Every year, we work hard to limit the impacts of the spring runoff well before it begins
Hydro-Québec’s presence in Mauricie:
- 11 generating stations in 9 locations
- 4 reservoirs created by the Gouin, Manouane, Matawin and Mékinac dams
- 1 buffer area consisting of Blanc reservoir
- 1 river stretching some 400 km, from downstream of Gouin dam to the Fleuve Saint‑Laurent
- 1 watershed covering over 42,500 km2, or the size of Switzerland
Mékinac dam is located at the southern tip of Mékinac reservoir/lake (Lac Mékinac), at the source of the Rivière Mékinac. Lac Mékinac is 16-km long and covers an area of 23 km2, while its watershed covers 880 km2. All the natural inflows in this watershed supply the Rivière Mékinac downstream of the dam. Lac Mékinac has little storage capacity for the size of its watershed. It requires close monitoring and frequent adjustments due to the high variation in its water inflows from rain, storm cells and snowmelt.
Lac Mékinac is an annual reservoir; it is filled by the water in its watershed and emptied over a one-year cycle. The water level in the lake is maintained by the dam’s stoplogs. These stoplogs can be added or removed manually to increase or decrease the flow discharged, which in turn changes the reservoir’s water level. The water that flows over the stoplogs spills into the Rivière Mékinac, where it helps sustain aquatic plants and wildlife.
The operating range of Lac Mékinac depends on the design criteria of the dam, which determine the maximum threshold that needs to be respected to ensure the safety of the dam and the public. The management of Mékinac dam is based on the water inflows anticipated. For example, if significant rainfall is expected in the coming days and the reservoir is already quite full, Hydro-Québec will need to release some of the stored water to accommodate the expected inflows. The safety of the public and our facilities is one of our core concerns and guides our every decision.
To learn more about the Saint-Maurice watershed, visit the website of the Bassin versant Saint-Maurice organization (site in French only).
Frequently asked questions
Could we find out what the flow of the Rivière Saint-Maurice and the level of the reservoirs in the Mauricie region are in real time, so that we can protect our property (docks, land, homes, cottages, etc.)?
When there is a potential for flooding, Hydro-Québec is in continuous contact with the Organisation régionale de la sécurité civile (ORSC), and we give them daily updates of the river’s flows. Since the 2017 spring flood, during the period when water inflows are closely monitored, the ORSC holds daily conferences for the municipalities who are tracking the situation. At these meetings, Hydro-Québec shares details about expected water inflows and answers questions.
Why is it that, during some flood periods, Blanc reservoir is not full while the areas downstream of it are flooded?
The Rapide-Blanc development has a small amount of upstream storage (sometimes known as pondage) that acts as a buffer between upstream and downstream when heavy rain is expected and the flood risk is high for the most at-risk downstream areas. However, the volume of this storage is limited and it can only hold back water for a short period. It should also be noted that the entire watershed covers an area of 42,651 km2 and the Saint-Maurice is 381-km long. Very often, in spring, while there may not be much snow left in the Rapide-Blanc area, there is still a thick layer of snow covering the ground in the north. In general, if the spring thaw starts late and there is still a lot of snow left in the north of Mauricie in mid-May, Blanc reservoir will fill up later than it does during an average spring.
Can Hydro-Québec ensure an optimal level at Blanc reservoir for the start of fishing season?
Blanc reservoir can only be used for a limited time during the spring thaw. Hydro-Québec manages the river with caution and diligence to reduce the impact of the spring runoff as much as possible on all neighboring communities and infrastructure, both upstream and downstream of the reservoir. In addition to the risk management involved in these efforts, we also take into account the various—and sometimes conflicting—expectations of the different communities and areas affected.
Can Hydro-Québec lower the level of the forebay at La Tuque generating station during flood periods to prevent water from backing up in the Rivière Croche?
La Tuque generating station is a run-of-river station, which means that it is powered directly by the river’s flow and has virtually no water storage capacity. The operation of this type of facility must therefore take into account rain, temperature and snowmelt conditions. Hydro-Québec manages the spring runoff to reduce its impact on all residents, without favoring any particular group. If we didn’t, the situation would be much worse every year. Residents living immediately downstream of our structures are in stretches of the river whose water level cannot be regulated during flood periods. They are therefore more vulnerable to the vagaries of the weather than the residents living around the bays upstream of the facility.
Why is it that, in 2017, the shorelines in the Grandes-Piles area were dried up, whereas downstream of Grand-Mère some of the properties were flooded?
The water storage capacity upstream of Rocher-de-Grand-Mère generating station is quite low (nearly 300 times lower than the capacity of Gouin reservoir). As a run-of-river facility, Rocher-de-Grand-Mère cannot hold back the spring flood in any significant way. The level of the upstream forebay is kept low to reduce the impact of the flood on this section of the river. If the upstream level were higher during the spring flood, it would increase the risk of impacts on the upstream section of the river, without reducing the floods downstream.
Why is Hydro-Québec slow to open the gates of the Shawinigan dams during flood season?
The two generating stations that are part of the Shawinigan complex are run-of-river stations, which means that they do not have a reservoir to hold back water. Hydro-Québec opens the gates of the Shawinigan dams when the quantity of water in transit is higher than the generating capacity of the two stations combined. Mother Nature determines when this quantity is reached.