Modeling Tides, Storm Surge, and Coastal Hydrodynamics in Broad and Narrow Shelved Regions

This work examines the development and application of high resolution numerical models, primarily using the ADvanced CIRCulation model (ADCIRC), for the purpose of simulating coastal hydrodynamics including tides and storm surges in Alaska and Puerto Rico and the U.S. Virgin Islands (PRVI). These regions are primarily differentiated by their geographic latitude and the shelf widths bordering their coasts.

The high latitude Alaskan coastal region is home to complex tides and is subject to strong extratropical cyclones. The resulting storm surges are amplified over the broad Bering Sea shelf and sea ice plays a role in coastal hydrodynamics. In this work an unstructured grid ADCIRC model resolving these processes is implemented. Comparisons to data assimilated tidal solutions and tide gauges show ADCIRC to have smaller tidal errors because of the high resolution provided. The model also shows considerable skill at simulating coastal surge and overland flooding during both open and ice covered periods. The effect of sea ice on storm surge is included through a parameterized wind drag coefficient, modifying the air sea momentum transfer under ice coverage. Discussions are made with regards to limitations of the model setup, particularly related to the ice influenced surface stress calculation. Suggestions for future model improvements are made.

Puerto Rico and the U.S. Virgin Islands are characterized by adjacent deep ocean, narrow shelves, and coral reef systems. Strong tropical cyclones and the resulting large waves and storm surges are of significant concern. In this work, hindcasts of waves and surge for 2017 Hurricanes Irma and Maria are examined and compared to wave and water level gauge data in the vicinity of PRVI using an unstructured grid wave-circulation coupled model (ADCIRC+SWAN) and a suite of atmospheric forcing products. The water level response analysis highlights the importance of atmospheric pressure driven surge, wind-driven surge over the narrow shelves and wave-induced setup in the nearshore. ADCIRC+SWAN is compared with a structured grid wave-circulation coupled model (SLOSH-FW). It is shown that although both models respond similarly to atmospheric forcing, wave setup is generally smaller nearshore in SLOSH-FW. Additional model strengths and shortcomings are discussed.