Large-scale laboratory study of breaking wave hydrodynamics over a fixed bar

Dominic A. Van Der A, Joep Van Der Zanden, Tom O'Donoghue, David Hurther, Ivan Cáceres, Stuart J. McLelland, Jan S. Ribberink

Research output: Contribution to journalArticle

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Abstract

A large-scale wave flume experiment has been carried out involving a T=4s regular wave with H=0.85 m wave height plunging over a fixed barred beach profile. Velocity profiles were measured at twelve locations along the breaker bar using LDA and ADV. A strong undertow is generated reaching magnitudes of 0.8 m/s on the shoreward side of the breaker bar. A circulation pattern occurs between the breaking area and the inner surf zone. Time-averaged turbulent kinetic energy (TKE) is largest in the breaking area on the shoreward side of the bar where the plunging jet penetrates the water column. At this location, and on the bar crest, TKE generated at the water surface in the breaking process reaches the bottom boundary layer. In the breaking area TKE does not reduce to zero within a wave cycle which leads to a high level of “residual” turbulence and therefore lower temporal variation in TKE compared to previous studies of breaking waves on plane beach slopes. It is argued that this residual turbulence results from the breaker bar-trough geometry, which enables larger length- and time-scales of breaking generated vortices and which enhances turbulence production within the water column compared to plane beaches. Transport of TKE is dominated by the undertow-related flux, whereas the wave-related and turbulent fluxes are approximately an order of magnitude smaller. Turbulence production and dissipation are largest in the breaker zone and of similar magnitude, but in the shoaling zone and inner surf zone production is negligible and dissipation dominates. This article is protected by copyright. All rights reserved.
Original languageEnglish
Pages (from-to)3287-3310
Number of pages34
JournalJournal of Geophysical Research: Oceans
Volume122
Issue number4
Early online date24 Apr 2017
DOIs
Publication statusPublished - Apr 2017

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breaking wave
kinetic energy
hydrodynamics
surf zone
turbulence
undertow
dissipation
beach
water column
beach profile
flume experiment
benthic boundary layer
wave height
velocity profile
vortex
trough
temporal variation
laboratory
timescale
surface water

Keywords

  • breaking wave
  • plunging wave
  • wave flume experiment
  • turbulence
  • fixed breaker bar

Cite this

Large-scale laboratory study of breaking wave hydrodynamics over a fixed bar. / Van Der A, Dominic A.; Van Der Zanden, Joep; O'Donoghue, Tom; Hurther, David; Cáceres, Ivan; McLelland, Stuart J. ; Ribberink, Jan S.

In: Journal of Geophysical Research: Oceans, Vol. 122, No. 4, 04.2017, p. 3287-3310.

Research output: Contribution to journalArticle

Van Der A, Dominic A. ; Van Der Zanden, Joep ; O'Donoghue, Tom ; Hurther, David ; Cáceres, Ivan ; McLelland, Stuart J. ; Ribberink, Jan S. / Large-scale laboratory study of breaking wave hydrodynamics over a fixed bar. In: Journal of Geophysical Research: Oceans. 2017 ; Vol. 122, No. 4. pp. 3287-3310.
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abstract = "A large-scale wave flume experiment has been carried out involving a T=4s regular wave with H=0.85 m wave height plunging over a fixed barred beach profile. Velocity profiles were measured at twelve locations along the breaker bar using LDA and ADV. A strong undertow is generated reaching magnitudes of 0.8 m/s on the shoreward side of the breaker bar. A circulation pattern occurs between the breaking area and the inner surf zone. Time-averaged turbulent kinetic energy (TKE) is largest in the breaking area on the shoreward side of the bar where the plunging jet penetrates the water column. At this location, and on the bar crest, TKE generated at the water surface in the breaking process reaches the bottom boundary layer. In the breaking area TKE does not reduce to zero within a wave cycle which leads to a high level of “residual” turbulence and therefore lower temporal variation in TKE compared to previous studies of breaking waves on plane beach slopes. It is argued that this residual turbulence results from the breaker bar-trough geometry, which enables larger length- and time-scales of breaking generated vortices and which enhances turbulence production within the water column compared to plane beaches. Transport of TKE is dominated by the undertow-related flux, whereas the wave-related and turbulent fluxes are approximately an order of magnitude smaller. Turbulence production and dissipation are largest in the breaker zone and of similar magnitude, but in the shoaling zone and inner surf zone production is negligible and dissipation dominates. This article is protected by copyright. All rights reserved.",
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AU - McLelland, Stuart J.

AU - Ribberink, Jan S.

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N2 - A large-scale wave flume experiment has been carried out involving a T=4s regular wave with H=0.85 m wave height plunging over a fixed barred beach profile. Velocity profiles were measured at twelve locations along the breaker bar using LDA and ADV. A strong undertow is generated reaching magnitudes of 0.8 m/s on the shoreward side of the breaker bar. A circulation pattern occurs between the breaking area and the inner surf zone. Time-averaged turbulent kinetic energy (TKE) is largest in the breaking area on the shoreward side of the bar where the plunging jet penetrates the water column. At this location, and on the bar crest, TKE generated at the water surface in the breaking process reaches the bottom boundary layer. In the breaking area TKE does not reduce to zero within a wave cycle which leads to a high level of “residual” turbulence and therefore lower temporal variation in TKE compared to previous studies of breaking waves on plane beach slopes. It is argued that this residual turbulence results from the breaker bar-trough geometry, which enables larger length- and time-scales of breaking generated vortices and which enhances turbulence production within the water column compared to plane beaches. Transport of TKE is dominated by the undertow-related flux, whereas the wave-related and turbulent fluxes are approximately an order of magnitude smaller. Turbulence production and dissipation are largest in the breaker zone and of similar magnitude, but in the shoaling zone and inner surf zone production is negligible and dissipation dominates. This article is protected by copyright. All rights reserved.

AB - A large-scale wave flume experiment has been carried out involving a T=4s regular wave with H=0.85 m wave height plunging over a fixed barred beach profile. Velocity profiles were measured at twelve locations along the breaker bar using LDA and ADV. A strong undertow is generated reaching magnitudes of 0.8 m/s on the shoreward side of the breaker bar. A circulation pattern occurs between the breaking area and the inner surf zone. Time-averaged turbulent kinetic energy (TKE) is largest in the breaking area on the shoreward side of the bar where the plunging jet penetrates the water column. At this location, and on the bar crest, TKE generated at the water surface in the breaking process reaches the bottom boundary layer. In the breaking area TKE does not reduce to zero within a wave cycle which leads to a high level of “residual” turbulence and therefore lower temporal variation in TKE compared to previous studies of breaking waves on plane beach slopes. It is argued that this residual turbulence results from the breaker bar-trough geometry, which enables larger length- and time-scales of breaking generated vortices and which enhances turbulence production within the water column compared to plane beaches. Transport of TKE is dominated by the undertow-related flux, whereas the wave-related and turbulent fluxes are approximately an order of magnitude smaller. Turbulence production and dissipation are largest in the breaker zone and of similar magnitude, but in the shoaling zone and inner surf zone production is negligible and dissipation dominates. This article is protected by copyright. All rights reserved.

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JO - Journal of Geophysical Research: Oceans

JF - Journal of Geophysical Research: Oceans

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