Pressure-gradient-driven nearshore circulation on a beach influenced by a large inlet-tidal shoal system

Journal of Geophysical Research C: Oceans
By: , and 

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Abstract

The nearshore circulation induced by a focused pattern of surface gravity waves is studied at a beach adjacent to a major inlet with a large ebb tidal shoal. Using a coupled wave and wave-averaged nearshore circulation model, it is found that the nearshore circulation is significantly affected by the heterogeneous wave patterns caused by wave refraction over the ebb tidal shoal. The model is used to predict waves and currents during field experiments conducted near the mouth of San Francisco Bay and nearby Ocean Beach. The field measurements indicate strong spatial variations in current magnitude and direction and in wave height and direction along Ocean Beach and across the ebb tidal shoal. Numerical simulations suggest that wave refraction over the ebb tidal shoal causes wave focusing toward a narrow region at Ocean Beach. Due to the resulting spatial variation in nearshore wave height, wave-induced setup exhibits a strong alongshore nonuniformity, resulting in a dramatic change in the pressure field compared to a simulation with only tidal forcing. The analysis of momentum balances inside the surf zone shows that, under wave conditions with intensive wave focusing, the alongshore pressure gradient associated with alongshore nonuniform wave setup can be a dominant force driving circulation, inducing heterogeneous alongshore currents. Pressure-gradient- forced alongshore currents can exhibit flow reversals and flow convergence or divergence, in contrast to the uniform alongshore currents typically caused by tides or homogeneous waves.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Pressure-gradient-driven nearshore circulation on a beach influenced by a large inlet-tidal shoal system
Series title Journal of Geophysical Research C: Oceans
DOI 10.1029/2010JC006788
Volume 116
Issue C4
Year Published 2011
Language English
Publisher Wiley
Contributing office(s) Pacific Coastal and Marine Science Center
Description 18 p.
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title Journal of Geophysical Research C: Oceans
Country United States
State California
City San Francisco
Other Geospatial Ocean Beach