Geophysical, geological and hydrogeological studies of groundwater distribution and flow in Nairobi urban area
Abstract
The study area is covered by a succession of lavas and
pyroclastics of Cainozoic age. These volcanic lavas are
associated with tectonic movements related to the rift system.
Generally, these rocks do form groundwater potential, when
they are weathered, fractured and where they form contact
zones between two successive lavas and or Old land surfaces.
Thus, the distribution and flow of the ground water are
governed by the rock structures, which are the subject of this
study. The Resistivity survey was carried out in the research area
and curve marching with computer program based on the linear
inverse theory were used to determine the physical parameters
of the subsurface layers. Geophysical and geological data
analyses have identified three geoelectrical units with
contrasting thicknesses and depths. The upper and the lower
units are conductive forming underground aquifers. The lower
conductive layer which underlies the whole of the study area
forms the main aquifer in the area. Geoelectrical profiles
have also identified horst and graben structures which affect
the flow of the water. The horst structures normally control
the lateral flow of ground water, while the grabens determine
the drainage pattern.