Alongshore Momentum Balance Over Shoreface-Connected Ridges, Fire Island, Ny

Abstract

Bathymetric variations, such as shoreface-connected ridges (SFCRs), modify inner shelf circulation, altering the significance of and relationships between alongshore momentum balance terms. The inner shelf of Fire Island, NY provides a study site representative of SFCRs around the world. During the winter of 2014, hydrodynamic observations (~12 m depth) from 6 ADCPs, 3 SeaGauge pressure sensors, 2 tide gauges, and 2 meteorological buoys were collected over a region of the inner shelf spanning a full wavelength of one such SFCR. Analysis of the data, under westward wind forcing, revealed a predominantly alongshore circulation with localized offshore (onshore) current veering over the SFCR crests (troughs). This circulation pattern, and its implied sediment dynamics, has long been recognized as the primary maintenance mechanism for SFCRs.Momentum balance analysis revealed local acceleration, advective acceleration, and bottom stress to be balanced by wind stress and large-scale (>100 km) pressure gradient force (correlation r=0.75). Current veering of alongshore flows is hypothesized to result from a frictional torque-induced rotation stemming from bottom stress variations across SFCRs.