Rainfall Erosivity And Topographic Influences On Runoff And Soil Loss In Contrasting Soils In Chandel District Of Manipur

Abstract

Soil erosion remains one of the most pressing environmental challenges in hilly agro-ecosystems, threatening agricultural productivity, water quality, and ecological sustainability. This study examined the combined influence of rainfall erosivity, slope length, and slope steepness on runoff and soil loss in red sandy loam and dark clay loam soils of Chandel District, Manipur, during 2015-2016. Field experiments were conducted using runoff plots of varying slope lengths (5 m, 10 m, and 15 m) and slope gradients (0%, 2%, and 5%), with erosive storms monitored for runoff volume and soil loss. Rainfall characteristics were quantified using the EI₃₀ index, with mean rainfall intensity recorded at 18.4 mm h⁻¹ and mean erosivity at 645 MJ•mm•ha⁻¹•h⁻¹. Results demonstrated a strong positive relationship between slope length and runoff, indicating that longer slopes facilitated greater water accumulation and surface flow. Similarly, soil loss increased markedly with slope steepness, showing nonlinear behaviour under 5% slopes, which suggests threshold responses that intensify erosion risks. Soil type played a critical role, with dark clay loam soils exhibiting consistently higher runoff and soil loss compared to red sandy loam soils, due to their lower infiltration capacity and weaker structural stability. These findings highlight the synergistic effects of climatic, topographic, and soil factors in driving erosion. The study underscores the need for slope-specific and soil-specific conservation strategies, such as terracing, contour bunding, and vegetative barriers, to mitigate land degradation. Incorporating localized rainfall erosivity data into predictive models can further strengthen erosion management in fragile hill ecosystems.