Proceedings of the 2023 Mississippi Water Resources Conference

Year: 2023 Authors: Fang J., Al-Hamdan M., O'Reilly A., Ozeren Y., Rigby J.

Sustainable groundwater management is a topic of interest in the Mississippi River Valley alluvial aquifer (MRVAA) where declines in groundwater levels have been reported over the last few decades. To find a solution to this problem, the Groundwater Transfer and Injection Pilot (GTIP) project is being conducted at Shellmound, Mississippi, by the U.S. Department of Agriculture (USDA), Agricultural Research Service (ARS), National Sedimentation Laboratory. The managed aquifer recharge (MAR) technology being tested takes source water acquired via riverbank filtration and then transfers and injects the water into a depleted section of the MRVAA. Field measurements are essential to the GTIP project for assessment of the feasibility of this MAR technology, while numerical modeling is important for the evaluation of potential designs. Therefore, a numerical groundwater model was developed for this pilot study site. In this area, the vadose zone of the MRVAA consists mainly of fine-grained sediments. Our numerical experiments revealed that the hydraulic properties of the unsaturated soil can significantly affect the hydrological processes controlling groundwater pumping during riverbank filtration and groundwater injection in the aquifer. Hence, in this study, precipitation, evapotranspiration and soil moisture data from the North American Land Data Assimilation System (NLDAS) were used to estimate the soil properties in the vadose zone through data assimilation. The estimated unsaturated soil properties were then implemented into the groundwater model in which aquifer resistivity data derived from airborne geophysical surveys by USGS were incorporated to consider the spatial variability of the aquifer hydraulic conductivity. An empirical formula was applied to translating the resistivity data into hydraulic conductivity. The coefficients in the empirical formula were determined by calibration of the numerical model with the measured groundwater hydraulic heads. Good agreement was found between the simulation results and the field data in both calibration and validation periods, indicating the potential of using this modeling technique to facilitate decision-making on the potential implementation of the MAR technology being tested by the GTIP project.