Predicting Bed Shear Stresses in Vegetated Channels

Research output: Contribution to journalArticle

5 Citations (Scopus)
208 Downloads (Pure)

Abstract

Shear stresses on vegetated beds play an important role in driving a wide range of processes at the sediment-water interface, including sediment transport. Existing methods for the estimation of bed shear stress are not applicable to vegetated beds due to the significant alteration of the near-bed velocity profile and turbulence intensities by the vegetation. In addition, bed shear stress distributions are highly spatially variable in the presence of vegetation. In this study, computational fluid dynamics simulations were used to investigate the spatial variability of bed shear stresses in the presence of emergent vegetation (modeled as arrays of circular cylinders) and the variation of bed stress with characteristics of both the bulk flow and the array. A recently proposed model that assumes a linear variation of stress in the viscous layer immediately above the bed is shown to be a reliable tool for estimating the spatially averaged bed shear stress over a wide range of flow conditions and vegetation densities. However, application of this model is found to be restrictive due to the lack of a reliable predictive tool for the thickness of the viscous layer. Based on a balance between turbulent kinetic energy production in the vegetation stem wakes and the viscous dissipation of turbulent kinetic energy at the bed, an enhanced formulation is proposed to predict the thickness of the viscous layer, which significantly improves the accuracy of model predictions. This improved model enhances the predictive capability for important benthic processes (such as sediment transport) in vegetated aquatic systems.

Original languageEnglish
Pages (from-to)9187-9206
Number of pages20
JournalWater Resources Research
Volume54
Issue number11
DOIs
Publication statusPublished - Nov 2018

Fingerprint

bottom stress
shear stress
vegetation
kinetic energy
sediment transport
sediment-water interface
velocity profile
computational fluid dynamics
dissipation
turbulence
stem
prediction
simulation

Cite this

@article{a7a606165c494f00a0cbbd717cdb7e89,
title = "Predicting Bed Shear Stresses in Vegetated Channels",
abstract = "Shear stresses on vegetated beds play an important role in driving a wide range of processes at the sediment-water interface, including sediment transport. Existing methods for the estimation of bed shear stress are not applicable to vegetated beds due to the significant alteration of the near-bed velocity profile and turbulence intensities by the vegetation. In addition, bed shear stress distributions are highly spatially variable in the presence of vegetation. In this study, computational fluid dynamics simulations were used to investigate the spatial variability of bed shear stresses in the presence of emergent vegetation (modeled as arrays of circular cylinders) and the variation of bed stress with characteristics of both the bulk flow and the array. A recently proposed model that assumes a linear variation of stress in the viscous layer immediately above the bed is shown to be a reliable tool for estimating the spatially averaged bed shear stress over a wide range of flow conditions and vegetation densities. However, application of this model is found to be restrictive due to the lack of a reliable predictive tool for the thickness of the viscous layer. Based on a balance between turbulent kinetic energy production in the vegetation stem wakes and the viscous dissipation of turbulent kinetic energy at the bed, an enhanced formulation is proposed to predict the thickness of the viscous layer, which significantly improves the accuracy of model predictions. This improved model enhances the predictive capability for important benthic processes (such as sediment transport) in vegetated aquatic systems.",
keywords = "bed shear stress, aquatic vegetation, turbulent kinetic energy, LARGE-EDDY SIMULATION, CIRCULAR-CYLINDER, TURBULENT-FLOW, DRAG, SCOUR, ARRAY",
author = "Vahid Etminan and Marco Ghisalberti and Lowe, {Ryan J.}",
year = "2018",
month = "11",
doi = "10.1029/2018WR022811",
language = "English",
volume = "54",
pages = "9187--9206",
journal = "Water Resources Research",
issn = "0043-1397",
publisher = "American Geophysical Union",
number = "11",

}

Predicting Bed Shear Stresses in Vegetated Channels. / Etminan, Vahid; Ghisalberti, Marco; Lowe, Ryan J.

In: Water Resources Research, Vol. 54, No. 11, 11.2018, p. 9187-9206.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Predicting Bed Shear Stresses in Vegetated Channels

AU - Etminan, Vahid

AU - Ghisalberti, Marco

AU - Lowe, Ryan J.

PY - 2018/11

Y1 - 2018/11

N2 - Shear stresses on vegetated beds play an important role in driving a wide range of processes at the sediment-water interface, including sediment transport. Existing methods for the estimation of bed shear stress are not applicable to vegetated beds due to the significant alteration of the near-bed velocity profile and turbulence intensities by the vegetation. In addition, bed shear stress distributions are highly spatially variable in the presence of vegetation. In this study, computational fluid dynamics simulations were used to investigate the spatial variability of bed shear stresses in the presence of emergent vegetation (modeled as arrays of circular cylinders) and the variation of bed stress with characteristics of both the bulk flow and the array. A recently proposed model that assumes a linear variation of stress in the viscous layer immediately above the bed is shown to be a reliable tool for estimating the spatially averaged bed shear stress over a wide range of flow conditions and vegetation densities. However, application of this model is found to be restrictive due to the lack of a reliable predictive tool for the thickness of the viscous layer. Based on a balance between turbulent kinetic energy production in the vegetation stem wakes and the viscous dissipation of turbulent kinetic energy at the bed, an enhanced formulation is proposed to predict the thickness of the viscous layer, which significantly improves the accuracy of model predictions. This improved model enhances the predictive capability for important benthic processes (such as sediment transport) in vegetated aquatic systems.

AB - Shear stresses on vegetated beds play an important role in driving a wide range of processes at the sediment-water interface, including sediment transport. Existing methods for the estimation of bed shear stress are not applicable to vegetated beds due to the significant alteration of the near-bed velocity profile and turbulence intensities by the vegetation. In addition, bed shear stress distributions are highly spatially variable in the presence of vegetation. In this study, computational fluid dynamics simulations were used to investigate the spatial variability of bed shear stresses in the presence of emergent vegetation (modeled as arrays of circular cylinders) and the variation of bed stress with characteristics of both the bulk flow and the array. A recently proposed model that assumes a linear variation of stress in the viscous layer immediately above the bed is shown to be a reliable tool for estimating the spatially averaged bed shear stress over a wide range of flow conditions and vegetation densities. However, application of this model is found to be restrictive due to the lack of a reliable predictive tool for the thickness of the viscous layer. Based on a balance between turbulent kinetic energy production in the vegetation stem wakes and the viscous dissipation of turbulent kinetic energy at the bed, an enhanced formulation is proposed to predict the thickness of the viscous layer, which significantly improves the accuracy of model predictions. This improved model enhances the predictive capability for important benthic processes (such as sediment transport) in vegetated aquatic systems.

KW - bed shear stress

KW - aquatic vegetation

KW - turbulent kinetic energy

KW - LARGE-EDDY SIMULATION

KW - CIRCULAR-CYLINDER

KW - TURBULENT-FLOW

KW - DRAG

KW - SCOUR

KW - ARRAY

UR - http://www.scopus.com/inward/record.url?scp=85056820009&partnerID=8YFLogxK

U2 - 10.1029/2018WR022811

DO - 10.1029/2018WR022811

M3 - Article

VL - 54

SP - 9187

EP - 9206

JO - Water Resources Research

JF - Water Resources Research

SN - 0043-1397

IS - 11

ER -