SEDIMENT YIELD AND LAND-USE IN TROPICAL CATCHMENTS

Analysis of sediment yields from 61 Kenyan catchments allows the refinement of regional relationships between the yields and their major controls. Land use, which has been ignored in earlier regional analyses, is the dominant control, but within each land-use category it is possible to recognize the effects of the climatic and topographic variables that other writers have stressed. The long-term geologic rate of erosion in these tropical environments is estimated to vary between 20 and 200 t km-2 yr.-1, depending mainly upon climate. These values agree closely with Douglas' estimate for undisturbed catchments. An analysis of the major sources of sediment in disturbed catchments suggest that rural roads contribute a large, and commonly ignored, fraction of the sediment leaving agricultural areas. The temporal pattern of sediment transport is also affected by land use, and emphasizes the significance of rare wet periods in the removal of soil from tropical catchments. © 1979.