Factors Influencing Impingement at 15 Ohio River Power Plants

Abstract.-Impingement abundance monitoring was conducted at 15 Ohio River power plants as part of the Ohio River Ecological Research Program. Impingement rates were compared with environmental, power plant design, and operational factors that varied within and among the power plants, including water temperature, river flow and stage, change in flow and stage during the sampling events, volume of cooling water pumped, design pumping capacity, approach velocity, location of the intakes along the river, intake type, and intake configuration. The study demonstrated similarities in species composition, size distributions, and seasonal patterns over nearly 1,400 river kilometers of the Ohio River, results that were consistent with studies conducted nearly 30 years earlier. Dramatic annual differences in impingement rates during the 2-year study indicated that impingement is largely a function of the recruitment levels of juvenile gizzard shad Dorosoma cepedianum, threadfin shad D. petenense, and freshwater drum Aplodinotus grunniens, measures that fluctuate widely in the Ohio River based on long-term monitoring data and unpredictably based on current knowledge of the impingement process. The study also showed that most physical variables had little or no effect on impingement rates. Water temperature was identified through multiple regression analyses as the most important physical variable, with impingement tending to increase during the winter. Actual pumping rate during sampling events-the only factor evaluated that is under the direct control of the participating power plants-was one of the least important factors affecting impingement rates