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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-64.13×10~6、-306.60×10~6和-639.27×10~6 m~3,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-28.61×10~6、-35.69×10~6和126.43×10~6 m~3,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109.21×10~6和-797.14×10~6 m~3,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-238.95×10~6、203.58×10~6和153.34×10~6 m~3,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-199.06×10~6、-504.61×10~6和-654.12×10~6 m~3,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92.34×10~6、193.01×10~6和-163.62×10~6 m~3,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-154.64×10~6和-511.79×10~6 m~3,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136.39×10~6、-658.28×10~6和-1 266.11×10~6 m~3,对应的变化率分别为5.62%、-20.73%和-26.06%。
River regime is the basic factor affecting the hydrodynamics and saltwater intrusion in estuaries. Based on the charts of the Yangtze River Estuary in the 1950s and 1970s, the numerical shoreline and the water depth, this paper analyzes the river depth changes of the Yangtze River estuary since the 1950s by using the measured water depth data of the Yangtze River estuary in 2012. The estuary of the Yangtze River is divided into estuaries and estuary. In the 1950s, it was only two divisions. Only by the 1970s was the formation of a three-level divisions and four rivers into the sea. In the 1970s, compared with the 1950s, the north branch had a large number of silt deposits with volumetric changes of -64.13 × 10-6, -306.60 × 10-6 and -639.27 × 10-6 m -3, respectively, corresponding to The rates of change were -16.30%, -22.74% and -25.69% respectively, both decreased significantly. The volumetric changes in the upper, middle and lower branches of the branch were -28.61 × 10 -6, -35.69 × 10 -6 and 126.43 × 10 ~ 6 m ~ 3, and the corresponding rates of change were -1.30%, -2.12% and 4.36%, respectively. Due to the shallowing of Chongming Shallow Bank and Hengsha Shallow Bank, the volume of the lower section of North Harbor decreased obviously. The volumetric changes of the upper section and the lower section were 109.21 × 10 ~ 6 and -797.14 × 10 ~ 6 m ~ 3, and the corresponding rates of change were 5.01% and -15.25%, respectively. Due to the decrease of the silting volume in the upper part of the Nankang section, , Resulting in the deepening of the water depth and the increase of the volume. The change of the south volume of the upper section and the lower section of the lower and lower sections were -238.95 × 10 ~ 6,203.58 × 10 ~ 6 and 153.34 × 10 ~ 6 m ~ 3, respectively. The corresponding rates of change were - 8.96%, 6.85% and 3.26% respectively. Compared with the 1970s, the volumetric changes of the upper, middle and lower reaches of the North Branch were -199.06 × 10 -6, -504.61 × 10 -6 and -654.12 × 10 -6, The corresponding rates of change were -60.45%, -48.44% and -35.38%, respectively. The volumetric changes in the upper, middle and lower segments of the south branch were 92.34 × 10 -6, 193.01 × 10 -6, and -163.62 × 10 ~ 6 m ~ 3, and the corresponding rates of change were 4.24%, 11.73% and -5.40% respectively. The reclamation of Qingcaosha Reservoir in the upper section of North Port and the reclamation of Hengsha East Beach in the lower section reduced the area and volume, The change rates are -154.64 × 10-6 and -511.79 × 10-6 m -3, respectively, the corresponding rates of change are -6.75% and -11.55%, respectively. Due to the deep brushing of the upper reaches of the river, , The reclamation led to an increase in the upper part of the volume and a decrease in the lower part. The changes in the south volume of the upper and lower segments in the north and lower segments were 136.39 × 10 -6, -658.28 × 10 -6 and -1 266.11 × 10 -6 m -3, respectively The rates of change were 5.62%, -20.73% and -26.06% respectively.