Yangtze Delta End Of The Sand And Then Suspended Its Influence

Field measurements of suspended sediment concentration, salinity, water depth, bedforms, grain sizes in the bottom, current velocity at 1 m under water surface were made at four fixed stations in the area that dunes distributed at the South Channel and North Channel, South Passage and North Passage of the Yangtze Estuary in 1998, 2000 and 2002. And the records of viewed near-bed turbulent burst, bed-sediment ejection with a continuous time scale of 14 hours were obtained by Acoustics Suspended Concentration Profiler (ACP). Particulate and dissolved heavy metal concentration were analyzed by Inductively Coupled Plasma-Atomic Emission (ICP-AEC). Statistics methods of correlative analysis, regression analysis, principal component analysis and spectrum analysis are applied for the winnowing of bed-sediment, mechanism, periods and influence of the bed sediment re-suspension. Results show that:1. According to the frequency and intensity of bed sediment re-suspension, three stages within a tide are divided as: (1) during the slack water, the frequency is lower, but the intensity is higher; (2) during the flood or ebb strength, the frequency is higher, but the intensity is lower; (3) during the transition, the frequency and intensity changes positively with the velocity fluctuation. These bed sediment re-suspension ejection characteristics might be due to interval, duration, frequency and intensity of the turbulent burst.2. The winnowing formula of fine-grained gummy sediment particles in the Yangtze Estuary are poly-regression imitated. The correlative coefficients are more than 0.85. The winnowing formula is more applicable than other theoretical and semi-experimental winnowing formula reported in the study area because the particles felt.3. Three remarkable periods of bed-sediment re-suspension in the area appear as:4.2h, 35mmand 2mm.The first peak value 4.2 hperhaps is corresponding to thetidal duration; the second peak value 35 min perhaps is corresponding to medium or large scale sand dunes movement; and the third peak value 2 min perhaps is corresponding to turbulent burst.4. Bed-sediment re-suspension concentration is mainly controlled by four factors as salinity, velocity, water depth and grain sizes. A good linear correlation exists between re-suspension concentration and salinity, velocity, water depth, grain sizes of suspension sediment, and linear correlative coefficient is 0.91. So the regression models are applicable for forecasting the bed sediment re-suspension concentration at the South Channel. The particulate heavy metals at the South Passage can be divided into 3 clusters, and it is also known that heavy metals are exchanged selectively in the area. The water quality is chiefly influenced by the concentration of the dissolved Cu, Zn, As and Cd at the South Passage, and the water quality during the flood or ebb strength is much better than that during the slack water. Therefore, the bed-sediment re-suspension contributes to the water's self-purification.