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Assessment of Soil Erosion in Uma Oya Catchment, Sri Lanka

Soil erosion is one of the major threats which affects farm productivity and water quality in river catchments. Quantification of human-induced soil loss is an imperative measure in catchment management. Among the catchments in Sri Lanka, the highest sediment yield has been reported from the Upper Uma Oya catchment (UOC) which is a sub-catchment of the Upper Mahaweli catchment. The Mahaweli watershed is the most important watershed in Sri Lanka since the size and the economic importance of it. Hence, this study was conducted considering the ten selected sub-watersheds of Uma Oya Watershed (UOW) in Sri Lanka to quantify soil erosion. Soil erosion of UOW was calculated using Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) Sediment Delivery Ratio (SDR) model. It was found that the current soil erosion rates in the watershed is varied between 14.0–648.6 t/ha/yr. Results of the study disclose that the soil erosion rates of UOW are 3 to 130 times faster than the soil loss tolerance in Sri Lanka. Findings of the study suggest that the implementation of sustainable watershed management options are crucial in order to reduce soil erosion and to enhance the quality of the watershed.