Predicting the vertical low suspended sediment concentration in vegetated flow using a random displacement model

Huai, Wenxin; Yang, Liu; Wang, Weijie; Guo, Yakun; Wang, Tao; Cheng, Yongguang

doi:10.1016/j.jhydrol.2019.124101

Cited by 53 publications

(43 citation statements)

References 58 publications

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“…In applications, error in the estimation of u * , k, β, ω s , h p , or d will lead to an error in suspension number, i.e., the exponent of the double-parameter modified Rouse formula Equation (24), and thus lead to an error in the estimation of the profile of suspended sediment concentration.…”

Section: Discussionmentioning

confidence: 99%

“…Equation (24) indicates that the concentration profile of fine suspended sediments is independent of the roughness height z 0 , neither of the constant C in the modified semi-logarithmic law of flow velocity expressed by Equation (5). Equation (24) also indicates that over dense plants, an equilibrium state of fine suspended sediments under the dynamic balance between turbulent diffusion and gravitational settling can be obtained. (Figure 8b).…”

Section: Equilibrium Equation Between Turbulent Diffusion and Gravitamentioning

confidence: 99%

“…Based on the generally upward-decreasing feature of the profile of ε m , Huai et al (2019) [24] assumed a zero-value of ε m at the water surface, and then assumed a linear profile of ε m between the water surface and the plant top. They successfully created a random displacement model for the prediction of the profile of the suspended sediment concentration profile (C s ).…”

Section: Introductionmentioning

confidence: 99%

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Vertical Distribution of Suspended Sediments above Dense Plants in Water Flow

Xie

2019

Water

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Plants in natural water flow can improve water quality by adhering and absorbing the fine suspended sediments. Dense plants usually form an additional permeable bottom boundary for the water flow over it. In the flow layer above dense plants, the flow velocity generally presents a zero-plane-displacement and roughness-height double modified semi-logarithmic profile. In addition, the second order shear turbulent moment (or the Reynolds stress) are different from that found in non-vegetated flow. As a result, the turbulent momentum diffusivity of flow and thus the diffusivity of sediment will shift, which will cause the vertical profile of suspended sediment and the corresponding Rouse formula deform. A set of physical experiments with three different diameters of fine suspended sediments was conducted in an indoor water flume. These experiments investigated a new distribution pattern of suspended sediment and the correspondingly deformed Rouse formula in the flow layer over the dense plants. Experimental results showed that above the dense plants, the shear turbulent momentum of flow presented a plant-height modified negative linear profile, which has been proposed by a previous study, and the vertical distribution of fine suspended sediments presented an equilibrium pattern. Based on the plant-modified profiles of flow velocity and the shear turbulent momentum a new zero-plane and plant-height double modified Rouse formula were analytically derived. This double-parameter modified Rouse formula agrees well with the measured profile of suspended sediment concentration experimentally observed in the present study. By adjusting the Prandtl-Schmidt number, i.e., the ratio of sediment diffusivity to flow diffusivity, the double-parameter modified Rouse formula can be applied to submerged dense plant occupied flow.

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Section: Discussionmentioning

confidence: 99%

Section: Equilibrium Equation Between Turbulent Diffusion and Gravitamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Vertical Distribution of Suspended Sediments above Dense Plants in Water Flow

Xie

2019

Water

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“…For example, flow structure changes caused by plants in channel flows significantly affect the hydrodynamics and thus the transport of contaminants (Z. B. Chen et al, 2013; Huai, Yang, et al, 2019; Nezu & Sanjou, 2009; Tanino & Nepf, 2008a; Wang & Chen, 2015, 2017; Wang & Zeng, 2019). It is therefore meaningful to determine the physical processes of the complex interactions between flow and vegetation.…”

Section: Introductionmentioning

confidence: 99%

Drag Coefficient of Emergent Flexible Vegetation in Steady Nonuniform Flow

Zhang

Wang

Cheng

et al. 2020

Water Resources Research

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Flexible vegetation plays key roles in the natural channel and riparian ecology. This paper investigates the drag coefficient Cdf of an emergent flexible vegetation array in a steady nonuniform flow. Laboratory flume tests of five vegetation densities exposed to a constant flow rate were conducted, and the variation in the water surface was accurately measured. The Saint‐Venant equation was applied to explore vegetation hydrodynamics under nonuniform conditions, and a more widely applicable formula for the vegetated drag of nonuniform flow was proposed. Furthermore, the flexible drag coefficient factor αb was used to represent the flexibility and drag reconfiguration, which were explored from the perspective of material mechanics. The results reveal that the calculated values of Cdf exhibit nonmonotonic variation with increasing Reynolds number along the streamwise direction due to the flow nonuniformity. There are two effects of blockage and sheltering in the emergent vegetated patch: The blockage effect increases the drag coefficient, while the sheltering effect—especially at the leading edge and tail of the vegetated patch—reduces the drag of the flexible canopy due to bending deformation. These two effects achieve equilibration in dense flexible canopies. Finally, by relating αb to flexibility through the slenderness Cauchy number CYS, a nonmonotonic pattern can be obtained for each test. A fitting formula was proposed based on αb as a function of CYS. The results presented in this study can potentially support applications related to the plant flexible dams and vegetated filter strips for river ecosystems.

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“…where Δu represents the velocity difference between the wake region of vegetation and overflow, which is approximately equal to 0.8u H − u w (where u H is the flow velocity at the water surface and can be expressed as the logarithmical profile (Huai et al, 2019) and…”

Section: Channels With the Submerged Vegetationmentioning

confidence: 99%

Analytical Solution of Suspended Sediment Concentration Profile: Relevance of Dispersive Flow Term in Vegetated Channels

Huai

Yang

Guo

2020

Water Resources Research

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Simulation of suspended sediment concentration (SSC) has great significance in predicting the sediment transport rate, vegetation growth, and the river ecosystem in channels. The present study focuses on investigating the vertical SSC profile in the vegetated open channel flows. To this end, a model of the dispersive flux is proposed in which the dispersive coefficient is expressed as partitioned linear profile above or below the half height of vegetation. The double‐averaging method, that is, time‐spatial average, is applied to investigate the vertical SSC profile in the vegetated open channel flows. The analytical solution of SSC in both submerged and emergent vegetated open channel flows is obtained by solving the vertical double‐averaging sediment advection‐diffusion equation. The morphological coefficient, a key factor of dispersive coefficient, is obtained by fitting the existing experimental data. The analytically predicted SSC agrees well with the experimental measurements, indicating that the proposed model can be used to accurately predict the SSC in the vegetated open channel flows. Results show that the dispersive term can be ignored in the region without vegetation, while the dispersive term has significant effect on the vertical SSC profile within the region of vegetation. The present study demonstrates that the dispersive coefficient is closely related to vegetation density, vegetation structure, and stem Reynolds number but has little relation with flow depth. With a few exceptions, the absolute value of the dispersive coefficient decreases with the increase of vegetation density and increases with the increase of stem Reynolds number in the submerged vegetated open channels.

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Predicting the vertical low suspended sediment concentration in vegetated flow using a random displacement model

Cited by 53 publications

References 58 publications

Vertical Distribution of Suspended Sediments above Dense Plants in Water Flow

Vertical Distribution of Suspended Sediments above Dense Plants in Water Flow

Drag Coefficient of Emergent Flexible Vegetation in Steady Nonuniform Flow

Analytical Solution of Suspended Sediment Concentration Profile: Relevance of Dispersive Flow Term in Vegetated Channels

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