River Input and Sedimentation Rate Threat to Bukit Merah Reservoir, Perak

Wan Ruslan ISMAIL, Sumayyah Aimi Mohd NAJIB, Zullyadini A. RAHAMAN
HydroGeomorphology Research Group, Section of Geography, School of Humanities, Universiti Sains Malaysia, 11800 Minden, Penang, Malaysia
E mail: wruslan@usm.my

Abstract

Bukit Merah reservoir in Perak, Malaysia, is one of the oldest reservoir in Malaysia which was built in 1902 and in operation in 1906. The fate of sedimentation in a water body such as reservoir is dependent upon the amount of sediment discharge of river inputs. The sediment discharge into the downstream water bodies is related to the erosion, transport and storage of sediment in the upstream or input channel. A study aimed to estimate the rate sedimentation Bukit Merah reservoir was carried out by monitoring river inputs and sedimentation rate in the reservoir in 2007. Four river inputs were monitored and sedimentation rate were measured at 5 locations in the reservoir. The four rivers comprises two major inputs- the Sg. Merah and Sg. Kurau; and 2 minor inputs- the Sg. Selarong and Sg. Jelutong. The present highest sediment discharge of Sg. Kurau for 2007 was estimated at 123 t day-1. Other inputs were Sg. Merah (9.8 t day-1) and Sg. Selarong (0.5 t day-1). The highest to the lowest suspended sediment yield from up-stream sources came through Sg. Merah (2.3 t km-2 day-1); Sg. Selarong (2.2 t km-2 day-1); Sg. Kurau (1.5 t km-2 day-1); Sg. Jelutong (0.5 t km-2 day-1).
The sedimentation rate was measured by means of an 8cm diameter PVC cylinder trap, deployed at a fixed location moored to the bottom of the lake with the trap stayed afloat about 1-2 meter from the water surface. The estimated average daily sedimentation rate was 71 t km-2 day-1. The high sediment yields and nutrients from feeder rivers could have encourage the growth of Bakong (Hanguana Malayana) that threatened and cause the surface area of the reservoir to shrink in size. Most of the nutrient came from the land uses in the catchment such as oil palm and rubber plantation. Almost 47% of the land use of Sg. Kurau catchment for example is rubber and oil palm. The dead plant tissues and sedimentation caused the lake depth to become shallower and the maximum depth now was only about 5-6 meters. Now, the water authority is clearing and dredging away the weedy plants and sandy material at the river mouth to enlarge capacity of water storage of the lake.