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 car could be moving at 60 mph, while air outside the car is motionless. 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.