Suspended sediment transport around a large-scale laboratory breaker bar

J. van der Zanden; D. A. van der A; D. Hurther; I. Cáceres; T. O'Donoghue; J. S. Ribberink

doi:10.1016/j.coastaleng.2017.03.007

Suspended sediment transport around a large-scale laboratory breaker bar

J. van der Zanden^* (Corresponding Author), D. A. van der A, D. Hurther, I. Cáceres, T. O'Donoghue, J. S. Ribberink

^*Corresponding author for this work

Engineering

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Abstract

This paper presents novel insights into suspended sediment concentrations and fluxes under a large-scale laboratory plunging wave. Measurements of sediment concentrations and velocities were taken at 12 locations around an evolving breaker bar, covering the complete breaking region from shoaling to inner surf zone, with particular high resolution near the bed using an Acoustic Concentration and Velocity Profiler. Wave breaking evidently affects sediment pick-up rates, which increase by an order of magnitude from shoaling to breaking zone. Time-averaged reference concentrations correlate poorly with periodic and time-averaged near-bed velocities, but correlate significantly with near-bed time-averaged turbulent kinetic energy. The net depth-integrated suspended transport is offshore-directed and primarily attributed to current-related fluxes (undertow) at outer-flow elevations (i.e. above the wave bottom boundary layer). The wave-related suspended transport is onshore-directed and is generally confined to the wave bottom boundary layer. Cross-shore gradients of sediment fluxes are quantified to explain spatial patterns of sediment pick-up and deposition and of cross-shore sediment advection. Suspended particles travel back and forth between the breaking and shoaling zones following the orbital motion, leading to local intra-wave concentration changes. At locations between the breaker bar crest and bar trough, intra-wave concentration changes are due to a combination of horizontal advection and of vertical exchange with the bedload layer: sediment is entrained in the bar trough during the wave trough phase, almost instantly advected offshore, and deposited near the bar crest during the wave crest phase. Finally, these results are used to suggest improvements for suspended sediment transport models.

Original language	English
Pages (from-to)	51-69
Number of pages	19
Journal	Coastal Engineering
Volume	125
Early online date	22 Apr 2017
DOIs	https://doi.org/10.1016/j.coastaleng.2017.03.007
Publication status	Published - 1 Jul 2017

Bibliographical note

The authors wish to thank the staff of CIEMLAB (Joaquim Sospedra, Oscar Galego and Ricardo Torres) and Mick Poppe from the University of Twente for their contributions to the experiments. We are also grateful to fellow SINBAD researchers and to prof. Peter Thorne for their feedback on preliminary results and to two anonymous reviewers and prof. dr. Suzanne J.M.H. Hulscher for their feedback on the draft manuscript. The research presented in this paper is part of the SINBAD project, funded by STW (12058) and EPSRC (EP/J00507X/1, EP/J005541/1). We further acknowledge the European Community’s FP7 project Hydralab IV (contract no. 261520) for funding the accompanying SandT-Pro experiments and the ACVP development by CNRS-LEGI (D. Hurther, P.-A. Barraud, J.-M. Barnoud).

Keywords

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

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Dominic Van der A
- Engineering, Engineering - Senior Lecturer
Person: Academic

Cite this

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title = "Suspended sediment transport around a large-scale laboratory breaker bar",

abstract = "This paper presents novel insights into suspended sediment concentrations and fluxes under a large-scale laboratory plunging wave. Measurements of sediment concentrations and velocities were taken at 12 locations around an evolving breaker bar, covering the complete breaking region from shoaling to inner surf zone, with particular high resolution near the bed using an Acoustic Concentration and Velocity Profiler. Wave breaking evidently affects sediment pick-up rates, which increase by an order of magnitude from shoaling to breaking zone. Time-averaged reference concentrations correlate poorly with periodic and time-averaged near-bed velocities, but correlate significantly with near-bed time-averaged turbulent kinetic energy. The net depth-integrated suspended transport is offshore-directed and primarily attributed to current-related fluxes (undertow) at outer-flow elevations (i.e. above the wave bottom boundary layer). The wave-related suspended transport is onshore-directed and is generally confined to the wave bottom boundary layer. Cross-shore gradients of sediment fluxes are quantified to explain spatial patterns of sediment pick-up and deposition and of cross-shore sediment advection. Suspended particles travel back and forth between the breaking and shoaling zones following the orbital motion, leading to local intra-wave concentration changes. At locations between the breaker bar crest and bar trough, intra-wave concentration changes are due to a combination of horizontal advection and of vertical exchange with the bedload layer: sediment is entrained in the bar trough during the wave trough phase, almost instantly advected offshore, and deposited near the bar crest during the wave crest phase. Finally, these results are used to suggest improvements for suspended sediment transport models. ",

keywords = "breaking waves, sediment transport, suspended sediment, wave bottom boundary layer, surf zone, wave flume experiment",

author = "{van der Zanden}, J. and {van der A}, {D. A.} and D. Hurther and I. C{\'a}ceres and T. O'Donoghue and Ribberink, {J. S.}",

note = "The authors wish to thank the staff of CIEMLAB (Joaquim Sospedra, Oscar Galego and Ricardo Torres) and Mick Poppe from the University of Twente for their contributions to the experiments. We are also grateful to fellow SINBAD researchers and to prof. Peter Thorne for their feedback on preliminary results and to two anonymous reviewers and prof. dr. Suzanne J.M.H. Hulscher for their feedback on the draft manuscript. The research presented in this paper is part of the SINBAD project, funded by STW (12058) and EPSRC (EP/J00507X/1, EP/J005541/1). We further acknowledge the European Community{\textquoteright}s FP7 project Hydralab IV (contract no. 261520) for funding the accompanying SandT-Pro experiments and the ACVP development by CNRS-LEGI (D. Hurther, P.-A. Barraud, J.-M. Barnoud).",

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T1 - Suspended sediment transport around a large-scale laboratory breaker bar

AU - van der Zanden, J.

AU - van der A, D. A.

AU - Hurther, D.

AU - Cáceres, I.

AU - O'Donoghue, T.

AU - Ribberink, J. S.

N1 - The authors wish to thank the staff of CIEMLAB (Joaquim Sospedra, Oscar Galego and Ricardo Torres) and Mick Poppe from the University of Twente for their contributions to the experiments. We are also grateful to fellow SINBAD researchers and to prof. Peter Thorne for their feedback on preliminary results and to two anonymous reviewers and prof. dr. Suzanne J.M.H. Hulscher for their feedback on the draft manuscript. The research presented in this paper is part of the SINBAD project, funded by STW (12058) and EPSRC (EP/J00507X/1, EP/J005541/1). We further acknowledge the European Community’s FP7 project Hydralab IV (contract no. 261520) for funding the accompanying SandT-Pro experiments and the ACVP development by CNRS-LEGI (D. Hurther, P.-A. Barraud, J.-M. Barnoud).

PY - 2017/7/1

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N2 - This paper presents novel insights into suspended sediment concentrations and fluxes under a large-scale laboratory plunging wave. Measurements of sediment concentrations and velocities were taken at 12 locations around an evolving breaker bar, covering the complete breaking region from shoaling to inner surf zone, with particular high resolution near the bed using an Acoustic Concentration and Velocity Profiler. Wave breaking evidently affects sediment pick-up rates, which increase by an order of magnitude from shoaling to breaking zone. Time-averaged reference concentrations correlate poorly with periodic and time-averaged near-bed velocities, but correlate significantly with near-bed time-averaged turbulent kinetic energy. The net depth-integrated suspended transport is offshore-directed and primarily attributed to current-related fluxes (undertow) at outer-flow elevations (i.e. above the wave bottom boundary layer). The wave-related suspended transport is onshore-directed and is generally confined to the wave bottom boundary layer. Cross-shore gradients of sediment fluxes are quantified to explain spatial patterns of sediment pick-up and deposition and of cross-shore sediment advection. Suspended particles travel back and forth between the breaking and shoaling zones following the orbital motion, leading to local intra-wave concentration changes. At locations between the breaker bar crest and bar trough, intra-wave concentration changes are due to a combination of horizontal advection and of vertical exchange with the bedload layer: sediment is entrained in the bar trough during the wave trough phase, almost instantly advected offshore, and deposited near the bar crest during the wave crest phase. Finally, these results are used to suggest improvements for suspended sediment transport models.

AB - This paper presents novel insights into suspended sediment concentrations and fluxes under a large-scale laboratory plunging wave. Measurements of sediment concentrations and velocities were taken at 12 locations around an evolving breaker bar, covering the complete breaking region from shoaling to inner surf zone, with particular high resolution near the bed using an Acoustic Concentration and Velocity Profiler. Wave breaking evidently affects sediment pick-up rates, which increase by an order of magnitude from shoaling to breaking zone. Time-averaged reference concentrations correlate poorly with periodic and time-averaged near-bed velocities, but correlate significantly with near-bed time-averaged turbulent kinetic energy. The net depth-integrated suspended transport is offshore-directed and primarily attributed to current-related fluxes (undertow) at outer-flow elevations (i.e. above the wave bottom boundary layer). The wave-related suspended transport is onshore-directed and is generally confined to the wave bottom boundary layer. Cross-shore gradients of sediment fluxes are quantified to explain spatial patterns of sediment pick-up and deposition and of cross-shore sediment advection. Suspended particles travel back and forth between the breaking and shoaling zones following the orbital motion, leading to local intra-wave concentration changes. At locations between the breaker bar crest and bar trough, intra-wave concentration changes are due to a combination of horizontal advection and of vertical exchange with the bedload layer: sediment is entrained in the bar trough during the wave trough phase, almost instantly advected offshore, and deposited near the bar crest during the wave crest phase. Finally, these results are used to suggest improvements for suspended sediment transport models.

KW - breaking waves

KW - sediment transport

KW - suspended sediment

KW - wave bottom boundary layer

KW - surf zone

KW - wave flume experiment

U2 - 10.1016/j.coastaleng.2017.03.007

DO - 10.1016/j.coastaleng.2017.03.007

M3 - Article

SN - 0378-3839

VL - 125

SP - 51

EP - 69

JO - Coastal Engineering

JF - Coastal Engineering

ER -

Suspended sediment transport around a large-scale laboratory breaker bar

Abstract

Bibliographical note

Keywords

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