GROUNDWATER EXPLORATION IN A BASEMENT COMPLEX TERRAIN USING ELECTRICAL RESISTIVITY SOUNDING (VES): A CASE STUDY OF RIMIN GADO TOWN AND ENVIRONS, KANO STATE NORTH CENTRAL NIGERIA

Groundwater occurrence and distribution in Basement Complex is localized and confined to weathered /fractured zones. Hence exploration for groundwater in such terrains posses a great challenge to groundwater development agencies as in most cases the risk of failure of such projects is very high. This study was carried out with the aim of demonstrating the application of vertical electrical sounding method of investigation in the exploration for groundwater in Rimin Gado town and environs. A total of 16 VES points were probed located in 4 settlements spread at a distance of 200-300m apart. ABEM SAS 300C terameter was used to generate field data applying the Schlumberger Array with an AB/2 of 1.5-100m. The field data were simulated using Zhody and OFFIX software.  The results show that there are 2-4 Geo-electric layers: topsoil (sandy/lateritic), highly weathered Basement (clay and sandy clay), slightly weathered/ fractured Basement (Clay,sand/clayey sand) and Fresh bed rock. Three basic resistivity zones were identified: low resistivity zone (49-95 ohm-m) corresponding to highly weathered Basement material, the high resistivity zone (294-1543 ohm-m) representing fresh bed rock and intermediate resistivity zone (114-219 ohm-m) corresponding to slightly weathered/ fractured Basement. ButuButu and Dan Isa with a weathered Basement thickness of 25-34m and resistivity of 66-140 ohm-m therefore have high potentials for good Borehole yields. It is suggested that groundwater exploration in Basement Complex terrain should include geophysical investigation especially VES along with geological methods as an integral part of the program.