Determination of Aquifer Characteristics from Geo-electrical Sounding data in parts of Anambra State, Nigeria

The execution of water borehole project is quite expensive, there is therefore need for surface resistivity measurements before drilling to gain sufficient knowledge on the subsurface geo-hydrological conditions of an area. In this study, geophysical investigation of groundwater is aimed at delineating the aquiferous units in the central part of Awka by determining their depths, thicknesses, resistivities and the potential borehole depth at various locations within the area employing the technique of Vertical Electric Sounding (VES) using the Schlumberger array. Ten (10) sounding stations were obtained. The data was interpreted using conventional partial curve matching and computer aided iteration techniques. The vertical electrical sounding curve types identified in the study area includes K, H, QH, HK, and QK. The HK-type sounding curves were predominant in the study area. About four to six geo-electric layers comprising the top soil, shaly- sand, sand, dry sand, water saturated sandstone, and shale were delineated with the shale usually occurring as the last layer. Lithologic log for the borehole located near one of the sounding station at Awka revealed that some of the geologic units were either suppressed or merged into a single geo-electric unit probably due to similarities in electrical resistivity. 3-D surface map of the aquifer characteristics were produced, it was observed that the aquifer properties ranges from 0.0262 to 0.7187cm/s, 1.2995-48.0092cm2/s, 139.14-3813.22 Ohm-m, 9,294.55-189,135.71 Ohm-m2, 0.0130-0.4801 Ohm-1 for hydraulic conductivity, transmissivity, resistivity, transverse resistance and longitudinal conductance respectively within the study area.