runoftheriver

Run-of-the-river is a method of hydroelectric power generation that uses the natural flow of a river with little or no reservoir storage. Water is diverted from the river through an intake into a forebay, channeled via a canal or penstock to turbines, and then returned to the river downstream. Because there is little or no large storage, generation depends largely on the existing flow and head at the site rather than on stored water.

In operation, the river’s discharge and topographic head drive the amount of water that can be converted to electricity. A small forebay or diversion structure may regulate intake, but there is typically no large reservoir to hold back water. The main components are the intake, diversion channel or penstock, turbine or turbine–generator unit, and a tailrace returning water to the river. Turbine selection varies with head and flow, commonly including Kaplan, Francis, or Pelton types depending on site conditions.

Advantages of run-of-the-river systems include lower land use and evaporation losses, reduced risk of dam failure, and often simpler, lower-impact construction compared with reservoir-based hydro. They can be sited along many rivers and allow continued water movement downstream, which can benefit ecosystems compared with large impoundments.

Limitations include variability and unpredictability of output due to seasonal and storm-related flows, making them less suitable for baseload power without complementary resources. They can affect downstream flows and sediment transport, and may pose fish passage or ecological concerns that require mitigation. Some projects include small forebays or limited storage, but they do not create large reservoirs.