Three-dimensional hydrothermal model of Onondaga Lake, New York

A three-dimensional time-dependent hydrodynamic model of Onondaga Lake, an inland lake in central New York, emphasizing the simulation of dynamics and thermal structure has been developed. The model is based on the ECOM famil y of models; this version, called ECOMsiz, employs a semi-implicit time spl itting algorithm and a z-level vertical coordinate system. Proper assignmen t of boundary conditions, especially surface heat fluxes, has been found cr ucial in simulating the lake's hydrothermal dynamics. Formulas for atmosphe ric radiation and sensible and latent heat fluxes are introduced, which hav e been found most appropriate for evaluating the heat budget for this midla titudinal urban lake. The ECOMsiz model has been calibrated and validated a gainst data for two years, 1985 and 1989, representing a wide spectrum of a tmospheric and hydrographic conditions in the lake. These two years, marked by significantly different freshwater inputs from tributary inflows, ionic waste loadings, wind forcing, and atmospheric heating and cooling, form a firm basis for evaluating the robustness of the hydrodynamic model. The sim ulation period chosen for both years, April through October, spans the enti re range of lake physical processes as it covers the well-mixed spring cond ition, the summer period marked by strong vertical stratification, and the well-mixed fall period. Significant differences in thermal structure have b een observed in 1985 and 1989 as a result of different meteorological condi tions. The mixed layer depth in 1985 is about 3 m deeper (about 9 m) than t hat in 1989 (about 6 m), consistent with a stronger prevailing wind in 1985 . The model has successfully predicted the mixed layer depth for both the y ears. The model computed total heat storage for both years is in good agree ment with the observed conditions.