Soil Erosion and Hydrological Study of the Bakun Dam Catchment Area, Sarawak Using Remote Sensing and Geographic Information System (GIS)
Roslinah Samad, Norizan Abdul Patah
Malaysian Centre For remote Sensing (MACRES),
P.P. Box 208, Lot CB 100,
5th Floor, City Square Centree,
Jalan Tun Razak, 50400 Kuala Lumpur, Malaysia.
Tel: 603-2645640, Fax: 6032645650,
E-mail : ipa@macres.gov.my
Abstract
The Universal Soil Loss equation (USLE) was applied to predict annual soil loss in the study area, using the integration of satellite remote sensing and Geographic Information System (GIS) technologies. Parameters of the USLE used to generate the relevant raster layers for soil erosion spatial modeling in the GIS are - (i) rainfall erosivity, (ii) slope length/gradient, (iii) cover- conservation method and (iv) soil erodibility. The analysis was done in MICSIS (Micro-computer spatial Information system), an image processing and GIS software package developed specifically for erosion modeling under the Malaysian-China coorperation, In the hydrological study, a three dimensional (ec) animation package (ed Studio software) was used to computer water inundation extent and storage at three flood levels in the catchment area of the Bakun dam. The current and potential erosion risk maps of the study generated, which will be useful for planning the land clearing activities at Bakun and estimating the severity of soil sedimentation in the dam area. At three predetermined flood levels 233 m, 228 m and 195 m, the extents of inundation, indicating the types of land cover affected, have been located. The extents of inundation the types of land cover affected, have been located. The corresponding water storage volume in the Bakun catchment at the three flood levels were also estimated.
1.0 Introduction
Soil erosion is one of the most serious environmental problem where its remove soils rich in nutrients, increase natural level of sedimentation in the river and cause flash flood at the construction area. Most of the soil erosion study done by other researchers were based on the Universal Soil Loss Equation (USLE) (Wischmeier and Smith, 1978) as a method to predict the soil loss. USLE take into account several factors such as rainfall, soil erodibility, slope, land cover and erosion control practice for soil erosion prediction. In this study, remote sensing date was used to drive land cover/use map for the Bakun catchment area. Malaysia and China embarked on this cooperative project during the period November 1995 -April, 1996. The objectives of the project were to output: (i) the soil erosion risk map of the study area, (ii) a general hydrological model to monitor inundation extent of the study area on a regular basis. However, this study was done to implement a special system for soil erosion modeling in Micro Computer Spatial Information system (MICSIS) which based on the parameter of USLE and also hydrological modeling.
2.0 The Study Area
The Bakun catchment area is located between latitudes 1.5°N and 3.0°N and longitudes 113.5°E and 115.3°E, encompassing Balui River and its tributaries some 37 km upstream of Belaga town.Its covers about 14,750 km
2 and its current land use/cover types are primary Forest (74%), selectively logged forest (21%) and shifting cultivation together with grass
Land/bust land (5%). The climate is characterized by an annual precipitation exceeding 4000 mm, mean annual evapotranspiration of about 1300 mm and average temperature of 25°C.
3.0 Materials
landsat TM data (1988 and 1994) with false colour composites band 4,5,3 were used in this study. Reainfall data, soils map and tophographic maps at scale 1 : 25,000 also were used as an ancillary data.
