Graduate Thesis Or Dissertation
 

Coupled wave and surge modeling of Tillamook Bay, Oregon : extreme events and climate change impacts

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/h989r618p

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  • Estuaries represent the confluence of land and ocean environments and encompass a number of complex interactions amongst tides, winds, offshore waves and the riverine contributions, all of which contribute to total water levels (TWLs). The study of TWLs and the relative weight of its components can assist local communities in mitigating inundation events as well as drive a deeper understanding of potential impacts on ecological processes. Accurate predictions of surge and TWLs benefit from both deterministic and probabilistic methods. This thesis presents two manuscripts which examine wave and surge behavior within a representative Pacific Northwest estuary, Tillamook Bay, for a pair of fundamentally distinct research objectives: a singular, extreme storm event and a long-term climatological impacts study. Both manuscripts utilize a two-way coupled tidal circulation and nearshore wave transformation model (ADCIRC-SWAN) to simulate wave and surge behavior within Tillamook Bay. The first manuscript details a storm hindcast of the Great Coastal Gale of 2007, a series of extra-tropical cyclones which impacted the Washington and Oregon coasts in December 2007. Wind and pressure data from the North American Regional Reanalysis (NARR) dataset were used to reproduce meteorological conditions. Non-tidal residuals were extracted at a number of locations of interest, including the tide gauge station, southern Tillamook, the jettied inlet and on open coast, in order to compare and contrast the relative influence of major physical processes to surge levels. From the suite of ADCIRC-SWAN parametric runs, it was found that offshore wave breaking produced an appreciable surge within the bay, even though wave heights quickly attenuate beyond the inlet. Meteorological forcing was the primary generator of complex circulation patterns and a surge in the northern portion of the bay. The model captures the max NTR at the peak of the storm but lacks skill in reproducing non-linear tide-surge interaction. The second manuscript examines changes in inundation patterns within the domain between historical and future climate conditions. Coupled ADCIRC-SWAN is run for two multi-decadal ranges from 1979-1998 and 2041-2060. Relative sea level rise is implemented by adding in 80 cm of water depth. Climate data from the North American Regional Climate Change Assessment Program (NARCCAP) is used to drive offshore wave modeling, streamflow modeling and the coupled circulation-wave model. Statistical bias correction of climate variables using NARR as a 'target' is performed first before forcing models. Wave information at the offshore boundary are derived from a regional WAVEWATCH-III hindcast and forecast, while riverine inputs are calculated using the MicroMet and HydroFlow runoff routing model.
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