Relating Offshore Wave Conditions to Incident Waves and Shoreline Water Levels at Ipan, Guam during Extreme Events.

Low-lying islands and atolls bounded by steep fringing reefs are vulnerable to wave-driven inundation events. Observations of elevated shoreline water levels forced by a range of incident wave conditions measured on the reef face have been analyzed using analytical, empirical and numerical models. While breaking wave setup and sea and swell band contributions to wave-driven inundation have been shown to scale with the bulk statistical parameters of the wave forcing and the local water level, the shoreline variability of infragravity and very low frequency energy is sensitive to the phasing of incident forcing. Further, as incident conditions typically are not available except during field campaigns, the relationship between the energetic low frequency shoreline response and the offshore wave conditions remains an open question. Here, we assess the relationship among CDIP buoy measurements, and the incident and shoreline low frequency observations collected from the ongoing PILOT field program at Ipan, Guam. Both buoy bulk parameters that include wave height, period and direction as well as buoy time-series and directional spectra are examined in an effort to reproduce the incident and shoreline observations. Particular emphasis is placed on the differences among extreme events in the observational record that include Tropical Storm ManYi (2007), and Typhoons Bavi and Dophin (2015).