Development of groundwater needs the capabilities to distinguish the different aquifer layers found in a region, and thereafter the parameters which can be used expressly to define the aquifer type. The past studies in the Olbanita sub-basin have accorded the area as having one aquifer, which has resulted into generalization of the aquifer parameters. The objective in this study is to

The integrated approach of various techniques which historically have been used independently is key to successful exploration, development, exploitation and management of the groundwater resources. The integration of Remote Sensing (RS), Geographical Information Systems (GIS) and Borehole data has been used in the study area to assess their applicability in groundwater investigation. The area of study lies in the arid and semi-arid lands (AS-ALs) where principally remote sensing data has been used in extraction of various thematic maps (lithology, lineament, drainage density, and Digital Elevation Model Maps) for groundwater assessment. The GIS platform was used in integrating the RS data and data of productive boreholes. The lineaments generated through remote sensing agree well with structural geology of the area, where high density lineament points overlays the points of intense faulting. Lineaments found in the area correlate well with fault zones, fractures, and lithological contrasts as supported by geological map and structural map. Weathering, faulting and fracturing of the rocks mean a possible increase or a reduction in specific capacities as observed in productive boreholes in sedimentary rocks or igneous/basaltic rocks of the area. Similarly, it is noted that the degree of faulting affects the degree of radius of influence of a borehole in a particular area. These analyses show that groundwater potential within the Sub-County varies spatially with high dependency on geological structures in the basement region and more on geology within the volcanic and younger sediments.

The use of gravity data has demonstrated capability for monitoring lithological changes on a large scale as a consequence of differentiating basement and sedimentary of buried valleys. Gravity anomalies are associated with lateral contrasts in density and therefore deformation by faulting or folding will be manifested if accompanied by lateral density changes, otherwise, the vice versa is true. The study's objective is to evaluate the effectiveness of gravity method in establishing different lithologies in an area. The study has revealed that regional anomaly gravity map presents high anomalies in the Northern region in the NW-SE trend and low anomalies in the southern trend in NW-SE, while the residual anomaly gravity map shows different trends for the low and high gravity anomalies. The gravity anomalies are well interpreted in line with the lithologies of the study area rather than the deformation of the same lithologies. There are observed high values of gravity anomaly values (ranging from −880.2 to −501.2 g.u.) where there are eolian unconsolidated rocks overlying the basement compared to low gravity anomaly values (ranging from −1338.9 to −1088.7 g.u.) where the andesites, trachytes and phonolites overly the basement. The different regional gravity anomalies relate well with different rock densities in the study area along the line profile for radially averaged power spectrum. The gravity highs are noted in the eastern point and are associated with andesites, trachytes, basalts and igneous rocks, while the gravity lows are associated with sandstone, greywacke, arkose, and eolian unconsolidated rock. The utilization of the information from the Power spectrum analysis demonstrates that the depth to the deepest basement rock is 12.8 km which is in the eastern flank, while the shallowest to the basement of 1.1 km to the western flank.

Turkana South Sub-County falls in the arid and semi-arid lands of Kenya, which are characterized temperatures of 20˚C to 41˚C with an average of 30.5˚C and precipitation in the range of 52 mm to 480 mm per year. The area has limited availability of water resources. The area has a land surface of 18,000 km 2 and lies between Longitudes 35˚10'00" and 36˚45'00" East and between Latitudes 1˚0'00" and 3˚0'00" North. The study area faces immense difficulties in trying to meet its water requirements for her rapidly increasing populace, livestock needs and other developmental programmes. Surface water in the area is becoming unobtainable, thus the choice of groundwater exploitation. Indeed with the snowballing demand necessitated by energy, agricultural and livestock production needs in this area, there is an appeal into investigation for groundwater in this greatly remote and extensive area. Thus, the success in the exploration, development and management of groundwater in such a large area calls for such methods that can easily be used to zero down to exploitable targets. Given the expansiveness of the study area, remote sensing (RS) has been used to map lineaments which in turn have been used to deduce faulting affecting the geology of the area. The mapping by RS helped in identifying weathered zones, the fracture systems and fault zones sign of deeper weathered zones which are interpreted to be potential areas since mainly water is stored within fractures and the weathered zones in subterranean and in hard rocks. In the field topographic expressions of faults and fractures which include; joints, fractures, scarps, river channels and slope How to cite this paper: Nyaberi, D. M.,

Much study has been done in the study area linking Vertical Electrical Sounding (VES) interpreted results to lithologies in the subsurface though only tend to indicate the vertical changes with the aim of mapping the occurrence of groundwater aquifers. Several boreholes have been drilled in the study area, though not much has been done to compare the vertical and lateral lithologic changes in the study area. This research is based on VES modelled geoelectric layers compared from point to point and using borehole logs as control data to establish inferences of certain lithology in the subsurface. The inversion of each VES curve was obtained using an AGI Earth Imager ID inversion automated computer program and resistivities and thicknesses of a geoelectric model were estimated. The analyzed VES data interpretation achieved using the curve matching technique resulted in mapping the subsurface of the area as portraying H-type; ρ 1 > ρ 2 < ρ 3 , K-type; ρ 1 < ρ 2 > ρ 3 , A-type; ρ 1 < ρ 2 < ρ 3 , Q-type; ρ 1 > ρ 2 > ρ 3 , representing 3-Layer subsurface and subsequently a combination of HK, HA and KHK types of curves representing 4-Layer and 5-Layer in the subsurface. The analysis further deployed the use of the surfer software capabilities which combined the VES data to generate profiles running in the west-east and the north-south direction. A closer analysis of the curve types indicates that there exists a sequence showing a shifting of the order of arrangement between the west and the east fragments which incidentally coincides with VES points 8, 9 and 10 in the West-East profiles. The lateral change is noted from the types of curves established and each curve indicates a vertical change in the subsurface. Control log data of lithologies from four boreholes BH1, BH2, BH3 and BH5 to show a qualification that different resistivity values portent different lithologies.