Dams and Reservoirs - Hydrogeology: Objectives, Methods, Applications - page 293

impermeable Jurassic formations, and the development of reservoirs in
the older sections of the river, widened by renewed erosion (Figure 137)
(Gignoux & Moret, 1952; Antoine & Barbier, 1973).
The Sautet, St Pierre-Cognet, and Monteynard reservoirs saturate the
Würmian fi ll and are subject to leaks that pass around the dams and, passing
through ancient, fi lled channels, fl ow out into tributary valleys.
In the case of the Sautet dam, fi nished in 1935, the bottom of the old
lateral valley is located 60 m below the high-water level of the reservoir,
causing losses of 2.5 m 3 ·s -1 , which then rejoin the Sézia valley.
The losses are smaller at the downstream reservoirs. They do not exceed
250 L·s -1 at the St Pierre-Cognet dam, fi nished in 1957, where they fl ow
into the Bonne valley, and do not exceed 400 L·s -1 at the Monteynard dam,
fi nished in 1957, where they short-cut into the Ars ravine (Letourneur &
Michel, 1971).
Figure 137 Hydroelectric infrastructure in the Drac valley (Isère) (from Gignoux & Moret,
1952 and Gignoux & Barbier, 1955).