Appraisal of the Water Resources of the Big Sioux Aquifer, Moody County, South Dakota

摘要

The Big Sioux aquifer in Moody County is a 55-square-mile, water-table aquifer hydraulically connected to the Big Sioux River. A digital model was developed to simulate ground-water flow in the Big Sioux aquifer in Moody County. The model was calibrated for steady-state conditions using average annual water levels, average recharge, evapotranspiration, well pumpage, river stage, and base-flow discharge in the Big Sioux River from 1970 through 1979. Steady-state simulated water levels from 11 wells averaged 0.4 feet higher than measured water levels. The average absolute difference between measured and simulated water levels was 1.57 feet. The model was calibrated for transient conditions using 1983 water levels. Measured water levels were compared to simulated water levels in 27 observation wells. Sensitivity analyses showed that recharge rate and evapotranspiration extinction depth had the largest effect on simulated water levels.