Groundwater flow and solute transport simulation test device and monitoring and identification method thereof

Abstract

The present application relates to the technical field of groundwater solute research, in particular to a groundwater flow and solute transport simulation test device and a monitoring and identification method thereof; comprising a seepage tank, a boundary stable water tank, a tide generating system, a constant head water supply system and an image acquisition assembly; the tide generating system drives water level fluctuation; the constant head water supply system provides a land side water head boundary; a slope protection plate is arranged on the slope surface of the sand slope; the image acquisition assembly is arranged opposite to the front surface and is used for shooting single frame or continuous images containing a standard color mark reference assembly and a sand slope flow field; the present application solves the problem that the traditional vertical boundary model does not match the actual coastal zone terrain, breaks through the technical bottleneck that the traditional image method is easily disturbed by the environment and has insufficient long-period precision, maintains the stability of the slope surface geometric boundary and the stability of the concentration monitoring and calibration conditions, realizes the synchronous high-precision monitoring of the water head field and the concentration field, and can provide a reliable test platform and data support for the mechanism research of coastal groundwater flow and solute transport.

Description

Technical Field

[0001] This invention relates to the field of groundwater solute research technology, specifically to a groundwater flow and solute transport simulation test device and its monitoring and identification method. Background Technology

[0002] Coastal areas are key intersections of terrestrial and marine hydrological cycles. Groundwater flow and solute transport in these areas are driven by a complex interplay of factors, including tidal fluctuations, shoreline topography, aquifer heterogeneity, and human activities. Research on groundwater flow and solute transport under tidal influences is of significant theoretical and engineering value for coastal groundwater resource protection, seawater intrusion control, and groundwater pollution remediation. Indoor physical sand flume experiments, which can reproduce hydrogeological processes under controlled boundary conditions, are a core research method for revealing the dynamic mechanisms of coastal groundwater seepage and solute migration.

[0003] Existing coastal aquifer physical simulation devices mostly use straight, permeable baffles perpendicular to the shoreline as the seaside boundary. They construct a stable head difference through brackish and freshwater chambers on both sides, and incorporate tidal generating devices to achieve periodic water level fluctuations. For example, Chinese patent CN120195362A discloses a device and method for simulating pollutant migration under mining and tidal conditions, which can simultaneously simulate the pollutant migration process under the combined effects of tidal fluctuations and groundwater extraction. However, these devices all construct seepage boundaries based on an idealized vertical shoreline assumption, failing to consider the natural slope commonly found on natural beaches. They cannot reproduce the "dynamic boundary" effect of seawater rising and falling on the slope during tidal rise and fall, resulting in significant differences from the actual hydrogeological conditions of the coastal zone. This makes it difficult to accurately characterize the regulatory effect of shoreline topography on the groundwater flow field and solute transport pathways.

[0004] In the field of solute transport monitoring technology, existing devices mainly employ two approaches: fixed-point sampling and image recognition. Chinese Patent CN116840103B discloses an experimental device and simulation method for studying pollutant transport in coastal underground reservoirs, which acquires the spatiotemporal distribution of pollutants through a back sampling port combined with a front imaging system. However, the fixed-point sampling method is limited by the number of sampling ports, has low spatial resolution, and the sampling operation easily disturbs the structure and flow field of the aquatic medium. While image recognition can achieve full-field monitoring, it typically relies on pre-calibrated color-concentration relationships. Fluctuations in light intensity, camera white balance, and exposure parameters during the experiment can lead to deviations in the concentration inversion results. Furthermore, the lack of in-situ correction within the same frame makes it difficult to guarantee the accuracy and stability of concentration monitoring in long-term experiments.

[0005] Furthermore, if a natural slope is constructed within the sand trough to simulate a real beach, the continuous scouring of the tidal flow can easily cause erosion and slippage of the sand grains on the slope, leading to slope morphology deformation and disrupting the consistency of experimental boundary conditions. Currently, existing devices lack an effective structure that balances slope water exchange and morphological protection, limiting the long-term stability and experimental repeatability of the physical model of natural slope sand.

[0006] In summary, existing coastal groundwater solute transport simulation technologies suffer from several technical deficiencies, including the lack of simulation of real shoreline dynamic boundaries, poor slope morphology erosion resistance, and susceptibility of full-field concentration monitoring accuracy to environmental interference. These technologies cannot simultaneously meet the experimental requirements of "realistic reproduction of natural terrain" and "high-precision full-field solute monitoring," necessitating the development of corresponding simulation experimental devices and monitoring and identification methods. Summary of the Invention

[0007] Based on the above description, the groundwater flow and solute transport simulation test device and its monitoring and identification method provided by the present invention solve the problem that the existing technology cannot simultaneously meet the experimental requirements of realistic reproduction of natural terrain and high-precision full-field solute monitoring.

[0008] To solve the above-mentioned technical problems, the present invention provides a groundwater flow and solute transport simulation test device, including a seepage tank, a boundary water stabilization tank, a tide generation system, a constant head water supply system, and an image acquisition component. The seepage channel is filled with a permeable medium to form a sand slope, and the slope surface of the sand slope is inclined along the length of the seepage channel. Two sets of boundary water stabilizing tanks are provided, and they are located at both ends of the seepage channel along its length. The two sets of boundary water stabilizing tanks are separated from the seepage channel by porous permeable baffles. The surface of the porous permeable baffles is covered with fine mesh that blocks the permeable medium. The tidal generation system is connected to a boundary water stabilization tank near the low side of the sand slope to drive water level fluctuations; The constant head water supply system is connected to a boundary stabilizing tank near the high side of the sand slope to provide a stable landside head boundary; The slope of the sand slope is provided with a slope protection board, and the slope protection board has water permeable holes on its surface. The water permeable holes are covered with a filter screen that blocks the water permeable medium. The vertical surface of the seepage channel located between the two sets of boundary water stabilization tanks is defined as the front side. The front side is made of transparent material. A standard color mark reference component is set inside or outside the front side. The standard color mark reference component contains multiple independent chambers. Each chamber is filled with the same water-permeable medium as the seepage channel and standard tracer solutions of different concentrations. The image acquisition component is positioned facing forward and is used to capture single-frame or continuous images that simultaneously include the standard color mark reference component and the sand slope flow field.

[0009] Based on the above technical solution, the present invention can be further improved as follows.

[0010] Furthermore, the tide generation system includes a first water stabilizing tank, which is divided into a first zone and a second zone by a vertically arranged first overflow plate. The first zone is connected to a first inlet pipe, and the second zone is connected to a first drain pipe and a first connecting pipe. The other end of the first connecting pipe is connected to an adjacent boundary water stabilizing tank. The first water stabilizing tank is connected to a first height adjustment mechanism, which includes a first servo control unit and a first threaded rod that are connected by a transmission. The first threaded rod is connected to the first water stabilizing tank, and the first servo control unit drives the first threaded rod to rotate, thereby raising and lowering the first water stabilizing tank. The water level of the adjacent boundary water stabilizing tank is adjusted by changing the height of the first overflow plate.

[0011] Furthermore, the constant head water supply system includes a second water stabilizing tank, which is divided into a third zone and a fourth zone by a vertically arranged second overflow plate. The third zone is connected to a second inlet pipe, and the fourth zone is connected to a second drain pipe and a second connecting pipe. The other end of the second connecting pipe is connected to an adjacent boundary water stabilizing tank. The first water stabilizing tank is connected to a second height adjustment mechanism, which includes a second servo control unit and a second threaded rod that are connected by a transmission. The second threaded rod is connected to the second water stabilizing tank, and the second servo control unit drives the second threaded rod to rotate, thereby raising and lowering the second water stabilizing tank. The water level of the adjacent boundary water stabilizing tank is adjusted by changing the height of the second overflow plate.

[0012] Furthermore, the standard color mark reference component is made of transparent material, is set adjacent to the front wall panel of the seepage tank, and is located within the shooting range of the image acquisition component at the same time as the experimental flow field area, and is illuminated by the same supplementary lighting frame to achieve color parameter calibration in the same frame.

[0013] Furthermore, the back of the seepage channel is provided with a monitoring hole array, which is connected to a pressure plate or pressure sensor via a flexible hose to monitor water head data at different locations.

[0014] Furthermore, the image acquisition component includes a surround lighting frame parallel to the front of the seepage channel and an image sensor located in the middle of the lighting frame. The surround lighting frame is used to provide uniform illumination for shooting.

[0015] The second aspect of this application provides a method for monitoring and identifying groundwater flow and solute transport simulation tests, using the groundwater flow and solute transport simulation test apparatus according to any one of claims 1-6, comprising the following steps: S1. Construct a sand slope with permeable medium in the seepage channel and saturate the permeable medium; fill each independent chamber of the standard color mark reference component with the same permeable medium and inject standard tracer solutions of different concentrations. S2. Start the tidal generation system and constant head water supply system to form a stable seepage field. The water flows through the slope protection board and acts on the permeable medium slope surface to simulate the dynamic boundary process of tidal rise and fall. S3. After the flow field stabilizes, inject a visual tracer into the permeable medium and start the image acquisition component to acquire continuous images that simultaneously include the standard color mark reference component and the flow field area. S4. Preprocess and convert the acquired images to color space, and extract the color parameters of the images; identify the image regions of each independent chamber in the standard color mark reference component, calculate the average color parameter value of each region, and establish the color parameter-concentration calibration relationship under the current shooting conditions by combining the known standard concentration of each chamber. S5. Substitute the color parameters of each pixel in the flow field region into the calibration relationship, and invert to obtain the tracer concentration value corresponding to each pixel, thereby generating the concentration field distribution of the entire flow field.

[0016] Furthermore, in step S4, the color space conversion involves converting the preprocessed RGB image into the HSV color space, which includes hue, saturation, and value. When the image has local uneven lighting or background interference, tracer region identification and mask selection are performed by combining saturation and value parameters.

[0017] Furthermore, after step S5, the method further includes: based on the concentration field obtained by inversion, extracting parameters such as solute halo contour, concentration contour lines, solute halo area, centroid coordinates, front position, tail position, main migration direction, diffusion range, aspect ratio, and migration velocity, and performing joint analysis with the extracted parameters and the head data obtained by the pressure plate or pressure sensor.

[0018] Furthermore, the color parameters include HSV chromaticity values, RGB components, grayscale values, or Lab color space parameters; the concentration inversion employs multinomial fitting, exponential functions, power functions, piecewise functions, or lookup table interpolation models.

[0019] Compared with the prior art, the technical solution of this application has the following beneficial technical effects: 1. Realizes simulation of tidal dynamic boundary and enables repeatable long-term stability tests of slopes. This invention simulates natural coastal beach topography by setting up an inclined sand slope in the seepage channel, and is equipped with a slope protection plate structure that fits the slope surface. The permeable holes of the slope protection plate ensure free hydraulic exchange between tidal water flow and the pores of the medium. At the same time, the filter screen prevents sand loss, and the rigid plate body counteracts the shearing and scouring effect of the tidal reciprocating flow. It solves the defects of traditional vertical permeable baffle models that cannot reproduce the dynamic boundary of tidal slope rise and fall and the easy collapse and deformation of unprotected sand slopes. It significantly extends the slope morphology stabilization time of long-period tidal tests, ensures consistent boundary conditions in multi-period solute transport tests, and improves the repeatability and data reliability of the test.

[0020] 2. In-situ standard color mark component within the same frame significantly reduces the overall concentration monitoring error. This invention places a multi-gradient concentration standard color mark reference component and the experimental flow field in the same shooting frame. The shooting distance, illumination, and camera optical parameters of the two are unified. Each frame of the image can build a unique color-concentration calibration relationship in real time based on the built-in standard concentration sample. Unlike the traditional offline calibration scheme before the experiment, it can dynamically offset the color recognition deviation caused by illumination fluctuations, camera white balance drift, and exposure changes during the experiment. No additional offline correction operation is required. It realizes high-precision, low-disturbance full-field visualization monitoring of tracer concentration in the entire sand dune, and significantly improves the data accuracy of long-term solute transport observation.

[0021] 3. Consistency between slope boundary disturbance control and image calibration benchmark improves the reliability of long-term solute test data. The aforementioned slope protection board and standard color mark reference component act on the physical model boundary and image monitoring baseline, respectively. The slope protection board reduces the disturbance of slope particles by tidal reciprocating flow, maintaining the consistency of the slope's geometric boundary during long-term experiments. The standard color mark reference component establishes a color parameter-concentration calibration relationship based on the current frame image, maintaining the consistency of the image concentration inversion baseline at different times. Together, they reduce the impact of geometric boundary changes and monitoring baseline drift on the experimental results, improving the comparability, repeatability, and reliability of time-series data from long-term tidal solute transport experiments.

[0022] 4. Simultaneous acquisition of head field and concentration field enables quantitative analysis of seepage-solute coupling. A complete two-dimensional head monitoring array is deployed on the back of the seepage channel, paired with a front image acquisition component, which can synchronously and temporally acquire global head distribution and two-dimensional concentration field data at different tidal stages. This overcomes the limitations of traditional devices where the head monitoring and solute imaging systems are not synchronized in time and are not spatially matched. It can fully characterize the coupled evolution law of groundwater oscillation and solute halo migration and diffusion under the tidal dynamic boundary, and provide synchronous complete experimental data for quantitatively analyzing the regulation mechanism of solute transport by slope topography and tidal parameters.

[0023] 5. The entire device is integrated into one unit, ensuring precise boundary control and convenient operation. The two independent boundary water tanks are matched with the tide generation system and the constant head water supply system, respectively. The periodic tidal water level on the sea side and the constant replenishment head on the land side are precisely controlled by raising and lowering the overflow plate. The water flow is buffered and eliminated by the porous permeable baffle, and the seepage field of the entire sand slope is uniform and stable. The whole set of devices integrates terrain simulation, hydraulic boundary control, in-situ concentration calibration and synchronous head monitoring. The medium, tracer and tidal curve can be flexibly replaced to adapt to a variety of test scenarios, and the device has strong versatility. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure provided for an embodiment of the present invention; Figure 2 This is a structural diagram of the standard color mark reference component; Figure 3 This is a schematic diagram of the tidal generation system; Figure 4 This is a schematic diagram of a constant head water supply system; Figure 5 This is a schematic diagram of the image acquisition component. Figure 6 This is a structural schematic diagram of the slope protection slab; Figure 7 A flowchart of the test monitoring and identification method provided in the embodiments of the present invention.

[0025] The attached diagram lists the components represented by each number as follows: 1. Seepage channel; 11. Filling and draining outlet; 2. Boundary water stabilization tank; 3. Porous permeable baffle; 4. Standard color mark reference component; 5. First water stabilization tank; 51. First water inlet pipe; 52. First drain pipe; 53. First servo control unit; 54. First connecting pipe; 55. First threaded rod; 56. First overflow plate; 6. Second water stabilization tank; 61. Second water inlet pipe; 62. Second drain pipe; 63. Second connecting pipe; 64. Second threaded rod; 65. Second overflow plate; 7. Pressure measuring plate; 8. Monitoring interface; 9. Image acquisition component; 91. Lighting frame; 92. Image sensor; 10. Slope protection plate; 101. Plate body; 102. Permeable hole; 103. Filter screen. Detailed Implementation

[0026] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings, which illustrate embodiments of the present application. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of this application will be thorough and complete.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0028] It should be noted that when one element is considered to be "connected" to another element, it can be directly connected to the other element or connected to the other element through an intermediary element. In the following embodiments, "connection" should be understood as "electrical connection," "communication connection," etc., if the connected circuits, modules, units, etc., have the transmission of electrical signals or data between them.

[0029] Example 1 like Figures 1-6 The groundwater flow and solute transport simulation test device shown includes a seepage tank 1, a boundary water stabilization tank 2, a porous permeable baffle 3, a standard color mark reference component 4, an image acquisition component 9, a slope protection board 10, and a water head monitoring component.

[0030] The seepage channel 1 is the main load-bearing structure of this device. It is a rectangular empty box. In this embodiment, it is 505cm long, 35cm wide and 150cm high. It adopts a combination structure of "transparent front and rigid back": the front is made of high-transmittance tempered glass with low optical distortion, which can provide a clear observation window for image acquisition and withstand the lateral pressure of sand and water. The back is made of high-strength steel plate with a 23-column × 8-row monitoring hole array on the plate, forming a two-dimensional monitoring profile covering different horizontal positions and vertical depths. Each monitoring hole is connected to an external monitoring interface 8.

[0031] Several filling and draining ports 11 are reserved on the side wall at the bottom of the seepage tank 1 for saturation filling during the experimental preparation stage and water drainage after the experiment. The combination of slow inlet and slow outlet operation can reduce the phenomenon of air blockage inside the medium.

[0032] The seepage channel 1 is filled with a permeable medium and piled up to form a natural sand slope. The slope of the sand slope is inclined along the length of the seepage channel, restoring the sedimentary topography of the natural coastal beach.

[0033] Technical Background: Natural coastal wetlands and beaches are mostly formed by the natural deposition of sediment under hydrodynamic forces, possessing continuous natural slopes. During tidal fluctuations, seawater rises and falls along the slope, a phenomenon known as the "dynamic boundary" effect in hydrogeology. Traditional simulation devices often employ straight, vertically cut boundaries, failing to reproduce the dynamic boundary process on the slope, leading to discrepancies between experimental results and actual conditions. This device, by constructing an inclined sand slope, provides a physical platform for simulating the realistic dynamic boundary process.

[0034] The permeable medium can be flexibly selected according to the experimental design objectives. It can be filled with quartz sand, or media with different particle sizes such as gravel and silt. It can also construct a layered heterogeneous structure to study the influence characteristics of different types of aquifers on tidal fluctuations and the transport patterns of pollutants. The particle size range, inhomogeneity coefficient (Cu), and permeability coefficient (K) of the medium can all be set according to the experimental objectives, and the device itself has wide media adaptability.

[0035] Two sets of boundary stabilizing tanks 2 are installed, located at both ends of the length of the seepage channel 1 (i.e., Figure 1 The width of the boundary 2 of a single set of water stabilizing tanks along its length is 20cm (on both sides of the center). The two sets of boundary water stabilizing tanks 2 are separated from the central sand-filling area by porous permeable baffles 3. The surface of the porous permeable baffles 3 is fully covered with fine mesh, and the pore size of the fine mesh is smaller than the minimum particle size of the permeable medium.

[0036] As an independent hydraulic buffer chamber, the boundary water stabilization tank can eliminate local turbulence in the incoming water flow, allowing the water head to be evenly transmitted to the sand filling section along the permeable baffle, thus preventing local high-speed water flow from scouring the sand body. The fine mesh screen, while ensuring smooth water flow and even water head transmission, prevents permeable medium particles from leaking into the water tank, maintaining the stability of the medium particle size distribution and pore structure in the sand filling area.

[0037] The slope protection board 10 is laid along the natural slope of the permeable medium and is a rigid permeable structure, including the board body 101, permeable holes 102, and filter screen 103. The permeable holes 102 are evenly distributed on the surface of the board body 101 to ensure smooth water exchange between the inside and outside of the slope and allow tidal water to freely enter and exit the pores of the slope. The slope protection board filter screen 103 covers the permeable holes 102. The pore size of the filter screen 103 is smaller than the minimum particle size of the permeable medium to prevent water from carrying sand particles out.

[0038] Tidal currents exert a continuous shearing and scouring effect on slopes. Unprotected natural sand slopes are prone to sand slippage and slope collapse under multi-cycle tidal action, leading to distorted boundary conditions. This slope protection panel 10 provides slope support through a rigid plate body, offsetting water scouring, while its permeable structure ensures unobstructed hydraulic connections. This significantly improves the long-term stability of the slope morphology without altering the seepage boundary, ensuring the repeatability of long-term experiments. Compared to exposed sand slopes, this structure significantly extends the duration of slope morphological stability, making it suitable for long-term observation of solute transport in multi-tidal cycles.

[0039] The standard color mark reference component 4 is set in the bottom area of ​​the front glass of the seepage tank, located inside or outside the seepage tank 1, preferably outside, and is made of transparent acrylic material. It contains multiple independent sealed chambers; each chamber is completely equidistant from the front glass and is entirely within the field of view of the image acquisition component 9.

[0040] Each chamber is filled with the same permeable medium as the main infiltration tank, and standard tracer solutions of different concentrations are injected, maintaining the same saturation level as the main tank. For accuracy, the standard color mark reference assembly in this embodiment comprises 37 independent chambers, with a standard color mark concentration range covering 0–1000 mg / L. 0 mg / L serves as a blank control, 20–1000 mg / L is the effective calibration range, and representative concentration points of 100, 300, 500, 700, and 1000 mg / L are retained. In practical implementation, multiple concentration levels can be configured according to actual needs, forming a continuous calibration gradient covering low, medium, and high concentrations.

[0041] By extracting color parameters such as Hue, Saturation, or Value from the standard color mark region, a color parameter-concentration calibration relationship under the current shooting conditions can be established in each frame of the image. Then, the color parameters of the pixels in the experimental flow field region are substituted into this relationship to invert the solute concentration. Compared with the traditional image method that only establishes a one-time color-concentration curve under a single fixed illumination condition, this scheme can synchronously correct color drift caused by changes in illumination intensity, exposure, and white balance with each image frame. The image acquisition component 9 is set facing the front of the seepage tank 1 and includes a surrounding supplementary lighting frame 91 and an image sensor 92: the surrounding supplementary lighting frame 91 is arranged parallel to the front of the seepage tank 1 and uses a uniform diffuse light source to form a uniform lighting environment without obvious shadows and reflections on the entire observation surface, eliminating the interference of local uneven illumination on color recognition; the image sensor 92 is located at the central axis of the supplementary lighting frame, and the lens optical axis is perpendicular to the front glass of the seepage tank, which can completely cover the standard color mark reference component and the entire sand slope flow field area.

[0042] The image sensor can be an industrial CCD or CMOS camera, supporting continuous acquisition at fixed intervals and externally triggered acquisition. The sampling frequency can be flexibly adjusted according to experimental requirements, taking into account both time resolution and storage space usage.

[0043] Head monitoring components The monitoring interface 8 on the back plate of the seepage channel 1 is connected to the pressure plate 7 on the top through a flexible hose. Based on the principle of communicating vessels, it can intuitively display the pressure head of each monitoring point, which is suitable for qualitative observation and manual reading scenarios.

[0044] The pressure plate 7 can be directly replaced by a pressure sensor array to automatically monitor changes in water head according to a set frequency. The sampling time interval of the pressure sensor is set to be less than the time interval of image capture to ensure accurate synchronization of water head data and image data in the time dimension, providing a time-matched data source for flow field-concentration field coupling analysis.

[0045] Example 2 The tidal generation system and the constant head water supply system are combined Figure 1 , Figure 3 , Figure 4 As shown, the tidal generation system is connected to the boundary stabilization tank 2 near the lower side of the sand slope, acting as the seaside boundary to drive periodic water level fluctuations; the constant head water supply system is connected to the boundary stabilization tank 2 near the higher side of the sand slope, providing a stable landside head boundary. Together, they constitute the hydraulic drive system of the model, simulating the coupled hydrological conditions of "tidal fluctuations + terrestrial groundwater discharge" under natural conditions.

[0046] The tidal generation system (sea side) includes a first water stabilization tank 5 (intelligent control water stabilization tank). The interior of the first water stabilization tank 5 is divided into a first zone and a second zone by a vertically arranged first overflow plate 56. The first zone is connected to a first water inlet pipe 51, and an external water supply device continuously and stably supplies water to the first zone through the first water inlet pipe. The second zone is connected to a first drain pipe 52 and a first connecting pipe 54. The other end of the first connecting pipe 54 is connected to the boundary water stabilization tank 2 on the sea side.

[0047] The first water tank 5 is connected to a first height adjustment mechanism on its side. The first height adjustment mechanism includes a first servo control unit 53 and a first threaded rod 55 that are connected by a transmission. The first servo control unit 53 drives the first threaded rod 55 to rotate, so that the first water tank 5 moves vertically up and down along the first threaded rod 55.

[0048] Working principle: External water supply continuously injects into the first zone. When the water level in the first zone is higher than the top elevation of the first overflow plate 56, the water overflows the overflow plate and enters the second zone. The second zone forms a communicating vessel structure with the boundary water stabilizing tank 2 through the first connecting pipe 54. Therefore, the equilibrium water level of the adjacent boundary water stabilizing tank 2 is always consistent with the top elevation of the first overflow plate 56. When the first servo control unit 53 drives the first water stabilizing tank 5 to rise or fall, the elevation of the first overflow plate 56 changes synchronously, thereby causing the water level of the boundary water stabilizing tank to rise or fall synchronously, realizing precise dynamic control of the seaside water level.

[0049] The first servo control unit has a built-in programmable control module that supports the import of custom tidal curves. It can output standard sinusoidal tides or reproduce irregular tidal processes measured on-site. The device uses the initial position of the water tank when it stops running as the average water level reference. The tidal amplitude and period can be flexibly set through the program without adjusting the hardware structure, thus adapting to the boundary requirements of different research scenarios.

[0050] The constant head water supply system (landside) includes a second water stabilization tank 6. The interior of the second water stabilization tank 6 is divided into a third zone and a fourth zone by a vertically arranged second overflow plate 65. The third zone is connected to the second inlet pipe 61, and external water is continuously supplied through the second inlet pipe. The fourth zone is connected to the second drain pipe 62 and the second connecting pipe 63. The other end of the second connecting pipe 63 is connected to the boundary water stabilization tank 2 on the landside. The second stable water tank 6 is connected to a second height adjustment mechanism. The second height adjustment mechanism includes a second servo control unit (not shown in the figure) and a second threaded rod 64 that are connected by a transmission. The second threaded rod 64 is connected to the second stable water tank 6. The second servo control unit drives the second threaded rod 64 to rotate, so that the second stable water tank 6 rises and falls, thereby changing the elevation of the second overflow plate 65 and finally setting the stable water level of the landside boundary.

[0051] Working principle: Under continuous water supply conditions, the water level remains stable at the top elevation of the second overflow plate 65. Excess water overflows the overflow plate and is discharged through the second drain pipe 62, thereby maintaining a constant head at the landside boundary. The landside water level is usually set higher than the average ocean water level to simulate the background hydraulic gradient of groundwater discharge from the land to the ocean under natural conditions; the specific water level elevation can be flexibly adjusted according to the requirements of the test plan.

[0052] Compared to the solution of directly controlling the water level using a peristaltic pump, this overflow plate type water tank structure has the advantages of high head stability, no water flow pulsation, and strong buffering capacity. It is especially suitable for simulating slowly changing tidal water level processes, avoiding the disturbance of fine particulate media by pump outlet pulsation, and ensuring the stability of the seepage field.

[0053] Example 3 Groundwater flow and solute transport simulation test monitoring and identification method, combined with Figure 7 As shown, this embodiment uses the above-mentioned device to carry out groundwater flow and solute transport experiments under tidal action, and completes high-precision monitoring and inversion of the concentration across the entire field.

[0054] The specific steps are as follows: S1, Medium loading, aquifer construction and color mark pre-setting The permeable medium is filled in layers in the seepage channel 1. The porosity and density of the medium are controlled by layer compaction and saturation settling, and a natural sand slope with a set slope is formed by piling it up. Water is slowly injected through the filling and draining ports 11 at the bottom of the tank, and the water level in the water stabilizing tanks on both sides gradually rises. The air bubbles inside the medium are discharged in a "bottom-up" saturation manner, so that the permeable medium reaches a completely saturated state. During the saturation process, the water inlet rate is strictly controlled to avoid rapid water inlet forming air blockage and affecting the seepage characteristics. Simultaneously, each independent chamber of the standard color mark reference component 4 is filled with the same permeable medium as the main tank, and a standard tracer solution of the corresponding concentration is injected to ensure that the medium in each chamber is saturated, free of air bubbles, and that the liquid level is consistent. In this embodiment, the tracer is preferably edible brilliant blue, which has stable color development, weak adsorption in quartz sand, and is environmentally friendly. It is a commonly used visual tracer for physical simulation of groundwater solute transport.

[0055] S2, Construction of Land-Sea Dynamic Boundary and Tidal Simulation The tidal generation system and the constant head water supply system were activated, and the tidal process on the sea side and the stable water level on the land side were set respectively. After the sea side water level fluctuations were buffered by the boundary water stabilization tank, they were evenly transmitted to the sand slope through the porous permeable baffle 3. The water flow acted on the sand slope surface through the permeable holes 102 and the filter screen 103 of the slope protection plate 10, forming a dynamic process of seawater rising and falling on the slope surface, realistically replicating the tidal dynamic boundary effect. After the system operated until the flow field reached dynamic stability, the periodic change law of the water head at each point was monitored by the pressure plate 7 or pressure sensor to verify the stability of the boundary conditions; at the same time, the slope morphology was observed, and if local scour occurred, fine adjustments could be made to ensure the stability of the slope morphology during the experiment.

[0056] S3, Tracer Injection and Image Acquisition After the flow field stabilizes, a visual tracer solution is injected into the designated location in the permeable medium. The tracer injection method can be flexibly selected according to the experimental objective, including various modes such as instantaneous point source, instantaneous line source, instantaneous surface source, continuous point source, continuous line source, and continuous surface source. In the instantaneous injection mode, a long needle with a diameter of 2mm is inserted into the medium at a preset depth to quickly inject a set volume of tracer solution. The thin needle can minimize the disturbance to the medium structure and flow field. In continuous injection mode, a peristaltic pump is connected to a syringe to continuously inject tracer at a constant rate to simulate a continuous leakage pollution source scenario.

[0057] To avoid the influence of wall-preferred flow (sidewall effect) on the experimental results, a long needle with uniformly perforated holes along the thickness direction can be used for injection, ensuring a uniform distribution of the tracer along the thickness direction of the seepage channel. Since the thickness-to-length ratio of this device is only 0.07, solute transport is predominantly longitudinal. By uniformly distributing injection holes along the thickness direction of the seepage channel, the initial distribution of the tracer in the thickness direction tends to be uniform, thus reducing the impact of the sidewall effect on the two-dimensional observation results. Simultaneously with tracer injection, the image acquisition component 9 is activated, continuously acquiring images at set time intervals. Each frame simultaneously includes both the standard color mark reference component area and the flow field area. The image sampling interval can be adjusted according to solute migration rate, tidal cycle, and data accuracy requirements. The head monitoring system is simultaneously activated, with the pressure sensor sampling frequency higher than the image acquisition frequency, ensuring that each frame of image has corresponding head data.

[0058] S4. Image Preprocessing and Same-Frame Calibration Image preprocessing: The acquired raw images are cropped, distortion corrected, perspective corrected, and coordinate transformed in sequence: irrelevant areas of the image are removed by cropping; lens distortion is corrected based on camera calibration parameters; perspective correction is performed using the calibration points on the front of the seepage channel to eliminate perspective distortion caused by the shooting angle; the image pixel coordinates are converted into the actual physical coordinates of the model so that the concentration inversion results can accurately correspond to the pressure measurement point location, water level line, and model geometry.

[0059] Color space conversion: Convert the preprocessed RGB image to the HSV color space. The HSV color space decomposes color information into three independent channels: hue, saturation, and value. Among them, the hue channel is much less affected by changes in light intensity than the RGB components, making it more suitable as a feature parameter for density inversion.

[0060] For edible brilliant blue tracers, the chromaticity Hue value is extracted first as the main color parameter. When there is interference such as uneven local illumination or background reflection in the image, threshold screening can be performed by combining saturation and brightness parameters to generate a tracer region mask, eliminate background interference, and improve inversion accuracy.

[0061] In-situ calibration within the same frame: Identify the independent chamber regions of the standard color mark reference component in the image and calculate the average chromaticity value of the effective pixels in each chamber. Since the tracer concentration in each chamber is known, multiple sets of "color parameter-concentration" sample points under the current shooting conditions can be obtained. By fitting, the color parameter-concentration calibration relationship corresponding to the current frame is established.

[0062] The calibration process is performed synchronously with each frame of the image, which is equivalent to completing an in-situ calibration every time the image is captured. This can offset the effects of light fluctuations, camera white balance drift, and changes in exposure parameters in real time, significantly improving the stability and reliability of concentration inversion in long-term experiments.

[0063] S5. Concentration field inversion and solute halo parameter extraction By substituting the color parameters of each pixel within the flow field region into the calibration relationship of the current frame, the tracer concentration value of the corresponding pixel is calculated, ultimately generating a two-dimensional concentration field (C=C(x,z,t)) for the entire flow field, where x is the horizontal coordinate, z is the vertical coordinate, and t is the shooting time. Based on the concentration field, isopleth maps of solute concentration at different times can be plotted, visually presenting the migration path, concentration decay, and diffusion range of the tracer under tidal action, and characterizing the transport characteristics of solute oscillating with groundwater flow. Based on the inverted concentration field, solute halo characteristic parameters are further extracted, and the quantitative definitions of each parameter are as follows: Solute halo boundary: 5% of the initial peak concentration is used as the contour boundary to define the effective influence range of the solute; this threshold can be flexibly adjusted according to the detection limit of the test tracer, and 5% is a commonly used value in the industry that takes into account both signal intensity and diffusion range; Leading position and trailing edge position: In the mainstream direction of solute transport, the coordinates of the farthest point reached by the solute halo boundary contour line are the leading position, and the coordinates of the last endpoint are the trailing edge position. These can be used to characterize the migration and propulsion distance of the solute and the magnitude of tidal fall. Centroid coordinates: Coordinates of the hypothetical concentration center point. The concentration center point is a hypothetical point on the concentration system where the concentration is considered to be concentrated; that is, the average position of the concentration distribution of a solute halo of a certain geometric shape. The calculation method for the concentration center point coordinates of the solute halo is as follows: Suppose a system of n particles, with concentrations of each particle being C1, C2, ..., C6. n If we use S1, S2, ..., S n Let represent the radius vectors of each particle in the system of particles relative to a fixed point (i.e., the origin of the coordinate system), and let S represent the radius vector of the center of mass.

[0064] Then there is .

[0065] Coordinates of the concentration center point (centroid coordinates) of the solute halo:

[0066]

[0067]

[0068] In the formula: This represents the concentration (mg / L) of the i-th concentration particle. Let and represent the radius vectors of the i-th concentration particle, respectively. In the coordinate system of this study, they can be specifically represented as... and It is described by the components of two coordinate axes, namely the radius vector (cm) of a certain concentration particle relative to the x-axis and z-axis; n is the total number of concentration particles used to calculate the concentration moment; It is the horizontal coordinate (cm) of the concentration center point G; It is the vertical coordinate (cm) of the concentration center point G; This is the concentration moment, where q is a constant, equal to 0 and 1 respectively. When q=0, This represents the sum of the concentrations of all particles. When q=1, This represents the sum of the products of the concentration of each particle and its radius vector.

[0069] The centroid coordinates can reflect the overall spatial position of the solute halo, eliminating the interference of local concentration fluctuations; Migration velocity: The centroid migration velocity, i.e. the displacement of the centroid coordinates per unit time, can be used to quantitatively characterize the overall migration rate of the solute. It can also be used to calculate the migration velocity during the high and low tide stages to analyze the tidal oscillation effect. Solute halo area: In a two-dimensional concentration field, the area enclosed by the contour lines of the solute halo boundary reflects the planar diffusion range of the solute.

[0070] By combining the above-mentioned solute halo parameters with the synchronously collected head data, we can systematically study the regulation mechanism of factors such as tidal amplitude, tidal period, landside hydraulic gradient, slope gradient, and medium permeability coefficient on groundwater flow and solute transport processes, and reveal the inherent law of solute "reciprocating" oscillatory transport under dynamic boundary conditions.

[0071] Selection of permeable media: Permeable media are not limited to quartz sand. They can be replaced with media of different particle sizes such as gravel, silt, and clay, or a layered heterogeneous media can be constructed, depending on the research objectives. The particle size range, non-uniformity coefficient, and permeability coefficient of the media can be flexibly set according to the experimental plan.

[0072] Tracer selection: Tracers are not limited to food-grade brilliant blue; other visual tracers such as rhodamine B and sodium fluorescein, which have stable color / fluorescence response and are not easily adsorbed into water-permeable media, can also be used. For fluorescent tracers, ultraviolet light sources and fluorescence imaging components can be used for data acquisition.

[0073] Color parameters and inversion models: Image color parameters are not limited to HSV chromaticity values, but can also use RGB single components, gray values, Lab color space parameters, or multi-channel combination parameters; the fitting model for density inversion is not limited to polynomial fitting, but can also use other models such as exponential functions, power functions, piecewise functions, lookup table interpolation, machine learning regression, etc.

[0074] Head monitoring methods: The pressure measurement system is not limited to pressure plates and pressure sensors. Other monitoring methods such as fiber optic grating sensors and distributed temperature sensors can also be used to achieve higher density head monitoring.

[0075] Tide generation method: The tide generation system is not limited to the lifting overflow plate type water stabilizing tank. Other controllable inlet and outlet devices such as peristaltic pump flow control, air pressure water level control, and servo push rod driven overflow weir can also be used to realize tidal water level simulation.

[0076] Slope protection board structural deformation: The shape, arrangement and opening ratio of the permeable holes of the slope protection board can be adjusted according to the particle size of the medium and the water flow conditions. Other rigid permeable materials such as permeable template cloth and porous ceramic plates can also be used. As long as the functions of slope protection and hydraulic exchange can be achieved at the same time, they all fall within the protection scope of this invention.

[0077] This invention, through a structural design of "sloping sandbank + slope protection board," achieves stable simulation of the dynamic boundary process of natural bank slopes in the physical model, reducing the disturbance of tidal reciprocating flow to the aquifer structure and maintaining the consistency of slope geometric boundaries during long-term experiments. This solves the problem of inconsistency between traditional vertical boundary models and actual coastal topography. The monitoring scheme of "same-image standard color mark + frame-by-frame in-situ calibration" sets the standard color mark reference component and the experimental flow field area within the same shooting field of view, and establishes a color parameter-concentration calibration relationship based on the current frame image. This corrects for color parameter shifts caused by changes in illumination, exposure, and white balance, maintaining the consistency of the concentration inversion benchmark at different times. This overcomes the technical bottlenecks of traditional image methods, which are susceptible to environmental interference and lack long-term accuracy. Simultaneously, it achieves synchronous high-precision monitoring of the head field and concentration field. The aforementioned structure and monitoring methods together improve the comparability, repeatability, and reliability of time series data from long-period tidal solute transport experiments. Furthermore, they can be combined with head data to analyze the coupling process between groundwater flow and solute transport, providing a reliable experimental platform and data support for the study of coastal groundwater flow and solute transport mechanisms.

[0078] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A simulation experimental device for groundwater flow and solute transport, characterized in that: Includes seepage channels, boundary water stabilization tanks, tidal generation systems, constant head water supply systems, and image acquisition components; The seepage channel is filled with a permeable medium to form a sand slope, and the slope surface of the sand slope is inclined along the length of the seepage channel. Two sets of boundary water stabilizing tanks are provided, and they are located at both ends of the seepage channel along its length. The two sets of boundary water stabilizing tanks are separated from the seepage channel by porous permeable baffles. The surface of the porous permeable baffles is covered with fine mesh that blocks the permeable medium. The tidal generation system is connected to a boundary water stabilization tank near the low side of the sand slope to drive water level fluctuations; The constant head water supply system is connected to a boundary stabilizing tank near the high side of the sand slope to provide a stable landside head boundary; The slope of the sand slope is provided with a slope protection board, and the slope protection board has water permeable holes on its surface. The water permeable holes are covered with a filter screen that blocks the water permeable medium. The vertical surface of the seepage channel located between the two sets of boundary water stabilization tanks is defined as the front side. The front side is made of transparent material. A standard color mark reference component is set inside or outside the front side. The standard color mark reference component contains multiple independent chambers. Each chamber is filled with the same water-permeable medium as the seepage channel and standard tracer solutions of different concentrations. The image acquisition component is positioned facing forward and is used to capture single-frame or continuous images that simultaneously include the standard color mark reference component and the sand slope flow field.

2. The groundwater flow and solute transport simulation experimental device according to claim 1, characterized in that, The tidal generation system includes a first water stabilizing tank, which is divided into a first zone and a second zone by a vertically arranged first overflow plate. The first zone is connected to a first inlet pipe, and the second zone is connected to a first drain pipe and a first connecting pipe. The other end of the first connecting pipe is connected to an adjacent boundary water stabilizing tank. The first water stabilizing tank is connected to a first height adjustment mechanism, which includes a first servo control unit and a first threaded rod that are connected by a transmission. The first threaded rod is connected to the first water stabilizing tank, and the first servo control unit drives the first threaded rod to rotate, thereby raising and lowering the first water stabilizing tank. The water level of the adjacent boundary water stabilizing tank is adjusted by changing the height of the first overflow plate.

3. The groundwater flow and solute transport simulation experimental device according to claim 1, characterized in that, The constant head water supply system includes a second water stabilizing tank. The second water stabilizing tank is divided into a third zone and a fourth zone by a vertically arranged second overflow plate. The third zone is connected to a second inlet pipe, and the fourth zone is connected to a second drain pipe and a second connecting pipe. The other end of the second connecting pipe is connected to an adjacent boundary water stabilizing tank. The second water stabilizing tank is connected to a second height adjustment mechanism, which includes a second servo control unit and a second threaded rod connected by a transmission connection. The second threaded rod is connected to the second water stabilizing tank, and the second servo control unit drives the second threaded rod to rotate, causing the second water stabilizing tank to rise and fall. The water level of the adjacent boundary water stabilizing tank is adjusted by changing the height of the second overflow plate.

4. The groundwater flow and solute transport simulation experimental device according to claim 1, characterized in that, The standard color mark reference component is made of transparent material. It is located near the front wall of the seepage tank and is simultaneously within the shooting range of the image acquisition component along with the experimental flow field area. They are illuminated by the same supplementary lighting frame to achieve color parameter calibration within the same frame.

5. The groundwater flow and solute transport simulation experimental device according to claim 1, characterized in that, The back of the seepage channel is equipped with a monitoring hole array, which is connected to a pressure plate or pressure sensor via a flexible hose to monitor water head data at different locations.

6. The groundwater flow and solute transport simulation experimental device according to claim 1, characterized in that, The image acquisition component includes a surround lighting frame parallel to the front of the seepage channel and an image sensor located in the middle of the lighting frame. The surround lighting frame is used to provide uniform illumination for shooting.

7. A method for monitoring and identifying groundwater flow and solute transport simulation experiments, using the groundwater flow and solute transport simulation experiment device as described in any one of claims 1-6, characterized in that, Includes the following steps: S1. Construct a sand slope with permeable medium in the seepage channel and saturate the permeable medium; fill each independent chamber of the standard color mark reference component with the same permeable medium and inject standard tracer solutions of different concentrations. S2. Start the tidal generation system and constant head water supply system to form a stable seepage field. The water flows through the slope protection board and acts on the permeable medium slope surface to simulate the dynamic boundary process of tidal rise and fall. S3. After the flow field stabilizes, inject a visual tracer into the permeable medium and start the image acquisition component to acquire continuous images that simultaneously include the standard color mark reference component and the flow field area. S4. Preprocess and convert the acquired images to color space, and extract the color parameters of the images; identify the image regions of each independent chamber in the standard color mark reference component, calculate the average color parameter value of each region, and establish the color parameter-concentration calibration relationship under the current shooting conditions by combining the known standard concentration of each chamber. S5. Substitute the color parameters of each pixel in the flow field region into the calibration relationship, and invert to obtain the tracer concentration value corresponding to each pixel, thereby generating the concentration field distribution of the entire flow field.

8. The method for monitoring and identifying groundwater flow and solute transport simulation experiments according to claim 7, characterized in that, The color space conversion in step S4 involves converting the preprocessed RGB image into the HSV color space, which includes hue, saturation, and value. When the image has local uneven lighting or background interference, tracer region identification and mask selection are performed by combining saturation and value parameters.

9. The method for monitoring and identifying groundwater flow and solute transport simulation experiments according to claim 7, characterized in that, Step S5 and the next steps include: based on the concentration field obtained by inversion, extracting parameters such as solute halo contour, concentration contour lines, solute halo area, centroid coordinates, front position, tail position, main migration direction, diffusion range, aspect ratio, and migration velocity, and then performing joint analysis with the head data obtained by the pressure plate or pressure sensor.

10. The method for monitoring and identifying groundwater flow and solute transport simulation experiments according to claim 7, characterized in that, The color parameters include HSV chromaticity values, RGB components, grayscale values, or Lab color space parameters; the concentration inversion employs polynomial fitting, exponential functions, power functions, piecewise functions, or lookup table interpolation models.

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