TITLE:
Delineation of Shallow Aquifers of Umuahia and Environs, Imo River Basin, Nigeria, Using Geo-Sounding Data
AUTHORS:
Uchenna Ugada, Alexander I. Opara, Theophilus T. Emberga, Frank D. Ibim, Alexander I. Omenikoro, Edwin N. Womuru
KEYWORDS:
Geo-Sounding; Aquifer Units; Resistivity; Transverse Resistance; Longitudinal Conductance; Nigeria
JOURNAL NAME:
Journal of Water Resource and Protection,
Vol.5 No.11,
November
29,
2013
ABSTRACT: This work was undertaken to study the hydrogeophysical
characteristics of Umuahia and environs,ImoRiver Basinusing geophysical data. Thirty (30) vertical electrical sounding data with a
maximum electrode spacing of (AB/2) of 500 meters were acquired using the
Schlumberger electrode configuration. The VES data were interpreted using the conventional partial curve matching technique to
obtain initial model parameters, which were used as input for computer iterative
modelling using the OFFIX software. The study revealed three (3) to six (6)
geo-electric layers with underlying shale beds. Aquifer apparent resistivity in
the study area ranges from about 50 to 850 Ωm with the aquifer
depth varying between 0.53 - 82.67 m. Similarly, the aquifer thickness in the
study area ranges from 0.8 - 110 m, with very low thicknesses around Ajata
Ibeku. These shallow aquifers with very small thicknesses in the western areas
around Ajata Ibeku are believed to be perched or fractured shale units with
very low or no yield. Finally, transverse resistances in the study area range
from 200 - 3400 Ωm2 with low values in the western part. Information
extracted from iso-resistivity models, geoelectric cross sections, litho logs
and electric logs revealed a sandy clay lithology at very shallow depths with a
thick layer of shale/clay extending to over 300 m within the
western part. These shallow aquiferous units are however perched, partially
saturated and may not have sufficient yield. Finally, this study has helped to
delineate the aquifers of the study into two distinct zones, thus revealing a groundwater divide.