Using Soil Erosion as an Indicator for Integrated Water Resources Management: A Case Study of Ruiru Drinking Water Reservoir, Kenya

Abstract

Functions and services provided by soils play an important role for numerous Sustainable Development Goals (SDGs) involving mainly food supply and environmental health. In many regions of the earth, water erosion is a major threat to soil functions and is mostly related to land use change or poor agricultural management. Selecting proper soil management practice, requires site-specific indicators such as water erosion, which follow a spatio-temporal variation. In this study, the Revised Universal Soil Loss Equation—RUSLE—complemented with the cubist-kriging interpolation method was applied to develop monthly soil erosion risk maps for the data-scarce catchment of the Ruiru drinking water reservoir located in Kenya. An erodibility map created with digital soil mapping methods (R2 = 0.63) revealed that 46% of the soils in the catchment have medium to high erodibility. The monthly erosion rates showed two distinct potential peaks of soil loss over the course of the year, which are consistent with the bimodal rainy season experienced in central Kenya. A higher soil loss of 2.24 t/ha was estimated for long rains (March- May) as compared to 1.68 t/ha for short rains (October- December). Bare land and cropland are the major contributors to soil loss. Furthermore, the spatial maps reveal that areas around the indigenous forest on the western and southern parts of the catchment have the highest erosion risk. In conclusion, erosion risk maps can be decisive for developing spatially explicit, efficient and timely soil management strategies thus allowing continued multi-functional use of land within the soil-water-food nexus.