Low Frequency Wave Generation in a Spectral Model

The nearshore and surf zone areas of the coast often have considerable low frequency energy, which serves to modulate breaking events and can be linked to the formation of larger-scale bottom features. One likely mechanism for the generation of this energy is subharmonic interactions, in which high frequency waves interact to augment energy in frequencies below the spectral peak. The performance of most phase-resolved frequency domain models has not been verified for subharmonic interactions, despite the fact that the necessary terms for these interactions are present in the models. In this study we investigate the generation of low frequency energy in two laboratory experiments and discuss the suitability of frequency domain phase resolved models for predicting this energy transfer. The effect of bottom slope and breaking (and their representation in the predictive models) will be evaluated. Of particular interest is the rate of energy transfer from spectral peak to subharmonic frequencies, and further down to very low frequencies. It has been surmised that energy in these very low frequency bands have potential for coastal flooding during storm events over reef systems; the application of this work to predictive capabilities in this regard will be discussed.