Comparison of Modeled and Observed Avoidance in a Thermally Loaded Reservoir

Conowingo Pond on the Susquehanna River is formed by Conowingo Hydroelectric Dam. Conowingo Hydroelectric Station generates 572 MWe and the Pond hosts Peach Bottom Atomic Power Station (2280 MWe), Muddy Run Pumped Storage Facility (1000 MWe), York Energy Center (565 MWe) and Holtwood Hydroelectric Plant (109 MWe). Peach Bottom uses open cycle cooling; the thermal plume is thought to exclude certain species/life stages from areas of the Pond under low flow conditions. A three-dimensional model of the Pond was developed and calibrated using two years of water temperature data from monitors located throughout the pond. The model includes all inflows and outflows and heat loads for the generation facilities. The model was used to calculate temperature increases due to Peach Bottom’s thermal discharge. The calculated increases were combined with laboratory-based acclimation temperature / avoidance temperature relationships and the model was used to delineate avoidance zones for each species of interest at various acclimation temperatures. Because the Peach Bottom studies also include an extensive biological sampling effort, these calculated avoidance zones can be compared to those determined from observations of fish populations. In general, the calculated avoidance zones are conservative and may be considered overprotective of the fishery resource.