Evaluation of aquifer characteristics and ground water potentials in Awka, South East Nigeria, using vertical electrical sounding

Abstract

Geoelectrical sounding method was adopted in the evaluation of the aquifer characteristics and ground water potentials in Enugu-Agidi to the SE of Awka. A total of 30 vertical electrical sounding stations were occupied along five traverse lines within a (l×l) km 2 area using the Schlumberger electrode configuration. The results show a 5-6 interpretable geoelectric layers with a lithologic sequence consisting of thick shale beds alternating with thin beds of sandstone. The lithology varies dominantly from shale towards the Offia river valley to the NW and grades into sandstone to the SE in all the traverses. The study delineated two confined aquifers along traverse one (1) at VES 2 and 3 locations and shallow unconfined aquifers in the entire traverse. The confined aquifers have resistivities varying from 252 to 277 Ωm, at the depth range of 130 to 205 m and thicknesses varying from 18 to 26 m, respectively. Estimated aquifer resistivities, depths, thicknesses and transmissivities for the unconfined aquifers varies from 292 to 6,500 Ωm, 25 to 87 m, 5.7 to 38.2 m and 1,027.50 to 105,000 Ωm 2, respectively. The aquifer depth and aquifer transmissivity maps generated from geoelectric parameters show that large aquifer depths corresponds to low transmissivity values and vice versa, which are attributed to the increase in shale content with depth. The viability of deep boreholes under unconfined aquifer condition is poor in the study site based on the depth of investigation, such that the prospects for shallow boreholes with high transmissivities is high towards the central and SE of the site from the river valley. This has serious consequences on the quality of the water and the sustainability of the boreholes. The general ground water potential in the site is poor due to its geological characteristics. Excellent and sustainable yields are obtained from confined aquifers in the area when intercepted at depth, which is highly localized. © 2010 Academic Journals Inc.