Hydropeaking and minimum flow : the French approach. P. Baran

1. CIS ECOSTAT - HYDROMORPHOLGY WORKSHOP 12th and 13th June 2012 - Brussels Hydropeaking and minimum flow : the French approach.P. Baran Pôle Ecohydraulique

2. French context of water storage • Total amount of water per year in stream : 200 billion m3 • In 2009, 33,4 billion m3 in total collected : • 64% for the production of electricity • 17% for drinking water • 10% for the industry •  9% for irrigation • The water storage has been developed for : • irrigation, • hydropower generation • drinking water • 126 000 samples of water whose 80,000 for agricultural use

3. French context for hydroelectricity • Production : • Between 60 to 70 TWh for hydroelectricity (550 TWh of total production), • 50% of the production by hydropower plants managed by hydropeak with to type of schemes : • organized in line (eg: Durance, Dordogne, Truyère). • organized with high-head storage (Alpine and Pyrenean mountains)

4. French approach • Identification and quantification of changes of flow regime with two priorities : • Low flow • Hydropeaking • Mitigation measures to increase low flow value (large scale (2014)) and/or to change locally the hydropeaking management.

5. Hydropeaking

6. Principales centrales hydrauliques Focus on hydropeaking • More than 150 hydroelectric schemes managed by hydropeaking in France. • ≈ 3000 kms of streams concerned by hydropeaking.

7. The French approach • 1. Identifications of flow modifications induced by hydropeaking Analysis of flow regime 7

8. The French approach • 2. Identifications of habitat alterations related to the flow modifications induced by hydropeaking Characterization of fish habitats by hydraulic models and habitat preference curves of species and life-stages 8

9. The French approach • 3. Proposal of mitigation measures and assessment Approach based on hydraulic models and habitat mapping 9

10. Index of hydrological perturbation

11. Method to characterize the hydrological disturbance • Data base : gauging stations • Hourly flow analysis • Identification of each flow variations • Differentiation between the hydropeak and natural variations

12. Method to characterize the hydrological disturbance • number of hydropeaks, • Each hydropeak is characterized by : • base flow, • maximum flow, • range, • rate of change,

13. Method to characterize the hydrological disturbance • For each year : • Number of hydropeaks • Statistical characteristics of : • base flow, • maximum flow, • range, • rate of change, Number of hydropeaks Rate of change Base flow Range

14. Daily hydropeaks Hourly hydropeaks Weekly hydropeaks

15. Characterization of hydrologic perturbation: • Construction underway of an indicator of hydrologic perturbation due to hydropeaking events. • Based on discriminant analysis : • base flow, • maximum flow, • range, • rate of change, • number of hydropeaks

16. Saint-Béat - 2006 Characterization of hydrologic perturbation: • The index just evaluate the hydrological perturbations and not ecological effects • The index allow to analyse the evolution of the perturbation along a stream or between years. Chaum - 2006 Upstream Valentine - 2006 Downstream

17. Global situation in France: • 80 stations were analysed in 50 french streams. 58% of stations with strong alterations of flow regime

18. Impact of hydrological perturbations on fish habitat

19. Two types of impacts on fish habitat depending on morphology of stream. Impacts on fish habitat Mountain steep stream : hydraulic conditions during high flow

20. Effects of hydropeaking management during life-stages of fish Impacts on fish habitat Lez river (MD : 1 m3/s) Hydrologic perturbation very marked, maximum discharge 4 m3/s (≈4 times MD), between 150 and 300 hydropeaks per year.

21. Two types of impacts on fish habitat depending on morphology of stream. Impacts on fish habitat Braided streams : Hourly variations on wetted perimeter dewatering fish habitats on shallow shoreline areas and trapping fry in disconnected secondary channels

22. Impacts on fish habitat • Monitoring two streams (MD :107 m3/s; MD : 20 m3/s) Line of lakes and hydropower plants Hydrologic perturbation very marked, maximum discharge 35 m3/s (≈1,8 times MD), between 150 and 300 hydropeaks per year. Hydrologic perturbation marked or very marked, maximum discharge 340 m3/s (≈3.2 times MD), between 100 and 240 hydropeaks per year.

23. Impacts on fish habitat • Monitoring ecological effecfs of hydropeaks • Dewatering of salmonid redds and mortality of eggs (30% of the total redds). • Trapping of fry in disconnected secondary channels and mortality (6000 fry/year on 6 kms of stream). Back to base flow During a hydropeak

24. Mitigation measures • Two types : • Changes on hydropeaking management : • Number of hydropeaks during specific biological periods, • Base flow, range, maximum flow, rate of change • Changes on stream morphology : • Connectivity of secondary channels, • River banks • Topography of gravel bar

25. Mitigation measures • Base flow increased : • from 0.5 m3/s to and 4 m3/s (5-20% of MD) in winter and spring, 1 m3/s the rest of the year • From 10 m3/s to 30 m3/s (28% of MD) in winter and spring (15/11-15/06), 10 m3/s the rest of the year. • Maximum discharge limited : • to 35 m3/s (less than 2 times MD), if possible, in spring (15/03-15/06). • to 190 m3/s (less than 2 times MD), if possible, in spring (15/03-15/06). • Discharge downramping rate of change limited : • to 20 m3/s/h in spring (15/03-15/06). • to 30 m3/s/h all year round. • Work on morphology to ensure permanent supply of secondary channels.

26. Mitigation measures • Efficiency: • Only ≈ 5% salmonid redds dewatered, instead of 30% without base flow increase. • Significant decrease of fry mortality in connected secondary channels.

27. Effects on electricity production • There were compensations for the losses of electricity production. In general, losses of production varied between 0,5 % to 2% of the total potential of peak production. • They remained quite limited because of the line organization. Only the production of the last hydropower plant is really affected. • All decisions of flow changes were made ​​in consultation with the electricity company

28. Minimum flow

29. Evolution of low flow • Analysis of the evolution of low flow at large scale during the 3 last decades (Guintoli and Renard, 2010). • Volume • Duration • Time (begining and end)

30. Evolution of low flow • Significant evolution of low flow conditions.

31. Fish communities and low flow Changes in fish communities in relation to low flow conditions

32. Fish communities and low flow

33. Fish communities and low flow

34. French approach • The French Water Law impose minimum values of flow : • 5% to 10% of mean annual flow in 2014 for all dams and weirs • Locally, for each dams or weirs, the value of minimum flow can be increased based on study using microhabitat methodology.

35. Conclusions • Modifications of flow regime are very important in France for a large part of water bodies. • A focus was made on hydroelectricity use with : • an evaluation at large scale for hydropeaking effects on flow regime, • the definition of mitigation measures at small scale • No direct relationships were established with biological index related to ecological status assessment of water bodies.