Sediment concentration and vertical mixing under breaking waves

Aagaard, Troels; Jensen, Stine G.

doi:10.1016/j.margeo.2012.11.015

Cited by 45 publications

(45 citation statements)

References 39 publications

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“…Understanding the physical processes that govern sediment resuspension has significant implications for aquatic ecosystems and fish habitats as well as sustainable engineering applications such as beach nourishment, maintenance of hydraulic structures, dam breaching flows, sedimentation in reservoirs, defence schemes against erosion due to floods, and aggregate dredging (Buffington, 1999;Paphitis, 2001; van Rijn et al, 2007;Thompson et al, 2011;Aagaard and Jensen, 2013;van Rijn, 2013), all of which require improved predictive models of sediment transport. However, resuspension of sediment is a complex mechanism due to the difficulty in defining the fluctuating nature of turbulent flow.…”

Section: Introductionmentioning

confidence: 99%

The influence of turbulent bursting on sediment resuspension under unidirectional currents

et al. 2017

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Abstract. Laboratory experiments were conducted in an open channel flume with a flat sandy bed to examine the role of turbulence on sediment resuspension. An acoustic Doppler velocimeter (ADV) was used to measure the instantaneous three-dimensional velocity components and acoustic backscatter as a proxy to suspended sediment concentration. Estimates of sediment transport assume that there is a mean critical velocity that needs to be exceeded before sediment transport is initiated. This approach does not consider the turbulent flow field that may initiate sediment resuspension through event-based processes such as the "bursting" phenomenon. In this paper, laboratory measurements were used to examine the sediment resuspension processes below and above the mean critical velocity. The results within a range above and below the measured mean critical velocity suggested that (1) the contribution of turbulent bursting events remained identical in both experimental conditions, (2) ejection and sweep events contributed more to the total sediment flux than up-acceleration and down-deceleration events, and (3) wavelet transform revealed a correlation between the momentum and sediment flux in both test conditions. Such similarities in conditions above and below the measured mean critical velocity highlight the need to re-evaluate the accuracy of a single time-averaged mean critical velocity for the initiation of sediment entrainment.

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Section: Introductionmentioning

confidence: 99%

The influence of turbulent bursting on sediment resuspension under unidirectional currents

et al. 2017

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“…Aagaard and Hughes [7] also conducted field measurements to investigate the role of coherent vortices generated by wave breaking on the suspended sediment concentration. Aagaard and Jensen [18] investigated the vertical distribution of sediment diffusivity according to the wave breaking types (e.g., spilling surf bores and plunging waves). They suggested that a different mixing mechanism was predominant for each wave breaking type: diffusion for spilling surf bores and convection for plunging waves.…”

Section: Introductionmentioning

confidence: 99%

Parameterization of Time-Averaged Suspended Sediment Concentration in the Nearshore

Yoon

Cox

Mori

2015

Water

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Abstract:To quantify the effect of wave breaking turbulence on sediment transport in the nearshore, the vertical distribution of time-averaged suspended sediment concentration (SSC) in the surf zone was parameterized in terms of the turbulent kinetic energy (TKE) at different cross-shore locations, including the bar crest, bar trough, and inner surf zone. Using data from a large-scale laboratory experiment, a simple relationship was developed between the time-averaged SSC and the time-averaged TKE. The vertical variation of the time-averaged SSC was fitted to an equation analogous to the turbulent dissipation rate term. At the bar crest, the proposed equation was slightly modified to incorporate the effect of near-bed sediment processes and yielded reasonable agreement. This parameterization yielded the best agreement at the bar trough, with a coefficient of determination R 2 ≥ 0.72 above the bottom boundary layer. The time-averaged SSC in the inner surf zone showed good agreement near the bed but poor agreement near the water surface, suggesting that there is a different sedimentation mechanism that controls the SSC in the inner surf zone.

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“…This lift is driven by an upward directed pressure gradient that is associated with bed shear induced ejected vortices (Sumer and Oguz, 1978). Once suspended, gravitational settling and vertical advective and diffusive mixing lead to vertical concentration profiles that follow an exponential or power function distribution, depending on the vertical distribution of turbulent kinetic energy (Aagaard and Jensen, 2013). Under breaking waves, higher entrainment and mixing rates lead to an increase in concentrations at outer flow elevations compared to shoaling locations (Nielsen, 1984;Nadaoka et al, 1988;Aagaard and Jensen, 2013).…”

Section: Suspended Sediment Transport Processesmentioning

confidence: 99%

“…Once suspended, gravitational settling and vertical advective and diffusive mixing lead to vertical concentration profiles that follow an exponential or power function distribution, depending on the vertical distribution of turbulent kinetic energy (Aagaard and Jensen, 2013). Under breaking waves, higher entrainment and mixing rates lead to an increase in concentrations at outer flow elevations compared to shoaling locations (Nielsen, 1984;Nadaoka et al, 1988;Aagaard and Jensen, 2013). The increased pick up rates under breaking waves can be attributed to high instantaneous bed shear stresses (Cox et al, 1996) and to upward directed pressure gradients in the bed under the breaking point (Sumer et al, 2013).…”

Section: Suspended Sediment Transport Processesmentioning

confidence: 99%

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Sand transport processes in the surf and swash zones

Zanden¹

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Sediment concentration and vertical mixing under breaking waves

Cited by 45 publications

References 39 publications

The influence of turbulent bursting on sediment resuspension under unidirectional currents

The influence of turbulent bursting on sediment resuspension under unidirectional currents

Parameterization of Time-Averaged Suspended Sediment Concentration in the Nearshore

Sand transport processes in the surf and swash zones

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