Submitted By Pacific Northwest National Laboratory, Richland, Washington
Fish passing through hydroelectric turbines are subjected to potentially lethal conditions including shear, turbulence, pressure, and cavitation. Many turbines are reaching their operational life expectancies and will be replaced with new turbines that incorporate "fish-friendly" designs devised to increase fish survival. To aid engineers in designing new turbines, The Pacific Northwest National Laboratory (PNNL) investigated the effects of shear strain on several species of anadromous fish. The objective of this effort was to identify threshold shear strain values that result in fish injury. Direction and oversight of these experiments is the responsibility of the Department of Energy, Oak Ridge National Laboratory, Idaho National Engineering and Environmental Laboratory, and the Advanced Hydropower Turbine System Technical Committee.
Figure 1. Juvenile salmon being introduced head-first into the shear stress test facility. Water velocities in the shear zone were measured at a fine scale (1 mm) and were used to estimate the strain rate to which the fish were exposed.
A full-scale test facility was constructed at PNNL's Aquatic laboratory in Richland to estimate injurious shear stress values upon which to develop turbine design criteria. A rectangular tank 1.2 x 1.2 x 9.1 m long was fitted with a pump/jet nozzle system capable of producing velocities of up to 24.4 m/s (80 feet/sec). The jet introduced high velocity water into the tank - creating a zone of high shear in the boundary layer between the fast and slow water. Test groups of fishes were introduced into this shear zone through an acrylic tube. Two orientations of fish entry into the shear zone were evaluated; head-first and tail-first. The paths of fish in the shear zone were videotaped and fish were collected and visually examined for evidence of injuries.
Sensitivity to the strain rate varied among the species tested. The table to the right shows the strain rate values (expressed as the strain rate across 1.8 cm (the width of a smolt); the units are (cm/s/cm (Dy=1.8 cm)) that resulted in no effect as well as the lowest observable effect to fish that were introduced head-first into the shear zone. American shad were the most susceptible to shear strain-caused injury, salmonids were generally intermediate, and juvenile Pacific lamprey were relatively unaffected by shear strain.
|Species||Size||No Effect*||Lowest Obs. Effect**|
|American shad||10 cm||341||517|
|Fall chinook||8.5 cm||517||1008|
|Fall chinook||14 cm||517||688|
|Spring chinook||14.5 cm||517||852|
|Rainbow trout||15.5 cm||688||No significant injury|
|Steelhead||21.5 cm||517||No significant injury|
|Pacific lamprey||13.6 cm||852||No significant injury|
* Highest strain rate where no significant injuries occurred.
** Lowest strain rate where significant major injuries occurred.
Figure 2. Juvenile fall chinook salmon injuries resulting from head-first entry into the shear zone in the test facility. Note bent operculum and missing eye.
Fish that were injured as a result of exposure to strain typically had damage to the head region, including bent or torn opercula (gill covers) and damaged or missing eyes (Figures 2 and 3). Lampreys, which lack gill covers, were the most resistant to injury caused by shear stress of all the species tested. Analyses of the data are continuing. Localized fish injuries due to the forces associated with small-scale turbulent eddies may cause mortality, even though shear stresses appear to be small. Also, analyses of existing and advanced turbines are being performed to determine the magnitude and location of injurious shear stress zones.
Figure 3. Bottom view of a steelhead smolt exposed to a strain rate of 852 cm/s/cm (Dy=1.8 cm) as recorded by a high speed video camera. Note expansion and bending of opercula.
The shear strain test facility built by PNNL has proven useful in evaluating the effects of shear stress on anadromous fishes. Fish species such as American shad and yearling fall chinook salmon are susceptible to the effects of shear strain similar to those they might encounter while passing down through turbines on their migration toward the sea. The data produced through this research should aid engineers who are working to design "fish-friendly" turbines.
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