九段沙沙洲演变及其与水沙变化的响应关系

Response Relationship of Evolution of Jiuduansha Island to Water and Sediment Variation

九段沙作为长江河口第三代冲积沙洲岛,自成为独立沙体以来,在各种河口水动力环境共同作用下地形不断发生变化。基于九段沙实测地形及卫星影像数据资料,通过相关软件分析了九段沙近期沙洲冲淤变化及地形演变,并研究了地形演变与水沙变化之间的响应关系。结果表明,1997~2008年受相关水利工程建设影响,0、-2m等深线沙体面积增加明显,-5m等深线沙体面积趋于稳定;同时,在陆海相互作用下,九段沙沙洲头部以冲刷为主,各年断面形态大致相似;沙洲中部各年淤积量逐步增大,特别是其尾部淤积尤为明显,断面形态有较大改变;沙洲尾端有冲刷趋势,这与沙洲尾端平面形态有关。但总体上,整个沙洲呈淤积大于冲刷趋势,其椭圆形态基本无变化;流域水沙变化与浅滩面积响应不明显,因而1997~2008年乃至其后一段时间内,长江口深水航道工程导堤阻流将是九段沙淤积响应的主要因素。

Jiuduansha as the third generation sand island of the Yangtze River estuary,under the joint action of various estuarine hydrodynamic environment,sandbar terrain is constantly changed since becoming an independent sand body.Based on the measured terrain and satellite imagery data of Jiuduansha,this paper analyzed the change of scouring and silting and the evolution of terrain in Jiuduansha sand,and studied the relationship between terrain evolution and water and sediment change.The results show that the area of sand bodies for 0 mand-2 mdepth contour are obviously increasing due to the influence of the relevant water conservancy project from 1997 to 2008,and the area of sand bodies for-5 mdepth contour is stable.Under the interaction of land and sea,the head of Jiuduansha island is mainly washed,and the cross section is similar in each year.Sandy central,annual siltation gradually increased in the center of sandbar.Tail siltation is particularly evident,and the cross-section shape has a greater change.There is erosion trend in the end of sand bar,which is associated with the sand plane at the end of the plane.On the whole,the evolution trend of the sand bar is siltation more than erosion,the elliptical shape is basically not changed.The response of water and sediment change to the shoal area is not obvious.Therefore,the diversion of the embankment of the Yangtze River estuary deepwater channel project was the main factor in the sedimentation response of the Jiuduansha from 1997 to 2008 and the future period.