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News

Researchers analyze role of shear in turbine passage

DOE/Pacific Northwest National Laboratory : 25 May, 2000  (Technical Article)
Although turbines have generated power at hydroelectric dams for more than 100 years, not much is known about how water flowing through the turbines may harm fish.
Researchers at the Department of Energy's Pacific Northwest National Laboratory are working to provide some answers. They have begun examining the relationship between water velocities within the turbine chamber and injuries to fish. Pacific Northwest researchers are studying one 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 most common effects on fish observed during this study have been tearing of the gill covers and loss of scales.

Findings from this study could provide hydroelectric dam operators with some of the information necessary to design fish-friendly turbines. Pacific Northwest's research is being done in cooperation with two other national laboratories, Idaho National Engineering and Environmental Laboratory and Oak Ridge National Laboratory, through DOE's Advanced Hydropower Turbine System Program.

To simulate the environment found within a turbine channel, Pacific Northwest researchers built a small-scale facility that uses an underwater jet nozzle to vary water velocity. Researchers have begun testing the impact to fish of velocities ranging from zero feet per second to 60 feet per second. They will identify the injury threshold - the points at which there are no, or few, injuries to fish.

'This is a fishery biologist's opportunity to provide specifications for use in turbine design,' said Duane Neitzel, Pacific Northwest project manager. 'Turbines are integral to the operation of hydroelectric dams, but they also can injure fish.'

Turbine passage can be considered one of the more fatal routes that fish take through hydroelectric dams. Mortality rates range from 4 to 20 percent, depending on factors such as type of turbine and type of fish.

During passage through a dam, a fish experiences several changes in water velocity and encounters shear forces during each velocity change. The most intense shear forces usually exist near the turbine blades and, most especially, the tips of the blades.

In field tests at Pacific Northwest's aquatic facility, researchers introduce fish individually through a tube above a water nozzle. As the fish leaves the tube and enters the pool, it encounters different water velocities, or shear force. A high-speed camera records the impact of the shear on the fish. Researchers then capture the fish and examine it for injuries. Fish are held for several days to examine their injuries over time.

'The concept of shear force is similar to a person sticking their head out the window of a moving car,' said Scott Abernethy, Pacific Northwest senior technical specialist. 'The car could be moving at 60 mph, 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.'

Pacific Northwest researchers are studying the impact of shear force on American shad, fall chinook salmon smolts, rainbow trout, steelhead and spring chinook salmon. Results could help engineers tailor turbine design based on the type of fish that would migrate through a specific waterway.

The AHTS program began in 1993. Two contracts were awarded for developing conceptual designs of turbines. During this phase, it was determined that more biological information was needed. Pacific Northwest became involved in 1996 with development of a prototype test facility. The current research will continue through 2000.
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