Hydrogeological Assessment Of Groundwater On Legon Campus: Application Of Geophysical And Numerical Techniques

ABSTRACT

The hydrogeological conditions of University of Ghana, Legon Campus was assessed using geophysical and numerical techniques. Data from borehole lithological logs and electrical resistivity survey was used to conceptualize the hydrogeological system of the terrain whiles using MODFLOW to generate groundwater flow simulation models under steady state conditions. The objective of the study was to conceptualize the hydrostratigraphy through geophysical techniques, develop a groundwater flow geometry for proper understanding of the mechanisms of groundwater flow in the area and to estimate groundwater budget and the responses of the aquifer system to stress. The calibrated steady state model together with a stochastic approach was used to simulate some scenarios of groundwater resource and its management in the area. The results of the study suggested three main lithostratigraphic units from geoelectric sections and the stratigraphic model and these units are phyllite, quartzite and laterite from the bottom to the top. Based on the borehole logs, the pseudo- sections and the geology of the area, the aquifer was encountered at a depth of about 38 m to 60 m which is attributed to probably the moderately weathered phyllite or quartzite giving an aquifer zone of thickness 22 m and this could be variable in space. The result suggests the dominance of local groundwater flow systems which results from the local changes in topography and hydraulic conductivity field. The estimated hydraulic conductivity values range between 4.0 m/day and 60.0 m/day and this is probably attributed to the local changes in the degree of weathering and/or fracturing in space. The estimated groundwater recharge ranges between 0.008 m/yr to 0.12 m/yr with an average of 0.064 m/yr representing 1% and 15%, with an average of 8.1% of the annual precipitation of 0.7 m in the area. The amount of water that entered the aquifer system through the general heads is 368368.08 m3/d and this is due to changes in the hydraulic

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heads and the interconnectivity of the system with other aquifer systems. The contribution of recharge to the water budget seem low because the vertical percolation of rainwater is restricted due to the clayey nature of the terrain and the many physical developments which are seen on the Legon Campus. From the scenario analysis that were performed, decrease in recharge did not have any significant change on the groundwater water system. However, when the initial abstraction rates were increased up to about 50%, dry cells were observed around some of the wells.