263-7 Hidden Highways: How Alluvial Fans May Recharge the Mississippi River Alluvial Aquifer (MRVAA)

Session: Exploring Groundwater Recharge and Management: Managed Aquifer Recharge and Other Innovative Tools for Water Supply Development and Operations (Posters)

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Recent trends in groundwater withdrawals from the Mississippi River Valley Alluvial Aquifer (MRVA) for agricultural and industrial uses have drastically lowered ground water levels, indicating ground waterwithdrawals far exceed natural recharge rates and are unsustainable. Artificial and induced recharge strategies such as surface water diversions into oxbow lake environments and digging surface trenches into sandy alluvium for surface water infiltration are subjects of ongoing research, but most research on aquifer recharge focuses on estimations and large-scale, basin-wide modelling. Other than a project that examined recharge through oxbow lake environments, studies to quantify recharge through other Mississippi Valley sub-environments are lacking. However, the identification of zones with enhanced natural recharge is important so they can be protected from development and contamination, and they could make artificial recharge projects more cost effective and efficient.

This research uses geophysics and borehole data to characterize the geologic framework of alluvial fans and examine the role that alluvial fans emanating from upland streams into the alluvial valley have on MRVA recharge. This research focused on fans along the eastern valley wall in Tallahatchie and Panola Counties in Mississippi and fans sourced from Crowley's Ridge in NE Arkansas. Geologic mapping has shown that some of these fans have coarse and fine gravel on the surface, and others are finer sand with mixtures of silt. Analysis of  U.S. Geological Survey AEM data, recently acquired for the Mississippi Embayment, reveals that not all fans are the same. Some alluvial fans have coarse sediments and appear to be connected to the MRVA, suggesting they aggraded contemporaneously, while other fans overlie the MRVA and are disconnected from it by finer sediments, suggesting they are younger deposits. Electrical resistivity geophysical profiles and some drill holes within the alluvial fans confirm that the relationships observed in AEM data are the same at shallower depths. Current results indicate there are at least two types of alluvial fans in the Mississippi Valley, but due to their complexity, especially in humid regions, further research is needed to distinguish between them and identify those with high potential for groundwater recharge.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

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