GIS-based RUSLE assessment of soil erosion risk and sediment contribution in the Adhaim Dam watershed, Iraq

Abstract

In arid and semi-arid areas, soil erosion is a significant environmental issue, as it causes land degradation, transportation of sediments, and loss of reservoir storage capacity. The present study aimed to estimate the spatial distribution of soil erosion in the Adhaim Dam watershed in Iraq by applying the Revised Universal Soil Loss Equation (RUSLE) coupled with geographic information system (GIS) and remote sensing techniques in the watershed of 11,905 km2. Rainfall erosivity (R), soil erodibility (K), slope length and steepness (LS), cover-management (C), and support-practice (P) factors were computed using CHIRPS rainfall data, FAO soil data, a 30-m Copernicus DEM, and Sentinel-2 imagery. The estimated gross annual soil loss was about 39.98 million t/year (or 33.31 million m3/year assuming a sediment bulk density of 1.2 t/m3). The sediment delivery ratio is approximately 32% as determined by comparison with the sediment reported delivered to Adhaim Reservoir (10.4 million m3/year). Spatially, 65.62% of the watershed was determined to be very low erosion risk, 18.62% low, 6.38% moderate, 2.78% high, 0.62% very high, and about 6% no data. The results indicate priority areas for erosion that can be mitigated through the implementation of check dams, revegetation, and better land management practices that will result in less sediment being delivered to the reservoir and ensure long-term storage sustainability.