MODFLOW-NWT model used in Simulation of Groundwater Flow, and Analysis of Projected Water Use for the Washita River Alluvial Aquifer, Western Oklahoma

The U.S. Geological Survey, in cooperation with the Oklahoma Water Resources Board,
constructed a finite-difference numerical groundwater-flow model of the Washita River
alluvial aquifer using MODFLOW-2005 with the Newton formulation solver (MODFLOW-NWT).
The 1973 Oklahoma Water Law (82 OK Stat § 82-1020.5) requires the Oklahoma Water
Resources Board to conduct hydrologic investigations of the State's aquifers to support a
determination of the maximum annual yield (MAY) for each groundwater basin. A permanent
MAY and EPS have not been established for the Washita River alluvial aquifer; thus, the U.S.
Geological Survey, in cooperation with the Oklahoma Water Resources Board, conducted
calibration and simulations of a numerical groundwater-flow model to evaluate the effects of
potential groundwater withdrawals on groundwater flow and availability in the Washita River
alluvial aquifer. Groundwater-availability scenarios were performed by using the calibrated
numerical groundwater-flow model to (1) estimate the EPS pumping rate that guarantees a
minimum 20-, 40-, and 50-year life of the aquifer, (2) quantify the potential effects of projected
well withdrawals on groundwater storage over a 50-year period, and (3) simulate the potential
effects of a hypothetical (10-year) drought on groundwater storage and lake storage. The
results of these groundwater-availability scenarios can be used by the Oklahoma Water
Resources Board to reevaluate the maximum annual yield of groundwater from the Washita
River alluvial aquifer in Oklahoma. This USGS data release contains all of the input and
output files for the simulations described in the associated model documentation report
(https://doi.org/10.3133/sir20205118).