Abstract

Two electromagnetic (EM) traverses and seven schlumberger vertical electrical soundings (VES) were carried out using “APEX MAXMIN” EM machine equipped with a transmitter and a receiver and a “GEOPULSE” resistivity meter to study formation strata that could host groundwater within the overburden and fracture/fault zones of the basement complex along Gwoza-Damboa road in Borno State, North-eastern Nigeria. Seven anomalies were identified from the two EM traverses which were followed by vertical electrical sounding to confirm the conductivities of each of the anomalies. The VES results produced one KH-type curve at VES02 while the remaining were H- types. Most of the points sounded are three layered except VES05 which is four layered. The thickness of first layers ranges from 2 - 11 m with resistivity ranges of 15 - 38 Ωm, second layer thickness ranges from 11 - 22 m with resistivity range of 10 - 20 Ωm, the third layers was interpreted as the basement at VES01, 02, 03, 04 and 06 with resistivity ranging from 600 – 896 Ωm. The third layer at VES05 had resistivity of 18 Ωm and thickness of 19 m; it is also the thickest of all the layers interpreted for all the sounding points. While all the points sounded are good groundwater targets, VES05 appeared to produce the highest groundwater yield needed for the purpose of this study because it is the thickest of all the layers obtained. Base on the interpreted results, all the seven VES points are groundwater prospects. However, in order of suitability, VES05, VES01, VES06 and VES04 were recommended and four productive boreholes were drilled to an average depth of 55 m with VES05 producing the highest yield.

Key words: Vertical electrical sounding, basement, weathered zone, fractured zone, electromagnetic, traversing.