Comparison Study Of Suspended Sediment Distribution In The Yangtze Estuary's Adjacent Sea Area In Recent 20 Years

Based on the in-situ hydrological and sediment data of 1982, 2003 and 2005, this thesis analyzes the temporal and spatial characteristics of suspended sediment concentration (SSC) in recent years and their similarities and differences between 1982 and recent years in the Yangtze estuary and its adjacent sea area in the flood seasons. The main study results are as the follows.(1) In recent flood seasons the SSC in the Hangzhou bay is the highest among the study area, and that in the Yangtze estuary is the next, and that in the Zhoushan sea areas is the lowest. The SSC reduces gradually from the near-shore area to the open sea. In the Yangtze estuary the SSC shows the trend of increasing firstly from the inner estuary to the mouth, and then decreasing from the mouth to the outer estuary. For the observation stations in the Hangzhou bay the SSC reduces from west to east. The SSC increases from north to south by transverse comparison of four stations in the outer estuary. The SSC increases gradually from the surface layers to the bottom layers, but the main types of SSC's vertical distributions are different in different waters. The SSC has obvious and complex variations with tidal cycle, tidal state resulting from the fluctuations of the tidal currents.(2) The SSC of the study area has remarkable variation with tidal state, tide cycle both in 1982 and recent years' flood seasons, but the SSC in recent years makes remarkable reduction compared with 1982's, and the reduction is more obvious in the spring tide than in the neap tide, and the characteristics of the variations with tide cycle of the same stations in the two periods is not all consistent. In the offshore area of the Yangtze estuary, the planar distribution characteristics of SSC in the two periods are both that the high concentration occurs in the west, south region and the near-shore area while the low concentration occurs in the east, north region and the open sea, but some different characteristics also exists and the isonephs of the same quantity in recent years move westward or southward clearly compared with 1982. Generally speaking, the SSC increases gradually from the surface layer to the bottom layer. The SSC in the surface and bottom layers and the increment between the surface and bottom layers' SSC of the same station in the spring is smaller in recent years than in 1982, while the like differences in the neap tide between the two periods is not too obvious, so the vertical profiles of SSC in the same station between the two periods almost parallels in the spring tide, and almost matches with each other in the neap tide. The significant decreasing trend of sediment flux from the Yangtze river into the seas and the great disparity of sediment discharge between the two periods are the main reasons for the differences of the distribution characteristic.