Development of thermal models for Hungry Horse Reservoir and Lake Koocanusa, northwestern Montana and British Columbia

Abstract

Thermal models were developed to simulate temperature profiles in Hungry Horse Reservoir and Lake Koocanusa in northwestern Montana. The results of the modeling effort will be useful to the Montana Department of Fish, Wildlife and Parks in evaluating the effects of alternative seasonal reservoir-drawdown schedules on fish production. The thermal models for Hungry Horse Reservoir and Lake Koocanusa were calibrated using 1984 data and verified using 1985 data. Initial values for unmeasured variables were based on 1965 data. Using data sets for 1984 and 1985, the thermal models simulated temperature profiles that differed from measured temperature profiles by less than about 2 Celsius degrees in the epilimnion and hypolimnion of both reservoirs. Differences between simulated and measured temperatures in the thermocline generally were less than 5 Celsius degrees. Simulated outflow temperatures for both reservoirs followed trends that were similar to measured temperatures. Differences between simulated and measured temperatures in outflow from both reservoirs range from 0 to 5 Celsius degrees. Comparisons of simulated temperature to measured temperature in Hungry Horse Reservoir and Lake Koocanusa indicate that the models were successfully calibrated and verified. Therefore, development and-use of similar models for similar reservoirs of northwestern Montana probably is valid. However, simulation results might be improved by changes in data collection and in the model routines. 8 ro-o o 48°