Study On The Characteristics Of Surface Sediment Distribution In Changjiang Estuary

Based on the surface sediment samples collected which covered large area of Changjiang Estuary from 2003, the temporal and spatial characteristics of surface sediment distribution and dynamic sediment environment of Changjiang Estuary were analyzed by sedimentary and hydrodynamic methods. The differences of surface sediment distribution in the last two decades were also discussed. The characteristics of surface sediment distribution and sedimentary hydrodynamics in the tidal flat of Changjiang Estuary were discussed, and the model of surface sediment distribution between channel and tidal flat and its dynamical factors were summarized. With the analysis of the hydrodynamic data during the same observation, the factors which affect the distribution of surface sediment and the hydrodynamic response of it were discussed.The results were shown that the D₅₀ of surface sediment was decreased gradually from Jiangyin to the mouth of estuary. The composition of surface sediment in upper Hengsha island was mainly sand, while in the mouth of estuary was mainly clayey silt. And in the Turbidity Maximum, it was much more complex and variational. hi the Turbidity Maximum, the coarsest surface sediment is in the North Channel. Then in the North Passage, the finest surface sediment was in the South Passage.The grain size of surface sediment in flood season was coarser than that in dry season, and that was much more obvious in the Turbidity Maximum, while in the mouth of the estuary surface sediment in flood season of 2004 was finer than that in 2003. The grain size of surface sediment in upper North Branch, distributary site of South and North Channels and Turbidity Maximum were much more changeable in the recent twenty years.The sedimentary and hydrodynamic characteristics of surface sediment were discussed by analyzing the distribution model of surface sediment in typical profiles in channel and tidal flat. The tidal flat of west Chongming island and South and North Channels which located in the inner Changjiang estuary, were influenced by both the runoff and tide, so the characteristics of surface sediment distribution in these areas showed that the grain size in channel was coarser than that of tidal flat. The tidal flat of east Chongming and Nanhui which faced the open sea, were influenced by the wave. So the characteristics of surface sediment distribution in these areas showed that the grain size in tidal flat was coarser than that of channel.