Three-Dimensional High-Resolution Numerical Study Of The Tide :and Circulation In The Pearl River Estuary And Its Adjacent Waters

Based on an unstructured grid and finite-volume coastal ocean model (FVCOM), including highly accurate coastline and bathymetry data, a three-dimension model with high resolution is constructed in the Pearl River Estuary and its adjacent sea area to reproduce tides, tidal currents and residual currents. The comparison between observations and numerical modeling indicates that the computing results fit the measured values well. More elaborate co-tidal charts and pictures of tidal current ellipse of the four principal tide constituents as well as figures of tides, tidal currents and residual currents illustrate characteristics of tides and circulation in the research areas. The results show that there is mixed semidiurnal tide existing in the Pearl River, and the tide-type factor ranges from 1.1 to 1.3. In the estuary, the tidal amplitude in the east side is higher than that in the west side, and the tide in the east propagates more quickly than that in the west; the tidal currents is mainly northwestern and southeastern with a rectilinear-current motion, and the maximum current velocity appears in the channel; the residual current in the channel flows towards the south, influenced by drainage of the runoff, while in the western shoal of the estuary, it flows towards the north, where a structure of circulation emerges. The tidal energy flux propagating from open sea, the maximum of which appears in the west and east channel of the estuary, mostly converges in the Pearl River Estuary, and circles counterclockwise around Qi’ao Island.The study calculated the transport of estuarine mass and the capacity of water exchange. The results indicate that, with an impact of tides, the capacity of the water exchange in the Pearl River Estuary is weak and the residence time of the waters is more than 90 days,. The runoff and the wind stress can enhance the capacity of the water exchange, and the residence time of the dye in the channel and the west (near entrances of the Pearl River) is shorter than that in the western shoal and the east (away from entrances of the Pearl River). Moreover, during the flood season, the mean concentration of the dye in the estuary maintain low and the residence time of it maintain short, driven by a southwestern wind. The capacities of the water exchange in entrances of the estuary and the sea area of Lingdingyang and Modaomen are strong, while in the sea area of Shenzhen Bay, Daya Bay and Mirs Bay, the capacities of the water exchange are relatively weak. Tracers of the estuary enter Huangmao Sea in the dry season and enter Daya Bay, Mirs Bay in the flood season. With impacts of the runoff and the wind stress, the capacity of the water exchange in the estuary and the velocity with which the tracers in entrances of the estuary transport are both enhanced. In the dry season, tracers move to the west and the maximum displacement is 285km in 90 days.In the flood season, tracers move to the east and the maximum displacement is 190km in 90 days. The tracers move forward in a helical way.