Hydropeaking impacts on the Dordogne river Definition of mitigation measures and assessment of their efficiency

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OATAO

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OATAO is an open access repository that collects the work of Toulouse researchers and

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This is an author-deposited version published in :

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Eprints ID : 11290

To cite this version : Chanseau, Mathieu and Clave, David and

Courret, Dominique and Guerri, Olivier and Lascaux, Jean-Marc and

Wibaux, Benoit Hydropeaking impacts on the Dordogne river

Definition of mitigation measures and assessment of their efficiency.

(2012) In: Eawag/Wasser-Agenda 21 Workshop on Hydropeaking, 19

June 2012 - 19 June 2012 (Zurich, Switzerland).

Any correspondance concerning this service should be sent to the repository

administrator:

[email protected]

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Hydropeaking impacts on the Dordogne river

Definition of mitigation measures and assessment

of their efficiency

In alphabetical order : Chanseau M5 _{, Clave D}1_{Courret D}6_,

Guerri O 3_{, Lascaux JM}2_{, & Wibaux B}4

Presented by Courret D ([email protected])

1 2 4 3 5 6 2

Dordogne river

• Dordogne river equipped with 5 principal dams in the

upper part, organized in line (storage capacity of 970

Mm3₎ _{200 km and 20 species affected}

+ 2 tributaries also equipped : Maronne and Cère river

Context : Hydroelectric schemes

Studied area affected by hydropeaks

River mean discharge : 107 m3_/s

Maximum turbine discharge : 340 m3_/s

Maximum turbine discharge : 44 m3_/s

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3 0 100 200 300 400 500 600 700 800 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012

Dordogne + petits af fluents Bassin Maronne Bassin Souvigne Bassin Vézère Bassin Corrèze Bassin Cère Bassin Bave

• Reintroduction plan under progress for Atlantic Salmon : 40% to 60%

of the reproduction activity of the basin.

• Several fish species with high patrimonial and/or fisheries values :

brown trout, grayling, dace, sculpin, planer lamprey, pike, perch, …

Context : Biological stakes on the Dordogne river

Number of large salmonid's redds per river of the basin, and per year

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Dordogne river

• Studies leaders :

Organisms involved in partnership :

• Technical operators :

• Funding agencies :

Territorial public institution of the Dordogne basin Association in charge of the

management of migratory fish populations National agency for water

and aquatic environments

Regional public water agency

Departmental and Regional council

ONEMA R&D team Engineering firms

• Hydroelectric

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• Biological surveys :

• Survey of large salmonid's reproduction since 1999/2000 (MIGADO – ECOGEA)

• Survey of stranding-trapping of salmonid's alevinssince 2005 (MIGADO / EPIDOR – ECOGEA)

• Survey of spawning and stranding-trapping of others fish species since 2006 (EPIDOR – ECOGEA)

• Survey of salmonid's juveniles abundances in riffles since 2003 (MIGADO – ONEMA)

• Survey of other species’ recruitment since 2010 (OMB, BAF, VAN, GOU, BRO, PER, …) (EPIDOR – ECOGEA).

• Hydrology and hydropeaks characterization updated each year (ECOGEA

– ONEMA R&D team).

Studies and biological surveys :

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Dordogne river

• Hydraulic modelling of several sections, ≈ 10 km in total, keyed on the

whole range of turbine flow (MIGADO – SIEE - ONEMA R&D team)

Studies and biological surveys :

89 90 91 92 93 94 95 96 97 98 99 0 500 1000 1500 2000 2500 3000

Distance à partir de l'aval (m)

A lt it u d e r e la ti v e ( m ) Thalweg Modèle 20 m3/s Mesure 20 m3/s Modèle 30 m3/s Mesure 30 m3/s Modèle 117 m3/s Mesure 117 m3/s Modèle 200 m3/s Mesure 200 m3/s Modèle 303 m3/s Mesure 303 m3/s 3D view of the Malpas section

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• Weekly and daily hydropeaks

• Between 50 and 150 hydropeaks

per year (2000-2010 period)

• Mainly from October to May

Hydropeaks characterization Dordogne river at ArgentatHydrogram extract

0% 20% 40% 60% 80% 100% 120% 140% 160% 180% 200% s a m d im lun _mar m e r je u v e n s a m d im lun _mar m e r je u v e n s a m d im lun Day F lo w ( % o f m e a n d is c h a rg e ) Weekly management Daily hydropeaks

Dordogne river at Argentat Number of hydropeaks per year

0 20 40 60 80 100 120 140 160 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 8

Dordogne river

• High variability of hydropeaks

• Characterization useful :

– To understand the impacts on fish populations

– To reflect on mitigation measures

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• Salmonid’s redds dewatering during returns at low flow.

• Trapping of salmonid’s alevins occurring :

– In channels margins during flow decreases, especially after long high flow periods

– At the disconnection of secondary channels

• Spawning dewatering and stranding-trapping of alevins of other

fish species

– On dewatered gravel bars

– At the disconnection of secondary channels and backwaters

Biological issues linked to hydropeaks

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Dordogne river

• 84 redds of large salmonid dewatered on the Dordogne river during the 2000 – 2006 period.

• Redds generally located at less than 5 m from the shore, due to the rarefaction of adequate gravels, related to blockage of sediment transport by dams .

Salmonid’s redds dewatering issue :

Maintaining a base flow of 35

m3_{/s (33% of mean discharge)}

in winter and spring (15/11-15/06)

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+ downgrading work on morphology of particularly sensitive sites :

Salmonid’s redds dewatering issue :

Before work at 32 m3_/s _{After work at 32 m}3_/s

% of watered redd

Flow (m3_/s)

≈ 95% of redds safeguardedwith

a base flow of 35 m3_{/s, instead of}

only 30% at the regulatory

minimum flow (10 m3_/s).

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Dordogne river

• Principally in potholes on channel margins during flow decreases, and especially after long high flow periods

Trapping of salmonid’s alevins :

Limiting maximum turbine discharge to

190 m3_{/s (180% of mean discharge)}

during spring (15/03-15/06), to the

extent permitted by natural hydrology.

During a hydropeak at 300 m3_/s

Back to 50 m3_/s Flow connection of

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+ work on morphology :

Before work After work

Trapping of salmonid’s alevins :

Deleting particularly tricky sites Work on secondary channels’ intakes to ensure their permanent connection 14

Dordogne river

Spawning dewatering and stranding-trapping of alevins of other species :

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Spawning dewatering and stranding-trapping of alevins of others species :

Sculpin spawning

Perch spawning Dace eggs

Grayling redds

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Dordogne river

Distribution of collected fishes by species

• At least 20 fish species are impacted, up to 200 km

downstream the Argentat dam

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Maintaining during spring (01/03-15/06) a base flow of : – 50 m3_{/s at Argentat (47% of mean} discharge) – 80 m3_{/s downstream Maronne} confluence (63% of mean discharge)

to the extent permitted by natural hydrology

Gradient of flow decrease limited

to 33 m3_/s/h_{(instead of 100 m}3_/s/h) Mean width (m) 50 55 60 65 70 75 80 85 90 0 20 40 60 80 100 120 140 160 180 200 Flow (m3_/s) Malpas Saulou Saulières-Rodanges Section 18

Dordogne river

Survey of salmonid's juveniles abundances :

It’s considered we have achieved significant improvements in abundance, notably since 2008

Abundance index 4 “historical” riffles

Abundance index Group of 8 riffles

Abundance index / reproduction activity Group of 8 riffles

Abundance index / reproduction activity 4 “historical” riffles

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19 0 1 2 3 4 5 6 7 8 9 10 B A F C H A G O U V A I LO F T R F C H E O B R V A N G A R A B L G O U B A F V A I C H E LO F O B R V A N C H A B A F G O U V A I V A N LO F G A R C H E A B L B A F C H E G O U V A I A B L LO F V A N G A R C H A S1 S2 S3 S4 0 500 1000 1500 2000 2500 3000 2010 2011 2010 2011 2010 2011 2010 2011 S1 S2 S3 S4 n b i n d / 1 0 0 E P A + 106 % + 69 % + 16 % + 54 %

Survey of other species’ recruitment :

• 2 years of feedback to this

day.

• Significant response of

populations to contrasted hydrology and hydropeaks regimes between 2010 and 2011.

• Need to continue to learn

more.

Overall abundance by sector

Abundances ratio 2011 / 2010 by species, on each sector

r < 0.5 0.5 < r < 0.8 0.8 < r < 1.5 1.5 < r < 3 r > 3 Upstream Downstream 20

Dordogne river

Conclusions

• A study approach taken as an example in France, combining :

– hydrologic analysis, hydraulic modelling

– and a very considerable effort in biological surveys on hydropeaks impacts' mechanisms and populations states

• An evolutionary approach with, each year, collegial discussions

between partners and the hydroelectric operator on measures for the following year

Reflections on the different characteristics of hydropeaks :

– Measures are mainly implemented on base flows and maximum flows – Improvements may still be possible on the gradients ?

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However, several impacts remain to be addressed :

• The reproduction of phytophil species, pike and perch especially,

which are severely affected if a significant drop of water level occurs during phases of egg and fixed larvae

• Seasonal stocking which can lead to early flow reductions in spring and summer and can affect :

– the dynamics of upstream and downstream fish migration – the ascent of estuarine silt plug

• Consequences on river morphology and habitat, due to the flood reduction and to the blockage of sediment transport :

– Riverbed paving and depletion of fine grain sizes (gravels) – Increased revegetation of channel margins

– Single channelization of the stream bed