三峡水库应急补水对2022年洪季长江口盐水入侵的影响

Impact of Emergent Water Supply of the Three Gorges Reservoir onSaltwater Intrusion in the Changjiang River Estuary in 2022

2022年汛期长江流域发生了历史罕见的流域性干旱,大通站9—10月份流量在11000 m 3/s上下浮动。9月份开始,叠加台风的影响,长江口遭遇了严重的盐水入侵事件,威胁上海市供水安全。结合实测流量、风速和盐度数据分析,认为此次盐水入侵由低流量和台风导致;基于此,采用三维河口海岸数值模型定量分析三峡水库应急补水的压咸效果。结果表明,应急补水削弱了长江口的盐水入侵,减小了咸潮上溯距离,南支—北港纵断面0.45 psu等盐度线下移了17 km,降低了水库取水口盐度,为青草沙水库争取了约6 h的取水窗口。10月份2次寒潮在一定程度上削弱了此次补水效果,为确保补水效果需加强河口地区水文、潮汐及气象综合监测能力,以保障上海市淡水利用安全。

During the flood season of 2022,the Changjiang River Basin experienced an unprecedented basin-wide drought.From September to October,the runoff at Datong Station fluctuated around 11,000 m 3/s.Since September,the Changjiang River Estuary has faced severe saltwater intrusion due to typhoons,jeopardizing the water supply security of Shanghai.Based on analysis of measured runoff,wind speed,and salinity data,we conclude that low runoff combined with typhoons triggered the saltwater intrusion.We employed a three-dimensional estuary and coastal numerical model to quantitatively assess the impact of emergent water supply from cascading reservoirs.The emergent water supply mitigated saltwater intrusion in the Changjiang River Estuary,reducing the upward distance of saline water and shifting the 0.45 psu isohaline towards downstream by 17 km in the South Branch-North Channel section.This action reduced the salinity of reservoir water intake and extended the water intake window for the Qingcaosha Reservoir by approximately 6 hours.However,two cold fronts in October weakened the effectiveness of the water supply to some extent.To enhance the reliability of the water supply,it is crucial to strengthen comprehensive monitoring of hydrology,tides,and meteorology in the estuarine area,thereby ensuring the safety of freshwater utilization in Shanghai.