Geophysical Investigation of Basement Rock Structures around a proposed Dam Site,
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Date
2017
Journal Title
Journal ISSN
Volume Title
Publisher
Adamawa Stete University
Abstract
A combination of carefully selected geophysical surveys comprising very low frequency electromagnetic
(VLF-EM) and electrical resistivity (VES) methods was employed to study the basement rock structures in
a proposed dam site within University of Ilorin campus. Data acquired in the survey were processed to
inverted subsurface geological model, 2D conductivity structures and geo-electric cross-sections for the
area. The results were interpreted to delineate the subsurface rock and structure, the number of geo-electric
layers, and to select a suitable area for the construction of dam extension. The four geo-electric layers
delineated correspond to lateritic top-soil layer, weathered rock layer, fractured rock layer, and the fresh
basement rock. The VLF-EM and resistivity cross-section revealed a series of competent and weak zones.
The weak zones are characterized by weathered/fractured rocks, and they correspond to areas of low
resistivity anomalies in VES survey and high conductivity anomalies in VLF-EM survey. Competent rock
zone corresponds to area of high electrical resistivity anomalies and low conductivities in VLF-EM
tomogram. Depth to fresh basement rock in the weak zone ranges from 7.8 – 14.8 m. The competent rock
zones correspond to high resistivity anomalies in electrical resistivity cross-section and low conductivity
anomalies in VLF-EM tomograms. Depth to fresh basement rock in the competent zone ranges from 3.3 –
6.8 m. the competent zone recommended for the construction of the dam extension.
Description
Keywords
Vertical electrical sounding, VES, Low frequency electromagnetic, Concrete dam, Dam seepage
Citation
Raji, W. O. and Ibrahim, K. O. (2017) Geophysical Investigation of Basement Rock Structures around a proposed Dam Site, Adamawa State University Journal of Scientific Research, Vol. 5(2), 38 - 49.