A method for investigating regional seawater intrusion

Abstract

This invention discloses a method for regional seawater intrusion survey, which includes the following steps: S1: Setting up several research points in the study area and collecting shallow groundwater cl ‑ Concentration, and plot cl ‑ Concentration contour maps were used to identify the target area for seawater intrusion in the study area; S2: Subsurface physical surveys were conducted within the seawater intrusion target area to provide a target area for geological drilling; S3: Hydrogeological drilling was conducted within the geological drilling target area based on the development of fault zones to obtain the spatial extension of geological fault zones; S4: Combining the spatial extension of fault zones, the pathways of seawater intrusion and their correlation with fault structures were obtained, thus determining the scope and extent of seawater intrusion. Based on clarifying the current status of seawater intrusion in the study area, this invention explored the intrusion mechanism of seawater in the underground bedrock area, and combined drilling, pumping experiments, and other methods to provide a basis for studying the development trend of seawater intrusion.

Description

Technical Field

[0001] This invention relates to the field of research technology on seawater intrusion in coastal areas, specifically to a method for regional seawater intrusion survey. Background Technology

[0002] Seawater intrusion is a process and phenomenon of water bodies entering a coastal aquifer due to changes in groundwater dynamics, causing seawater to migrate towards a freshwater aquifer on land. In many coastal areas surrounded by sea on three sides, the hydrodynamic balance between seawater and freshwater groundwater has been disrupted due to factors such as over-extraction of groundwater, leading to seawater intrusion.

[0003] In recent years, multi-disciplinary and multi-faceted investigations and research have been conducted on the issue of seawater intrusion, and research on seawater intrusion phenomena in coastal surface waters and Quaternary-covered coastal areas has become increasingly mature. Previous field surveys have revealed that seawater intrusion also exists in bedrock areas. In coastal bedrock outcrops, some collective and individual deep wells for drinking water have been intruded by seawater, resulting in deteriorated water quality or even abandonment. Currently, no relevant research has been conducted in this area, and the pathways and mechanisms of seawater intrusion remain unclear.

[0004] To ascertain the current status of seawater intrusion, study the relationship between seawater intrusion and bedrock fissures in bedrock areas, understand its intrusion forms, types, and mechanisms, and provide a reference for the next step of monitoring, research, and prevention of seawater intrusion in bedrock areas, it is urgent to propose a regional seawater intrusion survey method. Summary of the Invention

[0005] In view of the above-mentioned shortcomings of the prior art, the present invention provides a regional seawater intrusion survey method for understanding the variation law of seawater intrusion in bedrock fissures, providing a basis for in-depth research on seawater intrusion in island bedrock areas and the development and utilization of groundwater.

[0006] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0007] A method for investigating regional seawater intrusion is provided, comprising the following steps:

[0008] S1: Several research sites will be set up within the study area to collect shallow groundwater samples. Concentration, and plot Concentration contour maps were used to identify the target area of ​​Shanghai water intrusion in the study region.

[0009] S2: Conduct underground physical surveys within the seawater intrusion target area to provide target areas for geological drilling;

[0010] S3: Within the geological drilling target area, conduct hydrogeological drilling based on the development of the fault zone to obtain the spatial extension of the geological fault zone.

[0011] S4: By combining the spatial extension of the fault zone, we can obtain the pathways of seawater intrusion and its correlation with the fault structure, and thus the extent and degree of seawater intrusion.

[0012] Further, step S1 includes the following steps:

[0013] S11: Using all the tap water wells in the study area as research points, conduct pumping tests on the wells. During the pumping process, test the water quality of the pumped water at set intervals to obtain the pumped water quality data. concentration;

[0014] S12: Obtain the last measurement before the well water is completely pumped out. concentration a ,Will a Compared with the concentration threshold, if a If the concentration exceeds the concentration limit, it is determined that seawater intrusion has occurred in the area where the tap water well is located; otherwise, seawater intrusion has not occurred in the area where the tap water well is located.

[0015] S13: Using a water well experiencing seawater intrusion as the target area center, several drilling points are set up within a designated area of ​​the target area center. Boreholes are drilled at the drilling points to test the groundwater within the boreholes. concentration;

[0016] S14: Calculate the groundwater levels at all drilling sites. Concentration, and plotted. Concentration contour maps will The area on the concentration contour map that exceeds the concentration limit is taken as the study area, the target area for Shanghai water intrusion.

[0017] Further, step S2 includes the following steps:

[0018] S21: Select several underground physical survey points in the seawater intrusion target area, drill holes at each underground physical survey point, and perform full-hole coring.

[0019] S22: During core drilling, record the borehole depth at the locations of the initial water encounter and abrupt water volume changes. Based on the stratigraphic lithology and aquifer location of the extracted core samples, analyze the aquifer strata. If the strata... If the concentration exceeds the standard value, the rock strata at that location are determined to be eroded by seawater; otherwise, the rock strata at that location are determined not to be eroded by seawater.

[0020] S23: At the same time, based on the lithology of each layer of the core, the fracture layers on the core are obtained, and the underground physical survey points with fracture layers and seawater erosion are connected in series as geological drilling target areas.

[0021] Further, step S3 includes the following steps:

[0022] S31: All boreholes and water wells within the geological drilling target area will be flushed. After flushing and stabilization of the water level, the stable resistivity of the well or borehole under clear water conditions will be measured, along with the measured resistivity of the water level under clear water conditions. concentration;

[0023] S32: Select several points at the bottom of the well or borehole to detect the resistivity, and compare the resistivity with the stable resistivity. If the resistivity is less than the stable resistivity, it is determined that salt water is emerging at that point; otherwise, no salt water is emerging at that point.

[0024] S33: Drill down at the location where salt water is emerging, and inject the prepared salt water into the drilling location all at once. The clean water in the well is squeezed out and emerges to the surface. Test the resistance at each location in the well, connect the locations with high resistance in the well, and obtain the direction of the underground salt water emerging.

[0025] S34: The direction in which underground saline water emerges is taken as the direction of the extension of the underground geological fault zone.

[0026] Further, step S4 includes:

[0027] S41: Collect samples from wells or boreholes along the extension direction of geological fault zones. Concentration, relative to the distance of the well or borehole from the seawater in the direction of extension: Establishment The formula for the correlation curve between concentration and distance in seawater is: ln(Y) = -a*X + b, where Y is... Concentration, X is distance, and a and b are both relationship coefficients;

[0028] S42: Based on the correlation curve formula and the collected water samples from tap water wells and boreholes... Concentration was used to draw a map of seawater intrusion distribution in the study area, thus obtaining the extent and degree of seawater intrusion.

[0029] The beneficial effects of this invention are as follows: Based on clarifying the current status of seawater intrusion in the study area, this invention explores the intrusion mechanism of seawater in the underground bedrock area. Through comprehensive methods such as drilling and pumping experiments, the seawater intrusion pattern in the underground bedrock area of ​​the study area has been basically clarified, and the shape and direction of seawater intrusion have been identified. This was achieved through high-frequency... Concentration test data were used to explore the effects of mining conditions. The characteristics of concentration changes provide a basis for studying the development trend of seawater intrusion. Attached Figure Description

[0030] Figure 1 This is a curve showing the relationship between chloride ion concentration and distance from the coastline. Detailed Implementation

[0031] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0032] The regional seawater intrusion investigation method in this plan includes the following steps:

[0033] S1: Several research sites will be set up within the study area to collect shallow groundwater samples. Concentration, and plot Concentration contour maps were used to obtain the target area for Shanghai water intrusion in the study area; Step S1 includes the following steps:

[0034] S11: Using all the tap water wells in the study area as research points, conduct pumping tests on the wells. During the pumping process, test the water quality of the pumped water at set intervals to obtain the pumped water quality data. concentration;

[0035] S12: Obtain the last measurement before the well water is completely pumped out. concentration a ,Will a Compared with the concentration threshold, if a If the concentration exceeds the concentration limit, it is determined that seawater intrusion has occurred in the area where the tap water well is located; otherwise, seawater intrusion has not occurred in the area where the tap water well is located.

[0036] S13: Using a water well experiencing seawater intrusion as the target area center, several drilling points are set up within a designated area of ​​the target area center. Boreholes are drilled at the drilling points to test the groundwater within the boreholes. concentration;

[0037] S14: Calculate the groundwater levels at all drilling sites. Concentration, and plotted. Concentration contour maps will Areas exceeding concentration thresholds on the concentration contour map are designated as target areas for Shanghai water intrusion within the study area. In this embodiment, the shallow groundwater within the study area... When the concentration does not reach the concentration limit of 150 mg / L, it indicates that there is no risk of seawater intrusion.

[0038] S2: Conduct underground physical surveys within the seawater intrusion target area to provide target areas for geological drilling; Step S2 includes the following steps:

[0039] S21: Select several underground physical survey points in the seawater intrusion target area, drill holes at each underground physical survey point, and perform full-hole coring.

[0040] S22: During core drilling, record the borehole depth at the locations of the initial water encounter and abrupt water volume changes. Based on the stratigraphic lithology and aquifer location of the extracted core samples, analyze the aquifer strata. If the strata... If the concentration exceeds the standard value, the rock strata at that location are determined to be eroded by seawater; otherwise, the rock strata at that location are determined not to be eroded by seawater.

[0041] S23: At the same time, based on the lithology of each layer of the core, the fracture layers on the core are obtained, and the underground physical survey points with fracture layers and seawater erosion are connected in series as geological drilling target areas.

[0042] S3: Within the geological drilling target area, conduct hydrogeological drilling based on the development of the fault zone to obtain information on the spatial extension of the geological fault zone; Step S3 includes the following steps:

[0043] S31: All boreholes and water wells within the geological drilling target area will be flushed. After flushing and stabilization of the water level, the stable resistivity of the well or borehole under clear water conditions will be measured, along with the measured resistivity of the water level under clear water conditions. concentration;

[0044] S32: Select several points at the bottom of the well or borehole to detect the resistivity, and compare the resistivity with the stable resistivity. If the resistivity is less than the stable resistivity, it is determined that salt water is emerging at that point; otherwise, no salt water is emerging at that point.

[0045] S33: Drill down at the location where salt water is emerging, and inject the prepared salt water into the drilling location all at once. The clean water in the well is squeezed out and emerges to the surface. Test the resistance at each location in the well, connect the locations with high resistance in the well, and obtain the direction of the underground salt water emerging.

[0046] S34: The direction in which underground saline water emerges is taken as the direction of the extension of the underground geological fault zone.

[0047] S4: By combining the spatial extension of the fault zone, the pathways of seawater intrusion and their correlation with the fault structure are obtained, thus determining the extent and degree of seawater intrusion. Step S4 includes:

[0048] S41: Collect samples from wells or boreholes along the extension direction of geological fault zones. Concentration, relative to the distance of the well or borehole from the seawater in the direction of extension: Establishment The formula for the correlation curve between concentration and distance in seawater is: ln(Y) = -a*X + b, where Y is... Concentration, X is distance, and a and b are both relationship coefficients;

[0049] like Figure 1 As shown in the figure, this embodiment plots the chloride ion concentration and its distance from seawater, constructing the correlation curve formula: ln(Y) = -0.004*X + 9.76. The degree to which seawater intrudes into groundwater through fault zones is related to distance; the closer to the seawater, the higher the proportion of seawater mixed in the bedrock fissure water. The higher the concentration, the lower the proportion of seawater mixed in; conversely, the farther the distance, the lower the proportion of seawater mixed in. The lower the concentration, the better.

[0050] S42: Based on the correlation curve formula and the collected water samples from tap water wells and boreholes... Concentration was used to draw a map of seawater intrusion distribution in the study area, thus obtaining the extent and degree of seawater intrusion.

[0051] Based on the correlation curve formula, this embodiment estimates that the seawater intrusion distance along the fault zone in the study area is approximately 1059.63 m, the intrusion depth within the fault zone is approximately -25 m or deeper, the width of the intrusion zone is 200-300 m, and the intrusion area is approximately 0.2133 km². 2 The extent of seawater intrusion in this area is clearly controlled by the fault zone, and its intrusion pattern appears finger-like on the plane.

[0052] Based on an investigation of the current state of seawater intrusion in the study area, this invention explores the intrusion mechanism of seawater in the underground bedrock area. Through a combination of drilling and pumping experiments, the intrusion pattern of seawater in the underground bedrock area within the study area has been basically clarified, and the shape and direction of the seawater intrusion have been identified. This was achieved through high-frequency... Concentration test data were used to explore the effects of mining conditions. The characteristics of concentration changes provide a basis for studying the development trend of seawater intrusion.

Claims

1. A method for investigating regional seawater intrusion, characterized by, The method comprises the following steps: S1: Set up several research points in the study area, collect the concentration of shallow groundwater , and draw the concentration contour map to obtain the target area of seawater intrusion in the study area . S2: performing underground physical exploration in the seawater intrusion target area to provide a target area for geological drilling; S3: performing hydrogeological drilling in the geological drilling target area according to the development of the fault zone to obtain the spatial extension of the geological fault zone; S4: obtaining the seawater intrusion path and the correlation with the fault structure in combination with the spatial extension of the fault zone, obtaining the seawater intrusion range and degree; The step S4 comprises: S41: collecting the concentration of the seawater in the well or hole in the extension direction of the geological fault zone The distance between the concentration and the distance of the well or hole from the seawater in the extension direction: establish The concentration-distance-from-seawater correlation curve formula: ln(Y)=-a*X+b, wherein Y is The concentration, X is the distance, and a and b are both correlation coefficients; S42: According to the correlation curve formula and the concentration of water in the tap water well and the borehole collected Draw the seawater intrusion distribution map in the study area, and obtain the range and degree of seawater intrusion.

2. The method of investigating regional saltwater intrusion according to claim 1, wherein, The step S1 comprises the following steps: S11: All tap water wells in the study area are taken as study points, and pumping tests are conducted on the tap water wells. The water quality of the pumped water is detected every certain time interval during the pumping process, and the water quality of the pumped water is obtained concentration; S12: Obtain the last measurement before the well water is completely pumped out. concentration a ,Will a Compared with the concentration threshold, if a If the concentration exceeds the concentration limit, it is determined that seawater intrusion has occurred in the area where the tap water well is located; otherwise, seawater intrusion has not occurred in the area where the tap water well is located. S13: taking a tap water well with seawater intrusion as a target center, setting several drilling points in a set area range of the target center, drilling at the drilling points, and detecting underground water in the drill holes concentration; S14: Statistics of groundwater at all drilling points concentrations, and draw concentration contour map, and areas exceeding the concentration limit value on the concentration contour map as the target area of groundwater intrusion.

3. The method of investigating regional saltwater intrusion according to claim 1, wherein, The step S2 comprises the following steps: S21: selecting a plurality of underground physical exploration points on the seawater intrusion target area, drilling at each underground physical exploration point, and performing full-hole coring on the drilled hole; S22: In the process of drilling coring, the hole depth of the first water section and the water quantity mutation section position are recorded, the rock stratum of the aquifer is detected according to the stratum lithology and the aquifer position of the extracted core, if the concentration of the rock stratum exceeds the standard value, it is determined that the rock stratum at the position is eroded by seawater, otherwise, it is determined that the rock stratum at the position is not eroded by seawater; concentration exceeds the standard value, it is determined that the rock stratum at the position is eroded by seawater, otherwise, it is determined that the rock stratum at the position is not eroded by seawater; S23: simultaneously, obtaining the fault layer on the core according to the lithology of each layer of the core, and connecting the underground physical exploration points with the fault layer and subjected to seawater erosion as the geological drilling target area.

4. The method of investigating regional saltwater intrusion according to claim 1, wherein, The step S3 comprises the following steps: S31: all the drill holes and water wells in the geological drilling target area are washed, after the water height in the well is stable after the washing is completed, the stable resistivity in the well or hole under the clear water state is detected, and the stable resistivity in the well or hole under the clear water state is detected concentration; S32: selecting a plurality of points at the bottom of the well or hole to detect the resistivity, and comparing the resistivity with the stable resistivity, if the resistivity < stable resistivity, it is determined that the point position has emerged salt water, otherwise, the point position has not emerged salt water; S33: drilling at the position where salt water emerges, and injecting prepared salt water into the drilling position at one time, the fresh water in the well is squeezed out and emerges to the ground, the resistances of various positions in the well are tested, the positions with high resistance in the well are connected, and the direction of underground salt water emergence is obtained; S34: taking the direction of underground salt water emergence as the extension direction of the underground geological fault zone.

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