Vortex-induced suspension of sediment in the surf zone

Otsuka, Junichi; Saruwatari, Ayumi; Watanabe, Yasunori

doi:10.1016/j.advwatres.2017.08.021

Cited by 16 publications

(6 citation statements)

References 40 publications

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“…Over the last decades, turbulence under breaking waves has been of vast scientific interest because of its effects on near-shore morphodynamics. Several studies have reported the entrainment of significant amounts of sediments by breaking waves (Nielsen, 1984;Yu et al, 1993;Beach & Sternberg, 1996), and recent studies have attributed this to wave breaking turbulence that reaches the bed (Scott et al, 2009;Aagaard & Hughes, 2010;Sumer et al, 2013;Otsuka et al, 2017). The timing of wave breaking turbulence arrival at the bed has significant implications for the phase-dependent pickup of sediment (Yoon & Cox, 2012;Brinkkemper et al, 2017), and the advection of suspended grains is closely related to the transport of TKE (LeClaire & Ting, 2017;.…”

Section: Introductionmentioning

confidence: 99%

Spatial and temporal distributions of turbulence under bichromatic breaking waves

Zanden

Caceres

et al. 2019

Coastal Engineering

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The present study aims to extend insights of surf zone turbulence dynamics to wave groups. In a large-scale wave flume, bichromatic wave groups were produced with 31.5 s group period, 4.2 s mean wave period, and a 0.58 m maximum wave height near the paddle. This condition resulted in plunging-type wave breaking over a fixed, gravel-bed, barred profile. Optic, acoustic and electromagnetic instruments were used to measure the flow and the spatial and temporal distributions of turbulent kinetic energy (TKE). The measurements showed that turbulence in the shoaling region is primarily bed-generated and decays almost fully within one wave cycle, leading to TKE variations at the short wave frequency. The wave breaking-generated turbulence, in contrast, decays over multiple wave cycles, leading to a gradual increase and decay of TKE during a wave group cycle. In the wave breaking region, TKE dynamics are driven by the production and subsequent downward transport of turbulence under the successive breaking waves in the group. Consequently, the maximum near-bed TKE in the breaking region can lag the highest breaking wave by up to 2.5 wave cycles. The net cross-shore transport of TKE is in the shoaling region primarily driven by shortwave velocities and is shoreward-directed; in the wave breaking region, the TKE transport is seaward-directed by the undertow and the longwave velocities. Downward transport of TKE is driven by the vertical component of the timeaveraged flow. The cross-shore and vertical diffusive transport rates are small relative to the advective transport rates.

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Section: Introductionmentioning

confidence: 99%

Spatial and temporal distributions of turbulence under bichromatic breaking waves

Zanden

Caceres

et al. 2019

Coastal Engineering

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“…COMPUTATIONAL METHOD Three-dimensional Large Eddy Simulation was used to compute the turbulent flow under plunging wave-breaking over a uniformly sloping beach in the same manner as Otsuka (2017). We confirmed major features of the computed velocity and turbulent kinetic energy were in reasonably good agreement with the experimental ones.…”

Section: Introductionmentioning

confidence: 60%

“…Three-dimensional vortex structures involving obliquely descending eddies (ODE), produced by depth-induced breaking-waves, has been proved to be associated with local sediment suspension in the surf zone (Zhou et al, 2017); vertical velocity fluctuations around the ODEs induces sediment suspension near the bed. Otsuka et al (2017) explained the mechanical contributions of the ODEs to enhance local sediment suspension under the breaking waves and modeled the vortex-induced suspension to predict the profile of the equilibrium sediment concentration in the surf zone. In order to predict local behaviors of sediment, however, sediment-turbulence interactions in the transitional turbulence under breaking waves need to be understood.…”

Section: Introductionmentioning

confidence: 99%

Sediment Advection and Diffusion by Obliquely Descending Eddies

Saruwatari¹,

Otsuka²,

Watanabe³

2018

Int. Conf. Coastal. Eng.

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Three-dimensional vortex structures involving obliquely descending eddies (ODE), produced by depth-induced breaking-waves, has been proved to be associated with local sediment suspension in the surf zone (Zhou et al., 2017); vertical velocity fluctuations around the ODEs induces sediment suspension near the bed. Otsuka et al. (2017) explained the mechanical contributions of the ODEs to enhance local sediment suspension under the breaking waves and modeled the vortex-induced suspension to predict the profile of the equilibrium sediment concentration in the surf zone. In order to predict local behaviors of sediment, however, sediment-turbulence interactions in the transitional turbulence under breaking waves need to be understood. The interaction may be described in terms of Schmidt number (Sc). Sc has been empirically determined for trivial steady flows such as open channel or pipe flows. In the surf zone where organized flows evolve into a turbulent bore, the interaction may vary with the transitional feature of turbulence during a wave-breaking process, and thus Sc may be variable in time and space. No appropriate Sc model has been proposed for the surf zone flow. A parametric study on the sediment motion with respect to the variation of Sc is required for better prediction of sediment transport in the surf zone. In this study, contributions of the sediment advection and diffusion in the vortex structure to the concentration are computationally investigated. Effects of Sc to the sediment suspension and diffusion process will be also discussed in this work.

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“…As waves reach the shallower areas, bed shear stress increases gradually (Fleit et al 2016), resulting in the potential resuspension of fine sediments as well Houser 2011;Rapaglia et al 2015). Breaking waves are particularly responsible for even more intense sediment remobilization through mechanisms driven by organized vortices under the breakers (Otsuka et al 2017;Voulgaris and Collins 2000). The resulting sediment remobilization and transport play a key role in bank erosion processes (Duró et al 2020) and, moreover, have ecological impacts as well (Kucera-Hirzinger et al 2009;Schallenberg and Burns 2004;Utne-Palm 2004).…”

Section: Introductionmentioning

confidence: 99%

“…PIV was originally developed for experimental environments, with special precision instruments (cameras, lasers, synchronizers, etc.). PIV-based methods are rather common in the hydroscience community and in the analysis of wave hydrodynamics in particular (e.g., Chang and Liu 2000;Cowen et al 2003;Kimmoun and Branger 2007;Otsuka et al 2017).…”

Section: Introductionmentioning

confidence: 99%

LSPIV analysis of ship-induced wave wash

Fleit

Baranya

2022

Exp Fluids

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Ship-induced wave wash affects the hydromorphological and ecological state of rivers through various mechanisms. The direct proximity of the riverbank is usually the most exposed, as the hydrodynamic stresses are the highest in these shallow water areas. Contrary to the steady and almost still, natural flow conditions (i.e., no waves of anthropogenic source), shoaling and breaking of ship waves increase the hydrodynamic stresses by orders of magnitudes, having notable ecological consequences, and resulting in bank erosion as well. Due to the shallow water depths and temporary drying, conventional measurement techniques are no longer applicable in these areas. In this study, large-scale particle image velocimetry (LSPIV) is used to quantify the prevailing flow conditions. In the absence of ground truth data in the wave breaking region, a high-resolution computational fluid dynamics model—verified with field pressure and acoustic Doppler velocimetry data—is used for the cross-validation of the LSPIV results. The results underline the applicability of LSPIV for the hydrodynamic analysis of wave velocities in this special riverine swash zone, which is of key importance from the aspect of ecology and bank erosion as well. Graphical abstract

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Vortex-induced suspension of sediment in the surf zone

Cited by 16 publications

References 40 publications

Spatial and temporal distributions of turbulence under bichromatic breaking waves

Spatial and temporal distributions of turbulence under bichromatic breaking waves

Sediment Advection and Diffusion by Obliquely Descending Eddies

LSPIV analysis of ship-induced wave wash

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