Velocity Cap Effectiveness at Scattergood Generating Station (Los Angeles, CA)

Velocity caps are used at many coastal power plants in southern California to reduce the amount of fish entrained into cooling water intake systems. Historical laboratory and field studies indicated velocity caps reduced fish entrapment by >80%. Field studies were conducted at the Los Angeles Department of Water and Power’s Scattergood Generating Station in 2006-7 to estimate the entrapment reduction resulting from use of the velocity cap. To determine velocity cap effectiveness, impingement samples were collected during periods with the generating station operating in normal flow, where cooling water was withdrawn from the intake structure with the velocity cap, and in reverse flow, where cooling water was withdrawn from the discharge structure without the velocity cap. Hydroacoustic surveys were conducted during day and night in both normal and reverse flow conditions to determine if there were any significant differences in nearshore fish densities between the intake and discharge structures. The Scattergood velocity cap reduced fish impingement abundance by 97.6%, and fish impingement biomass by 95.3%. No significant differences in fish densities were detected between the intake and discharge structures, indicating differences were attributable to the use of the velocity cap.