Integrated High-Resolution Regional-Scale Lithologic and Groundwater Modeling of the Lower Mississippi-Gulf Region Aquifer Systems

Abstract Submission: The Coastal Lowlands aquifer system (CLAS) and the Mississippi Embayment aquifer system (MEAS) are essential for freshwater supply in the Lower Mississippi-Gulf Region (LMGR), spanning approximately 372,000 km² across nine states. This research outlines a detailed method for developing a high-resolution, regional-scale groundwater flow model utilizing MODFLOW 6's unstructured grid and parallel computing. Starting with the compilation of around 157,000 drillers’ logs and over 8,400 electrical logs, a detailed 15 hydrogeologic-unit lithologic model is constructed using an integration of a horizon-restoration technique and indicator kriging with nested variograms. The model is then validated against geological descriptions in the literature and the latest Airborne Electromagnetic (AEM) resistivity data released in 2020 and 2022. LMGR’s model domain includes over 9.5 million unstructured 3D cells, extending up to 3,000 ft deep. To handle the computational complexity, LMGR’s model is divided into 23 sub-models, each with less than 0.6 million cells, based on hydrologic unit code (HUC) watershed boundaries. The sub-models use unstructured grids that honor the hydrostratigraphic architecture, reducing the number of computational cells compared to structured grids. To enable efficient execution of the regional-scale model using parallel MODFLOW 6, flow exchange files are generated to ensure hydraulic connectivity between sub-models. MODFLOW 6’s unstructured-grid and parallel computing capabilities significantly enhance computational efficiency and reduce runtime, enabling detailed regional-scale groundwater modeling for the LMGR. This study advances hydrostratigraphic understanding of the LMGR aquifer systems and offers a large-scale groundwater model for informed water resource management and decision-making.

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