【作者】 郜昂；

【导师】 杨世伦；

【作者基本信息】 华东师范大学 ， 自然地理学， 2008， 博士

【摘要】 九段沙位处长江口拦门沙地区,它导致长江三角洲产生第三级分汉,是目前长江口最大的沙洲湿地,也是国家级河口湿地保护区。近50年来,由于自然条件(流域水沙、海洋动力、两翼河槽)变化以及人类活动(长江口深水航道工程)的影响,九段沙发生了剧烈的形态演变。对九段沙这一湿地的演化规律进行研究,不但可以深化陆海相互作用下分汉河口地貌发育理论的认识,而且能为九段沙湿地保护区的规划和管理提供重要的科学依据。本文利用过去50年的海图测量数据以及长江口来水来沙数据等资料,结合过去3年来通过RTK-GPS实地采集的地形数据等资料,建立了九段沙基础地理信息数据库,通过改进空间插值方法生成了九段沙不同时段的数字高程模型,利用GlS(Geographical Inforrnation System,地理信息系统)技术及空间分析技术对九段沙自1958年来的演变过程进行了多方面的定量分析,主要结论如下:1)近半个世纪九段沙湿地经历了强烈的地形演变。总体来说,由于不断淤积的过程主导研究时段内的九段沙演变,其5m等深线以上的面积及体积分别增加了96%和156%;其潮间带面积及体积分别增加了331%和504%。九段沙滩顶高程从0.3m淤高至4.9m,其盐沼植被带的面积从0增加至潮间带总面积的40%。以上结果反映九段沙的发育逐渐趋于成熟。2)九段沙的演变可划分为四个阶段:1958年至1971年是九段沙的新生时期,此阶段九段沙以散沙合并为主要特点,快速淤积扩大;1971年至1989年是九段沙的快速增长期,九段沙保持稳定的整体形状,总体快速淤长,其形态发生顺时针的旋转,总体位置向下游方向移动;1989年至1994年,江亚南沙并入九段沙系,使得九段沙总体形状发生了改变,其面积、体积亦有大幅度增长。并沙事件改变了原有的九段沙形态发育趋势,也改变了区域水动力状况;1994年至2005年是九段沙的稳定时期,此间九段沙的整体形态稳定,面积体积变化速率逐渐减小,工程建设使得九段沙的局部冲淤模式发生了调整。3)九段沙的演变受到流域和海洋、自然和人类活动的共同影响。流域来沙是九段沙发育的重要物质基础,它控制着九段沙面积和体积的长期变化趋势。河口动力条件是九段沙物质搬运的重要营力,同时制约着九段沙的几何形状的变化。沼泽植物具有明显的消能、捕沙作用,它促进了潮间带的成陆作用。近期的北槽深水航道工程南导堤一鱼咀工程改变了九段沙局部的动力条件和泥沙输移通量,对九段沙的演变产生了深刻影响。4)由于流域来沙的急剧减少和南、北槽的制约(因长江径流量变化不大,南北槽将不会有大的容积变化),已经趋于成熟的九段沙在未来几十年将不会迅速扩大,取而代之的是面积较为稳定和局部的冲淤调整。更多还原

【Abstract】 Jiuduansha shoals（JDS） are the neonatal wetland of the Yangtze Estuary that divide the South Channel into the North and South Passages and form the 3^rd fork of the Yangtze river mouth. They are of great significance to the local ecosystem, and also a National Nature Reserve of China. Different from other inland wetlands, Jiuduansha are surrounded by river channels and the open sea thus is highly dynamic. This paper endeavors to quantify the morphological change of the Jiuduansha shoals since their birth by using a bunch of geo-statistical and spatial analytical methods with Geographic Information System（GIS） software and discuss the possible causes of the evolution with historical data and events.Several Geographical Information System（GIS） techniques including analysis of geometry parameters, DEM construction and calculation of accretion and erosion were combined in this study to develop a detailed understanding of the morphological evolution of JDS in the Yangtze Estuary between 1958 and 2005. Elevation data from historical bathymetric maps, several in situ topographic surveys were collected as the major data sources for the topographic changes. Annual water discharge（WD） and sediment discharge（SD） were employed in this study as the backgrounds of the basic riverine characters. Analysis results indicate that:1) From 1958 to 2005, JDS underwent intense morphological evolution. The area and sediment volume of JDS increased by 96% and 156% above the 5m isobath and by 331% and 504% above the Lowest Astronomic Tide（LAT）. Specifically, the maximum elevation of the island increased from 0.3 to 4.9m above the LAT and the salt marsh increased from 0 to 40% of the intertidal area.2) During the last half century, JDS developed form neonatal（from 1958 to 1971） to two-phased fast developing（from 1971 to 1989 and from 1989 to 1994） and finally to stable（from 1994 to 2005）.3) Although persistently being affected by the trends of sediment supply, identical developing pattern of shoals in the Yangtze Estuary and local hydrodynamics, the evolution also severely affected by historical events such as big flood, shoal mergence and embankment, etc. The other factors such as sea-level rise, land subsidence and vegetation plantation contribute less significance to the evolution process. The dominant factors varied between periods. The evolution in neonatal period was mainly dominated by the riverine sediment supply and the identical pattern of the local shoals. The fast developing period was controlled by the variation of water and sediment fluxes between the two river channels that enclosed the shoals. During the latter part of this period a new shoal merged into Jiuduansha shoals system indicating that the paroxysm event dominated the developing process. At last, from 1994 to 2005 the evolution of the shoals turned modest and the local coastal engineering termed the Yangtze Estuary deepwater channel regulation phase-1 gained over the dominating position of the shoals development.4) Conservative estimation indicates that under the severe decreasing trend of riverine SD and the self-adaptation of the shoals to the engineering, the fast accretion of Jiuduansha shoals will be replaced by the general-stable-with-local-erosion period, and the erosion will possibly occurs first from the seaward bottom.更多还原