Getting Fish out of the Forebay Alive: A Lesson from a Southern California Power Plant

The pending rules enacting CWA section 316(b) include minimizing losses due to entrapment within an enclosed forebay. Many options exist including recovery after impingement and removal before impingement. Impingement on traveling water screens results in physical stress that can be fatal on a size- and species-specific basis. Removing fish from a forebay before impingement is also problematic. In this study, I describe the use and effectiveness of the "fish chase" procedure performed at San Onofre Nuclear Generating Station as a method of removing fish from an enclosed forebay while minimizing mortality. During a fish chase, the forebay water temperature was slowly raised, causing fish to enter the fish return area where most fish were successfully returned to the ocean alive. I also evaluated the application of these same principles to a power plant without a dedicated fish return system. In both cases, gradual increases in temperature resulted in greater live fish recovery rates until reaching a critical temperature of ca. 28°C. At temperatures above 28°C, most fish perished. Fish recovery rates were species-specific in both techniques.