2026-09-20T22:16:47Zhttps://dspace.mit.edu/server/oai/requestoai:dspace.mit.edu:1721.1/995802022-01-13T07:53:59Zcom_1721.1_7582com_1721.1_7581col_1721.1_131023
Heidi M. Nepf.
Yang, Qingjun (Judy Qingjun)
Massachusetts Institute of Technology. Department of Civil and Environmental Engineering.
Massachusetts Institute of Technology. Department of Civil and Environmental Engineering
2015-10-30T18:57:29Z
2015-10-30T18:57:29Z
2015
2015
http://hdl.handle.net/1721.1/99580
924882937
Thesis: S.M., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 69-77).
The shear stress at the bed of a channel influences important benthic processes such as sediment transport. Several methods exist to estimate the bed shear stress in bare channels without vegetation, but most of these are not appropriate for vegetated channels due to the impact of vegetation on the velocity profile and turbulence production. This study proposes a new model to estimate the bed shear stress in both vegetated and bare channels with smooth beds. The model, which is supported by measurements, indicates that for both bare and vegetated channels with smooth beds, within a viscous sub-layer at the bed, the viscous stress decreases linearly with increasing distance from the bed, resulting in a parabolic velocity profile at the bed. For bare channels, the model describes the velocity profile in the overlap region of the Law of the Wall. For emergent canopies of sufficient density (frontal area per unit canopy volume a >/= 4.3m⁻¹ ), the thickness of the linear-stress layer is set by the stem diameter, leading to a simple estimate for bed shear stress.
by Qingjun (Judy) Yang.
S.M.
77 pages
eng
Massachusetts Institute of Technology
M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.
http://dspace.mit.edu/handle/1721.1/7582
Civil and Environmental Engineering.
Estimation of the bed shear stress in vegetated and bare channels
Thesis
application/pdf
Publication
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unknown
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<Abstract>The shear stress at the bed of a channel influences important benthic processes such as sediment transport. Several methods exist to estimate the bed shear stress in bare channels without vegetation, but most of these are not appropriate for vegetated channels due to the impact of vegetation on the velocity profile and turbulence production. This study proposes a new model to estimate the bed shear stress in both vegetated and bare channels with smooth beds. The model, which is supported by measurements, indicates that for both bare and vegetated channels with smooth beds, within a viscous sub-layer at the bed, the viscous stress decreases linearly with increasing distance from the bed, resulting in a parabolic velocity profile at the bed. For bare channels, the model describes the velocity profile in the overlap region of the Law of the Wall. For emergent canopies of sufficient density (frontal area per unit canopy volume a >/= 4.3m⁻¹ ), the thickness of the linear-stress layer is set by the stem diameter, leading to a simple estimate for bed shear stress.</Abstract>
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