A water budget was prepared to identify the components of the hydrologic system in the Lake Wingra basin. The Lake Wingra basin, which includes a small eutrophic lake within the city of Madison, Wis., is partly a protected area and partly an urbanized area. Measured and estimated inflow and outflow to and from the lake in 1 year (June 1972 to May 1973) was about 4.5 metres (15 feet)—approximately twice the volume of the lake. Inflow to the lake is about 25 percent from direct precipitation on the lake surface, and the rest from nearly equal amounts of surface runoff and ground-water inflow. Outflow from the lake is about 10 percent ground-water outflow, 15 percent evaporation from the lake surface, and 75 percent discharge at the surface outlet. Increased withdrawal of water from municipal and industrial wells in Madison has slowed the rate of flow through the lake.
The calculated 1972 water budget for the lake showed gains of about 3,560 millimetres (140 inches) and losses of about 3,500 millimetres (138 inches). A discrepancy of about 60 millimetres (2 inches) probably was caused in part by uncertainties in ground-water inflow and outflow. Effects of evapotranspiration and ground-water inflow in the marsh area southwest of the lake also probably contribute to the discrepancy.
