Assessing the Entrainment Risk of Juvenile Anadromous Fishes, Chinook Salmon and Green Sturgeon, to Unscreened Diversion Pipes, Using a River-Simulation Flume

Emigrating, juvenile anadromous fishes risk entrainment (removal from river) via water-diversion pipes associated with municipal water or agricultural irrigation supplies.  We investigated the swimming performance and behavior of two anadromous fishes at the J. Amorocho Hydraulics Laboratory on the UC Davis campus via experiments in a large-sized (24 m L x 3.3 m W x 3.3 m H) outdoor flume, simulating environmental river flows.  The number of Chinook salmon and green sturgeon entrained through an 45-cm diameter unscreened pipe was investigated over a range of river currents (15, 38 and 61 cm/s) and water diversion flows (425 and 566 l/s).  Chinook salmon were less susceptible to entrainment than were green sturgeon.  Salmon frequently avoided swimming in the high-velocity zone at the pipe’s inlet, but sturgeon often swam directly under the pipe’s inlet and became entrained.  Green sturgeon entrainment rates increased with increased flume currents and pipe diversion rates.  Chinook salmon entrainment rates were higher during the night than during the day.  Species-specific swimming performances and behaviors probably contributed to their different entrainment rates. Research funded by the Anadromous Fish Screen Project of USBR and USFWS.