How run-of-river hydropower works

Inukjuak at sunset in Nunavik, Quebec. The fly-in Arctic community of just over 1,800 residents has replaced almost all diesel with locally owned hydro power. (photo: Lina Forero)

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Residents of Inukjuak, a Nunavik community located on the east coast of the Hudson Bay, are on track to reduce their greenhouse gas emissions by around 700,000 tonnes over the next 40 years, according to Hydro-Québec.

That reduction stems from Inukjuak’s hydroelectric plant, which opened upriver from the community in October 2023. Spearheaded and developed by Inukjuak’s landholding corporation, in partnership with Innergex Renewable Energy, the project has transitioned the community from depending on diesel generators for power to using cleaner hydroelectricity.

“The carbon footprint of their energy consumption really comes down by a lot,” said Lynn St-Laurent, a spokesperson for Hydro-Québec.

What sets the Innavik Hydroelectric Facility apart is not just where it is, but how it works. The facility is a run-of-river hydroelectric plant, a type of hydropower system that generates electricity with a smaller environmental footprint than traditional dams.

How run-of-river hydropower generates electricity

Unlike impoundment facilities, which require flooding vast areas of land for water storage, run-of-river facilities divert only a portion of a river’s natural flow through a turbine to generate electricity. The rest of the water continues downstream, largely uninterrupted.

Since they do not rely on large reservoirs, run-of-river projects typically cause less disruption to surrounding ecosystems, according to Jason Donev, professor at the University of Calgary.

“The process of flooding something, we’re now very aware of the environmental consequences, in a way that we just really didn’t care about when the Robert Bourassa Reservoir was being built,” he said.

Limits of run-of-river systems

That lighter footprint comes with limitations.

Impoundment facilities, which store large amounts of water, can adjust to changes in a community’s electricity demand by increasing or decreasing the flow of water into the hydro plant. In contrast, the electricity output of run-of-river facilities depends on a river’s natural flow, which varies seasonally and doesn’t always match a community’s electricity needs.

“The highest demand for electricity tends to be during winter, when you have the lowest flow of water,” Donev explained.

In Inukjuak, the community is still supplied by diesel generators, with one to two per cent of homes using their generator at any given time to maintain proper system functioning, according to Hydro-Québec. This backup system ensures that even when river flow is insufficient, residents can meet essential needs, such as keeping their homes warm in winter, says Donev.

What determines the design?

Choosing what type of hydroelectric facility to build isn’t as simple as picking run-of-river over impoundment, says Donev. Rather, it’s a question of geography.

“Sometimes run-of-river is the only thing that makes any sense whatsoever,” he said.

Rivers with a large elevation drop between upstream and downstream are well suited for run-of-river designs, he explains. On the other hand, in valleys, reservoir systems are often the only viable option.

In Québec, about two-thirds of hydroelectric facilities are run-of-river. Together, however, they account for only around one-third of Quebec’s total hydroelectric generation, according to Hydro-Québec.

Currently, no run-of-river facilities are being planned by Hydro-Québec. The electricity provider is focusing on adding additional renewable energy sources, including solar and wind, to complement its existing hydropower.

St-Laurent says Hydro-Québec is working to decarbonize the province’s power generation, including in off-grid communities.

“It’s part of our priorities. To create opportunities, collaborations, partnerships and improve relationships with indigenous communities,” she said.

For off-grid communities weighing alternatives to diesel, run-of-river hydropower offers a lower-impact option.