Abstract:

^{The characteristics of surface sediment types,distribution and deposition district in the Yangtze River Estuary and the north of Hangzhou Bay are investigated on the based of sediment particlesize data and corresponding morphology and hydrodynamics.The results suggested that the characteristics of sediment distribution are the result of combined actions among hydrodynamics,morphologic features and sediment sources.The longitudinal (from west to east) distribution of surface sediments of the Yangtze River Estuary presented from coarse to fine particle sizes,the degree of sorting from good to poor level,and transversely,in the three bifurcations of South Branch into the sea,sediment sizes gradually fined from the North Channel,North Passage to South passage.Sediment grain sizes are coarser in the main channels with strong hydrodynamics and mouth shoals with frequent wave actions,and the grain sizes are finer on the mouth tidal flats with weak hydrodynamics and on the adjacent sea area off the estuarine mouth.Moreover,according to the differences in the distribution and location of the sediments,the Yangtze River Estuary and its adjacent waters can be divided into four main sedimentary zones:(1) The bifurcational river channel section of Yangtze River Estuary,where the main channel sediments are mainly fine sand and silty sand with a median size of 25 to 4and good sorting,and its side flat silty clay with a median size of 7 to 8 and poor sorting;(2) The mouth bar area alternated shoals and troughs,where the shoal sediments are slightly coarse due to wave actions;(3) The offshore area,where sediments between north and south have greater differences to about 31 °20'N for the community,coarse grain sediment in the north due to shelf residual sands and North Jiangsu erosional sands,and fine grain sediment in the south because of Yangtze River source;and (4) The north of Hangzhou Bay,where sediments are mainly clayey silt.}

Key words: ^sediment, size characteristics, deposition district, Yangtze River Estuary, Hangzhou Bay