GIS-RUSLE Interphase Modelling of Soil Erosion Hazard and Estimation of Sediment Yield for River Nzoia Basin in Kenya

Abstract

River Nzoia basin is predisposed to degradation attributed to poor anthropogenic land use practices, soil erosion and sedimentation. The objective of this study was to model soil erosion hazard and estimate sediment yield for river Nzoia basin. Database of the basin comprised of 90 m DEM, LandSat imagery, rainfall, and soil data. Simulated RUSLE model factors (R, K, LS, and C) were multiplied using the raster calculator in ArcGIS 10.1. This generated the soil erosion hazard map for river Nzoia basin with an average annual soil loss rate of 0.51 and a maximum of 8.84 Mton ha-1 yr-1. This translates into a mean annual soil loss of 6.579 × 105 Mtonyr-1. Sediment Delivery Ratio (SDR) of 0.121 revealed that 87.9% of the soil eroded by water in the basin is deposited before reaching the basin outlet. Average annual sediment yield estimated was 0.06 Mtonyr-1. Soil erosion modeling results showed that river Nzoia basin is experiencing varying erosion rates spatially. The interplay among the RUSLE factors strongly influence average annual soil loss rates. Areas experiencing high soil loss rates are closely linked to annual cropland, deforested and high elevation points. Low rates of soil loss are attributable to soil conservation practices and protected areas such as game parks. Thus, there is a close coupling between soil loss and land use category in river Nzoia basin. Sustainable land use practices should be embraced to support conservation programmes to mitigate soil erosion, prevent sedimentation and reduce sediment yield in the river channel.