Author Type

Graduate Student

Date of Award

Summer 6-13-2026

Document Type

Dissertation

Publication Status

Version of Record

Submission Date

July 2026

Department

Geosciences

College Granting Degree

Charles E. Schmidt College of Science

Department Granting Degree

Geosciences

Degree Name

Doctor of Philosophy (PhD)

Thesis/Dissertation Advisor [Chair]

Eric Prokocki,

Thesis/Dissertation Co-Chair

Mingshun Jiang

Abstract

Nature-based morphological features in coastal areas, such as dunes, coral reefs, and seagrass, play dual roles as both receivers of threats from increasing human activity and climate change and defenders that mitigate potential impacts. Therefore, it is imperative to improve our understanding of how these features may affect hydrodynamic processes under various conditions. To address this need, the objectives of this research are two-fold: 1) to enhance our knowledge of changes of bedform morphology in response to different fluvial-tidal controls in the Lower Columbia River (LCR), and 2) to investigate how natural-based features may mitigate tropical storm impacts using a high-resolution coupled circulation-wave model for the South Florida region.

For the first objective, new analytical methods are proposed and applied to multibeam echosounder data collected in LCR to assess key bedform parameters, including roughness and shape. The results indicate that hydrodynamics and variations in sediment transport rates strongly influence dune morphology. For instance, LCR dunes that formed within bidirectional tidal flows under high suspended-load to bedload sediment transport conditions tend to be simple in form, are relatively small, have triangular stoss-sides and leesides, display shallower leeside angles, and thus have lower form roughness. However, fluvial-tidal dunes formed by unsteady, unidirectional, ebbtide dominated flows under lower suspended-load to bedload transport conditions are primarily compound, larger than tidal dunes, have triangular stoss-sides but rounded leesides, and steeper leeside angles. Fluvial-tidal dunes therefore have greater form roughness than tidal dunes, indicating that storm impact may also reduce from downstream to upstream as bed friction increases.

For the second objective, numerical simulations were conducted in 2017, during hurricane Irma's landfall in South Florida. The results indicate that bottom morphological features over the Florida Reef Tract not only significantly dissipate wave energy locally but also reduce storm surge regionally over the southwest Florida shelf. Without the bottom features, the peak wave energy dissipation shifts landward, and the storm surges are much stronger. Under sea-level rise, these features remain significant in mitigating storm impacts, yet the effectiveness will be reduced to some degree. Therefore, it is important to maintain healthy coral reefs and seagrass meadows.

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