Article,

Wind-driven modifications to the residual circulation in an ebb-tidal delta: Arcachon Lagoon, Southwestern France

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Journal of Geophysical Research: Oceans, 120 (2): 728-740 (2015)
DOI: 10.1002/2014JC010311

Abstract

A combination of observations and analytical solutions was used to determine the modifications caused by wind forcing on the residual or nontidal circulation in an ebb-tidal delta. Observations were obtained in the lower Arcachon Lagoon, southwestern France. The basic nontidal circulation was established with acoustic Doppler current profilers (ADCPs) that were (i) moored in the delta's two deepest channels, and (ii) towed along a cross-lagoon transect. The bathymetry of the lower lagoon, or ebb-tidal delta, featured two channels: North Pass (>9 m) and South Pass (>20 m). The basic nontidal circulation consisted of mostly inflow with weak surface outflow in the South Pass, and laterally sheared bidirectional flow, dominated by outflow, in the North Pass. Analytical solutions and comparison of observed dynamical terms suggested that, in addition to the conventionally accepted influence of tidal nonlinearities, density gradients contributed to the basic nontidal circulation in the lagoon. Observations also indicated that wind forcing altered the basic circulation by driving simultaneous upwind flows in both passes. This response was supported by an analytical solution to wind-driven flows over the bathymetry of the transect sampled. The response to seaward winds was to enhance inflow in South Pass and reduce outflow in North Pass. Landward winds caused diminished inflow in South Pass and increased outflow in North Pass. © 2015. American Geophysical Union. All Rights Reserved.

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