Maintaining Wetted Riverbeds

Keeping rivers wet when water flow is stopped by dams preserves aquatic life.

When dams on tributary rivers are producing power, they use water from reservoirs upstream and downstream riverbeds stay wet.
But when generation stops, so does water flow, and previously wetted river beds can be exposed for hours.
As a result, riverbeds can dry out, causing a loss of aquatic habitat and a decrease in abundance and availability of food.
These conditions affect the health and fitness of the fish that live in the waters below the dams.

When dams on tributary rivers use water from the reservoir upstream to generate power, there is plenty of water in the riverbed downstream. But when the demand for electricity drops off for a few hours each day, power generation—and water flowing through the dam—can stop. When this happens, large areas of previously wetted riverbed are exposed for hours at a time, until the next release from the upstream dam. The result of prolonged exposure is the loss of aquatic habitat and a decrease in the abundance and availability of food, conditions that can affect the health and fitness of the fish that live in the water below the dam, the tailwater.

TVA uses three different technologies to maintain water flow in the riverbed below tributary dams when hydroelectric generation is shut off:

Turbine pulsing

At some dams, TVA releases water through the dams at regular intervals throughout the day in a process called turbine pulsing. This technique helps to create an essentially steady flow of water within a few miles, maintaining a more constantly wetted habitat downstream of the dams.

Weirs

At other dams, TVA has built downstream weirs. These operate like small dams, holding back some of the water when power is being generated, then slowly releasing it when generation stops.

Small hydroelectric units

At two TVA hydropower plants (Blue Ridge and Nottely), small hydroelectric units run when the main turbine is not operating so that water is continuously released downstream.

The wetted riverbeds preserve aquatic habitats, ensure that there will be an ample supply and variety of food sources and protect downstream fish populations for the enjoyment of the people of the Tennessee Valley.