Flow And Sediment Ratios And Transport In The Yangtze River Estuary

Yangtze estuary is the largest estuary in china, locate in Eastern Coast. This dissertation based on this area, specific location was from Xuliujing to Hengsha island-Lianxing Islands, emphasis the hydrodynamic and sediment characteristics and mechanism of suspended sediment transportation. Focus on the two diffluence area, Xuliujing and Qingcaosha Waters, this dissertation based on the recently synchronous hydrologic data, including wet season in 2002 and dry season in 2005,2006.Hydroaraphy, sediment transport mechanics and mathematical statistics was used in this dissertation, the flow and sediment ratios and transportation was discussed in detail, flow and sediment ratios and transport mechanism was discussed under the support of software Mapinfo and Matlab, standard hydrography method was used to flow and sediment flux quantity calculation in representative cross sections of Yangtze estuary, based on the results, the flow, sediment and salinity characters influence on the Qingcaosha reservoir was stated.Results indicated that: the South Branch and North Branch of Yangtze estuary had obvious dry and wet season cycle and tide cycle characteristics, in wet season, the North Branch was dominated by the tidal current, high velocity, high suspended sediment Concentration was found in this area. Sediment flowed into both ends of North Branch which was in sedimentation mode. Net transportation of current and sediment released into Qinglong Harbor and Upstream-going in Lianxing Harbor, all the current and sediment was stored in the North Branch temporary, the North Branch had high salinity, had ocean water property. A new form of backward was found in North Branch, under effect of strong tidal current, the sediment was backward in to South Branch, the backward was happened in high water level period during spring tide and normal tide.The velocity in South Channel and North Channel cross sections in the lower reaches of South Branch was larger than that of Baimaosha cross section, the velocity in North Channel was a little larger than the velocity in South Branch, residual current was quite large in the entire area, varied a little with tidal type, the normal tide and neap tide basically had the same flow and sediment characteristics with the spring tide. The sediment ratio of Baimaosha South and North Waterway was 14:11, the North Waterway still had certain runoff and sediment transportation capacity. There was more sediment output In the low reaches than the sediment input in the upstream of South Branch, indicated that erosion may happened in the South Branch. The suspended sediment concentration in the North Channel is obviously larger than that of South Channel, net flow in the Baimaosha cross section and South Channel cross section was decreased along with the tide was increased, the net flow reached the biggest in the neap tide, however, the net release of sediment was opposite, reach the biggest in spring tide, flow released in neap tide while sediment released in spring tide, indicated that flow and sediment transportation characteristics in the main branch channel; the net flow and sediment release in the North Channel was increase with the tide increase, the flow and sediment transportation was coincident, indicated that flow and sediment transportation characteristics in the minor branch channel. There was more flow and sediment in the wet season in North Channel, the sediment movement was active. In the wet season, the flow and sediment transportation in the North Channel had an advantage over the South Channel, the suspended sediment concentration is far more lager in North Channel, especially in spring tide.The ratios of net release of flow discharge and sediment can be better used to describe the evolution of branch channels, the ratios of net flow of South Branch and North Branch is 96.7 % and 3.3 %, the ratios of net sediment of South Branch and North Branch is 81.7 % and 18.3 %, indicated that the South Branch is still growing, North Branch is declining. The flow and sediment movement in wet season in Yangtze estuary was runoff "main body released south", the inlet "minor channel deposited and main channel eroded", flow and sediment "transportation variation". The suspended sediment transportation macroscopically round a major cycle South Branch→sea→North Branch→South Branch.In dry season, the velocity of Qingcaosha was quite large, basically under the control of runoff, the runoff influenced North Channel much greater than that of South Channel. The direction of residual current pointed to the off Yangtze mouth, basically along the river channel, the residual current in mean-flow period was larger than in low-flow period, residual current was larger in the North Channel and runoff was the main component.The suspended sediment concentration of this area had great difference in distribution, because of the function of runoff, as far as the suspended sediment concentration and the gradient was concerned, in the low reach of diffluence area was greater than that of upside, the South Channel was greater than the North Channel, the sediment diffusion coefficient in the upside of the is bigger than the lower reaches, the North Channel area which Qingcaosha freshwater resources built have more runoff but less sediment, the water collection area had the Characteristics for short flood tide duration, slow flood current velocity, strong ebb current velocity, low suspended sediment concentration, all the characteristics was good for the Qingcaosha reservoir construction. The suspended sediment concentration in Xuliujing was quite low, The runoff in Xuliujing wasclose to that of Datong station.