Experimental apparatus and method for simulating solute migration and transformation in heterogeneous riparian subsurface current zones

Abstract

This invention proposes an experimental apparatus for simulating solute migration and transformation in a heterogeneous riparian subsurface flow zone. The apparatus includes: a riparian simulation tank comprising several identical plexiglass components A and two identical plexiglass components B, wherein the left end of plexiglass component A is a dynamic head flume simulating river water, the middle part is a sand flume simulating a portion of the riparian subsurface flow zone, and the right end is a constant head flume simulating groundwater; a water level control system including a water supply component, a drainage component, and a water level control component; and a pore water sampling system including several water sample collection components buried within the sand flume. Compared with existing technologies, this invention, by increasing the number of plexiglass components A and filling their sand flumes with different types of sand to simulate the three-dimensional heterogeneity of riparian sediments, combined with the water level control and pore water sampling system, can study the spatiotemporal evolution of solute migration and transformation in the heterogeneous riparian subsurface flow zone and its influence on solute migration and transformation in the subsurface flow zone.

Description

Technical Field

[0001] This invention relates to the field of hydraulic engineering testing, and in particular to a test apparatus and method for simulating solute migration and transformation in heterogeneous riverbank subsurface current zones. Background Technology

[0002] The subsurface flow zone refers to the water-saturated sediment layer beneath the riverbed, extending to the riverbanks and both sides. It is a highly dynamic, permeable, and interconnected mixed area, serving as a habitat for microbial and invertebrate communities. Complex biogeochemical processes occur within the subsurface flow zone, playing a vital role in purifying water quality; hence, it is often referred to as the "liver of the river," and is crucial for maintaining and improving the structure and function of the river's ecosystem.

[0003] The composition and type of sediments in the subsurface flow zone significantly influence the biogeochemical reactions of soluble substances during subsurface flow exchange. Bank sediments often vary considerably across different rivers, river sections, and cross-sections, leading to complex and variable processes of solute migration and transformation during lateral subsurface flow exchange. Currently, in-situ monitoring is a common method for subsurface flow zone research; however, the environment of the riparian subsurface flow zone is complex, and solute migration and transformation during subsurface flow exchange are influenced by multiple factors, making it difficult to control in-situ experimental conditions and replicate the experimental process. Although indoor model experiments exhibit some size effect, compared to in-situ monitoring, they allow for controlled experimental conditions, repeatable experimental processes, and quantification of the influence of single factors on solute migration and transformation.

[0004] However, existing indoor models are usually fixed in size, which often makes it difficult to simulate the highly heterogeneous natural riparian subsurface flow zone. When the size is large, it is also difficult to perform sampling analysis, and the hydrodynamic boundary conditions are difficult to keep consistent in repeated experiments. Therefore, there is an urgent need to develop an experimental device suitable for indoor experiments to simulate solute migration and transformation in heterogeneous riparian subsurface flow zones, so as to realize the simulation of river water level fluctuations and control of characteristic parameters. At the same time, by adding plexiglass components, it is possible to simulate riparian sediments with a high degree of heterogeneity, and reveal the laws of solute migration and transformation in natural riparian subsurface flow zones through experiments.

[0005] Chinese patent CN114112300A discloses a simulation device and experimental method for lateral subsurface flow exchange in tidal riverbanks. The device includes: an acrylic glass tank comprising a left-end water tank, a middle sand tank, and a right-end water tank, used to simulate tidal channels, riverbanks, and offshore groundwater, respectively; a water level control system including a water supply component, a drainage component, an automatic water level control component, and a sliding water level control component; and a monitoring system including a monitoring tube, a conductivity sensor, a pore water pressure sensor, a conductivity acquisition instrument, a static strain gauge, and a siphon. However, this patent can only be used for lateral subsurface flow exchange studies in two-dimensional cross-sections (lateral-vertical), making it difficult to simulate heterogeneous riverbank subsurface flow exchange at a three-dimensional river segment scale (lateral-vertical-longitudinal). Furthermore, this patent can only be used for subsurface hydraulic exchange and the migration of conservative solutes (such as sodium chloride), but not for the migration and transformation of non-conservative solutes (such as ammonium salts) in the riverbank subsurface flow zone. Summary of the Invention

[0006] The purpose of this invention is to overcome the defects of the prior art by providing an experimental apparatus and method for simulating solute migration and transformation in heterogeneous riverbank subsurface current zones.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] An experimental apparatus for simulating solute migration and transformation in heterogeneous riparian subsurface currents, the apparatus comprising:

[0009] Riverbank simulation tank: It consists of an adjustable number of acrylic glass components A and two acrylic glass components B. The acrylic glass components A are equipped with a water-permeable baffle, which divides the internal space into a left-end dynamic head water tank, a middle sand tank and a right-end constant head water tank, which are used to simulate river water, part of the riverbank subsurface flow zone and groundwater, respectively. The two acrylic glass components B are located at the front end and rear end of the left-end dynamic head water tank of the connecting body of several acrylic glass components A.

[0010] Water level control system: including a dynamic head water supply assembly and a dynamic head drainage assembly connected to the plexiglass component B, a transparent adhesive scale on the left side panel of the plexiglass component A, and a constant head water supply assembly and a constant head drainage assembly connected to the constant head water tank at the right end of the plexiglass component A.

[0011] Pore ​​water sampling system: includes several spherical water sample collectors in a sand tank and a pump connected to them via a rubber tube.

[0012] In one embodiment of the present invention, the plexiglass component A and plexiglass component B, as well as adjacent plexiglass components A, are all connected by bolt anchoring, and a water-stop rubber pad is provided at the connection to ensure the airtightness of the riverbank simulation trough.

[0013] In one embodiment of the present invention, the inner wall of the plexiglass component A is provided with three sets of symmetrical slots, and the three permeable baffles are fixed on the slots.

[0014] In one embodiment of the present invention, the permeable baffle is a porous plexiglass plate, which is wrapped with nylon gauze to prevent the experimental sand from being washed into the water tanks on both sides of the riverbank simulation tank.

[0015] In one embodiment of the present invention, the intermediate sand trough is provided with a reverse filter material layer and a test sand layer. The reverse filter material layer is connected to the left end dynamic head water trough, and the test sand layer is connected to the right end constant head water trough.

[0016] In one embodiment of the present invention, after the plexiglass component A is anchored and connected in a certain number, all the dynamic head water tanks on the left end are combined into a long and narrow water tank to simulate a part of the river section, while the fixed head water tanks on the right end remain relatively independent to simulate the spatial distribution of groundwater level on the riverbank.

[0017] In one embodiment of the present invention, the bottom panel and the top of the front panel of the fixed-head water tank on the right end of the plexiglass component A are respectively provided with a second drain hole and a second water inlet. The second water inlet is connected to the fixed-head water supply component. The second drain hole is used for drainage and sand removal at the bottom of the fixed-head water tank. It is sealed with a rubber plug during the test. The right side panel of the fixed-head water tank is provided with an array of faucets.

[0018] In one embodiment of the present invention, the bottom of the plexiglass component A is provided with a support, and the front panel of the plexiglass component A is provided with an array of water sample collection holes, which are coated with silicone to maintain airtightness during the test.

[0019] In one embodiment of the present invention, the rear panel and the top of the front panel of the two plexiglass components B in the riverbank simulation tank are respectively provided with a water inlet and a water outlet. The water inlet is connected to the dynamic head water supply component, and the water outlet is connected to the dynamic head drainage component.

[0020] Both acrylic glass components B have a drainage hole on their bottom panel for draining water and removing sand from the combined water tank. The hole is sealed with a rubber plug during testing.

[0021] In one embodiment of the present invention, the dynamic water head water supply assembly includes an inlet pipe and a water supply tank. One end of the inlet pipe is connected to the water supply tank, and the other end of the inlet pipe is connected to the inlet. A water pump is provided on the inlet pipe.

[0022] In one embodiment of the present invention, the dynamic head drainage assembly includes a second drain pipe and a first wastewater tank. One end of the second drain pipe is connected to the first wastewater tank, and the second drain pipe is connected to a water outlet. A second water pump is provided on the second drain pipe.

[0023] In one embodiment of the present invention, the constant head water supply assembly includes a second water inlet pipe and a second water supply tank. One end of the second water inlet pipe is connected to the second water supply tank, and the other end of the second water inlet pipe is connected to a second water inlet. A third water pump and a multi-port pipe connector are sequentially provided on the end of the second water inlet pipe near the second water supply tank, so as to facilitate simultaneous water injection into the constant head water tanks on the right side of multiple acrylic glass components A.

[0024] In one embodiment of the present invention, the constant head drainage assembly includes a drain pipe and a wastewater tank. One end of the drain pipe is connected to the wastewater tank, and the other end of the drain pipe is connected to the right-side constant head water tank via an array of faucets.

[0025] In one embodiment of the present invention, the water sample collector includes a hollow sphere and a hollow tube, both of which are made of PVC. The hollow sphere has evenly distributed permeable holes on its surface and is wrapped with nylon gauze to prevent fine sand particles from entering. One end of the hollow tube is connected to the hollow sphere, and the other end of the hollow tube is connected to a water pump through a rubber tube. The rubber tube is provided with a water-stop clamp.

[0026] Furthermore, the present invention also provides a method for simulating solute migration and transformation in heterogeneous riparian subsurface current zones. The method is carried out using the above-mentioned experimental apparatus, and the specific steps are as follows:

[0027] S1. Setup of the test sand filling and pore water sampling system:

[0028] S1.1 Anchor the acrylic glass components A and B used in the test with bolts and water-stop rubber pads. The drainage holes 2 and 1 at the bottom of the riverbank simulation trough are sealed with rubber plugs.

[0029] S1.2. Gravel and sand of different particle sizes are filled into the filter material layer and the test sand layer respectively. When filling the sand, a certain number of water sample collectors are placed horizontally in the test sand layer, with the hollow part of the collector buried in the sand and the other end of the hollow tube protruding from the water sample collection hole. The hole is sealed with a gasket and silicone. The protruding end of the water sample collector is inserted into a relatively thin rubber tube so that the pump can collect the sample.

[0030] S1.3 After the gravel and sand filling is completed, a water injection-drainage cycle test is conducted on the middle sand trough of the simulated riverbank trough to ensure that the sand is fully compacted.

[0031] S2. Water level control and water sampling:

[0032] S2.1 Drain all the water from the riverbank simulation tank, close all the faucets on the right panel of the fixed head water tank at the right end of the plexiglass component A, turn on water pump three, and continuously supply distilled water to the fixed head water tank at the right end of the plexiglass tank at a flow rate of q1. The water passes through the test sand layer and the reverse filter layer and enters the dynamic head water tank at the left end to simulate the state of groundwater replenishing the river channel from the shore. When the water level in the fixed head water tank rises to the set height h0, open the faucet at the height of h0 to release the water, so as to ensure that the water level in the fixed head water tank is kept at the height of h0, simulating the groundwater on the far bank that is not affected by the fluctuation of the river water.

[0033] S2.2 Simultaneously turn on water pump one and water pump two. Water pump one continuously injects a solute solution of the set concentration from water supply tank one into the left-end moving head water tank at a flow rate of q2. Water pump two pumps water from the left-end moving head water tank to wastewater tank one at a flow rate of q3. The water level in the left-end moving head water tank continues to drop until it reaches the set low water level H. min At this time, water is collected from all water sample collectors buried in the left-end dynamic water head trough and the test sand layer to analyze the initial state of solute concentration in the test.

[0034] S2.3. Swap the flow rates of water pump one and water pump two, so that the flow rate of water pump one is q3 and the flow rate of water pump two is q2. The water level in the left-end moving head tank will continue to rise until it reaches the set high water level H. max Then, the flow rates of water pump one and water pump two are swapped, and the water level in the left-end moving head tank continues to drop until it reaches the set low water level H. min During the rise and fall of the water level, water samples were collected periodically from the water sampler in the left end dynamic head flume and the test sand layer.

[0035] S2.4. Step S2.3 can be repeated several times until the experiment ends;

[0036] S3. Experimental Data Processing and Analysis:

[0037] S3.1, Water sample data processing:

[0038] The concentrations of solutes and possible conversion products were measured in all collected water samples. Distribution maps of solute concentrations and possible conversion product concentrations in the pore water of the test sand layer for different plexiglass components A at different times were plotted. Curves of changes in solute concentrations and possible conversion product concentrations in the left-hand dynamic head water tank during water level fluctuations were plotted.

[0039] S3.2 Analysis of experimental data:

[0040] By comparing the permeability coefficients of the test sand in different glass components A and the concentration distribution of solute and possible transformation products at the same time, the influence of heterogeneous beach sediments on the range of solute migration and transformation during the lateral subsurface exchange of rivers is analyzed.

[0041] In one embodiment of the present invention, in step S1.1, the number of the plexiglass components A is determined according to the non-uniformity and complexity of the sediments in the simulated riverbank subsurface flow zone.

[0042] In one embodiment of the present invention, in step S1.2, both gravel and sand are filled using a layered compaction method.

[0043] In one embodiment of the present invention, in step S1.2, the number and spacing of the water sample collectors can be adjusted according to the specific test conditions.

[0044] In one embodiment of the present invention, in step S2.2, q3 > q2, H min <h0。

[0045] In one embodiment of the present invention, in step S2.3, H max >h0.

[0046] Compared with the prior art, the advantages of the present invention are as follows:

[0047] I. This invention can simulate the fluctuation of river water level by starting and stopping two water pumps and controlling the flow rate, and can control the characteristic parameters of the fluctuation (such as the amplitude and period of water level fluctuation).

[0048] Second, the present invention can adjust the number of components of the test device according to the test requirements, so as to realize the simulation study of the riverbank subsurface flow zone with a high degree of heterogeneity.

[0049] Third, the water sample collection device of this invention, which is deployed in the test sand layer, can obtain water samples in a closed environment. Compared with the traditional method of deploying monitoring wells to collect water samples, it can greatly suppress the changes in the redox environment of the subsurface flow zone caused by the long-term exposure of groundwater to the air, thereby improving the accuracy of solute migration and transformation research.

[0050] Fourth, the riverbank simulation trough components described in this invention are easy to disassemble and install, simple to operate, quick to clean the water trough and sand trough, easy to maintain, and have a long service life. Attached Figure Description

[0051] Figure 1 This is a schematic diagram of the structure of the present invention;

[0052] Figure 2 This is a schematic diagram illustrating the adjustment of the quantity of acrylic component A in this invention;

[0053] Figure 3 This is a front view of acrylic component A of the present invention;

[0054] Figure 4 This is a side view of acrylic component A of the present invention;

[0055] Figure 5 This is a top view of the acrylic glass component A of the present invention;

[0056] Figure 6 This is a front view of the acrylic glass component B of the present invention;

[0057] Figure 7 This is a side view of the plexiglass component B of the present invention;

[0058] Figure 8 This is a top view of the plexiglass component B of the present invention;

[0059] Figure 9 This is a single-unit diagram of the pore water sampling device of the present invention.

[0060] Explanation of reference numerals: 1. Acrylic glass component A; 2. Acrylic glass component B; 3. Bolt; 4. Water-stop rubber gasket; 5. Slot; 6. Permeable baffle; 7. Inlet 1; 8. Outlet; 9. Water sample collector; 10. Rubber hose; 11. Faucet; 12. Drainage pipe 1; 13. Support; 14. Water supply tank 1; 15. Inlet pipe 1; 16. Water pump 1; 17. Wastewater tank 1; 18. Drainage pipe 2; 19. Water pump 2; 20. Filter media layer; 21. Drainage hole 1; 22. Drainage hole 2; 23. Rubber plug; 24. Water sample collection hole; 25. Water-stop clamp; 26. Inlet 2; 27. Multi-port pipe joint; 28. Water pump 3; 29. ​​Water supply tank 2; 30. Test sand layer. 31. Two water inlet pipes; 32. Transparent adhesive ruler; 33. Water pump; 34. Two wastewater tanks. Detailed Implementation

[0061] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0062] In the description of this invention, it should be noted that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0063] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0064] An experimental apparatus for simulating solute migration and transformation in heterogeneous riparian subsurface currents, the apparatus comprising:

[0065] Riverbank simulation tank: It consists of an adjustable number of plexiglass components A1 and two plexiglass components B2. The plexiglass component A1 is equipped with a water-permeable baffle 6, which divides the internal space into a left-end dynamic head water tank, a middle sand tank and a right-end fixed head water tank, which are used to simulate river water, part of the riverbank subsurface flow zone and groundwater, respectively. The two plexiglass components B2 are located at the front and rear ends of the left-end dynamic head water tank of the connecting body of several plexiglass components A1.

[0066] Water level control system: including a dynamic head water supply component and a dynamic head drainage component connected to the plexiglass component B2, a transparent adhesive scale 32 provided on the left side panel of the plexiglass component A1, and a constant head water supply component and a constant head drainage component connected to the constant head water tank at the right end of the plexiglass component A1.

[0067] Pore ​​water sampling system: including several spherical water sample collectors 9 in a sand tank and a pump 33 connected to them via a rubber tube 10.

[0068] In one embodiment of the present invention, the plexiglass component A1, the plexiglass component B2, and the adjacent plexiglass component A1 are all anchored and connected by bolts 3, and a water-stop rubber pad 4 is provided at the connection to ensure the airtightness of the riverbank simulation trough.

[0069] In one embodiment of the present invention, the inner wall of the plexiglass component A1 is provided with three sets of symmetrical slots 5, and three permeable baffles 6 are fixed on the slots 5.

[0070] In one embodiment of the present invention, the permeable baffle 6 is a porous plexiglass plate, which is wrapped with nylon gauze to prevent the experimental sand from being washed into the water tanks on both sides of the riverbank simulation tank.

[0071] In one embodiment of the present invention, the intermediate sand trough is provided with a reverse filter material layer 20 and a test sand layer 30. The reverse filter material layer 20 is connected to the left end dynamic head water trough, and the test sand layer 30 is connected to the right end fixed head water trough.

[0072] In one embodiment of the present invention, after the plexiglass component A1 is anchored and connected in a certain number, all the dynamic head water tanks on the left end are combined into a long and narrow water tank to simulate a part of the river section, while the fixed head water tanks on the right end remain relatively independent to simulate the spatial distribution of groundwater level on the riverbank.

[0073] In one embodiment of the present invention, the bottom panel and the top of the front panel of the fixed-head water tank on the right end of the plexiglass component A1 are respectively provided with a second drain hole 22 and a second water inlet 26. The second water inlet 26 is connected to the fixed-head water supply component. The second drain hole 22 is used for drainage and sand removal at the bottom of the fixed-head water tank. It is sealed with a rubber stopper 23 during the test. The right side panel of the fixed-head water tank is provided with an array of faucets 11.

[0074] In one embodiment of the present invention, the bottom of the plexiglass component A1 is provided with a support 13, and the front panel of the plexiglass component A1 is provided with an array of water sample collection holes 24, which are coated with silicone to maintain airtightness during the test.

[0075] In one embodiment of the present invention, the rear panel and the top of the front panel of the two plexiglass components B2 in the riverbank simulation tank are respectively provided with an inlet 7 and an outlet 8. The inlet 7 is connected to the dynamic head water supply component, and the outlet 8 is connected to the dynamic head drainage component.

[0076] Both plexiglass components B2 have drainage holes 21 on their bottom panels for draining water and removing sand from the combined water tank. These holes are sealed with rubber plugs 23 during testing.

[0077] In one embodiment of the present invention, the dynamic water head water supply assembly includes an inlet pipe 15 and a water supply tank 14. One end of the inlet pipe 15 is connected to the water supply tank 14, and the other end of the inlet pipe 15 is connected to the inlet 7. A water pump 16 is provided on the inlet pipe 15.

[0078] In one embodiment of the present invention, the dynamic head drainage assembly includes a second drain pipe 18 and a first wastewater tank 17. One end of the second drain pipe 18 is connected to the first wastewater tank 17, and the second drain pipe 18 is connected to the outlet 8. A second water pump 19 is provided on the second drain pipe 18.

[0079] In one embodiment of the present invention, the constant head water supply assembly includes a second water inlet pipe 31 and a second water supply tank 29. One end of the second water inlet pipe 31 is connected to the second water supply tank 29, and the other end of the second water inlet pipe 31 is connected to a second water inlet 26. A third water pump 28 and a multi-port pipe joint 27 are sequentially provided on the end of the second water inlet pipe 31 near the second water supply tank 29, so as to facilitate simultaneous water injection into the constant head water tanks on the right side of multiple plexiglass components A1.

[0080] In one embodiment of the present invention, the constant head drainage assembly includes a drain pipe 12 and a wastewater tank 34. One end of the drain pipe 12 is connected to the wastewater tank 34, and the other end of the drain pipe 12 is connected to the right-side constant head water tank through an array of faucets 11.

[0081] In one embodiment of the present invention, the water sample collector 9 includes a hollow sphere and a hollow tube, both of which are made of PVC. The hollow sphere has evenly distributed permeable holes on its surface and is wrapped with nylon gauze to prevent fine sand particles from entering. One end of the hollow tube is connected to the hollow sphere, and the other end of the hollow tube is connected to the water pump 33 through a rubber tube 10. The rubber tube 10 is provided with a water-stopping clamp 25.

[0082] Furthermore, the present invention also provides a method for simulating solute migration and transformation in heterogeneous riparian subsurface current zones. The method is carried out using the above-mentioned experimental apparatus, and the specific steps are as follows:

[0083] S1. Setup of the test sand filling and pore water sampling system:

[0084] S1.1 Anchor the acrylic glass components A1 and B2 used in the test using bolts 3 and water-stop rubber pads 4. The drainage holes 22 and 21 at the bottom of the riverbank simulation trough are sealed with rubber plugs 23.

[0085] S1.2. Gravel and sand of different particle sizes are filled into the filter material layer 20 and the test sand layer 30 respectively. When filling the sand, a certain number of water sample collectors 9 are placed horizontally in the test sand layer 30, with the hollow part of the collector buried in the sand and the other end of the hollow tube protruding from the water sample collection hole 24. The hole is sealed with a gasket and silicone. The protruding end of the water sample collector 9 is inserted into a relatively thin rubber tube 10 so that the pump 33 can collect the sample.

[0086] S1.3 After the gravel and sand filling is completed, a water injection-drainage cycle test is conducted on the middle sand trough of the simulated riverbank trough to ensure that the sand is fully compacted.

[0087] S2. Water level control and water sampling:

[0088] S2.1. Drain all the water in the riverbank simulation tank. Close all the faucets 11 on the right panel of the constant head tank at the right end of the plexiglass component A1, and open the water pump three 28. Continuously supply distilled water to the constant head tank at the right end of the plexiglass tank at a flow rate of q1. The water enters the moving head tank at the left end through the test sand layer 30 and the filter layer 20, simulating the state of bank groundwater recharge to the river. When the water level in the constant head tank rises to the set height h0, open the faucet 11 with a height of h0 to discharge water, so as to ensure that the water level in the constant head tank remains at the height of h0, simulating the far bank groundwater not affected by river fluctuations;

[0089] S2.2. At the same time, open the water pump one 16 and the water pump two 19. The water pump one 16 continuously injects a solute solution with a set concentration into the moving head tank at the left end from the water supply tank one 14 at a flow rate of q2, and the water pump two 19 pumps water from the moving head tank at the left end to the waste water tank one 17 at a flow rate of q3 (q3>q2). The water level in the moving head tank at the left end continuously drops until it reaches the set low water level H min (H min <h0). At this time, collect the water in all the water sample collectors 9 buried in the moving head tank at the left end and the test sand layer 30 to analyze the initial state of the solute concentration in the experiment;

[0090] S2.3. Swap the flow rates of the water pump one 16 and the water pump two 19, that is, the flow rate of the water pump one 16 is q3, and the flow rate of the water pump two 19 is q2. The water level in the moving head tank at the left end continuously rises until it reaches the set high water level H max (H max >h0). Then swap the flow rates of the water pump one 16 and the water pump two 19 again. The water level in the moving head tank at the left end continuously drops until it reaches the set low water level H min During the rise and fall of the water level, regularly collect the water in the water sample collectors 9 in the moving head tank at the left end and the test sand layer 30;

[0091] S2.4. Repeat step S2.3 several times until the experiment ends;

[0092] S3. Experimental data processing and analysis:

[0093] S3.1. Collection of water sample data processing:

[0094] Measure the solute concentration and the concentration of possible transformation products of all the collected water samples, draw the distribution maps of the solute concentration and the concentration of possible transformation products in the pore water of the test sand layer 30 of different plexiglass components A1 at different times, and draw the change curves of the solute concentration and the concentration of possible transformation products in the moving head tank at the left end during the water level fluctuation process;

[0095] S3.2. Analysis of experimental data:

[0096] By comparing the permeability coefficients of the test sand in different glass components A1 and the concentration distribution of solute and possible transformation products at the same time, the influence of heterogeneous beach sediments on the range of solute migration and transformation during the lateral subsurface exchange of rivers is analyzed.

[0097] In one embodiment of the present invention, in step S1.1, the number of the plexiglass components A1 is determined according to the non-uniformity and complexity of the sediments in the simulated riverbank subsurface flow zone.

[0098] In one embodiment of the present invention, in step S1.2, both gravel and sand are filled using a layered compaction method.

[0099] In one embodiment of the present invention, in step S1.2, the number and spacing of the water sample collectors 9 can be adjusted according to the specific test conditions.

[0100] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0101] Example 1

[0102] refer to Figures 1 to 9 This embodiment provides an experimental apparatus and method for simulating solute migration and transformation in heterogeneous riverbank subsurface current zones.

[0103] like Figure 1 As shown, the present invention provides an experimental device for simulating solute migration and transformation in heterogeneous riverbank subsurface current zones. The device includes a riverbank simulation tank, a water level control system, and a pore water sampling system.

[0104] like Figure 1 and Figure 2 As shown, the simulated riverbank trough is constructed from an adjustable number of acrylic glass components A1 and two acrylic glass components B2, anchored together by bolts 3 and water-stop rubber pads 4. All acrylic glass components are made of 2cm thick acrylic glass sheets. Acrylic glass component A1 has an internal space 160cm long and 100cm high, with three symmetrical pairs of slots 5 on its front and rear inner walls. Each slot 5 has a wall thickness of 0.5cm. Three permeable baffles 6, each 1cm thick porous acrylic glass sheet, are vertically placed by inserting them into each pair of slots 5. The exterior of each baffle is secured with 8... Wrapped in 0-mesh nylon gauze, the internal space of the acrylic component A1 is divided into a left-end dynamic water head tank, a middle sand tank, and a right-end fixed water head tank by three permeable baffles 6. The internal space of the left-end dynamic water head tank is 20cm long and 42cm wide, the internal space of the right-end fixed water head tank is 19cm long and 20cm wide, the middle sand tank is further divided into a reverse filter material layer 20 and a test sand layer 30, with lengths of 7cm and 110.5cm respectively, and a width of 20cm for both. The internal space of the acrylic component B2 is 20cm long, 9cm wide, and 100cm high.

[0105] like Figures 1 to 8 As shown, inlet 7, outlet 8, drain hole 21, inlet 26, and drain hole 22 are all circular holes with a diameter of 2cm. Inlet 7, outlet 8, and drain hole 21 are located on the rear panel, front panel, and bottom plate of the dynamic head water tank at the left end of the riverbank simulation tank, respectively. Inlet 26 and drain hole 22 are located on the front panel and bottom plate of the fixed head water tank at the right end of the plexiglass component A1, respectively. The height of inlet 7, outlet 8, and inlet 26 is 95cm from the bottom surface of the tank. Drain hole 21 and drain hole 22 are used for drainage and sand removal in the combined water tank and are sealed with rubber plug 23 during the test.

[0106] like Figures 2 to 5 As shown, the bottom of the plexiglass component A1 is provided with multiple supports 13, and a transparent adhesive ruler 32 is attached to its left side panel. The front panel of the middle sand trough is provided with water sample collection holes 24 arranged in a 4-row x 5-column pattern. All of them are round holes with a diameter of 2cm, with a horizontal spacing of 20cm and a vertical spacing of 20cm. The water sample collector 9 is coated with silicone after it passes through to maintain airtightness.

[0107] like Figure 1 , Figure 3 , Figure 4 and Figure 5 As shown, the water level control system consists of a water supply / drainage assembly and a transparent adhesive ruler 32. The water supply / drainage assembly consists of a hose, inlet, outlet, water supply tank, wastewater tank, faucet, and water pump.

[0108] like Figure 1 , Figure 3 , Figure 4 and Figure 5 As shown, the dynamic water head water supply assembly includes an inlet pipe 15 and a water supply tank 14. One end of the inlet pipe 15 is connected to the water supply tank 14, and the other end of the inlet pipe 15 is connected to the inlet 7. A water pump 16 is provided on the inlet pipe 15.

[0109] The dynamic head drainage assembly includes a second drain pipe 18 and a first wastewater tank 17. One end of the second drain pipe 18 is connected to the first wastewater tank 17, and the second drain pipe 18 is connected to the outlet 8. A second water pump 19 is provided on the second drain pipe 18.

[0110] The constant head water supply assembly includes an inlet pipe 31 and a water supply tank 29. One end of the inlet pipe 31 is connected to the water supply tank 29, and the other end of the inlet pipe 31 is connected to the inlet 26. A water pump 28 and a multi-port connector 27 are sequentially provided on the end of the inlet pipe 31 near the water supply tank 29, which facilitates the simultaneous injection of water into the constant head water tanks on the right side of multiple acrylic glass components A1.

[0111] The constant head drainage assembly includes a drain pipe 12 and a wastewater tank 34. One end of the drain pipe 12 is connected to the wastewater tank 34, and the other end of the drain pipe 12 is connected to the right-side constant head water tank through an array of faucets 11.

[0112] Pump 16, Pump 29, and Pump 328 have the same flow range, with a maximum flow rate of 1.6 L / min and a minimum flow rate of 0.1 ml / min. The faucets are arranged in 8 rows x 3 columns, with a horizontal spacing of 5 cm and a vertical spacing of 10 cm.

[0113] like Figures 1 to 9 As shown, the pore water sampling system consists of a water sample collector 9 arranged in a 4-row x 5-column configuration, a rubber tube 10, and a pump 33.

[0114] like Figure 9 As shown, the water sample collector 9 is a hollow sphere and a hollow tube made of PVC. The inner diameter of the hollow sphere is 4 cm, and the hollow tube is 12 cm long with an inner diameter of 1.5 cm. The surface of the hollow sphere has evenly distributed perforations with a diameter of 2 mm, wrapped with 80-mesh nylon gauze to prevent fine sand particles from entering. The other end of the hollow tube is connected to the pump 33 via a rubber tube 10, which is equipped with a water-stop clamp 25. The pump 33 is a 20 ml plastic syringe.

[0115] In this example, the method using a simulated solute migration and transformation test apparatus in a heterogeneous riverbank subsurface current zone specifically includes the following steps:

[0116] Step 1: Setting up the test sand filling and pore water sampling system

[0117] Based on the type and distribution characteristics of sediments in the simulated riverbank subsurface flow zone, four plexiglass components A1 were selected, and four plexiglass components A2 and two plexiglass components B2 used in the experiment were anchored and formed by bolts 3 and water-stop rubber pads 4. All drainage and sand discharge holes at the bottom of the water tank were sealed with rubber plugs 23.

[0118] Well-graded gravel is filled into the filter media layer 20 of all plexiglass components A1. Then, sand of different particle sizes, such as medium sand, fine sand, and silt, is mixed evenly in different proportions and filled into the test sand layer 30 of different plexiglass components A1. Both gravel and sand are filled using a layered compaction method. When filling the sand, a certain number of water sample collectors 9 are placed horizontally in the test sand layer 30, with their hollow spheres buried in the sand. The other end of their hollow tubes protrudes from the water sample collection hole 24. The hole is sealed with a gasket and silicone. The protruding end of the water sample collector 9 is inserted into a relatively thin rubber tube 10 so that the pump 33 can collect the sample.

[0119] After the gravel and sand filling is completed, a water injection-drainage cycle test is conducted on the sand trough in the middle of the simulated riverbank trough to ensure that the sand is fully compacted.

[0120] Step 2: Water level control and water sampling

[0121] All water in the riverbank simulation tank is drained. All faucets 11 on the right panel of the fixed head water tank at the right end of the plexiglass component A1 are closed. Water pump 28 is turned on and distilled water is continuously supplied to the fixed head water tank at the right end of the plexiglass tank at a flow rate of q1. The water passes through the test sand layer 30 and the reverse filter layer 20 and enters the dynamic head water tank at the left end to simulate the state of groundwater replenishing the river channel from the beach. When the water level in the fixed head water tank rises to the set height h0, the faucets 11 at a height of h0 (40cm above the bottom of the tank) are opened to release the water to ensure that the water level in the fixed head water tank is kept at the height of h0, simulating the groundwater on the far bank that is not affected by the fluctuation of the river water.

[0122] Simultaneously, water pump 16 and water pump 2 19 are turned on. Water pump 16 continuously injects ammonium chloride solution with a set concentration of 50 mg / L from water supply tank 14 into the left-end moving head water tank at a flow rate of q2. Water pump 2 19 pumps water from the left-end moving head water tank to wastewater tank 17 at a flow rate of q3 (q3>q2). The water level in the left-end moving head water tank continues to drop until it reaches the set low water level H. min (20cm above the bottom of the tank), at this time, collect water from all the water sample collectors 9 buried in the left end dynamic water head tank and the test sand layer 30 to analyze the concentration of ammonia nitrogen and nitrate nitrogen in the tank and sand tank at the beginning of the test;

[0123] When the flow rates of water pump 16 and water pump 2 are interchanged, i.e., the flow rate of water pump 16 is q3 and the flow rate of water pump 2 is q2, the water level in the left-end moving head tank continues to rise until it reaches the set high water level H. max (70cm above the bottom of the tank), then swap the flow rates of water pump 16 and water pump 29. The water level in the tank at the left end of the moving head will continue to drop until it reaches the set low water level H. min During the rise and fall of the water level, water samples were collected periodically from the water sampler 9 in the left end dynamic head water tank and the test sand layer 30;

[0124] Step 3: Experimental Data Processing and Analysis

[0125] The concentrations of ammonia nitrogen and nitrate nitrogen in all collected water samples were determined by Nessler's reagent spectrophotometry and ion chromatography, respectively. Distribution maps of ammonia nitrogen and nitrate nitrogen concentrations in the pore water of the test sand layer 30 of different plexiglass components A1 at different times were plotted. Curves of ammonia nitrogen and nitrate nitrogen concentration changes in the left end water tank during water level fluctuations were plotted.

[0126] By comparing the permeability coefficients of the test sand in different glass components A1 and the concentration distributions of ammonia nitrogen and nitrate nitrogen at the same time, the influence of heterogeneous beach sediments on the migration range and transformation of ammonia nitrogen during the lateral subsurface exchange process of the river is analyzed.

[0127] The undescribed parts of this invention are the same as or implemented using existing technology.

[0128] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. An experimental apparatus for simulating solute migration and transformation in heterogeneous riverbank subsurface current zones, characterized in that, The test apparatus includes: Riverbank simulation tank: It consists of an adjustable number of plexiglass components A (1) and two plexiglass components B (2). The plexiglass component A (1) is equipped with a permeable baffle (6) to divide the internal space into a left-end dynamic head water tank, a middle sand tank and a right-end fixed head water tank, which are used to simulate river water, part of the riverbank subsurface flow zone and groundwater, respectively. The two plexiglass components B (2) are located at the front end and rear end of the left-end dynamic head water tank of the connecting body of several plexiglass components A (1); Water level control system: including a dynamic head water supply component and a dynamic head drainage component connected to the plexiglass component B (2), a transparent adhesive scale (32) provided on the left side panel of the plexiglass component A (1), and a constant head water supply component and a constant head drainage component connected to the constant head water tank at the right end of the plexiglass component A (1). Pore ​​water sampling system: including several spherical water sample collectors (9) in a sand tank and a pump (33) connected to them via a rubber tube (10); The intermediate sand trough is provided with a reverse filter material layer (20) and a test sand layer (30). The reverse filter material layer (20) is connected to the left end dynamic water head trough, and the test sand layer (30) is connected to the right end fixed water head trough. After the organic glass component A (1) is anchored and connected in a certain number, all the dynamic head water tanks on the left end are combined into a narrow water tank to simulate part of the river section, while the fixed head water tank on the right end remains relatively independent to simulate the spatial distribution of groundwater level on the riverbank. The water sample collector (9) includes a hollow sphere and a hollow tube. Both the hollow sphere and the hollow tube are made of PVC. The surface of the hollow sphere is provided with evenly distributed permeable holes. It is wrapped with nylon gauze to prevent fine sand particles from entering. One end of the hollow tube is connected to the hollow sphere, and the other end of the hollow tube is connected to the pump (33) through a rubber tube (10). The rubber tube (10) is provided with a water-stop clamp (25).

2. The experimental apparatus for simulating solute migration and transformation in heterogeneous riverbank subsurface current zones according to claim 1, characterized in that, The plexiglass component A (1) and plexiglass component B (2) as well as the adjacent plexiglass component A (1) are all anchored and connected by bolts (3), and a water-stop rubber pad (4) is set at the connection to ensure the airtightness of the riverbank simulation trough.

3. The experimental apparatus for simulating solute migration and transformation in heterogeneous riverbank subsurface current zones according to claim 1, characterized in that, The inner wall of the plexiglass component A (1) is provided with 3 sets of symmetrical slots (5), and 3 permeable baffles (6) are fixed on the slots (5); The permeable baffle (6) is a porous organic glass plate, which is wrapped with nylon gauze to prevent the experimental sand from being washed into the water tanks on both sides of the riverbank simulation tank.

4. The experimental apparatus for simulating solute migration and transformation in heterogeneous riverbank subsurface current zones according to claim 1, characterized in that, The bottom of the plexiglass component A (1) is provided with a support (13), and the front panel of the plexiglass component A (1) is provided with an array of water sample collection holes (24). During the test, silicone is coated to maintain airtightness.

5. The experimental apparatus for simulating solute migration and transformation in heterogeneous riverbank subsurface current zones according to claim 1, characterized in that, The bottom panel and the top of the front panel of the fixed head water tank on the right end of the plexiglass component A (1) are respectively provided with a drain hole two (22) and a water inlet two (26). The water inlet two (26) is connected to the fixed head water supply component. The drain hole two (22) is used for drainage and sand removal at the bottom of the fixed head water tank. It is sealed with a rubber stopper (23) during the test. The right side panel of the fixed head water tank is provided with an array of faucets (11). The two organic glass components B (2) in the riverbank simulation tank are provided with an inlet (7) and an outlet (8) on the top of the rear panel and the front panel, respectively. The inlet (7) is connected to the dynamic head water supply component, and the outlet (8) is connected to the dynamic head drainage component. Both of the two plexiglass components B (2) have drainage holes (21) on their bottom panels for draining and removing sand from the combined water tank. During the test, they are sealed with rubber plugs (23).

6. The experimental apparatus for simulating solute migration and transformation in heterogeneous riverbank subsurface current zones according to claim 5, characterized in that, The moving head water supply assembly includes an inlet pipe (15) and a water supply tank (14). One end of the inlet pipe (15) is connected to the water supply tank (14), and the other end of the inlet pipe (15) is connected to the inlet (7). A water pump (16) is provided on the inlet pipe (15). The dynamic head drainage assembly includes a second drain pipe (18) and a first wastewater tank (17). One end of the second drain pipe (18) is connected to the first wastewater tank (17), and the second drain pipe (18) is connected to the outlet (8). A second water pump (19) is provided on the second drain pipe (18). The constant head water supply assembly includes a second water inlet pipe (31) and a second water supply tank (29). One end of the second water inlet pipe (31) is connected to the second water supply tank (29), and the other end of the second water inlet pipe (31) is connected to the second water inlet (26). The end of the second water inlet pipe (31) near the second water supply tank (29) is provided with a third water pump (28) and a multi-port pipe joint (27) to facilitate simultaneous water injection into the constant head water tanks on the right side of multiple plexiglass components A (1). The constant head drainage assembly includes a drain pipe (12) and a wastewater tank (34). One end of the drain pipe (12) is connected to the wastewater tank (34), and the other end of the drain pipe (12) is connected to the right-side constant head water tank through an array of faucets (11).

7. A method for simulating solute migration and transformation in heterogeneous riverbank subsurface current zones, characterized in that, The method is performed using the test apparatus as described in any one of claims 1-6, and the specific steps are as follows: S1. Setup of the test sand filling and pore water sampling system: S1.1 Anchor the acrylic glass component A (1) and acrylic glass component B (2) used in the test by bolts (3) and water-stop rubber pads (4). The drainage holes 2 (22) and 1 (21) at the bottom of the riverbank simulation trough are sealed with rubber plugs (23). S1.

2. Gravel and sand of different particle sizes are filled into the filter material layer (20) and the test sand layer (30) respectively. When filling the sand, a certain number of water sample collectors (9) are placed horizontally in the test sand layer (30). The hollow part of the collector is buried in the sand, and the other end of the hollow tube is passed through the water sample collection hole (24). The hole is sealed with a gasket and silicone. The protruding end of the water sample collector (9) is inserted into a relatively thin rubber tube (10) so that the pump (33) can collect the sample. S1.3 After the gravel and sand filling is completed, a water injection-drainage cycle test is conducted on the middle sand trough of the simulated riverbank trough to ensure that the sand is fully compacted. S2. Water level control and water sampling: S2.1 Drain all the water in the riverbank simulation tank, close all the taps (11) on the right side panel of the fixed head water tank at the right end of the plexiglass component A (1), turn on the water pump three (28), and continuously supply distilled water to the fixed head water tank at the right end of the plexiglass tank at a flow rate of q1. The water enters the dynamic head water tank at the left end through the test sand layer (30) and the reverse filter layer (20) to simulate the state of the groundwater on the shore replenishing the river. When the water level of the fixed head water tank rises to the set height h0, open the tap (11) at the height of h0 to release the water, so as to ensure that the water level of the fixed head water tank is kept at the height of h0, and simulate the groundwater on the far shore that is not affected by the fluctuation of the river water. S2.2 Simultaneously turn on water pump one (16) and water pump two (19). Water pump one (16) continuously injects a solute solution of a set concentration from water supply tank one (14) to the left end moving head water tank at a flow rate of q2. Water pump two (19) pumps water from the left end moving head water tank to wastewater tank one (17) at a flow rate of q3. The water level in the left end moving head water tank continues to drop until it reaches the set low water level H. min At this time, water is collected from all water sample collectors (9) buried in the left end dynamic water head water tank and the test sand layer (30) to analyze the initial state of solute concentration in the test. S2.

3. The flow rates of water pump one (16) and water pump two (19) are reversed, that is, the flow rate of water pump one (16) is q3 and the flow rate of water pump two (19) is q2. The water level in the left end moving head tank continues to rise until it reaches the set high water level H. max Then, the flow rates of water pump one (16) and water pump two (19) are interchanged, and the water level in the left end moving head tank continues to drop until it reaches the set low water level H. min During the rise and fall of the water level, water samples were collected periodically from the water sampler (9) in the left end dynamic head water tank and the test sand layer (30); S2.

4. Step S2.3 can be repeated several times until the experiment ends; S3. Experimental Data Processing and Analysis: S3.1, Water sample data processing: The concentrations of solutes and possible conversion products were measured for all collected water samples. The distribution of solute concentrations and possible conversion product concentrations in the pore water of the test sand layer (30) of different organic glass components A (1) at different times was plotted. The change curves of solute concentrations and possible conversion product concentrations in the left end dynamic head water tank during the water level fluctuation were plotted. S3.2 Analysis of experimental data: By comparing the permeability coefficient of the test sand in different glass components A(1) and the concentration distribution of solute and possible transformation products at the same time, the influence of heterogeneous beach sediments on the range of solute migration and transformation during the lateral subsurface exchange of the river is analyzed.

8. The method for simulating solute migration and transformation in heterogeneous riparian subsurface current zones according to claim 7, characterized in that, In step S1.1, the number of the plexiglass component A (1) is determined according to the heterogeneity and complexity of the sediments in the simulated riverbank subsurface flow zone; In step S1.2, both gravel and sand are filled using a layered compaction method; In step S1.2, the number and spacing of the water sample collectors (9) can be adjusted according to the specific test conditions; In step S2.2, q3 > q2, H min < h0; In step S2.3, H max >h0.

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