Tidal Exchange through a Strait: A Numerical Experiment Using a Simple Model Basin

In order to investigate the mechanism of tidal exchange through a strait,the authors numerically tracked the Lagrangian movement of water particles over a full cycle of the M sub(2) tide. As a result, the spatially rapid changes of the amplitude and the phase lag of the M sub(2) current in the vicinity of the strait were found to cause the exchange of an extremely large amount of water through the strait. The tidally induced residual circulation in the vicinity of the strait also plays an important role in the water exchange. The calculated exchange ratio over one tidal cycle is similar to 87% (i.e., the greater part of the outer water entering into the inner basin through the strait stays in the inner basin, while an equal amount of basin water is drawn out after a cycle of the M sub(2) tide). This fact suggests that the major part of the water exchange through a strait is generated by the dynamic process of the tidal current, not by turbulent diffusion.