Daily Water Temperature Simulations for Lake Mille Lacs (1983-2002)

Each year the Minnesota Department of Natural Resources (MNDNR), Division of Fisheries, assesses the walleye population in Mille Lacs Lake to provide a forecast for the upcoming fishing season. Water temperature is a controlling factor in the estimate. Because water temperature measurements in Mille Lacs Lake are only available for recent years, the MNDNR requested simulations of daily water temperatures for Mille Lacs Lake from 1983 - 2002. Temperatures in September and October were of particular interest. MINLAKE 96, a one dimensional, unsteady water quality model was employed to simulate the water temperatures. Weather data from Brainerd and Duluth, were used as input. Water temperature measurements from 2000 to 2002 were used to validate the simulations. It was detennined that the weather data from Brainerd provided the best simulation for the summer, fall and winter. However, the Duluth data offered a better estimate for the spring. Since the walleye assessment takes place in September of each year, the Brainerd simulation should provide the best water temperature estimates. For the years when the Brainerd data is not available, the Duluth measurements can be used with a correction factor.