Simulation of Groundwater Flow, and Analysis of Projected Water Use for the Rush Springs Aquifer, Western Oklahoma

In 2018 The U.S. Geological Survey, in cooperation with the U.S. Bureau of Reclamation
and the Oklahoma Water Resources Board, published a calibrated numerical groundwater-
flow model and associated model documentation report that evaluated the effects of potential
groundwater withdrawals on groundwater flow and availability in the Rush Springs aquifer in
western Oklahoma. The results of groundwater-availability scenarios run on the calibrated
numerical groundwater-flow model could be used by the Oklahoma Water Resources Board
to evaluate the maximum annual yield of groundwater from the Rush Springs aquifer in
Oklahoma. A conceptual groundwater-flow model is a simplified description of the major
inflow and outflow sources (hydrologic boundaries) of a groundwater-flow system as well
as an accounting of the estimated mean flows from those sources (water budget) for a
specified period of time. The conceptual model was necessary to provide constraints used
in the construction and calibration of a scientifically defensible numerical groundwater-flow
model that reasonably represents the groundwater-flow system.

A finite-difference numerical groundwater-flow model of the Rush Springs aquifer was
constructed by using MODFLOW-2005 with the Newton formulation solver (MODFLOW-NWT).
Data inputs for each package were specified in machine-readable text files. The numerical
model of the Rush Springs aquifer had 1,362 rows, 1,083 columns, about 554,000 active
cells of 500 by 500 ft, and 3 convertible layers. The top layer (layer 1) represented the
Permian-age Cloud Chief Formation. The Rush Springs aquifer is composed of Permian-age
Whitehorse Group. The second layer (layer 2) represented the undifferentiated Quaternary-age
alluvium and terrace deposits, as well as the upper 30 ft of the Whitehorse Group. The
bottom layer (layer 3) represented the remainder of the Rush Springs Formation. The model
active area was modified from Neel and others (2018). The numerical model was temporally
discretized into 444 monthly transient stress periods representing the period 1979-2015. An
initial steady-state stress period, in which the groundwater-flow equation had no storage
component, represented mean annual inflows to and outflows from the aquifer and produced
a solution that was used as the initial condition for subsequent transient stress periods. The
numerical model was constructed in units of meters and days. 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/sir20185136)