The Response of Salinity in Dry Season to Vertical Circulation in the Modaomen Estuary of the Pearl River, China

In recent years, salt intrusion in estuaries of the Pearl River has become a serious problem for local water supply in dry season. Water level, circulation and salinity around mouth of the Modaomen estuary in spring and neap were examined respectively through field measurements. The results indicated that mild water level process reinforced baroclinic action to cause notable circulation downstream, which was more durable in neap. And, the current in lower layer was generally faster than that in upper layer during the neap circulation. These two probably resulted in higher bottom salinity in neap than in spring within the upper mouth, which was on the contrary to the lower mouth as well as the open coastal sea nearby. The activity of observed salt wedge by tidal force within the lower mouth contributed to local salinity variation. Thus, the saline processes and distributions in the estuary mouth depended on cooperation of estuarine circulation and tidal driving in the absence of river flow and wind.