Keywords: 
• sediment flux /
• bathymetric evolution /
• waterway regulation /
• Yangtze River Estuary

Abstract: Understanding histrorical and future morphdynamic evolution processes is of critical importance to the longterm development and regulation of estuarine deltas. Based on a series of bathymetric and hydrologic data from 2001 to 2015, the influence of Yangtze fluvial sediment decline on the bathymetric evolution of the Yangtze River Estuary and adjacent seas is presented. After the completion of the Three Gorges Dam Project, the sediment flux is 135 million ton per year (keep relatively lower level comparing to the past), and an updated stable relationship between riverine discharge and fluvial sediment flux has been taken shape. Impacted by the sediment reduction, the suspended sediment concentration at the South Branch, South Channel and at the upper reach of the North Channel experienced a sharp decline after 2008, accompanied with channel erosion and channel-volume increasing. Meanwhile the channel shape tended to be narrower and deeper than the past. In recent years, the upstream and outlets of the Mouth Bar area are scoured, the length of the shallow area is cut down. Two erosion areas are found at the front of underwater deltas of the Yangtze River Estuary, one is located at the outlet of the North Channel, and another is at the outlet of South and North Passage. From 2007 to 2015, the annual average scour thickness is 0.1 m, and the yearly erosion amount reaches 71 million m³. The influence of fluvial sediment decline on the bathymetric evolutions in the Yangtze River Estuary and adjacent seas is still in progress, and it will likely overturn the traditional seaward sedimentation pattern in this area.