Comprehensive Study Of Seawater Invasion Monitoring Based On High Density

Coastal area,as an interactive area between land freshwater and ocean saline water,is an indispensable part of the global land-ocean water cycle.The shortage of freshwater resources and water environmental pollution are the main factors that restrict the development of coastal countries or regions.At the same time,they pose a serious threat to the safety of groundwater.It is a simple and efficient method to study seawater intrusion by high density resistivity method,which has theoretical and practical significance.Comparing the exploration results of different electrode arrangement is helpful for inversion analysis of field survey data.Using the forward function of EarthImager 2D software,the resolution responses of different electrical devices to horizontal and vertical anomalies,the number of electrodes and the distance between electrodes were compared.Some conclusions are drawn as follows: for Winner and Schlumberger devices,if the horizontal resistance anomaly is arranged adjacent to each other and the distance between them is less than 0.5 times or less than the horizontal size of the anomaly,the forward image of the anomaly body is connected as a whole;the response of the dipole-dipole device to the anomaly body in the vertical direction is more sensitive,and the vertical distribution of multiple high resistance anomaly bodies can be achieved.The position and size of the abnormal bodies in the shallow and middle layers are displayed,the forward images in the shallow layers are clear and the resolution in the middle layer is poor;the vertical resolution of Schlumberger device is higher than that of Winner device,but neither of them can respond to the abnormal bodies in the middle and deep layers;the number of electrodes increases and merges with the same abnormal bodies in the same distance between electrodes.On the contrary,with the increase of the number of electrodes,the bigger the deviation between the simulated value and the actual value,the lower the resolution.When the number of electrodes is unchanged,it is not the longer the distance between electrodes is,the higher the resolution is,the resolution will increase first and then decrease with the increase of the distance between electrodes,and the distance between electrodes is generally not changed in actual measurement.It should exceed 10 meters.It is a fast and effective method to determine the saltwater-freshwater interface of seawater intrusion by high-density resistivity method.This paper collects data from a typical profile in Longkou City.Through indoor inversion,it is determined that the saltwater-freshwater interface of Shanghai water intrusion in this profile is 2.55 km away from the coast.The location of saltwater boundary determined by high density resistivity method is more precise than that determined by hydrochemical analysis method,and it can also delineate the form of seawater intrusion.Tides have a certain driving effect on sea water intrusion.In this paper,small-scale high-density resistivity measurements have been carried out on the northern coast of Longkou City.It is found that the resistivity of strata increases in the transitional layers of flood and ebb tides.When the tide rises,the sea level rises,the sea water moves inland,and the brine in the aquifer is diluted,resulting in an increase in formation resistivity;when the tide falls,the sea water retreats and the salt content in the coastal aquifer decreases,resulting in an increase in formation resistivity.