Hydrologic Budget For Eagle Lake Near Willmar, Minnesota

Eagle Lake occupies 890 acres of a 9,000-acre watershed in central Minnesota. Because of its proximity to Willmar, many homes and sunnier cabins have been built around the lake. At present (1978), the shore is more than 90 percent developed. One effect of this development is accelerated eutrophication, most commonly shown by algae blooms. An annual hydrologic budget for Eagle Lake was prepared for the 1978 water year in support of a nutrient study prepared by the University of Minnesota at Marris. Results show that the amount of water that flowed through Eagle Lake in the 1978 water year was 6,670 acre-feet. Inflow to the lake was 45 percent surface water, 22 percent ground water, and 33 percent precipitation. Outflow was 73 percent surface water, 25 percent evaporation, and slightly greater than 2 percent net change in lake storage. Estimates for the ground-water component were derived both as a residual in the hydrologic-budget equation and by flow-net analyses. The residual value of 1,450 acre-feet compared favorably with the flow-net value of 1,400 acre-feet.