Alternative World Water Forum

Hydropower projects described as run of river evoke images of unimpeded rivers delivering clean power without the environmental and social costs of traditional dams. And influential institutions like the World Bank tout the share of run of river projects in their hydro portfolios, suggesting such projects have few adverse impacts. However, the reality is often very different.

Run-of-river (ROR) hydropower schemes have become popular among dam proponents as a supposedly “low-impact” alternative to storage dams. Forbes Magazine declared that “Run of river just might be the ultimate in green power.” But while run-of-river projects may avoid some of the impacts commonly associated with storage dams, such as large reservoirs, their overall impacts can be even worse. ROR projects can be particularly detrimental to the ecology of rivers that provide vital services to people living downstream.

WHAT DOES “RUN-OF-RIVER” MEAN?

The term “run-of-river” is misleading because it suggests harnessing a river’s natural flow and generating energy as it passes, but that’s not what run-of-river hydro does. All hydropower projects impound water and impact rivers. Most ROR projects withhold water either behind a dam or through diversion tunnels.

There is no common defi nition of what constitutes a run-of-river project. Generally, “run-of-river” refers to a hydropower project either with a small reservoir or no reservoir. They differ from traditional reservoir dams, which store great quantities of water during the wet season to allow year-round releases to generate power. Instead, because they have comparatively limited storage capacity, ROR projects are generally built on rivers with fairly consistent annual flows, which are either naturally occurring or are regulated by a storage dam upstream.

In practice, the term “run-of-river” is used very loosely. This lack of specificity, and the claimed green credentials the term connotes, gives license to a wide spectrum of projects being indiscriminately referred to as “run-of-river.” The term ROR has been applied to everything
from micro-hydro projects providing electricity in remote villages to the Belo Monte mega-dam in Brazil, the world’s third largest hydroelectric project, which will devastate an extensive area of the Brazilian rainforest, displace over 20,000 people, and threaten the survival of indigenous tribes that depend on the river.

While the term suggests otherwise, most run-of-river projects store water, though application varies widely. In some cases, the ROR label has been applied to dams that withhold water for weeks or even months. The World Bank generally uses the term to refer to dams that can store up to a day’s worth of a river’s flows – a definition that is stricter than most, though such projects are not without impacts, as discussed in subsequent sections.

Read more of the factsheet on the website of International Rivers

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