Runoff and soil erosion on cultivated rainfed terraces in the Middle Hills of Nepal

Abstract

The paper presents runoff and soil erosion measurements from plots on outward-sloping rainfed agricultural terraces in the Likhu Khola drainage basin, Middle Hills, Nepal, for the pre-monsoon and monsoon periods of 1992 and 1993. Runoff coefficients ranged from 5% to over 50%, depending on the nature of the rainfall event and the characteristics of the terrace. Total rainfall amount provided the highest level of explanation for the variation in runoff. Soil losses ranged from 2.7 to 8.2 t ha –1 for 1993 and up to 12.9 t ha –1 for 1992. The higher losses were associated with red, finer-grained soils. The majority of these rates are lower than the rates of soil loss that have been commonly perceived for the Middle Hills of the Himalaya. However, they are broadly similar to rates obtained from the few other studies that have examined runoff and erosion under traditional rainfed cultivation. The results suggest that a re-evaluation of the degree of land degradation in such areas may be necessary. Relationships between soil loss and rainfall characteristics were highly variable but were improved considerably when vegetation cover was included. This indicates that the maintenance of some form of ground cover is advisable if runoff and erosion are to be minimized.