A Positive Barrier Fish Guidance System Designed to Improve Safe Downstream Passage of Juvenile Anadromous Fish

Many anadromous fish species, such as Pacific and Atlantic salmon (Onchorhynchus spp. and Salmo salar) and some clupeids, such as the Atlantic shad and river herring (Alosa spp.), are in danger of extinction throughout some or all of their range.  A number of governments now mandate protection of these and other fish populations.  Impacts to these populations include, among other things, entrainment at hydroelectric dams and other water conveyance facilities as juveniles migrate downstream to the marine environment.  Facility operators must often implement physical or operational modifications to reduce fish entrainment or improve fish passage survival.  This paper documents a new design for a positive barrier Fish Guidance System (FGS) which successfully guides actively migrating juvenile anadromous fish to a bypass or collection systems.  Most juvenile anadromous species migrate downstream in the river thalweg, exploiting higher water velocities to speed their migration.  The FGS takes advantage of this migratory behavior and guides fish to a safer point of egress.  The FGS is composed of a series of floating panels anchored across the channel above an intake structure.  The design and configuration of the FGS varies at each site according to hydraulic conditions and species present.  The FGS has been installed as a single structure to guide fish to an existing bypass system, and in combination with an existing fish collection system to improve attraction and collection efficiency.  Recent research demonstrates that the FGS provides variable, but significant, guidance for many juvenile fish species in a variety of hydraulic conditions.  A prototype FGS installed in a high velocity environment, at the Bonneville Dam forebay on the Columbia River, improved guidance of juvenile spring chinook (O. tshawytscha) to an existing fish bypass system by up to 15%.  In a low velocity environment at the forebay of the Cowlitz Falls Dam in Washington State, an FGS successfully concentrated juvenile Pacific salmon and steelhead (O. mykiss) at the entrance of a surface fish collector.  In preliminary evaluations, over 90% of radio tagged juvenile fish were guided to a surface collector.  Large scale tests in 2010 indicate the FGS concentrated all species tested near the surface collector.  The FGS may also afford protection to fish species that demonstrate iteoparity (e.g., steelhead, Atlantic salmon and the anadromous clupeids) as they migrate back downstream to the marine environment after spawning.  Fish guidance efficiency will be tested at several FGS installations in North America in 2011.