Characteristics of surface sediment distribution and its hydrodynamic responses in the Yangtze River Estuary

The analysis results of 58 surface sediment samples collected in February 2003 showed that the median diameter of surface sediment (D₅₀) was decreased gradually from Jiangyin to the mouth of the Yangtze River Estuary, and the value decreased from 217.8 μm of Jiangyin to 12.1 μm of the mouth of South Passage. In Turbidity Maximum, the coarsest surface sediment was in North Channel, and the average median diameter was 126.2 μm. The coarser surface sediment was in North Passage, and the average median diameter was 48.4 μm. The finest surface sediment was in South Passage, and the average median diameter was 14.2 μm. While in the mouth of the estuary, the coarsest surface sediment was in North Passage, then in North Channel, and the finest surface sediment was in South Passage. The median diameter of the mouth of North Passage was 22.4 μm, and that of North Channel 16.5 μm, and South Passage 12.1 μm. The sorting of surface sediment was mainly moderately sorted to very poorly sorted, and the greater the median diameter, the smaller the sorting coefficient. The skewness was mainly nearly symmetrical to very positive. The kurtosis was mesokurtic to extremely leptokurtic. The composition of surface sediment in upper Hengsha island was mainly sand, while in the mouth of the estuary was mainly clayey silt. In Turbidity Maximum, it was much more complex and variational. There was positive relationship between the D₅₀ of surface sediment and the ebb tidal duration, value of V_e/V_f and residual current speed in channel of the Yangtze River Estuary, and the ebb current condition was the main dynamic factor to determine D₅₀.