The rule of sediment transport on the Nanhui tidal flat in the Changjiang Estuary

The Nanhui tidal flat is located in the area of slow current where the ebb currents from the Changjiang Estuaryand the Hangzhou Bay converge and the flood current from the sea diverges into the estuary and the bay.The flat extends seaward in tongue shape and has a wide and gentle surface with a marked difference of tidal levels on its two sides,which results in the sediment longitudinal transport on the flat.The water-sediment conditions are diverse at different locations.The velocity and sediment concentration in intertidal zone are higher during the flood tide than those during the ebb tide.The net sediment transport is landward,resulting in a large amount of deposition of sediments on the shoal.However,the ebb current is the dominant one in deep-water area where the net sediment transport is seaward.There exist two circulation systems in plane view on the shoal and in its adjacent deep-water area,which results in the sediment exchanges between the flat and channel and between the estuary and the bay.