Evaluation of a prototype surface flow bypass for juvenile salmon and steelhead at the powerhouse of Lower Granite Dam, Snake River, Washington, 1996-2000

Publication Date



anadromous fish, bypass, bypass systems, dams, efficiency, entrance, forebay, hydroelectric, hydroelectric dams, juvenile, juvenile salmon, Lower Granite Dam, Lower Snake River, passage efficiency, prototype, salmon, Snake River, steelhead, surface bypass, surface orientation, survival, water supply, water velocity

Journal or Book Title

North American Journal of Fisheries Management


A surface flow bypass takes advantage of the natural surface orientation of most juvenile salmon Oncorhynchus spp. and steelhead O. mykiss by providing a route in the upper water column that downstream migrant fishes can use to pass a hydroelectric dam safely. A prototype structure, called the surface bypass and collector (SBC), was retrofitted on the powerhouse of Lower Granite Dam and was evaluated annually with biotelemetry and hydroacoustic techniques during the 5-year life span of the structure (1996-2000) to determine the entrance configuration that maximized passage efficiency and minimized forebay residence time. The best tested entrance configuration had maximum inflow (99 m(3)/s) concentrated in a single surface entrance (5 m wide, 8.5 m deep). We identified five important considerations for future surface flow bypass development in the lower Snake River and elsewhere: (1) an extensive flow net should be formed in the forebay by use of relatively high surface flow bypass discharge (> 7% of total project discharge); (2) a gradual increase in water velocity with increasing proximity to the surface flow bypass (ideally, acceleration < 1 m/s per meter) should be created; (3) water velocities at an entrance should be high enough (> 3 m/s) to entrain the subject juvenile fishes; (4) the shape and orientation of the surface entrance(s) should be adapted to fit site-specific features; and (5) construction of a forebay wall to increase fish availability to the surface flow bypass should be considered. The efficiency of the SBC was not high enough (maximum of 62% relative to passage at turbine units 4-5) for the SBC to operate as a stand-alone bypass. Anywhere that surface-oriented anadromous fish must negotiate hydroelectric dams, surface flow bypass systems can provide cost-effective use of typically limited water supplies to increase the nonturbine passage, and presumably survival, of downstream migrants







This document is currently not available here.