Application of Hydrogeophysical Techniques in Delineating Aquifers for Estimating Groundwater Recharge Potential to Enhance Water Allocation in Groundwater-Dependent Systems, Northern Cape, South Africa

Application of aquifer delineation using hydro-geophysical techniques was conducted in De Aar, the eastern part of the Karoo region, Northern, South Africa. This study is aimed at demonstrating the use of hydrogeophycal techniques in delineating aquifer systems into unconfined and confined to estimate areas and zones likely to control ground-water recharge. An integrated hydrogeophysical approach using vertical electrical resistivity sounding (VES) and ground telluric methods was applied to delineate subsurface structures. Six VES surveys and seven profile surveys were measured using a Wenner array configuration and ground telluric method respectively. VES data was processed using IPI2win software and used to produce a 2D inference of the subsurface electrical resistivity model. The telluric passive surveys were processed through an automated in-built algorithm to generate 2D profile maps while the electric potential difference curve was interpreted with the lithological cross section constructed 2D conceptual model. The VES results showed four significant layers of low (0.9-8.1 Ωm), moderate (22.4-125 Ωm), and high 68-177 Ωm) electrical resistivity values which are suggestive of the different lithological formations. Additionally, the subsurface model from ground telluric methods supported shallow groundwater potential boreholes with the inference of fewer groundwater accumulations below 50 m. These hydrogeophysics results were compared to the drill chip lithological results and both suggested a double-layer aquifer system, which may therefore suggest that recharge estimation needs to be carried out in two different aquifers. The study therefore successfully demonstrated the use of geophysics techniques in delineating aquifer systems, thereby enhancing the identification of potential recharge areas.