The violent floods of Roya have created historical damage on the walls of the village, along the river. The need to contain the floods, for the safeguarding of the lake control valve that feeds the hydroelectric plant at Piène-Basse, has benefited the banks of the village and the neighborhood facing it.
If the Roya river level is higher than the side dam’s located upstream of the village, the flood is contained and part of the water is sent through the two tunnels downstream the village. It protects the village banks of the river as well as the EDF restraint.
The structure consists of a small lateral dam on the left bank, followed by two drains leading water into the two spillway tunnels passing under the rocky ridge of the village.
The lateral dam determines the level of water preserved in the river, and lets the high water flow.
The two tunnels were dug in the Cretaceous rock. Their facade, dam and drains, were equipped with masonry stone cladding. The dam and drains were concreted afterwards for better flood resistance.