Georesistivity, Aquifer Hydraulic Characteristics and Groundwater Potential Zones Using Vertical Electrical Sounding and Dar-Zarrouk Parameters at Umunze, Anambra State

A geophysical survey using Vertical Electrical Sounding and Dar – Zarrouk parameters was conducted at Umunze in Orumba South L.G.A of Anambra State, Nigeria to investigate the georesistivity, aquifer hydraulic characteristics, and groundwater potential zones. The survey areas lies between longitudes 7°14’1.85†E – 7°14’21.43†E and latitudes 5°57’27.49†N – 5°59’14.38″N. Vertical Electrical Sounding (VES) was carried out with a digital read out resistivity meter (ABEM SAS 1000). A total of four (4) soundings was carried out in the area. The VES data interpretations were done using INTERPEX software and the VES results were presented in terms of resistivity, thickness, depth and lithology. The lithology was inferred to the layers by correlating the lithology log of one of the boreholes drilled in the study area and the geology of the study area. The VES result shows 5 – 6 lithologic layers with the subsurface sequence varying as follows: Lateritic Silty Shaly Sand, Dry Silty Sandy top, Dry Sandstone, Silty Shale, Shaly Silty Sandy soil, Silty Lateritic Sandstone, Lateritic Sandstone, Sandstone, Silty – Sandstone, Water Saturated Silty Sand, Water Saturated Sandstone and Water Saturated Silty Shale.. The water saturated silty sand, water saturated sandstone and water saturated silty shale layers constituted the aquifer unit in the area and its thicknesses ranges from 37.5 – 89.1m. The aquifer transmissivity was determined by calculating for hydraulic conductivity and multiplying with the thickness of the aquifer layer. The aquifer transmissivity values obtained for VES 1 – 4 are 41814.81, 61487.78, 65731.90 and 85658.13 m2/day which indicates a very good aquifer transmissivities respectively. VES 1 and 4 have been identified as the best areas for productive and sustainable borehole yield because of their high aquifer thickness and transmissivity.