Analysis of recharge and groundwater flow in parts of a weathered aquifer system in Northern Ghana

Abstract

Stable isotope data were used to relate recent meteoric water to groundwater in parts of the Nabogo sub-catchment of the Voltaian Basin. Estimates of the rates of evaporation of recharging groundwater in transit were made on the basis of the stable isotope data. This study finds that groundwater recharge within the weathered zone aquifer system in the study area is of recent meteoric origin. There is, however, evidence of significant evaporation of recharging water in the range of 34–70%, as a result of high temperatures and low relative humidities. This high level of evaporation of rainwater prior to or in the process of recharge is attributed partly to slow infiltration due to significant clay content of the intervening material between the saturated zone and the surface. It suggests limited but variable fortunes in terms of groundwater recharge from precipitation in the area and ties in with previous findings in relation to groundwater recharge estimates. This justified the use of previous estimates of groundwater recharge in other parts of the terrain for the conceptualization of the groundwater flow through a numerical model under steady-state conditions. This study determines that the general groundwater flow is controlled by local flow systems with no obvious preferred direction of flow. Calibrated hydraulic conductivity estimates range between 0.35 and 5.14 m/d. This is consistent with the nature of the material of the aquifer, and will provide the basis for assessing the hydrogeological conditions of the weathered zone.