Infragravity Waves in Storm Conditions

Abstract

Nearshore sediment is actively reworked during major storms,often significantly altering the nearshore morphology. It has been suggested that infragravity waves with wave periods 30-300 seconds are very important in the formation of major nearshore features. A field study to further understand the nature of infragravity waves was carried out in Martinique Beach, Nova Scotia. Velocity measurements were taken using three electromagnetic flowmeters. Incident conditions varied from calm to swell and wind waves generated by hurricane Belle. Spectral analysis of the low tides revealed a sharp increase in the infragravity band energy associated with the storm. Throughout the storm the spectra of all three instruments were dominated by a strong 100 second peak which remained constant in frequency despite significant changes in the incident wave field. This peak is found to satisfy edge wave theory. A frequency selection mechanism based on longshore topographic trapping of edge waves is suggested.