Water budget and vertical conductance for Lowry (Sand Hill) Lake in north-central Florida, USA

Abstract

Water-budget components and the vertical conductance were determined for Lowry (Sand Hill) Lake in north-central Florida, USA. In this type of lake, which interacts with both the surface-water and groundwater systems, the inflow components are precipitation, surface-water inflow, groundwater inflow, and direct runoff (i.e. overland flow), and the outflow components are evaporation, groundwater outflow, and surface-water outflow. In a lake and groundwater system that is typical of many karst lakes in Florida, a large part of the groundwater outflow occurs by means of vertical leakage through an underlying confining unit to a deeper, highly transmissive aquifer called the upper Floridan aquifer. The water-budget component that represents vertical leakage to the upper Floridan aquifer was calculated as a residual using the water-budget equation. For the 13 month period from August 1994 to August 1995, relative to the surface area of the lake, rainfall at Lowry Lake was 1.55 m yr −1, surficial aquifer inflow was 0.79 m yr −1, surface-water inflow was 1.92 m yr −1, and direct runoff was 0.01 m yr −1. Lake evaporation was 1.11 m yr −1, and surface-water outflow was 1.61 m yr −1. The lake stage increased 0.07 m yr −1, and the vertical leakage to the upper Floridan aquifer was 1.48 m yr −1. Surficial aquifer outflow from the lake was negligible. At Lowry Lake, vertical leakage is a major component of the water budget, comprising about 35% of the outflow during the study period. The vertical conductance ( K V/ b), a coefficient that represents the average of the vertical conductances of the hydrogeologic units between the bottom of a lake and the top of the upper Floridan aquifer, was determined to be 2.51 × 10 −4 day −1 for Lowry Lake.