Simulation of ground-water flow in the High Plains aquifer, southern sandhills area, west-central Nebraska

A generalized ground-water flow model was prepared for the High Plains aquifer in the southern sandhills area of west-central Nebraska. A grid of 4- by 4-mile nodes was established over the study area. Steady-state water levels were simulated using a distribution of recharge from a soil-moisture budget model and from estimates of hydraulic conductivity obtained from logs of test holes in the area. The final calibrated simulation used hydraulic- conductivity values that were 122 percent, and recharge rates that were 89 percent of the original values used in the model. Sixty-seven percent of the simulated recharge to the High Plains aquifer discharges to rivers, streams, and lakes. Discharges through ground-water evapotranspiration and from pumping wells account for 20 percent, with the wells accounting for less than 10 percent of the total discharge, and subsurface boundary outflow accounts for 13 percent. Twenty years of simulated pumping, assuming one additional well would be added to each township annually for 10 years, and two wells per township would be added each year for the succeeding 10 years, produced a maximum simulated drawdown of less than 10 feet when a uniform specific yield of 16 percent for the aquifer in the study area was assumed.