A three-dimensional groundwater flow model (MODFLOW-2005) of the Mississippi embayment, South-Central United States, was developed as part of a national project initiated by the U.S. Geological Survey Groundwater Resources Program to provide updated assessments of groundwater availability in important principal aquifers across the United States. The goals of the national assessment are to document effects of human activities on water levels and groundwater storage, explore climate variability effects on the regional water budget, and evaluate the adequacy of data networks at a regional scale. The Mississippi embayment was chosen because of the substantial dependency on groundwater for agriculture and municipal needs.

Since the development of the original Mississippi Embayment Regional Aquifer system (MERAS) model in 2009, the model has been updated and enhanced and is proving an invaluable tool to evaluate and develop water management pumping strategies. The construction and calibration of the original model (MERAS 1.0) is documented in the U.S. Geological Survey (USGS) Scientific Investigations Report 2009-5172 (https://doi.org/10.3133/sir20095172). MERAS 1.0 contains one transient simulation that quantifies the groundwater availability in the aquifer system from January 1870 to April 2007. The USGS Professional Paper 1785 (https://doi.org/10.3133/pp1785) describes the historical background of the hydrologic system, analyses of the transient water budget, effects of climate change on the groundwater system, and evaluation of the groundwater monitoring network. Minor modifications were done to the model to improve the simulation of groundwater flow (MERAS 1.1) and two climate scenarios were completed using this model. USGS Scientific Investigations Report 2013-5161 (https://doi.org/10.3133/sir20135161) investigated ways to improve the match of observed to simulated groundwater levels within the Mississippi River Valley alluvial and middle Claiborne (Sparta) aquifers. The model was updated with improved water-use estimates and refined parameter estimation by using pilot points (MERAS 2.0). Three water-supply scenarios considered by the State of Arkansas were completed with the MERAS 2.0 model.

To assess proposed alternative water-supply scenarios and their impact on future water-supply in the Mississippi Delta, the USGS and the Mississippi Department of Environmental Quality collaborated to update and enhance the MERAS 2.0 model. The MERAS 2.0 model has been updated to April 2014 with the most recent water-use data, precipitation and recharge data, and streamflow and water-level observation data to make MERAS version 2.1 (https://doi.org/10.3133/sir20195116). Five different water-supply options (with a total of 22 sub-scenarios) are run using the MERAS 2.1 model and include: irrigation efficiency, on-farm storage and tailwater recovery, weirs for surface-water augmentation, surface-water transfer, and groundwater transfer and injection. All scenarios are compared with a base scenario which provides a standard for the alternate water-management scenarios. This USGS data release contains all of the input and output files for the simulation of these water-supply option using the new MERAS 2.1 model described in the associated model documentation report (https://doi.org/10.3133/sir20195116).