Impact of Vegetation on Bed Load Transport Rate and Bedform Characteristics

J. Q. Yang; H. M. Nepf

doi:10.1029/2018WR024404

Impact of Vegetation on Bed Load Transport Rate and Bedform Characteristics

J. Q. Yang, H. M. Nepf

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67 Scopus citations

Abstract

The impacts of aquatic vegetation on bed load transport rate and bedform characteristics were quantified using flume measurements with model emergent vegetation. First, a model for predicting the turbulent kinetic energy, k_t, in vegetated channels from channel average velocity U and vegetation volume fraction ϕ was validated for mobile sediment beds. Second, using data from several studies, the predicted k_t was shown to be a good predictor of bed load transport rate, Q_s, allowing Q_s to be predicted from U and ϕ for vegetated channels. The control of Q_s by k_t was explained by statistics of individual grain motion recorded by a camera, which showed that the number of sediment grains in motion per bed area was correlated with k_t. Third, ripples were observed and characterized in channels with and without model vegetation. For low vegetation solid volume fraction (ϕ ≤ 0.012), the ripple wavelength was constrained by stem spacing. However, at higher vegetation solid volume fraction (ϕ=0.025), distinct ripples were not observed, suggesting a transition to sheet flow, which is sediment transport over a plane bed without the formation of bedforms. The fraction of the bed load flux carried by migrating ripples decreased with increasing ϕ, again suggesting that vegetation facilitated the formation of sheet flow.

Original language	English (US)
Pages (from-to)	6109-6124
Number of pages	16
Journal	Water Resources Research
Volume	55
Issue number	7
DOIs	https://doi.org/10.1029/2018WR024404
State	Published - 2019
Externally published	Yes

Bibliographical note

Funding Information:
The work was supported by NSF grant EAR 1414499. Judy Q. Yang was supported by the Fellowship for Sustainability funded by the Martin Foundation. 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/). The authors thank Milani Chatterji-Len and Yinghao Zhang for their assistance with the experiments and John Trowbridge for his insightful comments.

Publisher Copyright:
© 2019. American Geophysical Union. All Rights Reserved.

Keywords

bed load
bedform migration
sediment transport
sheet flow
turbulent kinetic energy
vegetation

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10.1029/2018WR024404

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abstract = "The impacts of aquatic vegetation on bed load transport rate and bedform characteristics were quantified using flume measurements with model emergent vegetation. First, a model for predicting the turbulent kinetic energy, kt, in vegetated channels from channel average velocity U and vegetation volume fraction ϕ was validated for mobile sediment beds. Second, using data from several studies, the predicted kt was shown to be a good predictor of bed load transport rate, Qs, allowing Qs to be predicted from U and ϕ for vegetated channels. The control of Qs by kt was explained by statistics of individual grain motion recorded by a camera, which showed that the number of sediment grains in motion per bed area was correlated with kt. Third, ripples were observed and characterized in channels with and without model vegetation. For low vegetation solid volume fraction (ϕ ≤ 0.012), the ripple wavelength was constrained by stem spacing. However, at higher vegetation solid volume fraction (ϕ=0.025), distinct ripples were not observed, suggesting a transition to sheet flow, which is sediment transport over a plane bed without the formation of bedforms. The fraction of the bed load flux carried by migrating ripples decreased with increasing ϕ, again suggesting that vegetation facilitated the formation of sheet flow.",

keywords = "bed load, bedform migration, sediment transport, sheet flow, turbulent kinetic energy, vegetation",

author = "Yang, {J. Q.} and Nepf, {H. M.}",

note = "Funding Information: The work was supported by NSF grant EAR 1414499. Judy Q. Yang was supported by the Fellowship for Sustainability funded by the Martin Foundation. 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/). The authors thank Milani Chatterji-Len and Yinghao Zhang for their assistance with the experiments and John Trowbridge for his insightful comments. Publisher Copyright: {\textcopyright} 2019. American Geophysical Union. All Rights Reserved.",

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PY - 2019

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N2 - The impacts of aquatic vegetation on bed load transport rate and bedform characteristics were quantified using flume measurements with model emergent vegetation. First, a model for predicting the turbulent kinetic energy, kt, in vegetated channels from channel average velocity U and vegetation volume fraction ϕ was validated for mobile sediment beds. Second, using data from several studies, the predicted kt was shown to be a good predictor of bed load transport rate, Qs, allowing Qs to be predicted from U and ϕ for vegetated channels. The control of Qs by kt was explained by statistics of individual grain motion recorded by a camera, which showed that the number of sediment grains in motion per bed area was correlated with kt. Third, ripples were observed and characterized in channels with and without model vegetation. For low vegetation solid volume fraction (ϕ ≤ 0.012), the ripple wavelength was constrained by stem spacing. However, at higher vegetation solid volume fraction (ϕ=0.025), distinct ripples were not observed, suggesting a transition to sheet flow, which is sediment transport over a plane bed without the formation of bedforms. The fraction of the bed load flux carried by migrating ripples decreased with increasing ϕ, again suggesting that vegetation facilitated the formation of sheet flow.

AB - The impacts of aquatic vegetation on bed load transport rate and bedform characteristics were quantified using flume measurements with model emergent vegetation. First, a model for predicting the turbulent kinetic energy, kt, in vegetated channels from channel average velocity U and vegetation volume fraction ϕ was validated for mobile sediment beds. Second, using data from several studies, the predicted kt was shown to be a good predictor of bed load transport rate, Qs, allowing Qs to be predicted from U and ϕ for vegetated channels. The control of Qs by kt was explained by statistics of individual grain motion recorded by a camera, which showed that the number of sediment grains in motion per bed area was correlated with kt. Third, ripples were observed and characterized in channels with and without model vegetation. For low vegetation solid volume fraction (ϕ ≤ 0.012), the ripple wavelength was constrained by stem spacing. However, at higher vegetation solid volume fraction (ϕ=0.025), distinct ripples were not observed, suggesting a transition to sheet flow, which is sediment transport over a plane bed without the formation of bedforms. The fraction of the bed load flux carried by migrating ripples decreased with increasing ϕ, again suggesting that vegetation facilitated the formation of sheet flow.

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Impact of Vegetation on Bed Load Transport Rate and Bedform Characteristics

Abstract

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