Grand Prairie Historical Calibration Period Groundwater-Flow Model

The Mississippi Alluvial Plain (MAP) is one of the most important agricultural regions in the United States and underlies about 32,000 square miles of Missouri, Kentucky, Tennessee, Mississippi, Louisiana, and Arkansas. The MAP region supports a multibillion-dollar agricultural industry. The MAP is part of the Mississippi Embayment with several water-bearing units that make up the Mississippi Embayment Regional Aquifer System (MERAS). These water bearing units include the Mississippi River Valley Alluvial aquifer, Claiborne aquifers and Wilcox aquifers. The Grand Prairie area has been designated as a Critical Groundwater area because of decades of groundwater declines that resulted from past and current water use. The objective of the report associated with this data release is to document and describe the construction, calibration, and results of the inset groundwater-flow model developed for the Grand Prairie Critical Groundwater Area using the latest MODFLOW-6 code. The model derived boundary conditions from the parent MERAS 3 regional model to provide higher resolution simulations in the Grand Prairie focus area. The Grand Prairie model was spatially discretized into 500-meter x 500-meter orthogonal cells on a grid. The Grand Prairie model had 19 vertical layers, 245 rows, and 206 columns and simulated the Quaternary-age alluvial aquifer with 5-m constant thickness layers and increasing thickness layers for the Tertiary-age units below the alluvial aquifer. The Grand Prairie model included 148 stress periods with a simulation period from January 1, 1900 through December 31, 2018 where stress periods: April 1, 2007 through December 31, 2018 where monthly stress periods. Areal recharge was simulated by a soil-water-balance model of the MERAS and passed to the groundwater models. The model simulated agricultural, municipal, and thermoelectric pumping. The model simulated groundwater-surface water interactions and total streamflow by adding runoff from the soil-water-balance model. The model featured high-dimensional parameterization schemes for calibration using the PEST++ Iterative Ensemble Smoother. Mean absolute residuals for calibrated priority well observations were 2.71 meters for the Grand Prairie model. Mean horizontal hydraulic conductivity for the alluvial aquifer was about 63 meters per day for the Grand Prairie model. Calibrated areal recharge was 3.4 inches for the Grand Prairie model. Primary groundwater outflows represented in the model were from agricultural wells.

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                                            {
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                                            [
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