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 language | English |
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Pages (from-to) | 6482-6506 |
Number of pages | 15 |
Journal | Journal of Geophysical Research: Oceans |
Volume | 121 |
Issue number | 8 |
Early online date | 31 Aug 2016 |
DOIs | |
Publication status | Published - Aug 2016 |
Bibliographical note
Funded byThe research presented in this paper is part of the SINBAD project. Grant Number: STW (12058) and EPSRC (EP/J00507X/1, EP/J005541/1)
Keywords
- wave bottom boundary layer
- breaking waves
- surf zone
- turbulence
- wave flume experiment
- sediment transport