INFRAGRAVITY WAVE PROPAGATION AND DISSIPATION ON A LOW-SLOPING LABORATORY BEACH

An extensive new laboratory dataset, obtained on a 1:80 sloping fixed beach, is analyzed to obtain further insight into infragravity-wave propagation and dissipation. In our dataset, infragravity waves originate from the non-linear energy transfer from short waves. The previously reported change in phase lag of the infragravity waves behind the short wave group is also observed in our data, and induces a frequency-dependent infragravity growth rate during shoaling. Ultimately, negative zero-lag correlations with the short wave groups offshore of the surf zone change into positive correlations in shallow water, indicating depth modulation of the short waves by the infragravity waves. Ninety % of the incoming infragravity-wave energy is observed to dissipate, which initiates at the start of short-wave breaking. About half of that 90% is dissipated very close to shore (swash zone) potentially because of infragravity-wave breaking.