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Fish Response to Hydroelectric Turbines Tested Environmental News Network - June 7, 1999

Dams have never been popular with environmentalists for a host of reasons, including their impact on freshwater biodiversity, displacement of human communities and alterations to the natural landscape.

The turbines that generate power at hydroelectric dams are also blamed for high rates of fish mortality, bringing several species to the edge of extinction.

As part of an effort to make these turbines more fish friendly, researchers at the Department of Energy's Pacific Northwest National Laboratory are examining the relationship between water velocities within the turbine chamber and injuries to fish.

The researchers are looking at a particular phenomenon, called "shear force," which occurs when two different water velocities collide. Depending on the shear's intensity, a fish may be disoriented momentarily, lose its scales, or be bruised or cut.

"The concept of shear force is similar to a person sticking their head out the window of a moving car," said Scott Abernethy, a senior technical specialist at the laboratory. "The car could be moving at 60 miles per hour, while air outside the car is motionless. At slower speeds, the impact might just mess up the person's hair; at higher speeds, the skin may be stretched back."

Findings from the research could provide hydroelectric dam operators with some of the information necessary to design fish-friendly turbines. Researchers have begun testing the impact of different water velocities on the fish, hoping to pinpoint the injury threshold -- the point at which there are no, or few, injuries to fish. Although this threshold has been identified in preliminary results, the laboratory is not cleared to publicly release the data, said Staci West, a spokesperson at the laboratory.

Mortality rates due to turbines range from four to 20 percent, depending on factors such as the type of turbine and the type of fish.

The impact of shear force is being tested on American shad, fall chinook salmon smolts, rainbow trout, steelhead and spring chinook salmon. The research will continue through 1999.