Date of Award

Summer 8-19-2022

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Civil Engineering

Advisor

Lauren Ross

Second Committee Member

Kimberly Huguenard

Third Committee Member

Gregory Gerbi

Abstract

The dynamics of the coastal ocean are driven by wind, buoyancy, tidal, and wave processes. In the context of the variability of the coastal ocean driven wave action, storm surge, and sea level rise, understanding interactions between physical processes and means to mitigate their effects is necessary. It is the goal of this study to extend the understanding of (i) wave and tidal hydrodynamics in coastal areas and (ii) explore adaptable coastal defense strategies for these environments. These goals are addressed through process-oriented hydrodynamic-wave simulations. As tides enter the coastal ocean, nonlinear interactions from bathymetry, friction, and variations in tidal phase speeds create tidal asymmetries through the generation of higher order harmonics known as overtides. Process-oriented simulations of a tidal inlet system with wave and tidal forcing show that the presence of waves enhance overtide amplitudes in current velocities, with increasing wave height accounting for the greatest enhancement. Analysis of the depth-averaged momentum balance identify wave-driven overtide generating mechanisms: wave streaming, enhanced bottom stress, and the enhanced pressure gradient. Phase averaged wave effects produce a shoreward bottom current and an offshore directed return flow that persist throughout the tidal cycle to create asymmetries between flood and ebb. This inner shelf circulation is disrupted by traditional coastal defense measures, such as offshore rubble mound breakwaters. Floating breakwaters, however, have shown to attenuate the energy of short-period waves while mitigating the adverse effects on ecosystems and natural sediment transport and circulation. In support of the second goal, hydrodynamic-wave simulations of a floating breakwater technology assess its performance across a range of breakwater geometries and wave conditions. Performance metrics based on the area of protection suitable for nearshore operations identify the upper limit of acceptable performance to be with incident waves 1.5 m high and 5 s periods, while performance remained consistent at 18 m and 10 m depths. Results support future breakwater implementation in semi-sheltered macrotidal environments, although validation of the breakwater numerical implementation and site specific study is needed. Collectively, this thesis extends the understanding of coastal processes and mitigation strategies to accommodate the variability of the coastal ocean.

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