摘要
2007—2021年长江口重大圈围工程导致河道缩窄,显著改变局部地形。文章利用2007—2025年的实测地形和盐度资料,分析期间长江口河势变化和咸潮入侵格局变化,并利用数值模式揭示格局变化的成因。由于工程致使长江口北支下段南侧发生严重淤积,北支上端出现新生沙体,导致北支下段和上端2021年的河槽容积比2007年分别减小了33.33%和13.26%。2007年和2025年枯季盐度观测资料表明,北支咸潮入侵和北支盐水倒灌显著减弱,而北港咸潮入侵在气候态风时减弱、强北风时加剧。月平均径流量和风作用的数值模拟结果表明,从2007年至2021年,咸潮入侵在北支大幅减弱,在北港上段和中段大部分区域减弱,在南港、北槽和南槽显著加剧;北支盐水倒灌大幅减弱导致南支咸潮入侵减弱。2021年与2007年相比:北支2月大潮、小潮期间纳潮量分别减小了2.88×10^(8)m^(3)、1.98×10^(8)m^(3),进入南支的净水通量分别减小了423m^(3)·s^(-1)、369m^(3)·s^(-1),盐分倒灌的净盐通量分别减小了10.06kg·s^(-1)、1.10kg·s^(-1);北支上段净单宽盐通量变化也说明北支盐分向南支输运大幅减小;2007年北支盐水倒灌显著,2021年几乎消失。北港2月大潮、小潮期间纳潮量分别减小了1.92×10^(8)m^(3)、1.86×10^(8)m^(3),净水通量分别增加了857m^(3)·s^(-1)、1379m^(3)·s^(-1),分流比分别增加了12.79%、7.79%,向海的净盐通量减小了2.28kg·s^(-1)、5.42kg·s^(-1)。这些因素的变化解释了北港上段和中段大部分区域咸潮入侵减弱的原因。北港分流比的明显增加和相应的南港分流比减小说明了南港、北槽和南槽咸潮入侵加剧的成因。北港中段大潮期间小部分区域盐度上升是由横沙小港净盐通量从北槽向北港输运显著增加造成的。
Studying changes in estuarine saltwater intrusion patterns can deepen the understanding of its mechanism and help better ensure the safe use of freshwater resources.Based on measured topographic and salinity data,this paper analyzes changes in river regime and saltwater intrusion patterns in the Changjiang Estuary.A numerical model is used to reveal the causes of these pattern changes.From 2007 to 2021,major reclamation projects in the estuary led to channel narrowing and significant local topographic changes.Due to severe siltation on the south side of the lower North Branch and the emergence of a new sand body at its upper end,the channel volume decreased by 33.33%and 13.26%(with the negative sign denoting northward transport from the south),respectively.Salinity observations in the dry seasons of 2007 and 2025 indicate a significant weakening of saltwater intrusion and of the North Branch saltwater backflow into the South Branch.In the North Channel,saltwater intrusion weakened under prevailing climatic winds but intensified under strong northerly winds.Overall,the saltwater intrusion pattern in the Changjiang Estuary has changed.Numerical simulations,considering multi-year monthly mean river discharge and wind,show that from 2007 to 2021,saltwater intrusion weakened significantly in the North Branch,weakened in the upper and most middle reaches of the North Channel,but intensified significantly in the South Channel,North Passage,and South Passage.The saltwater backflow from the North Branch into the South Branch was greatly reduced,resulting in weakened saltwater intrusion in the South Branch,which is conducive to water intakes at source areas.In the North Branch,the tidal prism decreased by 2.88×10^(8)m^(3)and 1.98×10^(8)m^(3)during spring and neap tides in February,respectively.The net water flux into the South Branch decreased by 423 m^(3)·s^(-1)and 369 m^(3)·s^(-1),and the net salt flux into the South Branch decreased by 10.06 kg·s^(-1)and 1.10 kg·s^(-1).The variation of net unit-width salt flux in the upper North Branch also indicates a major reduction in salt transport to the South Branch.Significant North Branch backflow observed in 2007 had nearly disappeared by 2021.In the North Channel,during February spring and neap tides,the tidal prism decreased by 1.92×10^(8)m^(3)and 1.86×10^(8)m^(3),while the net water flux increased by 857 m^(3)·s^(-1)and 1379 m^(3)·s^(-1).The water diversion ratio increased by 12.79%and 7.79%,and the net seaward salt flux decreased by 2.28 kg·s^(-1)and 5.42 kg·s^(-1).These changes explain the weakening of saltwater intrusion in the upper and most middle reaches of the North Channel.The obvious increase in the North Channel’s water diversion ratio(corresponding to a decrease in the South Channel’s ratio)also accounts for the intensification of saltwater intrusion in the South Channel,North Passage,and South Passage.A localized salinity rise in a small part of the North Channel during spring tide is caused by a significant increase in the net salt flux from the North Passage into the North Channel.This paper reveals the hydrodynamic causes of the changing saltwater intrusion pattern in the Changjiang Estuary through changes in net water flux,net salt flux,tidal prism,and water diversion ratio.
作者
裘诚
朱宜平
朱建荣
QIU Cheng;ZHU Yiping;ZHU Jianrong(Shanghai Marine Monitoring and Forecasting Centre,Shanghai 200062,China;Shanghai Chengtou Raw Water Limited Company,Shanghai 200125,China;State Key Laboratory of Estuarine and Coastal Research(East China Normal University),Shanghai 200241,China)
出处
《热带海洋学报》
北大核心
2026年第2期42-58,共17页
Journal of Tropical Oceanography
基金
上海市科委重点项目(23DZ1203002)
国家自然科学基金项目(U2340225、42276174)。
关键词
河势变化
咸潮入侵
纳潮量
分流比
盐通量
river regime change
saltwater intrusion
tidal prism
water diversion ratio
net salt flux
