Author(s): Xiaonan Tang; Suyang Zhang; Jiaze Cao; Hanyi Wang; Nanyu Xiao; Yutong Guan

Linked Author(s): Xiaonan Tang

Keywords: Vegetated flow; Multiple vegetation; Aquatic environment; Velocity; Open-channel

Abstract: Vegetation of various heights widely co-exists in natural rivers and wetlands, where the ecological environment and flow process are affected by the riparian vegetation, which has drawn great attention in river engineering and aquatic environmental management. Majority of studies in the past have been mainly focused on the understanding of flow through vegetation of single-layered vegetation. However, in natural riverine environments, mixing vegetation with different heights often occurs in natural rivers, which have a different effect on the flow than the single-layered vegetation does. In a flow condition under multiple layered vegetation, it is limited known about the impact of such vegetation on the flow velocity of channel, which is pre-requisite for many problems in river engineering and environmental management. In this paper, a novel experiment was designed to study the flow characteristics in an open-channel with vegetation of three different heights that exists on the channel bed, with a focus on the effect of the vegetation on the velocity distribution. Experiments were conducted in both partially submerged and fully submerged conditions. Three heights of dowels, 10, 15 and 20 cm, were used to mimic rigid vegetation in a staggered pattern for each type of dowel. Velocities at various locations across a section of channel were measured by Acoustic Doppler Velocimetry (ADV) and propeller velocimetry. Experimental results showed that the vertical velocity distribution is affected by vegetation heights. The results also revealed that the vegetation height have significant impact on the vertical distribution of velocity between and behind the vegetation. The vertical change of velocity behind TP (tall vegetation) and MP (medium vegetation) increases slowly beneath medium vegetation’s height (15cm) and then rapidly increases to the water surface. While the vertical change of velocity behind SP (short vegetation) and BP (blank space between vegetation) decreases a short amount beneath water height 5cm and increases rapidly to the water surface. Generally, the steamwise velocities at short vegetation zone and blank space are larger than tall vegetation zone and medium vegetation zone. These findings on the flow with multiple layered vegetation would be helpful for riparian management practices to maintain healthy ecological and habitat zones.

DOI: https://doi.org/10.3850/IAHR-39WC252171192022133

Year: 2022