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Abstract This study illustrates the spatial variability of erosion and subsequent sediment transportation rates in heavy rainfall regions of the Himalaya through a watershed based RUSLE geospatial modelling. The selected watershed, viz. Siji watershed falls in the Gai river basin, eastern Himalaya, Assam (India). Geospatial modelling analyzed all key parameters of the Revised Universal Soil Loss Equation (RUSLE) model: rainfall erosivity (R), soil erodibility (K), topographic factor (LS), cover management (C), and support practice factors (P) are considered for analysis of average annual soil loss. The RUSELE test values of these five key parameters integrated to generate an erosion intensity map of the watershed, advocates that the spatial variability of sediment transportation rates ranges from 0 to 383.37t ha-1 year-1 under diverse geo-environmental conditions. The areas of thick forest cover and low slope gradient have very low rate of erosion and sediment transport (< 25t ha-1yr-1), the areas under shrubs land, built-up land it ranges 25-50t ha-1yr-1, the areas under crop land, barren land with steep slopes it ranges 50-200t ha-1 year-1, whereas the areas under river banks, landslide zones, new road construction sites, excavation sites have highest rates of erosion and sediment transportation, ranges 200-383t ha-1yr-1. Result reflects that geo-environmentally the region is highly vulnerable to erosion and sediment transportation due to highly erodible, fragmented geomorphology, unconsolidated rocks, and heavy annual rainfall (1600–3600 mm). Despite that, anthropogenic activities have been enhancing this geo-environmental vulnerability, causing accelerated erosion and sediment transportation rates. The key anthropogenic activities which are responsible for accelerating erosion and sediment rate in the study area are identified as quarrying, mining; excavation on a large scale using heavy digging machines, land use change, deforestation, and shifting cultivation practices a large scale. Therefore, there has been an urgent need to address this worsening environmental issue to avert its associated natural hazards and disasters in the near future. To mitigate the accelerated rates of erosion and sediment transportation, the present study suggests an integrated watershed management (IWM) plan for the study area, which can be implemented across the Himalaya mountain region as well as across the globe, having similar geo-environmental characteristics.
Rawat et al. (Mon,) studied this question.