Reducing the impact of spring runoff: A team effort between Hydro-Québec and its partners
The Rivière Gatineau and the Rivière des Outaouais (Ottawa River) are part of the Outaouais watershed. They are the only rivers in this watershed that are home to Hydro-Québec’s hydropower facilities. Excluding the Abitibi-Témiscamingue region, the facilities we manage within the watershed are Baskatong and Cabonga reservoirs, on the Gatineau, and seven generating stations: Mercier, Paugan, Chelsea and Rapides-Farmer on the Gatineau; Bryson and Carillon on the lower stretch of the Outaouais; and Chute-des-Chats which is operated by Ontario Power Generation in partnership with Hydro‑Québec.
Hydro-Québec is not the only operator of reservoirs and generating stations on the Rivière des Outaouais
The management of the water levels and flows in this river is a collaborative effort between partners. Every drop of water in the river is monitored by the Ottawa River Regulation Planning Board (ORRPB).
The ORRPB is made up of all the agencies that participate in managing the Outaouais watershed: the Ministère de l’Environnement et de la Lutte contre les changements climatiques du Québec, the Ministry of Natural Resources and Forestry of Ontario, Environment and Climate Change Canada, Public Services and Procurement Canada, the Canadian Coast Guard, Ontario Power Generation and Hydro‑Québec.
The members of the ORRPB work together to effectively reduce the impacts of spring runoff.
We reduce spring flooding in 40% of the Outaouais watershed
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 flood 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.
The Rivière des Outaouais is 1,120 km in length, making it Québec’s longest river. It flows from Abitibi-Témiscamingue to Montréal. Hydro-Québec operates two generating stations on the lower Outaouais: Bryson and Carillon. Chute-des-Chats generating station is operated by Ontario Power Generation, in partnership with Hydro-Québec. All these facilities are run-of-river generating stations, which means that they cannot hold back water or store it in a reservoir. Find out how Hydro-Québec manages the spring runoff along the Outaouais.
Duration : 4 minutes 11 seconds [In French Only]
Our expert explains how we manage the Rivière des Outaouais (Ottawa River)
Cabonga reservoir is spread out across two regions: Outaouais and Abitibi-Témiscamingue. Its two outlets discharge its waters to the south and west. When the water flows southward, through the Rivière Gens de Terre, it joins Baskatong reservoir, which regulates the Rivière Gatineau. When the water flows westward, it reaches Dozois reservoir, which controls the inflows to the Outaouais.
In the winter, the water levels in Cabonga reservoir are drawn down, making room for it to store the water inflows that arrive in the spring from the north. Its two discharge structures remain closed during most of the spring runoff period.
Rivière Gatineau: Flood control at Baskatong reservoir and Mercier dam
Hydro-Québec operates four generating stations on the Rivière Gatineau. From north to south, these are: Mercier, Paugan, Chelsea and Rapides-Farmer. Paugan, Chelsea and Rapides-Farmer are run-of-river generating stations and are supplied with water from Baskatong reservoir and Mercier generating station. Since they do not have reservoirs, these generating stations cannot retain the water inflows (rain, snowmelt and runoff) that occur downstream of Baskatong reservoir.
The management of a reservoir, such as Baskatong reservoir, is dependent on the vagaries of the weather and requires constant adjustments.
From December to March, we gradually empty Baskatong reservoir. When the spring thaw begins, it contains almost no water. From early April to early June, we fill it up again to almost capacity and store the water as long as possible to limit inflows to the Gatineau and, further downstream, to the Outaouais, which are already swollen with water from the surrounding watersheds. However, despite its size, Baskatong reservoir has limited storage capacity. It must release a minimum amount of water to ensure the safety of facilities and prevent an overflow.
Thanks to Cabonga reservoir, Baskatong reservoir and Mercier dam, Hydro-Québec can ensure the sound management of the flows and levels in the Gatineau, a tributary of the Outaouais.
Covering a distance of 443 km, the Rivière Gatineau flows through Baskatong reservoir and empties into the Outaouais. It is the largest tributary of the Outaouais. Find out how Hydro-Québec manages spring runoff along this river.
Duration : 4 minutes 21 secondes [In French Only]
Our expert explains how we manage the Rivière Gatineau
Le contenu qui suit est un diaporama d’images sur : Les normes
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.
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?
Emptying a reservoir means releasing its water to draw down the level in the reservoir to the minimum operating level. This is done to prepare for the spring runoff. The emptying starts in December and lasts several months. Filling a reservoir means letting water accumulate in the reservoir. The water will be used to generate the energy required to meet electricity demand for the rest of the year. During dry summer periods, a full reservoir allows us to maintain a minimum flow in the downstream stretch of the river. Throughout the period when the reservoir is at nearly maximum operating level, there are much fewer fluctuations in water levels. The water level variations in the reservoir and river during this time depend mainly on the weather. For example, a rainy summer will lead to higher-than-average levels and flows.
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.
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.