West Maui – A Stellar Example of Spatial Variability of the Wave-Driven Components of Runup and Inundation

One of Hawaiʻi’s main cultural and socio-economic regions is the West Maui coastline where the increasing impact of wave-driven runup events are threatening both public safety and infrastructure. To provide guidance to the community, a deeper understanding of the wave-driven components that lead to impactful runup is necessary. Of these components, we have observed and modeled both long period infragravity responses and shorter period swash. The results indicate high variability alongshore including complicated infragravity structures. These infragravity waves have frequency dependent alongshore energy patterns which are dependent on the nearshore bathymetry. Also, cross shore observations and model analysis indicate the presence of leaky, edge, and resonant infragravity waves. An analysis of coherent structures at particular frequencies has been carried out using an array of pressure gauges deployed in Nov. of 2018 and covering multiple swell events during the 2018-19 winter. Hindcasts using the Boussinesq Ocean and Surf Zone (BOSZ) phase resolving model forced by a high resolution SWAN model extend the spatial view for these infragravity structures beyond the observation array. This project is an integral piece of a multi-agency collaborative effort to better understand the wave-driven coastal flooding events along West Maui with the ultimate objective of establishing ongoing, short-lead-time wave runup forecasts as a function of distance along the coast.