Effects of land use and management systems on water and sediment yields: Evaluation from several micro catchments in Southeast Asia

In an effort to develop economically promising and environmentally benign catchmentscale upland management systems, the Management of Soil Erosion Consortium (MSEC) initiated intensive soil erosion studies in selected catchments in the Philippines, Thailand, Laos, Vietnam, Nepal, and Indonesia. Hydrological stations were equipped with automatic water level recorders and staff gauges to measure water and sediment yields from each catchment and sub-catchment. Rainfall data were collected using automatic weather stations and manual rain gauges. Sediment and water yields were analyzed as these relate to land use and management systems at the micro catchment scale. The analysis showed that land use and management techniques greatly affect sediment and water yields. Catchments with good landscape filter systems such as orchards and forest with natural undergrowth, and catchments with grass strips as hedgerows showed better control of erosion than those under intensive cultivation of annual crops, or perennial trees but no undergrowth cover. Smaller sub-catchments used intensively for annual crops exhibited a shorter lag time between the peak of rainfall and the peak of runoff. Moreover, their runoff coefficients were relatively higher than those of catchments with perennial trees and good undergrowth and litter cover. This translates to the higher flood mitigation functions of better-covered catchments. Erosion from paddy fields is negligible and usually higher during tillage operation. Better regulation in waterflow between plots can significantly control the sediment outflow from terraced paddy fields.