Complex Morphologic Controls on Nearshore Hydrodynamics and Erosion on Sandy Beaches
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Authors
Szczyrba, Laura
Date
2024-09-29
Type
thesis
Language
eng
Keyword
Coastal , Nearshore , Numerical modeling , Remote sensing , Sediment transport
Alternative Title
Abstract
In the nearshore region, incident waves respond to depth variations in the underlying morphology, and this dynamic interplay drives hydrodynamics and bed level changes. Many regions around the world are characterized by complex bathymetric environments that are controlled by antecedent geology, and these areas are often associated with exceptionally high rates of erosion. However, the influence of these features on wave transformations, currents, and sediment transport is not fully understood, especially under storm conditions. In this dissertation, two sandy field sites are analyzed with new field measurements, hydrodynamic modeling, and morphodynamic modeling to investigate, for the first time, the mechanisms by which complex morphodynamic features influence nearshore processes.
Spatially continuous wave refraction is studied with new methods to extract observations of wave refraction from a remote sensing system. These observations compare well with model simulations and in-situ observations. Results indicate a high degree of variability in wave approach angles over small distances, particularly in areas with high bathymetric gradients. This approach is then applied to a site with shore-oblique nearshore features. During energetic conditions, the bathymetric features force alongshore variations in depth-induced breaking, generate gradients in the water surface elevation, and induce offshore currents near the shore-oblique features. These observations are supported by a numerical model.
This same field site is also studied with a morphodynamic model to understand how complex bathymetric features modify sediment transport patterns before and after beach nourishment. Under a variety of storm conditions, similar patterns of shoreface erosion and accretion occur. Near the shore-oblique features, sediment transport is heightened. After nourishment, similar volumes of sediment are mobilized and similar transport patterns emerge, suggesting that the shore-oblique features exert the predominant control over sediment transport. The technical advancements made in this dissertation inform better mitigation practices that promote coastal resilience. A review of societal interactions within coastal systems is provided and a new conceptual framework of resilience that integrates technical and social variables is introduced. This dissertation emphasizes that an accurate understanding of the influence of complex factors, including nonuniform bathymetry as well as social variables, is needed to inform coastal engineering decisions that protect beach communities.
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Attribution-NonCommercial-NoDerivatives 4.0 International