Contributions to the wave-mean momentum balance in the surf zone

Jebbe J. van der Werf, Jan S. Ribberink, Wouter Kranenburg, Kevin Neessen, M. Boers

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Fig. 1. (a) Measured wave heights, (b) bed level and still water level


Fig. 2. Vertical profiles of undertow at four cross-shore positions around the first…


Fig. 3. Mean normal stress for (a) Test 1B and (b) Test 1C


Fig. 4. Vertical profiles of mean normal stress at four cross-shore positions around…


Fig. 5. Vertical profiles of mean normal stress for Test 1B (bar crest located at x=20


Fig. 6. Mean shear stress for (a) Test 1B and (b) Test 1C















Elsevier


Coastal Engineering

Volume 121, March 2017, Pages 212-220

Coastal Engineering

Contributions to the wave-mean momentum balance in the surf zone




Author links open overlay panel Jebbe van der Werf a, b, Jan Ribberink b, Wouter Kranenburg a, Kevin Neessen b, c, Marien Boers a
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https://doi.org/10.1016/j.coastaleng.2016.12.007Get rights and content







Highlights


We investigate stresses and forces that control mean surfzone hydrodynamics based on detailed wave flume velocity measurements above a fixed sloping bed including two breaker bars.

A significant part of the normal stress is concentrated between the wave trough and crest level; the vertical distribution below the wave trough level is fairly uniform.

The wave Reynolds stress is an important contribution to the total shear stress.

Apart from the horizontal normal stress gradients, the vertical shear stress gradients are important in the force balance for the breaker zone.

These experimental observations have implications for the cross-shore mean flow modeling in the surf zone.


Mean (wave-averaged) cross-shore flow in the surfzone has a strong vertical variation. Good understanding and prediction of this mean velocity profile is of crucial importance, as it determines the advective transport of constituents, such as sediment, and consequently the coastal morphological evolution. Most modeling systems for coastal hydrodynamics and morphodynamics do no resolve the wave motion, and wave-current coupling is a challenging topic. This paper investigates stresses and forces that control mean surfzone hydrodynamics based on detailed wave flume velocity measurements above a fixed sloping bed including two breaker bars. The data show that the vertical distribution of normal stress below the wave trough level is fairly uniform. At the same time, the data suggest that a significant part is concentrated between the wave trough and crest level. Furthermore, it is concluded that the horizontal radiation stress gradients and the vertical shear stress gradients can be of the same order of magnitude in the vicinity of the breaker bar. Although usually ignored in 3D mean flow modeling systems, the wave Reynolds stress makes an important contribution to the mean shear stress. The normal stress below the wave trough level could be reasonably well predicted using the classical [16] expression, accounting for the contribution between wave crest and trough. The model of [39] reproduces the main trends in the wave Reynolds stresses above the bottom boundary layer.
Original languageEnglish
Pages (from-to)212-220
JournalCoastal engineering
Volume121
DOIs
Publication statusPublished - 2016

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