Wind Effects on Shoaling Wave Shape

Abstract

Near the shore, cross-shore winds strongly affect the location of the break point and the breaking-wave height. From casual observation from the beach, wind direction (onshore or offshore) and speed also appear to affect wave shape (i.e., skewness and asymmetry), although as of yet this effect has not been quantified near the shore. The effect of wind on shoaling wave shape is investigated with laboratory experiments using monochromatic waves and onshore-directed wind. Wind increases the shoaling wave energy at discrete multiples of the primary frequency and has a significant effect on the wave shape at both a deeper and shallower shoaling locations. At the shallower location, the ratio of wave energy at 2 times the primary frequency to the primary frequency is also a function of wind speed, indicating interaction between the wind and the nonlinear wave shoaling process. Nearshore wave models do not account for these wind effects. Incorrect predictions of third-order velocity moments (wave shape), believed to control wave-driven sediment transport, would result in incorrect beach morphological evolution predictions.