长江河口九段沙沙洲形成和演变过程研究

九段沙继崇明岛、长兴岛和横沙岛后成为长江河口第三代新生冲积沙洲(岛),为河口第三级分汊口沙洲,如今0m以上沙洲面积为126km2,5m水深包络的面积为448.7km2,平面外形成长椭圆沙洲。自从上世纪50年代中期九段沙成为独立沙体以来,在河口水流的作用下,不断地承接上游河道推移而来的底沙,沙洲持续淤涨,0m以上沙洲面积是原始面积的3.3倍,2m水深包络的平面面积是原始面积的2.5倍,5m水深包络的平面面积是原始面积的2.0倍多。与此同时,在陆海相互作用及南北槽分水分沙比值不断更替变化过程中,九段沙沙体本身也发生了较大变化,表现为沙头冲刷后退,沙尾淤涨延伸,南侧淤涨幅度大于北侧,而沙洲基座长轴位置移动不大。目前九段沙头部鱼嘴和北部导堤工程的建设改变了九段沙浅滩的水沙运动过程,因九段沙北侧边界基本固定,导致南侧边滩冲淤变化必将会增大,需采取相应的人工干预措施,才能使国家级生态保护区九段沙朝着健康的演变方向发展,同时减少对与沙洲相邻的南北槽通海航道水深的影响,确保通海航道畅通无阻。

Study on the formation and evolution of Jiuduan shoal in the Changjiang estuary

Jiuduan shoal is the third-class alluviation shoal in the Changjiang estuary,the areas surrounded by 0m and 5m isobath are 126 km~2 and 488.74km~2 respectively,with a elliptic planform.Since Jiuduan shoal became the separate shoal in 1950's,a continuous accumulative deposition has happened due to the hydro-dynamic factor,and the areas of the shoal above 0m,2m,and 5m have increased 3.3 times,2.5 times and 2.0 times,respectively.At the same time,under the sea-land interaction and changed water and sediment condition,Jiuduan shoal exlibited an obvious change,which the head of the shoal was eroded and the tail of the shoal was accumulated,and the extent of accumulation in the south area was greater than that in the north area,but the long axes of the base has no obvious motion.At the present time,the constructions of spit of Jiuduan shoal and the barrier in the north area have changed the water and sediment condition of the Jiuduan shoal,so the boundary of north Jiuduan shoal becomes stable,but the south shoal still changes a lot,and the artificial measurements should be taken to reduce the negative effect on the navigation channels close to the shoal.