A WATER FRAMEWORK DIRECTIVE (WFD) COMPLIANT DETERMINATION OF ECOLOGICALLY ACCEPTABLE FLOWS FOR ALPINE RIVERS IN AUSTRIA A. ZITEK 1 , P. JÄGER 2 , B. ZEIRINGER 3 1 EcoScience, Environmental Studies, Goldschlagstraße 209/6 1140 Vienna, Email: [email protected]2 Ingenieurbüro für Ökologie und Umweltbiologie Brunn 147, 5201 Seekirchen am Wallersee, Austria Email: [email protected]3 Institute of Hydrobiology and Aquatic Ecosystem Management, University of Natural Resources and Life Sciences, Vienna, Austria Email: [email protected]
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A WATER FRAMEWORK DIRECTIVE (WFD) COMPLIANT DETERMINATION OF ECOLOGICALLY ACCEPTABLE
• Study area• Aim of the study• Residual flow assessments
• Methods• Results
• Conclusion
Mur
Salzach
Study sites in Salzburg -Austria
Water abstraction sites at 20 power plants at mainly wadeablerivers at 63 river stretches (40 water abstraction sites, 23 full water sites),
Residual flow < MALFResidual flow > MALF
Hydropeaking < 1:5
Hydropeaking > 1:5
Characteristics of the assessedriver stretches
Slop
e%
Aim of the study
• Evaluation of the existing hydromorphologicalsignificance criteria used to pre-classify the currentecological status of rivers with regard to the EU Water Framework Directive formacrozoobenthos and fish with regard to:•• EcologicallyEcologically acceptableacceptable minimumminimum flowflow at at waterwater
abstractionabstraction sitessites
•• Central Central questionquestion: : cancan thethe good good ecologicalecologicalstatusstatus ((WFDWFD--terminologyterminology) ) cancan bebeachieved/maintainedachieved/maintained whenwhen usingusing thisthissignificancesignificance criteriacriteria ??
Methods
Structure of the residual flow assessmentSignificance criteriaSignificance criteria
Target: systematic and stratified assessment of depth-flow velocity patterns at different discharges- Hydro-morphological units HMU) for orientation and stratification (7-15 measurements per HMU).
Characterisation of Characterisation of instreaminstream sediment sediment incl. qualitative assessment of incl. qualitative assessment of embeddednessembeddedness and proportion of fines, and proportion of fines, instreaminstream structures (different types structures (different types -- no, no, existing, abundant), shoreline structure existing, abundant), shoreline structure and land useand land use
Pressure/Site Site 1 Site 2 Site 3 Site 4Water abstractionHydro-peakingMorphological changeTemperature changeImpoundmentConnectivity lossEmbeddednessCatchment Land useSediment flushingWater quality
Identification of pressure combinations and main pressures
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Date
Dis
char
ge [m
³/s]
Qresidual
Qdefined
Daily mean discharge at abstraction site
Is this enough to fulfil ecological requirements?
Constructing the hydrograph at water abstraction sites
Turbine uptake capacity
Natural minimum flow
Main resultshydraulicmapping
Results hydraulic mapping: Changes of flow velocity distributions with
decreasing discharge
Reducation of substrate movingdischarges (MAF+20%)
KW Spannberg 2003 Wasserfassung
Vergleich natürliche Jahresganglinie mit Jahresganglinie in Ausleitung
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Datum
Dur
chflu
ss [m
³*s-1
]
Tagesmittel anWasserfassung
QKons
Qrest1
MQ+20%
Zeit MQ+20%
Dynamic discharge in residual flow stretches
KW Winkler 2003 Wasserfassung
Vergleich natürliche Jahresganglinie mit Jahresganglinie in Ausleitung
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.2003
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.2003
Datum
Dur
chflu
ss [m
³*s-1
]
Tagesmittel anWasserfassung
QKons
Qrest
MQ+20%
Zeit über MQ+20%
KW Winkler 2004 Wasserfassung
Vergleich natürliche Jahresganglinie mit Jahresganglinie in Ausleitung
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.2004
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.2004
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.2004
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.2004
Datum
Dur
chflu
ss [m
³*s-1
]
Tagesmittel anWasserfassung
QKons
Qrest
MQ+20%
Zeit über MQ+20%
After After flushingflushing
FlushingFlushing of of sedimentssediments fromfromimpoundmentsimpoundments
Reduction of substrate movingdischarges (MAF+20%) and percentage
of area with medium/high fine sedimentsFi
nes
in s
edim
entm
ediu
m/h
igh
(% o
f tot
al a
rea
map
ped)
Reduction of days with sediment moving discharges
Summary results hydraulicmapping
• At ADMF the highest flow velocity classes were lost in most situations – maintained above MALF.
• Below ADMF flow velocities between 0,0 – 0,4 became dominant– loss of river type specific flow variability and habitats.– increased sedimentation of fines and
• Below ADMF a significant loss of wetted width in relation to the wetted width at MALF leading to significantly reduced ecologically available wetted habitats.
• Below ADMF limits for connectivity for fish like maximum depth at the pessimum profile and minimum flow velocity in thalweg are undercut – sometimes these parameters require more water to be fulfilled!
35 % of significantly abstractedsites with good ecological status
• Situated in smaller and steeper rivers, with two of them being situated at the upper end of the fish bearing zone.
• Situated within the trout region with brown trout being the only dominant species.
• Larger mean choriotope size lead to higher values of relative roughness -> habitat heterogeneity -> different size classes of trout -> higher variance of fish lengths -> better judgement of the age distribution.
• The biomass was always considered as satisfyingand biomass KO criterion was never actuated.
Results Macrozoobenthos –reduction of rheophilous species
Num
bero
f rhe
ophi
lous
taxa
Abstraction sites (n=13) Reference (n=10)N
umbe
rof r
heoh
ilous
and
rheb
iont
taxa
Abstraction sites (n=13) Reference (n=10)
Saproby Index failed to assess the impact of waterabstraction on ecological status!
Conclusions• ADMF represents a valid base for determining the ecologically
acceptable base flow -> additional parameters help to maintain important functions like connectivity.
• Experiences: in steep alpine rivers in some cases its hard to reachthe cut value for minimum depth (15-20 cm), in lowland rivers thetrend goes to discharges bigger ADMF to maintain flow velocitiesand depth, some types of rivers show a trend to decreasingminimum flows (climate change) which also needs to beconsidered adequately – next step is regionalisation!
• ADMF = a natural catastrophic event -> a dynamic component to this minimum base flow to maintain the river type specific flow variability is recommended, contributing to the maintenance of natural geomorphologic (e.g. sediment quality) and ecological processes linked to natural flow patterns.
• ADMF and hydromorphological cut values implemented in National Water Act for WFD!
Thank you for your attention!Thank you for your attention!