长江口南港近期的演变及其与重大工程之间的关系

长江口为典型的多级分汊中等潮汐河口，口门宽阔、径潮流强劲、泥沙运动复杂、河槽交替多变，给河口综合治理带来困难。长江口各分流汊道演变过程中，此消彼长是永恒的主旋律，其产生、发展、扭曲、萎缩、消亡具有周期性演变规律。为发挥长江黄金水道的优势，促进国民经济发展，长江口先后实施了深水航道治理工程、南北港分流口处的新浏河沙护滩和南沙头通道限流工程，以及中央沙促淤圈围工程和青草沙水源地工程等，南北港和南北槽分流口河段得到有效控制，对长江口未来的演变产生深远影响。基于南北港分流口以下丰富的地形、水文现场资料，对近年来南港地形演变进行了深入分析，在肯定工程稳定河势的同时，认为目前南北港分流口以下，尚存在南港主流偏离南岸致使发生近岸淤积，以及瑞丰沙中下段沙体刷深导致水流分散，不利于河势稳定等问题。并探讨了长江口“先下后上”治理模式的优缺点，建议在长江口河势尚未发生较大变化时，站在整体的高度，综合考虑河势、航道、水土资源、防洪潮及排灌、生态环境保护等诸多因素，尽快实施长江口综合整治工程。

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 the“golden”waterway 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 the“downstream prior to upstream”pattern 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.