Recent Morphological Evolution Of The South And North Channel In The Yangtze Estuary And Sediment Carrying Capacity Research

In recent years, due to the decrease in the sediment load of the Yangtze River, with a number of regulation projects constructed in the South and North channel diffluence pass, the estuarine hydrodynamics and riverbed topography inevitably experienced some new changes. Methods of geomorphology, hydrology statistics, sediment transportation.etc are used to study and summarize the difference of hydrodynamics and sediment characters, and the evolution of typical sandbank in the South and North channels. Besides, by analyzing data collected from a field observation during a neap-mean-spring tidal period which lasted9days, sediment transport capacities at the South and North Channels were investigated which obtained the following results.The evolution of the South and North Channel diffluence pass and bottom silt movement have an immediate impact on the two channels’ morphological evolution, and the runoff and sediment load of Changjiang River also play an important role on it. When the position of the talweg goes one channel, the development coming with it, opposite also established. And the two channels show a erosion on the upside and deposion in the below, the phenomenon was due to the ebb flow is the dominant driving force in South and North channel. In recent years, the position of talwag is further north in the upside of North channel, and the further north in the below, Baozhen sandbank moves down in the flow function, the North Channel evolved to the channe which the ebb and rising flow in same warerway. Changxing rising tide waterway gradually die at the state, Ruifeng sandbank have also shrunk because of human sand mining. The proportion of human activities influence is increasing gradually. Since2004, projects as Zhongyang Sandbank enclosure, protect beach engineering of the new Liuhe sandbank, submerged bar of the North sandbank waterway, the Qingcao sandbank reservoir.etc were builded in recent years, it helped to control the river regime, fix the stream sandbar, stable the diversion waterway, and optimize the channel depth.Comparison analysis of the measured data in the flood season, we come to the conclusion that, both the two channels’ dominant driving force are the ebb flow direction, but the rising tide in the South Channel is more stronger. By analyzing data collected from the field observation during a neap-mean-spring tidal period in South and North channels, sediment concentration during the spring tide was much higher than that of the neap tide, indicating strong resuspension of sediment during spring tide with strong tidal dynamics. The long time series of hydrology and sediment observation greatly reduces the randomness of the data, and has a better result.Based on the basic theory of river dynamics and open channel sediment carrying capacity, formulas with fine correlation of sediment carrying capacity were fitted by the field observation data in recent years. Through a comparative analysis of index of formulas, we found the sediment carrying capacity in mean tide has a lot of enhancement compare to neap tide, but the increase is not obvious between the spring tide and mean tide period. Formulas describing the correlation between the sediment concentration and the tidal current velocity were obtained for spring, mean and neap tides, respectively. The result shows that there was strong correlation between the sediment concentration and the tidal current velocity, and the degree of sediment transport capacity was determined by tidal current velocity.