Residual circulation in tidally dominated bay with asymmetric lateral depth variation

Tide induced residual current has important role in the sediment distribution of bays. There have been extensive studies about the residual circulation in tidally dominated bay having symmetric lateral depth variation. The residual circulation in a bay with asymmetric lateral depth variation, however, is not known well. Tide induced residual current has important role in the sediment distribution of such bays. The Gomso Bay, west coast of Korea, has asymmetric lateral depth variation and large tidal range. The width and length are about 4 km and 20 km, respectively. A narrow deep channel of about 15 m depth is on the northern side, and a wide macrotidal flat is on the southern side.

In the present study, the residual circulation in the Gomso Bay is described by analytical and numerical models. The analytical model solves the depth-averaged, shallow water momentum and continuity equations. The FVCOM is used as a numerical model. For both models, a semidiurnal (M2) tide of uniform amplitude and phase is imposed at the open end.

Results of both models consistently show that there exists a large clockwise circultion in southern shallow area as a residual circulation. Through the decomposition of residual transport velocity from the analytical model, three causes of the residual velocity are analyzed. The flow from bottom friction and asymmetric tidal height, is mainly inward. The advection induces inward flow throughout whole area. The mean pressure gradient force generates outward flow due to accumulated water mass inside the bay. In the shallow area, the mean pressure gradient force overrides the effect of bottom friction and asymmetric tidal height, so that the net flow is mainly outward. In the deep area, since the advective transport balances the mean pressure gradient force, the net flow is inward.