Persistent shoreline shape induced from offshore geologic framework : effects of shoreface connected ridges
Date
2017-11-15Author
Safak, Ilgar
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List, Jeffrey H.
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Warner, John C.
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Schwab, William C.
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https://hdl.handle.net/1912/9472As published
https://doi.org/10.1002/2017JC012808DOI
10.1002/2017JC012808Keyword
Surface waves; Sediment transport; Shoreline change; Longshore transport; Sand ridges; Fire IslandAbstract
Mechanisms relating offshore geologic framework to shoreline evolution are determined through geologic investigations, oceanographic deployments, and numerical modeling. Analysis of shoreline positions from the past 50 years along Fire Island, New York, a 50 km long barrier island, demonstrates a persistent undulating shape along the western half of the island. The shelf offshore of these persistent undulations is characterized with shoreface-connected sand ridges (SFCR) of a similar alongshore length scale, leading to a hypothesis that the ridges control the shoreline shape through the modification of flow. To evaluate this, a hydrodynamic model was configured to start with the US East Coast and scale down to resolve the Fire Island nearshore. The model was validated using observations along western Fire Island and buoy data, and used to compute waves, currents and sediment fluxes. To isolate the influence of the SFCR on the generation of the persistent shoreline shape, simulations were performed with a linearized nearshore bathymetry to remove alongshore transport gradients associated with shoreline shape. The model accurately predicts the scale and variation of the alongshore transport that would generate the persistent shoreline undulations. In one location, however, the ridge crest connects to the nearshore and leads to an offshore-directed transport that produces a difference in the shoreline shape. This qualitatively supports the hypothesized effect of cross-shore fluxes on coastal evolution. Alongshore flows in the nearshore during a representative storm are driven by wave breaking, vortex force, advection and pressure gradient, all of which are affected by the SFCR.
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This paper is not subject to U.S. copyright. The definitive version was published in Journal of Geophysical Research: Oceans 122 (2017): 8721–8738, doi:10.1002/2017JC012808.
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Journal of Geophysical Research: Oceans 122 (2017): 8721–8738The following license files are associated with this item:
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