Managed aquifer recharge assessment in the Nabogo Basin of Ghana using a combined electrical resistivity tomography infiltration method

The shallow aquifer in the Nabogo Basin of Ghana is under stress due to unavailability of surface water during the dry seasons. As a result, managed aquifer recharge (MAR) has been proposed to augment recharge to the aquifer, through the use of excess runoff in the rainy seasons, to enhance their sustainability. Therefore, this study has assessed the suitability of the aquifer for subsurface water storage by employing a combined electrical resistivity tomography (ERT) and infiltration approach to delineate the aquifer geometry, monitor infiltration, and estimate hydraulic parameters. The approach first involved conducting ERT surveys on traverse lines across and along the inlet of a small reservoir (used as recharge zone) in the basin to map the subsurface lithologies. Afterwards, a time-lapse ERT-controlled infiltration test was conducted at the reservoir inlet to monitor infiltration in the subsurface. The study results revealed an aquifer geometry comprising lateritic soil of high resistivity at the top, weathered-fractured mudstone/siltstone of medium to low resistivity at 5–40 m depth, and fresh siltstone of high resistivity to a depth of approximately 50 m. Also, the saturated hydraulic conductivity was estimated to be 2.04–3.20 cm/h using three infiltration models, which together with the weathered-fractured zone thickness showed the aquifer to be suitable for MAR. Additionally, the time-lapse ERT images identified the wetting front of the infiltrating water and were consistent with the cumulative infiltration depth, thus indicating the effectiveness of the combined ERT-infiltration method in modeling subsurface saturation for practical evaluation of managed recharge.