Mapping of Point and Non-Point Sources of Pollution within Nairobi River Basin and Mbagathi Sub-Basin

Abstract

Water is the source of life covering 70% of the Earth surface. However only a small portion of this precious natural resource is fit for human consumption. We mapped various point and non-point sources of pollution within Nairobi River Basin and Mbagathi Sub-basin, with aim of taking an inventory for future clean ups and protection of the basins. The water from the basins flow to Tana River basin downstream of Nairobi and Mbagathi Rivers. Nairobi River Basin (NRB) is traversed by several rivers that include; Ngong/Motoine, Nairobi, Mathare, Kiu, Riara, Ruiru and their tributaries. This research was conducted through field assessment by taking GPS coordinates of possible pollution points downstream of the suspected area of pollution. Insitu physiochemical analysis of COD, TDS, EC, BOD, T ALK and TSS done and samples were taken for analysis of heavy metals and pesticides. QGIS version 2.6 with the shapefiles of Kenya water basins, Kenya major rivers and tributaries, wetlands, protected areas and forests and major towns were used in mapping of these points within the basins. There were high values of physiochemical parameters in the mid catchment, TDS of 6146, COD of 4314 and high traces of heavy metals in the mid catchment, pesticides in the upper and lower catchments. It was therefore concluded that much of the pollution in Nairobi and Mbagathi sub basin emanate from poor management and handling of waste water and from anthropogenic activities such as settlements/build up areas and Agriculture. Pollution is mainly from sewer line discharges, effluents from the Water Services Providers, solid waste disposals and industrial effluents at the middle catchment, sediments and pesticides/herbicides from farming activities within the upstream and downstream parts of the sub catchments.