水文气象条件变化对长江口盐水入侵影响研究

Influence of hydrometeorological variation on saltwater intrusion in Changjiang River Estuary

分析论述了长江口盐水入侵的研究现状、影响因素、入侵变化规律及时空分布特征,将三维数值模式EFDC应用于长江口及其邻近海域,对长江口、杭州湾及邻近海区的水动力特性及盐度进行数值计算,研究结果表明,北港的盐水入侵强度高于北槽,北槽的盐水入侵强度又高于南槽,并且北港淡水往外冲淡的强度也高于南、北槽。在模拟长江口水动力特征和盐度分布的基础上,通过15组数值试验计算研究了枯季三峡水库调节量和南水北调最大调水量等不利状况下,径流量、海平面上升、风速、风向等水文气象环境因子变化单独和综合作用对长江口盐水入侵趋势和影响距离等的不同影响。结果表明,枯季不利状况径流量对长江口盐水入侵影响显著,径流量减少,盐水入侵加重;南水北调工程枯季流量、南水北调和三峡工程联合调节后的枯季流量时,南支水体盐度均超过0.5。径流量所引起的影响变化并不等效,径流量越小,影响程度越大,且对表层作用大于底层,南水北调工程枯季流量较多年枯季平均流量减小4 310 m3/s,表层1.5等盐度线影响距离则增加21.9 km,底层增加25.6 km。海平面上升后,盐水入侵加剧,上升越多,作用越显著,表、底层影响距离变化接近,海平面上升0.3 m,表层1.5等盐度线最大影响距离较海平面不上升的正常情况增加了约4.0 km;海平面上升0.6 m,影响距离则增加了7.6 km。不同的风速、风向对长江口各个汊道的盐水入侵有着不同的影响,10 m/s的北风较10 m/s的东北风影响距离增加了5.5 km,较5 m/s的东北风和北风增加了近24.0 km。综合径流量、海平面上升和风共同作用的最不利状况对盐水入侵影响最大,2等盐度线已接近南北支分叉口。

Current situation of the study on the intrusion of saltwater and its influence factors,variation rules and temporal-spatial distribution in Changjiang River Estuary were discussed.3D numerical model（EFDC） was applied to the numerical calculation of hydrodynamic features and salinity of Changjiang River Estuary,Hangzhou Bay and their adjacent waters.The results were calibrated and verified with observed data.The results of the study show that the saltwater intrusion strength of the North Channel is higher than the North Passage,and the North Passage is higher than the South Passage;the outward diluting strength of the freshwater of the North Channel is also higher than the North and South Passages.Based on the simulation of the hydrodynamic features and salinity and through 15 groups of numerical experiments,the individual and integrated impacts of runoff,sea level rise,wind velocity and direction,different regulated flows of the Three Gorge Project and South-to-North Water Diversion Project（SNWDP） on the trend and effecting distance of the seawater intrusion were calculated,which shows that（1） the runoff change in dry season has a significant impact on the saltwater intrusion in Changjiang River Estuary,the less the runoff is,the stronger the saltwater intrusion becomes;（2） for the dry season flow of the SNWDP,and the dry season flow after the combined regulation of SNWDP and the Three-Gorge Project,the salinity in the South Branch is more than 0.5,and when the runoff reduced by 4 310 m3/s,the saltwater intrusion distance at the surface and bottom increased by 21.9 km and 25.6 km respectively,the effect on the surface is stronger than that on the bottom;（3） when the sea-level rises,the saltwater intrusion becomes stronger,and 0.3 m and 0.6 m of sea-level rise results in an increase of 4.0 km and 7.6 km of the saltwater intrusion distance at 1.5 salinity contours;（4） different wind velocity and direction have different influences on the saltwater intrusion,the intrusion distance resulted from 10 m/s north wind is 5.5 km and 24.0 km longer than that resulted from 10 m/s northeast wind and 5 m/s north wind or northeast wind separately.