Ground subsidence and its socio-economic implications on the population: acase study of the Nakuru area in Central Rift Valley, Kenya

Several areas of Nakuru Town and its environs often undergo subsidence alon g the parallel fault zones during and after heavy rainfall. During the rain y season, when most of the subsidence occurs, the overlying unconsolidated volcanoclastic sediments become oversaturated with water. The water reduces the shear strength of the sediments and also introduces extra loading thro ugh saturation leading to subterranean erosion along faults. The unconsolid ated sediments then collapse into the subsurface water channels which close ly follow the fault zones, leading to formation of "sinkholes". The frequen t incidences of ground subsidence in the study area, have caused several fa talities, destroyed settlements and physical infrastructure. Furthermore pe rsistent subsidence has increased the cost of construction and the repair o f the destroyed properties. Apart from being hazardous, ground subsidence d egrades environment when sewage water, refuse and garbage enter into the gr oundwater systems through the sinkholes. The fissures formed after subsiden ce also stand prominently as ugly features from the rest of the terrain. Mi tigation measures including control, channelizing of drainage, proper engin eering practices and appropriate land use are suggested in this paper.