Spatial and temporal variations of sedimentation rate in the Timah Tasoh Water Reservoir, Perlis, Malaysia

rvoir, Perlis, Malaysia. Human activities such as logging, land conservation, road construction and other disturbances in watersheds will increase erosion rate and thus the amount of sediment transported into the river that reaches lakes, rese-rvoirs and sea. Accelerated sedimentation rate in the reservoir can signifi cantly reduce a reservoir’s surface area, eliminating wetland area surrounding the reservoir and shallow the areas near the shore of the reservoir. A study of sedimentation rate in the Timah Tasoh water reservoir was carried out from May 2001 to April 2002 by means of sedi-ment traps. The aim of this study is to determine the spatial and temporal pattern of sedimentation rates in the reservoir. The sediment traps were installed at fi ve different locations in the rese-rvoir and replaced every month. Gross sedimen-tation rates measured in the sediment traps vary from about an average of 1.4 kg/m2/month or 16.3 kg/m2/yr in the deepest part of the reservoir to about 79.2 kg/m2/yr (monthly average of 6.6 kg/m2/month) and 47.1 kg/m2/yr (monthly ave-rage of 3.9 kg/m2/month) near the inlet of the Pelarit River and the Tasoh River respectively. The sedimentation rate near the Pelarit River and the Tasoh River infl ow is correlated with the water and suspended sediment discharge in the river, owing to its proximity to the rivers and the fl ooding effect, mainly during the wet season. The sedimentation rate decreases southward along the reservoir, as a result of increasing distance from the river mouth. The total suspended sediment load of the Upper Pelarit River and the Jarum River fl owing into the reservoir is 11.4 × 103 ton/year and 5.41 × 103 ton/ /year respectively. Key words: reservoir sedimentation, sediment trap, sediment discharge, Timah Tasoh, Perlis