长江口南汇边滩围垦工程对流场和盐水入侵的影响

Impacts of the reclamation project of Nanhui tidal flat on the currents and saltwater intrusion in the Changjiang estuary

考虑枯季一般状况的径流量和风况,数值计算和动力分析南汇边滩围垦工程对长江河口流场和盐水入侵的影响.南汇边滩围垦工程实施后,南槽喇叭口形状减小,改变了涨潮流和纳潮量.研究表明,围垦工程导致南槽大潮期间纳潮量减少13%,小潮期间减少16%,越过深水航道导堤的涨潮流减小;从南槽向北的越堤盐通量减小,导致北槽向海的盐通量减弱,中上段向陆的盐通量减弱,工程东南侧向陆的盐通量减弱,但因南槽口门处缩窄向陆的盐通量增强.围垦工程后南槽盐度锋面减弱,大潮期间南槽口门处和工程东南侧盐度上升,量值超过1.0;因纳潮量、越堤流和向陆盐通量减小,南槽中上段、北槽和横沙东滩盐度下降,量值超过0.5;北港和崇明东滩盐度上升,盐度超过0.5.小潮期间因潮动力减弱口门处的涨潮流和向陆盐通量减小,整个南槽盐度下降,量值超过1.5.因围垦工程后南槽盐度锋面减弱,阻挡径流进入南港的作用减弱,大潮和小潮期间北港净分流比略微减小,南槽的分流比大潮和小潮期间分别比工程前增加了1.57%和1.50%.

Considering the averaged river discharge and wind in dry season,the impacts of reclamation project of Nanhui tidal flat on the currents and saltwater intrusion were numerically calculated and dynamically analyzed. The funnel shape was reduced,flood current and tidal prism in the South Passage were changed after the reclamation project. The reclamation project resulted in tidal prism in the South Passage reducing 13% in spring tide and 16% in neap tide,and the flood currents spilling over the dikes of the deep water channel decreased; The northward salt fluxes spilling over the dykes fromthe South Passage were weakened which made the seaward salt flux in the North Passage reduced,the landward salt flux decreased the upper and middle reaches of the South Passage and on the southeast side of the project,whereas was increased at the mouth of the South Passage. After the reclamation project,the salinity front in the South Passage was weakened,the salinity in spring tide increases with exceeding 1. 0 in the area near the mouth of the South passage and on the southeast side of the project;the salinity decreased with greater than 0. 5 at the upper and middle reaches of the South Passage,in the North Passage and in the Hengsha eastern beach due to the decreases of the tidal prism,current spilling over the dikes and landward salt flux. The salinity in neap tide decreased in the whole South passage with greater than 1. 5 because of the decreases of the flood current and salt flux at the mouth caused by the weaker tide. The net water diversion ratios were reduced slightly in spring and neap tide in the North Channel,increased 1. 57% in spring tide and 1. 50% in neap tide in the South Passage because the salinity front in the South Passage was weakened after the reclamation project,which weakened the block effect of the river water into the South Channel.