Rapid changes of sediment dynamic processes in Yalu River Estuary under anthropogenic impacts

The response of the Yalu River Estuary to human activities was investigated. Changes of sediment dynamics during the past 10 years were explored through hydrodynamic calculation, as well as heavy mineral and grain size analysis. In addition, the characteristics of estuarine geomorphological evolution were compared with historical data. The long-term sediment dynamic process and geomorphological evolution were primarily affected by the decrease of water discharge and sediment supply resulting from human activities. The entire estuarine system of Yalu River Estuary has also undergone significant changes since 1941 that are associated with water reduction and sediment discharge affected by construction reservoirs. The estuary eventually formed the current patterns in the 1980s. Compared with variations of water and sediment discharge, sand dredging directly affected the estuarine sediment dynamics in the past 10 years. Data from six hydrodynamic stations measured in 2009 indicated that the bedload transport flux has substantially decreased during a tidal cycle compared with that surveyed in 1996. The bedload transport direction also changed from seaward in 1996 to landward in 2009. In addition, the estuarine bed load movement changes were： （a） sediment from areas with water depth being less than 5 m was transported from the sea towards the land; （b） sediment transport from areas with water depth between 5 to 20 m was oriented towards the sea; and （c） sediment from areas with water depth greater than 20 m was conveyed from the sea towards the land.