Persistent shoreline shape induced from offshore geologic framework: Effects of shoreface connected ridges

Journal of Geophysical Research C: Oceans
By: , and 

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Abstract

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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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Persistent shoreline shape induced from offshore geologic framework: Effects of shoreface connected ridges
Series title Journal of Geophysical Research C: Oceans
DOI 10.1002/2017JC012808
Volume 122
Issue 11
Year Published 2017
Language English
Publisher AGU
Contributing office(s) Woods Hole Coastal and Marine Science Center
Description 18 p.
First page 8721
Last page 8738
Country United States
State New York
Other Geospatial Fire Island