The Yangtze River Estuary Hydrodynamic Processes, Sediment Transport And Erosion And Deposition Changes

Tidal flats in the Yangtze estuary were influenced by the interaction between the sea and terrestrial. Hydrodynamics factors, such as wave, current, flesh water inflow, played important role during the morphodynamic process of the tidal flat. The sediment transport and substance exchanging occurred frequently on the intertidal zone. The Yangtze River annually carries a large sediment load to the Yangtze estuary. This sediment feeds the tidal flats along the coast, which have expanded seaward. But the economic actives on the coast, which induced decreased the biodiversity and debase the eco-environmental quality, have a potential threaten to the sustainable development of the estuarine area.Process of water-sediment transport and variation of erosion-deposition variation were regarded as the key tache of the tidal flat research by the scholar. But, as well known, it's hard to approach the tidal flat, which limited field work of the hydrodynamics investigation. The lack of relative data has baffled the creating integrated model of current-sediment transfer and cumbered study on the law of sediment transport.Supported by the key subject of national science foundation (40131020), Biogeochemical Cycling of Pollution in Complex Environment of Tidal Flats in the Yangtze Estuary, the fieldwork were carried out on the open coast of Dongtan Flat, Chongming. Under the calm weather condition, hydrology factors were recorded and more than 4000 data, about water lever, current direction, current velocity, sediment concentration and sediment grain size, were collected. Draw a conclusion:1. The characters of the hydrodynamics on the different part of tidal flat were analyzed. The time of flood and ebb phase was approximately equal on the bare flat, while the flood phase is shorter than ebb phase in the pioneer zone of slat marsh. On the bare flat, maximum current velocity appeared just after water immersed and before the flat exposure, which could be described as twain-peak type. In winter and spring, current velocity process in the pioneer zone of slat marsh, also, present twain-peak character. In summer and autumn, on the contrast, the peak value ofcurrent velocity at the end of ebb disappeared in the pioneer zone, which could be described as sole-peak type. Current velocity process in the inner salt marsh, for all the year, always present the sole-peak character, but twain-peak in the tidal creek. The current direction turned rapidly during high water period, indicating a circulatory flow. And it is founded that water lever variation on the flat is according with the predicted water lever of Hensha hydrology monitor site.2.Base on the field data, the integrated hydrodynamic model on the tidal flat were created. It include: 1) water depth model (based on the Hensha data, can be used to predict the water depth of the study site); 2) current velocity model (based on the maximum water depth during the immersing period, predict the maximum and average current velocity of both flood and ebb phase); 3 ) cross-shore current velocity model (based on instantaneous water depth, predicted the instantaneous velocity); 4) total water flux model (based on the maximum water depth during the tidal period, predict the total water flux). Through the F test, significant of model 2 is better than 0.05, while significant of other models are better than 0.01. The predicted data of these models were accord with the actual data.3.Suspended sediment concentration variation was accord with hydrodynamics. The peak value of suspended sediment concentration appeared at the beginning and end of the immersed period on the bare flat, similar to the twain-peak character of current velocity. Also, according with the current velocity, the suspended sediment concentration in the pioneer zone presented the twain-peak character in winter and spring, and presented sole-peak character in summer and autumn. Sole-peak character presented in the inner salt marsh during all the seasons. The average suspended sediment concentration on the bare flat and in the p...