Scour potential at Laouzas Dam

Laouzas Dam, owned and operated by Electricite de France (EDF), is a 52 m high double-curvature arch dam in a large valley located on the Vebre River in the Languedoc-Roussillon Midi Pyrenees region of France. The dam is founded on heavily fractured granite and migmatite rock. It houses a surface spillway equipped with 3 radial gates. The radial gates are positioned such that their gate lip is systematically located about 1m upstream of the spillway crest itself. This particular design generates aerated jets that do not behave like normal falling jets. Despite the absence of severe spillages since dam construction in 1961-1965, the ones observed in the past have allowed creating locally a 5 m deep scour hole along the right hand side of the rock mass. The granite and migmatite have significant unconfined compressive strength. The rock mass fracturing is composed of 3-4 joint sets and shows desquamation joints affecting both abutments. EDF has commissioned a numerical study to assess scour potential downstream of the dam as well as the positive influence of rock anchors, by using the Comprehensive Scour Model (CSM).