Downstream migrating fish are instinctively attracted toward increasing water velocities, called attraction flows. The Smith-Root Downstream Guidance and Repelling systems are designed to guide downstream migrating fish away from dangerous attraction flows. Our design uses electrical pulses that do not tetanize fish or in any way reduce their swimming ability. Tetanized fish would be swept further into the electrified zone by water flow. To avoid the tetanizing effect, very short DC pulses are used which provide a sensation much like pins and needles. Repelled fish are guided towards an alternate waterway, with an attraction flow, or repelled toward open water, in the case of resident fish in a lake or reservoir.

Downstream Guidance Hydraulics

Downstream guidance systems should be located in areas of moderate water velocity and positioned well upstream from turbine intakes, pumps, etc. For downstream anadromous migration, an alternative attraction flow or bypass is required.

The best response is achieved when fish approach the electric field tail-first, as they typically will if the flow is at least 1 to 2 fish body length/sec. In addition, the electric field is designed to have an abrupt edge which increases the startle effect. The startle effect causes fish to dart ahead of the electrode array. To guide fish toward a bypass, the electrode array is often angled with relation to stream flow.

Once the fish have been guided into a bypass, it is essential to maintain a natural flow with uniform velocity well into the bypass so that fish will not reject it. Sudden increases in velocity within the bypass often spook downstream migrants, causing them to reject the bypass. For migrating Coho and Steelhead smolts, experimental tests indicate that velocities of 1 to 2 feet/sec work well. For Pinks, Chinook fry, and other small fish, somewhat lower velocities are desirable.