Abstract

Erosion susceptibility studies on a basin scale is critical to integrated water resources planning of a river basin. Rapid urbanization, uncontrolled deforestation and overgrazing have made these studies even more important for development of strategies for soil conservation and land management in river basins. In this study, maps were developed to describe the spatial susceptibility to soil erosion within the Owena River basin using the RUSLE model. The parameters of the model include rainfall erosivity factor, soil erodibility factor, slope steepness and length factor, cover management factor and support practice factor. Rainfall erosivity was high in the southern and coastal parts of the river basin (RB) but had little erosion severity impact due to low slope steepness and length factor, and low cover management factor that characterized most of the RB. These low values were due to the flat topography of the basin and that 89% of the basin is of dense vegetation landscape. The soil erodibility range for the RB was low to moderate. The predominant soil erosion rate estimated was 0 – 10 ton/ha/yr and it covered 97% of the RB. This range implies that soil loss due to water erosion in the basin was low to moderate. However, low to moderate soil erosion susceptibility degrades agricultural topsoil in long-term, underscoring the need for sustainable land use and agricultural practices. High to severe erosion rates affected 1, 646 hectares of the RB and was mostly in grass lands and urban areas of the RB. This is attributed to rapid urbanization, which increased runoff and its erosive force, and overgrazed grasslands, which are more vulnerable to erosion due to vegetation loss. The annual soil loss for the whole RB is 5.5 tons/ha/yr while the total the annual soil loss from the RB was calculated as 38, 316 tons. This study has provided important information on parts of the RB needing targeted soil conservation and land management applications.