Assessment of soil erosion in a tropical mountain river basin of the southern Western Ghats, India using RUSLE and GIS

Revised Universal Soil Loss Equation (RUSLE) model coupled with transport limited sediment delivery (TLSD) function was used to predict the longtime average annual soil loss, and to identify the critical erosion-/deposition-prone areas in a tropical mountain river basin, viz., Muthirapuzha River Basin (MRB; area = 271.75 km2), in the southern Western Ghats, India. Mean gross soil erosion in MRB is 14.36 t ha−1 yr−1, whereas mean net soil erosion (i.e., gross erosion–deposition) is only 3.60 t ha−1 yr−1 (i.e., roughly 25% of the gross erosion). Majority of the basin area (∼86%) experiences only slight erosion (<5 t ha−1 yr−1), and nearly 3% of the area functions as depositional environment for the eroded sediments (e.g., the terraces of stream reaches, the gentle plains as well as the foot slopes of the plateau scarps and the terrain with concordant summits). Although mean gross soil erosion rates in the natural vegetation belts are relatively higher, compared to agriculture, settlement/built-up areas and tea plantation, the sediment transport efficiency in agricultural areas and tea plantation is significantly high, reflecting the role of human activities on accelerated soil erosion. In MRB, on a mean basis, 0.42 t of soil organic carbon (SOC) content is being eroded per hectare annually, and SOC loss from the 4th order sub-basins shows considerable differences, mainly due to the spatial variability in the gross soil erosion rates among the sub-basins. The quantitative results, on soil erosion and deposition, modelled using RUSLE and TLSD, are expected to be beneficial while formulating comprehensive land management strategies for reducing the extent of soil degradation in tropical mountain river basins.