Groundwater Mapping of Makueni County, Eastern Kenya Using Remote Sensing and Geographical Information System (GIS) Technologies

Abstract

Occurrence of groundwater in the basement complex terrain of Makueni County, Eastern Kenya is controlled by secondary porosity developed through weathering, fracturing and cracking of the bed rocks. Makueni falls in semi-arid region that is characterised by erratic rainfall. Surface water from a very few rivers is inadequate and the only option to supply both human and animal population is groundwater. To avoid the ever common incidences of borehole failing to yield any water or drying up soon after commissioning, groundwater mapping is paramount. In this study, remote sensing (RS) and Geographical Information System (GIS) techniques have been used to identify and map groundwater potential zones using rainfall, drainage and drainage density, lineament, geology, soil texture, slope and land cover. These thematic layers were selected for groundwater mapping based on literature and geophysical investigations and data appropriately weighted in a modified DRASTIC model based overlay scheme. Land cover was derived from Land sat imagery classification with lineament density being obtained from the same satellite imagery/product. The Geospatial evaluation produced a groundwater potential map in which the study area was characterized into zones; very good, good, moderately good and poor. The map showed that the central and eastern regions of Makueni County are the most suitable for groundwater exploitation.