Date of Award

2017

Degree Type

Thesis

Degree Name

Master of Science in Ocean Engineering

Department

Ocean Engineering

First Advisor

M. Reza Hashemi

Abstract

This document contains two papers which address threats by tropical and extratropical systems in the northeastern United States. A suite of numerical models are used to assess waves, storm surge and coastal erosion during extreme storms.

Modeling Waves and Sediment Transport Around Artificial Reefs: Simulation of the Impact of Multi-purpose Reefs on Dune Erosion in Southern Rhode Island Barrier Beaches

The objective of this study is to set up a suite of numerical models capable of simulating the impacts of storms on coastal flooding and erosion, and use it to assess performance of mitigation measures. Three numerical models were used to analyze the possible erosion due to inundation and overwash for a small section of coast in southern Rhode Island. SWAN (Simulating Waves Nearshore), a third-generation wave model was used to compute the wave conditions. ADCIRC (ADvanced CIRCulation Model), a three-dimensional circulation model used atmospheric and tidal forcing to generate water levels, and currents. A regional coupled SWAN+ADCIRC model was used to calculate water levels and wave conditions over an unstructured mesh. XBeach, a sediment transport model, encompasses a barrier system on the southern coast of Rhode Island, and is nested within the regional domain. A non-uniform cartesian grid with a resolution across dunes of 5x10 meters is used to calculate the sediment transport during storms, the resolution decreases to 25x25 meters resolution at the boundaries. Hurricane Sandy (2012) was used to calibrate the models, where volume of erosion was compared along transects monitored by the University of Rhode Island. The model was then forced with winds from Hurricane Irene (2011) for validation. The regional model had a root mean squared error (RMSE) of 0.21 meters for storm surge, and a RMSE of 0.18 meters for offshore significant wave height. The nearshore model was able to estimate erosion with an error of 24.26%. Once validated, two synthetic storms from the North Atlantic Coast Comprehensive Study (NACCS) were modeled. These storms both produced storm surges of around the same magnitude in comparison to the 100-year event in Rhode Island.

Development of a Realtime Wave and Storm Surge Forecasting Model For Rhode Island

A set of MATLAB and bash programs were designed for preprocessing and automating the coupled wave and hydrodynamic model SWAN+ADCIRC for real time forecasting of waves and storm surge. The method allows the user to locally preprocess, package, and automate the system, while running the system externally using High Performance Computing (HPC). Each of the user input files are described, and the forecasting process is explained. The system is then applied to a SWAN+ADCIRC domain in Rhode Island, and tested during Stella, an extratropical event in March 2017, Nor'Easter Stella. The three day forecast system had a maximum offshore significant wave height Root Mean Squared Error (RMSE) of less than 1.2 m, and a storm surge RMSE of less than 0.2 meters during simulation of Nor’Easter Stella. The system was shown to be conveniently activated and monitored in the event of an emergency.

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