长江河口北支新村沙围垦工程对盐水入侵的影响

Impact of the reclamation project of Xincunsha on the saltwater intrusion in the North Branch of the Changjiang Estuary

长江河口北支新村沙围垦和南水道封堵工程于2012年实施，人为改变了北支河势．本文采用长期应用、改进和验证的长江河口三维盐水入侵数值模式，考虑1月和2月平均径流量和风况，计算和分析北支新村沙围垦工程对北支盐水倒灌以及南支青草沙水库、陈行水库和东风西沙水库取水的影响．在北支新村沙下游，围垦工程导致盐水入侵加强，盐度上升0．05～0．10；在新村沙上游，盐水人侵减弱，盐度下降0．05～1．0．工程导致在大潮后中潮、小潮、小潮后中潮、大潮期间北支上段断面平均倒灌盐通量分别下降百分比分别为7．52％、16．48％、10．17％、6．94％．北支倒灌的减弱，导致南支盐度低于0．45的淡水面积增大．大潮后中潮、小潮、小潮后中潮、大潮期间表层平均盐度在东风西沙水库取水口分别下降了4．52％、10．23％、9．15％、5．81％，连续不宜取水时间由10．1d减少到9．3d；陈行水库取水口分别下降了10．59％、13．11％、32．89％、13．95％，连续不宜取水时间由5d减少到4．4d；青草沙水库取水口分别下降了10．50％、8．19％、9．17％、II．99％，连续不宜取水时间由6．2d减少到5．1d．北支新村沙围垦工程缩窄了过水断面，减弱了北支倒灌，有利于南支水源地淡水资源的利用．

The reclamation project of enclose Xincunsha and block its southern channel in the North Branch of the Changjiang Estuary was conducted in 2012, resulting in the river regime changed artificially. Considering the monthly mean river discharge and wind in January and Feb- ruary, the 3-D saltwater intrusion numerical model in the Changjiang estuary, which has been applied, improved and validated for long-term, was used to investigate the influences of the salt- water-spill-over （SSO） from the north branch into the South Branch and the water intakes of Qingcaosha, Chenhang and Dongfengxish reservoirs due to the project. The saltwater intrusionis enhanced and salinity increases 0.05-0.10 downstream Xincunsha, whereas is weakened and salinity decreases 0.05 ~ 1.0 upstream Xincunsha due to the project. The tidally averaged salt fluxes of SSO cross the section at upper reaches of the North Branch reduced 7.52%, 16.48% 10.17%, 6.49% during moderate tide following spring tide, neap tide, moderate tide following neap tide, spring tide after the project, respectively. The reduce of the SSO induces an increase of freshwater area in the South Branch. The tidally averaged surface salinity at the water intakes of reservoir during moderate tide following spring tide, neap tide, moderate tide following neap tide, spring tide is reduced by 4. 52%, 10. 23%, 9. 15%, 5. 81% at Dongfengxisha, by 10.59%, 13. 11%, 32. 89%, 13. 95% at Chenhang, and by 10. 50%, 8. 19%, 9. 17%, 11.99% at Qingchaosha, respectively. Correspondingly, the longest continuous unsuitable days for water intake decrease from 10.1 to 9.3 days at Dongfengxisha, from 5 to 4.4 days at Chen- hang, and from 6.2 to 5.1days at Qingchaosha. The reclamation project of Xineunsha narrowed water flow cross section, and weakened the SSO, which is favor of the utilization of freshwater in the South Branch.