Erosion and Sedimentation at Headwater Stream: A Case Study for Pergau Water Intake

Abstract

Headwater stream can be defined as colluvial and fluvial system located at mountainous areas where stream order of less than four is recorded from the source to the outlet point of interest. This river system is crucial not only for impounding activities but high kinetic energy at highland areas able to entrain and transport large amount of sediment particles from upstream to the downstream river reach. Due to strategic location for water intake facilities, a study was carried out to determine the extent of erosion and sedimentation process at Pergau water intakes that conveyed water into Pergau Lake. Three specific aims were formulated: Soil loss determination at catchment scale, sediment load determination at reach scale and river bank stability and toe erosion near the intake facility. A desktop study using remote sensing and GIS tools was executed to determine the extent of soil loss at catchment scale. The sediment load and river bank stability were measured in the field using wading technique. It was concluded that all seven TNB water intake are having low soil loss rate (<10 ton/ha.year) should the current settings of forest land cover is maintained. The recorded sediment load (bed load) only occurred at Suda and Renyok 1 water intake with a rate of 0.0024 kg/s and 0.03 kg/s, respectively. High eroded material at toe was simulated at Renyok 1 and Suda Intake. The high sediment load at Renyok 1 is a manifest from unstable toe material near the water intake. Therefore, a close monitoring should be attained at the upstream from Renyok 1 intake to assess any land use change or disturbance activities.