Understanding the linkages between land-use transitions and soil erosion/sediment deposition: A case study of the transboundary Sio-Malaba-Malakisi watershed in Kenya and Uganda

Abstract

Soil erosion consequent of unsustainable land-use practices represents one of the world's most pressing environmental problems affecting many watersheds. An assessment of sediment sources and delivery paths is essential for the development of site-specific soil management strategies for curbing environmental degradation. The present study employed a physically-based lumped approach to estimate soil erosion and sediment deposition patterns across the transboundary Sio-Malaba-Malakisi (SMM) watershed. The Unit Stream Power-based Erosion Deposition (USPED) model was adopted for the study, and integrated with physically-based parameters derived in a Geographical Information System (GIS). A land-use map for 2017 was used for simulating the reference soil erosion and deposition status of the basin. Furthermore, the impacts of two land-use scenarios representing options for cropland expansion (Scenario-I), and land reclamation (Scenario-II), were evaluated for the period 2047, corresponding to a thirty-year period used in assessing catchment management planning for SMM. The annual soil erosion ranged between 0 and 460 t. ha−1yr−1, with a mean erosion rate of 160 t.ha−1yr−1 for the baseline condition. Deposition zones were mainly concentrated along stream banks and floodplain in low-lying sub-catchments. The mean soil erosion rate increased by 61 % and 16 % for scenarios I and II respectively. Overall, the modelled erosion/deposition values were correlated with available sediment data for the basin, realizing a coefficient determination (R2) value of 0.74. These results could serve as a benchmark against which future trends in land-use changes can be compared in the region and hence support the development of regional soil erosion conservation strategies.