GIS支持下的长江口拦门沙泥沙冲淤定量计算

GIS supporting study on calculation of the amount of siltation and erosion in mouth bars of the Changjiang Estuary

依据1842～1997年10幅不同年代的长江口海图资料,利用地理信息系统和数字化仪进行处理,建立不同时期的长江口水下数字高程模型,以此作为基础资料,实现了从横剖面、深泓线纵剖面、平面变化等不同角度对长江口拦门沙地区滩槽演变、岸线侵蚀、沙岛形成与变迁等进行研究.通过计算河槽容积,实现了对不同时段泥沙冲淤量的计算.结果表明,155a来拦门沙总的趋势是不断淤积,但不同时期淤积速度大不一样,个别时期甚至会发生一定程度的冲刷,这主要与动力条件的波动有关.1842～1997年,共淤积泥沙38.10亿t,平均每年淤积 0.246亿t,约占长江来沙的5％,年均淤厚为1.1cm 泥沙淤积部位主要在九段沙、横沙及横沙东滩、崇明东滩三处.发生冲刷的范围较小,仅占总面积的21.4％,主要在北槽,北港上段和南槽局部也有轻微的冲刷发生.

Supported by GIS, 10 pieces of charts of the Changjiang Estuary from 1842 to 1997 are studied. Digital elevation model of the Changjiang Estuary is established with Kriging gridding method to research evolution of channel, change of coasts, formation and evolution of islands in mouth bar area with different points of view: transverse sections, longitudinal profiles, plane change, etc. Furthermore channel-fill volumes are calculated andcalculations of amount of deposition and erosion in different scopes between different years are conducted. The calculated results show that the evolution of mouth bar area of the Changjiang Estuary was complex in near 155 a (1842~ 1997): deposition has its trend, but the speeds of deposition in different terms are different and erosion occurs place in a few terms which mainly are related to dynamic conditions. About 3.81 Gt of sediment was deposited between 1842 and 1997, with average annual deposition rate of 24.6 Mt which amounts to 5% of sediment form the Changjiang River. Jiuduansha , Hengsha and its east beach, and east beach of Chongming Island are the main positions of siltation and the current North Passage is the main position of erosion. In addition, there is slight erosion in the upper part of the North Channel and part of the South Passage. Together, the area of erosion is limited and it only amounts to 21.4% of total study area.