Estimation of Soil Erosion Rates and Eroded Sediment in a Degraded Catchment of the Siwalik Hills, Nepal

The Siwalik Hills is one of the most fragile and vulnerable ecosystems in the Nepalese Himalaya where soil erosion and land degradation issues are fundamental. There is very limited knowledge on soil erosion processes and rates in this region in comparison to other regions of the Himalaya. The aims of the present paper are to document, measure and interpret key soil erosion processes and provide an estimate of erosion rates in the Khajuri Stream catchment located in the eastern Siwalik Hills. We used erosion pins to monitor sheet erosion, gully erosion, landslides and stream bank erosion over the period from 2002 to 2004. Sheet erosion from forest and shrubs generally varied from 0.8–1.2 mm·yr⁻¹ with a mean erosion rate of ~16 t·ha⁻¹·yr⁻¹. Gully erosion rate was estimated to be ~14 t·ha⁻¹·yr⁻¹. Erosion from landslides was significantly higher which was estimated to be ~26 t·ha⁻¹·yr⁻¹. Stream bank erosion varied widely from 0.03 to 0.25 m·yr⁻¹ with a mean erosion rate of ~8 t·ha⁻¹·yr⁻¹. Based on these rates, it was estimated that ~21,000 m³ (64 t·ha⁻¹) of sediment was being eroded within the catchment annually. In comparison to the erosion rates of other regions of the Himalaya these rates are significantly higher.