00027-009-0117-z)

Cushman, RM, 1985, Review of ecological effects of rapidly varying flows downstream fromhydroelectric facilities, N. Am. J. Fish. Manag. 5: 330–339.

Dai,L.,1995,IntegrateddevelopmentoftheLanchangRiverandbiodiversityconservation,YunnanEnvironmentalScience,14(4):14-19,(inMandarin).

DAOHuyGiap,TatpornKUNPRADID,ChandaVONGSOMBATH,DOThiBichLoc,andPRUMSomany, 2010, Report on the 2008 biomonitoring survey of the lower Mekong River and selected tributaries,MRCTechnicalPaperNo.27.MekongRiverCommission,Vientiane.69pp.

Darby,S.E.,Trieu,H.Q.,Carling,P.A.,Sarkkula,J.,Koponen,J.,Kummu,M.,Conlan,I.,andJ.Leyland,2010,Aphysicallybasedmodeltopredicthydraulicerosionoffine-grainedriverbanks:The role of form roughness in limiting erosion, Journal of Geophysical research, Vol. 115, F04003.

Daubert,JT,Young,RA,1981,Recreationaldemandsformaintaininginstreamflows:acontingentvaluation approach. Am J Agric Econ 63: 666–676.

DeGraafG.J.andChinh,N.D.,2000,FloodplainFisheriesintheSouthernProvincesofVietNam.

DeGraaf,G,Born,B,Uddin,AMK,Marttin,F,2011,FloodsandFishermen,EightYearsExperienceswith Flood Plain Fisheries, Fish Migration, Fisheries Modelling and Fish Bio Diversity in theCompartmentalizationPilotProject,Bangladesh.1stEdn.MohiuddinAhmed,TheUniversityPressLimited, Bangladesh, 110p.

DepartmentofEnergyandClimateChang(UK),2009,SevernEmbryonicTechnologiesScheme.

Deshmukh, C.2013, Greenhouse gas emissions (CH4, CO2 and N2O) from a newly floodedhydroelectricreservoirinsubtropicalSouthAsia:ThecaseofNamTheun2Reservoir,LaoPDR.Ocean,Atmosphere.Universit´ePaulSabatier-ToulouseIII,English.

DHI, 2014, Study on the Impacts of Mainstream Hydropower on the Mekong River, Draft Baseline AssessmentReport,PreparedforMinistryofNaturalResourcesandEnvironment,GovernmentofViet Nam, DHI, Denmark

270

Do, T.N. , and J. Bennett, 2007, Estimating Wetland Biodiversity Values: A choice modelling application in Vietnam’s Mekong River Delta. In Economics and Environment Network Working PaperEEN0704:AustralianNationalUniversity,Canberra.

DoELaos,2004,LaoElectricPowerTechnicalStandards,DepartmentofElectricity.

DoveV.,2009,MortalityinvestigationoftheMekongIrrawaddyriverdolphin(OrcaellaBrevirostris)in Cambodia based on necropsy sample analysis. WWF Technical Report

Dove,V.,Dove,D.,Trujillo,F.andZanre,R,2008,AbundanceestimationoftheMekongIrrawaddydolphinOrcaellaBrevirostrisbasedonmarkandrecaptureanalysisofphotoidentifiedindividuals.WWF Cambodia Technical Report.

Dubeau,P.;Ouch,P.andSjorslev,J.G.,2001,Estimatingfishandaquaticproductivity/yieldperareainKampongTralach:anintegratedapproach.MekongConferenceSeries,1:20-43.

Dugan P., 2008, Mainstream dams as barriers to fish migration: international learning andimplicationsfortheMekong,CatchandCulture,14(3):pp9-15.

Dumont U., 2005, Entwicklung eines beispielhaften bundeseinheitlichen Genehmingungsverfahrens für den wasserrechtlichen Vollzug mit Anwendungsbeispielen im Hinblick auf die Novellierung des EEG- Gutachten für das Umweltbundesamt. Ingenieurbüro Floecksmühle.

Dyson, M, Berkamp, G, Scanlon, J, 2003, Flow: The Essentials of Environmental Flows, IUCN, Gland, Switzerland, Cambridge.

DWA, 2005, Fischschutz- und Fischabstiegsanlagen – Bemessung, Gestaltung, Funktionskontrolle DWA-Themen: 256 p.

DWA, 2010, draft, Merkblatt DWA-M 509 – Fischaufstiegsanlagen und fischpassierbareQuerbauwerke – Gestaltung, Bemessung, Qualitätssicherung: 285 p.

EAMP,2005,EnvironmentalAssessment&ManagementPlanoftheNamTheun2HydroelectricProject.239p.

Eberstaller,J,Zauner,G,Friedl,T,Kerschbaumer,G,2001,SedimentationinFlussstauhaltungen-ÖkologischeAspekte,ÖsterreichischeWasser-undAbfallwirtschaft.53(11/12):269-275.

EdFandScottWilson, 2010,Pre-Feasibility&FeasibilityStudiesofDalHydropowerProject –Feasibility Study Report.

Electrowatt Engineering, 1998, Nam Ngum 2 Hydroelectric Project, Lao PDR. EnvironmentalImpact Assessment.



Emerton,L.,S.Bouttavong,L.Kettavong,S. Manivong,andS.Sivannavong,2002,LaoPDRBiodiversity: Economic Assessment. Science, Technology and Environment Agency, Vientiane.

EuropeanInlandFisheriesAdvisoryCommittee(EIFAC),1965,WaterqualitycriteriaforEuropeanfreshwaterfish:Reportonfinelydividedsolidsandinlandfisheries.PreparedbyEIFACWorkingPartyonWaterQualityCriteriaorEuropeanFreshwaterFish.AirWaterPollut.9(3):151-168.

Fact Sheet FA-27, Department of Fisheries and Aquatic Sciences, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Reviewed May 1997, February2003.WebSiteathttp://edis.ifas.ufl.edu.)

Fisher,Brendan,R.KerryTurner,andPaulMorling,2009, “Definingandclassifyingecosystemservices for decision making.” Ecological Economics no. 68 (3):643-653. doi: 10.1016/j.ecolecon.2008.09.014.

Fishtek Consulting, 2015a, Xayaburi Hydroelectric power project. Fish migration facilities. Presentation in Vientiane, 15th July 2015 by Coe T, at: http://www.poweringprogress.org/new/images/PDF/DEB_and_DEPP_Presentation/6%20150715%20Fishtek%20-%20Fish%20Migration%20Facilities.pdf(01.09.2015)

Fishtek Consulting, 2015b, Xayaburi Hydroelectric power project. Fish migration facilities. PresentationinVientiane,15thJuly2015byMorier-GenoudG.,at:http://www.poweringprogress.org/new/images/PDF/DEB_and_DEPP_Presentation/5%20150715%20Poyry%20-%20Adapted%20Design%20of%20Xayaburi%20HPP%20%5BCompatibility%20Mode%5D.pdf(01.09.2015)

FEMA,2004,FederalGuidelinesforDamSafety–EmergencyActionPlanningforDamOwners.

Ferguson J.W., Poe T.P. & Carlson T.J. (1998): Surface-oriented bypass systems for juvenilesalmonidson theColumbiaRiver,USA. In: JungwirthM.,SchmutzS.&WeissS. (Eds.), FishMigrationandFishBypasses.BlackwellPublishingFishingNewsBooks/BlackwellScienceLtd.Publisher,Oxford,UK,(Chapter22):pp281–299.

FishBase:www.fishbase.org/

FisheriesOfficeandNTFP2000.AstudyoftheDownstreamImpactsoftheYaliFallsDamintheSesanRiverBasininRatanakiriProvince,NorthEastCambodia.,TheFisheriesOfficeinRatanakiriProvince inCooperationwith theNonTimberForestProductsProject,StungTreng,Cambodia,May 29 2000.

Forman,R.T.T.andGordon,M.,1986,Landscapeecology,NewYork,Wiley.

Friberg,N,2010,Pressure-responserelationshipsinstreamecology:introductionandsynthesis,FreshwaterBiology55:1367-1381(doi:10.1111/j.1365-2427.2010.02442.x).

272

FroeseR.&PaulyD.(2010):FishBase.WorldWideWebElectronicPublication.www.fishbase.org(October2010).

Fu, K.D., andHe,D.M., 2007,Analysis and prediction of sediment trapping efficiencies of thereservoirs in the mainstream of the Lancang River Chinese Science Bulletin, Supplement II: 117-122.

Garrod,Guy,andKennethG.Willis,eds,1999,EconomicValuationoftheEnvironment.Cheltenham,UK:EdwardElgarPublishingLimited.

Garric,J,Migeon,B,Vindimian,E,1990,LethaleffectsofdrainingonBrowntrout.Apredictivemodelbasedonfieldandlaboratorystudies.WaterResearch,24:59-65.

Garzon,CE,1984,WaterQualityinHydroelectricProjects,ConsiderationsforPlanninginTropicalForestRegionsWorldBankTechnicalPaperNumber20.

Geist D.R., Abernethy C.S., Blanton S.L. & Cullinan V.I., 2000, The use of electromyogram telemetry to estimate energy e Geesthacht expenditure of adult fall Chinook salmon. Trans. Am. Fish. Soc. 129(1):pp126–135.

Geist,DR,Arntzen,EV,Murray,CJ,McGrath,KE,Bott,YJ,Hanrahan,TP,2008,Influenceofriverlevel on temperature and hydraulic gradients in chcum and fall Chinook salmon spawning areas downstream of Bonneville Dam, Columbia River, N Am J Fish Manag, 28: 30–41.

Gerrard,P.,2004,IntegratingWetlandEcosystemValuesintoUrbanPlanning:TheCaseofThatLuangMarsh,Vientiane,LaoPDR.Laos,Vientiane:IUCN−TheWorldConservationUnion,AsiaRegionalEnvironmentalEconomicsProgrammeandWWF.

Goniea T.M., Keefer M.L., Bjornn T.C., Peery C.A., Bennett D.H. & Stuehrenberg L.C., 2006,Behavioral thermoregulation and slowed migration by adult fall Chinook salmon in response to high Columbia River water temperatures. Trans. Am. Fish. Soc. 135: pp 408–419.

GrantCJ.ReregulationofthePergauHydroelectricPowerStation–ProceedingsoftheInstitutionofCivilEngineers–WaterandMaritimeEngineering–PaperNo11787,June1999.

Grant C.J. & LibauxA. Power from the Mersey – Hydro 2011 – HydroActivities in Europe.Hydropower&DamsConference-Prague.

Grill G., Ouellet Dallaire C., Fluet Chouinard E., Sindorf N. and B. Lehner, 2014, Development of new

indicatorstoevaluateriverfragmentationandflowregulationatlargescales:Acase



study for the Mekong River Basin, Ecol. Indicators, 45, 148-59.

Gupta,AD, 2008, Implication of environmental flows in river basinmanagement, Physics andChemistry of the Earth 33: 298-303.

GuptaAD.,2008, Implicationofenvironmentalflows in riverbasinmanagement.PhydyricsandChemistry of the Earth 33: 298-303.

HallsA.S.,PaxtonB.R.,HallN.,HortleK.G.,SoN.,CheaT.,ChhengP.,PutreaS.,LiengS.,PengBunN.,PengbyN.,ChanS.,VuV.A.,NguyenNguyenD.,DoanV.T.,SinthavongV.,DouangkhamS., Vannaxay S., Renu S., Suntornaratana U., Tiwarat T. & Boonsong S., 2013, Integrated analysis ofdatafromMRCfisheriesmonitoringprogrammesintheLowerMekongBasin,MRCTechnicalPaperNo.33,MekongRiverCommission,PhnomPenh,Cambodia:158p.ISSN:1683-1489.

Halls,A.S.,I.Conlan,W.Wisesjindawat,K.Phouthavongs,S.Viravong,S.Chan&V.A.Vu(2013)AtlasofdeeppoolsintheLowerMekongRiverandsomeofitstributaries.MRCTechnicalPaperNo.31.MekongRiverCommission,PhnomPenh,Cambodia.69pp.ISSN:1683-1489.

Halls,AS,Kshatriya,M,2009,ModellingthecumulativebarrierandpassageeffectsofmainstreamhydropowerdamsonmigratoryfishpopulationsintheLowerMekongBasinMRCTechnicalPaperNo. 25. Mekong River Commission, Vientiane. 104 pp.

Halls,AS,Lieng,S,Ngor,P,TunP,2008,Newresearchrevealsecologicalinsightsintodaifishery,CatchandCulture14(1):8-12.

Hamilton,R,Buell,JW,1976,EffectsofmodifiedhydrologyonCampbellRiversalmonids,CanFishMarServTechRep,Pac/T-76-20,Vancouver.

HammondandJones,2008, InventoryofCarbonandEnergy(ICE),DepartmentofMechanicalEngineering,UniversityofBath,UK.

Harby,A,Noack,M,2013,Rapidflowfluctuationsandimpactsonfishandtheaquaticecosystem,InEcohydraulics:AnIntegratedApproach.Maddock,J,Harby,A,Kemp,P,Wood,P,(eds).JohnWiley & Sons: 323–335.

HardwickJD,GrantCJ,AnAdjustableAirRegulatedSiphonspillway–ProceedingsoftheInstiutionofCivilEngineers–WaterandMaritmeEngineering–PaperNo11192June1997.

HaroA.&KynardB., 1997,Videoevaluationof passageefficiencyofAmericanshadandsealampreyinamodifiedIceHarborfishway.N.Am.J.Fish.Manag.17:pp981–987.

Hartmann J., Harrison D, Opperman J., 2013, The new frontier of hydropower sustainability: PlanningattheSystemScale.TheNatureConservancy2013.112p.

274

Hateley,J.andGregory,J.,2006,Evaluationofamulti-beamimagingsonarsystem(DIDSON)as Fisheries Monitoring Tool: Exploiting the Acoustic Advantage. Technical Report. Environment Agency. Warrington.

He,D.,Lu,Y.,Li,Z.,andLi,S.,2009,WatercourseEnvironmentalChangeinUpperMekonginTheMekong:BiophysicalEnvironmentofanInternationalRiverBasin,Campbell,IC,(Ed)Academic,NY.

Hein,Lars,KrisvanKoppen,RudolfS.deGroot,andEkkoC.vanIerland,2006,“Spatialscales,stakeholdersandthevaluationofecosystemservices.”EcologicalEconomicsno.57(2):209-228.doi: DOI: 10.1016/j.ecolecon.2005.04.005.

Henley,WF,Patterson,MA,Neves,RJ,Lemly,AD,2000,Effectsofsedimentationundturbidityon lotic food webs: a concise review for natural resource managers. Reviews in Fisheries Science 8(2):125-139.

Hering, D., L. Carvalho, C. Argillier, M. Beklioglu, A. Borja, A. C. Cardoso, H. Duel, T. Ferreira, L. Globevnik,J.Hanganu,S.Hellsten,E.Jeppesen,V.Kodeš,A.L.Solheim,T.Nõges,S.Ormerod,Y.Panagopoulos,S.Schmutz,M.Venohr,&S.Birk, 2015.Managingaquaticecosystemsandwater resources under multiple stress - An introduction to the MARS project. The Science of the total environment 504: 10–21.

HighB.,PeeryC.A.&BennettD.H.,2006,TemporarystrayingofColumbiaRiversummersteelheadincoolwaterareasanditseffectonmigrationrates.Trans.Am.Fish.Soc.135:pp519–528.

Hoffarth,P,2004,EvaluationofjuvenilefallChinooksalmonentrapmentintheHanfordReachofthe Columbia River, Washington Department of Fish and Wildlife.

HoganZ.,MoyleP.,MayB.,VanderZandenJ.&BairdI.,2004,TheimperiledgiantsoftheMekong:ecologistsstruggletounderstand-andprotect-SoutheastAsia’slargemigratorycatfish,AmericanScientist 92: pp 228-237.

HolznerM., 2000, Untersuchungen über die Schädigungen von Fischen bei der Passage desMainkraftwerks Dettelbachs. Dissertation an der Technischen Universität München, Inst. f. Tierwissenschaften. München: 333 p.

Hook, Jacob; Novak, Susan and Johnston, Robyn, 2003, Social Atlas of the Lower Mekong Basin. MekongRiverCommission,PhnomPenh.154pages.ISSN

HortleK.G.,2009,FishesoftheMekong–howmanyspeciesarethere?CatchandCulture25(2):pp 4-12.

HortleK.G.,2009,FisheriesoftheMekongRiverBasin:pp199-253inCampbellI.C.(ed.).TheMekong:BiophysicalEnvironmentofaTransboundaryRiver,Elsevier,NewYork.



Hortle,KG,2007,Consumptionand theyieldoffishandotheraquaticanimals fromtheLowerMekongbasin,MRCTechnicalPaperNo.16,MekongRiverCommission,Vientiane:87p.

Hortle, KG, 2009, Fisheries of theMekongRiver basin, Pp, 197-249 In, Hesse LW, StalnakerCB,BensonNG,Zoboy JR (eds):RestorationPlanning for theRivers of theMississippiRiverEcosystem.Washington (DC):USDepartmentof Interior,NationalBiologicalSurvey,BiologicalReport 19.

Hortle KG. Khounsavan O., Phetsamone PC., Singhanouvong D., Viravong S., 2012, Drift ofichthyoplanktonintheMekongRiverinupperLaoPDRintheearlywetseasonof2010.92p.

HortleK.G.andBamrungrachP.,2015,FisheriesHabitatandYieldintheLowerMekongBasin.MRCTechnicalPaperNo.47.MekongRiverCommission,PhnomPenh,Cambodia.80pp.ISSN:1683-1489.

HuangX.,LiK.,DuJ.&LiR.,2010,Effectsofgassupersaturationon lethalityandavoidanceresponsesinjuvenilerockcarp(ProcyprisrabaudiTchang).JZhejiangUnivSciB.;11(10):806–811. doi: 10.1631/jzus.B1000006.

Hunter,M,1992,Hydropowerflowfluctuationsandsalmonids:areviewofthebiologicaleffects,mechanical causes and options for mitigation, Technical report number 119. State of Washington Department of Fisheries: Olympia.

ICEM, 2010, MRC SEA for Hydropower on the Mekong Mainstream, Social Systems Baseline Assessment,WorkingPaper,VolumeII.

ICEM, 2010, MRC Strategic EnvironmentalAssessment (SEA) of hydropower on theMekongmainstream, Hanoi, Viet Nam.

ICEM,2008,StrategicEnvironmentalAssessmentoftheQuangNamProvinceHydropowerPlanfortheVuGia-ThuBonRiverBasin,PreparedfortheADB,MONRE,MOITT&EVN,Hanoi,VietNam.

ICPDR (InternationalCommission for theProtectionof theDanubeRiver),2013,Measures forensuringfishmigrationattransversalstructures.Technicalpaper.Authors:SchmutzS.&MielachC., p24.

IEA(InternationalEnergyAgency)(2015)Hydropowertechnologies,at:https://www.iea.org/topics/renewables/subtopics/hydropower/(14.09.2015)

International Energy Agency, 2006, Implementing Agreement for Hydropower Technologies and ProgrammesAnnexVIII, HydropowerGoodPractices: EnvironmentalMitigationMeasures andBenefits.

276

IUCN, 2013, Ecological Survey of the Mekong River between Louangphabang and Vientiane Cities, LaoPDR,2011-2012.Vientiane,LaoPDR.IUCN

Iucnredlist.org

IntralavanA.,WoodD.andR.Frankel,2015,WorkingPaperonEconomic,EnvironmentalandSocial Impacts of Hydropower Development in the Lower Mekong Basin, Oxfam.

JohnsonG.E.&DaubleD.D., 2006,Surfaceflowoutlets toprotect juvenile salmonidspassingthrough hydropower dams. Rev. Fish. Sci. 14: pp 213–244.

Jones,JI,Murphy,JFJ,Collins,AL,Sear,DA,Naden,PS,Armitage,PD,2012,TheimpactoffinesedimentonMacro-Invertebrates.RiverResearchandApplication,1071(May2011):1055–1071(doi:10.1002/rra).

Jungwirth M., 1998, River continuum and fishmigration – going beyond the longitudinal rivercorridor inunderstandingecological integrity.JungwirthM.,SchmutzS.&WeissS. (Eds.)FishMigrationandfishBypasses.FishingNewsBooks,Oxford:pp19-32.

Jungwirth, M., Haidvogl, G., Moog, O., Muhar, S., Schmutz, S., 2003, Angewandte Fischökologie an Fließgewässern, 552; Facultas Universitätsverlag,Wien; ISBN 3-8252-2113-X

KangB.,DamingH.,PerrettL.,WangH.,HuW.,DengW.&WuY.,2009,FishandfisheriesintheUpperMekong:currentassessmentofthefishcommunity,threatsandconservation.Rev.Rish.Biol. Fisheries 19: pp 465-480.

Kantoush,S.A.,andSumi,T,2010,RiverMorphologyandSedimentmanagementStrategiesforSustainableReservoirinJapanandEuropeanAlps,AnnualsofDisas.Prev.ResInst.,KyotoUni.,No53B.

KarppinenP.,MakinenT.S.,ErkinaroJ.,KostinV.V.,SadkovskijR.V.,LupandinA.I.&KaukorantaM., 2002, Migratory and route-seeking behaviour of ascending Atlantic salmon in the regulated RiverTuloma.Hydrobiology,483(1–3):pp23–30.

Karr, JR, 1991, Biological integrity: a long–neglected aspect of water resource management,Ecological Applications 1, pp66-84.

Ke,J.&Gao,Q.2013.OnlyOneMekong:DevelopingTransboundaryEIAProceduresofMekongRiverBasin.30PaceEnvtl.L.Rev.950.

KeeferM.L.,PeeryC.A.,BjornnT.C.,JepsonM.A.&StuehrenbergL.C.,2004,Hydrosystem,dam,and reservoir passage rates of adult chinook salmon and steelhead in the Columbia and Snake Rivers.Trans.Am.Fish.Soc.133(6):pp1413–1439.



KeeferM.L.,PeeryC.A.,DaigleW.R.,JepsonM.A.,LeeS.R.,BoggsC.T.,TolottiK.R.&BurkeB.A.,2005, Escapement, harvest, and unknown loss of radio-tagged adult salmonids in the Columbia River – Snake River hydrosystem. Can. J. Fish. Aquat. Sci. 62: pp 930–949.

Kemp,P,Sear,D,Collins,A,Naden,P,Jones,I,2011,Theimpactsoffinesedimentonriverinefish.HydrologicalProcesses,25(11):1800–1821(doi:10.1002/hyp.7940).

Keskinen M. and M. Kummu, 2010, Impact Assessment in the Mekong: Review of StrategicEnvironmentalAssessment(SEA)&CumulativeImpactAssessment(CIA),TKK-WD-08,Water&DevelopmentPublications–AaltoUniversity.

KeyConsultantsCambodia(KCC),2008,EIAReportforLowerSesan2HPP.

KieckhäferH.,1973,Arehydropowerplantskillingourfish(inGermanlanguage).DerFischwirt:Jg. 23. H. 2.

KingA.J.,TonkinZ.andMahoneyJ.,2009,Environmentalflowenhancesnativefishspawningandrecruitment in the Murray River, Australia, River Research and Applications 25, 1205–1218.

KingJM,TharmeRE,BrownCA,1999,Definitionandimplementationofinstreamflows,ThematicReport for the World Commission on Dams, Southern Waters Ecological Research and Consulting, Cape Town, South Africa. 63p.

King, J, Brown, C, Sabet, H, 2003,A scenario-based holistic approach to environmental flowassessmentsforrivers,riverResearchandApplications19:619-639(DOI:10.1002/rra.709).

King, JM, Tharme, RE, 1994,Assessment of the instream flow incremental methodology andinitialdevelopmentofalternative instreamflowmethodologiesforSouthAfrica.WaterResearchCommissionReportNo.295/1/94.WaterResearchCommission,Pretoria:590p.

KnightPiesold&MerzandMcLellan,1988,BujagaliPowerProject,FeasibilityStudy.

KoehnkenL.,2015),DischargeSedimentMonitoringProject (DSMP)2009–2013Summary&AnalysisofResults,MRCTechnicalReport(inpress).

Kummu,MandVaris,O,2007,Sediment-relatedimpactsduetoupstreamreservoirtrapping,theLower Mekong River. Geomorphology, volume 85, numbers 3-4, pages275-293.

Lai,J-S,Lee,F-Z,Sumi,T,Liao,Y-JandTan,Y-C,2015,Reductionofreservoirsedimentationbyadopting sediment bypass tunnel, E-proceedings of the 36th IAHR World Congress, 28 June – 3 July, 2015, The Hague, the Netherlands.

Lamarque,P,FQuetier,andSLavorel,2011,“Thediversityoftheecosystemservicesconceptandits implications for their assessment and management.” Comptes Rendus Biologies no. 334:441-449.

278

LarinierM., 2000,Dams and fishmigration, InDams, ecosystem functions and environmentalrestoration, Thematic Review II.1 prepared as input to the World Commission on Dams, Cape Town,BerkampG.,McCartneyM.,DuganP.,McNeelyJ.&AcremanM.(eds.).

Larinier,M,Travade,F,Porcher,JP,2002,Fishways:biologicalbasis,designcriteriaandmonitoring,Bull.Fr.PechePiscic.364(Supplement).

LarinierM.&TravadeF.,2002,Downstreammigration:problemsandfacilities.Bull.Fr.PechePiscic364: pp 181-207.

LarinierM.,2002,Locationoffishways.BulletinFrançaisde laPêcheetde laPisciculture364(Supplement):pp39-53.

Lassalle, G., Crouzet, P., Rochard, E., 2009, Modelling the current distribution ofEuropeandiadromousfishes:anapproachintegratingregionalanthropogenicpressures.Freshwat.Biol.54,587–606.LefecreS,HuongDTT,HaNTK,WangT,PhuongNT,BayleyM.(2011):Atelemetrystudyofswimmingdepthandoxygenlevel inPangasiuspondintheMekongDelta.Aquaculture315:p410-413.

Lauri,H.,Moel,D.Ward,H.,Rasanen,P.J.,Keskinen,T.A.andKumma,M,2012,FutureChangesin Mekong River Hydrology: Impacts of Climate Change and Reservoir Operation on Discharge. Hydrology and Earth System Sciences, 16

LiJ,DongS,LiuS,YangZ,PengM,ZhaoC.,2013a,Effectsofcascadinghydropowerdamson the composition, biomass and biological integrity of phytoplankton assemblages in the middle Lancang-Mekong River. Ecological Engineering 60: 316-324.

Li,K,Zhu,C,Wu,L,andHuang,L,2013b,ProblemscausedbytheThreeGorgesDamconstructionintheYangtze,Environ.Rev.21:127–135,dx.doi.org/10.1139/er-2012-0051.

Lieng,S.andZalinge,N.P.van,2001,FishyieldestimationinthefloodplainsoftheTonleSap-GreatLakeandRiver,Cambodia.CambodiaFisheriesTechnicalPaperSeries,3:23-26.

LiengS.,YimC.&vanZalingeN.P.,1995,FreshwaterfisheriesofCambodia,I:thebagnet(dai)fisheryintheTonleSapRiver.AsianFisheriesScience8:pp255-262.

LillehammerL. (ed.). 2013.TanzaniaHydropowerSustainabilityAssessment. InceptionReport.World Bank/MEM.

Lillehammer L., O. San Martin and S. Dhillion (eds), 2011, Benefit Sharing and Hydropower:EnhancingDevelopmentBenefitsofHydropowerInvestmentsThroughanOperationalFramework,Synthesis Report, Sweco Report for the World Bank.

Lim,P.;Villanueva,M.C.;Chhouk,B.;Chay,K.K.;Brun,J.M.andMoreau,J.,2005,Fishassessment



intherehabilitatedpoldersofPreyNup(Cambodia).AsianFisheriesScience,18:241-253.

Lisle,TE,Lewis,J,1992,Effectsofsedimenttransportonsurvivalofsalmonidembryosinanaturalstream: A simulation approach. Canadian Journal of Fisheries und Aquatic Sciences. 49: 2337-2344.

Loisel,H,Mangain,A,Vantrepotte,V,Dessailly,D,DinhDN,Garnesson,P,Ouillon,S,Lefebvre,J-P,Mériaux,X,andPhan,TM,2014,VariabilityofsuspendedparticulatematterconcentrationincoastalwatersundertheMekong’sinfluencefromoceancolor(MERIS)remotesensingoverthelast decade, Remote Sensing of Environment 150, pp218–230.

Louca V., Lindsay S.W. and LucasM. C., 2009, Factors triggering floodplain fish emigration:Importanceoffishdensityandfoodavailability.EcologyofFreshwaterFish18,60–64.

LoucksD.P.andE.vanBeek,eds.,2005,WaterResourcesSystems.PlanningandManagement.An introduction to Methods, Models and Application, Studies and Reports in Hydrology, UNESCO Publishing.

Lowe-McConnellR.L.1999.Estudosecológicosdecomunidadesdepeixestropicais.SãoPaulo,EDUSP.

Lu,XX,Siew,RY,2005,WaterdischargeandsedimentfluxchangesintheLowerMekongRiver,Hydrological Earth System Science Discussion, 2: 2287-2325.

LucasM.&FrearP., 1997,Effects of a flow-gaugingweir on themigratory behaviour of adultbarbel, a riverine cyprinid. J. Fish Biol. 50: pp 382–396.

LucasM.&BarasE.,2001,Migrationoffreshwaterfishes.BlackwellScience,Oxford:420p.

Lundqvist,H,Rivinoja,P,Leonardsson,K,McKinnell,S,2008,UpstreampassageproblemsforwildAtlanticsalmon(SalmosalarL.)inaregulatedriveranditseffectonthepopulation,Hydrobiologia2008: 111–12.7

Ly,K.,Larsen,H.andVanDuyen,N,2015,2013LowerMekongRegionalWaterQualityMonitoringReport,MRCTechnicalPaperNo.51.MekongRiverCommission,Vientiane,63pp.

Lyu, X, 2015, From Manwan to Nuozhadu: The political ecology of hydropower on China’s Lanchang River,In;MatthewsN.andK.Geheb(eds.),2015,HydropowerDevelopmentintheMekongRegion:Political,socio-economicandenvironmentalperspectives,EarthscanStudiesinWaterResourcesManagement, Earthscan from Routledge.

March,PA.,Brice,TA,Mobley,MHandCybularz,JM.,1992,TurbinesforSolvingtheDODilemma,Hydro Review vol 11, Number 1, March 1992.

280

MarchandM.,MeijerK.,SloofK.,PasschierR.,LillehammerL.,HaL.T.,NhungandOseH,2014,Mitigating Cumulative Impacts of Small-Scale Hydropower Cascades: Case Studies from Vietnam. ProceedingsPaperfortheInternationalSymposiumonEcohydraulics2014,TrondheimNorway.

MattewsN.andK.Geheb,2015(eds.),HydropowerDevelopmentintheMekongRegion.Political,socio-economic and environmental perspectives. Earthscan.

Mattson,N.S.;Balavong,V.;Nilsson,H.;Phounsavath,S.andHartmann,W.,2001,ChangesinfisheriesyieldandcatchcompositionattheNamNgumReservoir,LaoPDR.ACIARProceedings,98: 48-55.

McVittie,Alistair,andDominicMoran,2010,“Valuingthenon-usebenefitsofmarineconservationzones:AnapplicationtotheUKMarineBill.”EcologicalEconomicsno.70(2):413-424.

Meynell P, 2014, Improving reservoir ecologywith constructedwetlands.Hydropower &Dams2014(3),78-80.

Milhous,RT,1990,ThecalculationofflushingflowsforgravelandcobbleBedRivers,In:ChangHH,HillJC(eds)Hydraulicengineering.AmericanSocietyofCivilEngineers,NewYork.

Millennium Ecosystem Assessment, 2005, Ecosystems and Human Well-being: Synthesis. Island Press,Washington,DC.

MonyakeV.andL.Lillehammer,2011,LesothoHighlandsWaterProject–CaseStudyReport:BenefitSharingandHydropower:EnhancingDevelopmentBenefitsofHydropowerInvestmentsThrough an Operational Framework. World Bank.

Morris, 2015, Management alternatives to combat reservoir sedimentation, paper presented at the InternationalWorkshoponSedimentBypassTunnels,April27–29,Zurich,Switzerland

Morris,G.L.,&Fan,J.,1998,Reservoirsedimentationhandbook,NewYork:MCGraw-HillBookCo.

MoserM.L.,DarazsdiA.M.&Hall,J.R.,2000,ImprovingpassageefficiencyofadultAmericanshadatlow-elevationdamswithnavigationlocks.N.Am.J.Fish.Manag.20(2):pp376–385.

MRC, 2001, Fish Migrations and Spawning Habits in the Mekong Mainstream. CD ROM.

MRC. 2001. MRC Hydropower Development Strategy.

MRC,2003,ProceduresforNotification,PriorConsultationandAgreement.

MRC, 2005, Overview of the Hydrology of the Mekong Basin, November 2005.



MRC, 2005, Deep pools as dry season habitats in the Mekong River basin. Mekong Fisheries management Recommendation No. 3. The Technical Advisory Body for Fisheries Management (TAB).August2005,7p.

MRC,2007,DiagnosticstudyofwaterqualityintheLowerMekongBasin,MRCTechnicalPaperNo. 15.

MRC, 2007, An Introduction to the Mekong Fisheries of Thailand, Mekong Development Series No. 5, Mekong River Commission.

MRC, 2008, The Mekong River Report Card on Water Quality 2000 – 2006.

MRC, 2009, An assessment of the hydrology at proposed dam sites on the mainstream of the Mekong upstream of Vientiane. Report for the Ministry of Energy and Mines, Department of Electricity,LaoPDR,January2009

MRC,2009,BasinDevelopmentPlan,Programme2011-2015,ProgrammeDocument,MekongRiverCommission,Vientiane,LaoPDR.

MRC, 2009, The Flow of the Mekong – Meeting the needs, keeping the balance, MRC Management Information booklet series No. 2. 12p.

MRC, 2009, Basin Development Plan Programme, Phase 2, Technical Note 2, Economic,environmental and social impact assessment of basin-wide water resources development scenarios, Assessment methodology, October 2009: 257p.

MRC,2009,Preliminarydesignguidance forproposedmainstreamdams in theLowerMekongBasin.MekongRiverCommission,Vientiane,LaoPDR:38p.

MRC,2010,ImpactsonRiverMorphology(fordiscussion),BasinDevelopmentPlanProgrammePhase2AssessmentofBasinWideDevelopmentScenarios,TechnicalNote4.

MRC, 2010, Impacts on Wetlands and Biodiversity, Assessment of Basin-wide development scenarios,MRCBasinDevelopmentPlanProgramme,Phase2,TechnicalNot9.

MRC,2010,InitiativeonSustainableHydropower(ISH),2011-2015Document.

MRC, 2010, Social assessment, Technical Note 12 for discussion, Assessment of basin-wide developmentscenarios,BasinDevelopmentPlanProgramme,Phase2,MekongRiverCommission

MRC,2010,Social ImpactMonitoringandVulnerabilityAssessmentReportonaRegionalPilotStudyfortheMekongCorridor,MRCTechnicalPaperNo30,MekongRiverCommission

282

MRC,2011,BasinDevelopmentPlan,includingPlanningAtlasofthelowerMekongRiverBasin.

MRC, 2011, Assessment of Basin-wide Development Scenarios – Cumulative impact assessment of the riparian countries’ water resources development plans, including mainstream dams and diversion,BasinDevelopmentPlanProgramme,Phase2:229p.

MRC,2011,Procedures forNotification,PriorConsultationandAgreement(PNPCA),ProposedXayaburiDamProject–MekongRiver,Priorconsultationprojectreviewreport,MRC2011:109p.

MRC, 2011, IWRM-based Basin Development Strategy.

MRC, 2013, Improved Environmental and Socio-Economic Baseline Information for Hydropower Planning,DraftISH11Phase2Report.

MRC, 2014, The Council Study, Study on the sustainable management and development of the Mekong river, including impacts of mainstream hydropower projects – Inception Stage Literature Review. Draft Final on 31. Mach 2014: 131p.

MRC, 2014, The Council Study, Study on the sustainable management and development of the Mekong river, including impacts of mainstream hydropower projects: Inception Report. Draft Final 27. October 2014: 77p.

MRC, 2015, Discussion Note on MRC Ecosystem and Ecosystem Services Assessment Activities, 18August2015,Vientiane,LaoPDR.

MRC,2016,MRCStrategicPlan2016-2020.

MRC,2016,MRCBasinDevelopmentPlan,2016-2020.

MRC, 2017, Hydropower Development Strategy Update for Sustainable Development in the Lower Mekong Basin. Concept Note – Draft Version, 31 January 2017.

MRC, 2018a, Final Hydropower Risks and Impact Mitigation Guidelines and Recommendations.

MRC,2018b,FinalHydropowerRisksandImpactMitigationMANUAL–KeyHydropowerRisks,Impacts and Vulnerabilities and General Mitigation Options for Lower Mekong.

MRC, 2018c, Final Case Study Report – Mainstream Dams Assessment Including Alternative Schemes Layouts.

MuirT.C.,2010,TributarySignificanceStudy-Hydropower,MekongRiverCommission.



MuirW.D.,MarshD.M.,SandfordB.P.,SmithS.G.,WilliamsJ.G.,2006,Post-hydropowersystemdelayed mortality of transported Snake River stream-type Chinook salmon: unraveling the mystery. Trans. Am. Fish. Soc. 135: pp 1523-1534.

Muir W.D. & Williams J.G., 2012, Improving connectivity between freshwater and marine environments for salmon migrating through the lower Snake and Columbia River hydropower system. Ecological Envineering 48: pp 19-24.

Nachaipherm,J.;Nuengsit,S.;Rukaewma,P.;Taruwan,W.;Nakkaew,S.andSinsoontorn,S.,2003, Fisheries activities and catch assessments of three reservoirs: Nam Oon in Sakon Nakhon province,KaengLawa inKhonKaenprovinceandHuaiMuk inMukdahanprovince,Thailand.MRC Conference Series, 4: 185-193.

Nagrodski,A,Raby,GD,Hasler,CT,Taylor,MK,Cooke,SJ,2012,Fishstranding in freshwatersystems: sources, consequences, and mitigation, Journal of Environmental Management, 103: 133–141.

NakataniK.,BaumgartnerG.&CavicchioliM.,1997,Ecologiadeovoselarvasdepeixes,InAplanfeiedeinundaräodoaltorioParand:aspectosjfsicos,biol6gicosesocioeconomicos,VazzolerAEAM,AgostinhoAA,HahnNS(eds),Eduem,UEM-Nupelia:Maringa:pp281-306.

Nam Theun 2 Power Company Ltd., 2005, Nam Theun 2 Hydroelectric Project – OwnersRequirements.

National Consulting Company Vientiane (NCCV), 2013, Don Sahong hydropower project, LaoPDR,Environmentalimpactassessment,FinalJanuary2013,133p.

National Hydroelectric Power Corporation (India), undated, Presentation on Sedimentation inReservoirs – Case Studies, http://www.irtces.org/zt/training2007/ppt/India.pdf.

NationalConsultingCompanyVientiane (NCCV), 2013,Cumulative ImpactAssessment –DonSahonghydropowerproject,LaoPDR,EnvironmentalandSocialstudies.PreparedforMegafirstcorporation berhad: 76p.

NaughtonG.P.,CaudillC.C.,KeeferM.L.,BjornnT.C.&StruehrenbergL.C.,2005,Late-seasonmortalityduringmigrationof radio-taggedadultSockeyesalmon (Onchorhynchusnerka) in theColumbia River. Can. J. Fish. Aquat. Sci. 62: pp 30–47.

Newcombe,CP,1994,Suspendedsediments inaquaticecosystems: illeffectsasa functionofconcentrationunddurationofexposure.HabitatProtectionBranch,BritishColumbiaMinistryofEnvironment,LandsundParks.Victoria,BritishColumbia,Canada:298p.

Newcombe,CP,2003,ImpactAssessmentforclearwaterfishesexposedtoexcessivelycloudywater,JournaloftheAmericanWaterResourcesAssociation39(3):529-544.

284

Newcombe,CP,Jensen,JOT,1996,ChannelSuspendedSedimentundFisheries:aSynthesisforQuantitative Assessment of Risk und Impact. North American Journal of Fisheries Management 16: 693-694.

Newcombe,CP,MacDonald,DD,1991,Effectsofsuspendedsedimentsonaquaticecosystems.North American Journal of Fisheries Management 11: 72- 82.

NGOForum,2009,LowerSesan2HydroProjectEIAReview,preparedbytheNGOForumonCambodia,PhnomPenh,Cambodia,August2009:18p.

NielsenN.M.,R.S.Brown,&Z.D.Deng.,(inpress),ReviewofExistingKnowledgeontheEffectivenessandtheEconomicsofFish-FriendlyTurbines.PhnomPenh,MekongRiverCommission.74pp.

Nissanka,C.,2001,EffectofhydrologicalregimesonfishyieldsinreservoirsofSriLanka.ACIARProceedings,98:93-100.

NN3PowerCompany,2011,EnvironmentalImpactAssessmentoftheNamNgum3HydropowerProject,October2011:514p.

NNPC,2012,NamNgiep1HydropowerProject(LaoPeople’sDemocraticRepublic),MainReport,Prepared by NamNgiep Power Company Ltd. with assistance from ERM-SiamCo., Ltd.AndEnvironmental Research Institute, Chulalongkorn University for the Asian Development Bank.

Noble, B, 2010, Introduction to Environmental Impact Assess¬ment: Guide to Principles andPractice,2ndedition,DonMills,Canada:OxfordUniversityPress.

NORPLANHydropowerLtd.,2014.NgonyeFallsHydroelectricScheme–DraftFeasibilityStudyInterim Report.

Northcote T.G., 1978. Migratory strategies and production in freshwater fishes, In: Ecology ofFreshwaterFishProduction.GerkingS.D.(Ed.).BlackwellScientificPublications,Oxford-London-Edinburgh-Melbourne: pp 326-359.

NorthcoteT.G.,1984.Mechanismsoffishmigrationinrivers,In:Mechanismsofmigrationinfishes.McCeaveJ.D.,AtnoldG.P.,DodsonJ.J.andNeilW.H.(Eds.),PlenumPress,NewYork–London:pp 317-355.

NorthcoteT.G.,1998,Migratorybehaviouroffishanditssignificancetomovementthroughriverinefishpassagefacilities,InS.Weiss(ed.)FishMigrationandFishBypasses,FishingnewsBooks,Oxford: pp 3-18.

Nogueira,M.G.,Ferrareze,M.,Moreira,M.L.,Gouvêa,R.M.,2010,Phytoplanktonassemblagesinareservoircascadeofalargetropical–subtropicalriver(SE,Brazil).Braz.J.Biol.70,781–793.



OEPP,2002,AninventoryofwetlandsofinternationalandnationalimportanceinThailand.OfficeofEnvironmentalPolicyandPlanning,MinistryofScience,TechnologyandEnvironment.Bangkok,Thailand.

Olangunju, A.O, 2012, Selecting Valued Ecosystem Compo¬nents for Cumulative Effects inFederallyAssessedRoadInfrastructureProjectsinCanada,UniversityofSaskatch¬ewan,Canada.

Olson, F, 1990, Downramping regime for power operations to minimize stranding of salmon fry in SultanRiver,ReportbyCH2MHillforSnohomishCountyPUD1,Bellevue.

Olson, FW, Metzgar, RG, 1987, Downramping to minimize stranding of salmonid fry, In: Clowes BW (ed)Waterpower’87,internationalconferenceonhydropower.AmericanSocietyofCivilEngineers,NewYork.

Ongley E., 2009, Water Quality of the Lower Mekong River, in: Campbell C. (ed.) Mekong.Biophysical Environment of an International River Basin.

Ormerod, SJ, Dobson, M, Hildrew, AG, Townsend, CR, 2010, Multiple stressors in freshwater ecosystems, Freshw. Biol., 55: 1-4.

Opperman,J.,G.GrillandJ.Hartmann,2015,ThePowerofRivers:Findingbalancebetweenenergy and conservation in hydropower development. The Nature Conservancy: Washington, D.C.

Opperman,J.,J.Hartmann,J.Raepple,H.Angarita,P.Beames.,E.Chapin,R.Geressu,G.Grill,J.Harou,A.Hurford,D.Kammen,R.Kelman,E.Martin,T.Martins,R.Peters,C.Rogéliz,andR.Shirley.2017.ThePowerofRivers:ABusinessCase.TheNatureConservancy:Washington,D.C.\

Pagdee,A.,S.Homchuen,N.Sangpradab,C.Hanjavanit,andP.Uttharak,2007,“BiodiversityandeconomicvalueofwetlandresourcesatNongHan,UdonthaniProvince,NortheastThailand“NaturalHistoryBulletinoftheSiamSocietyno.55(2):323-339.

Parasiewicz,P,2001,MesoHABSIM:aconcept forapplicationof instreamflowmodels in riverrestoration planning, Fisheries, 26: 6–13.

Parasiewicz,P,Schmutz,S,Moog,O,1998,Theeffectofmanagedhydropowerpeakingonthephysicalhabitat,benthosandfishfaunaintheriverBregenzerachinAustria.FisheriesManagementand Ecology 5: 403–417.

PavlovD.S.,1989,Structuresassistingthemigrationsofnon-salmonidfish:USSR.FAO,Rome:97 p.

PCE–Furnas–Odebrecht,2004,RioMadeiraHydroelectricComplexFeasibilityStudies.

Pelicice, F.M. & A.A. Agostinho, 2008, Fish-Passage Facilities as Ecological Traps in Large

286

Neotropical Rivers. Conservation Biology 22: 180-188. doi: 10.1111/j.1523-1739.2007.00849.x

Pengbun,N.&H.Chanthoeun,2001,AnalysisoftheDaicatchesinPhnomPenh/Kandal.p.44-51.In:Matics,K.I.Editor.ProceedingsfromtheThirdTechnicalSymposiumonMekongFisheries,8-9December2000.MekongConferenceSeriesNo.1.MekongRiverCommission,PhnomPenh.

Perbiche-Neves, G., Ferreira, R.A.R., Nogueira, M.G., 2011, Phytoplankton structure in twocontrasting cascade reservoirs (Paranapanema River, Southeast Brazil). Biologia (Bratisl.) 66,967–976.

Petts,GE,1984,Impoundedrivers:perspectivesforecologicalmanagement.Wiley,NewYork.

Phittayaphone S, 2003, Classification and inventory of wetland/ aquatic ecosystem Lao PDR.MRCS consultancy report.

Pholprasith,S.andSirimongkonthaworn,R.,1999,ThefishcommunityofUbolratanaReservoir,Thailand. In Fish and Fisheries of Lakes and Reservoirs in Southeast Asia and Africa. (Eds WLT vanDensen,MJMorris).WestburyPublishing:Otley,UK.

Piman,T,Lennaerts,T,Southalack,P,2013,Assessmentofhydrological changes in the lowerMekong

Pholprasith,S.andSirimongkonthaworn,R,1999,ThefishcommunityofUbolratanaReservoir,Thailand. In Fish and Fisheries of Lakes and Reservoirs in Southeast Asia and Africa. (Eds WLT vanDensen,MJMorris).WestburyPublishing:Otley,UK.

Piman,T.,Cochrane,T.,Arias,M.,Green,A.,andDat,N.,2013,AssessmentofFlowChangesfromHydropower Development and Operations in Sekong, Sesan and Srepok Rivers of the Mekong Basin,JournalofWaterResourcesPlanningandManagement,139(6),723–732.

Poff,NL,Allan,JD,Bain,MB,Karr,JR,Prestegaard,KL,Richter,BD,Sparks,RE,Stromberg,JC,1997, The Natural Flow Regime – A paradigm for river conservation and restoration. BioScience 47(11):769-784.

Poff,NL,Allan,JD,Palmer,MA,Hart,DD,Richter,BD,Arthington,AH,Rogers,KH,Meyer,JL,Stanford, JA, 2003, River flows andwater wars: emerging science for environmental decisionmaking, Frontiers in Ecology and the Environment 1: 298-306.

Poff,NL,Richter,BD,Arthington,AH,Bunn,SE,Naiman,RJ,Kendy,E,Acreman,M,Apse,C,Bledsoe,BP,Freeman,MC,Henriksen,J,Jacobson,RB,Kennen,JG,Merritt,DM,O’Keeffe,JH,Oldgen,JD,RogersK,Tharme,RE,Warner,A,2010,Theecologicallimitsofhydrologicalteration(ELOHA): a new framework for developing regional environmental flow standards, FreshwaterBiology 55: 147-170.



PoffN.L.,BrownC.M.,GranthamT.E.,Matthews J.H.,PalmerM.A.,SpenceC.M.,WilbyR.L.,HaasnootM.MendozaG.F.,DominiqueK.C.andBaezaA.,2015,Sustainablewatermanagementunder future uncertainty with eco.-engineering decision scaling. Nature climate change 2015. doi:10.1038/nclimate2765.

PompeuP.S.,NogueiraL.B.,GodinhoH.P.&MartinezC.B.,2011,Downstreampassageoffishlarvaeandeggsthroughasmall-sizedreservoir,MucuriRiver,Brazil.Zoologia28(6):pp739-746.

Postel,S,Richter,B,2003,RiversforLife:ManagingWaterforPeopleandNature.IslandPress.Washington, DC.

Poulsen,A.F.andJ.Valbo-Jørgensen(editors),2000,FishmigrationsandspawninghabitsintheMekong Mainstream – a survey using local knowledge. AMFC Technical Report. Mekong River Commission.

PoulsenA.F., 2003, Fishmovements and their implications for river basinmanagement in theMekongRiverBasin,Presentedat:Thesecondinternationalsymposiumonthemanagementoflarge rivers for fisheries, at: http://www.lars2.org/unedited_papers/unedited_paper/Poulsen%20migration.pdf.

PoulsenA.F.,HortleKG.,Valbo-JorgensenJ.,ChanS.,ChhuonC.K.,ViravongS.,BouakhamvongsaK.,SuntornratanaU.,YoorongN.,NguyenT.T.&TranB.Q.,2004,DistributionandecologyofsomeimportantriverinefishspeciesoftheMekongRiverbasin.MRCTechnicalPaperNo.10,MekongRiverCommission,PhnomPenh.

PoulsenA.F.,OuchO.,SintavongV.,UbolratanaS.&NguyenT.T.,2002,FishmigrationsoftheLower Mekong River basin: implications for development, planning and environmental management, MRCtechnicalpaperno.8.PhnomPenh:MRC.

Poulsen,AF,Hortle,KG,Valbo-Jorgensen,J,Chan,S,Chhuon,CK,Viravong,S,Bouakhamvongsa,K,Suntornratana,U,Yoorong,N,Nguyen,TT,Tran,BQ,2004,DistributionandecologyofsomeimportantriverinefishspeciesoftheMekongRiverbasin.MRCTechnicalPaperNo.10,MekongRiverCommission,PhnomPenh,Cambodia:116pp(ISSN:1683-1489).

Pöyre,2011,Xayaburi:EffectsonTonleSap.EffectsofXayaburiHPPontheHydrologyofTonleSap.

QuL.,LiR.,LiJ.,LiK.F.&DengY.,2011,Fieldobservationoftotaldissolvedgassupersaturationofhigh-dams.SciChinaTechnolSci.2011;54(1):156–162.doi:10.1007/s11431-010-4217-8.

Rainboth,W.J.,1996,FAOSpecies identificationfieldguide forfisherypurposes.Fishesof theCambodian Mekong, Rome, FAO, 1996 ISBN 92-5-103743-4, 256 pp.

Räsänen,T.A., 2014,HydrologicalChanges in theMekongRiverBasin.Theeffectsof climatevariabilityandhydropowerdevelopment,PhDThesis,AaltoUniversity,Finland.

288

RaymondH.L.,1979,EffectsofdamsandimpoundmentsonmigrationsofjuvenileChinooksalmonand steelhead from the Snake River. 1966 to 1975. Trans. Am. Fish. Soc. 108: pp 505–529.

Reiser,DW,Wesche,TA,Estes,C,1989b,StatusofinstreamflowlegislationandpracticeinNorthAmerica,Fisheries14(2):22-29.

Reiser,DW,Ramey,MP,Wesche,TA,1989a,Flushingflows In:Alternative inRegulatedRivermanagement,Gore,JA,Petts,GE(eds).CRCPress:Florida.

Richter, B, Baumgartner, JV, Powell, J, Braun, DP, 1996, A method for assessing hydrologicalteration withing ecosystems. Conservation Biology 10: 1163-1174.

Richter,BD,Baumgartner,JV,Wigington,R,Braun,DP,1997,Howmuchwaterdoesariverneed?Freshwater Biology 37: 231-249.

RinglerC,2001,OptimalwaterallocationintheMekongRiverBasin.ZEF–DiscussionPapersonDevelopmentPolicyNo.38.Bonn,Germany.

Roberts,T.R.andI.G.Baird,1995,TraditionalfisheriesandfishcologyontheMekongRiveratKhoneWaterfallsinSouthernLaos.NaturalHistoryBulletinoftheSiamSociety43:219-262.

Roland,KM.,Foust,JM.,Lewis,GDandSigmon,JC,2010,Equipment: AeratingTurbines forDukeEnergy’sNewBridgwaterPowerhouse,HydroReview,http://www.hydroworld.com/articles/hr/print/volume-29/issue-3/articles/equipment--aerating.html

Ruggles C.P. & Murray D.G., 1983, A review of fish response to spillways. Freshwater andAnadromous Div., Resource Branch Dept. of Fisheries and Oceans, Halifax, Nova Scotia, Can. Tech. Rep. of Fisheries and Aquatic Sci. 1172: 30 p.

RyanB.A.,DawleyE.M.,&NelsonR.A.,2000,Modelingtheeffectsofsupersaturateddissolvedgas on resident aquatic biota in the mainstem Snake and Columbia Rivers. North American Journal of Fisheries Management 20:192-204.

Ryon,M.G.,Cada,G.F.,Smith,J.G.,2004),Furthertestsofchangesinfishescapebehaviourresulting from sub-lethal stresses associated with hydroelectric turbine passage, Report ORNL/TM-2003/288,U.S.DepartmentofEnergy(DOE).

Sakurai,TandKobayashi,K.,2015,Operationsofthesedimentbypasstunnelandexaminationof theauxiliarysedimentationmeasurefacilityatMiwaDam,Proc.First InternationalWorkshoponSedimentBypassTunnels,VAW–Mitteilungen232(R.M.Does,ed.),LaboratoryofHydraulics,HydrologyandGlaciology(VAW),ETHZurich,Switzerland.

SarkkulaJ,KoponenJ,KummuM.,2005,ToolsforintegratedbasinflowmanagementatLowerMekongbasin floodplains. In: ZergerA,ArgentM. (eds)MODSIM2005 international congress



on modelling and simulation. Canberra: Modelling and Simulation Society of Australia and New Zealand,2153-2159.

Saunders, JW, Smith, MW, 1965, Changes in a stream population of trout associated with increased silt.JournalofFisheriesResearchBoardofCanada.22(2):396-404.

ScheuerellM.D.,ZabelR.S.,SandfordB.P.,2009,RelatingjuvenilemigrationtimingandsurvivaltoadulthoodintwospeciesofthreatenedPacificsalmon(Oncorhynchusspp.).J.Appl.Ecol.4:pp983–990.

SchmutzS.,ZitekA.&DorningerC.,1997,Anewautomaticdriftsamplerforriverinefish,Arch.Hydrobiol, 139: pp 449-460.

Schmutz,S,1999:FischereilicheAuswirkungenStauraumspülungKWUnzmarkt.UnveröffentlichtesGutachten.

Schmutz,S, 2001,FischereilicheAuswirkungenStaulegungKWUnzmarkt -SchadensfallApril1997.UnveröffentlichtesGutachten.

Schmutz, S, Bakken, TH, Friedrich, T, Greimel, F, Harby, A, Jungwirth, M, Melcher, A, Unfer, G, Zeiringer,B,2014,ResponseoffishcommunitiestohydrologicalandmorphologicalalterationsinhydropeakingriversofAustria,RiverRes.Applic.2014(DOI:10.1002/rra.2795).

Schmutz,S,Kremser,H,Melcher,A,Jungwirth,M,Muhar,S,Waidbacher,H,Zauner,G,2013,Ecological effects of rehabilitation measures at the Austrian Danube: a meta-analysis of fishassemblages.Hydrobiologia(DOI10.1007/s10750-013-1511-z)

Schmutz,S,Mielach,C,2015,ReviewofExistingResearchonFishPassagethroughLargeDamsanditsApplicabilitytotheMekongMainstreamDams,MRCTechnicalPaperNo.48.MekongRiverCommission,PhnomPenh,Cambodia:164pp(ISSN:1683-1489).

ScienceDaily2007.Cambodianvulturenestsofferhopeforspecies.ScienceDaily,Feb21,2007.

Schmitt,R.J.P,Casteletti,A.,BizziS.andG.M.Kondolf.2017.TheNewFrontierinHydropower–ImprovingHydropowerOutcomesThroughStrategicPortfolioPlanning.HydropowerSustainabilityForum:Mekong+,Oslo4-6September.AjointMRC,GIZandMulticonsultevent.

ScottD.A.(ed.),1989,AdirectoryofAsianwetlands.IUCN,Gland,Switzerland.

Scruton,DA,Pennell,C,Ollerhead,LMN,Alfredsen,K,Stickler,M,Harby,A,Robertson,M,Clarke,KD,LeDrew,LJ,2008,Asynopsisof“hydropeaking”studiesontheresponseofjuvenileAtlanticsalmontoexperimentalflowalteration,Hydrobiologia609:263–275.

Scullion,J,Miller,N,1979,Reviewofeffectsofnaturalandartificialflowpatternsundsediment

290

dynamics on benthic invertebrates und salmonids in upland rivers. The University of Wales. Institute ofScienceandTechnology.Cardiff.DeptartmentofAppliedBiology.

Seifert, 2012, Praxishandbuch “Fischaufstiegsanlagen in Bayern”, on behalf of theLandesfischereiverbandBayernandtheBayerischesLandesamtfürUmwelt,p150.

Sen, S.P, 2014, Presentation on Sediment Management for Rangit Dam, India, http://www.hydroworld.com/articles/print/volume-22/issue-2/articles/operations-maintenance/sediment-management-for-rangit-dam-in-india.html

Shaozu,HandJinze,M,1989TamingtheYellowRiver:SiltandFloods,InTamingtheYellowRiverSiltandFloods,Brush,LM.,Wolman,MG,andBing-Wei,H.(eds),KluwerAcademicPublishers,Dordrecht, The Netherlands.

Shoemaker,D,1994,CumulativeEnvironmentalAssessment,DepartmentofGeographyPublicationNo. 42, Waterloo, ON: University of Waterloo.

Singer, U.,2013, Livelihoods and Resource Management Survey on the Mekong between Louang PhabangandVientianeCities,LaoPDR.Vientiane,LaoPDR:IUCN.

SinohydroCorporationLtd&HydrochinaKummingCorporation,2011,NamOuFirstPhase(2,5&6)FeasibilityStudy.

SchiltC.R.,2007,Developingfishpassageandprotectionathydropowerdams.Appliedanimalbehaviour science 104: pp 295-325.

Sloff,C.J.,S.WrightandM.Kaplinski,2009,Highresolutionthreedimensionalmodellingofrivereddy sandbars, Grand Canyon, U.S.A., Coastal and Estuarine morphodynamics, RCEM 2009, TaylorandFrancis/Balkema.,Proc.Sept.2009,SantaFe,Argentina.

Sloff, Kees, Bas Nieuwboer, Brandy Logan and Jonathan Nelson, 2012, Effect of sedimententrainmentandavalanchingonmodelingofGrandCanyoneddybars,Proc.RiverFlow2012–Murillo(Ed.)Taylor&FrancisGroup,London,ISBN978-0-415-62129-8,p.791.

Sloff,C.J.,Omer,A.Y.A.,Heynert,K.,Mohamed,Y.A.,2015,Designandmodellingof reservoiroperation strategies for sediment management, RCEM2015 - River and Coastal and Estuarine Morphodynamics,Peru,August2015.

Smokorowski,KE,Metcalfe,RA,Finucan,SD,Jones,N,Marty,J,Power,M,Pyrce,RS,Steele,R,2011,Ecosystemlevelassessmentofenvironmentallybasedflowrestrictionsformaintainingecosystemintegrity:acomparisonofamodifiedpeakingversusunalteredriver,Ecohydrology4:791–806.;

Stalnaker,C,Lamb,BL,Henriksen,J,Bovee,K,Bartolow,J,1995,TheInstreamFlowIncremental



Methodology: A primer for IFIM. Biological Report 29, US department of the Interior, National Biological Service: Washington, DC.

Stanford J.A. and J.V. Ward, 2001, Revisiting the Serial Discontinuity Concept, Regulated Rivers: Research and Management, 17. pp 303-310.

Stewardson,JM,Grippel,CJ,2003,Incorporatingflowvariabilityintoenvironmentalflowregimesusingthefloweventsmethod,RiverResearchandApplications19:459-472.

StoneR.(2007):ThelastoftheLeviathans.Science316:pp1684-1688.

Stone,M,Droppo,IG,1994,In-channelsurficialfine-grainedsedimentlaminae(partII):chemicalcharacteristicsandimplicationsforcontaminanttransportinfluvialsystems,HydrologicalProcesses8(2):113–124.

StuartB.L.,Sok,K.,NeangT, 2006,A collection of amphibians and reptiles fromhilly easternCambodia.TheRafflesBulletinofZoology54.

Stuart, B.L, 2005, New frog records from Laos. Herpetological Review 36.

Sumi, T, 2010, river Morphology and Sediment Management Strategies for Sustainable Reservoir inJapanandEuropeanAlps,AnnualsofDisas.Prev.Res.Inst.,KyotoUniv.,No53B.

Sumi, T. 2015, Comprehensive reservoir sedimentation countermeasures in Japan, Proc. FirstInternationalWorkshoponSedimentBypassTunnels,VAW–Mitteilungen232(R.M.Does,ed.),LaboratoryofHydraulics,HydrologyandGlaciology(VAW),ETHZurich,Switzerland.

Sumi,T.andKantoush,S.A.,2011,Sedimentmanagementstrategies forsustainable reservoir,Proc.of theInternationalSymposiumonDamsandReservoirsunderChangingChallenges, the79th Annual Meeting of ICOLD, 353-362.

Sumi,T.,Kantosh,S.,Esmaeli,TandOck,G.,2015,Reservoirsedimentflushingandreplenishmentbelow dams: insights from Japanese case studies, paper presented at Gravel Bed Rivers and Disasters,KyotoJapan,Sep14–18,2015.

Suwannapeng,N., 2007,Distributionandcatchof freshwater clamCorbicula spp. inLumPaoReservoir, Kalasin province. IFRDBTechnical Paper, 49: 1-33. Inland FisheriesResearch andDevelopment Bureau, Department of Fisheries, Bangkok, Thailand.

Sverdrup-Jensen, S., 2002, Fisheries in the Lower Mekong Basin: status and perspectives. MRC TechnicalPaper,6:1-95.

Swales, S, Harris, JH, 1995, The Expert Panel Assessment Method (EPAM): a new tool for

292

Determining Environmental Flows in Regulated Rivers. In: The Ecological Basis for River management,Harper,DM,Ferguson,AJD,(Eds.),Wiley,Chichester,UK.

SWECO, 2006, Environmental Impact Assessment on the Cambodian Side of the Srepok River due toHydropowerDevelopment inVietnam,PreparedbySWECOGrøner inassociationwithNorwegian Institute for Water Research, EVIORO-DEV, ENS Consult: 141p.

Szuster, B., andM. Flaherty, 2002,CumulativeEnvironmen¬tal Effects of LowSalinityShrimpFarminginThailand,ImpactAssessmentandProjectAppraisal,20(2):189–200.

Team Consulting Engineering and Management, 2010, Environmental Impact Assessment, XayaburiHydroelectricPowerProject,LaoPRD,August2010,399p.

TEEB,2010,TheEconomicsofEcosystemandBiodiversityforLocalandRegionalPolicyMakers.

Tennant,DL,1976,Instreamflowregimesforfish,wildlife,recreationandrelatedenvironmentalresources. InstreamFlowNeeds(Eds.Orsborn,JF,Allman,CH,),359-373.AmericanFisheriesSociety, Bethesda, Maryland, USA.

Tennessee Valley Authority, 2015, Tailwater Improvements, http://www.tva.com/environment/water/rri_index.htm

Termvidchakorn,A.andK.G.Hortle,2013,AguidetolarvaeandjuvenilesofsomecommonfishspeciesfromtheMekongRiverBasin,MRCTechnicalPaperNo.38,MekongRiverCommission,PhnomPenh.234pp.ISSN:1683-1489.

ThailandEnvironmentInstitute(TEI),2007,GreaterMekongEnvironmentOutlook,UnitedNationsEnvironmentProgramme(UNEP)RegionalOfficeforAsiaandthePacific,BangkokThailand

Tharme,RE,2003,Aglobalperspectiveonenvironmentalflowassessment:emergingtrendsinthedevelopmentandapplicationofenvironmentalflowmethodologiesforrivers,RiverResearchand Applications 19: 397-441.

Tharme,RE,KingJM,1998,Developmentof thebuildingblockmethodology for instreamflowassessments and supporting research on the effects of different magnitude flows on riverineecosystems, Report to Water Research Commission, 576/1/98. Cape Town, South Africa.

TherivelR.andB.Ross,2007,Cumulativeeffectsassessment:Doesscalematter?,EnvironmentalImpactsAssessmentReview,27.(5).pp365-385.

ThinhP.T,2003,Findingsfromwetlandsclassificationandinventoryofwetlands/aquaticecosystemin the Mekong Basin of Viet Nam. MRCS consultancy report.

Thompson, D.M.; J.M. Nelson and E.E. Wohl, 1998, Interaction between pool geometry and



hydraulics.WaterResourcesResearch,34(12):3673-3681.

ThompsonC.2008.FirstcontactintheGreaterMekong.WWFGreaterMekongProgramme.15December 2008.

Thoms,MC,Sheldon, F,Roberts, J,Harris, J,Hillman,TJ, 1996,ScientificPanelAssessmentofenvironmentalflowsfortheBarwon-DarlingRiver,NewsouthWalesDepartmentofLandandWater Conservation, Australia.

Thorne,C,Annandale,G,Jensen,J,Jensen,E,Green,T,Kopenen,J,2011,ReporttoMRCSbySedimentExpertGroup,Annex3MRCSXayaburiPriorConsultationProjectReviewReport.

Thornton, J., Steel, A., and Rast, W., 1996, Chapter 8 – Reservoirs Water Quality Assessments - A Guide to Use of Biota, Sediments and Water in Environmental Monitoring - Second Edition, Chapman(Ed),UNESCO/WHO/UNEP,ISBN0419215905(HB)0419216006(PB)

TonkinZ.,KingA.J.andMahoneyJ.(2008)EffectsoffloodingonrecruitmentanddispersaloftheSouthernPygmyPerch(Nannopercaaustralis)ataMurrayRiverfloodplainwetland.EcologicalManagement & Restoration 9, 196–201.

Tran,T.V.;Do,T.L.;Nguyen,N.V.;Phan,D.P.;Phan,T.H.;Thai,N.C.;Nguyen,Q.A.andSollows,J.D.,2001,AnassessmentofthefisheriesoffourstockedreservoirsinthecentralhighlandsofVietNam.ACIARProceedings,98:81-92.

Trandem A., 2013, China’s overseas dam-building in the Mekong River Basin, presentation delivered totheRegionalPublicForum:Mekongand3SHydropowerDams,3-4June2013,PhnomPenh.

Tremblay A, Varfalvy L, Roehm C., and Garneau M. 2009, The Issue of Greenhous Gases fron HydroelectricReservoirsformBorealtoTropicalRegions,UNSustainableDevelopmentKnowledgePlatform,http://www.un.org/esa/sustdev/sdissues/energy/op/hydro_tremblaypaper.pdf

Troeung,R.;Aun,S.;Lieng,S.;Deap,L.andZalinge,N.van,2003,AcomparisonoffishyieldsandspeciescompositionbetweenonefishinglotinBattambangprovinceandtwofishinglotsinPreyVeng province, Cambodia. MRC Conference Series, 4: 9-16.

Tsadik,G.G.andKutty,M.N.,1987,.“InfluenceofAmbientOxygenonFeedingandGrowthoftheTilapia,Oreochromisniloticus(Linnaeus).FAOWorkingPaperARAC/87/WP/10,PortHarcourt(Nigeria).

TurnpennyA.W.H., 1998, Mechanisms of fish damage in low-head turbines: an experimentalappraisal. In:FishMigrationandFishBypasses (Eds.: JungwirthM.,SchmutzS.&WeissS.).Fishing News Books, Oxford, Blackwell: pp 300-314.

294

UNEP,2013,WaterHyacinth–Canitsaggressiveinvasionbecontrolled?GlobalEnvironmentalAlertSeries,http://www.unep.org/pdf/UNEP_GEAS_APRIL_2013.pdf

USGS, 1995, Mercury Contamination of Aquatic Ecosystems, Fact Sheet FS-216-95, U.S. Department of the Interior–U.S. Geological Survey.

USGS, 1998, Changes in Sediment and Nutrient Storage in Three Reservoirs in the Lower Susquehanna River Basin and Implications for the Chesapeake Bay, USGS Fact Sheeet 003 – 98. http://pa.water.usgs.gov/reports/fs003-98.html.

USIAD Mekong Adaptation and Resilience to Climate Change. 2015. Valuing Ecosystem Services in the Lower Mekong Basin: Country Report for Cambodia, Laos, Thailand, and Vietnam.

USDepartmentofEnergy,1994,TheAdvancedHydropowerTurbineSystemProgram,ElectricPowerResearchInstitute.

Valbo-Jørgensen,J.andPoulsen,A.F.,2000,Usinglocalknowledgeasaresearchtoolinthestudyofriverfishbiology:experiencesfromtheMekong.Environment,DevelopmentandSustainability2, 253-276.

Valbo-JorgensenJ.,CoatesD.,HortleK.,2009,FishdiversityintheMekongRiverBasin.Pages161-196

inCampbell(ed.):TheMekongbiophysicalenvironmentofaninternationalriverbasin;Elsevier,

Amsterdam, Netherland. 432 pp.

VanZalinge,N.,Nao,T. &Tana,T. S., 2000,Where there iswater, there is fish?CambodianfisheriesissuesinaMekongRiverbasinperspective.InCommonPropertyintheMekong:IssuesofSustainabilityandSubsistence(Ahmed,M.&Hirsch,P.,eds),pp.37–48.Manila:ICLARM.

VanZalingeN.,DegenP.,PongsriC.,NuovS.,JensenJ.G.NguyenV.H.&ChoulamanX.,2004,TheMekongRiversystem.InWelcommeR.&Petr.E.(eds.):ProceedingsofthesecondinternationalsymposiumonthemanagementoflargeriversforfisheriesVolume1.FAORegionalOfficeforAsiaandthePacific,Bangkok,Thailand,RAPPublication2004/16:pp335-357.

VanZalinge,N,Degen,P,Pongsri,C,Nuov,S,Jensen,JG,Nguyen,VH,Choulamany,X,2003,TheMekongRiverSystem,Proceedingsofthesecondinternationalsymposiumonthemanagementoflargeriversforfisheries.11-14February2003,PhomPenh,Cambodia.

VathanaK,2003,ReviewofwetlandandaquaticecosysteminthelowerMekongRiverBasinofCambodia. MRCS consultancy report.

Vattenfall,2008,LaoPeople’sDemocraticRepublic:PreparingthecumulativeImpactAssessment



forthenamNgum3HydropowerProject,preparedbyVattenfallPowerConsultantABinassociationwith Ramboll natura AB and Earth Systems Lao. 394p.

Vidthayanon C. 2008. Field Guide to Fishes of the Mekong Delta. Mekong River Commission, Vientiane,LaoPDR.

Viravong,S,Phounsavath,S,Phytitay,C,Putrea,S,Chan,S,Kolding, J,Valbo-Jorgensen, J,Phoutavong,K,2006,Hydro-acousticsurveyofdeeppoolsintheMekongRiverinsouthernLaoPDRandnorthernCambodia.MRCTechnicalPaper11:1-76.

Visser T.A.M., Valbo-Jorgensen J., Ratanachookmanee T., 2003, MFD, Introduction and data sources.MekongRiverCommission,PhnomPenh,Cambodia63p.

Vörösmarty,C.J.,McIntyre,P.B.,Gessner,M.O.,Dudgeon,D.,Prusevich,A.,Green,P.,Glidden,S.,Bunn,S.E.,Sullivan,C.a.,Liermann,C.R.,Davies,P.M.,2010.Globalthreatstohumanwatersecurity and river biodiversity. Nature 467,555–561.

Wallace,KenJ,2007,“Classificationofecosystemservices:Problemsandsolutions.”BiologicalConservation no. 139:235-246.

Walker, L.J. and Johnston, J., 1999, Guidelines for the assessment of indirect and cumulative impactsaswellasimpactinteractions,ECDGXIEnvironment,NuclearSafety&CivilProtection.

Wang, Z.Y., undated, Management of the Three Gorges Dam (Presentation on InternationalAssociation of Hydro Environment and Engineering Research website) http://www.iahr.org/uploadedfiles/userfiles/files/management%20of%20TGP%20dam.pdf.

Ward J.V, 1989, The four-dimensional nature of lothic ecosystems, Jr. N. Am. Bentho. Soc, 8. pp 2-8.

Ward J.V. and J.A. Stanford, 1983, The serial discontinuity concept of lotic ecosystems, In Dynamics ofLoticEcosystems,FontaineT.D.andS.M.Bartell (eds.)AnnArborScientificPublishers,AnnArbor. MI. pp 29-42.

Ward J.V. and J.A. Stanford, 1995, Ecological connectivity in alluvial river ecosystems and its disruptionbyflowregulation.Regulatedrivers:ResearchandManagement11:105-119.

Waters,BF,1976,Amethodologyforevaluatingtheeffectsofdifferentstreamflowsonsalmonidhabitat. In: Instream Flow Needs (Eds. Osborn, JF,Allman, CH,)American Fisheries Society,Bethseda, Maryland, USA: 254-266.

Waters,TF,1995,Sedimentinstreams:sources,biologicaleffectsundcontrol.AmericanFisheriesSociety Monograph 7. Bethesda, Maryland.

296

Wei,GL,Yang,ZF,Cui,BS,Li,B,Chen,H,Bai,JHandDong,SK,2009,ImpactofDamConstructiononWaterQualityandWaterSelf-PurificationCapacityoftheLancangRiver,China,WaterResourManage 23:1763–1780, DOI 10.1007/s11269-008-9351-8

Weitkamp D. E., 2008, Total dissolved gas supersaturation biological effects, literaturereview 1980-2007,draft, http://www.ecy.wa.gov/programs/wq/tmdl/columbiarvr/062308mtg/TDGeffectsLitRev080615.pdf

Weitkamp, D. E., R. D. Sullivan, T. Swant, and J. DosSantos, 2003, Behavior of Resident Fish Relative to TDG Supersaturation in the Lower Clark Fork River. Transactions of the American Fisheries Society 132: 856-864.

WelchD.W.,RechiskyE.L.,MelnychukM.C.,PorterA.D.,WaltersC.J.,ClementsS.,ClemensB.J.,McKinleyR.S.,SchreckC.,2008,Survivalofmigratingsalmonsmoltsinlargeriverswithandwithoutdams.PLoSBiol.6(10),xe265,doi:10.1371/journalpbio.0060265.

WelcommeR.,1985,Riverfisheries,FAOFisheriesTechnicalPaper262:358p.

WelcommeR.,2001,Inlandfisheriesecologyandmanagement.FishingNewsBooks,BlackwellScience, Oxford: 358 p.

White,W.R.,2000,Contributingpaperflushingofsedimentsfromreservoirs.Preparedforthematicreview IV.5: operation, monitoring and decommissioning of dams. Cape Town: World Commission on Dams. White W. R, and Bettess R., 1984.

WhiteWR,AttewillL,AckersJ,WingfieldR.,1999,Guidelinesfortheflushingofsedimentfromreservoirs, HR Wallingford, Report SR 563, November.

Wiemann P., Müller G. and J. Senior, 2008, Risk Management and Resolution Strategies forEstablished and Novel Technologies in the Low Head Small Hydropower Market, University of Southampton, School of Civil Engineering.

WilliamsJ.G.&MatthewsG.M.,1995,Areviewofflowandsurvivalrelationshipsforspringandsummer Chinook salmon, Oncorhynchus tshawytscha from the Snake River Basin. Fish. Bull. 93: pp 732–740.

Williams J.G., 1998, Fish passage in the Columbia River, USA and its tributaries: problems and solutions.InFishmigrationandfishbypass.EditedbyM.Jungwirth,S.Schmutz,andS.Weiss.Fishing News Books, Oxford: pp 180–191.

Williams,J.G.,Smith,S.G.,Zabel,R.W.,Muir,W.D.,Scheuerell,M.D.,Sandford,B.P.,Marsh,D.M.,McNatt,R.A.,Achord,S.,2005,EffectsoftheFederalColumbiaRiverPowerSystemonSalmonPopulations.U.S.Dept.Commer.,NOAATech.Memo.NMFS-NWFSC-63,Seattle(availableonlineathttp://www.nwfsc.noaa.gov/publications),p.150.



WilliamsJ.G.,ArmstrongG.,KatapodisC.,LarinierM.&TravadeF.,2012,Thinking likeafish:a key ingredient for development of effective fish passage facilities at river obstructions,RiverResearch and Applications 28: pp 407-417.

Winemiller et al., 2016, Balancing hydropower and biodiversity in the Amazon, Congo, and Mekong. Science. Vol. 351. Issue 6269. pp. 128-129.

WolstencroftJ.,ParrJ.W.K.andGoodeyM,1993,SurveyofWetlandsinNortheastThailand.AsianWetlandBureau,KualaLumpur,Malaysia.AWBPublicationNo.83.

WorldBank,2001,WorldBankOperationalPolicyontheSafetyofDams.

World Bank, 2002, Regulatory Frameworks for Dam Safety – A Comparative Study.

World Bank, 2009, Directions in Hydropower.

World Bank/AusAID, 2014, Cumulative Impacts and Joint Operation of Small-Scale Hydropower Cascades: Case Studies for Selected River Basins in Northwestern Vietnam.

WorldCommissiononDams(WCD),2000,PakMunDamMekongRiverBasinThailand,FinalReport: 191p.

WorldFishCenter,2007,Studyof theInfluenceofBuiltStructuresontheFisheriesof theTonleSap,FinalReport for theKingdonofCambodia.ADBTechnicalAssistanceConsultantsReport,Proj37576,July2007.

WrightH,BuckinghamDandDolmanP,2009,Dryseasonhabitatusebycriticallyendangeredwhite-shouldered ibis in northern Cambodia. Animal Conservation.

Wu, B.S, and Wang, Z.Y, 2014, Impacts of Sanmenxia Dam and management strategies, inHydraulics of Dams and River Structures, Yazdandoost &Attari (eds) Taylor & FrancisGroupLondon, ISBN 90 5809 632 7.

WWF-Greater Mekong, 2013. The Economic Value of Ecosystem Services in the Mekong Basin: WhatWeKnow,andWhatWeNeedtoKnow.InWWFReportOctober2013.

WWF,2014,SummaryofscientificreviewsfromthreeinternationalfishpassageexpertsontheDon Sahon dam EIA and technical reports related to project design and mitigation measures. WWF-Cambodia: 14p.

Xie,SW,Li,ZJ,2003, Inlandfisheriesstatistics inChina.Pp20-26 in „Newapproaches for theImprovementofInlandcapturefisherystatisticsintheMekongbasin”,Ad.ocexpertconsultation,Udon Thani, Thailand, 2-5 September 2002, FAO RAP publication 2003/01, FAO, Bangkok,Thailand. 145p.

298

Yang,Sl,Milliman,JD,Xu,KH,Deng,B,Zhang,XY,Luo,XX,2014,DownstreamsedimentaryandgeomorphicimpactsoftheThreeGorgesDamontheYangtzeRiver,Ear.Sci.Rev.,138:469-486.

YellowRiverConservancyCommission(YRCC),2012,YellowRiverBasinissuesandmanagementreport, River Health and Environment al Flow in China Project, Australia-China EnvironmentDevelopment partnership, http://watercentre.org/portfolio/rhef/attachments/report-cards/yellow-river-basin-issues-and-management-report

Zhang,R.,2001,ReviewonevaluationsoftheecologicalenvironmentoftheManwanHydroelectricStationontheLancangRiver,HydroelectricPowerStationDesign,17(4):27-32,(inMandarin).

Zhang,J.L.,Zheng,B.H.,Liu,L.S.,Wang,L.P.,Huang,M.S.,Wu,G.Y.,2010,Seasonalvariationofphytoplankton in the DaNing River and its relationships with environmental factors after impounding oftheThreeGorgesReservoir:afour-yearstudy.ProcediaEnviron.Sci.2,1479–1490.

Zhai,H,Cui,B,Hu,B,Sun,T,Zhao,H, 2009,Ecological security andHydropowerdamsandTransboundaryRiver,PaperpresentedattheInternationalRiverSymposium.

Young,PS,CechJr.,JJ,Thompson,LC,2011,Hydropower-relatedpulsed-flowimpactsonstreamfishes:abrief review,conceptualmodel,knowledgegaps,andresearchneeds,Rev.Fish.Biol.Fisheries 21: 713-731.

ZiglerS.J.,DeweyM.R.,KnightsB.C.,RunstrumA.L.,SteingraeberM.T.(2004):Hydrologicandhydraulic factorsaffectingpassageofpaddlefish throughdamson theupperMississippiRiver.Trans. Am. Fish. Soc. 133: pp 160–172.

ZitekA.,HaidvoglG.,JungwirthM.,PavlasP.&SchmutzS.,2007,Einökologisch-strategischerLeitfaden zur Wiederherstellung der Durchgängigkeit von Fließgewässern für die Fischfauna in Österreich.AP5desMIRRProjektes -AModelbased Instrument forRiverRestoration.Wien,InstitutfürHydrobiologieundGewässermanagement,BOKU:139pp.

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ACKNOWLEDGEMENT

301 | Chapter: Acknowledgement


This document and related project was supervised and coordinated by the Initiative on Sustainable Hydropower(ISH)/MekongRiverCommissionSecretariat(MRCS)withthefollowingkeypersonnel:

• Mr.VoradethPhonekeo

• Mr.SimonKrohn

• Ms.PravianLimbanboon

• Mr.PalakornChanbanyong

• Ms.MariaKoenig

The following key-experts have been involved:

• Mr.LeifLillehammer(TeamLeader,Multiconsult)

• Mr.ChrisGrant(HydropowerDesignandOperationsExpert,Multiconsult)

• Mr.Jean-PierreBramslev(HydropowerModellerandEconomicsExpert,Multiconsult)

• Mr.RonPasschier(HydrologistandWaterResourcesModeller,Deltares)

• Dr.KeesSloff(HydraulicandSedimentModellingExpert,Deltares)

• Dr.LoisKoehnken(SedimentandWaterQualityExpert,IndividualConsultant,Australia)

• ProfessorStefanSchmutz(FisheriesandAquaticEcologyExpert,BOKUUniversity,Vienna)

• Mrs.CarinaSeliger(AquaticEcologist,BOKUUniversity,Vienna)

• Ms.KristineWalløe-Lilleeng(HydropowerEngineer,Multiconsult)

Theteamincludesalsothefollowingnon-keyexpertsandsupportstaff:

• Ms.JennyPronker(HydraulicExpert–DeltaAssessment,Deltares)

• Dr.JørnStaveandMr.JensJohanLaugen(EnvironmentalandSocialImpactAssessmentandSafeguardsExperts,Multiconsult)

• Mr.BjørnStensethandWilliamGreene(PowerEconomists,Multiconsult)

• Dr.SanjayGiri(HydraulicExpert,Deltares)

• Mr.AmgadOmer(ReservoirSedimentationexpert,Deltares)

• Mr.BernhardZeiringer(Fish-PassEco-Engineer,BOKUUniversity,Vienna)

• Ms.RagnhildHeimstad(TerrestrialEcologists,KnowledgeBaseResponsible,Multiconsult)

• Mrs.IreneN.Koksæter(LivelihoodsExpertandKnowledgeBase,Multiconsult)

• Ms.KirtyManandhar(KnowledgeBase,Multiconsult)

The following National Consultants also provided input:

• LaoPDR:Ms.ThipsathianeKhamvongsa(EnvironmentandWaterResources)

• LaoPDR:Mr.LamphoneDimanivong(HydropowerandEnergy)

• Cambodia:Dr.HengSokchay(HydropowerandEnergy)

• Vietnam:DrNguyenQuangTrung(EnvironmentandWaterResources)

• Vietnam:Dr.HoangMinhTuyen(HydropowerandEnergy)

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