Bound and free infragravity waves over a bar

Abstract

This study aims to investigate the changes in the infragravity wave energy under partial short-wave breaking conditions induced by a longshore bar. Field observations of near-bottom pressure records on a cross-shore array were analysed for such purpose. The bispectrum was employed to detect the phase-coupling between short and infragravity wave frequencies. This allowed to separate the infragravity wave energy in bound and free energy components. The bar crest induced a decrease on the short-wave energy due to depth-induced breaking. At the same location, a damping on the bound infragravity wave energy was observed. This damping coincides with a negative value of the short-wave radiation stress cross-shore gradient. This provides evidence that bound infragravity wave energy decreases with a reduction in the forcing.