Hydrogeophysical Investigation and Aquifer Evaluation of the Formations in Nsukka Area, Southeastern Nigeria

Emmanuel O Ezim ,I I Obiadi

doi:10.7176/jees/11-7-04

Abstract

The study targeted the aquiferous Ajali Sandstone and Nsukka Formations that underlies the Nsukka metropolis and its environs (within Latitudes 6 o 80 1 N and 6 o 89 1 N; Longitudes 7 o 21 1 E and 7 o 30 1 E), covering an area of about 210 square kilometres. Thirty four (34) cross array Vertical Electrical Sounding (using the Schlumberger electrode configuration) and records from four (4) selected boreholes have been used to investigate the subsurface distribution of electrical resistivity and to delineate hydraulic properties of aquifers in Nsukka area, Southeastern, Nigeria.The electrical surveys of the area show high values of permeability, ranging from 0.0075 to 0.015cm 2 , hydraulic conductivity, ranging from 8.29 to 16.64m/s, transmissivity, between 455.87 and 1002.48m 2 s -1 , and specific yield, ranging from 2.35 to 4.76m 3 . A tie with the results of borehole logs analysis reveals the presence of at least four layers of contrasting hydraulic conductivity. Analyses, however, suggests that the Nsukka Formation (which overlies the Ajali Sandstone) is thick and poorly conductive while the Ajali Sandstone unit is homogenous and anisotropic and has higher conductivity (especially beyond the depth of 100 m), suggesting a prolific water-bearing formation at such depth and beyond. The Ajali Sandstone aquifer in the area is thick and prolific. The distribution of major geological units, well log data, static water level data were shown to have influence on the groundwater occurrence and flow pattern in the area. Keywords: Ajali Sandstone Aquifer, Nsukka Metropolis, Resistivity measurements, Well data DOI: 10.7176/JEES/11-7-04 Publication date: July 31 st 2021

Highlights

The Nsukka area, southeastern Nigeria has little or no surface water, resulting to some water resources problem and to high dependent of groundwater
The need for adequate water supply in the Nsukka area necessitated the use of vertical electrical sounding to evaluate the hydrogeological potential of the Ajali Sandstone
The results indicate that the borehole at the Abuja Building (A02), Franco Refactory (F03) and the Energy Centre (E04) [University of Nigeria, Nsukka (UNN)] all penetrated the Ajali Sandstone aquifer; with respective depths up to 720 ft (220m), 670fts (210m) and 682fts

Summary

Introduction

The Nsukka area, southeastern Nigeria has little or no surface water, resulting to some water resources problem and to high dependent of groundwater. Mamah and Ekine (1989) had conducted a geo-electrical survey on the Nsukka Formation and distinguished two to three layers of the basal sandstone within the formation. Mamah (1997), suggested with the aid of the resistivity sounding survey data carried out at Orba for the UNDP, that the depth to water table in the area is about 95 m and that the aquifer is the Ajali Sandstone. The characteristics of this aquifer with respect to well yield remain uncertain, as most boreholes and hand dug wells in the area turn abortive.

Methods

Results

Conclusion