Integrated Resistivity Techniques for Groundwater Potential Evaluation in Matuu, Machakos County, Kenya.
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Date
2016-01
Journal Title
Journal ISSN
Volume Title
Publisher
Journal of Multidisciplinary Engineering Science and Technology (JMEST)
Abstract
In order to evaluate groundwater
potential of Matuu-Kilango area an understanding of its
subsurface formations and associated geo-electric
parameters was critical alongside delineation of faults
and fractures which are groundwater conduits. Earlier
use of geological reconnaissance report only or none at
all in siting boreholes has led to recorded cases of
borehole failure in Matuu. Integrated resistivity survey
involving Wenner and Schlumberger array techniques
was applied over a 25 square kilometre area with an aim
of locating groundwater aquifer and the associated
characteristic and geometry. Control resistivity
measurement was conducted adjacent to existing
boreholes to synchronize resistivity results with
borehole logging report. Qualitative interpretation
involving generation of contour maps for resistivity
values from Wenner array was attempted and an
anomalous low resistivity zone was observed at the
western part of Matuu-Kilango area. Inversion results
from vertical electrical soundings were obtained using
IPI2Win software giving three to four layered geo
electrical sections having the inferred aquiferous layer
in between resistive black top soil and hard gneiss
basement. Fractured/faulted zone was identified to the
west of Matuu-Kilango area with the inferred aquifer
existing at about 100 meters depth having general
orientation of South-East to North-West and an average
width of 1500 meters. Along the faulted zone were
prevalent increasing values of transverse resistance as
well as longitudinal conductance calculated from
resistivity sounding results, an indication of availability
of groundwater resource.