Integrated Geophysical Techniques For Ground Water Potential Evaluation In Matuu: Machakos County, Kenya.

Abstract

Matuu-Kilango area in Yatta is fall in an arid area with high rate of evaporation its rivers are dry for the better part of the year, there is therefore need to help identify alternative sources that include underground water for domestic and agricultural use. This study was aimed at evaluating groundwater potential of Matuu-Kilango area in Yatta District using integrated geophysical techniques so as to eliminate borehole failures associated with lack of proper techniques for siting boreholes. Resistivity and magnetic geophysical techniques supported by borehole logs were used to delineate subsurface fluid conduits and determine aquifer characteristics. For magnetic survey, Geometrics 856 Proton Precession Magnetometer was used, 189 measurement points were established, data subjected to corrections and upon processing, disjointed formations revealed by Euler plots under magnetic anomalous area led to inference of a fault in the NW-SE direction to the west of study area. Wenner and Schlumberger arrays were applied in Resistivity survey; Grids were established in the 25 Km2 area within which 11 measurement stations were located. Apparent resistivity data obtained from Wenner array measurements were subjected to contour plotting using Surfer 10 software with contour interval of 10 Ωm, VES data from the 11 stations were subjected to digital inversion using IPI2Win software, geo-electric parameters were calculated. Data averages from self-potential measurements were analysed as well as transmissivity attributes of the aquifer zones of the study area. Integrating the results, groundwater potential indicators (primers) such as fault, fractures, low resistivity layer (approximately 130 Ωm), negative self-potential zone with ranges between -10 mV to -90 mV, average transmissivity value of 10 m2/day and an inferred aquifer, were found to characterize the western zone of Matuu-Kilango area. The aquifer had a lateral stretch of about 1500 metres, a depth of about 100 meters and thickness ranging from 10 metres to about 80 metres northwards. A conceptual model for Matuu-Kilango groundwater potential zone was developed showing the north western part of the study area as the best zones for siting bore holes.