Abstract

Over the last two decades, the role of vegetation in the environmental and ecological restoration of surface water bodies has received much attention. In this context, the momentum exchange between the flow through the main channel and the riparian zone is a key mechanism. The primary goal of this study is to investigate the role of bank vegetation density on flow dynamics across the whole channel. This experimental study presents the major findings from a series of flow measurements across a channel having a sloping bank with vegetation at varying densities. The experiments are conducted under the same, uniform flow and fixed bed conditions, for a range of six linear and rectilinear arrangements of incremental streambank vegetation densities. A set of ten velocity profiles is obtained across the test cross-section of the channel, including the riverbank, for each vegetation density. These flow measurements are analyzed to derive roughness coefficients, which are related to the bulk flow velocities through the main channel and the riverbank and discuss the redistribution of flow velocities. An approximate doubling for the estimates of time-averaged boundary shear stress at the main channel, is observed for the case of no to dense vegetation, which enable further discussing implications for the stability of bed surface material. It is found that the vegetation arrangement, in addition to vegetation density, can have a strong impact in modifying the mean flow velocity at the main channel, for low riparian densities (φ < 0.6%).

Highlights

• Flow dynamics are measured across the whole channel, including the vegetated riverbank.

• As stem density increases, mean flow velocity in the main channel increases while mean flow at the riverbank decreases.

• The arrangement of riparian vegetation can be as important as that of the density, in modifying the mean flow field of the main channel, for low riparian densities.

• Bed shear stresses at the main channel are estimated to increase with riverbank vegetation, reducing the stability of the stream’s bed surface.

中文翻译：

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增加河岸植被密度对非对称河道水流动力学的作用

摘要

在过去的二十年中，植被在地表水体的环境和生态恢复中的作用受到了广泛关注。在这种情况下，通过主要水道和河岸带的水流之间的动量交换是关键机制。这项研究的主要目的是研究河岸植被密度对整个河道水流动力学的作用。这项实验研究提出了一系列流量测量的主要发现，这些流量测量通过一个具有倾斜的河岸且密度不同的植被的河道。在相同的，均匀的流量和固定床的条件下，对递增的河岸植被密度的六种线性和直线排列进行了实验。在通道的测试横截面中获得了一组十个速度分布图，包括每个植被密度的河岸。分析这些流量测量结果以得出粗糙度系数，该系数与通过主河道和河岸的整体流速有关，并讨论了流速的重新分布。对于没有茂密植被的情况，在主通道处的时间平均边界剪切应力的估计值大约增加了一倍，这使得可以进一步讨论对床面材料稳定性的影响。研究发现，对于低河岸密度而言，除植被密度外，植被布置对改变主要河道的平均流速有很大的影响（这与通过主河道和河岸的整体流速有关，并讨论了流速的重新分配。对于没有茂密植被的情况，在主通道处的时间平均边界剪切应力的估计值大约增加了一倍，这使得可以进一步讨论对床面材料稳定性的影响。研究发现，对于低河岸密度而言，除植被密度外，植被布置对改变主要河道的平均流速有很大的影响（这与通过主河道和河岸的整体流速有关，并讨论了流速的重新分配。对于没有茂密植被的情况，在主通道处的时间平均边界剪切应力的估计值大约增加了一倍，这使得可以进一步讨论对床面材料稳定性的影响。研究发现，对于低河岸密度而言，除植被密度外，植被布置对改变主要河道的平均流速有很大的影响（这使得可以进一步讨论对床表面材料稳定性的影响。研究发现，对于低河岸密度而言，除植被密度外，植被布置对改变主要河道的平均流速有很大的影响（这使得可以进一步讨论对床表面材料稳定性的影响。研究发现，对于低河岸密度而言，除植被密度外，植被布置对改变主要河道的平均流速有很大的影响（φ  <0.6％）。

强调

• 在整个通道（包括植被河岸）上测量流量动态。

• 随着茎密度的增加，主河道的平均流速增加，而河岸的平均流量减少。

• 对于低河岸密度，河岸植被的布置与密度的布置一样重要，可以改变主河道的平均流场。

• 据估计，主河道的河床切应力随河岸植被的增加而增加，从而降低了河床河床表面的稳定性。