Characteristics and Driving Mechanisms of Salinity Stratification during the Wet Season in the Pearl River Estuary, China

In an estuary, stratification processes play a major role in inhibiting estuarine circulation, sediment transport, and the estuarine ecosystem. A detailed examination of the salinity stratification through the gradient Richardson number and the potential energy anomaly equation has been undertaken along the West Channel of the Pearl River Estuary, China. The results show that the estuarine circulation within the West Channel is much weaker on a spring tide than that on a neap tide, exhibiting apparent spring–neap tidal variability. The calculated gradient Richardson number displays its intratidal and spring–neap tidal variability within the West Channel, indicating the existence of intratidal and spring–neap tidal variability of stratification. In addition, the tidally averaged change rate of total potential energy anomaly within the West Channel suggests more than a 4.53 × 10−3 W·m−3 increase from spring to neap tides, demonstrating strong stratification on a neap tide. The longitudinal advection and the longitudinal depth-mean straining are the leading physical mechanisms contributing to intratidal and spring–neap variability of salinity stratification within the West Channel. However, the effects of the lateral terms cannot be ignored especially on a neap tide.