Montréal & Laval

In the administrative regions of Montréal and Laval, Hydro‑Québec operates a single hydroelectric development: Rivière-des-Prairies generating station, on the river of the same name. The management of the flood is based on the facilities and watersheds located upstream of the island of Montréal and the Île Jésus (Rivière des Outaouais and Fleuve Saint‑Laurent).

We reduce spring flooding thanks to our reservoirs. Find out how.

From December to March, Hydro‑Québec gradually empties its reservoirs located in the northern Outaouais and Abitibi-Témiscamingue regions. When the spring thaw begins, they contain almost no water. From early April to early June, we hold back the water in our reservoirs as long as possible to limit inflows to the Outaouais and Saint-Laurent rivers, which are already swollen with water from the surrounding watersheds. However, the reservoirs can hold only 40% of the water inflows. The remaining 60% are from watercourses that do not run through our reservoirs; they flow freely and cannot be retained.

All the generating stations located on these watercourses are run-of-river and do not have reservoirs to hold water. The only facilities that impact the magnitude of the spring flood are the reservoirs located north of the watershed, which we manage in collaboration with our partners.

For more information on the Rivière des Outaouais watershed, visit the Ministère de l’Environnement et de la Lutte contre les changements climatiques (web page in French only).

Hydro‑Québec does not manage the level of the Fleuve Saint-Laurent. The ILO‑SLRB does.

The inflows to the Fleuve Saint-Laurent (St. Lawrence River) are managed in conjunction with the International Lake Ontario – Saint Lawrence River Board (ILO-SLRB), which ensures that the regulation of the levels and flows in Lake Ontario and the Saint-Laurent complies with the legal requirements of the International Joint Commission (IJC). The mandate of the ILO-SLRB covers the entire watershed, from the Great Lakes to Lac Saint-Pierre and to the Montréal archipelago area.

The ILO-SLRB works daily with numerous stakeholders, including the St. Lawrence Seaway Management Corporation, the Canadian Coast Guard, U.S. and Ontario hydropower producers and Hydro‑Québec.

Hydro‑Québec has a direct role in managing the Beauharnois–Les Cèdres hydropower complex, located in the west of the Montérégie region. We work with the ILO-SLRB to safely manage the ice near the complex facilities. The complex is made up of only run-of-river generating stations and therefore cannot retain water. For example, Beauharnois generating station receives the water that comes through the Beauharnois canal, runs it through turbines and then redirects it toward Lac Saint-Louis. It should be noted that Hydro‑Québec does not manage the level of the river.

During the spring thaw, the members of the ORRPB and the ILO-SLRB work together to reduce the inflows to the Montréal archipelago area. Since Hydro‑Québec operates the two generating stations closest to the archipelago, our experts play a key role in this aspect of flood management every spring.