Wave–current interaction by Typhoon Fongwong on saline water intrusion and vertical stratification in the Yangtze River Estuary

Abstract

Saline water intrusion and vertical stratification are two important phenomena in estuaries, and thereby inextricably related to water mixing. In this study, a coupled 3D current-wave-salinity transport modeling is used to evaluate the effects of strong wind, wave and current on salt intrusion and water mixing in the Yangtze River Estuary (YRE) during typhoon Fongwong (2014). The model is validated by the measured wave height and period, tidal level, current velocity and salinity data. The model results show that: 1) wave-current interaction (WCI) during the typhoon period increased the current velocity and tidal level while decreased the air pressure, causing a storm surge by 1.2 m in the YRE; 2) the strong waves and winds strengthened the salinity intrusion in the YRE and the North Branch (NB) presented evident changes. After typhoon passage, the high saline water did not flush out immediately, indicating the typhoon effects were a fast process but the recovery of two weeks was slow; 3) The effect of the WCI showed a significant increase of water mixing and destratification during the typhoon event. Similar to the salinity intrusion, the process of regaining stratification needed a relatively long time. This research highlights that the WCI effects are important in the typhoon period on the hydrodynamics and salinity variation in the horizontal and vertical directions.