Rain erosion hazard evaluated from microtopographic erosion features on arable fields and forest: A case study in Nepal

Erosion hazard has been studied under the existing conditions in 12 sites, representative of physiographic landscape units in the Likhu Khola watershed, which is located 50 km. northwest of Kathmandu, Nepal. For this purpose the accumulated effect of erosion has been recorded as expressed by microtopographic erosion features formed in a rainy period. Seven types of microtopographic features are used: resistant clods, eroding clods, flow paths, prerills, rills, depressions and basal plant cover. As a measure of erosion hazard, the observed erosion intensity was expressed by an indicator using the percentage of shallow flow features and the more heavily weighted features of incision. Soil erosion hazard on the maize-wheat sites was found to be various, partly due to different soil surface texture of the sites. The hazard was lower on sites of dense Sal forest. Crown canopy, a seasonal litter layer and a good permeability limit the erosion. The erosion hazard is lower still on sites with degraded Sal forest. These sites have a substantial basal plant cover. The erosion intensity derived from microtopographic features did not correlate with results of the Bouyoucos test, but had a good correlation with the Crusting index.