The Contributions to Storm Tides in Pacific Northwest Estuaries: Tillamook Bay, Oregon, and the December 2007 Storm

The December 2007 storm, otherwise known as the Great Coastal Gale of 2007, was a series of extratropical cyclones that brought highly unprecedented wind speeds and precipitation to the Oregon and Washington coasts of the United States. A storm hindcast using the coupled Advanced Circulation (ADCIRC) and Simulating Waves Nearshore (SWAN) models was conducted within Tillamook Bay, Oregon, from 28 November to 5 December 2007. ADCIRC computes two-dimensional circulation forced by astronomic tides, streamflow, and storm surge, while SWAN solves the wave action density equations for radiation stresses. Modeled nontidal residuals were compared to observed data collected by the National Oceanic and Atmospheric Administration at the Garibaldi, Oregon, tide gauge station. The relative contributions of meteorological forcing, offshore waves, and streamflow to storm tides were next assessed at four locations of interest within and outside the estuary by conducting a set of model runs where each major process was omitted in turn. The dominant mechanism for storm tides in the estuary was offshore wave breaking. Streamflow, locally (in estuary) generated waves, and locally generated surge led to minor variations in storm tides in the estuary.