| Seawater intrusion is one of the major resource and environmental problems that exist all over the world.It has the important theoretical and practical value which mastering the laws and characteristics of seawater intrusion for the management and protection of groundwater resources in coastal areas and the improvement of the environment.The occurrence and development of seawater intrusion is affected by many factors.With systematic and long-term monitoring data support,it is possible to accurately monitor and objectively evaluate seawater intrusion in a region.The physical experiment of seawater intrusion can relatively reveal the law of seawater intrusion and migration under different hydrogeological conditions or hydrodynamic conditions.It has become an important method for studying seawater intrusion.On the basis of analyzed the domestic and foreign research status in the field of seawater intrusion,this paper took the no damage High-density Electrical Resistivity Tomography as the main data acquisition method through physical model,from the perspective of resistivity studied the law and characteristics of seawater intrusion on the meter scale.As shown below,it is the main research results and understanding.(1)When no seawater intrusion occurs,the aquifer resistivity on the obtained resistivity image is about 60-320 ?·m.Affected by the electrode layout and the aquifer density,the electrical structure has a low resistance value in the region above 0.1 m and a high resistance in the region below 0.1 m.Relative to the upper low-resistance region,the electrical structure of the lower high-resistance region is evenly distributed.(2)The invasion of seawater leads to an increase in the salinity of groundwater in the aquifer and a decrease in electrical resistivity.The resistivity is negatively correlated with salinity as a whole.When the salinity of 1000mg/L is used as the standard for the classification of seawater and fresh water,the area where the resistivity value is less than 24 ?·m is determined as the seawater intrusion zone.(3)When the seawater is the same as the fresh water head,the seawater gradually invades into the freshwater aquifer due to the control of difference density and concentration.On the resistivity image,there is a significant wedge-shaped low-resistance zone spatially continuous in the seawater intrusion zone relative to the resistivity characteristics before intrusion.The low resistance zone is caused by seawater intrusion and displacement of fresh water.The characteristics of the low-resistance zone in the resistivity image at different times clearly reflect the process and law of seawater intrusion.The 24?·m contour(face)better corresponds to the interface of seawater and fresh water.The two-dimensional and three-dimensional High-density Electrical Resistivity Tomography inferred the fresh water-seawater interface,which is basically concave and parabolic,gradually invading the freshwater area.The scope of seawater intrusion has gradually expanded and eventually stabilized.(4)Groundwater exploitation increases the extent of seawater intrusion.On the resistivity images of different dimensions,the morphology and migration of seawater wedges are consistent.Wherein,the pumping pressure is the first to focus on the middle and lower part of the aquifer,inducing the rising cone phenomenon in the middle of the sea wedge and the retreat at the bottom of the aquifer respectively.Then it focuses on the surface of the aquifer,increasing the extent of seawater intrusion on the surface.Finally,the interface of seawater and fresh water at different positions of the seawater wedge body has a vertical front and is stable at a horizontal distance of 0.1 m from the pumping well. |
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