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Flows and Fish Behavior: Large Double‐Entry Screening Systems
Author(s) -
Fletcher R. Ian
Publication year - 1994
Publication title -
transactions of the american fisheries society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.696
H-Index - 86
eISSN - 1548-8659
pISSN - 0002-8487
DOI - 10.1577/1548-8659(1994)123<0866:fafbld>2.3.co;2
Subject(s) - flow (mathematics) , fish <actinopterygii> , environmental science , mechanics , dual (grammatical number) , volumetric flow rate , computer science , marine engineering , fishery , physics , biology , engineering , art , literature
Facilities that draw water in large quantities from natural sources are commonly equipped with mechanically driven barrier screens for removing indrawn debris and captive fish. Owing to the mistransport of debris into the works of the facility by the cyclic action of conventional screening apparatus, many plant operators favor the refitting of intake systems with alternative devices called dual‐flow screens, whose manner of operation precludes the deposition of debris downstream of the screen location. Fish‐catching devices, otherwise suited to the flows and mechanics of a conventional screen, are often attached without alteration to the screen panels of a dual‐flow machine in the hopes of rescuing entrapped fish. Dual‐flow machines are thought to be superior to conventional intake screening systems in saving impounded fish, but the full‐scale experiments reported here show why the flow patterns and water speeds associated with a (double‐entry) dual‐flow screen are actually more adverse to live fish recovery than flows through a conventional screen. Owing to flow separations at the entries of these devices and the resulting concentration of flow over a restricted portion of the screening, fluid speeds comparable to flows of 30 and 45 cm/s through conventional screens increased to 90 and 140 cm/s at free‐flow regions of the screenfront. In experiments with two species of juvenile fishes, survival without injury was nil. Flow trajectories were mapped by streak photography, and details of fish behavior were recorded on videotape and 35‐mm film. Equations for the flow distributions were resolved from two‐component vector measurements of water velocities. Also shown is an experimental apparatus (a frontwall fairing) that eliminates the flow separations, resulting in a redistribution of the inflow across the full width of the available screening.