Retaining Structures

One of the purposes of retaining structures is to create large bodies of water, or reservoirs, that have a variety of functions, including land irrigation, power generation, water supply and flood control.

The retaining structures used to build reservoirs are called dams and dikes. A dam is built on the riverbed; it serves to hold back water and raise the water level of the resulting reservoir. Dikes are often built to increase a dam's effectiveness by preventing water from leaving the reservoir through secondary valleys.

There are close to 6,000 retaining structures of various sizes in Québec. The Ministère du Développement durable, de l'Environnement et des Parcs owns most of them; Hydro-Québec owns and operates only one out of 10 such structures.

Other dam owners, including municipalities, outfitters and companies like Alcan, are also involved in dam and dike operation, in addition to water management of the related reservoirs.

Earthfill dam

A dam is considered an earthfill dam when more than half its fill volume is composed of compacted fine materials.

The building of such a dam is dependent on the availability of raw materials.

Rockfill dam

Till is the loose sediment deposited by glaciers, and it's the perfect material for making a dam watertight. It forms the core of most rockfill dams owned by Hydro-Québec, including some of the retaining structures in the La Grande complex.

Gravity dam (concrete)

The stability of this concrete dam is ensured by the structure's weight.

Arch dam (concrete)

A concrete dam with a convex arch facing upstream which transmits the greater part of the force of water to the lateral abutments.


A dam characterized by its length, designed to inhibit water movement (currents or tides) or to hold back water.

Timber dam

East Angus dam, belonging to Brompton Pulp and Paper (1950)

A dam built by assembling timber to form stone-filled cribs.

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