A Piano Key Weir to improve the discharge capacity of the Oule Dam spillway (France)

The Oule dam spillway (France) is made of a lateral weir on the right bank of the reservoir, a collecting channel, a macro-steps channel and a downstream lateral weir for water release in the natural river bed. This spillway presents a deficit in discharge capacity. In order to solve this problem, several rehabilitation solutions have been analyzed. From this process, a piano key weir solution to improve the discharge capacity of the lateral upstream weir has been selected. This piano key weir will replace the existing ogee crest while keeping weir level and thus normal reservoir elevation constant. The piano key weir, 1 m high, has been designed with steel and is made of 22.5 units for a total width of 33 m. Its main advantage is to drastically increase the discharge capacity at low heads, enabling the release of the design flood peak discharge just below the reservoir maximum elevation by optimizing the reservoir temporary storage.