Modeled nearshore wave parameters

The spectral wave model SWAN was applied using the Delft3D-Wave modeling system (Deltares, 2024) to simulate wave transformation and dynamics from offshore of the continental shelf to the coastline. The model application consisted of nested grids with resolutions varying between 750 m for the largest grid to about 80 m for the two detailed grids that cover the Grays Harbor and Columbia River inlets. Model bathymetry was derived from recent data sets collected by the USGS, NOAA, and USACE between 2004 and 2020 as described in Stevens and others (2020). Wave energy was discretized into 24 frequency bins between 0.03 and 1 Hz and 72 directional bins. The model was forced on the open lateral boundaries with bulk wave parameters obtained from the ERA5 reanalysis (Herschbach and others, 2023) and on the free surface with space- and time-varying wind vectors from the High Resolution Rapid Refresh (Dowell and others, 2022) operational forecast model with roughly 3 km spatial resolution. Wind growth and white-capping were based on Komen (1984). The JONSWAP bottom friction model with a coefficient of 0.038 m2s-3 and wave breaking based on Battjes and Jannsen (1978) with default settings (alpha = 1, gamma =0.73) were used. SWAN was run as a stand-alone wave model neglecting the effects of wave current interaction. Convergence criteria were set to 98 percent of cells and a maximum of 15 iterations during the simulations.

The forcing conditions were updated and wave dynamics were solved within the model domains at 1-hr intervals in stationary mode between 2014 and 2023 (h1). A second hindcast was run between July 2010 to September 2011 (h2) to simulate seasonal variations in wave climate during the Southwest Washington Littoral Drift Restoration (SWLDR) beach nourishment and monitoring study (Stevens and others, 2012). The HRRR wind forcing was not available for this time period, so an alternative downscaled wind product was used (CONUS404, Rasmussen and others, 2023). CONUS404 is a high-resolution meteorological reanalysis created by downscaling ERA5 data to a 4-km spatial resolution over the continental United States using the Weather Research and Forecasting (WRF) Model.

A series of 221 shore normal transects were defined throughout the study area that extended from the coastline to the -15 m NAVD88 elevation (about 16.5 m average water depth). For each hourly time step in the wave hindcast simulations, the estimated fraction of breaking waves was interpolated onto transect locations with a cross-shore resolution of 50 m. The location of the break point, or location just outside the surf zone, varied dynamically based on the local bathymetry and wave conditions. A threshold of 0.01 of the fraction of waves breaking was used to define the time- and space-varying break point along each transect. Model output parameters including significant wave height, peak wave period, mean wave direction, and water depth at this location were extracted for each time step and transect.

Modeled wave parameters were compiled into netCDF files for distribution.