地下截渗墙影响下的咸水入侵规律研究
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摘要
修建地下截渗墙是防治海水入侵的有效方法之一。本文利用OpenGeoSys软件建立二维饱和多孔介质变密度地下水流的溶质运移模型,对地下截渗墙影响下的咸水入侵问题进行了数值模拟。数值模拟结果和实验室物理模型实验的结果吻合较好,表明所建数值模型能够准确地描述自然条件下和有截渗墙存在情况下的浓度场,并跟踪咸淡水分界面随着时间的运移情况。接着,利用验证后的数值模型,分析了咸、淡水侧水位差、截渗墙高度及截渗墙位置对咸水入侵规律的影响,得出结论:(1)淡水侧水位越小,咸水楔向前入侵的距离越大,导致横向距离同一位置咸水楔越厚,上覆淡水层越薄;安装截渗墙后,淡水侧水位越小,截渗墙右侧残留咸水体完全消散所用的时间越长。这表明要从根本上解决咸水入侵问题,必须提高滨海地区向陆一侧的地下淡水水位。(2)对于不同的截渗墙高度,残留咸水的消散特性也不同。要排净残留咸水,截渗墙有最小高度要求,且相对较低的截渗墙更有利于残留咸水被冲散。(3)在截渗墙高度大于最小高度要求的情况下,截渗墙离咸水侧距离越远,残留咸水排净所需的时间越少。本文的研究不仅揭示了地下截渗墙影响下的咸水入侵规律,而且对地下截渗墙的结构设计和规划布置、以及有效防治咸水入侵提供了理论依据。
The installation ofsubsurface cutoff wall is one of the effective strategies proposed to controlseawater intrusion on coastal groundwater systems.In this work,a 2 Dsaturated porous medium,densitydependent flow andsolute transport model is developed based on the scientific modelling package OpenGeoSys to investigate the effect of subsurface cutoff wall on saltwater intrusion.The numerical results agree well with the results observed from the physical modelling experiment,and the migration of the saltwater intrusion wedgeis clearly represented before and after the installation of subsurface cutoff wall.Simulations are conducted to analyze the behavior ofsaltwater intrusion on different factorssuch as saltwaterfreshwater level difference,the height and the location of cutoff wall.The lower the freshwater-side level is,the longerdistance the saltwater wedge intrudes forward,which leads to the saltwater wedge from the same lateral distance becoming thicker and the overlying freshwater aquifers becoming thinner.After installation of the cutoff wall,numerical results indicate that a lower freshwater-sidelevel achieves a faster residual saltwater removal rate.Therefore,the underground freshwater level at the landward sides should be raised to fundamentally control saltwater intrusion.Residual saltwater would be flushed out completely when the height of cutoff wall exceeds the minimum height requirements and a shortercutoff wall achieved a faster residual saltwater removal rate thana higher cutoff wall.Moreover,the further cutoff wall is installed from seaward position,the shorter time the complete dissipation of residual saltwater takes.Theresearch will not only be helpful for understanding the mechanism of seawaterintrusion under the construction of subsurface cutoff wall,but also provide scientific and theoretical basis on properly designing of the cutoff wall structure,planning of its layout and effectively controlling seawater intrusion in coastal aquifers.
The installation ofsubsurface cutoff wall is one of the effective strategies proposed to controlseawater intrusion on coastal groundwater systems.In this work,a 2 Dsaturated porous medium,densitydependent flow andsolute transport model is developed based on the scientific modelling package OpenGeoSys to investigate the effect of subsurface cutoff wall on saltwater intrusion.The numerical results agree well with the results observed from the physical modelling experiment,and the migration of the saltwater intrusion wedgeis clearly represented before and after the installation of subsurface cutoff wall.Simulations are conducted to analyze the behavior ofsaltwater intrusion on different factorssuch as saltwaterfreshwater level difference,the height and the location of cutoff wall.The lower the freshwater-side level is,the longerdistance the saltwater wedge intrudes forward,which leads to the saltwater wedge from the same lateral distance becoming thicker and the overlying freshwater aquifers becoming thinner.After installation of the cutoff wall,numerical results indicate that a lower freshwater-sidelevel achieves a faster residual saltwater removal rate.Therefore,the underground freshwater level at the landward sides should be raised to fundamentally control saltwater intrusion.Residual saltwater would be flushed out completely when the height of cutoff wall exceeds the minimum height requirements and a shortercutoff wall achieved a faster residual saltwater removal rate thana higher cutoff wall.Moreover,the further cutoff wall is installed from seaward position,the shorter time the complete dissipation of residual saltwater takes.Theresearch will not only be helpful for understanding the mechanism of seawaterintrusion under the construction of subsurface cutoff wall,but also provide scientific and theoretical basis on properly designing of the cutoff wall structure,planning of its layout and effectively controlling seawater intrusion in coastal aquifers.
引文
[1]郭占荣,黄奕普.海水入侵问题研究综述[J].水文,2003,23(3):10-15.GUO Zhan-rong,HUANG Yi-pu.Comprehensive study on seawater intrusion[J].Hydrology,2003,23(3):10-15.
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[6]郭鑫,赵全升,张建伟,等.大沽河下游地区地下水及地表植被对截渗墙的响应[J].干旱区资源与环境,2014,28(1):142-147.GUO Xin,ZHAO Quansheng,ZHANG Jianwei,et al.Response of groundwater and vegetation to the cutoff wall in the lower reachesof Dagu River[J].Journal of Arid Land Resources and Environment,2014,28(1):142-147.
[7]Onder H,Yilmaz M.Underground Dams-A tool of sustainable development and management of groundwater resources[J].European Water,2005,11/12:35-45
[8]Roger L Jr,Kazuro M,Kei N.Laboratory-scale saltwater behavior due to subsurface cutoff wall[J].Journal of Hydrology,2009,377:227-236.
[9]贺国平,邵景力,崔亚莉.黄河下游截渗墙对地下水影响的数学模型与评价[J].人民黄河,2003,25(1):22-23.He Guoping,Shao Jingli,Cui Yali.Mathematical model and evaluation of the influence of cutoff wall on groundwater in the lower reaches of the Yellow River[J].Yellow River,2003,25(1):22-23.
[10]韩志勇.大沽河下游地下咸水恢复方案的优化研究[D].青岛:中国海洋大学,2004.Han Zhiyong.Research of the Optimization on Restoration Schemesof Saline Groundwater at the Low Reach of DaguRiver[D].Qingdao:Ocean University of China,2004.
[11]袁益让,梁栋,芮洪兴.三维海水入侵及防治工程的渗流力学数值模拟及分析[J].中国科学,2009,39(2):222-236.Yuan Yirang,Liang Dong,Rui Hongxing.Numerical simulation and analysis of 3Dseepage mechanics in seawater intrusion prevention project[J].Science in China,2009,39(2):222-236.
[2]McAnally W H,Pritchard D W.Salinity control in Mississippi River under drought flows[J].Journal of Waterway,Port,Coastal,and Ocean Engineering,1997,123(1):34-40.
[3]Mundzer Hasan Basri.Two New Methods for Optimal Design of Subsurface Barrier to Control Seawater Intrusion[D].Winnipeg,Manitoba:University of Manitoba,2001.
[4]Ishida S,Tsuchihara T,Yoshimoto S,et al.Sustainable use of groundwater with underground dams[J].Japan Agricultural Research Quarterly,2011,45(1):51-61.
[5]林少伟,徐梁,赵鸿旭.龙口市防治海水入侵措施与对策[J].山东水利,2010,8:58-59.LIN Shao-wei,XuLiang,Zhao Hong-xu.Counter measures for the prevention of seawater intrusion in Longkou City[J].Shandong Water Resources,2010,8:58-59.
[6]郭鑫,赵全升,张建伟,等.大沽河下游地区地下水及地表植被对截渗墙的响应[J].干旱区资源与环境,2014,28(1):142-147.GUO Xin,ZHAO Quansheng,ZHANG Jianwei,et al.Response of groundwater and vegetation to the cutoff wall in the lower reachesof Dagu River[J].Journal of Arid Land Resources and Environment,2014,28(1):142-147.
[7]Onder H,Yilmaz M.Underground Dams-A tool of sustainable development and management of groundwater resources[J].European Water,2005,11/12:35-45
[8]Roger L Jr,Kazuro M,Kei N.Laboratory-scale saltwater behavior due to subsurface cutoff wall[J].Journal of Hydrology,2009,377:227-236.
[9]贺国平,邵景力,崔亚莉.黄河下游截渗墙对地下水影响的数学模型与评价[J].人民黄河,2003,25(1):22-23.He Guoping,Shao Jingli,Cui Yali.Mathematical model and evaluation of the influence of cutoff wall on groundwater in the lower reaches of the Yellow River[J].Yellow River,2003,25(1):22-23.
[10]韩志勇.大沽河下游地下咸水恢复方案的优化研究[D].青岛:中国海洋大学,2004.Han Zhiyong.Research of the Optimization on Restoration Schemesof Saline Groundwater at the Low Reach of DaguRiver[D].Qingdao:Ocean University of China,2004.
[11]袁益让,梁栋,芮洪兴.三维海水入侵及防治工程的渗流力学数值模拟及分析[J].中国科学,2009,39(2):222-236.Yuan Yirang,Liang Dong,Rui Hongxing.Numerical simulation and analysis of 3Dseepage mechanics in seawater intrusion prevention project[J].Science in China,2009,39(2):222-236.