Turbulent Attraction Flows for Guiding Juvenile Salmonids at Dams
Behavioral Technologies for Fish Guidance: American Fisheries Society Symposium
American Fisheries Society
Induction of mild turbulence and increased water velocity in slowly moving water in dam forebays is proposed as a way to attract and guide downstream-migrating juvenile salmonids to dam bypasses. Attraction flows have been used successfully for decades at the downstream ends of fish ladders to attract adult salmonids to fish ladder entrances. Similar hydraulic concepts for simulating a turbulent stream have generally not been implemented to divert juvenile migrants into dam bypasses and away from damaging turbine intakes. Turbulent flow appears to he a normal feature of water movement in natural rivers that guides and assists juvenile salmon migration. It is hypothesized that enhancement of turbulent flow in selected zones of quiescent dam forebays would spatially expand the opportunities for fish to discover entrances to fish bypasses (such as surface-flow bypasses). A 'trail of turbulence' could lead fish to surface bypass entrances. Enhanced turbulence at bypass entrances and within bypass channels could also improve the effectiveness of juvenile salmonid guidance and retention in the bypasses. Turbulence could be enhanced by passive (using existing flow momentum or head directed by vanes) and active (pumped water jets or propellers) methods, which can be tailored to specific situations. Initial tests have confirmed the validity of the concept.