Open channel flow through vegetation with different heights: Velocity characteristics

Vegetationof various heights commonly co-exists in natural rivers and wetlands, where vegetation becomes an important part of the flow processes, ecological environment, and habit biodiversity. Understanding the impact of vegetation on the velocity distribution and morpho-logic change has drawn great attention in river engineering and aquatic environmental management. Due to the complex interaction between vegetation and flow, most previous studies have mainly focused on the flow through single-layered vegetation over the entire channel.It remains un-known how the different height vegetation affects the flow structure in an open chan nel partially covered with vegetation, particularly the effect of lateral velocity distribution, which is pre-requisite for many problems in river engineering, stream bed and bank stabilization, and environmental management. In this paper, a novel experiment was conducted to investigate the flow characteristics in a flume partially covered with the vegetation of two different heights, focusing on the study of velocity changes vertically and laterally.Experimental results show that the vegetation will significantly reduce the velocity, resulting the low velocity in the vegetated zone and a large transition zone between the vegetated and non-vegetated zones. Due to the retarding effect of vegetation, the velocity profile in the vegetated zone differentiates from the one in the non-vegetated zone, where the logarithmic velocity profile does not hold in this case.