La Bathie: simultaneous power increase and river safety improvement

Equipped with six Pelton runners, the La Bathie plant had an initial installed capacity of 500 MW for a 50 m3/s discharge when it was commissioned in 1961; it has been upgraded in 1975 by increasing the discharge to 55 m3/s. To benefit from a change in the French regulation that allows enhancing the installed capacity by 20%, a check of the hydraulic circuit showed that the discharge could go up to 60 m3/s, hence bringing the capacity to 600 MW. The studies conducted to find the best technico-economic compromises concluded that, to do so, the six runners and transformers have to be replaced, and 4 of the 6 stators have to be reconstructed, providing thus a better efficiency. However, as there are recreational activities in the River and as the plant is operated for peaking, there is a public safety issue downstream. So far, the way this problem is tackled is however not fully satisfactory, from both the safety and asset management point of view, and it was decided to build a demodulating basin and a regulation gate. This device is used to temporarily store water and reduce the flow rate released to the river, so as to create an "alert wave" of 16 m3/s during 26 mn in the Isere River. The alert wave was defined according to a risk assessment method elaborated by EDF in the framework of its own public safety management policy. As a result, the project will provide 50 MW of extra power and allow to significantly increase the peaking capacity of the plant.