TIDAL MODEL STUDIES OF PARTICLE TRAJECTORIES AROUND A SHALLOW COASTAL BANK

Barotropic tidal and tidal residual currents calculated with a finite-element model of the southwest coast of Vancouver Island are combined with Lagrangian particle-tracking techniques to follow drifters deployed around a shallow bank whose horizontal scale is comparable with the tidal excursion. Two estimates of the average Stokes and Lagrangian velocities arising from eight tidal constituent velocities are calculated. The less accurate Lagrangian estimate indicates an eddy that is much weaker than the Eulerian residual eddy due to tidal rectification, whereas the second estimate indicates virtually no Lagrangian eddy. The accuracy of these estimates is confirmed with a series of 29-day drifter experiments using the numerical model. It is also shown that the Eulerian gyre does not convey any energy advantage to simple fish that wish to remain in the vicinity of the bank.