Characterization of Aquifers Using Electrical Resistivity and Induced Polarization Surveys in River Sosiani Sub-Catchment, Uasin Gishu County, Kenya

Freshwater is a critical resource for domestic and agricultural use, but its occurrence presents a challenge. Utilization of electrical resistivity methods in aquifer delineation underscores their importance in the field of hydrogeology. The Sosiani sub-catchment is a geologically complex area where saline groundwater has been sporadically encountered, and while the electrical resistivity method has been used for groundwater prospecting in the area, it has not been effective in distinguishing between saline and freshwater zones on its own. This research characterized aquifers of Sosiani sub-catchment in terms of salinity using the Electrical Resistivity and Induced Polarization methods that involved 31 Vertical Electrical Soundings. Validation of observed aquifer salinity from ER/IP surveys was performed using Electrical Conductivity tests of 20 water samples collected from boreholes in the sub-catchment. The VES results indicate a shallow saline aquifer at 14 - 37 m and a deep freshwater aquifer at 100 - 193 m. Observations from interpolated aquifer depths indicate a shallow aquifer at 3.7 - 30.2 m and a deep aquifer at 43.0 - 149 m depths. The borehole completion reports from selected boreholes in the sub-catchment also confirm these indicating aquifers at 2 - 35 m, 50 - 85 m and 100 - 195 m depths. An aquifer depth contour map generated in QGIS revealed both aquifers occurring throughout the sub-catchment, with low chargeability and high salinity zones coinciding. The findings of this research indicate that characterization of shallow aquifers in terms of salinity is possible through ER/IP methods. It also provides knowledge on the aquifer distribution and Salinity variation in the Sosiani sub-catchment, which serves as a guide in the siting of groundwater boreholes.