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Observations on a mildly sloping beach suggest that the largest runup events are related to bore‐bore capture (BBC). A numerical model based on the Reynolds‐averaged Navier‐Stokes equations is implemented to evaluate the effects that BBC have on runup. From simulations with realistic sea states, BBC is found to be a necessary but not sufficient condition for large runup generation. The dominant dynamics leading to BBC are amplitude dispersion and interactions with infragravity waves in the outer and inner surf zone, respectively. When the effects of BBC are isolated, it is found that the runup associated with the merging of two bores is at least 50% larger than that associated with the larger of the two waves in a monochromatic wave train. The phase difference of the incident waves with the infragravity wave can generate up to 30% variability of the runup maxima. The majority of the shoreward directed momentum flux, prior to runup initiation, is related to the interaction between the bores and the infragravity wave followed by that of the incident infragravity waves alone.

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Total water levels (TWLs) within estuaries are influenced by tides, wind, offshore waves, and streamflow, all of which are uniquely affected by climate change. The magnitude of TWL associated with various return periods is relevant to understanding how the hydrodynamics of a bay or estuary may evolve under distinct climate scenarios. A methodology for assessing the hydrodynamic response of a small estuary under major boundary condition perturbations is presented in this study. The coupled Advanced Circulation (ADCIRC) and Simulating Waves Nearshore (SWAN) model was used to simulate wave and water elevation conditions within Tillamook Bay, OR, USA for two long-term scenarios; 1979-1998 and 2041-2060. The model output provided multidecadal time series of TWLs for statistical analysis. Regional climate data from the North American Regional Climate Change Assessment Program (NARCCAP) were used to drive streamflow modeling (MicroMet/SnowModel/HydroFlow) and meteorological forcing within ADCIRC-SWAN. WAVEWATCH III, which was forced with global climate data from the Community Climate Science Model (CCSM, a contributing model to NARCCAP), was used to produce open boundary wave forcing. Latitudinal and seasonal gradients were found in TWLs associated with varying return periods for both the hindcast and forecast. Changes in TWLs from hindcast to forecast included the sea level rise component and were also modulated by changes in boundary conditions.

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An operational inner-shelf wave forecasting system was implemented for the Oregon and southwest Washington coast in the U.S. Pacific Northwest (PNW). High-resolution wave forecasts are useful for navigational planning, identifying wave energy resources, providing information for site-specific coastal flood models, and having an informed recreational beach user group, among other things. This forecasting model is run once a day at 1200 UTC producing 84-h forecasts. A series of nested grids with increasing resolution shoreward are implemented to achieve a 30-arc-second resolution at the shelf level. This resolution is significantly higher than what the current operational models produce, thus improving the ability to quantify the alongshore variations of wave conditions on the PNW coast. Normalized root-mean-squared errors in significant wave height and mean wave period range from 0.13 to 0.24 and from 0.13 to 0.26, respectively. Visualization of the forecasts is made available online and is presently being used by recreational beach users and the scientific community. A series of simulations, taking advantage of having a validated shelf-scale numerical wave model, suggests that neither dissipation due to bottom friction nor wind generation is important in the region at this scale for wave forecasting and hindcasting when considering bulk parameters as opposed to the processes of refraction and shoaling. The Astoria and McArthur Canyons; the Stonewall, Perpetua, and Heceta Banks; and Cape Blanco are significant bathymetric features that are shown to be capable of producing alongshore variability of wave heights on the shelf.