A Turbulence-Based Bed-Load Transport Model for Bare and Vegetated Channels

J. Q. Yang; H. M. Nepf

doi:10.1029/2018GL079319

A Turbulence-Based Bed-Load Transport Model for Bare and Vegetated Channels

J. Q. Yang, H. M. Nepf

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Abstract

Previous studies have shown that sediment transport models based on bed shear stress (τ) are not accurate for regions with vegetation. The present study demonstrated that the inaccuracy arises from the influence of vegetation-generated turbulence. Bed-load transport rate, Q_s, and near-bed velocity were measured in a sediment-recirculating flume with model vegetation of different vegetation volume fractions (ϕ) and with bare sand beds. At the same τ, the measured Q_s increased with increasing ϕ, suggesting that vegetation-generated turbulence, which also increased with increasing ϕ, was augmenting the bed-load transport. At the same near-bed turbulent kinetic energy, k_t, the Q_s measured in both bare and vegetated channels agreed within uncertainty, suggesting that k_t may be a more universal predictor of bed-load transport than bed shear stress. A τ-based bed-load transport model was reinterpreted as a k_t-based model. The new k_t-based model predicted the Q_s measurements for both bare and vegetated channels.

Original language	English (US)
Pages (from-to)	10,428-10,436
Journal	Geophysical Research Letters
Volume	45
Issue number	19
DOIs	https://doi.org/10.1029/2018GL079319
State	Published - Oct 16 2018
Externally published	Yes

Bibliographical note

Funding Information:
The authors thank Milani Chatterji-Len and Yinghao Zhang for their assistance with the experiments. We also thank John Trowbridge, Francesco Ballio, and another anonymous reviewer for their insightful comments. The work was supported by NSF grant EAR 1414499. Judy Q. Yang was supported by the Martin Family Society for Sustainability. The data in this study are tabulated in Judy Qingjun Yang's thesis, which will be available on MIT D-Space (https://dspace.mit.edu/).

Funding Information:
The authors thank Milani Chatterji-Len and Yinghao Zhang for their assistance with the experiments. We also thank John Trowbridge, Francesco Ballio, and another anonymous reviewer for their insightful comments. The work was supported by NSF grant EAR 1414499. Judy Q. Yang was supported by the Martin Family Society for Sustainability. The data in this study are tabulated in Judy Qingjun Yang’s thesis, which will be available on MIT D-Space (https://dspace.mit.edu/).

Publisher Copyright:
©2018. American Geophysical Union. All Rights Reserved.

Keywords

bed shear stress
bed-load transport rate
erosion
sediment transport
turbulence
vegetation

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title = "A Turbulence-Based Bed-Load Transport Model for Bare and Vegetated Channels",

abstract = "Previous studies have shown that sediment transport models based on bed shear stress (τ) are not accurate for regions with vegetation. The present study demonstrated that the inaccuracy arises from the influence of vegetation-generated turbulence. Bed-load transport rate, Qs, and near-bed velocity were measured in a sediment-recirculating flume with model vegetation of different vegetation volume fractions (ϕ) and with bare sand beds. At the same τ, the measured Qs increased with increasing ϕ, suggesting that vegetation-generated turbulence, which also increased with increasing ϕ, was augmenting the bed-load transport. At the same near-bed turbulent kinetic energy, kt, the Qs measured in both bare and vegetated channels agreed within uncertainty, suggesting that kt may be a more universal predictor of bed-load transport than bed shear stress. A τ-based bed-load transport model was reinterpreted as a kt-based model. The new kt-based model predicted the Qs measurements for both bare and vegetated channels.",

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N2 - Previous studies have shown that sediment transport models based on bed shear stress (τ) are not accurate for regions with vegetation. The present study demonstrated that the inaccuracy arises from the influence of vegetation-generated turbulence. Bed-load transport rate, Qs, and near-bed velocity were measured in a sediment-recirculating flume with model vegetation of different vegetation volume fractions (ϕ) and with bare sand beds. At the same τ, the measured Qs increased with increasing ϕ, suggesting that vegetation-generated turbulence, which also increased with increasing ϕ, was augmenting the bed-load transport. At the same near-bed turbulent kinetic energy, kt, the Qs measured in both bare and vegetated channels agreed within uncertainty, suggesting that kt may be a more universal predictor of bed-load transport than bed shear stress. A τ-based bed-load transport model was reinterpreted as a kt-based model. The new kt-based model predicted the Qs measurements for both bare and vegetated channels.

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A Turbulence-Based Bed-Load Transport Model for Bare and Vegetated Channels

Abstract

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Keywords

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