PHYSICAL MODELLING SIMILITUDE : A STUDY OF SEDIMENT DEPOSITION IN RESERVOIR

Abstract

Changes in rainfall pattern, rapid urbanization, infrastructure development and uncontrolled agricultural activities have been found as major sources to contribute to excessive reservoir sedimentation problem in Malaysia, thus significantly shorten the design life of a reservoir. Hence, reservoir functions have deteriorated, such as reduction in power generation capacity, additional lateral load affected to dam stability and decrease in storage capacity for flood control. The objective of this study is to model, simulate and propose alternative method for sediment removal control in Ringlet Reservoir. The construction of physical model of Ringlet Reservoir took place in the Hydraulic and Instrumentation Laboratory, National Hydraulic Research Institute of Malaysia (NAHRIM), with geometric similitude of 1:30. Three different average recurrent intervals (ARI) of 1, 5 and 100 were tested at Sungai Habu and Ringlet. Groyne was identified as a control mitigation structure for sediment control, and a total of 23 groynes were constructed. Physical modelling execution explicitly showed the gross deposition and erosion is linear as the return period rose. Bed sediment for a 100 year ARI was eroded more than that of 1 and 5 year ARI, due to local scour resulting from the flow transition from fixed bed to mobile bed. At Ringlet, sediment was deposited mostly before the first check dam for 1 year ARI. For 5 and 100 ARI, sediment was further transported before the second check dam. Finding in Habu, showed morphological changes was due to the local flow. The movement of bed sediment at the end of Habu, were deposited much early before the check dam, thus not travelling further downstream. Geometrical similitude of this modelling was carried out successfully, and gained recognition from the Malaysia Book of Records as the Biggest Hydraulic Model.