Abstract
In order to experimentally investigate the effects of rigid vegetation on the characteristics of flow, the vegetations were modeled by rigid cylindrical rod. Flow field is measured under the conditions of submerged rigid rod in flume with single layer and double layer vegetations. Experiments were performed for various spacings of the rigid rods. The vegetation models were aligned with the approaching flow in a rectangular channel. Vertical distributions of time-averaged velocity at various streamwise distances were evaluated using an acoustic Doppler velocimeter (ADV). The results indicate that, in submerged conditions, it is difficult to described velocity distribution along the entire depth using unified function. The characteristic of vertical distribution of longitudinal velocity is the presence of inflection. Under the inflection, the line is convex and groove above inflection. The interaction of high and low momentum fluids causes the flow to fold and creates strong vortices within each mixing layer. Understanding the flow phenomena in the area surrounding the tall vegetation, especially in the downstream region, is very important when modeling or studying the riparian environment. ADV measures of rigid vegetation distribution of the flow velocity field can give people a new understanding.
Highlights
Vegetation plays an important role in altering flow characteristics compared with nonvegetated conditions in rivers [1]
The height of the rigid rod used in the arrangements (a) and (b) was 8 mm, and the heights in arrangements (c) and (d) were 4 mm and 8 mm arranged in staggered configurations (Figure 2)
The vertical distribution of velocity with rigid vegetation could be divided into two layers: the upper y/H
Summary
Vegetation plays an important role in altering flow characteristics (such as velocity distribution, Reynolds number, and Manning coefficient) compared with nonvegetated conditions in rivers [1]. The influence mechanism of aquatic plant on flow is very complicated, which is dependent on the cross-sectional shape of river, water depth, discharge and on the species, bending rigidity, distribution, shape of vegetation, and whether it is submerged [3]. Laboratory studies on fully developed flows with submerged vegetation have demonstrated reduced velocities within the vegetation zone [7, 8]. The objective of this work is to describe the detailed characteristics of flow through a simulated array of rigid vegetation by examining its effects on the velocity and observing the influence of vegetation density and heights.
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