From groundwater occurrence to accessibility: An integrated hydrogeophysical assessment in semi-arid regions, based on ERT, MRS, and seismic investigations

Abstract

Groundwater is the primary freshwater source in arid regions, yet its sustainable management is often hindered by limited knowledge of aquifer properties, especially when borehole data are sparse. Herein, we demonstrate the benefits of combining different geophysical methods, using new results from electrical resistivity tomography (ERT), magnetic resonance sounding (MRS), and seismic surveys (refraction and reflection), and previous legacy vertical electrical soundings (VES) and borehole lithological data. By jointly exploiting the strengths of each method and calibrating against field observations, our integrated approach resolves key hydrogeological uncertainties that single techniques fail to capture. The combined interpretation of ERT and VES results delineate a conductive Plio-Quaternary (PQ) infill (>80 m) underlain by moderately resistive marly‑carbonate horizons, whereas MRS identifies two hydrogeophysical zones: a shallow zone (7–8 m) characterized by variable water content and inferred low transmissivity, strongly impacted by evaporative salinization, and a deeper zone (30–150 m) with greater storage but limited transmissivity. Seismic imaging refines basin-fill thickness (~220 m), corroborate the depth to the Lutetian aquifer (90–180 m), and maps structural features controlling groundwater flow, including a chaotic unit (U4) linked to saline horizons. This integrated framework emphasizes the distinction between water presence and accessibility, underscoring the risks of overestimating resource potential when salinity and permeability are not jointly considered. Finally, a schematic 3D model integrates geophysical, geological, and hydrogeological results into a coherent framework, improving visualization of PQ deposits and aquifer compartmentalization. Our approach represents a framework that can be adapted for groundwater assessment in other data-scarce arid and semi-arid basins.