263-8 Electrical Resistivity Imaging of Irrigation-Induced Recharge Pathways Through Shallow and Perched Aquifers in a Pecan Orchard, Tornillo, TX

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

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Groundwater recharge from seasonal irrigation remains poorly understood, particularly in agroforestry systems such as pecan orchards. Understanding the spatial and temporal pathways of recharge following irrigation is essential for sustaining groundwater resources in arid regions. This study investigates the spatial and temporal pathways of irrigation-induced recharge using electrical resistivity tomography (ERT) in a managed agricultural plot adjacent to the Rio Grande in Tornillo, Texas. A heterogeneous alluvial system, characterized by interbedded gravels, clays, and sands, typical of a dynamic river floodplain, as the Rio Grande, underlies the study area. These variations influence infiltration rates and appear to create preferential flow paths in the subsurface.

We conducted monthly 2D ERT measurements across a single irrigation season, using Dipole–Dipole and Wenner–Schlumberger configurations. Inversion results consistently reveal a shallow saturated zone, 1–10 m deep, with low resistivity values (2.7–6.0 Ω·m), interpreted as a shallow aquifer that persists across all irrigation events. Beneath this, we observe a 35–40 m thick heterogeneous perched aquifer zone (7.0–13.7 Ω·m) composed of alternating clays, sands, and gravels. At depths greater than 65 m, the regional aquifer, the Hueco Bolson, is characterized by lower resistivity (~5.9 Ω·m).

From the first irrigation event onward, we observed how irrigation water saturates the shallow aquifer and begins to infiltrate downward into the perched zone. The contrast in resistivity between these layers establishes a vertical gradient that highlights infiltration pathways.

Following multiple irrigation events, each contributing approximately 127 mm of water sourced from either the Rio Grande or groundwater, we observed evidence of preferential flow paths that allow irrigation return flow to bypass the shallow aquifer and enter the deeper perched zone. These infiltration channels became increasingly distinct over time.

These results demonstrate that irrigation return flow contributes variably to subsurface recharge depending on lithologic heterogeneity and water source. The use of ERT in this agricultural context reveals vertical and lateral moisture fluxes not captured by traditional well monitoring. This study demonstrates the potential for ERT to evaluate groundwater recharge in managed agricultural systems and contributes to a better understanding of hydrologic processes in arid agroforestry systems.

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

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