Generation Mechanisms of Extreme Infragravity Wave Induced Runup

Energetic infragravity (EIG) wave induced runup has been observed around the world and have led to loss of lives and damages to property. In this study, a total of 5 extreme runup events were identified out of 1,875,000 simulated waves. An envelope analysis of the offshore free surface elevations revealed that EIG wave runup events depend on the arrival time of the pulses, the amplitudes and periods of the waves in each packet, the duration of each packet, and the geometric properties of the shelf. The wavelet analysis revealed that the reef resonance contributes to the generation of EIG waves and that for an EIG wave event to occur significant amount of energy has to be leaked or transferred to low frequencies and have to be in resonance with the reef. Furthermore, a synthetic timeseries analysis revealed that most of the times more than 2 envelopes are needed to condition the shoreline, excite the reef and generate an extreme runup event. Finally, the 1D Empirical Orthogonal Function (EOF) analysis in the reef showed that the four EOF leading modes explain 98% of the IG variance on the reef. The variance is strongly dominated by the first mode since its eigen value explains 70% of the IG variance on the reef.