Lakes Clara and Vandercook are 33- and 43-hectare lakes, respectively, located in predominantly sandy outwash in north-central Wisconsin. Annual precipitation at National Weather Service stations during the 1951-80 calendar years averaged 794 millimeters near Lake Clara and 834 millimeters near Vandercook Lake. During the 1981 water year, annual precipitation measured at the lakes as part of this study was 3 percent below average for Lake Clara and 16 percent below average for Vandercook Lake. Annual precipitation was 6 to 21 percent above average for the two lakes during the 1982 and 1983 water years. Lake stage and water-table altitudes were relatively constant at Lake Clara throughout the 3 water years of study and at Vandercook Lake during the 1981 and 1982 water years; however, Vandercook Lake stage increased 0.2 meter, and the upgradient water table increased 0.3 meter, during the 1983 water year.
Hydrologic budgets show that lake inflow was dominated by precipitation (77 to 91 percent for Lake Clara and 79 to 87 percent for Vandercook Lake). Ground water accounted for the remaining inflow to Vandercook Lake; however, Lake Clara received approximately equal contributions from ground-water inflow and overland flow. Evaporation was the major form of lake outflow (59 to 75 percent for Lake Clara and 59 to 63 percent for Vandercook Lake). The remaining outflow from Vandercook Lake was to the ground-water system, but Lake Clara lost approximately equal amounts by surface and ground-water outflow. Hydraulic residence times were 4 to 5 years for both lakes. Chemical residence times for conservative constituents were 11 to 21 years for Lake Clara and 10 to 13 years for Vandercook Lake.
