Abstract
Robust measurements of bed shear stress under wave runup flows are necessary to inform beachface sediment transport modelling. In this study, direct measurements of swash zone bed shear stress were obtained in medium and prototype-scale laboratory experiments on steep slopes. Peak shear stresses coincided with the arrival of uprush swash fronts and high-resolution measurement of swash surface profiles indicated a consistently seaward sloping swash surface with minimal evidence of a landward sloping swash front. The quadratic stress law was applied to back-calculate time-varying friction factors, which were observed to decrease with increasing Reynolds number on smooth slopes, consistent with theory for steady flows. Additionally, friction factors remained relatively constant throughout the swash cycle (except around flow reversal), with a variation of approximately ±20% from the mean value and with only small differences between uprush and backwash. Measured friction factors were observed to be larger than expected when plotted on the Moody or wave friction diagram for a given Reynolds number and relative roughness, consistent with previous field and laboratory studies at various scales.
Original language | English |
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Article number | 358 |
Journal | Journal of Marine Science and Engineering |
Volume | 7 |
Issue number | 10 |
DOIs | |
Publication status | Published - 9 Oct 2019 |
Funding
This research was funded by the Australian Research Council, grant number DP110101176. J. Puleo was supported by the National Science Foundation (OCE-1332703). The authors would like to acknowledge Michael Allis, Stefan Schimmels, Matthias Kudella and their colleagues at the GWK for their assistance with the experimental work described in this paper.
Keywords
- Bed shear stress
- Friction coefficient
- Runup
- Shear plate
- Swash
ASJC Scopus subject areas
- Civil and Structural Engineering
- Water Science and Technology
- Ocean Engineering