Orifice Placement in Gatewells of Turbine Intakes for Bypassing Juvenile Fish around Dams

Four locations of an orifice within a turbine intake gatewell were tested to determine which was the most effective in facilitating the passage of fingerling Pacific salmon (Oncorhynchus spp.) and steelhead trout (Salmo gairdneri) from the gatewell into an adjoining trash sluice. The orifice positions tested with natural light were: (1) center of gatewell, 1.5-m depth; (2) corner of gatewell, 1.5-m depth; (3) center of gatewell, 4.6-m depth; and (4) corner of gatewell, 4.6-m depth. Hatchery-reared coho salmon (O. kisutch) placed in the gatewell and wild chinook salmon (O. tshawytscha) and steelhead trout that migrated downstream and entered the gatewell were used to evaluate response to different placements. The most effective location was in the corner of the gatewell at a depth of 1.5 meters. Changes from natural to artificial lighting did not improve passage. A darkened gatewell with artificial light over the orifice did affect passage efficiency, however, and should receive careful attention in any future application of a gatewell bypass system.