HyMoCARES case studies monitoring of hydromorphological restoration projects in alpine rivers coordinated by Frédéric Liébault (Irstea Grenoble) www.alpine-space.eu/hymocares www.facebook.com/HyMoCARES HyMoCARES Final conference Bolzano-Bozen, October 2, 2019
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…The morphology and sediment transport of alpine rivers have been strongly altered during the last 70 years • Gravel mining • Hydropower • Flood protection works
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HyMoCARES case studiesmonitoring of
hydromorphological restoration projects in alpine
rivers
coordinated byFrédéric Liébault (Irstea Grenoble)
www.alpine-space.eu/hymocares
www.facebook.com/HyMoCARES
HyMoCARES Final conference Bolzano-Bozen, October 2, 2019
The morphology and sediment transport of alpine rivers have been strongly altered during the last 70 years
• Gravel mining
• Hydropower
• Flood protection works
• Erosion-control works in mountains
• Global changes (climate and land-use)
www.alpine-space.eu/hymocares
www.facebook.com/HyMoCARES
Lech River (LFV)
Stramentizzo dam (PAT)Gravel pit in the Durance (@B.Terrier)
Hydrogeomorphic responses to human pressures have been particularly strong in the Alpine Space
• Channel incision and narrowing
• Rapid shifting of emblematic alpine channel patterns (e.g. braiding, and anastomosing)
• Channel clogging with fine sediments
www.alpine-space.eu/hymocares
www.facebook.com/HyMoCARES
1952 2015
Arve River (IGN)
Channel incision in soft bedrock, Salzach 1969 (BAW-IWB)
Fluvial remote sensing data now offer powerful tool to monitor physical effects of stream restoration projects, providing high-resolution data covering large spatial scales (airborne LiDAR, UAV-SfM surveys, thermal infra-red imagery, RFID sediment tracing)
www.alpine-space.eu/hymocares
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Talvera DoD from bathymetric LiDAR surveys(APC-PAB)
Bedload tracing experiments of HyMoCARES highlight rapid bedload transfer rates in Alpine rivers (several km per years). This implies relatively short residence time of gravels in restored reaches, but also a strong sediment connectivity with upstream sediment sources.
Sediment replenishment is a successful solution to stop channel incision or to recreate braided morphology in highly altered alpine gravel bed rivers (Drac and Buëch case studies)
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gravel wave
Active channel elevation change downstream of the St Sauveur dam
Brousse et al., 2019
Front of the gravel wave of the Buëch (Irstea)
Spontaneous recovery of braidingDrac (@SIGosphere)
Bed widening is a successful solution to improve morphological conditions and subsequent habitat heterogeneity of large embanked alpine rivers, provided that the sediment supply is high (Drau, Wertach)
Ecological effects of hydromorphological restoration are still difficult to demonstrate using data from monitoring programs, even if some trends reveal positive effects on fish populations or macroinvertebrates communities
Much more ambitious monitoring programs exploring longer spatial and temporal scales are needed to statistically isolate restoration effects from other forcings/controls and to go beyond case study applications (e.g. MBACI and EPT designs)
Long-term physical and ecological effects of restoration projects are still highly uncertain (mainly due to the natural variability of sediment supply and hydrological regimes, and to the long term recovery processes), and it is of crucial importance to pursue monitoring efforts in the future
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Evolution of the proportion of fast-flowing flow fish species
Two highly altered gravel-bed braided rivers in the Southern French Alps: Buëch and Upper-Drac
• Accelerated incision of the Upper Drac under the effect of intensive gravel mining (cutting through lacustrine clay deposits)
• Strong incision of the Buëch River downstream of the St Sauveur dam (associated with the stabilization of the braided pattern)
• In both cases, local effects of human pressures have been likely amplified by a general context of sediment supply decrease from the catchment (reforestation, end of Little Ice Age)
Two highly altered gravel-bed braided rivers in the Southern French Alps: Buëch and Upper-Drac
• Accelerated incision of the Upper Drac under the effect of intensive gravel mining (cutting through lacustrine clay deposits)
• Strong incision of the Buëch River downstream of the St Sauveur dam (associated with the stabilization of the braided pattern)
• In both cases, local effects of human pressures have been likely amplified by a general context of sediment supply decrease from the catchment (reforestation, end of Little Ice Age)
Active channel narrowing and incision of the Upper Drac
Two highly altered gravel-bed braided rivers in the Southern French Alps: Buëch and Upper-Drac
• Accelerated incision of the Upper Drac under the effect of intensive gravel mining (cutting through lacustrine clay deposits)
• Strong incision of the Buëch River downstream of the St Sauveur dam (associated with the stabilization of the braided pattern)
• In both cases, local effects of human pressures have been likely amplified by a general context of sediment supply decrease from the catchment (reforestation, end of Little Ice Age)
40 000 m3 of gravel replenishment downstream of the St Sauveur dam in 2016 (EDF) to stop channel incision
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Two ambitious gravel replenishment operations
355 000 m3 of coarse sediment used to recreate a braided channel along the Upper Drac (2013-2014, CLEDA)
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Morphological effects of gravel replenishment
• Sediment replenishment in the Buëch effectively stop channel incision by generating a 40-cm deep gravel wave with a front stopping at 2.3 km from the dam after a 5-yr flood
• 52% of the artificial berms eroded during the 5-yr flood (good efficiency of the replenishment design)
• A spontaneous recovery of braided morphology is observed along the Upper Drac, through the self-formation of anabranches
• Bedload tracing confirms sediment continuity between the restored reach of the Drac and its first upstream sediment source (Chabottes braided plain) at the yearly scale
LiDAR DEM differencing of the Buëch after the November 2016 flood (Brousse et al., 2019 RRA)
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Morphological effects of gravel replenishment
• Sediment replenishment in the Buëch effectively stop channel incision by generating a 40-cm deep gravel wave with a front stopping at 2.3 km from the dam after a 5-yr flood
• 52% of the artificial berms eroded during the 5-yr flood (good efficiency of the replenishment design)
• A spontaneous recovery of braided morphology is observed along the Upper Drac, through the self-formation of anabranches
• Bedload tracing confirms sediment continuity between the restored reach of the Drac and its first upstream sediment source (Chabottes braided plain) at the yearly scale
Bedload tracing in the Drac(Brousse PhD)
Spontaneous recovery of the braided channel in 2018 (SIGosphere UAV photo)
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Ecological effects of gravel replenishment (biological communities)
• Drac: improvement of the biological quality indicators after restoration (but difficult to isolate restoration effects from improved wastewater treatment in upper catchment)
• Drac: spectacular increase of brown trout population in the restored reach (effect of restoration or fish pass deployment?)
• Buëch: differences in biological quality between restored and control sites are dominated by the dam effect (no clear effects of the gravel replenishment on the ecological quality)
Bank erosion measurements (in cooperation with/executed by BOKU Vienna)
• Estimating bank retreat and interaction with the depositing sediment supplied from
upstream
• Two tests – borehole shear test to estimate cohesion shear strength (bank geotechnical
stability) and jet test to estimate erosion rate dependence on shear stress (bank fluvial
erodibility)
y = 0.738x + 15.5R² = 0.9976
0
50
100
150
200
0 50 100 150 200 250
sh
ea
r s
tre
ng
th
(k
Pa
)
normal stress (kPa) 0.0000
0.0005
0.0010
0.0015
0.0020
0.0025
0.0030
0 5 10 15 20
Ero
sio
n R
ate
(m
/s)
Shear Stress (Pa)
Result Comparison
Langendoen
Jet
test
Borehole
shear test
Bank geotechnical
stability rate on
shear strength
Bank fluvial erodibility rate
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Results of monitoring campaigns• Results of three monitoring campaigns measuring suspended sediment concentration served as
key input data to establish sediment transport model,
• Sediment transport model was used as a (recognized) WPT2 tool to assess the effect of restoration action on hydromorphology (Zlatoličje bank stabilization with groynes) and to provide base for developing habitat model as another WPT2 tool to assess restoration action (E-flow amendment) effect on habitats (adult Danube salmon as a representative species)
Max deposition 4 vs 8 groynes
Max erosion 4 vs 8 groynes
Normalized preference curves
Habitat suitability vs
Q (SI>0,75)
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Highlights of the main results
Case studies in Germany:Lech River
FVB-IGB and LFV
EURAC, Bolzano 02.10.2019
Leibniz Institute for Freshwater Ecology and Inland Fisheries, Berlin
Bavarian Fishery Association
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Case study at Lech river• Planning of an artificial oxbow• Installation of spawning grounds for
danube salmon• Sediment introduction• Creation of a multitude of habitats
for aquatic life• Introduction of logwood and wood
debris
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Echo bathymetric monitoringBefore the sediment introduction:
• the Lech stretch shows only little variance in depth
• There is no flow refuge, neither juvenile nor winter habitat
• No spawning ground
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After the sediment introduction:
• Increase in depth variance• Increase in habitats provided for
aquatic and amphibic species• Key habitats for umbrella species• Flow refuge and juvenile habitat• Habitat connectivity• Increase in available Ecosystem
Services
Echo bathymetric monitoring
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Increase in habitat connectivity
Introduction of macroforms
Introduction of woody debris
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Measure Hydromorphological impact
ES affected
Lech
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Ecosystem services Case study Action Effect
Habitat related services
Adige River (Ischiello) Removal of levee +Habitat related services
Avisio River, Buech River, Drac River
Artificial sediment replenishment +
Habitat related services
Isarco River (Bozen), Lech River (Bayern)
Creation of bedforms and artificial sediment replenishment
+
Habitat related services
Talvera River (Bozen),Drava River (Slovenia)
Ensuring environmental flow +
Habitat related services
Wertach River (Bayern)
Channel widening +
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Ecosystem services Case study Action Effect
Water activities Drac River Artificial sediment replenishment +
Water activities Isarco River (Bozen), Adige River (Lana)
Creation of bedforms and artificial sediment replenishment
+
Water activities Drava River (Slovenia) Ensuring environmental flow +Flood risk mitigation Wertach River
(Bayern)Channel widening +
Flood risk mitigation Drac River Artificial sediment replenishment +
Hydropower Drava River Ensuring environmental flow -
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Ecosystem services Case study Action Effect
Education of science Adige River (Ischiello) Removal of levee +Cultivated crops Adige River (Ischiello) Removal of levee -Aesthetics of landscape