Volumetric estimation of groundwater reserve in Akwa Ibom State University main campus, southern Nigeria using surficial resistivity measurements

Abstract Recent changes in climatic conditions and the resulting changes in demands for potable water call for a thorough understanding of groundwater resources. In this research, the usability of the electrical resistivity technique in the volumetric estimation of groundwater reserve is demonstrated. Sixteen (16) vertical electrical soundings were made at predetermined locations in Akwa Ibom State University campus, southern Nigeria with the main aim of delineating the hydrostratigraphic units and estimating the groundwater reserve in the area. Three to four geoelectric layers comprising poorly sorted continental sands with minor clay intercalations have been identified in the study site. Groundwater extraction in the area takes place in the second and third layers, based on location, at depths ranging from 0.7 to 84.7 m. The aquifer system is shown to have a mean effective porosity of 0.32, mean specific yield of 0.23 and mean specific retention of 0.09. The total aquifer volume is estimated to be 1.65 x 108 m3 while the effective water volume reserve in the area is 5.3 x 107 m3. The usable groundwater volume releasable by the aquifer during pumping is shown to be 71.9 % of the effective volumetric groundwater reserve while the fractional volume retainable by the aquifer is 28.1 %. This, by implication is an indication that the area has good groundwater potential for sustainability of water wells. The regression equations derived in this study can be used for easy and rapid prediction of aquifer porosity and specific yield/retention from surface resistivity data in regions with similar geological characteristics. These outcomes are very auspicious, particularly in devising sustainable groundwater development and exploitable schemes to meet current and future needs of the university community.