河势是影响河口水动力和盐水入侵基本因子。本文利用20世纪50和70年代长江河口海图，数值化岸线和水深，结合2012年长江河口实测水深资料，分析长江河口自50年代以来的河势变化。长江河口为分汊河口，50年代仅为二级分汊，至70年代才形成三级分汊，四口入海的河势格局。70年代相比于50年代，北支淤浅严重，其上、中、下段容积变化分别为－64．13×106、－306．60×106和－639．27×106 m3，对应的变化率分别为－16．30％、－22．74％和－25．69％，均显著减小；南支的上、中、下段容积变化分别为－28．61×106、－35．69×106和126．43×106 m3，相应的变化率分别为－1．30％、－2．12％和4．36％；北港由于崇明浅滩和横沙浅滩的淤浅，下段容积明显减小，其上段和下段容积变化分别为109．21×106和－797．14×106 m3，对应的变化率分别为5．01％和－15．25％；南港上段由于河道淤浅容积减小，下段北由于铜沙浅滩被冲开形成北槽，导致水深变深、容积增加，其上段、下段北和下段南容积变化分别为－238．95×106、203．58×106和153．34×106 m3，对应的变化率分别为－8．96％、6．85％和3．26％。2012年相比于70年代，北支由于大量淤浅和围垦容积大幅减小，其上、中、下段容积变化分别为－199．06×106、－504．61×106和－654．12×106 m3，对应的变化率分别为－60．45％、－48．44％和－35．38％；南支的上、中、下段容积变化分别为92．34×106、193．01×106和－163．62×106 m3，相应的变化率分别为4．24％、11．73％和－5．40％；北港上段青草沙水库的围垦和下段横沙东滩的围垦造成面积和容积减小，其上段和下段容积变化分别为－154．64×106和－511．79×106 m3，对应的变化率分别为－6．75％和－11．55％；南港由于上段河道刷深而下段九段沙以及南汇边滩淤浅、围垦，导致其容积上段增加，下段减小，上段、下段北和下段南容积变化分别为136．39×106、－658．28×106和－1266．11×106 m3，对应的变化率分别为5．62％、－20．73％和－26．06％。%ches of the South Branch had changed by-28.61 ×106 ,-35.69 ×106 and 126.43 ×106 m3 ,the rates were-1.30%,-2.12% and 4.36%;the volumes of upper reaches and lower reaches of the North Channel had changed by 109.21×106 and -797.14×106 m3 ,the rates were 5.01% and -15.25%,the volume of lower rea-ches decreased significantly because of the siltation of Chongming Shoal and Hengsha Shoal;the volumes of upper reaches、north lower reaches and south lower reaches of the South Channel had changed by -238.95×106 ,203.58 ×106 and 153.34×106 m3 ,the rates were -8.96%,6.85% and 3.26%,the volume of upper reaches decreased because of the siltation,the volume of northern lower reaches had increased because the cutting off of Tongsha Shoal increased the depth of water.Comparing the Changjiang Estuary in 2012 and in 1970s,the volumes of upper reaches、middle reaches and lower reaches of the North Branch had changed by -199.06×106 ,-504.61×106 and-654.12×106 m3 ,the rates were -60.45%,-48.44% and -35.38%,the volume of the North Branch de-creased significantly because of the serious siltation and reclamation;the volumes of upper reaches、middle reaches and lower reaches of the South Branch had changed by 92.34×106 ,193.01×106 and -163.62×106 m3 ,the rates were 4.24%,11.73% and -5.40%;the volumes of upper reaches and lower reaches of the North Channel had changed -154.64×106 and -511.79 ×106 m3 ,the rates were -6.75% and -11.55%,the volumes had de-creased because of the reclamation of Qingcaosha Reservoir and Hengsha eastern tidal flat;the volumes of upper reaches、north lower reaches and south lower reaches of the South Channel had changed by 136.39×106 ,-658.28 ×106 and -1 266.11×106 m3 ,the rates were 5.62%,-20.73% and -26.06%,the volume of upper reaches had increased because the channel in the upper reaches became deeper and the volume of lower reaches had de-creased because of the siltation and reclamation of Jiuduansha and Nanhui tidal flat.
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