Profiles of Streamwise Velocity and Bed Topography in Area of Non-vegetated and Vegetated Sand Bars

Abstract

Sand bar is one of the bed features occurs resulting from the instability of flow and sediment in river. The existence of sand bar could alter the river channels in terms of channel geometry and flow properties. The sand bar can be formed in non-vegetated and vegetated conditions. The streamwise velocity and bed topography continuously changing at this bar as the flow and sediment were unstable. The profiles of the streamwise velocity and bed topography need to be observed to enhance the understanding on the effect of vegetated sand bars to the river system especially in terms of hydraulics and morphology. This study was conducted to provide an analysis of the streamwise velocity and bed topography in non-vegetated and vegetated sand bars. The study was based on the experimental approach. A straight flume channel with a size of 10 m long and 1 m wide was used. The bed and velocity profile as well as wavelength and height of bar were measured. It was found that the streamwise velocity reduced at the sand bar as the flow depth lower and increased at the opposite area. The presence of vegetation significantly increased flow resistance thus induced sediment deposition. The sand bars have shown an increasing approximately 15% for wavelength and up to 100% for height after vegetation was applied. Therefore, the sand bar was actively developed when vegetation grew on it.