A Comparison of Wave and Erosion Modeling Methods for the 100-Year Storm in Southern Rhode Island

• Main Author: Schambach, Lauren
• Format: Text
• Language: unknown
• Published: DigitalCommons@URI 2017
• Subjects: North Atlantic
• Online Access: https://digitalcommons.uri.edu/theses/978; https://doi.org/10.23860/thesis-schambach-lauren-2017; https://digitalcommons.uri.edu/context/theses/article/2000/viewcontent/Schambach_uri_0186M_11606.pdf

This body of work consists of two manuscripts related to modeling ocean waves and erosion associated with the 100-year storm in southern Rhode Island. Predicting the 100-year storm inundation along the Narragansett Bay shoreline The lack of confidence in FEMA maps after Hurricane Sandy (2012) led to question the accuracy of the methodology used in FEMA Flood Insurance Rate Maps (FIRM). The present analysis presents a case study, re-computing the 100- year inundation maps in Washington County, RI, using a chain of two-dimensional models. Presented results focus on the West Passage of the Narragansett Bay, Rhode Island, USA, an area characterized by a complex shoreline. The selection of the initial and boundary conditions for ocean wave simulations are based on results of fully coupled 2-D surge and wave models, the ADvanced CIRCulation model (ADCIRC) and the phase-averaged STeady state spectral WAVE model (STWAVE), respectively, from the North Atlantic Coast Comprehensive Study (NACCS) performed by the U.S. Army Corps of Engineers. Waves are simulated using STWAVE over a series of high-resolution grids in near-shore and overland areas. The method is referred to as the NAST method. Results are mapped and compared with FEMA's results along transects. Cross-sections across the Base Flood Elevation (BFE) at the site of the FEMA 1-D transects are in relatively good agreement using both methodologies, with larger discrepancies shown in the northern section of the bay. Discrepancies are primarily due to a difference in the 100-year wind assumption and secondarily to the 100-year storm surge assumption, which, besides defining the depth and extension of the inundation, controls the wave impact over land. Mapping the results reinforces the importance of adopting a 2-D approach to fully represent the inundation, showing that the selected transects often miss the sites of the most extreme wave incursion and most destructive impacts. The analysis highlights the differences in methods and results but also suggests adopting, ...