Experimental device and simulation method for influence of tide and underground dam coupling on terrestrial source solute transport

Abstract

The invention discloses an experimental device for influence of tide and underground dam coupling on terrestrial source solute transport. The experimental device comprises a saline water tank, a sand tank and a fresh water tank, a variable-height overflow device is arranged in the saline water tank; the sand tank is communicated with the saline water tank through a saline water filter screen, an extractable water-stop sheet is arranged at the communication interval, the sand tank is filled with a porous medium, a slot is formed in the sand tank, an underground dam is arranged in the slot, the porous medium located between the underground dam and the saline water tank forms a lower slope towards the saline water tank, and a peristaltic pump is arranged above the lower slope. A terrestrial solute injection device is arranged between the underground dam and the fresh water tank, and a terrestrial solute solution is introduced into the porous medium; the fresh water tank is communicated with the sand tank through a fresh water filter screen, is connected with a fresh water supply device and is internally provided with an overflow pipe for adjusting the water level in the tank. According to the invention, the independent and coupling effects of the tide and the underground dam can be comprehensively considered, and the spatial and temporal distribution, retention and diffusion effects of the terrestrial solute can be observed.

Description

Technical Field

[0001] The present invention relates to the field of groundwater remediation and simulation technology, and specifically to an experimental device and a simulation method for the coupling of tides and underground dams to affect the migration of terrestrial solutes. Background Art

[0002] Coastal aquifers are located in the sea-land interaction zone and carry important ecological and economic functions. The migration and distribution of salt-fresh water mixing zones and terrigenous solutes (nutrients, heavy metals and organic pollutants, etc.) are affected by a variety of complex factors, which may cause a series of ecological and environmental problems. On the one hand, tides, as one of the significant marine dynamics in coastal areas, form active mixing zones in the intertidal zone, changing the migration path and retention time of terrigenous solutes; on the other hand, physical barrier projects such as underground dams, which are widely built to prevent seawater intrusion, change the flow field of aquifers, causing terrigenous solutes to be retained on the upstream side of underground dams and mixed with residual salt water. The difficulty of studying the migration mechanism of terrigenous solutes under the dual driving force of tides and underground dams lies in the immaturity of physical experimental equipment and the large error between simulation and actual process. In-depth analysis of the response of terrigenous solute migration to the coupling of tides and underground dams has important scientific significance and practical value for the protection and management of coastal groundwater resources.

[0003] At present, the research on the transport of terrigenous solutes is mostly concentrated on numerical simulation methods, and most of them focus on the influence of a single ocean driving force such as tides, without considering the role of human activities such as underground dams, making it difficult to accurately characterize the hydrodynamic process of coastal aquifers under underground physical barrier conditions. In addition, there is a lack of physical experimental equipment for studying the transport of terrigenous solutes under the coupling of tides and underground dams. The research on the transport of terrigenous solutes that relies on numerical simulation lacks indoor experimental support, making it difficult to verify its reliability. The law of terrigenous solute transport under the coupling of tides and underground dams is more complicated and is still unclear at this stage. There are still deficiencies in the experimental and simulation techniques for analyzing the influence of multiple factors on the transport of terrigenous solutes. Summary of the invention

[0004] Purpose of the invention: In order to overcome the shortcomings of the background technology, the first purpose of the present invention is to disclose an experimental device for the coupling of tides and underground dams to affect the migration of terrigenous solutes; The second purpose is to disclose a simulation method for the effects of tide and underground dam coupling on the migration of terrestrial solutes based on the above-mentioned experimental device, which can comprehensively consider the individual and coupled effects of tide and underground dam, realize the observation of the spatiotemporal distribution, retention and diffusion effects of terrestrial solutes, and track and calculate the trajectory and retention time of terrestrial solute migration.

[0005] Technical solution: The experimental device disclosed in the present invention for the coupling of tide and underground dam to affect the migration of terrigenous solutes comprises: a salt water tank, a sand tank and a fresh water tank arranged in sequence; The salt water tank is connected to the salt water supply device, and a variable height overflow device for tidal generation is provided in the salt water tank; The sand trough is connected to the brine trough through a brine filter, and a removable water-blocking plate is provided at the connecting interval. The sand trough is filled with porous media, and a narrow slot is provided in the trough. A removable underground dam is provided in the narrow slot. The porous media between the underground dam and the brine trough forms a downward slope toward the brine trough. A peristaltic pump for sucking surface fresh water is provided above the porous media on the downward slope. A land-source solute injection device is provided between the underground dam and the fresh water trough to introduce land-source solute solution into the porous media. The fresh water tank is connected to the sand tank through a fresh water filter, the fresh water tank is connected to a fresh water supply device, and an overflow pipe for adjusting the water level in the tank is arranged in the fresh water tank.

[0006] Furthermore, the brine supply device comprises a brine barrel, the brine barrel is connected to the brine tank via a brine hose, and a brine pump is arranged on the brine hose.

[0007] Furthermore, the variable height overflow device includes a servo motor, a coupling connected to the servo motor, a linear slide, and a servo slider connected to the linear slide, the servo slider is connected to the overflow groove, and the servo motor is connected to a motor controller.

[0008] Furthermore, the land-source solute injection device is a long needle syringe structure.

[0009] Furthermore, the terrigenous solute solution is different from the salt water in color.

[0010] Furthermore, the fresh water supply device comprises a fresh water barrel, the fresh water barrel is connected to the fresh water tank via a fresh water hose, and a fresh water pump is arranged on the fresh water hose.

[0011] Furthermore, it also includes a recording device, which includes a camera and a shading cloth.

[0012] A simulation method for the effect of tide and underground dam coupling on land-based solute transport adopts the above-mentioned experimental device for the effect of tide and underground dam coupling on land-based solute transport, including a physical experimental process, a numerical simulation process and an imaging analysis verification process.

[0013] Furthermore, the physical experiment process includes: S1-1. Prepare fresh water, salt water, terrigenous solute solution and porous medium materials; S1-2, insert baffles to prevent salt water from seeping into the sand tank, inject fresh water into the sand tank, fill the porous medium layer by layer, and the water level exceeds the filling material; S1-3. Adjust the water level in the salt water tank and the fresh water tank, remove the baffle, and allow the salt water to invade from the bottom of the sand tank. Turn on the peristaltic pump to absorb the surface fresh water to maintain a stable salt water concentration. After the salt water invasion reaches a stable state, start the variable height overflow device to move 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 salt water invasion reaches a quasi-steady state again, slowly insert the underground dam into the narrow slot, introduce the terrigenous solute solution through the terrigenous solute injection device, take photos with a camera at regular intervals, and observe and record the migration process of the terrigenous solute. The numerical simulation process includes: S2-1. According to the physical experiment process, a numerical model of groundwater flow and solute transport based on the physical experiment process is established with the sand tank size and the grid is divided. The salt water and fresh water fixed head boundaries are set. According to the boundary head size, the pressure value of each subdivided cell is calculated and assigned. According to the porosity and permeability coefficient of the porous medium in the physical experiment, the hydrogeological parameters related to the numerical model are confirmed, and the appropriate algorithm is selected to solve the mass conservation equation of the multi-component solute to obtain the model characteristic value. S2-2, run the static boundary numerical model, and update the grid salinity value, pressure value and flow velocity at each time step until steady state; S2-3, set tidal boundary conditions, run the dynamic boundary numerical model, and update the grid salinity value, pressure value and flow velocity at each time step until a quasi-steady state is reached; S2-4. According to the height and position of the underground dam in the physical experiment, set the impermeable area in the numerical model, set the initial position and concentration of the terrigenous solute, run the terrigenous solute migration model, and update the grid terrigenous solute concentration value, salinity value, pressure value and flow rate at each time step until the terrigenous solute is completely discharged into the salt water boundary; The imaging analysis verification process includes: S3-1. Import the physical experiment photos into the image processing software, crop the sand trough part and establish the coordinate system, and mark the scale; S3-2. On the processed image, according to the migration time of the physical experimental model, the isoconcentration lines of the terrigenous solute migration numerical model corresponding to the operation time are drawn, and the isoconcentration lines of the terrigenous solute are compared with the solute dyeing edge of the physical experiment to verify the reliability of the simulation; S3-3. Estimate the concentration of terrigenous solutes in the stained part of the physical experiment by comparing the isoconcentration lines with the edges of the physical experiment staining, calculate the residence time, diffusion area and migration path of terrigenous solutes, and analyze the migration characteristics of terrigenous solutes.

[0014] Beneficial effects: Compared with the prior art, the present invention: 1. It can effectively analyze the influence of the coupling effect of tides and underground dams on the migration of terrigenous solutes. The scale of tidal fluctuations is usually small, but it will cause changes in the velocity and even direction of groundwater near the boundary. Considering the tidal effect is crucial for the exchange of matter and energy and the migration of solutes in coastal aquifers. At the same time, underground dams with effective heights form low-velocity areas behind the dams, and long-term retained salt water may mix with terrigenous solutes, changing the migration path and retention time. This method combines indoor physical experiments with numerical simulations to quantify the relationship between the migration characteristics of terrigenous solutes and multiple factors such as tides and underground dams. It solves the problem that traditional simulation devices are difficult to comprehensively reflect the hydrodynamic conditions of aquifers, and is helpful to systematically explore the migration process of terrigenous solutes in coastal aquifers under the dual driving effects of natural factors and human activities.

[0015] 2. This method can not only observe the retention and diffusion characteristics of terrigenous solutes, but also obtain the scaled spatiotemporal distribution of sand trough solutes by further processing the digital photos of physical experiments, and then quantitatively analyze the position coordinates, residence time, migration path and other parameters of terrigenous solutes.

[0016] 3. In this method, parameters such as the release position and concentration of terrigenous solutes, tidal amplitude and frequency, and underground dam height can be adjusted, which is conducive to in-depth research on the migration process of terrigenous solutes under different hydrodynamic conditions; at the same time, by selecting quartz sand with different particle sizes and gradations, homogeneous aquifers or layered heterogeneous aquifers can be simulated to reflect different hydrogeological conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a diagram of the physical experiment device and a schematic diagram of the numerical simulation system of the present invention; Figure 2 is the aquifer streamline distribution diagram with and without tidal conditions obtained by numerical simulation; Figure 3 This is the spatiotemporal distribution diagram of terrigenous solute transport concentration obtained by numerical simulation. DETAILED DESCRIPTION

[0018] The technical solution of the present invention will be further described below in conjunction with the accompanying drawings. like Figure 1 The experimental device for the influence of tidal and underground dam coupling on the migration of terrigenous solutes shown includes: a salt water tank 1, a sand tank 2 and a fresh water tank 3 arranged in sequence. Effective sealing means are used between the components in the device to ensure good sealing performance and prevent leakage.

[0019] The salt water tank 1 is connected to the salt water supply device, and a variable height overflow device 4 for tidal generation is provided in the salt water tank 1; The sand trough 2 is connected to the brine trough 1 through a brine filter 5, and a removable baffle 6 is provided at the connecting interval. The sand trough 2 is filled with a porous medium 7, and a narrow groove 8 is provided in the trough. A removable underground dam 9 is provided in the narrow groove 8. The porous medium 7 between the underground dam 9 and the brine trough 1 forms a downward slope toward the brine trough 1. A peristaltic pump 10 for sucking surface fresh water is provided above the porous medium of the downward slope to maintain a constant salinity in the brine trough 1. A terrigenous solute injection device 11 is provided between the underground dam 9 and the freshwater trough 3 to introduce a terrigenous solute solution 12 into the porous medium 7; The fresh water tank 3 is connected to the sand tank 2 through a fresh water filter 13. The fresh water tank 3 is connected to a fresh water supply device. An overflow pipe 14 is provided in the fresh water tank 3 for adjusting the water level in the tank to adjust the water level height in the tank and provide a constant head fresh water boundary.

[0020] The brine supply device comprises a brine barrel 1-1, the brine barrel 1-1 is connected to the brine tank 1 through a brine hose 1-2, and a brine pump 1-3 is arranged on the brine hose 1-2.

[0021] The variable height overflow device 4 includes a servo motor 4-1, a coupling 4-2 connected to the servo motor, a linear slide 4-3 and a servo slider 4-4 connected to the linear slide, the servo slider 4-4 is connected to the overflow groove 4-5, and the servo motor 4-1 is connected to the motor controller 4-6.

[0022] The land-source solute injection device 11 is a long needle syringe structure.

[0023] The terrigenous solute solution 12 is different from the salt water in color. The salt water is prepared by mixing deionized water and table salt and dyed with red food dye to facilitate visualization of the distribution of invading salt water. The terrigenous solute solution 12 is dyed with bright blue food dye to facilitate visualization of its migration process.

[0024] The fresh water supply device comprises a fresh water barrel 3-1, the fresh water barrel 3-1 is connected to the fresh water tank 3 through a fresh water hose 3-2, and a fresh water pump 3-3 is arranged on the fresh water hose 3-2.

[0025] It also includes a recording device, which includes a camera and a shading cloth. The camera is placed in front of the sand trough to take images of the experimental trough at regular intervals to record the migration process of terrigenous solutes. The shading cloth is placed behind or to the side of the sand trough according to the light conditions of the site to prevent the trough plate from reflecting light.

[0026] The above experimental device of the coupling of tide and underground dam to influence the transport of terrigenous solutes was used to carry out physical experiments, numerical simulations and imaging analysis verification.

[0027] The physical experiment process includes: S1-1. Prepare fresh water, salt water, terrigenous solute solution and porous medium materials; S1-2, insert the baffle 6 to prevent the salt water from penetrating into the sand tank 2, inject fresh water into the sand tank 2, fill the porous medium 7 layer by layer, and the water level exceeds the filling material; S1-3, adjust the water level in the salt water tank 1 and the fresh water tank 3, remove the baffle 6, salt water starts to invade from the bottom of the sand tank 2, turn on the peristaltic pump 10, absorb the surface fresh water, and maintain the stability of the salt water concentration; after the salt water invasion reaches a stable state, start the variable height overflow device 4 to move up and down periodically, simulate the sinusoidal tide, and observe the formation of the upper salt water plume and the change of the salt water wedge; after the salt water invasion reaches a quasi-steady state again, slowly insert the underground dam 9 into the narrow slot 8, introduce the terrigenous solute solution 12 through the terrigenous solute injection device 11, take pictures with a camera at regular intervals, observe and record the migration process of the terrigenous solute. Add high-concentration salt water to the salt water barrel at regular intervals and measure its salinity to ensure that the salinity of the salt water boundary remains stable.

[0028] The numerical simulation process includes: S2-1. According to the physical experiment process, a numerical model of groundwater flow and solute transport based on the physical experiment process is established with the size of sand tank 2 and the grid is divided. The salt water and fresh water fixed head boundaries are set. According to the size of the boundary head, the pressure value of each subdivided cell is calculated and assigned. According to the porosity and permeability coefficient of the porous medium in the physical experiment, the hydrogeological parameters related to the numerical model are confirmed, and the appropriate algorithm is selected to solve the mass conservation equation of the multi-component solute to obtain the model characteristic value. S2-2, run the static boundary numerical model, and update the grid salinity value, pressure value and flow velocity at each time step until steady state; S2-3, set tidal boundary conditions, run the dynamic boundary numerical model, and update the grid salinity value, pressure value and flow velocity at each time step until a quasi-steady state is reached; S2-4. According to the height and position of the underground dam 9 in the physical experiment, the impermeable area in the numerical model is set, and the initial position and concentration of the terrigenous solute are set. The terrigenous solute migration model is run, and the grid terrigenous solute concentration value, salinity value, pressure value and flow rate are updated at each time step until the terrigenous solute is completely discharged into the brine boundary.

[0029] The imaging analysis verification process includes: S3-1. Import the physical experiment photos into the image processing software, cut out the two parts of the sand trough, establish the coordinate system, and mark the scale; S3-2. On the processed image, according to the migration time of the physical experimental model, the isoconcentration lines of the terrigenous solute migration numerical model corresponding to the operation time are drawn, and the isoconcentration lines of the terrigenous solute are compared with the solute dyeing edge of the physical experiment to verify the reliability of the simulation; S3-3. Estimate the concentration of terrigenous solutes in the stained part of the physical experiment by comparing the isoconcentration lines with the edges of the physical experiment staining, calculate the residence time, diffusion area and migration path of terrigenous solutes, and analyze the migration characteristics of terrigenous solutes.

[0030] The main purpose of this example is to analyze the effect of tide and underground dam coupling on the migration of terrigenous solutes, which is achieved by combining the physical experiment system with the numerical simulation system, and the reliability of the simulation is verified by the imaging analysis verification system. 50 =0.60~1.25 mm) as porous media to simulate coastal aquifers, and the resulting aquifer area is assumed to meet homogeneous isotropic conditions. The sand trough is made of tempered glass plate, with a length × height × width of 1.2 m × 0.45 m × 0.02 m. In order to simulate the cross section of a two-dimensional unconfined aquifer, the sand trough adopts a smaller width to facilitate the observation of the distribution of terrigenous solutes in the cross section. The aquifer height is 0.35 m, the slope of the coastal slope is 1:2.5, and the height of the ocean side boundary is 0.15 m. A narrow slot is set at 0.5 m from the sea boundary of the sand trough to divide the sand trough into the downstream side and the upstream side. An extractable underground dam with a water retaining height of 0.12 m is set in the narrow slot.

[0031] The present invention is used to analyze the influence of tide and underground dam coupling on the migration of terrigenous solutes, including the following parts: 1. Physical experiment part: prepare deionized water as fresh water, and prepare simulated seawater with a salinity of 35 ppt. The specific method is as follows: add sodium chloride to deionized water, stir continuously until it is completely dissolved, and dye it with red food dye to facilitate visualization of the distribution of invading salt water. Use a salinometer to measure the density and salinity of the salt water, so that the salt water density is accurately stabilized at 1025 kg / m³ and the salinity is stabilized at 35 ppt; prepare a conservative terrigenous solute solution with a salinity of 0 ppt, and dye it with bright blue food dye to facilitate visualization of the distribution of terrigenous solutes; prepare quartz sand with an average particle size of 0.60~1.25 mm, rinse it with deionized water several times and dry it; insert a baffle between the sand trough and the salt water trough to prevent salt water from infiltrating the sand trough, inject fresh water into the sand trough, and fill in quartz sand layer by layer. Note that the water level exceeds the quartz sand by 5 cm during the sand filling process to avoid bubbles and stratification. The filling height of the ocean boundary is 0.15m, and a slope with a slope of 1:2.5 is formed on the upper part of the sea boundary. The filling height of the fresh water boundary is 0.35 m; the water levels in the salt water tank and the fresh water tank were adjusted to 0.29 m and 0.298 m respectively, the baffle between the sand tank and the salt water tank was removed to simulate the invasion of seawater from the bottom of the sand tank, and the peristaltic pump above the porous medium slope at the top of the sand tank was turned on to absorb surface fresh water to maintain a stable salt water concentration; after the seawater intrusion reached a stable state, the tidal control system was started, and the tidal amplitude was set to 0.02 m and the period was 60 s, so that the variable height overflow device moved up and down periodically to simulate the sinusoidal tide, and the formation of the upper salt water plume and the change of the salt water wedge were observed; after the seawater intrusion reached a quasi-steady state again, an acrylic plate with a water retaining height of 0.12 m was slowly inserted into the narrow slot as an underground dam, and at the same time, a terrigenous solute solution was introduced through an injection device at a position 0.8 m away from the sea boundary and 0.05 m high. During the experiment, a camera was used to take high-resolution digital photos of the experimental tank at regular intervals to observe and record the migration process of terrigenous solutes; 2. Numerical simulation: According to the physical experiment part, a numerical model of groundwater flow and solute transport based on physical processes was established with the sand tank size and divided into grids. The boundary heads of seawater and freshwater were set to 0.29 m and 0.298 m respectively, and the pressure value of each subdivided cell was calculated and assigned. The hydrogeological parameters related to the numerical model were confirmed according to the parameters such as the porosity and permeability coefficient of the porous media in the physical experiment, and the mass conservation equation of the multi-component solute was solved to obtain the model eigenvalues. The static boundary numerical model was run to update the grid salinity value, pressure value and flow velocity and other eigenvalues ​​of each time step until the steady state was reached. The tidal amplitude was set to 0.02 m and the period was 60 s. The dynamic boundary numerical model was run to update the grid salinity value, pressure value and flow velocity and other eigenvalues ​​of each time step until the steady state was reached. The impermeable area in the numerical model was set to a rectangular area with a distance of 0.5 m from the sea boundary, a width of 0.01 m and a height of 0.12 m, and the initial position (0.8 m, 0.05 m) and the concentration of 0.1 were set. g / L, run the terrigenous solute transport model, and update the grid terrigenous solute concentration value, salinity value, flow velocity and other characteristic values ​​at each time step until the terrigenous solute is completely discharged into the ocean boundary; 3. Imaging analysis and verification part: Import the digital photos of the physical experiment into the image processing software, crop the sand trough part in the photo, establish the coordinate system and add scales to obtain the spatiotemporal distribution of terrigenous solute migration. On the preprocessed image, according to the migration time of the physical experiment model, draw the isoconcentration lines of the numerical model of terrigenous solute migration corresponding to the running time, compare the isoconcentration lines with the edge of the solute staining in the physical experiment, and verify the reliability of the simulation; according to the comparison between the isoconcentration lines and the edge of the staining of the physical experiment, estimate the concentration of terrigenous solutes in the stained part of the physical experiment, calculate the residence time, diffusion area and migration path of terrigenous solutes, and analyze the migration characteristics of terrigenous solutes; compare and verify the experimental results under different scenarios, and study the influence mechanism of the coupling of tides and underground dams on the migration of terrigenous solutes.

[0032] The examples are used to study the distribution of aquifer streamlines under the influence of underground dams with and without tidal conditions. Figure 2 As shown in the figure, the numbers above the streamlines represent the total residence time of particles moving along the streamline trajectory in the aquifer, and the migration process of terrigenous solutes under the coupling of tides and underground dams is analyzed, as shown in Figure 3As shown in the figure, the black solid line represents the 50% and 90% isoconcentration lines of terrigenous solutes. The results show that tidal action causes the aquifer to form a new circulation in the intertidal zone, and the migration speed of the freshwater area slows down; under the coupling of tide and underground dam, a low-velocity area is formed on the upstream side of the underground dam that is higher than the minimum effective dam height, blocking the terrigenous solute plume, causing it to rise along the edge of the salt water wedge, cross the top of the underground dam, and discharge into the sea through the freshwater discharge channel. Some terrigenous solutes mix with the residual salt water upstream of the underground dam and stay in the low-velocity area behind the dam for a long time. Tidal action causes the direction and size of the flow field in the aquifer to change periodically, prolonging the residence time of terrigenous solutes, increasing the diffusion area, enhancing the longitudinal diffusion but weakening the lateral diffusion. This change is more significant under larger tidal amplitudes; the higher the height of the underground dam, the longer the residence time of terrigenous solutes.

Claims

1. An experimental device for the effect of tide and underground dam coupling on the transport of terrigenous solutes, characterized in that: include: A salt water tank (1), a sand tank (2) and a fresh water tank (3) are arranged in sequence; The salt water tank (1) is connected to a salt water supply device, and a variable height overflow device (4) for tidal generation is provided in the salt water tank (1); The sand trough (2) is connected to the salt water trough (1) via a salt water filter (5), and a removable water barrier (6) is provided at the connecting interval. The sand trough (2) is filled with a porous medium (7), and a narrow groove (8) is provided in the trough. A removable underground dam (9) is provided in the narrow groove (8). The porous medium (7) between the underground dam (9) and the salt water trough (1) forms a downward slope toward the salt water trough (1). A peristaltic pump (10) for sucking surface fresh water is provided above the porous medium on the downward slope. A land-source solute injection device (11) is provided between the underground dam (9) and the fresh water trough (3) to introduce a land-source solute solution (12) into the porous medium (7); The fresh water tank (3) is connected to the sand tank (2) via a fresh water filter (13); the fresh water tank (3) is connected to a fresh water supply device; an overflow pipe (14) for adjusting the water level in the tank is provided in the fresh water tank (3).

2. The experimental device for the effect of tidal and underground dam coupling on land-derived solute transport according to claim 1, characterized in that: The brine supply device comprises a brine barrel (1-1), the brine barrel (1-1) being connected to a brine tank (1) via a brine hose (1-2), and a brine pump (1-3) being arranged on the brine hose (1-2).

3. The experimental device for the effect of tidal and underground dam coupling on land-derived solute transport according to claim 1, characterized in that: The variable height overflow device (4) comprises a servo motor (4-1), a coupling (4-2) connected to the servo motor, a linear slide (4-3), and a servo slider (4-4) connected to the linear slide, the servo slider (4-4) being connected to the overflow trough (4-5), and the servo motor (4-1) being connected to a motor controller (4-6).

4. The experimental device for the effect of tidal and underground dam coupling on land-based solute transport according to claim 1, characterized in that: The terrigenous solute injection device (11) is a long needle syringe structure.

5. The experimental device for the effect of tidal and underground dam coupling on land-derived solute transport according to claim 1, characterized in that: The terrigenous solute solution (12) is different in color from the salt water.

6. The experimental device for the effect of tidal and underground dam coupling on land-based solute transport according to claim 1, characterized in that: The fresh water supply device comprises a fresh water bucket (3-1), the fresh water bucket (3-1) is connected to a fresh water tank (3) via a fresh water hose (3-2), and a fresh water pump (3-3) is arranged on the fresh water hose (3-2).

7. The experimental device for the effect of tide and underground dam coupling on land-source solute transport according to claim 1, characterized in that: Also included is a recording device, which includes a camera and a blackout cloth.

8. A method for simulating the effects of tide and underground dam coupling on the transport of terrigenous solutes, characterized by: The experimental device for the tidal and underground dam coupling effects on terrigenous solute transport as described in claim 1 includes a physical experimental process, a numerical simulation process and an imaging analysis verification process.

9. The method for simulating the tidal and underground dam coupling effects on land-based solute transport according to claim 8, characterized in that: The physical experiment process includes: S1-1. Prepare fresh water, salt water, terrigenous solute solution and porous medium materials; S1-2, inserting a water-blocking plate (6) to prevent salt water from seeping into the sand tank (2), injecting fresh water into the sand tank (2), and filling the porous medium (7) layer by layer until the water level exceeds the filling material; S1-3, adjusting the water level in the salt water tank (1) and the fresh water tank (3), removing the baffle (6), allowing salt water to invade from the bottom of the sand tank (2), turning on the peristaltic pump (10) to absorb surface fresh water and maintain a stable salt water concentration; after the salt water invasion reaches a stable state, starting the variable height overflow device (4) to periodically move up and down to simulate a sinusoidal tide, and observing the formation of an upper salt water plume and changes in the salt water wedge; after the salt water invasion reaches a quasi-steady state again, slowly inserting an underground dam (9) into the narrow slot (8), introducing a terrigenous solute solution (12) through a terrigenous solute injection device (11), taking photos with a camera at regular intervals, and observing and recording the migration process of the terrigenous solute; The numerical simulation process includes: S2-1. According to the physical experiment process, a numerical model of groundwater flow and solute transport based on the physical experiment process is established with the size of the sand tank (2) and the grid is divided. The salt water and fresh water fixed head boundaries are set. According to the size of the boundary head, the pressure value of each divided cell is calculated and assigned. According to the porosity and permeability coefficient of the porous medium in the physical experiment, the hydrogeological parameters related to the numerical model are confirmed, and a suitable algorithm is selected to solve the mass conservation equation of the multi-component solute to obtain the model characteristic value. S2-2, run the static boundary numerical model, and update the grid salinity value, pressure value and flow velocity at each time step until steady state; S2-3, set tidal boundary conditions, run the dynamic boundary numerical model, and update the grid salinity value, pressure value and flow velocity at each time step until a quasi-steady state is reached; S2-4. According to the height and position of the underground dam (9) in the physical experiment, the impermeable area in the numerical model is set, and the initial position and concentration of the terrigenous solute are set, and the terrigenous solute transport model is run to update the grid terrigenous solute concentration value, salinity value, pressure value and flow rate at each time step until the terrigenous solute is completely discharged into the salt water boundary; The imaging analysis verification process includes: S3-1. Import the physical experiment photo into the image processing software, cut out the sand trough (2) part and establish a coordinate system, and mark the scale; S3-2. On the processed image, according to the migration time of the physical experimental model, the isoconcentration lines of the terrigenous solute migration numerical model corresponding to the operation time are drawn, and the isoconcentration lines of the terrigenous solute are compared with the solute dyeing edge of the physical experiment to verify the reliability of the simulation; S3-3. Estimate the concentration of terrigenous solutes in the stained part of the physical experiment by comparing the isoconcentration lines with the edges of the physical experiment staining, calculate the residence time, diffusion area and migration path of terrigenous solutes, and analyze the migration characteristics of terrigenous solutes.

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