PNNL

Abstract

The use of surface flows (2-20 m deep) as a basis for smolt bypass development was recommended in salmon recovery plans as a means to improve passage conditions for juvenile salmonids (smolts) migrating through main stem Columbia and Snake River dams. A prototype structure called the surface bypass and collector (SBC) was retrofit on Lower Granite Dam, tested during its five-year life span (1996-2000), and compared to other options, such as intake screens and spill, providing a non-turbine passage route. Approximately 62% of the smolts immediately upstream of the SBC passed into the collector during a surface sluice configuration in 1998 and a high flow single chute configuration in 2000. Another potential smolt protection measure, a Behavioral Guidance Structure (BGS) was attached to the SBC and evaluated in 1998. The BGS diverted 79% of the fish intended for the turbines behind it to other passage routes. When used in combination with spill and/or intake screens, a SBC in conjunction with a BGS would provide a high level (> 90%) of non-turbine passage and give operational flexibility to fish management agencies charged with enhancing smolt survival.