Physical test system and method for researching non-point source pollution migration and restoration of coastal cascade underground reservoir

Abstract

The invention discloses a physical test system for researching non-point source pollution migration and restoration of a coastal cascade underground reservoir. The physical test system comprises an experimental tank system, a cascade underground reservoir simulation system, a pollution source distribution simulation system and an imaging analysis system, the experimental tank system comprises a central chamber as well as a seawater tank and a fresh water tank which are arranged at two ends of the central chamber, the seawater tank and the fresh water tank are respectively partitioned by a seawater partition plate and a fresh water partition plate capable of vertically extracting, the central chamber is filled with a porous medium, and an extraction and injection well hole connected with a peristaltic pump and a sampling hole for collecting a water sample are formed in the outer wall of the central chamber; the seawater tank and the fresh water tank are both connected with a seawater and fresh water input mechanism, and overflow devices are arranged in the seawater tank and the fresh water tank as tidal generators; and the imaging analysis system shoots images of the porous medium in the experimental tank at regular time and records seawater invasion and non-point source pollutant migration processes. According to the method, the comprehensive influence of the complex sea-land hydrodynamic boundary on pollutant migration in the cascade underground reservoir can be fully considered at the same time.

Description

Technical Field

[0001] The present invention relates to the technical field of soil and groundwater pollution control and treatment, and in particular to a physical test system and method for studying the migration and remediation of non-point source pollution in a stepped coastal underground reservoir. Background Art

[0002] An underground dam is usually a physical cut-off wall built at the bottom of an aquifer at the downstream position of a basin, allowing only groundwater to flow over its top, which has an actual effect on blocking seawater intrusion and land-source pollution. The construction of an underground dam can form a "salt-blocking and fresh-water storage" coastal underground reservoir, using the formation voids as a water storage space, with the dual benefits of regulating water resources and preventing seawater intrusion. While effectively blocking seawater intrusion, the coastal underground reservoir also brings obvious problems. A large amount of underground salt water remains on the upstream side of the underground dam, resulting in an excessive chloride content in the groundwater quality of the reservoir area and serious groundwater salinization problems, making it impossible to normally exploit the groundwater source. At the same time, a large number of land-source pollutants generated by coastal engineering, agricultural production and living will not only accumulate in the coastal aquifer, but also be discharged into the sea through groundwater, damaging the near-sea water environment and seriously restricting the sustainable development of the economy and society.

[0003] The residual underground salt water upstream of the underground reservoir will mix with pollutants, thereby affecting the pollutant migration and excretion characteristics. Clarifying the pollutant migration theory and mechanism of the coastal underground reservoir has strong practical guiding significance for the pollution control and remediation of the coastal aquifer. However, at present, the research on non-point source pollution migration in coastal underground reservoirs mainly focuses on numerical simulation work, lacking the analysis of systematic physical test models and methods. In particular, how to establish an effective physical test method system to deeply study the pollution remediation of stepped coastal underground reservoirs is an urgent problem to be solved at present. It is worth mentioning that a few devices only consider the influence of the tidal water level fluctuation on the single side of the ocean, lacking the consideration of the significant effect of the water level or flow fluctuation at the inland boundary on the non-point source pollution migration dynamics. Such devices cannot simulate stepped underground reservoirs, let alone depict the kinetic process of pollutant migration in underground reservoirs under complex inland hydrodynamic boundary conditions. Summary of the Invention

[0004] Object of the Invention: The first object of the present invention is to provide a physical test system for studying the migration and remediation of non-point source pollution in a stepped coastal underground reservoir; the second object is to provide a physical test method for studying the migration and remediation of non-point source pollution in a stepped coastal underground reservoir using the above system; on the one hand, the present invention can overcome the problems of scarce data, significant model uncertainty and high calculation cost faced by over-reliance on numerical simulation; on the other hand, it can fully consider the comprehensive influence of complex sea-land hydrodynamic boundaries on pollutant migration in stepped underground reservoirs, and further explore the remediation effect of groundwater extraction strategies on pollutants.

[0005] Technical solution: The physical test system for studying the migration and remediation of non-point source pollution in a coastal stepped groundwater reservoir provided by the present invention includes: an experimental tank system, a stepped groundwater reservoir simulation system, a pollution source spraying simulation system, and an imaging analysis system; The experimental tank system includes: A central chamber, a seawater tank and a fresh water tank provided at both ends thereof, which are separated by a seawater partition and a fresh water partition that can be drawn up and down respectively. The central chamber is filled with a porous medium for simulating a coastal aquifer, and pumping and injection well holes connected to a peristaltic pump are opened on the outer wall to simulate the extraction of groundwater pollutants for aquifer remediation and treatment, and sampling holes for collecting water samples are also opened; both the seawater tank and the fresh water tank are connected to input mechanisms for seawater and fresh water, and variable-height overflow devices are provided in both the seawater tank and the fresh water tank as tidal generators to make the water level in the tank fluctuate periodically; The stepped groundwater reservoir simulation system includes: A plurality of slots are arranged at intervals in the direction of seawater intrusion in the central chamber, and a size-matched and drawable underground dam is provided in each slot to simulate a stepped groundwater reservoir; The pollution source spraying simulation system includes: A non-point source pollution spreader for pollutants, which is horizontally movable on the top of the central chamber to simulate different pollution source positions; The imaging analysis system periodically takes images of the porous medium in the experimental tank to record the process of seawater intrusion and non-point source pollutant migration.

[0006] Further, a plurality of pumping and injection well holes and sampling holes are arranged at horizontal and vertical intervals on the outer wall of the central chamber, and based on the simulation of the migration dynamics of groundwater pollutants, the data is more persuasive.

[0007] Further, the overflow device is driven by an electric drive assembly, and the electric drive assembly includes: a parameter controller, a servo motor, a coupling, a linear slide table and a servo slider; the parameter controller is connected to control the telescopic movement of the servo motor, the telescopic end of the servo motor is connected to the servo slider through a coupling to control the movement of the servo slider on the linear slide table, and the overflow device is fixedly connected to the servo slider. The movement parameters of the overflow device can be adjusted adaptively according to experimental needs.

[0008] Further, a seawater bucket is provided at the bottom of the seawater tank, and the seawater bucket pumps seawater into the seawater tank through a water pump. A fresh water bucket is provided at the bottom of the fresh water tank, and the fresh water bucket pumps fresh water into the fresh water tank through a water pump; The side of the fresh water tank is provided with a plurality of uniformly distributed water outlet pipes connected to the fresh water tank input pipeline to simulate a constant flow rate. A stop clamp is provided on the water outlet pipe. When using the tidal generator to simulate the water level fluctuation in the fresh water tank, the flow rate input is closed through the stop clamp.

[0009] Further, the seawater is simulated by mixing salt and deionized water, and the fresh water is simulated by deionized water. The seawater and fresh water are distinguished by different colors to facilitate visualizing the distribution of the invading seawater.

[0010] Further, a sealing strip is provided on the inner side edge of the slot, and its two side surfaces are covered with water passing holes. When the underground dam is inserted, the sealing strip is squeezed with the periphery of the underground dam to form a seal. The underground dam includes an underground dam water blocking area in contact with the bottom of the slot in the lower section, an underground dam water passing area provided in the upper section of the underground dam water blocking area, and a handle provided on the underground dam water passing area. The underground dam water blocking area at different positions and different heights is set according to experimental needs to simulate a stepped underground dam, and the underground dam is located within the seawater intrusion range in the central chamber.

[0011] Further, the pollution source sprinkling simulation system further includes a solution tank and a peristaltic pump connected to the pollutant area source sprinkler. The solution tank is filled with a nitrate solution. A horizontal slideway is provided at the top of the central chamber. The bottom of the pollutant area source sprinkler is covered with holes and is arranged on the horizontal slideway and can move freely horizontally.

[0012] Further, the imaging analysis system includes a camera and a light-shielding cloth. The camera is installed on the front of the central chamber and periodically takes images of the porous medium in the experimental tank to record the process of seawater intrusion and surface source pollutant migration. The light-shielding cloth is placed behind or on the side of the experimental tank according to the site light conditions to prevent the tank plate from reflecting light.

[0013] Further, the seawater concentration inside the seawater tank is 35 g / L, and the density is 1025 g / L; the fresh water in the fresh water tank has a salinity of 0 g / L and a density of 1000 g / L.

[0014] Correspondingly, the present application also provides a physical test method for studying the migration and remediation of surface source pollution in a coastal stepped underground reservoir, which is realized based on the above physical test system for studying the migration and remediation of surface source pollution in a coastal stepped underground reservoir, and includes the following steps: S1. Prepare seawater, fresh water, pollutant solution and white quartz sand; S2. Layer by layer and evenly fill the saturated porous medium in the central chamber, and let it stand saturated after filling; S3. Insert the seawater partition board between the seawater tank and the central chamber to prevent seawater from infiltrating into the central chamber; S4. Adjust the water level heights in the seawater tank and the freshwater tank respectively, pull out the seawater partition and the freshwater partition, and simulate the intrusion of seawater starting from the bottom of the central chamber; after the seawater intrusion reaches a steady state, move the overflow device up and down periodically to simulate sinusoidal tides, and observe the formation of the upper saline plume and the change of the saltwater wedge; after the seawater intrusion reaches a quasi-steady state again, slowly insert a subsurface dam into the narrow slot, and at the same time, by opening the pollutant non-point source sprinkler, release the pre-prepared nitrate solution into the porous medium, and observe the migration process of groundwater nitrate pollutants; for the freshwater tank, if simulating periodic water level fluctuations, move the overflow device up and down periodically to simulate sinusoidal tides, and if simulating a fixed flow rate, inject fresh water into the freshwater tank at a fixed flow rate. S5. According to the dynamic migration of groundwater pollutants, connect the injection and extraction well holes at different positions in the central chamber through multiple peristaltic pumps, and extract the contaminated groundwater at a fixed flow rate to repair the aquifer, observe the change of the pollution concentration range, and the experiment can be terminated when the pollution range in the central chamber does not change within 1 minute. S6. Take photos of the experimental tank regularly with a camera, record the migration process of pollutants in the central chamber and the change of the pollution range, smooth the obtained experimental digital photos, convert the pixel values of the photos into optical density, and then obtain the concentration distribution according to the pre-calibrated relationship curve between solute concentration and optical density. S7. Collect water samples at different sampling holes in the central chamber, measure the content of nitrate nitrogen with an ultraviolet spectrophotometer, and compare it with the nitrate concentration after photo conversion to verify its effectiveness.

[0015] Advantageous effects: Compared with the prior art, the significant advantages of the present invention are as follows: 1. The present invention can fully and simultaneously consider the complex changes of hydrodynamic boundary conditions on both the land and sea sides, more comprehensively simulate the dynamic process of pollutant migration in a coastal stepped groundwater reservoir, overcome the limitations of single boundary condition simulation in the prior art, and can effectively analyze the influence of the coupling effect of tides and subsurface dams on the non-point source pollution transport in the stepped groundwater reservoir, which helps to systematically explore the non-point source pollution transport process in the coastal aquifer under the dual driving of natural elements and human activities.

[0016] 2. By considering different pollutant source distributions, different dynamic boundary conditions, and different remediation strategies, the invention system can quantify the temporal and spatial distribution, retention and diffusion effects of pollutants. The consideration of such comprehensive factors makes the research results more valuable for practical applications, and can capture the dynamic process of pollutant migration in the stepped reservoir under the combined action of multiple complex factors. In contrast, the prior art mainly relies on numerical simulation methods and lacks systematic physical experiment verification and multi-factor interaction analysis.

[0017] 3. This device can provide a more reliable and operable research method, especially providing more practical guidance in aspects such as the spatio-temporal changes of pollutant migration and the effects of remediation strategies. In addition, the concentration measurement of pollutants mainly uses indirect methods (such as photography, transformation, extraction) and is verified by direct methods such as sampling and chemical analysis, which not only ensures the accuracy of measurement but also improves work efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is the overall schematic diagram of the system of the present invention; Figure 2 is the side view of the slot of the present invention; Figure 3 is the cross-sectional view of the underground dam of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] The technical solutions of the present invention will be further described below with reference to the drawings and embodiments.

[0020] As Figures 1 - 3 shown, the physical test system for studying the non-point source pollution migration and remediation of the coastal stepped underground reservoir includes: an experimental tank system, a stepped underground reservoir simulation system, a pollution source sprinkling simulation system, and an imaging analysis system.

[0021] The experimental tank system includes: The central chamber 1, which is erected on multiple columns, and the seawater tank 2 and fresh water tank 3 provided at both ends thereof, and are respectively separated by a seawater partition plate 4 and a fresh water partition plate 5 that can be drawn up and down to prevent seawater from seeping into the porous medium before the experiment starts.

[0022] The central chamber 1 is filled with a porous medium 6 for simulating the coastal aquifer, and injection and extraction well holes 7 connected to a peristaltic pump are opened on the outer wall to simulate the extraction of groundwater pollutants for aquifer remediation, and sampling holes 8 for collecting water samples are also opened. The injection and extraction well holes 7 and sampling holes 8 are arranged horizontally and vertically at intervals on the outer wall of the central chamber 1.

[0023] The porous medium 6 is quartz sand, and the seawater partition plate 4 and the fresh water partition plate 5 are acrylic plates.

[0024] Both the seawater tank 2 and the fresh water tank 3 are connected to the input mechanisms of seawater and fresh water. Variable-height overflow devices 9 are provided in both the seawater tank 2 and the fresh water tank 3 as tidal generators to make the water level in the tank fluctuate periodically; an overflow pipe is provided in the fresh water tank 3 to adjust the water level height in the tank and provide a constant-head fresh water boundary.

[0025] The overflow device 9 is driven by an electric drive assembly, which includes: a parameter controller 10, a servo motor 11, a coupling 12, a linear slide 13 and a servo slider 14; the parameter controller 10 is connected to control the telescopic movement of the servo motor 11, and the telescopic end of the servo motor 11 is connected to the servo slider 14 through the coupling 12 to control the movement of the servo slider 14 on the linear slide 13, and the overflow device 9 is fixedly connected to the servo slider 14.

[0026] A seawater bucket 15 is provided at the bottom of the seawater tank 2, and the seawater bucket 15 pumps seawater into the seawater tank 2 through a water pump. A freshwater bucket 16 is provided at the bottom of the freshwater tank 3, and the freshwater bucket 16 pumps fresh water into the freshwater tank 3 through a water pump.

[0027] A multi-layer evenly distributed water outlet pipe 17 is provided on the side of the fresh water tank 3 and connected to the input pipe of the fresh water tank 3 to simulate a constant flow rate. A water stop clamp 18 is provided on the water outlet pipe 17. If a tidal generator is used to simulate water level fluctuations in the fresh water tank, the flow input is closed by the water stop clamp 18.

[0028] The seawater is simulated by a mixture of table salt and deionized water, and is dyed with red food dye to facilitate visualization of the distribution of invading seawater. The freshwater is simulated by deionized water, and the seawater concentration inside the seawater tank 2 is 35 g / L and the density is 1025 g / L. The freshwater in the freshwater tank 3 has a salinity of 0 g / L and a density of 1000 g / L.

[0029] The cascade groundwater reservoir simulation system includes: A plurality of slots 19 are arranged at intervals in the central chamber 1 in the direction of seawater intrusion, and each slot 19 is provided with an underground dam 20 of matching size and capable of being pumped up and down to simulate a cascade underground reservoir.

[0030] A sealing strip 19-1 is provided on the inner side of the narrow groove 19, and water holes 19-2 are distributed on both sides thereof. When the underground dam 20 is inserted, the sealing strip 19-1 is squeezed with the periphery of the underground dam 20 to form a seal. The underground dam 20 comprises an underground dam water retaining area 20-1 located in the lower section and in contact with the bottom of the groove, an underground dam water passing area 20-2 located in the upper section of the underground dam water retaining area 20-1, and a handle 20-3 located on the underground dam water passing area 20-2. According to experimental needs, underground dam water retaining areas 20-1 at different positions and heights are set to simulate the step underground dam 20. The underground dam 20 is located within the seawater intrusion range in the central chamber 1.

[0031] In this embodiment, according to experimental requirements, two underground dam retaining areas at different positions and heights of 15 cm and 13 cm are set to simulate a cascade underground dam. The underground dam is located within the seawater intrusion range of the central chamber.

[0032] The pollution source distribution simulation system includes: Pollutant surface source sprinkler 21, and a solution tank 22 and a peristaltic pump 23 connected thereto. The solution tank 22 is filled with nitrate solution. Brilliant blue (food additive) and sodium nitrate are added to deionized water to prepare a nitrate standard solution of 0.1 g / L for a tracer test. Other concentrations (such as 0.2 g / L, 0.3 g / L) can be obtained by dilution.

[0033] A horizontal slideway is provided at the top of the central chamber 1. The bottom of the pollutant surface source sprinkler 21 is covered with holes and is arranged on the horizontal slideway and can move freely horizontally to simulate different pollutant source positions, which are quantified by the distance from the freshwater boundary.

[0034] The imaging analysis system includes: A camera and a light-shielding cloth. The camera is mounted on the front of the central chamber 1 to periodically take images of the porous medium in the experimental tank to record the process of seawater intrusion and the migration of surface source pollutants. The light-shielding cloth is placed behind or on the side of the experimental tank according to the site light conditions to prevent the tank plate from reflecting light.

[0035] Using the above system to conduct a physical experiment on the migration and remediation of surface source pollution in a coastal stepped underground reservoir, including the following steps: a. In the physical experiment system of this embodiment, 4# quartz sand (d 50 = 0.60~1.25 mm) is filled in the central chamber as the porous medium. The material of the tank is tempered glass, with a length × height × width of 1.2 m × 0.45 m × 0.02 m. To simulate a two-dimensional unconfined aquifer cross-section, a smaller width is used for the sand tank to facilitate the observation of the distribution of land-source solutes in the cross-section. The height of the aquifer is 0.35 m, the slope of the coastal slope is 1:2.5, the height of the ocean side boundary is 0.15 m, and a narrow slot is set at a distance of 0.5 m from the sea boundary of the sand tank to divide the sand tank into a downstream side and an upstream side. Two underground dams with different positions and different heights of 0.15 m and 0.13 m are respectively set in the narrow slot; b. Fresh water is injected into the sand tank, and 4# quartz sand is filled layer by layer. Note that the water level exceeds the quartz sand by 5 cm during the sand filling process to avoid air bubbles and stratification. After filling, it is left standing saturated for 5 hours; c. Sodium chloride is added to deionized water and continuously stirred until completely dissolved, and it is dyed with red food dye to facilitate visualizing the distribution of the intruded seawater. A salinometer is used to measure the concentration and density of the salt water so that the seawater concentration is 35 g / L and the density is 1025 g / L; d. Adjust the water levels in the seawater tank and the freshwater tank to 0.29 m and 0.298 m respectively. Pull out the seawater partition and the freshwater partition to simulate the intrusion of seawater starting from the bottom of the central chamber. After the seawater intrusion reaches a steady state, start the seawater-side tidal control system, set the tidal amplitude to 0.02 m and the period to 60 s, and make the variable-height overflow device move up and down periodically to simulate a sinusoidal tide. Observe the formation of the upper saline plume and the change of the saltwater wedge. After the seawater intrusion reaches a quasi-steady state again, slowly insert the underground dam into the narrow slot. At the same time, by opening the surface source sprinkler, release the pre-prepared 0.1 g / L nitrate solution into the porous medium at a fixed flow rate of 0.01 m 3 / d, and observe the migration process of groundwater nitrate pollutants. For the freshwater tank, if a periodic water level fluctuation is simulated (such as simulating the situation of an island with ocean tides on both sides), the freshwater-side tidal control system can be started, the tidal amplitude can be set to 0.02 m, and the period can be set to 60 s, and the variable-height overflow device can be made to move up and down periodically to simulate a sinusoidal tide. If a fixed-flow boundary is simulated (such as the incoming water of an inland river), the stopcock can be opened, and freshwater can be injected into the freshwater tank at a fixed flow rate of 0.02m 3 / d. e. According to the dynamic migration of groundwater pollutants, connect the well holes at different positions in the central chamber through multiple peristaltic pumps, and extract the contaminated groundwater at a fixed flow rate of 0.01 m 3 / d to repair the aquifer, observe the change of the pollution concentration range. When the pollution range in the central chamber no longer changes within 1 minute, the experiment can be terminated. f. During the experiment, use a camera to take high-resolution digital photos of the experimental tank every 1 minute to record the migration process of pollutants in the central chamber and the change of the pollution range until the land-source solute is completely discharged into the ocean boundary. The obtained experimental digital photos are smoothed, the pixel values of the photos are converted into optical density, and then the pollutant concentration distribution is obtained according to the pre-calibrated relationship curve between solute concentration and optical density. g. Collect water samples at different sampling holes in the central chamber, use an ultraviolet spectrophotometer to measure the content of nitrate nitrogen, and compare it with the nitrate concentration after photo conversion to verify the accuracy and effectiveness of the experimental results.

Claims

1. A physical test system for studying the migration and remediation of non-point source pollution in a coastal stepped underground reservoir, characterized in that Comprising: An experimental tank system, a stepped underground reservoir simulation system, a pollution source spraying simulation system, and an imaging analysis system; The experimental tank system comprises: A central chamber (1), a seawater tank (2) and a freshwater tank (3) provided at both ends thereof, which are separated by a seawater partition plate (4) and a freshwater partition plate (5) that can be drawn up and down respectively. The central chamber (1) is filled with a porous medium (6) for simulating a coastal aquifer, and injection and production well holes (7) connected to a peristaltic pump are opened on the outer wall to simulate the extraction of groundwater pollutants for aquifer remediation, and sampling holes (8) for collecting water samples are also opened. The seawater tank (2) and the freshwater tank (3) are both connected to input mechanisms for seawater and freshwater. Variable-height overflow devices (9) are provided in both the seawater tank (2) and the freshwater tank (3) as tidal generators to cause the water level in the tank to fluctuate periodically; The stepped underground reservoir simulation system comprises: A plurality of slots (19) arranged at intervals in the seawater intrusion direction in the central chamber (1). Each slot (19) is provided with a sub-surface dam (20) that matches in size and can be drawn up and down to simulate a stepped underground reservoir; The pollution source spraying simulation system comprises: A pollutant non-point source sprinkler (21), which is horizontally movably arranged on the top of the central chamber (1) to simulate different pollution source positions; The imaging analysis system periodically takes pictures of the porous medium in the experimental tank to record the process of seawater intrusion and non-point source pollutant migration.

2. The physical test system for studying the migration and remediation of non-point source pollution in the coastal stepped underground reservoir according to claim 1, characterized in that: A plurality of injection and production well holes (7) and sampling holes (8) are arranged at horizontal and vertical intervals on the outer wall of the central chamber (1).

3. The physical test system for studying the migration and remediation of non-point source pollution in the coastal stepped underground reservoir according to claim 1, characterized in that: The overflow device (9) is driven by an electric drive assembly. The electric drive assembly comprises: a parameter controller (10), a servo motor (11), a coupling (12), a linear slide (13) and a servo slider (14); the parameter controller (10) is connected to control the telescopic movement of the servo motor (11). The telescopic end of the servo motor (11) is connected to the servo slider (14) through the coupling (12) to control the movement of the servo slider (14) on the linear slide (13). The overflow device (9) is fixedly connected to the servo slider (14).

4. The physical test system for studying the migration and remediation of non-point source pollution in a coastal stepped underground reservoir according to claim 1, characterized in that: A seawater bucket (15) is provided at the bottom of the seawater tank (2). The seawater bucket (15) pumps seawater into the seawater tank (2) through a water pump. A freshwater bucket (16) is provided at the bottom of the freshwater tank (3). The freshwater bucket (16) pumps freshwater into the freshwater tank (3) through a water pump; A plurality of uniformly distributed water outlet pipes (17) are provided on the side of the freshwater tank (3) and are connected to the input pipeline of the freshwater tank (3) to simulate a constant flow rate. A stop clamp (18) is provided on the water outlet pipe (17). When using the tidal generator to simulate the water level fluctuation in the freshwater tank, the flow rate input is closed through the stop clamp (18).

5. The physical test system for studying the migration and remediation of non-point source pollution in the coastal stepped underground reservoir according to claim 1, characterized in that: The seawater is simulated by mixing table salt and deionized water, and the freshwater is simulated by deionized water. The seawater and the freshwater are distinguished by different colors to facilitate visualizing the distribution of the intruded seawater.

6. The physical test system for studying the migration and remediation of non-point source pollution in a coastal stepped underground reservoir according to claim 1, characterized in that: The inner side of the narrow groove (19) is provided with a sealing strip (19-1), and the two side surfaces thereof are covered with water holes (19-2). When the underground dam (20) is inserted, the sealing strip (19-1) is squeezed with the periphery of the underground dam (20) to form a seal. The underground dam (20) comprises an underground dam water retaining area (20-1) located at the lower section and in contact with the groove bottom, an underground dam water passing area (20-2) located at the upper section of the underground dam water retaining area (20-1), and a handle (20-3) located on the underground dam water passing area (20-2). The underground dam water retaining areas (20-1) at different positions and different heights are arranged according to experimental needs to simulate the cascade underground dam (20). The underground dam (20) is located in the seawater intrusion range in the central chamber (1).

7. The physical test system for studying the migration and remediation of non-point source pollution in the stepped underground reservoir in the coastal area according to claim 1, characterized in that: The pollution source spreading simulation system further comprises a solution tank (22) and a peristaltic pump (23) connected to the pollutant surface source spreader (21); the solution tank (22) is loaded with a nitrate solution; a horizontal slide is provided on the top of the central chamber (1); the bottom of the pollutant surface source spreader (21) is covered with holes and is provided on the horizontal slide so as to be freely movable horizontally.

8. The physical test system for studying the migration and remediation of non-point source pollution in the coastal stepped underground reservoir according to claim 1, characterized in that: The imaging analysis system comprises a camera and a shading cloth. The camera is mounted on the front of the central chamber (1) to periodically capture images of the porous media in the experimental tank and record the seawater intrusion and non-point source pollutant migration process. The shading cloth is placed behind or to the side of the experimental tank according to the site light conditions to prevent the tank plate from reflecting light.

9. The physical test system for studying the migration and remediation of non-point source pollution in a coastal stepped underground reservoir according to claim 1, characterized in that: The seawater concentration in the seawater tank (2) is 35 g / L and the density is 1025 g / L; the freshwater in the freshwater tank (3) has a salinity of 0 g / L and a density of 1000 g / L.

10. A physical test method for studying the migration and remediation of non-point source pollution in a coastal stepped underground reservoir, characterized in that: The physical test system for studying the migration and restoration of non-point source pollution in coastal cascade underground reservoirs according to claim 1 is implemented, comprising the following steps: S1. Prepare seawater, fresh water, pollutant solution and white quartz sand; S2, the central chamber is filled with saturated porous media evenly layer by layer, and after filling, it is left to stand saturated with water; S3, inserting a seawater baffle between the seawater tank and the central chamber to prevent seawater from infiltrating the central chamber; S4. Adjust the water levels in the seawater tank and the freshwater tank respectively, pull out the seawater baffle and the freshwater baffle to simulate the invasion of seawater from the bottom of the central chamber; after the seawater invasion reaches a stable state, move the overflow device up and down periodically to simulate the sinusoidal tide, and observe the formation of the upper salt water plume and the change of the salt water wedge; after the seawater invasion reaches a quasi-steady state again, slowly insert the underground dam into the narrow slot, and at the same time, release the pre-prepared nitrate solution into the porous medium by opening the pollutant surface source sprinkler to observe the migration process of nitrate pollutants in groundwater; For the freshwater tank, if the water level is simulated to fluctuate periodically, the overflow device is moved up and down periodically to simulate the sinusoidal tide. If a constant flow rate is simulated, fresh water is injected into the freshwater tank at a fixed flow rate. S5. According to the migration dynamics of groundwater pollutants, multiple peristaltic pumps are used to connect the injection wells at different locations in the central chamber, and the contaminated groundwater is extracted at a fixed flow rate to repair the aquifer and observe the changes in the pollution concentration range. The experiment can be terminated when the pollution range in the central chamber does not change within 1 minute; S6. Take pictures of the experimental tank at regular intervals with a camera to record the migration process of pollutants in the central chamber and the change in the pollution range. The obtained experimental digital photos are smoothed, the pixel values of the photos are converted into optical density, and then the concentration distribution is obtained according to the pre-calibrated relationship curve between solute concentration and optical density; S7. Collect water samples at different sampling holes in the central chamber, use an ultraviolet spectrophotometer to measure the content of nitrate nitrogen, and compare it with the nitrate concentration after photo conversion to verify its effectiveness.

Images