| With the rapid economic development and frequent human activities in coastal areas,unreasonable exploitation has caused imbalance in groundwater exploitation and replenishment,seawater intrusion has intensified.Seawater intrusion pollutes groundwater,which makes the water consumption situation in coastal areas more tense and seriously restricts economic and social development.Therefore,it is of great significance to study how to effectively prevent seawater intrusion.The construction of underground dam is an important measure to prevent seawater intrusion,which can successfully cut off the hydraulic connection between salt and fresh water and curb seawater intrusion.In this study,based on the sandbox model and numerical simulation discusses the prevention and control effect of underground dam on seawater intrusion,optimizes the construction parameters of underground dam,and provides scientific basis for the construction of underground dam.The basic research conclusions are as follows:（1）Through building a sandbox model to simulate the migration characteristics of fresh water-salt water interface with and without underground dam,the influence of impermeability of underground dams on seawater intrusion rate under different head differences is revealed.The results show that the salt water head changes from small to large,fresh water-salt water interface changes from slow to steep,and the migration rate of seawater wedge area and toe angle increases.The prevention effects of underground dam permeability coefficients of 10-5cm/s,10-4 cm/s and 10-3 cm/s decrease in turn,and the permeability coefficient of 10-5 cm/s plays a basic prevention effect,and the driving effect of the head difference on seawater intrusion has weakened,however,the smaller the salt water head,the better the control effect when the permeability coefficient is 10-4 cm/s and 10-3 cm/s.（2）SEAWAT is used to optimize the construction parameters of totally enclosed,suspended and overflow underground dams,and the influence of horizontal construction distance,construction depth and permeability coefficient of underground dams on seawater intrusion and the influence of head difference on the prevention and control effect of underground dams are analyzed.The results show that the horizontal construction positions of three different types of underground dams should be as close as possible to the sea boundary.It is recommended to use semi-permeable materials combined with large head difference for fully enclosed underground dams.The proposed construction depth of suspended underground dam is about 80%of the aquifer thickness,and the seepage coefficient of underground dam is 10-6cm/s,which can meet the seepage control requirements.It is recommended to adopt the minimum effective dam height（slightly lower than the natural seawater wedge thickness）for the construction height of overflow underground dam,which can significantly reduce the seawater intrusion area.The smaller the permeability coefficient,the greater the horizontal construction distance and the greater the head difference,all make the minimum effective dam height smaller.（3）Based on the analysis of the construction parameters of the underground dam in the lower reaches of Huangshui River,the prevention and control effect and environmental efficiency of the underground dam are further improved.The results show that the prevention and control effect of the suspended underground dam in the seawater wedge is better than that of the overflow underground dam in this research area.When the horizontal construction distance is 450 m and the construction depth is 34 m,the regression coefficient is 44%. |
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