Characterization of Aquifers in Afikpo Local Government Area, Southeastern Nigeria

ABSTRACT 

Before the exploitation of groundwater in a region, it is usually necessary to determine the hydraulic characteristics which allow the flow of water through aquifer and the amount of water that aquifer yields to well due to compression or dewatering of the aquifer. Hydrogeological work was carried out to characterize the aquifers of Afikpo-North L.G.A., Southeastern Nigeria. The study area lies within the lower Benue Trough of Nigeria and is underlain by Turonian Ezeaku Formation and Campanian Nkporo Formation. The methodologies employed in the study include Vertical Electrical Sounding, pumping test (recovery test method) and well logging approach to determine aquifer hydraulic parameters (hydraulic conductivity and transmissivity), aquifer thickness, and to describe the lithologic information in order to deduce the specific yields for the aquiferous zones of 20 locations in the study area. Water table informations from bore holes in the area were used to construct regional map of static water level depths and groundwater flow directions. Analytical calculations using Darcy’s law were used to estimate the specific discharge, flow per unit width and average linear velocity for the basin. The hydraulic conductivity and transmissivity, range from 0.0025m/day to 0.5517m/day and 0.0535m 2 /day to 16.58795m2 /day respectively. Depths to aquifer vary from 24m to 57m while the aquifer thickness ranges from 11.6m to 36.1m. The specific discharge ranges from 0.00045m/day to 0.00867m/day, the flow per unit width varies from 0.0127m2 /day to 0.19378m2 /day and average linear velocity varies from 0.00188m/day to 0.03613m/day. The hydraulic head map reveals two divergence and three convergence zones. The aquifers in the basin are mostly underlain by the predominantly sandstone and shaly formations. Groundwater potentials of the basin were thoroughly characterized using transmissivity within unit cells. Four groundwater potential ratings were defined based on the aquifer transmissivity data from the 20 locations. 5% of the locations were rated imperceptible. 20% were rated very low, 70% were rated low and 5% were rated intermediate. The usable storage capacity (water in storage) was determined to be 1.63 bm3 . Regional maps of the various hydrogeological parameters have been produced for lateral and vertical extents in order to characterize the aquifers in this basin. The aquifers were delineated into four groundwater potential zones (as stated above) for future development and choice for drilling sites.