Identification of Soil Ero1sion Hotspots and Estimation of Sediment Yield Using Integrated GIS and Hydrological Modeling in the Dirma River Watershed, Lake Tana Basin, Ethiopia

Abstract

Soil erosion and sediment transport pose substantial threats to agricultural production, reservoir sustainability, and water quality in the Dirma River watershed of the Lake Tana Basin. This investigation sought to delineate erosion-prone areas and quantify sediment yield by integrating GIS-based multicriteria assessment with hydrological modeling. Spatial datasets from field surveys and government agencies were processed, and missing observations were estimated using the arithmetic mean method. Erosion susceptibility was mapped in ArcGIS by combining nine thematic layers through Weighted Overlay Analysis (WOA) and the Analytical Hierarchy Process (AHP). ArcSWAT, incorporating the Modified Universal Soil Loss Equation (MUSLE), was used to simulate sediment yield from long-term meteorological, hydrological, and suspended sediment concentration records. The model was calibrated for 2000–2013 and validated for 2014–2020 using SWAT-CUP. The spatial assessment categorized 2.1% of the watershed as low risk, 35.8% as moderate risk, 61.7% as high risk, and 0.4% as very high risk. Soil erodibility (K), support practice (P), and minimum land cover (C) emerged as the most influential model parameters. Model performance was satisfactory, with R² and NSE values of 0.82 and 0.73 during calibration and 0.78 and 0.87 during validation, respectively. Estimated average annual sediment yields ranged from 38 to 345 t ha⁻¹ yr⁻¹. These results offer evidence for targeting conservation interventions, reducing soil loss, safeguarding reservoirs, and supporting agricultural productivity and sustainable watershed management in areas with limited monitoring data.