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Numerical modelling of circulation and dispersion processes in Boulogne-sur-Mer harbour (Eastern English Channel): sensitivity to physical forcing and harbour design

TitleNumerical modelling of circulation and dispersion processes in Boulogne-sur-Mer harbour (Eastern English Channel): sensitivity to physical forcing and harbour design
Publication TypeJournal Article
Year of Publication2013
AuthorsJouanneau, N, Sentchev, A, Dumas, F
JournalOcean Dynamics
Volume63
Pagination1321–1340
Date Publisheddec
ISSN1616-7341, 1616-7228
KeywordsAtmospheric Sciences, Environmental Monitoring/Analysis, Fluid- and Aerodynamics, Geophysics/Geodesy, Lagrangian tracking, Numerical modelling, Oceanography, Residence time, Tidal currents, Water quality
Abstract

The {MARS}-3D model in conjunction with the particle tracking module Ichthyop is used to study circulation and tracer dynamics under a variety of forcing conditions in the eastern English Channel, and in the Boulogne-sur-Mer harbour (referred to hereafter as {BLH}). Results of hydrodynamic modelling are validated against the tidal gauge data, {VHF} radar surface velocities and {ADCP} measurements. Lagrangian tracking experiments are performed with passive particles to study tracer dispersal along the northern French coast, with special emphasis on the {BLH}. Simulations revealed an anticyclonic eddy generated in the harbour at rising tide. Tracers, released during flood tide at the Liane river mouth, move northward with powerful clockwise rotating current. After the high water, the current direction changes to westward, and tracers leave the harbour through the open boundary. During ebb tide, currents convergence along the western open boundary but no eddy is formed, surface currents inside the harbour are much weaker and the tracer excursion length is small. After the current reversal at low water, particles are advected shoreward resulting in a significant increase of the residence time of tracers released during ebb tide. The effect of wind on particle dispersion was found to be particularly strong. Under strong {SW} wind, the residence time of particles released during flood tide increases from 1.5 to 6 days. For release during ebb tide, {SW} wind weakens the southward tidally induced drift and thus the residence time decreases. Similar effects are observed when the freshwater inflow to the harbour is increased from 2 to 10 m3/s during the ebb tide flow. For flood tide conditions, the effect of freshwater inflow is less significant. We also demonstrate an example of innovative coastal management targeted at the reduction of the residence time of the pathogenic material accidentally released in the harbour.

URLhttp://link.springer.com/article/10.1007/s10236-013-0659-4
DOI10.1007/s10236-013-0659-4