长江河口河槽演变过程对大型工程的响应

The project responds principally to Topic 9(1) "Medium and small scale of marine process" in the field of earth science 2013. As a specific component of marine environment, the estuary transports a large amount of sediments, nutrients and dissolved materials to the sea and medium and small scale of variation in estuarine morphodynamic process must accordinglly originate change in the adjacent marine process. For recent decades, significant changes in sediment source, depositional morphodynamic processes have occurred in the Yangzte estuary in response to both obvious variations in water and sediment discharge from the river watershed and large engineering programs as deep navigation channel and freshwater reservior in the estuary. These changes must lead to the adjustments of estuarine channels and new characteristics of estuarine morphological pattern composed of three bifurcations and four outlets to the sea. They also impact on the dynamic sedimentation and geochemical process in the adjacent East China Sea and Yellow Sea. So, it is quite urgent and necessary to study the morphodynamic process and pattern of estuarine channels by a strong human intervention within the watershed including the estuary in a scale of whole estuarine system.. The project will highlite the variations in water and sediment dishacharge during the implementation of large engineering programs within the watershed and estuary based on large quantity of historical data and in-situ measured records. The mechanics and pattern will be approached with an emphasis on the change in distribution of water dischage, suspended sediment concentration, bed sediment, morphological type of estuarine channels in response to those large engineering programs. And then development trend of channel pattern will be simulated using semi-analytical model. The approach is a hot spot of earth system science research issue with a theorectical significance. It also has an application prospect for the disaster prevention and control of large engineering programs in the estuary.

河口是海洋的特殊组成部分，河口过程中小尺度上的变化必然导致邻近海域中小尺度过程的改变。近30年来，长江流域水土保持、三峡大坝和河口区滩涂围垦、深水航道、青草沙水库等重大工程建设导致河口河槽冲淤演变相应调整，使得近两千年来自然作用形成的三级分汊四口入海格局出现了新的变化，因此迫切需要开展新形势下长江河口河槽演变过程的研究。. 本项目针对新的流域与河口边界条件，以大量历史资料和最新实测数据为基础，注重现场第一手原型资料的观测，采用历史对比分析和多学科交叉研究手段，研究流域与河口大型工程运行过程中的水沙变异特征，河口河道水沙分布及变化对大型工程的响应，大型工程运行条件下河口河槽形态与沉积物对水沙变化的响应及河口河槽演变趋势模拟分析。这是国际地球系统科学关注的焦点和核心研究中的新课题。其成果可为河口重大工程灾害防治和规划提供可靠的科学依据，在理论和应用上都具有重要意义。

2014年4月、6月、7月和11月分别对长江口潮区界大通河段河槽和河口段四个主槽的动力、沉积、地貌进行了定点和走航式测量，将其与1997~ 2013年洪枯季水文测验和实测水下地形及1970~ 2013年间海图等资料进行对比，运用统计学、机制分解、尖点突变模型、调和分析等方法，分析河口河槽水沙输移特性及其对流域和河口大型工程的响应。获得以下主要创新成果：.(1) 流域水土保持和三峡大坝工程后，潮区界河段河槽横断面刷深2~4m，河口段主槽整体上处于微冲刷环境，河床活动沙较活跃，表层沉积物粗化，床面沙波发育更明显，口门外侧海域地形略有冲刷蚀退。.(2) 深水航道工程导致北槽中上段浅水分潮增强，潮动力非线性特征加强，且M4分潮振幅变化幅度远大于M2分潮，洪枯季大潮平均潮差减小，涨落潮平均流速减小，优势流减小；M2分潮流长轴洪季大潮增大、枯季减小，长轴向均向北偏转且椭率减少；洪枯季涨落潮平均含沙量均增多，优势沙减小。.(3) 青草沙水库和长江大桥建成后，北港中上段落潮优势明显增强，洪季大潮涨落潮垂线平均含沙量减少，枯季大潮涨落潮垂线平均含沙量增多，河势趋稳。东海大桥和近岸工程建设导致南汇南滩水域洪季落潮优势增强、枯季落潮优势减弱。.此外，在承担者原有大量资料基础上，并在研究内容相近的项目支撑下，本项目执行期间，，共发表SCI论文2篇，中文核心期刊论文4篇，录用待刊论文16篇，远超预期目标和任务。