Modeling of Temperature Distributions in Mount Hope Bay Due to Thermal Discharges from the Brayton Point Station

Abstract

Brayton Point Station is a 1600-MW electrical generating station located on Brayton Point, in Somerset, MA. The Station draws water from Mount Hope Bay at the Taunton and Lee Rivers for cooling purposes, and discharges the water back into the Bay, through a discharge canal. Mount Hope Bay is a shallow estuary located on the boundary between Rhode Island and Massachusetts. In connection with the renewal of the permit authorizing the withdrawal and discharge of cooling water, a series of studies on Mount Hope Bay were initiated by the owners of Brayton Point Station. These studies included both field and computer modeling components. A hydrothermal model capable of simulating the effects of Brayton Point Station on the Mount Hope Bay waters under a variety of operating scenarios was calibrated using the observed data. Additional cases were run to evaluate the effects of reduced discharges of heated effluent incorporating a cooling tower (enhanced multi mode operation) as well as the case of no discharge. Model results indicated that the temporal temperature variations occur over tidal to annual time scales. Seasonal variations were most discernible in the shallow upper reaches of the Bay, showing warmer than average temperatures during summer and cooler during winter. The calibrated hydrothermal model was also used to estimate the bottom area and water column volume coverage versus temperatures, which helps to quantify the effects of station heat load on the biological functions of winter flounder in Mount Hope Bay.