Erosion in the Western Middle Mountain Watersheds of Nepal : A Review

Soil erosion and mass movement are the major causes of the middle mountain environmental degradation in Nepal. The middle mountain region comprises about 30% of the country area, which ranges between the elevations of 300 m to 3000 m above the sea level. The number of landslide distribution per 100 ha area in 5 different watersheds varies from 0.89 to 3.20. The number of landslides by land use type per 100 ha is largest at grassland with 6.98, followed by non-irrigated cultivated land with 1.90 and least at irrigated cultivated land with 0.85. The shallow landslides are greater in number at above 30° slope angle. The estimated soil loss from grassland and farmland is more than 170-180 ton/ha/year. The onsite significance of surface erosion is reduction of the productivity. While its off-site significance is in causing siltation, water pollution etc. in the downstream areas.