UC San Diego

Infragravity (IG) waves are long period ocean waves (25 to 250 seconds) generated by nonlinear, long period variations in the momentum flux of incident sea swell (short period) wave groups in shallow water. IG waves are ubiquitous on the shoreline, can dominate the runup during storms, and contributes to wave driven flooding. Methods for predicting IG waves are a current topic for research in Nearshore Physical Oceanography. Typical methods are either empirical parametrizations or numerical wave models. In chapter 1, we test the nonhydrostatic numerical wave model SWASH for predicting infragravity waves by simulating waves from offshore measurements in 6m depth, along a 1D transect to shore, and comparing to LiDAR observations of wave runup and overtopping in Imperial Beach, CA. SWASH (1D) demonstrates high skill for predicting wave by wave runup and overtopping. In chapter 2, we challenge the 1D assumption inherent in chapter 1 by examining the impacts of infragravity edge waves, which propagate alongshore (in 2D) rather than cross-shore, over 2 months at Torrey Pines. Edge waves can be up to 25% of the runup, and are extremely significant for alongshore velocities. In contradiction, SWASH 1D, which lacks edge waves, overpredicts, showing that edge waves are one of several dynamics that may contribute to errors in 1D methodologies. In the appendix, SWASH 2D is used to simulate infragravity edge waves, but emergent dynamics demonstrate a need for further development of modeling methodologies for considering the impacts of edge waves.