Direct bed shear stress measurements in bore-driven swash

Barnes, M. P., O'Donoghue, T., Alsina, J. M. and Baldock, T. E. (2009) Direct bed shear stress measurements in bore-driven swash. Coastal Engineering, 56 8: 853-867. doi:10.1016/j.coastaleng.2009.04.004

Author Barnes, M. P.
O'Donoghue, T.
Alsina, J. M.
Baldock, T. E.
Title Direct bed shear stress measurements in bore-driven swash
Journal name Coastal Engineering   Check publisher's open access policy
ISSN 0378-3839
Publication date 2009-08-01
Year available 2009
Sub-type Article (original research)
DOI 10.1016/j.coastaleng.2009.04.004
Open Access Status
Volume 56
Issue 8
Start page 853
End page 867
Total pages 14
Place of publication Amsterdam, Netherlands
Publisher Elsevier
Language eng
Subject 960902 Coastal and Estuarine Land Management
0905 Civil Engineering
Abstract Direct measurements of bed shear in the swash zone are presented. The data were obtained using a shear plate in medium and large-scale laboratory bore-driven swash and cover a wide range of bed roughness. Data were obtained across the full width of the swash zone and are contrasted with data from the inner surf zone. Estimates of the flow velocities through the full swash cycle were obtained through numerical modelling and calibrated against measured velocity data. The measured stresses and calculated flow velocities were subsequently used to back-calculate instantaneous local skin friction coefficients using the quadratic drag law. The data show rapid temporal variation of the bed shear stress through the leading edge of the uprush, which is typically two-four times greater than the backwash shear stresses at corresponding flow velocity. The measurements indicate strong temporal variation in the skin friction coefficient, particularly in the backwash. The general behaviour of the skin friction coefficient with Reynolds number is consistent with classical theory for certain stages of the swash cycle. A spatial variation in skin friction coefficient is also identified, which is greatest across the surf-swash boundary and likely related to variations in local turbulent intensities. Skin friction coefficients during the uprush are approximately twice those in the backwash at corresponding Reynolds number and cross-shore location. It is suggested that this is a result of the no-slip condition at the tip leading to a continually developing leading edge and boundary layer, into which high velocity fluid and momentum are constantly injected from the flow behind and above the tip region. Finally, the measured stress data are used to determine the asymmetry and cross-shore variation in potential sediment transport predicted by three forms of sediment transport formulae. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.
Keyword Bed shear stress
Swash zone
Friction coefficient
Beach morphodynamics
Sediment transport
Boundary layer
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: 2010 Higher Education Research Data Collection
School of Civil Engineering Publications
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Citation counts: TR Web of Science Citation Count  Cited 51 times in Thomson Reuters Web of Science Article | Citations
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Created: Thu, 03 Sep 2009, 17:54:22 EST by Mr Andrew Martlew on behalf of School of Civil Engineering