Important reminder: In the event of a flood, contact your municipality. They will advise the Ministère de la Sécurité publique du Québec, which coordinates all flood-related operations.
Questions on how Hydro‑Québec facilities are managed? Contact us at RAMRichelieu@hydro.qc.ca.
Why can’t Hydro-Québec hold back water upstream of the Coteau dams on the Saint‑Laurent?
The hydraulic and hydropower facilities in the Montérégie region, including the Coteau dams, are run-of-river and have no way of storing water. The dams and generating stations must allow the water to flow through, without holding it back. Some of the water is used to generate electricity, and the rest is discharged through the gates of the dam or spillway.
Why has the flow in the Saint-Laurent been higher since 2017?
Inflows to the Saint-Laurent come mainly from Lake Ontario, the most downstream of the Great Lakes. Throughout the decades, these lakes have gone through wet cycles and dry cycles. The latest wet cycle, which began in 2015, led to a gradual rise in the water levels of the Great Lakes, and a subsequent increase in the flow of the Saint-Laurent. Since 2017, the levels of the Great Lakes have been higher than average and these lakes have also been receiving above-normal precipitation. It is therefore necessary to accept higher flows in the Saint-Laurent to ensure the safe management of this major river. Similar conditions were observed in the 1970s and 1990s.
How does the emptying and filling of basins along the Saint-Laurent work? Would it be possible to have water year‑round?
Following the reduction in flow that occurred in the natural riverbed of the Saint-Laurent from 1930 to 1960, structures were built to maintain water levels that met the community’s needs, including vacationing needs. In addition, because managing the ice on the Saint-Laurent is a challenge every winter, some structures have been designed to stay open during the winter to reduce ice-related problems. Due to their design, these structures cannot be operated in the winter. Water levels are therefore always low during this season.
On the Rivière des Outaouais (Ottawa River), could more water be held back by the facilities located in the north so that less water flows to the south?
In spring, Hydro-Québec and its partners fill their reservoirs to almost capacity and store the water to reduce the impact of spring runoff on communities. However, the reservoirs located in the northern part of the Outaouais watershed have access to only 40% of the water inflows. The remaining 60% come from the southern part of the watershed, downstream of the facilities that can hold back water. As a result, the water flowing south of the reservoirs cannot be managed or held back. Although the collaborative efforts of Hydro-Québec and its partners can reduce flows during spring runoff periods, they cannot prevent floods in certain areas when the inflows are too high, since only four drops of water out of ten flow through control structures