Outaouais

Why can't Hydro-Québec hold back more water at Chelsea generating station?

Chelsea is a run-of-river generating station, which means that it does not have a reservoir to retain water.

Why doesn’t Hydro-Québec close the water intake structures at Paugan and Chelsea generating stations to reduce or prevent floods?

Paugan and Chelsea are run-of-river generating stations. If we tried to use these generating stations to retain water, the water would overflow in at most a few hours and escape around the sides of the station. This would damage the station and would not reduce the impacts of spring runoff in any way.

How does the emptying and filling of Baskatong reservoir work?

Does Hydro-Québec hold back water at Carillon generating station to reduce the impact of spring flooding on residents downstream?

No. Carillon generating station is a run-of-river generating station, which means that it does not have a reservoir to hold back spring flooding. During flood periods, the spillway discharges the excess water. If the spillway gates were closed at the peak of the flood, the water would spill over the facility within a few hours!

Since flows and water levels can change rapidly, why doesn’t Hydro-Québec give advance notice to the people who live along the Gatineau and Outaouais rivers?

Several variations can occur in a single day depending on the constraints of electricity generation and spring flood management. Despite Hydro-Québec’s planning efforts, there are times when decisions have to be made very quickly. Please remember to always stay clear of our facilities and not go past the safety buoys.

Why does the level in Baskatong reservoir vary from year to year?

Baskatong reservoir is an annual reservoir, which means that it is emptied and filled once a year. After the reservoir is filled, at the end of the spring runoff, its level fluctuates in the upper end of its operating range until it is emptied the following winter. Since all the water received during the year needs to be released into the river, the level of the reservoir and the flow leaving the reservoir are managed based on weather conditions. More specifically, the management of Baskatong reservoir is directly related to the amount of water received (rainfall runoff and snowmelt) and the time of year the water arrives. A year of drought will be managed differently than a year of record rainfall or snowfall.

How are citizens informed of the progress of the flood on the Rivière des Outaouais?

The Sécurité civile and municipalities are responsible for informing citizens and managing emergency response operations, including in the event of a flood risk. In collaboration with the Ottawa River Regulation Planning Board (ORRPB), Hydro-Québec informs the Sécurité civile and municipalities of the water level variations in the Outaouais during flood periods.

Visit the ORRPB website to track the hydraulic conditions of the Rivière des Outaouais watershed, which includes the Rivière Gatineau.

Why does the level of the Rivière Gatineau vary so much?

Several variations can occur in a single day depending on electricity needs, maintenance requirements, operating constraints and approaches, and inflows from heavy precipitation or snowmelt. Hydro-Québec must ensure sound management of the Rivière Gatineau based on all these constraints.

Why is it that, during runoff periods, there is very little water immediately upstream of Chelsea generating station, while the water levels downstream are very high?

A few days before the spring runoff period starts, Hydro-Québec lowers the water level upstream of the generating station in order to reduce the effect of the station on the river flow and limit the backup effect that can occur at high flow rates. You could say that we try to make the river behave as it would in its natural state, that is, before the generating station was built. The water level upstream of the generating station may lower over a distance of several kilometres, depending on the river’s natural profile. The river flow is then determined solely by natural restrictions (islands, narrows, shoals or rapids), which cause the water levels to rise.

When water levels are lowered, the effect downstream of the generating station is negligible. To reduce water levels upstream, we temporarily increase the flow through the generating station for a few hours or a few days before the water inflows increase. Once the upstream level has been lowered, the run-of-river generating station lets the river’s natural flow pass through, no more, no less. The return to normal operating levels takes place when the spring flood subsides.

Could Hydro-Québec change the management of Baskatong reservoir to prevent floods?

Unfortunately, floods cannot be entirely avoided during years when water inflows are very high, since reservoirs only drain 40% of the Rivière des Outaouais watershed and have limited capacity. The main way to reduce spring flood flows is to make as much room as possible in the reservoir (emptying) before the flood begins and to let water accumulate in it during the flood. This means the flow leaving the reservoir will be as low as possible when the water level in the river downstream is highest. This management approach is the best way to reduce the magnitude of spring flooding. It should also be noted that the management of Baskatong reservoir is directly linked to the amount of water received and the time of year when the water arrives.

Why doesn’t Hydro-Québec close the gates of Bryson and Carillon generating stations to reduce or prevent floods?

Bryson and Carillon are run-of-river generating stations, which means that they do not have a reservoir for storing water. If we tried to retain water at these generating stations, it would overflow in at most a few hours and escape on the sides of the station. This would damage the station and would not reduce the spring flood in any way.

Is Hydro-Québec able to protect residents living upstream and downstream of its generating stations from flooding, or does it need to choose one group over the other?

The safety of all residents, whether they live upstream or downstream of our facilities, is one of Hydro-Québec's priorities. We manage the Rivière des Outaouais and all our facilities cautiously and safely in order to limit flooding of all riverside communities and infrastructure.

Through the management of our reservoirs, we help reduce flows at the height of the flood, for several days. This benefits all residents downstream of the reservoirs.

Since most of our generating stations on the Rivière des Outaouais are run-of-river facilities, they do not impact downstream water levels. However, for residents living upstream of these facilities, Hydro-Québec lowers the operating level of the generating station in order to reduce the effect of the station on the river flow and limit the backup effect that can occur at high flow rates. The water level upstream of the generating station may lower over a distance of several kilometers, depending on the river’s natural profile. This intervention improves hydraulic conditions for the riverside residents living upstream of the generating station, even if there is still a risk of flooding in years when spring runoff is high.