Study on the Seasonal Estuarine Turbidity Maximum Variations of the Yangtze Estuary, China

Abstract

In this study, measurements were used to characterize the dry–wet seasonal factors that control hydrodynamics and sediment transport in the Deepwater Navigational Channel (DNC) located in the North Passage of the Yangtze Estuary. The measured data showed the following: (1) The estuarine turbidity maximum (ETM) location remained in the middle and lower reaches of the DNC, regardless of season or tide, and (2) density stratification and saltwater-intrusion length were found to significantly impact seasonal differences in the estuarine turbidity maximum. Subsequently, a physical-based three-dimensional numerical model was developed to simulate seasonal variations in fine-grained suspended sediment dynamics in the Yangtze Estuary. A series of numerical experiments focused on river discharge, seasonal wind, and mean sea level was performed to explore the primary mechanisms. Finally, the complexity of water circulation and sediment dynamics related to the seasonal variability of channel siltation in the channel was determined. The modeling results showed that (1) river discharge has a strong impact on the horizontal and vertical distribution of residual currents, especially near the bottom during the wet season; (2) seasonally varying wind can significantly alter residual currents near the riverine limit, and the wind in the dry season favors the delivery of sediments from river to sea; and (3) seasonally varying mean sea level and wind climate jointly shape the saltwater-intrusion length near the estuarine front. This study represents a preliminary exploration of physical phenomena and their contribution to siltation of the Yangtze Estuary navigation channel. The results of this study provide crucial data for the development of measures to mitigate channel siltation.