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Modeling of Coastal and Estuarine Processes: Hybrid Statistical-Dynamical Prediction of Nearshore Waves and Dynamical Simulation of Tidal Flow in Idealized Estuarine Embayments

  • Author(s): Hegermiller, Christie
  • Advisor(s): Edwards, Christopher A
  • et al.
Creative Commons 'BY-ND' version 4.0 license

Climate change exerts physical influence on estuarine and open coastal morphology through sea level rise and changes to wave energy, precipitation, and sediment supply, resulting in flooding and erosion hazards to coastal communities. Along open coasts, the distribution of wave energy in the nearshore is of critical importance for assessing local vulnerability to climate change. Two methods are frequently used to predict wave conditions based on global climate model outputs of atmospheric circulation: dynamical downscaling and statistical downscaling. Statistical downscaling relies on empirical relationships between waves and atmospheric conditions. Statistical downscaling has been applied with success in relatively small ocean basins (e.g., Mediterranean, Atlantic) where waves are generated over a small area and arrive at the coast within a few days of generation. However, in the Pacific Basin, waves are generated over large and distant regions of both the North and South Pacific. Furthermore, waves can travel up to 3 weeks before arriving at the coast (e.g., Southern Ocean-generated waves arriving in Southern California). These challenges have resulted in statistical downscaling studies with limited success. Chapter 2 of this dissertation addresses these challenges by 1) partitioning wave spectra into families that have unique, discrete generation areas and 2) accounting for the time lag between wave generation and wave arrival at the coast. The success of this work in Southern California bodes well for the proliferation of wave climate projections in large ocean basins.

To project future coastal hazards, deep-water waves predicted using the methods described above must be transformed over shelf bathymetry to the nearshore. In complex coastal regions, offshore canyons, shoals, and islands complicate the linkage of nearshore waves to deep-water waves and the atmospheric conditions that generated them. In Chapter 3 of this dissertation, a hybrid statistical-dynamical approach is taken to explore significant spatial variability in nearshore wave conditions of the Southern California Bight, a complex coastal region. It is found that variability is driven by not only static bathymetric controls, but also dynamic large-scale atmospheric patterns. Climate change effects on these atmospheric patterns will lead to new distributions of wave energy along the Southern California Bight coastline and other coastlines around the world.

Along estuarine coasts, the distribution of tracers, such as salt, sediment, and pollutants, is a key factor in determining vulnerability to climate change and development. Extensive scientific effort has yielded a comprehensive understanding of sediment and salt transport in varied estuarine systems. However, tidal dynamics in shallow embayments, which are commonly found flanking deep estuarine channels, have not been described thoroughly. Chapter 4 of this dissertation examines the momentum and salt forcing associated with a shallow, estuarine embayment. This work illuminates mechanisms likely responsible for trapping of sediments in shallow bays and the supply of sediment to estuarine marshes.

The suite of studies presented in this dissertation seeks to contribute to our scientific understanding of open and estuarine coastal response to climate change and to provide information that can readily be applied to coastal policy and engineering.

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