Hydrogeology of lake nakuru drainage basin using electrical resistivity survey.

Abstract

The Lake Nakuru Drainage Basin is underlain by volcanic and volcano-sedimentary rocks of PliocenePleistocene-Recent Periods. These rock types are common water bearing formations, especially the weathered,fractured or transition zones along faults and at interfaces of the various volcanic flows. Consequently,any groundwater investigations are usually based on methods aimed at detecting such underground structures. The Geographical Information System (GIS) database was designed and thereafter used to analyze fissure and fracture zones, and drainage termination areas, in order to locate surface water seepage into and away from the Basin. Stored GIS information was used to construct Iso-resistivity maps by employing a program code-namedILWIS (Integrated Land and Water Information System). Electrical resistivity studies conducted inthe Lake Nakuru Drainage Basin Area, have indicated a low resistivity layer sand withed between two high resistivity layers in earths subsurface. Below Lake Nakuru, the low resistivity layer extends both Northward and Eastward. The western part of the Lake is characterised by very high resistivities.The analysis of resistivity data was first done by partial curve matching prior to use of linear inverse theory in the determination of the most probable physical parameters of the subsurface layers necessary for two-dimensional interpretation of the underlying geology. From the results, three distinctive layers were recognised in terms of their resistivities and thicknesses. The main conductive layer is one of those three layers,immediately overlying the resistive substratum