Cross-shore wind-induced changes to field-scale overturning wave shape

The shape of depth-limited breaking-wave overturns is important for turbulence injection, bubble entrainment and sediment suspension. Overturning wave shape depends on a nonlinearity parameter H/h, where H is the wave height, and h is the water depth. Cross-shore wind direction (offshore/onshore) and magnitude affect laboratory shoaling wave shape and breakpoint location X-bp, but wind effects on overturning wave shape are largely unstudied. We perform field-scale experiments at the Surf Ranch wave basin with fixed bathymetry and asymptotic to 2.25 m shoaling solitons with small height variations propagating at C = 6.7 m s(-1). Observed non-dimensional cross-wave wind U-w was onshore and offshore, varying realistically (-1.2 < U-w/C < 0.7). Georectified images, a wave staff, and lidar are used to estimate X-bp, H/h, overturn area A and aspect ratio for 22 waves. The non-dimensionalized X-bp was inversely related to U-w/C. The non-dimensional overturn area and aspect ratio also were inversely related to U-w/C, with smaller and narrower overturns for increasing onshore wind. No overturning shape dependence on the weakly varying H/h was seen. The overturning shape variation was as large as prior laboratory experiments with strong H/h variations without wind. An idealized potential air flow simulation on steep shoaling soliton shape has strong surface pressure variations, potentially inducing overturning shape changes. Through wave-overturning impacts on turbulence and sediment suspension, coastal wind variations could be relevant for near-shore morphology.

Automated summary

The shape of shallow water breaking waves is important for various processes such as turbulence injection and sediment suspension. The shape of breaking waves depends on a nonlinear parameter H/h, where H is the wave height and h is the water depth. The effects of cross-shore wind on breaking wave shape are understudied.