Author(s): Yuhong Zeng; Jing Qin; Yongyan Wu; Wenxin Huai
Linked Author(s): Wenxin Huai, Yuhong Zeng, Yongyan Wu
Keywords: Vegetation roughness; Lateral momentum exchange; ADV; Mixing layer; Quadrant analysis
Abstract: Natural rivers are commonly covered with randomly distributed vegetations, and the vegetation may not fully cover the channel bed. In this paper an idealized parallel flow caused by lateral bed roughness difference due to partial vegetation across the channel was investigated. Similar with compound channel, there are mixing layers adjacent the interface between the roughness side and smooth side, and lateral momentum exchange will occur between the slow-moving water in the roughness lane and the fast-moving water in the smooth lane. Under a uniform flow condition, the 3-D instantaneous velocities of two cases of experiment with different discharge and water depth have been measured by a 16M Hz Acoustic Doppler Velocimeter (Micro ADV). The longitudinal variation of streamwise velocity, vertical variation of Reynolds stress etc were analyzed, and quadrant analysis was adopted to investigate the outward and inward interaction, ejection and sweep phenomenon caused by vegetation variation across the channel. The results show that the flow character on the vegetation lane is similar to open channel fully covered with submerged vegetation, and flow character on the smooth lane is similar to that on a free open channel. There is a mixing layer between the fast moving smooth and slow moving vegetation lane, and for the cases studied here the width of the mixing region is about 10% of a single lane on located mainly on the smooth half.