Runups of Unusual Size: Predicting Unexpectedly Large Swash Events

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The goal of this project is to improve our understanding of unusually large wave runup events on ocean beaches. Such runup events are seen with only a small fraction of the waves, yet they are important for the prediction of dune erosion, inundation and coastal flooding during storms. A second type of unusual runup event is also distinguished in that it is sudden and unexpected even if the landward reach of the runup is not a statistical extreme. These large and unusual runup events are the leading cause of death by drowning along the U.S. Pacific Northwest. In order to understand the causes of unexpectedly large runup events, and to begin to forecast their potential occurrence, this project will use existing data, a new multi-year data set and a hierarchy of numerical model simulations and link the events to various generation mechanisms. Finally a model will be developed and tested for forecasting the risk of such events. The team will work with the National Weather Service offices as well as exploring other outlets to communicate severe event forecasts to the public. In addition to increased public safety, this project will also help coastal management efforts. These efforts rely on predictions to outline flood hazard zones and regions appropriate for development. Additionally, findings from the numerical modeling portion of the study will document and potentially advance the accuracy/capabilities of nearshore hydrodynamic models, which will benefit coastal zone management in other geographic settings. Finally the project will contribute to education efforts by directly involving graduate and undergraduate students in the research, paying specific attention to the entrainment of individuals from under-represented groups.The study of swash zone hydrodynamics has seen sustained progress over the last decade, with much of the focus on the characterization of bulk and extreme runup statistics. However, the physical causes of large, and especially of unexpected, events have received considerably less attention. This project will conduct data collection and analysis and numerical model studies designed to distinguish between linear generation mechanisms related to super-position and nonlinear generation mechanisms related to bore-bore capture, incident wave-infragravity wave interactions and uprush-backwash events for large as well as unexpected runup events. Morphodynamic differences between two drastically different beaches, Agate Beach, OR and Duck, NC, will help reveal the role of beach type on the generation of both large and unusual runup events. The observations will allow the team to test and improve the skill of simple extreme runup parametric models during storms.