Hydrology of Little Rock Lake in Vilas County, North-central Wisconsin
Water budgets were developed for Little Rock Lake for October 1983 through September 1990 as part of a study to evaluate the chemical and biological effects of artificially acidifying one basin of the two-basin lake. The 17.9-hectare seepage lake is situated in 60- to 90-meter-thick, predominantly sand and gravel glacial deposits of Vilas County, north-central Wisconsin. Annual precipitation during the study varied from 647 to 926 mm (millimeters). Average annual precipitation during 1951-80, based on nearby National Weather Service stations, was 825 mm. Annual evaporation from the lake surface ranged from 495 to 648 mm. Total lake-stage fluctuation was 930 mm during the study. Lake volume at the maximum stage was 31 percent greater than at the minimum lake stage. Inflow to the lake was dominated by precipitation, which was about 99 percent of total inflow. Ground-water inflow to the lake was transient, occurring only intermittently during October 1983 through September 1986, and amounted to only about 1 percent of total inflow. No ground water flowed into the lake from October 1986 through September 1990. Evaporation accounted for about two-thirds of total outflow from the lake, and lake water dis- charging to the underlying aquifer accounted for the remainder. The average hydraulic residence times for the 7-year study period were 3.9, 3.3, and 4 years for the entire lake, the south basin, and the north basin, respectively; corresponding chemical residence times were 10.9, 9.3, and 10 years.