Warm water discharge from the Brayton Point Power plant in Mount Hope Bay, Rhode Island, USA is thought to have a destabilizing effect on local ecosystems. This study was performed to shed light on the extent of the plant's thermal influence on the bay's waters. Theoretical heat capacity calculations showed that the plant increased its heat input to the bay by 50 % after 1981, thereby increasing its contribution to the bay's heat budget from 6 % to 9 % in the summer and 8 % to 12 % in the winter. Using in-situ temperature stratification data for 1972-1992, a linear correlation relating surface and bottom water temperature 900 m from the discharge point and 3.7 km away was constructed. Surf ace temperatures between the two points correlated significantly as did bottom temperatures. The year-round persistence of this relationship suggests that the plant drives a temperature gradient 3.7 km down-bay from its discharge point.

A syno ptic view of the temperature for Narragansett Bay was constructed using thermal infra-red satellite imagery. The data consistently indicated that Mount Hope Bay is warmer than other areas in Narragansett Bay (9/7/84, 11/26/84, 8/9/85, 10/26/85 and 9/1 6/87) by an average of 1.6 K. The extent of the Brayton Point Power Plant's thermal influence was clearly visible in temperature isotherms produced using a black body inversion algorithm. In the summer and fall scenes, this influence extended over th e entire bay. The very strong correlations between surface and bottom temperatures 3.7 km apart (mean R² > 0.95) in the well mixed water column of Mount Hope Bay, coupled with the Brayton Point Power Plant's clearly visible thermal influence on surfac e water temperatures of Mount Hope Bay are evidence that the plant plays a strong role in elevating the bay's temperature.