Effects of Pressure Reductions in a Proposed Siphon Water Lift System at St. Stephen Dam, South Carolina, on Mortality Rates of Juvenile American Shad and Blueback Herring.
ARMY ENGINEER WATERWAYS EXPERIMENT STATION VICKSBURG MS ENVIRONMENTAL LAB
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This report presents results of studies to predict the mortality rate of juvenile blueback herring Alosa aestivalis and American shad A. sapidissima associated with reduced pressure as they pass downstream through a proposed siphon water lift system at S. Stephen Dam, South Carolina. The primary function of the siphon is to increase attracting flow to better guide upstream migrating adult herring of both species into the existing fish lift for upstream passage. The U.S. Army Engineer district, Charleston, wishes to consider the siphon as an alternative bypass route through the dam for downstream migrating juvenile and adult herring. A pressure-reduction testing system that emulates some of the pressure characteristics of the siphon was used to determine the approximate percentage of juvenile fishes that could be reasonably expected to be killed passing through the reduced pressures anticipated for the siphon water lift system. The testing system could duplicate the range of pressure change anticipated for the siphon lift system but could not obtain pressures lower than 4.1 psi, whereas pressures for some design alternatives may approach the theoretical minimum pressure of 0.0 psi. Study results indicate that the mortality rate is probably about 20 percent. Power analysis indicates that mortality rate above 30 percent is unlikely. Conducting additional mortality studies is recommended to refine predicted mortality rates. Measures should be taken to prevent juvenile fish from entering the siphon lift system if excessive mortality rates are observed.