MODFLOW NWT groundwater flow model used to evaluate conditions in the Northern High Plains Aquifer in Colorado, Kansas, Nebraska, South Dakota, and Wyoming

A three-dimensional groundwater flow model was developed to characterize groundwater resources and the interaction of groundwater with streams and other hydrologic features in the Northern High Plains aquifer. The Northern High Plains aquifer is generally unconfined; most of the water withdrawn from the aquifer is used for irrigation. Recharge was estmated using a modified version of a previously published soil-water-balance (SWB) model and other data. SWB estimates recharge using climatic, soils, landcover data, in addition to data for groundwater withdrawals for irrigation. The SWB output was adjusted in areas where surface water is used for irrigation. The groundwater flow model results were calibrated using parameter estimation to measured groundwater levels and estimated stream base flows. The model was designed as a tool for regional evaluations of groundwater resources and of groundwater interactions with streams and other hydrologic features resulting from current or forecasted conditions. This USGS data release contains all of the input and output files for the model described in the associated model documentation report (http://dx.doi.org/10.3133/sir20165153). This data release also includes (1) MODFLOW NWT (version 1.0.9) source code, and (2) SWB source code in two formats.