Performance of Surface Flow Outlets for Passing Smolts at Hydroelectric Projects

Routing a large proportion of the smolt population through safe passage routes has been a long-term goal at hydroelectric dams on the Snake and Columbia rivers. Over the decades a variety of devices and operations have been used in an effort to provide safer passage, e.g., screened turbine intakes, fish friendly turbines, spill, etc..  In recent decades, strategies have focused on the design and installation of surface flow outlets.  These devices are  strategically located, site-specific in design, and take advantage of the natural surface orientation of smolts. They can stand alone or be incorporated into spillways or powerhouses.  This paper briefly surveys the various designs of these systems, the status of installations across the basin, and discusses the performance of these systems in passing smolts in a safe and effective manner.