Hydroelectric developments include flood-control structures designed to let excess water escape safely from the reservoir. This "safety valve" prevents water from spilling over the dam crest. It takes the form of a spillway, a weir or sometimes a combination of both.

Spillways at La Grande-3 and La Grande-4 hydropower stations   Safety regulations

The spillway at Robert-Bourassa dam is called "the giant's staircase." The structure is named after its unique shape, which features 10 steps, each 10 metres high and 122 metres wide. The spillway has a discharge capacity of 16,280 cubic metres of water per second, about twice the flow of the St. Lawrence River at Montréal. This phenomenal capacity corresponds to an exceptional flood likely to occur once every 10,000 years.