The use of InVEST-SDR model to evaluate soil erosion and sedimentation in the closer catchment of a proposed tropical reservoir in Sri Lanka

Soil erosion is a significant environmental threat, impacting water quality and the siltation of the productive capacity of reservoirs. To prioritize soil conservation areas for sustainable land management, quantitative spatial assessment of soil erosion is essential, particularly in the catchment of a reservoir. The current study aims to evaluate the soil erosion severity and sediment generation in the closer catchment of a proposed reservoir, the lower Malwathu Oya Reservoir in Sri Lanka. Erosion modeling has proven cost-effective in assessing the spatial distribution of soil erosion severity. This current study utilized the Integrated valuation of ecosystem services and tradeoffs sediment delivery ratio (InVEST-SDR) model to analyze the spatial distribution of soil erosion and sediment export. A digital elevation model (30 m × 30 m), 22 years of rainfall data, land use and land cover data, soil map, and cropping factors were used as model inputs. The results revealed an average annual soil loss ranging from 0 to 15.55 t/(ha·y) in the catchment and a mean annual sediment export of 0.016 t/(ha·y). Erosion severity was classified into four hazard classes, i.e., insignificant (<0.5 t/(ha·y)), weak (0.5–3 t/(ha·y)), considerable (3–12 t/(ha·y)), and severe (12 < t/(ha·y)). A critical 0.12% area was identified as a considerable soil erosion hazard area, necessitating urgent measures for erosion control. High-risk areas were at Galpottegama, Asirikgama, Puleliya, Navodagama, and Thuppitiyawa Grama Niladari. These findings provide valuable insight for formulating and implementing soil conservation practices in the catchment to reduce the siltation of the proposed lower Malwathu Oya reservoir. The study is an example of using InVEST-SDR to evaluate the sedimentation of a proposed reservoir.