Process-oriented study of the circulation and river plume in the Pearl River Estuary: Response to the wind and tidal forcing

A three-dimensional, primitive equation numerical model is utilized to study the responses of the river plume and estuarine circulation to the wind and tidal forcing in an idealized Pearl River Estuary (PRE) with simplified geometry and physical forcing. This process-oriented study shows that without any other physical forcing, the buoyant-driven circulation, under the Earth rotation effect, forms an anticyclonic eddy in a funneled estuary with a concave bathymetry. However, this eddy disappears with additional wind or tidal forcing. The movement of the buoyant plume is retarded, and the thickness of the plume is largely increased by the tidal forcing as a result of the great enhancement of the vertical mixing inside the estuary and around the mouth of the estuary on the shelf. On the other hand, with wind forcing, the plume moves faster along the seaward branch of the wind-induced estuarine circulation with a narrower width confined by the current. And the wind-induced circulation increases the intrusion of the oceanic saltier water into the estuary, especially in upwelling case, and the consequently enhanced stratification along the axis of the estuary reduces the vertical mixing and the thickness of the plume. The study reveals the interactive roles of the buoyant plume, tidal, and wind forcing on the circulation in the estuary and adjacent shelf waters