Evaluation of the prototype surface bypass for salmonid smolts in spring 1996 and 1997 at Lower Granite Dam on the Snake River, Washington

In spring 1996 and 1997, we studied the prototype surface bypass and collec tor (SBC) at Lower Granite Dam on the Snake River in Washington. Our object ives were to determine the most efficient SBC configuration and to describe smolt movements and swimming behavior in the forebay. To do this, we used hydroacoustic and radiotelemetry techniques. The SBC was retrofitted onto t he upstream face of the north half of the powerhouse to test the surface by pass method of diverting smolts from turbines. The SBC had three entrances, with mean velocities ranging from 0.37 to 1.92 m/s, and it discharged 113 m(3)/s through its outlet at Spill Bay I, which was adjacent to the powerho use. Different SBC configurations were created by altering the size and sha pe of entrances. During spring 1996 and 1997, river discharge was well abov e normal (123 and 154% of average, respectively). Powerhouse operations cau sed a strong downward component of flow upstream of the SBC. Many smolts (p rimarily steelhead and secondarily chinook salmon) were observed actively s wimming upward in the water column. There were four times as many smolts di verted from turbines per unit volume of water with SBC flow than with spill flow, which indicated that the SBC may be an especially important bypass c onsideration in moderate- or low-flow years. The highest SBC efficiency (th e proportion of total fish passing through the north half of the powerhouse by all routes that passed through the SEC) for any configuration tested wa s about 40%. Although no single SBC configuration stood out as the most eff icient, the horizontal surface and maximum area configurations, or some com bination of the two. are worth further investigation because they were mode rately efficient.