Abstract: The Pearl River Estuary is affected by river discharge, tidal currents and the near-shore circulation in the South China Sea. Thus, its hydrodynamic condition is very complicated. The tide at the Pearl River Estuary is mainly irregular semidiurnal type, its tidal amplitude increases from south to north, and its tidal flow reciprocates obviously along the coastline. The tidal front is related to the tidal dynamics and river discharge. The surface and bottom salinity fronts are mainly parallel to the shoreline. In winter, the surface front is apparently near the west coastline of the estuary, whilst in summer, the front spreads away from the estuary because of river discharge. The bottom front is not affected obviously by the season, and in both summer and winter seasons, the bottom front is stronger than the surface front. The tidal dynamics could affect the saline water intrusion. When the river discharge is weak, the tidal dynamics become predominant; therefore, the strength of the saline water intrusion becomes stronger, and the saline water intrusion could influence the strength and position of the front. Furthermore, because the tide and upwelling could destroy the water stratification occasionally, the direction and the strength of vertical convection of dissolved oxygen could change periodically with tides. The hydrodynamics of the Pearl River Estuary obviously influence the bottom hypoxia of the estuary. This paper summarizes the progress on the hydrodynamic characteristics and the hypoxia, and discusses some issues that are worth studying in the future.

Key words: tidal current, front, saline water intrusion, hypoxia, Pearl River Estuary