A Two Depth Averaged Numerical Temperature Model of Narragansett Bay

Abstract

The numerical temperature model proposed in this thesis approximates the temperature distributions produced by natural or man made conditions in Narragansett Bay. The model approximates the temperature distribution by averaging the vertical structure over depth. A two dimensional, planar coordinate system continuously specifies the temperatures within the bay. A hydrodynamic model calculates the necessary velocities and depths required by the thermal model. The combined thermal-hydraulic model calculates r bottom roughness, Coriolis acceleration, non-linear convective terms, astronomical tidal series for Rhode Island Sound, and air-water heat exchange. Known river flow inputs are used as boundary conditions. To simplify the model geometry the Mount Hope Bay structure is replaced by a boundary flow rate at the Mount Hope Bridge grids. Narragansett Bay has an average depth of 32 feet and a length of approximately 24 nautical miles with a maximum width of six nautical miles. By specifing a total of 325 square grids with eleven boundary grids 1/2 nautical mile in length the model approximates the features of the estuary. Verification of the model is achieved through conservation of mass analysis and comparison of predicted temperatures for given meteorological and water temperature data. The model is used to predict the thermal fields from a proposed power plant near Rome Point in the West Passage of Narragansett Bay. By specifying plant flow rates and dispersion coefficients characteristic temperature field conditions are observed. Under specified plant operating conditions, 0 a max imum temperature rise of 5.5 C above ambient in the discharge grid is predicted. For a temperature rise of 5.5°c the area encompassed by the 1°c excess isotherm is approximately two square miles while the 0.5°c isotherm area is about four square miles. Temperature isotherms over a tidal cycle retain the same general shape, especially 0 in the far field where temperatures fall below 0.4 C excess. This model can simulate salinity or other non-decaying constituents if appropriate boundary condition changes are made. In summary, the thermal model gives valuable insight into natural and man-made temperature distributions that will aid the marine scientist in preserving and understanding the dynamics of Narragansett Bay.