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The small versus large debate

Large dams on big rivers generate huge amounts of electricity. With these benefits, there are significant impacts on the environment: flooding large areas and changing the water flow in a river, just to name two examples.

Although most of Canada’s dams are of this kind, there also exist small-scale hydro operations providing output ranging from 100 kilowatts to 30 megawatts.

Environmentalists, hydro developers and other interest groups have debated the benefits and impacts of large and small-scale hydro projects. As a simple comparison shows, there is no easy answer. Each type of project offers different advantages and disadvantages.

Studies of hydro projects show that the nature and size of their environmental impacts are determined by the specific site conditions. Whether the project is large or small, run-of-the-river or storage, each project must be judged on its own merits.

Small run-of-the-river hydro	Large run-of-the-river hydro	Large hydro with reservoir
Advantages can benefit from existence of upstream reservoir quicker to build avoids flooding can be built close to communities	Advantages can benefit from existence of upstream reservoir avoids flooding often a least cost option	Advantages provides more reliable generation that can follow demand patterns provides flood control reservoir can be used for recreation often very cost-effective generation can be quickly started and stopped to back up intermittent energy sources such as wind power
Disadvantages generally provides electricity at higher cost than large projects generation cannot follow electricity demand patterns cumulative impacts of many small projects may be higher per kilowatt-hour than one large project	Disadvantages long timelines for regulatory approvals and construction	Disadvantages causes flooding of land causes fluctuations in river flow long timelines for regulatory approvals and construction