Modeling Shoreline Morphological Evolution

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Many coastal areas are undergoing tremendous morphological change, resulting in deterioration of habitats and livelihoods, and altering the exchanges between land and ocean. For example, near Katama Bay, Martha's Vineyard, Massachussetts, sediment transport and morphological evolution is affecting water quality, oyster farms, tourism, and homes and structures. Waves from Hurricanes Irene and Sandy combined with strong currents caused 2.5 meter of erosion and accretion near Katama Inlet. In addition, the inlet is migrating hundreds of meters per year, and eventually will close until a storm again breaches the barrier beach separating the bay from the ocean. This project will use a combination of existing field observations and numerical model simulations to determine the causes of such morphological evolution. By investigating the effects of tides, waves, and currents on the dynamic coast of Martha's Vineyard, this research project will lead to an improved understanding of the processes driving shoreline evolution on ocean beaches and in or near inlets. The team will collaborate with U.S. Geological Survey scientists on model development for addressing a range of future scenarios and will work with local stake holders and managers to provide simulations and information about possible changes to the shoreline in response to different forcing and management choices, as well as to help plan for inlet closings and the associated changes in water quality and access. The project will also produce video lessons for high school students on relevant STEM topics.The study will address the hypotheses that: (i) migration of the inlet is owing to a combination of large nor'easters and hurricanes, more frequent, but more moderate wave events, and strong tidal flows, (ii) the timing of storms relative to flood and ebb flows and the storm duration are important to the morphological evolution, (iii) accretion inside the bay is caused by sand carried alongshore and subsequently transported into the inlet during flood flows, and (iv) closure of the inlet occurs when a large storm coincides with one or more spring flood tides, carrying sand into the inlet. The large morphological signal combined with existing observations of waves, currents, and the changing bathymetry make this site an ideal location to address hypotheses for shoreline morphological evolution, to calibrate, test, and improve numerical models that simulate the observed evolution, and to use models to predict future changes for different scenarios. Although this study will focus on the Martha's Vineyard site where there is substantial observational data and model infrastructure, the results will be applicable to a wide range of shoreline systems, with or without inlets. The dominant processes may differ from site to site, but the fundamental physics incorporated in the model are similar.