Generation of Free Infragravity Waves by Time-Varying Breakpoint with Real Wave Conditions

Abstract

Contardo, S. and Symonds, G., 2016. Generation of free infragravity waves by time-varying breakpoint with real wave conditions. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 836–840. Coconut Creek (Florida), ISSN 0749-0208.Breakpoint forcing is one of the major mechanisms for generation of free infragravity waves in the surf zone. Steep bed slopes, normalised to the incident sea-swell wavelength, are recognized to favor breakpoint forcing, but no study assesses the infragravity energy generated by breakpoint forcing in real conditions. We extend the breakpoint forcing model from bichromatic to spectral forcing and dimenzionalize the model output, and we estimate the sensitivity of the model to various spectral parameters on a plane beach. Steep beaches and short period waves (wind-sea) are favourable to breakpoint forcing, as expected. We also find that more energy is generated with real, multipeak, spectral forcing than with Jonswap spectra. The predicted infragravity response is consistent with observations on a barred beach suggesting breakpoint forcing is a major mechanism for the generation of free infragravity waves in the surf zone.