Delineation of shallow groundwater aquifers in coastal plain sands of Calabar area (Southern Nigeria) using surface resistivity and hydrogeological data

A combination of surface resistivity and hydrogeological data has been used to identify different water bearing horizons within the coastal plain sands of the Calabar area in southern Nigeria. Results show that two major water bearing horizons exist in the area: (i) an upper zone consisting of medium- to coarse-grained sands and gravels having a mean formation resistivity of 1500 Ωm (gravelly zone) and (ii) a lower zone consisting of fine- to mediumgrained sands with a mean formation resistivity of 320 Ωm (sandy zone). The estimated aquifer parameters (hydraulic conductivity k, transmissivity T, specific capacity SC, specific capacity index I, coefficient of aquifer capacity CAC, coefficient of aquifer variability CAV) are higher in the gravelly zone in comparison to the sandy zone. Rating of these zones on the basis of formation resistivity (aquifer layer resistivity), FR, specific capacity, transmissivity, T and total dissolved solids, TDS show that the upper and the lower zones can best be described as very good (VG) and slightly good (SG), respectively, in terms of quantity of groundwater. However, the upper zone is highly vulnerable to surface pollution compared to the lower zone. © 2002 Published by Elsevier Science Ltd.