Near-bed hydrodynamics and turbulence below a large-scale plunging breaking wave over a mobile barred bed profile

J. Van Der Zanden, D A Van Der A, D. Hurther, I Caceres, T O'Donoghue, J. S. Ribberink

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Abstract

Detailed measurements are presented of velocities and turbulence under a large-scale regular plunging breaking wave in a wave flume. Measurements were obtained at 12 cross-shore locations around a mobile medium-sand breaker bar. They focused particularly on the dynamics of the wave bottom boundary layer (WBL) and near-bed turbulent kinetic energy (TKE), measured with an Acoustic Concentration and Velocity Profiler (ACVP). The breaking process and outer-flow hydrodynamics are in agreement with previous laboratory and field observations of plunging waves, including a strong undertow in the bar trough region. The WBL thickness matches with previous studies at locations offshore from the bar crest, but it increases near the breaking-wave plunge point. This relates possibly to breaking-induced TKE or to the diverging flow at the shoreward slope of the bar. Outer-flow TKE is dominated by wave breaking and exhibits strong spatial variation with largest TKE above the breaker bar crest. Below the plunge point, breaking-induced turbulence invades the WBL during both crest and trough half-cycle. This results in an increase in the time-averaged TKE in the WBL (with a factor 3) and an increase in peak onshore and offshore near-bed Reynolds stresses (with a factor 2) from shoaling to breaking region. A fraction of locally-produced TKE is advected offshore over a distance of a few meters to shoaling locations during the wave trough phase, and travels back onshore during the crest half-cycle. The results imply that breaking-induced turbulence, for large-scale conditions, may significantly affect near-bed sediment transport processes. This article is protected by copyright. All rights reserved.
Original languageEnglish
Pages (from-to)6482-6506
Number of pages15
JournalJournal of Geophysical Research: Oceans
Volume121
Issue number8
Early online date31 Aug 2016
DOIs
Publication statusPublished - Aug 2016

Keywords

  • wave bottom boundary layer
  • breaking waves
  • surf zone
  • turbulence
  • wave flume experiment
  • sediment transport

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