CURRENT EVOLUTION OF THE SOUTH CHANNEL OF THE YANGTZE ESTUARY AND ITS IMPACTS ON MAJOR PROJECTS

The Yangtze Estuary is a typical medium tidal estuary with multi-order bifurcations.Its significant width,strong tidal flows,complicated sediment movement,and the diversity of alternated channel and floodplain contribute the difficulties of comprehensive regulation of the estuary.During the evolution of multiple branches,the balance of one branch developing and the other decaying among these branches is always the constant rule;meanwhile,the cycle of creation,development,distortion,decay and disappearance for an individual branch presents a periodic evolution law.In order to strengthen the benefits of thegoldenwaterway of the Yangtze River,and contribute to the domestic economic development,a series of projects have been carried out recently,including the Yangtze Estuary deepwater channel regulation,sand protection project of the Xinliuhe sand at the diversion between the South and North Channel,Nanshatou project of constraining flow,the enclosure at Zhongyangsha and protecting the water source site at Qingcaosha etc.As a result,the diversion of the South and North Channel has been stabilized effectively,and the future evolution of the Yangtze Estuary will be influenced significantly.This paper presented that based on abundant topographical and hydrological data of downstream the diversion of the South and North Channel,thorough analysis of the recent evolution of the South Channel,South and North Passages were conducted.Affirming that the projects contribute to the stabilization of river regime,the paper also pointed out that the following problems still exist at the downstream diversion of the South and North Channel.Sedimentation occurs close to the South incurred by the main flow of the South Channel deviating from the south bank.Scour and deepening at the middle and end sections of Ruifeng Sandbar causes flow dispersion,and has negative impacts on the stabilization of river regime and etc.Besides,the paper also discussed the advantages and disadvantages of thedownstream prior to upstreampattern of regulation,and suggested that with strategic considerations of river-regime,navigable channel,soil and water resources conservation,flood and tide protection,drainage and irrigation,ecological environment protection and other factors,before the current Yangtze Estuary regime occurs significant alternation,and the comprehensive treatment projects of the Yangtze Estuary should be implemented as soon as possible.