Coastal inundation on the U.S. West Coast is often caused by the co-occurrence of high tides and energetic ocean waves. During storms, wave run-up can reach several meters above the tide level. Existing simple inundation models yield qualitative general information but not the information most valuable for issuing site-specific warnings for highway closures and sand-bagging. Quantitative inundation observations are critically needed to improve model accuracy. With rising sea levels and El Niño winters, it is crucial that a West Coast inundation model be developed for future safety and protection of coastal communities.

During 2018-19, we used observations of coastal runup, offshore waves, and beach morphology at Imperial Beach, Cardiff, and Coronado to examine empirical relationships of runup for use in a planned product set of extreme water levels based on CDIP nowcasts and hindcasts of waves and water level. A standard parameterization of runup (Stockdon et al., 2006), that has been used in CDIP total water level estimates, was found to be insufficient based on the field data comparisons, and so our work plan for the past year was altered as we sought to develop an improved parameterization. We are in the final stages of testing a new runup parameterization that incorporates more information from the full incident wave spectrum, available from CDIP products. Once that runup estimate is finalized, we will complete our deconstruction of extreme total water level events during 2019-20, quantifying relative contributions from the tide, nontidal residual sea level, and wave runup at Cardiff, Coronado, and Imperial Beach. The product will provide an ongoing assessment of how various processes combine to cause coastal flooding. The information will be used to develop extreme water level statistics and return periods specific to each site. In addition, the seasonality of total water levels will be specified, with a depiction of tidal, wave, and water level contributions in each season. The influence of sea-level rise on extreme water level statistics will be evaluated, providing the public with a understanding of what causes high water level events today, with impacts on beach erosion and coastal flooding, and how the probability of occurrence of extreme water levels is likely to change in the future.

During the past year, websites have been developed for Cardiff and Imperial Beach. These websites will be expanded in the coming year to include the new coastal runup and extreme water level products, as well as a beach profile viewer that is in the final stages of development. During 2019-2020, we will develop coastal hazard websites at Coronado and Huntington Beach (based on previously collected field observations at both sites, which is critical for tuning of the runup parameterization). In collaboration with a proposed State Parks funded project, new field data will be obtained at a site in the northern SCCOOS region (likely Malibu or Santa Monica). Once those data are available, we will develop a webpage for this site based on the Cardiff and Imperial Beach templates. Given the need for field validation data, we will delay our proposed product development in Santa Barbara County until a field deployment can be arranged.

Stockdon, H. F., R. A. Holman, and A. H. Sallenger, Jr. (2006), Empirical parameterization of setup, swash, and runup, Coastal Eng., 53, 573-588.