TITLE:
Electrical Resistivity Sounding for Groundwater Investigation around Enugu Metropolis and the Environs, Southeast Nigeria
AUTHORS:
Claris C. Nwachukwu, Charles C. Ugbor, Osim Jethro Ogboke
KEYWORDS:
Electrical Method, Vertical Electrical Sounding, Groundwater, Aquifer, Apparent Resistivity
JOURNAL NAME:
International Journal of Geosciences,
Vol.13 No.1,
January
29,
2022
ABSTRACT: This report evaluates the
use of electrical method and borehole data to investigate the subsurface to
delineate the groundwater potential in Enugu metropolis and the environs,
south-eastern Nigeria other than rely only on resistivity method which could lead to interpretation error.
Integrating these 2 data sets is key in this study. The study area is located
in the Anambra Basin and is underlain by Nkporo/Enugu Shale which is overlain
by the Mamu Formation. It is bounded by Latitudes 6°2 0'00"N to
6°30'00"N and Longitudes 7°25'00"E to 7°35'00"E and covers surface area of about 342 m2. Thirty-one vertical electrical
soundings (VES) were carried out across the area using the Schlumberger
electrode array with current electrode separation from 2 to 500 m to identify
the depths and resistivity values of the identified geo-electric layers.
Through data analysis using WinResist software, the apparent resistivity,
thicknesses and depths and the thicknesses of the aquifers were generated. The
resistivity and
depths were modelled to generate resistivity map and depth map. The resistivity
of the aquiferous zone within the study area varied from 20.55- 427.8
ohm-m at depths of between 10.7 - 40.05
m. Depth to the water table appears to be shallow at the south western part of
the map. The interpreted geo-electric layers show a sequence of lateritic top
soil, shale, sand and shale. The frequency distribution of the VES curves
generated shows the presence of 3 to 5 layers with HK type as the highest.
Also, a 2D model was generated using the correlation of VES to VES data and
borehole data to VES data to show the underlying stratigraphy beneath the study
area as well as the direction of ground water flow. Result of the VES curve
analysis reveals that the
sub-surface is underlain by three lithological layers namely: lateritic top
soil, shale, sand and shales with NW direction of groundwater flow from the 2D
model. Groundwater prospective zones can be seen along NW, SW and central parts
of the study area which have low resistivity values.