Surface Roller Modeling for Mean Longshore Current over a Barred Beach in a Random Wave Environment

Boussinesq modeling of longshore currents in the SandyDuck experiment under directional random wave conditions

“…This is equivalent to the results of Johnson and Pattiaratchi (2006) showing the vorticity trailing off the ends of short-crested breaking waves and the results of Long and Özkan-Haller (2009) showing the vortices induced by the transverse wave-group forcing. The fluctuations with scattered evolution of vortex pairs seem more energetic than the shear fluctuations in the simulation of Choi and Yoon (2011), Choi et al (2012), and others which exclude the effect of the phase interaction of multidirectional waves. Moreover, the energetic fluctuations seem more complicated than in the results of Chen et al (2003), in which the wave energy dissipation due to wave breaking is more gradual than in the measurements.…”

“…3. Based on the SandyDuck experiments, Choi et al (2012) described the random wave breaking process as one that can be divided into a partial breaking state and an intense breaking state. The former state corresponds to a relatively weak breaker zone where spilling breakers dominate and whitecapping occurs, whereas the latter state corresponds to a relatively strong breaker zone where plunging breakers dominate.…”

“…This is perhaps because the cross-shore velocity is very dependent on the vertical positions of the gauges used in the measurements, since the vertical profile of the cross-shore current includes not only the bottom boundary layer but also the boundary layer of shear flow due to Lagrangian mass flux and undertow. Choi et al (2012) mentioned that in the longshore array of the SandyDuck experiment the gauges closest to the shoreline (x = 175 m) were vertically located on about 50%-70% of the water column (measured upward from the bottom) and the other gauges were on about 30% of the water column. The current velocity in the present model is the velocity at the reference elevation, which is 47% of the water height (measured upward from the bottom).…”

“…Such motions include setup and setdown of the mean surface, Lagrangian mass flux between wave trough and wave crest, undertow below the wave trough, rip currents outward from the surf zone, and infragravity waves. These wave-induced phenomena, which are mean motions at gravity-wave scale but unsteady motions at infragravity-wave scale, interact with instantaneous turbulent motions due to breaking waves and thus significantly influence morphological change in coastal areas (Choi et al, 2012).…”

“…Recently, Choi and Yoon (2011) and Choi et al (2012) studied nearshore circulation in the SandyDuck experiment for random wave conditions by using the combined model SWAN-SHORECIRC (Shi et al, 2012). These studies, and many like them (Noyes et al, 2005, for example), make use of a wave-averaged formulation where forcing (either in the form of radiation stress gradients or wave dissipation (Dingemans et al, 1987;Smith, 2006)) takes the form of a smooth function which varies at surf zone scale but has no spatial structure at wave crest scale.…”