Evaluating Two-Layer Models for Velocity Profiles in Open-Channels with Submerged Vegetation

Tang, Xiaonan

doi:10.4236/gep.2019.71006

Cited by 14 publications

(13 citation statements)

References 16 publications

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“…Rigid submerged vegetation has been the subject of a large number of investigations [7,61,62,[73][74][75][76][77] and comparisons [78][79][80][81][82][83]. Some researchers provided the average velocity values in the two layers, while others derived the velocity distribution and the average values [7,73,74,76].…”

Section: Submerged Rigid Vegetationmentioning

confidence: 99%

Flow Resistance in Open Channel Due to Vegetation at Reach Scale: A Review

D’Ippolito

Calomino

Alfonsi

et al. 2021

Water

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Vegetation on the banks and flooding areas of watercourses significantly affects energy losses. To take the latter into account, computational models make use of resistance coefficients based on the evaluation of bed and walls roughness besides the resistance to flow offered by vegetation. This paper, after summarizing the classical approaches based on descriptions and pictures, considers the recent advancements related to the analytical methods relative both to rigid and flexible vegetation. In particular, emergent rigid vegetation is first analyzed by focusing on the methods for determining the drag coefficient, then submerged rigid vegetation is analyzed, highlighting briefly the principles on which the different models are based and recalling the comparisons made in the literature. Then, the models used in the case of both emergent and submerged rigid vegetation are highlighted. As to flexible vegetation, the paper reminds first the flow conditions that cause the vegetation to lay on the channel bed, and then the classical resistance laws that were developed for the design of irrigation canals. The most recent developments in the case of submerged and emergent flexible vegetation are then presented. Since turbulence studies should be considered as the basis of flow resistance, even though the path toward practical use is still long, the new developments in the field of 3D numerical methods are briefly reviewed, presently used to assess the characteristics of turbulence and the transport of sediments and pollutants. The use of remote sensing to map riparian vegetation and estimating biomechanical parameters is briefly analyzed. Finally, some applications are presented, aimed at highlighting, in real cases, the influence exerted by vegetation on water depth and maintenance interventions.

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Section: Submerged Rigid Vegetationmentioning

confidence: 99%

Flow Resistance in Open Channel Due to Vegetation at Reach Scale: A Review

D’Ippolito

Calomino

Alfonsi

et al. 2021

Water

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“…In the evaluation of the above models and other models, Tang & Ali (2013) and Tang (2019a) showed that the predicted velocity distribution by the above mentioned models is acceptable only for certain experimental datasets, but they do not agree with other datasets. In addition, the predictions by these models show significant differences even for the same dataset.…”

Section: Introductionmentioning

confidence: 97%

“…Tsujimoto & Kitamur, 1990, Shimizu & Tsujimoto, 1994Nepf & Koch, 1999;Ghisalberti & Nepf, 2004;Kubrak, et al, 2008;Tang & Knight, 2009;Tang et al, 2010Tang et al, , 2011Nguyen, 2012;Hao et al, 2014). Many investigators have attempted to predict vertical velocity distribution based on semi-empiricism and/or analytical solution of the momentum equation with closure schemes, in which the modelling of eddy viscosity is to describe the turbulent stresses (Klopstra et al, 1997;Meijer & Van Velzen, 1999;Defina & Bixio, 2005;Baptist et al, 2007;Huai, et al, 2009Huai, et al, , 2014Yang & Choi, 2010;Dimitris & Panayotis, 2011;Nepf, 2012;Nikora et al, 2013;Tang, 2018aTang, , 2019aSingh et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

“…The flow structure in this region is governed through the mixing length of eddy and vertical turbulent transport of momentum from the surface flow, with the negligible contribution from the pressure gradient. The effect of the shear length scale can be related to the vegetation height and flow depth (Klopstra et al, 1997;Defina & Bixio, 2005;Tang, 2018aTang, , 2018bTang, , 2019aSingh et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

“…A review on the studies on the vertical velocity distribution of flow with submerged rigid vegetation shows that different models are used to predict the vertical velocity distribution through and above submerged vegetation (Tang & Ali, X. Tang Journal of Geoscience and Environment Protection 2013; Tang, 2019a). These models are so-called two-layer or three-layer methods.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

An Improved Analytical Model for Vertical Velocity Distribution of Vegetated Channel Flows

Tang¹

2019

GEP

Self Cite

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The existence of vegetation plays an important role to protect the ecosystem and water environment in natural rivers and wetlands, but it alters the velocity field of flow, consequently influencing the transport of pollutant and biomass. As a prerequisite for the analysis of environmental capacity in a channel, the vertical velocity distribution of flows has attracted much research attention; however, there is yet lack of a good prediction model available. For the channel with submerged vegetation, the vertical velocity distribution in the lower vegetation layer will be different from that in the upper flow layer of non-vegetation. In this paper, after review on the most recent two-layer model proposed by Baptist et al., the author has proposed an improved two-layer analytical model by introducing a different mixing length scale (λ). The proposed model is based on the momentum equation of flow with the turbulent eddy viscosity assumed as a linear relationship with the local velocity. The proposed model is compared with the Baptist model for different datasets published in the literature, which shows that the proposed analytical model can improve the vertical velocity distribution prediction well compared with the Baptist model for a range of data. This study reveals that the λ is well related with the submergence of vegetation (H/h), as suggested by

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An experimental study of the hydrodynamics and contaminant transport in a Y‐shaped confluence with flexible submerged vegetation

Tong

Liu

Yang

et al. 2022

Hydrological Processes

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Vegetation greatly affects the flow characteristics and contaminant transport in river confluences. In this study, the flow characteristics and contaminant transport in the non‐vegetated/vegetated Y‐shaped confluence were explored systematically through a series of experiments. A total of 10 scenarios were designed to answer the three main research questions: what is the difference between the flow characteristics and contaminant transport in (1) asymmetrical and Y‐shaped confluences; (2) non‐vegetated/vegetated Y‐shaped confluences; (3) vegetated Y‐shaped confluences with different confluence ratios? The experimental results revealed that vegetation remarkably changes the internal flow structure in Y‐shaped confluences. Briefly, the velocity profile can be divided into three vertical layers within the vegetated system, but it remains nearly constant in the non‐vegetated channel. Vegetation changes the circulation location and reduces the intensity of the secondary current, weakening the strength of contaminant mixing. However, the turbulent kinetic energy within the vegetated system is larger than that in the non‐vegetated case, and it peaks at the top of the vegetation canopy. Under different confluence ratio cases, the overall fluctuation of the longitudinal dispersion coefficients along the cross‐sections in the mainstream was similar but increasing the confluence ratio causes the circulation to appear to advance and enhances its intensity. In addition, the vegetation density (200 item/m2) in this study render the manning roughness coefficient at 0.068, which is larger than that under lower vegetation density cases. The outcomes from this study are helpful for both environmental and river management applications.

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Evaluating Two-Layer Models for Velocity Profiles in Open-Channels with Submerged Vegetation

Cited by 14 publications

References 16 publications

Flow Resistance in Open Channel Due to Vegetation at Reach Scale: A Review

Flow Resistance in Open Channel Due to Vegetation at Reach Scale: A Review

An Improved Analytical Model for Vertical Velocity Distribution of Vegetated Channel Flows

An experimental study of the hydrodynamics and contaminant transport in a Y‐shaped confluence with flexible submerged vegetation

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