Study of Flow Characteristic of Side Channel Spillway at Flood Control Dry Dam

Spillway is a structure that provides controlling exceeding water as water reaches elevation limit of reservoir. Outflow that overflows a weir occurs flow characteristic changes from upstream to downstream. Those characteristic changes are consisted of flow velocity, Froude number, and water level. Flow velocity that comes from upper stream should be reduced to prevent from scoring and damaging downstream structures. One of methods to reduce energy caused by flow itself is using baffle block. According to previous studies, C-shape and Stepped shape baffle block produces better performance than the one used in Ciawi dam (USBR Type II) in aspect of their physical modelling case. This study aims to compare actual baffle block in Ciawi dam with 2 other baffle block shapes with FLOW-3D numerical modelling. Dimension of each baffle block models were calculated based on USBR guideline. As a result of study analysis, USBR Type II is the most effective shape in reducing hydraulic energy with Q100, Q1000 and QPMF while C-shape and Stepped-shape resulted acceptable energy reduction with Q100 and Q1000 only.