RUSLE-Based Estimation of Annual Soil Loss and Its Environmental Geoscience Implications in the Mansiri River Basin, Assam, India

Abstract

Soil erosion poses a major environmental and agricultural threat, depleting fertile topsoil, reducing crop productivity, and increasing sedimentation in river systems. The Mansiri River Basin in Assam, situated within the dynamic geomorphic setting of the Brahmaputra valley, is highly susceptible to erosion due to its fragile terrain, intense monsoonal precipitation, and rapid land use transformation. This study assesses the spatial variability and magnitude of annual soil loss in the Mansiri basin using the Revised Universal Soil Loss Equation (RUSLE) integrated with Geographic Information System (GIS) techniques. The model incorporates key parameters—rainfall erosivity (R), soil erodibility (K), slope length and steepness (LS), cover management (C), and conservation practices (P)—to estimate soil loss and identify erosion-prone zones. The analysis reveals that annual soil loss in the basin ranges from 0 to 1038 t/ha/yr, with pronounced spatial variability across physiographic zones. Approximately 63.75% of the total area experiences low erosion rates (0–2 t/ha/yr), indicating relatively stable soil conditions under dense vegetation and minimal slope gradients. Moderate erosion (2–5 t/ha/yr) affects 34.18% of the basin, while about 2% of the area—primarily in the downstream and deforested sectors—faces high to very high erosion risk (>5 t/ha/yr). Rainfall intensity, loose soil texture (particularly silty loams), and sparse vegetative cover were identified as the dominant drivers of soil loss. The findings underscore the urgent need for location-specific soil conservation strategies such as contour bunding, agroforestry, vegetative barriers, and small check dams to mitigate erosion and sediment transport. The study demonstrates the efficacy of integrating RUSLE with GIS and remote sensing datasets for watershed-scale erosion assessment and management planning. Overall, this research provides a scientific basis for developing sustainable land management and conservation policies to safeguard agricultural productivity, water quality, and ecological stability across the Brahmaputra valley region.