Abstract
The overall objective of our studies was to specify an index describing the hydraulic force that fish experience when subjected to a shear environment. Fluid shear is a phenomenon that is important to fish. However, elevated levels of shear may result in strain rates that injure or kill fish. At hydroelectric generating facilities, concerns have been expressed that strain rates associated with passage through turbines, spillways, and fish bypass systems may adversely affect migrating fish. Development of fish friendly hydroelectric turbines requires knowledge of the physical forces (injury mechanisms) that impact entrained fish and the fish’s tolerance to these forces. It requires up-front, pre-design specifications for the environmental conditions that occur within the turbine system; in other words, determining or assuming conditions known to injure fish will assist engineers in the design of a fish friendly turbine system. These biological specifications must be carefully and thoroughly documented throughout the design of an advanced turbine. To address the development of biological specifications, we designed and built a test facility where juvenile fish could be subjected to a range of shear environments and quantified their biological response.
Test fish included juvenile rainbow trout, Oncorhynchus mykiss, spring and fall chinook salmon, O. tshawytscha, and American shad, Alosa sapidissima. Fish were exposed to a shear environment produced by a submerged jet over a range of exit velocities from 0 to 21.3 m/s (0 to 70 ft/s). They were introduced in either a headfirst or tailfirst orientation and to the edge of the jet stream (slow-fish-to-fastwater scenario) or within and upstream of the jet stream (fast-fish-to-slow-water scenario). Test fish were captured after leaving the shear environment and specific biological responses noted (i.e., injury and mortality). The behavior or reaction of fish in the shear environment was recorded on high-speed video cameras. Fluid velocities were measured in the jet with a Pitot tube and a Laser Doppler Velocimeter (LDV). Statistical tests were applied to the fish data to estimate the lowest observed effect level and no observed effect level, or the strain rate at which fish were not injured after being subjected to the shear environment.
The Pitot tube provided mean velocity information in the axial direction. The mean-flow velocity measurements obtained using the Pitot tube were used to describe the jet centerline velocity and fluid strain rate. This report refers to the mean change in water velocity (u) over distance (y) as strain rate (e).