Persistent Shoreline Shape Induced From Offshore Geologic Framework: Effects of Shoreface Connected Ridges. Issue 11 (15th November 2017)

• Record Type: Journal Article
• Authors: Safak, Ilgar; List, Jeffrey H.; Warner, John C.; Schwab, William C.
• Is Part Of: Journal of geophysical research. Volume 122:Issue 11(2017)
• Page Start: 8721
• Page End: 8738
• Publication Date: 2017-11-15
• Subjects: surface waves -- sediment transport -- shoreline change -- longshore transport -- sand ridges -- Fire Island; Oceanography -- Periodicals; 551.4605
• DOI: 10.1002/2017JC012808
• Languages: English
• ISSNs: 2169-9275

Abstract

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. Key Points: Persistent shoreline shape linked to effect of shelf geologic framework on nearshore sediment fluxes Cross‐shore flows between shelf and nearshore are important in decadal scale coastal evolution Shoreline shape controlled by ridge effects on wave breaking, vortex force, advection, pressure gradient