Abstract

Shrubby and woody vegetation growing on floodplains profoundly influences hydrodynamic and transport processes in riverine systems. Existing hydrodynamic research is mostly focused on conditions with aquatic plants and rigid model vegetation. To appreciate the different hydrodynamic impacts of submerged floodplain and riverbank vegetation, a novel flume investigation was carried out. We simulated conditions found in riparian environments in terms of vegetation density, plant structure and flexibility, and presence of a grassy understory. Four experimental cases were defined so that vegetation exhibited different degrees of bending and streamlining. Extensive set of velocity measurements allowed reliable description of the double averaged flow. Vegetation morphology, with the flexibility-induced streamlining and dynamic motion controlled the magnitude and distribution of the vegetative drag, shaping the shear penetration within the canopy. The flows were highly heterogeneous, thus calling for spatially averaged approaches for the flow field investigation. The relative importance of dispersive momentum fluxes was high in the canopy bottom region where both Reynolds and dispersive stresses were small. The contribution of dispersive fluxes to momentum transport decreased with increasing reconfiguration. The results revealed the shear layers over floodplain vegetation to be dynamically similar to other environmental flows over porous obstructions. However, the velocity-dependent vegetative drag and deflected height introduced additional complexity in the flow simulation. Altogether our findings implied that accurate description of vegetated floodplain flows can be achieved only when plant morphology and flexibility are appropriately described in drag models.

Article highlights

• A novel experimental setup with flexible woody plants and grasses was used to model the hydrodynamics of vegetated floodplains.

• Plant morphology and flexibility controlled the vegetative drag, affecting key shear layer features, including the shear penetration.

• The spatially heterogeneous flows had higher dispersive stresses at the canopy bottom, where the total fluid stress was small.

中文翻译：

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泛滥平原植被上的剪切层，考虑弯曲和流线型效应

摘要

漫滩上生长的灌木和木本植被对河流系统的水动力和运输过程产生了深远的影响。现有的水动力研究主要集中在水生植物和刚性模型植被的条件下。为了了解淹没漫滩和河岸植被的不同水动力影响，进行了一项新的水槽调查。我们模拟了在河岸环境中发现的植被密度、植物结构和灵活性以及草地下层的存在情况。定义了四个实验案例，使植被表现出不同程度的弯曲和流线型。广泛的速度测量集允许可靠地描述双平均流。植被形态，柔性引起的流线型和动态运动控制了植物阻力的大小和分布，塑造了树冠内的剪切渗透。流动高度异质，因此需要空间平均方法进行流场调查。分散动量通量的相对重要性在雷诺和分散应力都较小的冠层底部区域较高。色散通量对动量传输的贡献随着重新配置的增加而降低。结果表明，泛滥平原植被上的剪切层与多孔障碍物上的其他环境流动动态相似。然而，速度相关的植物阻力和偏转高度在流动模拟中引入了额外的复杂性。

文章重点

• 使用具有柔性木本植物和草的新型实验装置来模拟植被泛滥平原的流体动力学。

• 植物形态和柔韧性控制植物阻力，影响关键剪切层特征，包括剪切穿透。

• 空间异质流动在冠层底部具有较高的分散应力，总流体应力较小。