Larry Pax Chegbeleh

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

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.

Hydrogeological Conditions of a Crystalline Aquifer: Simulation of Optimal Abstraction Rates under Scenarios of Reduced Recharge

A steady state numerical groundwater flow model has been calibrated to characterize the spatial distribution of a key hydraulic parameter in a crystalline aquifer in southwestern Ghana. This was to provide an initial basis for characterizing the hydrogeology of the terrain with a view to assisting in the large scale development of groundwater resources for various uses. The results suggest that the structural entities that control groundwater occurrence in the area are quite heterogeneous in their nature and orientation, ascribing hydraulic conductivity values in the range of 4.5 m/d to over 70 m/d to the simulated aquifer. Aquifer heterogeneities, coupled possibly with topographical trends, have led to the development of five prominent groundwater flowpaths in the area. Estimated groundwater recharge at calibration ranges between 0.25% and 9.13% of the total annual rainfall and appears to hold significant promise for large-scale groundwater development to support irrigation schemes. However, the model suggests that with reduced recharge by up to 30% of the current rates, the system can only sustain increased groundwater abstraction by up to 150% of the current abstraction rates. Prudent management of the resource will require a much more detailed hydrogeological study that identifies all the aquifers in the basin for the assessment of sustainable basin yield.