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Advances in Groundwater Modeling for the Mississippi Delta from the Mississippi Alluvial Plain (MAP) Project
Proceedings of the 2022 Mississippi Water Resources Conference

Year: 2022 Authors: Duncan L.L., Haugh C.J.

The goal of the regional groundwater availability study of the Mississippi Alluvial Plain (MAP) is to improve estimates of water availability, both past and present, and to determine how groundwater resources will respond to current and future stresses. Groundwater withdrawals from the Mississippi River Valley alluvial aquifer within the Mississippi Delta have been vital for agricultural production. Despite the apparent stabilization of groundwater levels in some places across the Mississippi Delta following several recent years with above-average rainfall, long term sustainability of the aquifer remains a concern due to the large groundwater-level declines over the last century, increasing demand for irrigation from groundwater, and uncertainty about future climate.

The MAP study builds upon the previously developed Mississippi Embayment Regional Aquifer Study (MERAS). The Mississippi Delta inset groundwater flow model offers several enhancements over older versions of the regional groundwater flow model, including higher spatial, vertical, and temporal resolutions. The inset model uses the newer MODFLOW 6 and PEST++-IES modeling and parameter estimation technology, providing more robust calibration. The inset model incorporates information from airborne electromagnetic surveys through a new surficial aquifer base, updated confining unit thickness, and zoned parameterization of aquifer properties. The inset model also uses Soil-Water-Balance model estimates for recharge and runoff estimates, agricultural water use estimates partially derived from the Mississippi Department of Environmental Quality voluntary metering program, and a denser streamflow routing network.

Accurate assessments of water availability in the Delta are critical to informing management decisions, establishing best practices for water use, and contending with projected changes to the regional water cycle. The groundwater response to different combinations of water management practices and anticipated changes in water budget components is examined using the groundwater model. This study is intended to provide improved estimates of historical, current, and future groundwater availability and to aid water resource managers in making decisions that can help sustain agricultural and industrial practices in the MAP region using a numerical groundwater model.

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