Percentage of Hypothetical Well Pumpage Causing Depletions to Simulated Base Flow, Evapotranspiration, and Groundwater Storage in the Elkhorn and Loup River Basins, 2006 through 2055

This data release includes a polygon shapefile of grid cells attributed with values representing the simulated base-flow, evapotranspiration, and groundwater-storage depletions as a percentage of hypothetical well pumpage for the 2006-2055 time period. Depletions were simulated by the Phase-Two Elkhorn-Loup Model (ELM), constructed using MODFLOW-2005 (Harbaugh, 2005) with the Groundwater Vistas, version 5, software (Environmental Simulations, Inc., 2009). Each polygon represents one model grid cell. All values are estimates and approximations.

The Phase-Two ELM simulated the High Plains aquifer in north-central Nebraska from predevelopment (pre-1895) through 2055 (Stanton and others, 2010). The simulation was calibrated using an automated parameter-estimation method to optimize the fit of simulation outputs to three sets of calibration targets: estimated 1939 groundwater levels and base flows (representing pre-1940 conditions), 1945-through-2005 decadal groundwater-level changes, and 1940-through-2005 annual base flows. The calibrated simulation was used to estimate volumetric ratios of the reductions in base flow, evapotranspiration, and groundwater storage to the total volume of water pumped from a hypothetical well for a 50-year future time period. Ratios were then multiplied by 100 to obtain percentages. The 50-year period was selected because base-flow depletion percentages for 40- to 50-year periods are the basis of groundwater and surface-water management decisions in Nebraska.