Wave-wave interactions near the shore

Abstract

Wave-wave interaction on a beach may be regarded as a rather special example of second order, resonant interaction within a rapidly changing wave spectrum. However, the existence of trapped modes, edge waves, having a very different dispersion relation from that of the incoming waves provides the possibility of transferring energy efficiently to much lower frequencies than are normally observed in the open sea. Any detailed analysis of these interactions is, however, greatly complicated by the breaking of the incoming waves as they reach water depths of the order of their wave height. Recent field and laboratory data suggest that,although the wave breaking introduces new effects, nearshore currents and set-up for example, the forcing of the purely wave-wave interaction is not greatly altered by the breaking process. However, the increased effective viscosity of the region associated with the turbulent surf zone seems to play a significant role in suppressing resonance. Given equal forcing, edge waves whose offshore length scales are large compared to the surf zone width are therefore more likely to exist.