MODFLOW-NWT model used in simulation of groundwater flow and availability in the North Fork Red River aquifer, southwest Oklahoma, 1980-2013

In 2017 the U.S. Geological Survey, in cooperation with 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 North Fork Red River aquifer in 
southwest 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 reevaluate the maximum 
annual yield of groundwater from the North Fork Red River aquifer in Oklahoma. The numerical groundwater-flow 
model was built on a hydrogeologic framework and a conceptual groundwater-flow model derived from previously 
published and newly collected hydrologic data. A hydrogeologic framework is a three-dimensional representation 
of the aquifer and the surrounding geologic units at a scale that captures the regional controls on groundwater flow. 
The hydrogeologic framework for the North Fork Red River aquifer included a definition of the aquifer extent and 
potentiometric surface, as well as a description of the textural and hydraulic properties of aquifer materials. 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 hydrogeologic framework and conceptual model are necessary 
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 North Fork Red River 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 North Fork Red River aquifer had 385 rows, 460 
columns, about 27,600 active cells of 886 by 886 ft (270 by 270 meters), and 2 convertible layers. The top layer 
(layer 1) represented the undifferentiated Quaternary alluvium and terrace deposits with variable thickness determined 
from the hydrogeologic framework, and the bottom layer (layer 2) represented the Permian bedrock with a nominal 
thickness of about 100 feet. The model active area was created from the North Fork Red River aquifer extent and 
expanded in some areas to ensure that each active cell was in connection with at least one other active cell. One 
terrace lobe in northern Beckham County was not included in the model active area because it was almost separated 
spatially and hydraulically from the rest of the North Fork Red River aquifer. The numerical model was temporally 
discretized into 408 monthly transient stress periods (each with 2 time steps) representing the period 1980–2013. 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/sir20175098).

Tags: beckham-county, environment, geoscientificinformation, greer-county, groundwater, groundwater-and-surface-water-interaction, groundwater-model, inlandwaters, jackson-county, kiowa-county, lake-altus, modflow-nwt, north-fork-red-river, oklahoma, pest, roger-mills-county, soil-water-balance, tom-steed-reservoir, usgs-d34e3086-129b-42fd-8615-8baa79a9e41d, usgsgroundwatermodel
Organization: Department of the Interior