EPRI's Evaluation of the Elwha Dam Eicher Screen and Subsequent Design Changes and Hydraulic Tests.

The Electric Power Research Institute (EPRI) has conducted two years of biological evaluations of an Eicher Screen installed in a 9-foot (2.7 m) diameter penstock at the Elwha Hydroelectric Project in Washington state. Testing has shown passage survival to equal or exceed 98.7% for steelhead trout Oncorhynchus mykiss smolts and coho salmon O. kisutch and chinook salmon O. tshawytscha smolts and fingerlings. Scale loss injuries were minimal at velocities of 4-6 fps, but increased at higher velocities. Most injuries occurred from fish contacting the screen in an area where it transitions from 63% porosity to 32% porosity wedgewire material, where the velocity component perpendicular to the screen was relatively high. Hydraulic model studies conducted in 1992 indicated that a more gradual reduction of the porosity in the downstream end of the screen would reduce the observed velocity peak by approximately 10%, but would not achieve a fully uniform flow distribution.