Our reservoirs in Bas-Saint-Laurent limit the impacts of spring runoff
Mitis watershed: Although the magnitude of spring runoff depends on the weather, it is reduced by our reservoirs
The Rivière Mitis watershed includes two headwater reservoirs (Mitis and Mistigougèche lakes) and two run-of-river generating stations (Mitis-1 and Mitis-2). In addition to the flow from the headwater reservoirs, Mitis-1 and Mitis-2 facilities receive significant inflows from Rivière Neigette and from the watersheds of Mitis and Mistigougèche rivers, over which Hydro-Québec has no influence.
Every year, Hydro-Québec gradually drains its reservoirs in the winter, to make room for as much water as possible during the spring flood. However, Mistigougèche and Mitis lakes cannot absorb all the spring runoff. The water that flows into the Mitis downstream of these structures is only about 30% of the volume of water coming from the many tributaries of this river.
When the spring runoff starts, Hydro-Québec closes the gates of its facilities to minimize the volume of water released into the Mitis, which in turn limits the impacts of the runoff. The amount of water released into the river is only increased again after the runoff has slowed and flood risks for neighboring communities have declined.
The intensity of the spring runoff depends entirely on weather conditions. For example, there is less runoff when accumulated snow absorbs less heat and there is little rain. On the other hand, warm, rainy springs accelerate snowmelt and increase flood-related risks.