Impact of Partially-covered Mixed-heighted Vegetation on the Lateral Velocity and Discharge of Open Channel Flow

Vegetation of various heights commonly co-exists along natural rivers and wetlands, where sediment, ecological environment, and habit biodiversity are drawing increasing attention in the research in eco-environment and river restoration. In the past, many researchers studied the impact of vegetation on the flow, such as velocity, flow resistance, and Reynolds stresses. Due to the extremely complex interaction between vegetation and flow, previous studies mainly focus on uniform vegetation through flow in open channels. However, in natural rivers, vegetation of various heights often co-exists and grows along the river bank. In this regard, flow characteristics in such flow conditions, i.e., flow with a mixing array of short and tall vegetation along a channel, are not yet understood. This paper is to perform a novel experimental study on a water flume, which is partially covered by mixed vegetation of different heights along one side of the channel, to understand the effect of vegetation on the lateral distribution of velocity and discharge. Two different heights of dowels, 5 cm and 10 cm, were used in the water flume of Xi’an Jiaotong-Liverpool University (XJTLU) to represent the short and tall rigid vegetation, respectively. Experiments under a certain flow depth were undertaken to represent different submergence ratios of vegetation and velocities at various locations, which were measured by a micro propeller velocimetry. Experimental results show that the vegetation will significantly reduce the velocity, resulting in 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. The results also show that the discharge in the vegetated zone is much lower than that in the non-vegetated zone for the same width.