Date of Award

2018

Degree Type

Thesis

Degree Name

Master of Science in Ocean Engineering

Department

Ocean Engineering

First Advisor

Annette Grilli

Abstract

The key role of beach dunes in protecting coastal developments from damages caused by seasonal storm and hurricanes (e.g. Hurricane Sandy 2012), prompted series of studies devoted to assess their stability during these conditions. A 2-D numerical study for a “100-year storm” event (1% probability of annual exceedance) in Rhode Island indicate extreme dune erosion can occur when these structural barriers become submerged during coastal flooding events, making them ephemeral solutions only (Schambach et al., 2018). In contrast, areas with dense vegetation experienced less morphological changes due to reduced wave energy. Model predictions however remain uncertain due to the lack of comparative studies with field data. The study provides a performance evaluation assessment of four modeling scenarios used to assess the stability of a vegetated dune system in barrier beaches during storm events. These are combination of two wave models (phase averaging vs. phase resolving) with two approaches to modeling the affect of vegetation on sediment transport (bed friction formulations vs. wave damping formulations). Best estimates of the post dune profiles were obtained when using the phase averaged wave model with vegetation described by bed friction coefficients. This scenario was able to predict accurate changes of the along shore crest height elevations, making it a good assessment tool for determining the vulnerability of coastal communities in Rhode Island.

In a second chapter, we address the potential use of Geotextile Sand-filled Containers (GSCs) to reinforce and stabilize a dune system during storm events. A new classification of the damage states associated with these “soft-structures” used for coastal protection are identified and described. Modeling approaches to identify each damage level during a storm were validated using post survey measurements taken from a storm which caused damage to a new project site where reinforced dune system with GSCs was constructed. Two hydraulic stability formulas for GSCs were used to determine the critical conditions for the instability of the GSC structure. Results indicate lower confidence when using Hudson’s (1956) based stability equations when compared with Recio and Oumeraci (2008) semi-empirical formulations. Overall good prediction of the damage levels was obtained when compared with measurements, suggesting a potential tool for predicting the stability of the structure.

Available for download on Saturday, July 27, 2019

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