Alongshore momentum balance over shoreface-connected ridges, Fire Island, NY

Continental Shelf Research
By: , and 



Hydrodynamic and hydrographic data collected on the inner shelf of Fire Island, NY, over a region of shoreface-connected ridges (SFCRs) are used to describe wind-driven circulation over uneven topographies along relatively straight coastlines. The data revealed a predominantly alongshore flow, under westward wind forcing, with localized offshore current veering over the SFCR crests associated with an onshore veering over the adjacent troughs. Momentum balance analysis of the observations revealed that local acceleration, advective acceleration, and bottom stress are balanced by wind stress and regional (>100 km) pressure gradient force. Numerical model results based on simulations of an idealized SFCR bathymetry, as in Warner et al. (2014) but forced with the observed winds, are used to verify the experimentally derived results and constraint inaccuracies in the momentum balance term relationships revealed using the field data. As with previous SFCR studies, our experimental results indicate a current veering over ridge crests. Veering is driven primarily by two processes: cross-shore variation of alongshore advective acceleration which creates cross-shore pressure gradient and drives flow (described as a Bernoulli-like process), and, bottom frictional-torque. A synthesis of the numerical and experimental data revealed that the total pressure gradient force can be considered as the sum of a local and a regional pressure gradient force. The former is correlated with the alongshore advective acceleration that develops over the crest of the ridges resembling a Bernoulli-like pressure-flow relationship. The regional pressure gradient force is related to wind stress with which maintains a strong, negative relationship. The realistic driving force analysis revealed the different contributions of the local and regional scale pressure gradients. Under realistic and variable wind conditions the regional pressure gradients are more important and the influence of the local scale pressure gradient increases as the flow reaches quasi steady-state conditions. A time scale of 6 hours was defined as the temporal scale required for the local pressure gradients to have an effect

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Publication type Article
Publication Subtype Journal Article
Title Alongshore momentum balance over shoreface-connected ridges, Fire Island, NY
Series title Continental Shelf Research
DOI 10.1016/j.csr.2019.07.005
Volume 186
Year Published 2019
Language English
Publisher Elsevier
Contributing office(s) Woods Hole Coastal and Marine Science Center
Description 13 p.
First page 21
Last page 33
Country United States
State New York
Other Geospatial Fire Island
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