Rip currents and alongshore flows in single channels dredged in the surf zone

Journal of Geophysical Research: Oceans
By: , and 

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Abstract

To investigate the dynamics of flows near nonuniform bathymetry, single channels (on average 30 m wide and 1.5 m deep) were dredged across the surf zone at five different times, and the subsequent evolution of currents and morphology was observed for a range of wave and tidal conditions. In addition, circulation was simulated with the numerical modeling system COAWST, initialized with the observed incident waves and channel bathymetry, and with an extended set of wave conditions and channel geometries. The simulated flows are consistent with alongshore flows and rip-current circulation patterns observed in the surf zone. Near the offshore-directed flows that develop in the channel, the dominant terms in modeled momentum balances are wave-breaking accelerations, pressure gradients, advection, and the vortex force. The balances vary spatially, and are sensitive to wave conditions and the channel geometry. The observed and modeled maximum offshore-directed flow speeds are correlated with a parameter based on the alongshore gradient in breaking-wave-driven-setup across the nonuniform bathymetry (a function of wave height and angle, water depths in the channel and on the sandbar, and a breaking threshold) and the breaking-wave-driven alongshore flow speed. The offshore-directed flow speed increases with dissipation on the bar and reaches a maximum (when the surf zone is saturated) set by the vertical scale of the bathymetric variability.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Rip currents and alongshore flows in single channels dredged in the surf zone
Series title Journal of Geophysical Research: Oceans
DOI 10.1002/2016JC012222
Volume 122
Issue 5
Year Published 2017
Language English
Publisher AGU
Contributing office(s) Woods Hole Coastal and Marine Science Center
Description 18 p.
First page 3799
Last page 3816