Estimation of soil loss and identification of erosion risk zones in a forested region in Sarawak, Malaysia, Northern Borneo

Abstract

Soil loss has been quantified and land area categorized for soil erosion vulnerability in a partially forested subwatershed of the Baram River basin (Sarawak, Malaysia) using Revised Universal Soil Loss Equation, which considers climatic and terrain variables. The quantification of soil loss was achieved by integrating the parameters related to rainfall (R), soils (K), terrain (LS) and land use practices (C). The resultant maps of soil erosion show soil losses ranging from 0 to 1190 t ha -1 year -1 with a mean of 28 t ha -1 year -1 in the 1029 km 2 Sungai Patah subwatershed study area. The subwatershed was mapped using ArcGIS into five classes of soil erosion risk vulnerability. Among the five classes identified, very high and critically vulnerable zones show linear distribution in some areas which together constitute 13% of the total study area. High and medium erosion vulnerable zones cover 30 and 19%, respectively. Low erosion risk zones cover 36% of the total area. Mean soil loss assessed for each LULC (land use/land cover) class indicates that barren land with high slopes contributes comparatively high rates of soil loss (343 t ha -1 year -1 ). Field surveys in the study region have enabled identification of erosion hot spots, such as logging areas, shifting cultivation areas and road construction, which intensely modify the terrain, and explain the linearity of critical and severe erosion risk features. The output of the present study will help to frame appropriate management strategies to minimize erosion through implementation of alternative methods in logging activities and terrain management programs.