Spillways

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.

"The Giant's Staircase"

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 Saint-Laurent at Montréal. This phenomenal capacity corresponds to an exceptional flood likely to occur once every 10,000 years.

A ski jump

The spillways at La Grande-3 and La Grande-4 have a curved design that looks like a ski jump. The upward lip is designed to project the jet of water dozens of metres into the air, which dissipates part of its energy and prevents structural damage.