| Variations in the level of lakes are strongly influenced by lake evaporation, which is difficult to measure or estimate. One approach to deriving lake evaporation estimates is through simulation modeling. In this dissertation, a model of the evolution of the thermal structure and energy balance of a lake is developed, validated, and applied for modeling lake-level variations.;The model is based on a one-dimensional eddy diffusion model that simulates changes in lake heat storage, as determined by the balance between net incoming radiation and the flux of radiant, latent, and sensible heat across the water-atmosphere boundary. Data for incoming short- and longwave radiation, wind velocity, air temperature, and air vapor pressure are required by the model, and temperature and evaporation are simulated. No lake-specific fitting of model parameters is required. When the model is combined with water balance data for a lake, variations in lake level can be simulated as well.;Results from the validation experiments for Salton Sea, California and Pretty Lake, Indiana indicated that the model is capable of accurately simulating the seasonal cycles of lake thermal structure, lake evaporation, and the lake energy balance components in diverse physical and climatological settings. Results from lake-level validations indicated that the full lake-level model is capable of accurately simulating lake-level fluctuations over both intra- and interannual time periods.;The lake-level model was applied to simulate fluctuations in the level of Harney-Malheur Lake, Oregon between 1980 and 1986. Input to the model consisted of estimated and observed meteorological and hydrological data. Simulated lake-levels were in excellent agreement with observation data prior to and during the sharp rise of Harney-Malheur Lake. For perpetual 1983 conditions, when precipitation was 160% of the 43 year mean, a simulated equilibrium elevation of 1260m was reached after 200 years. This level exceeds the estimated elevation (1255m) of the sill that controlled outflow from Paleo Lake Malheur. For perpetual 1980 conditions, when precipitation was about equal to the 43 year mean, the model simulated a fall in lake level to an equilibrium elevation of 1249m in 15 years. |
