Numerical study of the tidal residual current structure and the water half-exchange time in Xiangshangang bay

Based on the three-dimensional FVCOM module, which is coupled with Lagrangian particle tracking model and conservative pollutant transport model, the hydrodynamic, the conservative pollutant transport, the tidal-induced residual current, the trajectories of characteristic particles and water half-exchange time were simulated. The results showed that tides in Xiangshan bay are irregular semidiurnal ones, of which M2 is dominant. The spatial pattern of tide residual currents was obvious, which could be divided into two branches. The first branch was flowing in from the east of Niubishan waterway, and then flowed out into the south of Fodu waterway bypassing Liuheng Island. The other was flowing in from the Fodu waterway, and flowed out from the east of Niubishan waterway, the part of which was joining in the first branch. The residual current in the west of Xilugang bay is pointing to the entrance of Xiangshangang bay, and the residual current in Xilugang bay is pointing to the harbor entrance. By considering the exchange of conservative pollutant in the whole Xiangshangang bay with the open sea, the water half-exchange time in Xilugang bay is 90 days, and which in Huangdungang and Tiegang bay is near 180 days, and the water half-exchange time in range of the branches is within 20 days.