Effect of Bent Flexible Vegetation on Fluvial-bed Change Under Flood Conditions

Jin-Fu LI and Su-Chin CHEN

To understand the effects of vegetation on sand-bed, we designed three different densities and nine random distributions of bent flexible vegetation in flume experiments. Current velocity was controlled to be larger than the critical velocity and sediments were supplied upstream during the experiment to simulate the real river condition under flood conditions. Ultrasound Velocity Profiler (UVP) was used to measure the flow field and a high-precision laser scanner (F5, Mantis Vision) was used to measure the final topography of sand-bed in each experiment. The results showed that the evolutionary process of sand-bed can be divided into four stages; scouring stage, growth stage, supplement stage, and deposition stage, forming a dynamic cycle. The deposition was dominant in front of the vegetation area, while scour dominated the area behind the vegetation. However, in the vegetation area, sand-bed was mainly affected by the concentration and blockage effects of vegetation, so it changed from depositional to erosive as vegetation density increases. The findings from this study will provide crucial information towards river management through understanding the links between channel bed, flow and vegetation.

2018/1 53-60