1. The utility model provides a simulation is indoor sand groove experimental apparatus of riverside groundwater exploitation which characterized in that: the device comprises a water supply system (A), a sand tank (B), a river channel simulation device (C), a dissolved oxygen monitoring module (D), an excretion system (E) and a pressure monitoring module (F):

the water supply system (A) consists of a liquid supply box (1), a water pump (2), a plurality of guide pipes (3) and a flowmeter (4), wherein the liquid supply box (1) is used for storing solution required by an experiment, the water pump (2) and the flowmeter (4) are sequentially connected through the guide pipes (3) and then are connected with a water inlet hole (11) in the side wall of the sand tank, the water pump (2) is used for controlling infiltration speed, and the flowmeter (4) is used for monitoring infiltration flow through a river channel simulation device in the experiment process;

the sand tank (B) is vertically arranged, the interior of the sand tank is divided into a left subchamber (B1), a middle subchamber (B2) and a right subchamber (B3) from left to right, the left subchamber (B1) is a water head height adjusting device and is connected with a water supply system (A), the middle subchamber (B2) is a sand tank main body part and is used for filling undisturbed riverbed sediments and aquifer media in a field, the right subchamber (B3) is a device for simulating a field mining well and is connected with a drainage system (E), the left subchamber (B1) and the middle subchamber (B2) are separated by a water permeable plate (6) and a water-stop plate (9), the water permeable plate (6) is positioned at the upper part, and the water-stop plate (9) is positioned at the lower part; the right sub-chamber (B3) and the middle sub-chamber (B2) are separated by a water permeable plate (6), and a plurality of water permeable holes are uniformly and densely distributed on the water permeable plate (6);

a water inlet hole (11) and a plurality of first water outlet holes (5) are distributed on the side wall of the left sub-chamber (B1) of the sand tank (B), wherein the water inlet (11) is positioned at the lower end of the side wall of the sand tank (B) and is connected with the liquid supply tank (1), used for providing liquid required by the experiment for the sand tank (B), a plurality of first water outlet holes (5) are positioned at different heights at the upper end of the side wall of the left sub-chamber (B1) of the sand tank (B), the water level of different river waters is controlled by opening the first water outlet hole (5) with the response height, the lower end of the side wall of the right sub-chamber (B3) of the sand tank (B) is provided with a second water outlet hole (16), the second water outlet hole (16) is communicated with the Mariotte bottle (14), the second water outlet hole (16) is connected with the Mariotte bottles (14) with different heights to control the drainage water level, the drainage water level of the Mariotte bottle (14) is lower than that of the first water outlet hole (5), and the water head difference between the river waters and the drainage water level is used as a driving force to promote the river waters to infiltrate and supply groundwater;

the river channel simulation device (C) is positioned at the upper left part of a middle sub-chamber (B2) of the sand tank (B), the bottom of the river channel simulation device (C) is an inclined water permeable plate (6), the inclined water permeable plate (6) is a simulated river channel, the slope of the river channel is simulated by scaling according to the river bed sediment structure under natural conditions, the left side, the right side and the lower side of the river channel simulation device (C) are the water permeable plates (6) and are used for simulating the vertical infiltration and lateral infiltration processes of the river, and siltation layers (7) with different thicknesses are paved on the simulated river channel of the river channel simulation device (C) so as to simulate different erosion and deposition degrees of the river;

the dissolved oxygen monitoring module (D) is composed of a dissolved oxygen diaphragm (20), an optical fiber data collector (12) and a dissolved oxygen data processing system (13), wherein the dissolved oxygen diaphragm (20) is adhered to the inner wall of the sand tank (B) at a position close to the pore water sampling hole (8), one end of the optical fiber data collector (12) is connected with the dissolved oxygen data processing system (13), one end of the optical fiber data collector (12) is vertically irradiated on the dissolved oxygen diaphragm (20), the optical fiber data collector (12) can automatically record the measurement information of the dissolved oxygen diaphragm (20) in real time and transmit the data to the dissolved oxygen data processing system (13), and the dissolved oxygen data processing system (13) automatically converts the received signals into dissolved oxygen concentration information according to the temperature and pressure changes in the experimental process, so that the in-situ monitoring of the dissolved oxygen concentration is realized;

the drainage system (E) consists of a Mariotte bottle (14) and a height adjusting device (15), and the Mariotte bottle (14) is placed on the height adjusting device (15); the height of the Mariotte bottle (14) is adjusted and the Mariotte bottle is connected with a second water outlet hole (16) of the sand tank (B) to control different drainage water levels;

the pressure monitoring module (F) is composed of a pressure transmitter, a pressure data collector (18) and a pressure data processing system (19), the pressure transmitter is arranged in a pressure sensor arrangement hole (17) of the sand tank (B), one end of the data collector (18) is connected with the pressure sensor, the other end of the data collector (18) is connected with the pressure data processing system (19), the measuring electrode can monitor the change condition of the water content in the sand tank and transmit the information to the pressure data collector (18), the pressure data collector (18) can automatically record the measuring information of the electrode in real time and transmit the data to the pressure data processing system (19), and the pressure data processing system (19) converts the received signals into pressure information, so that the in-situ monitoring of the change condition of the pressure in the sand tank is realized.

2. The experimental method of the indoor sand tank experimental facility for simulating the underground water exploitation of the riverside as claimed in claim 1, is characterized in that: the method comprises the following steps:

1) and sticking the dissolved oxygen membrane: the black side of the dissolved oxygen membrane (20) is in contact with a medium, the pink/green side is adhered to the inner wall of the sand tank (B), the dissolved oxygen membrane is placed for 12 hours after the adhesion is finished, the glue is completely dried, if the dissolved oxygen membrane (20) comes from the same batch, only one sensor needs to be calibrated according to the specification, and each sensor does not need to be calibrated independently;

2) and filling the sand tank: the gauze is stuck on the permeable plates (6) at the two sides of the middle part subchamber (B1) in advance to prevent the medium particles from blocking the permeable holes; according to the actual field riverbed sediment and aquifer structure, selecting the field riverbed sediment and an aqueous medium as filling media of the simulation tank, and simultaneously filling according to the natural volume weight of the field riverbed sediment and the aquifer medium; the siltation layer (7) is compacted once every 5cm of height is filled, so that gap and crack are avoided, priority flow is prevented, and the medium in the simulation tank is close to the riverbed sediment and aquifer medium in a natural state to the maximum extent;

3) and arranging a pressure transmitter: connecting all the electrodes with a data collector (18) and calibrating; setting the electrode arrangement depth in advance, synchronously embedding a pressure transmitter into an arrangement hole (17) of a pressure sensor on the side wall of the experimental groove in the filling process of the sand groove (B), and filling other parts of the sand groove (B) with a medium after the electrode with a certain depth is arranged, so that the formation of a large pore in the sand groove (B) is avoided, the preferential flow is caused, and the measurement error is further caused;

4) and water saturation of the sand tank: after the sand tank (B) is filled, a water inlet hole (11) at the bottom of a water inlet area is connected with a liquid supply tank (1) by a guide pipe (3), the speed of a water pump (2) is controlled, ultrapure water is slowly fed from bottom to top, the ultrapure water is water which is fed with argon for a period of time and ensures that the oxygen concentration is less than 0.2mg/L, when water flows out of an underground water sampling hole (10), a water stop clamp is closed, water supply continues after the water head in the sand tank (B) rises by 5cm every time, the air in the sand tank (B) is completely exhausted, and the water supply continues after the sand tank (B) is saturated with water;

5) and injecting a tracer: connecting a sand tank (B) with a water supply system (A) and an excretion system (E), fixing the height of a first water outlet (5) of the sand tank (B), adjusting the height of a second water outlet (16) of the sand tank (B) to control the seepage gradient of river water, wherein a tracer is NaCl, preparing NaCl solution with preset concentration under the conditions of a given river level and an excretion level, and introducing the NaCl solution into a seepage tank at a preset speed by using a water pump (2);

6) collecting, testing and processing samples: after the tracer is injected, the sampling and testing work can be started, the sampling time interval is selected according to the seepage velocity, the seepage velocity is calculated through the amount of water discharged by a second water outlet (16) of the sand tank (B), the seepage velocity is high, the set sampling time interval is small, and otherwise, the time interval can be increased; after the sample is collected, measuring the conductivity until the conductivity in the pore water sampling hole (8) and the underground water sampling hole (10) reaches the peak value and is stable and unchanged; processing the acquired data to respectively obtain concentration change conditions of different positions at the same time and different times at the same position, drawing a concentration contour map, observing tracer migration conditions and determining distribution ranges of a dispersion zone, a transition zone and a convection zone;

7) and washing the sand tank: after the experiment is finished, deionized water is used for replacing a tracer solution and continuously introduced into the sand tank (B), the introduction speed is controlled by using the water pump (2), and the conductivity of the seepage liquid of the pore water sampling hole (8) and the underground water sampling hole (10) is detected until the conductivity data is reduced to be below a background value, which indicates that the washing process is finished;

8) injecting and monitoring experimental water: in the experimental process, a seepage water source is configured according to the actually measured river water chemical index, the configured seepage solution is used for replacing deionized water and is led into a sand tank (B), the height of a first water outlet hole (5) of the sand tank (B) is fixed, and the height of a second water outlet hole (16) of the sand tank (B) is adjusted to control the river water seepage speed;

9) and collecting and testing samples: in the experimental process, a dissolved oxygen membrane (20) is used for monitoring the oxygen concentration in the sand tank (B) in real time, setting the sampling frequency and testing the concentration of relevant indexes, the seepage velocity and other relevant index change rules are synchronously monitored in the experimental process, and the change rules of the relevant indexes of the simulated river and the simulated water outlet are tested at the same time; and after the experiment is finished, collecting sediment medium samples in a layering position, and testing the change rule of the relevant indexes.

3. The experimental method of the indoor sand tank experimental facility for simulating the underground water mining of the riverside according to the claim 2, is characterized in that: gauze is stuck on both sides of the permeable plate (6) with 100 meshes; the thickness of the coating (7) is set to be 2cm, 3cm and 5cm respectively, and the average particle size of the coating (7) is set to be 20 mu m.

Background

River mining, as a main human activity for changing hydrodynamic conditions of river water and underground water, can strongly influence the hydraulic connection between the river water and the underground water, and is influenced by river scouring and silting effects, so that the infiltration strength, the water retention time, the nutrient flux and the redox conditions of the river water can be changed, and the biogeochemical process in the river water infiltration process is complicated. In addition, due to the action of physical, chemical and biological gradients in the river infiltration process, the ferromanganese related minerals in the sediments can generate reductive dissolution under the anaerobic condition, so that ferromanganese ions and toxic and harmful metalloids As are released into underground water, and the water quality safety of the underground water is threatened.

The composition, the structure and the thickness of the riverbed sediments are dynamically changed under the field condition, the operation mode and the exploitation amount of the exploitation well are diversified, and a large amount of manpower and material resources are consumed for systematically exploring the pollution migration and transformation rule. In addition, at present, under the heterogeneous conditions of riverbed sediments and aquifers, river water-underground water hydraulic connection and related biogeochemical process changes under the combined action of riverbed dredging and underground water mining are not clear.

Disclosure of Invention

The invention provides an indoor sand tank experimental device for simulating riverside underground water exploitation, which comprises a water supply system, a sand tank, a riverway simulation device, a dissolved oxygen monitoring module, a drainage system and a pressure monitoring module, wherein the water supply system comprises a water tank, a sand tank, a riverway simulation device, a dissolved oxygen monitoring module, a drainage system and a pressure monitoring module, and the water supply system comprises:

the water supply system consists of a liquid supply tank, a water pump, a plurality of guide pipes and a flowmeter, wherein the liquid supply tank is used for storing a solution required by an experiment, the liquid supply tank is sequentially connected with the water pump and the flowmeter through the guide pipes and then is connected with a water inlet hole in the side wall of the sand tank, the water pump is used for controlling infiltration speed, and the flowmeter is used for monitoring infiltration flow passing through a river channel simulation device in the experiment process;

the sand tank is vertically arranged, the interior of the sand tank is divided into a left subchamber, a middle subchamber and a right subchamber from left to right, the left subchamber is a water head height adjusting device and is connected with a water supply system, the middle subchamber is a main body part of the sand tank and is used for filling undisturbed riverbed sediments and aquifer media of a site, the right subchamber is a device for simulating a site exploitation well and is connected with a drainage system, the left subchamber and the middle subchamber are separated by a water permeable plate and a water-stop baffle, the water permeable plate is positioned at the upper part, and the water-stop baffle is positioned at the lower part; the right sub-chamber and the middle sub-chamber are separated by a permeable plate, and a plurality of permeable holes are uniformly and densely distributed on the permeable plate;

the side wall of the left sub-chamber of the sand tank is provided with a water inlet hole and a plurality of first water outlet holes, wherein the water inlet hole is positioned at the lower end of the side wall of the sand tank and is connected with a liquid supply tank for supplying liquid required by an experiment to the sand tank;

the river channel simulation device is positioned at the left upper part of the middle sub-chamber of the sand tank, the bottom of the river channel simulation device is an inclined water permeable plate which is used for simulating a river channel, the slope of the river channel is simulated according to equal scaling by considering the structure of river bed sediments under natural conditions, the left side, the right side and the lower side of the river channel simulation device are provided with water permeable plates which are used for simulating the vertical infiltration and lateral infiltration processes of the river, and a silting layer with different thicknesses is laid on the simulated river channel of the river channel simulation device so as to simulate different erosion and deposition degrees of the river;

the dissolved oxygen monitoring module consists of a dissolved oxygen diaphragm, an optical fiber data acquisition device and a dissolved oxygen data processing system, wherein the dissolved oxygen diaphragm is adhered to the inner wall of the sand tank at a position close to the pore water sampling hole, one end of the optical fiber data acquisition device is connected with the dissolved oxygen data processing system, one end of the optical fiber data acquisition device vertically irradiates on the dissolved oxygen diaphragm, the optical fiber data acquisition device can automatically record the measured information of the dissolved oxygen diaphragm in real time and transmit the data to the dissolved oxygen data processing system, and the dissolved oxygen data processing system automatically converts the received signals into dissolved oxygen concentration information according to the temperature and pressure changes in the experimental process, thereby realizing the in-situ monitoring of the dissolved oxygen concentration;

the excretion system consists of a Mariotte bottle and a height adjusting device, and the Mariotte bottle is placed on the height adjusting device; the height of the Mariotte bottle is adjusted and is connected with a second water outlet hole of the sand tank so as to control different drainage water levels;

the pressure monitoring module is composed of a pressure transmitter, a pressure data collector and a pressure data processing system, the pressure transmitter is arranged in a pressure sensor arrangement hole of the sand tank, one end of the data collector is connected with the pressure sensor, the other end of the data collector is connected with the pressure data processing system, the measuring electrode can monitor the change situation of the water content in the sand tank and transmit information to the pressure data collector, the pressure data collector can automatically record the measuring information of the electrode in real time and transmit data to the pressure data processing system, and the pressure data processing system converts the received signal into pressure information, so that the in-situ monitoring of the change situation of the pressure in the sand tank is realized.

The water head height adjusting device of the indoor sand tank experiment device for simulating the underground water exploitation of the riverside can realize different hydraulic connection modes of river water and underground water, and can simulate the saturated connection of the river water and the underground water to the complete disjointing process by adjusting the infiltration water level and the drainage water level.

The non-invasive patch type oxygen sensor of the indoor sand tank experimental device for simulating the underground water exploitation of the riverside can realize the non-contact real-time measurement of the dissolved oxygen concentration in the experimental tank, and the signal is not limited by the flow speed.

The indoor sand tank experimental device for simulating the underground water exploitation of the riverside has the advantages that the data collector can realize real-time automatic monitoring of data, no redundant manual operation is needed after the device is started, and the sensor can automatically run together with the data collection system.

An experimental method of an indoor sand tank experimental device for simulating riverside underground water exploitation comprises the following steps:

1) and sticking the dissolved oxygen membrane: the black side of the dissolved oxygen membrane is in contact with a medium, the pink/green side is adhered to the inner wall of the sand tank, the dissolved oxygen membrane is placed for 12 hours after the adhesion is finished, the glue is completely dried, if the dissolved oxygen membrane comes from the same batch, only one sensor needs to be calibrated according to the specification, and each sensor does not need to be calibrated independently;

2) and filling the sand tank: the gauze is stuck on the permeable plates at the two sides of the middle part subchamber in advance to prevent the medium particles from blocking the permeable holes; according to the actual field riverbed sediment and aquifer structure, selecting the field riverbed sediment and an aqueous medium as filling media of the simulation tank, and simultaneously filling according to the natural volume weight of the field riverbed sediment and the aquifer medium; compacting the sediment layer once every 5cm of height is filled, so that gap cracks and the like are avoided, and priority flow is prevented from being generated, so that the medium in the simulation tank is close to the river bed sediment and the aquifer medium in a natural state to the maximum extent;

3) and arranging a pressure transmitter: connecting all the electrodes with a data acquisition unit and calibrating; setting the electrode arrangement depth in advance, synchronously embedding a pressure transmitter into an arrangement hole of a pressure sensor on the side wall of an experimental groove in the filling process of the sand groove, and filling other parts of the sand groove with a medium after arranging the electrode with a certain depth to avoid forming a larger hole in the sand groove to cause preferential flow and further cause measurement errors;

4) and water saturation of the sand tank: after the sand tank is filled, connecting a water inlet hole at the bottom of a water inlet area with a liquid supply tank by using a guide pipe, controlling the speed of a water pump, and slowly feeding water from bottom to top by using ultrapure water, wherein the ultrapure water is water which is introduced with argon for a period of time and ensures that the oxygen concentration is less than 0.2mg/L, when a groundwater sampling hole has water flow to flow out, closing a water stop clamp at the position, continuously supplying water after the water head in the sand tank rises for 5cm every time, completely exhausting air in the sand tank, and continuously supplying water after the sand tank is saturated with water;

5) and injecting a tracer: connecting the sand tank with a water supply system and a drainage system, fixing the height of a first water outlet hole of the sand tank, adjusting the height of a second water outlet hole of the sand tank to control the seepage gradient of river water, taking NaCl as an example as a tracer, preparing NaCl solution with preset concentration under the conditions of a given river water level and drainage water level, and introducing the NaCl solution into a seepage tank at a preset speed by using a water pump;

6) collecting, testing and processing samples: after the tracer is injected, the sampling and testing work can be started, the sampling time interval is selected according to the seepage speed, the seepage speed is obtained by calculating the water discharge quantity of a second water outlet of the sand tank, the seepage speed is high, the set sampling time interval is small, and otherwise, the time interval can be increased; after the sample is collected, measuring the conductivity until the conductivity in the pore water sampling hole and the underground water sampling hole reaches the peak value and is stable and unchanged; processing the acquired data to respectively obtain concentration change conditions of different positions at the same time and different times at the same position, drawing a concentration contour map, observing tracer migration conditions and determining distribution ranges of a dispersion zone, a transition zone and a convection zone;

7) and washing the sand tank: after the experiment is finished, deionized water is used for replacing a tracer solution and continuously introduced into the sand tank, the introduction speed is controlled by a water pump, and the conductivity of seepage liquid of the pore water sampling hole and the underground water sampling hole is detected until the conductivity data is reduced to be below a background value, which indicates that the washing process is finished;

8) injecting and monitoring experimental water: in the experimental process, a seepage water source is configured according to the actually measured river water chemical index, the configured seepage solution is used for replacing deionized water and is introduced into the sand tank, the height of a first water outlet hole of the sand tank is fixed, and the height of a second water outlet hole of the sand tank is adjusted to control the seepage speed of the river water;

9) and collecting and testing samples: in the experimental process, the dissolved oxygen membrane is used for monitoring the oxygen concentration in the sand tank in real time, setting the sampling frequency and testing the concentration of related indexes, the seepage speed and other related index change rules are synchronously monitored in the experimental process, and meanwhile, the change rules of related indexes of the simulated river water and the simulated water outlet are tested; and after the experiment is finished, collecting sediment medium samples in a layering position, and testing the change rule of the relevant indexes.

The experimental method of the indoor sand tank experimental device for simulating the underground water exploitation of the riverside can be used for realizing a river water-underground water evolution relation simulation experiment under the heterogeneous conditions of riverbed sediments and aquifers by applying an optical fiber oxygen measuring technology and combining an in-situ negative pressure monitoring system.

According to the experimental method of the indoor sand tank experimental device for simulating the underground water exploitation of the riverside, after a complete simulation experiment is completed, only the last three steps need to be repeated, so that repeated comparison experiments can be performed, and the reliability of experimental results can be verified conveniently;

the invention has the beneficial effects that:

1. the simulation in the underground water mining room of the riverside can be realized under the more economic condition;

2. through the design of the water head height adjusting device, the simulation of the process from saturation connection of river-underground water to transition disjunction to complete disjunction can be realized;

3. by applying undisturbed riverbed sediments and aquifer medium samples, a simulation experiment of river-underground water evolution relation under the heterogeneous condition of the riverbed sediments and the aquifer can be realized;

4. the non-invasive dissolved oxygen concentration measurement and the real-time automatic monitoring process of the pressure data can save the labor cost, and the reliability of the data result is higher. The experimental process can be repeated, and has certain reproducibility.

Drawings

FIG. 1 is a front view of an indoor sand tank experimental facility for groundwater mining in the riverside.

Fig. 2 is a rear view of an indoor sand tank experimental facility for groundwater mining in the riverside.

FIG. 3 is a schematic view of the bonding of the dissolved oxygen membrane.

In the figure: a, a water supply system, B, a sand tank, C, a river channel simulation device, D, a dissolved oxygen monitoring module, E, an excretion system and F, a pressure monitoring module; 1-liquid feed case, 2-water pump, 3-pipe, 4-flowmeters, 5-first apopore, 6-porous disk, 7-siltation, 8-pore water thief hole, 9-water-stop sheet, 10-groundwater thief hole, 11-inlet opening, 12-optic fibre data collection station, 13-dissolved oxygen data processing system, 14-Ma shi bottle, 15-altitude mixture control device, 16-second apopore, 17-pressure sensor lays the hole, 18-pressure data collection station, 19-pressure data processing system, 20-dissolved oxygen diaphragm.

Detailed Description

As shown in fig. 1 to 3, an indoor sand tank experimental device for simulating riverside groundwater mining comprises a water supply system a, a sand tank B, a river channel simulation device C, a dissolved oxygen monitoring module D, an excretion system E and a pressure monitoring module F:

the water supply system A consists of a liquid supply tank 1, a water pump 2, a plurality of guide pipes 3 and a flowmeter 4, wherein the liquid supply tank 1 is used for storing solution required by an experiment, the water pump 2 and the flowmeter 4 are sequentially connected through the guide pipes 3 and then are connected with a water inlet hole 11 on the side wall of the sand tank, the water pump 2 is used for controlling infiltration speed, and the flowmeter 4 is used for monitoring infiltration flow passing through a river channel simulation device in the experiment process;

the sand tank B is vertically arranged, the interior of the sand tank B is divided into a left subchamber B1, a middle subchamber B2 and a right subchamber B3 from left to right, the left subchamber B1 is a water head height adjusting device and is connected with a water supply system A, the middle subchamber B2 is a main body part of the sand tank and is used for filling undisturbed riverbed sediments and aquifer media in a field, the right subchamber B3 is a device for simulating a field exploitation well and is connected with a drainage system E, the left subchamber B1 and the middle subchamber B2 are separated by a water permeable plate 6 and a water-stop plate 9, the water permeable plate 6 is positioned at the upper part, and the water-stop plate 9 is positioned at the lower part; the right sub-chamber B3 and the middle sub-chamber B2 are separated by a water permeable plate 6, and a plurality of water permeable holes are uniformly and densely distributed on the water permeable plate 6;

a water inlet hole 11 and a plurality of first water outlet holes 5 are distributed on the side wall of a left sub-chamber B1 of the sand tank B, wherein the water inlet hole 11 is positioned at the lower end of the side wall of the sand tank B and is connected with a liquid supply tank 1 for supplying liquid required by an experiment for the sand tank B, the plurality of first water outlet holes 5 are positioned at different heights at the upper end of the side wall of a left sub-chamber B1 of the sand tank B, the first water outlet holes 5 with response heights are opened to control different river water levels, a second water outlet hole 16 is distributed at the lower end of the side wall of a right sub-chamber B3 of the sand tank B, the second water outlet hole 16 is communicated with a March's flask 14, the second water outlet hole 16 is connected with the March's flasks 14 with different heights to control drainage water levels, the drainage water level of the March's flask 14 is lower than the first water outlet holes 5, and the difference between the river water level and the drainage water level is used as a driving force to promote the river water to enter the seepage and supply underground water;

the river channel simulation device C is positioned at the left upper part of the middle sub-chamber B2 of the sand tank B, the bottom of the river channel simulation device C is an inclined water permeable plate 6, the inclined water permeable plate 6 is a simulation river channel, the slope of the river channel is simulated according to equal scaling considering the sediment structure of a river bed under natural conditions, the left side, the right side and the lower side of the river channel simulation device C are the water permeable plates 6 and are used for simulating the vertical infiltration and lateral infiltration processes of the river, and siltation layers 7 with different thicknesses are paved on the simulation river channel of the river channel simulation device C to simulate different erosion and deposition degrees of the river;

the dissolved oxygen monitoring module D is composed of a dissolved oxygen diaphragm 20, an optical fiber data collector 12 and a dissolved oxygen data processing system 13, wherein the dissolved oxygen diaphragm 20 is adhered to the inner wall of the sand tank B at a position close to the pore water sampling hole 8, one end of the optical fiber data collector 12 is connected with the dissolved oxygen data processing system 13, one end of the optical fiber data collector 12 vertically irradiates the dissolved oxygen diaphragm 20, the optical fiber data collector 12 can automatically record the measurement information of the dissolved oxygen diaphragm 20 in real time and transmit the data to the dissolved oxygen data processing system 13, and the dissolved oxygen data processing system 13 automatically converts the received signals into dissolved oxygen concentration information according to the temperature and pressure changes in the experimental process, so that the in-situ monitoring of the dissolved oxygen concentration is realized;

the drainage system E consists of a Mariotte bottle 14 and a height adjusting device 15, wherein the Mariotte bottle 14 is placed on the height adjusting device 15; the different drainage water levels are controlled by adjusting the height of the Mariotte bottle 14 and connecting the Mariotte bottle with the second water outlet hole 16 of the sand tank B;

the pressure monitoring module F is composed of a pressure transmitter, a pressure data collector 18 and a pressure data processing system 19, the pressure transmitter is arranged in a pressure sensor arrangement hole 17 of the sand tank B, one end of the data collector 18 is connected with the pressure sensor, the other end of the data collector 18 is connected with the pressure data processing system 19, the measuring electrode can monitor the change situation of the water content in the sand tank and transmit the information to the pressure data collector 18, the pressure data collector 18 can automatically record the measuring information of the electrode in real time and transmit the data to the pressure data processing system 19, and the pressure data processing system 19 converts the received signals into pressure information, so that the in-situ monitoring of the change situation of the pressure in the sand tank is realized.

According to the invention, the riverbed sediments and the aquifer medium in the sand groove are prepared according to the particle data of the experimental site, and can be selected automatically according to different experimental sites; the sand groove B is made of organic glass, the thickness of the glass plate is set to be 1.5cm, the size of the sand groove is set to be 1.5m multiplied by 0.2m multiplied by 1.0m in length multiplied by width multiplied by height, the length of the left sub-chamber is 5cm, the length of the middle sub-chamber is 140cm, the length of the right sub-chamber is 5cm, the thicknesses of the water permeable plate 6 and the water-stop baffle 9 are 5mm, and the inner diameter and the outer diameter of the water inlet hole 11, the inner diameter and the outer diameter of the first water outlet hole 5 and the outer diameter of the second water outlet hole 16 are respectively 10mm and 12 mm; the liquid supply tank 1 and the drainage device E are all 25L-volume Mariotte bottles, the guide pipe 3 is a latex pipe with the inner diameter and the outer diameter of 6mm and 9mm respectively, the dissolved oxygen diaphragm 20 is a circular patch with the diameter of 5mm, the pressure transmitter front end material is a clay head which is connected with a stainless steel pipe with the diameter of 10mm, the length of the steel pipe and the length of the clay head are 10cm in total, and the clay head at the pressure transmitter front end needs to be horizontally placed in a sand tank.

An experimental method of an indoor sand tank experimental device for simulating riverside underground water exploitation comprises the following steps:

1) and sticking the dissolved oxygen membrane: the black side of the dissolved oxygen membrane 20 is in contact with a medium, the pink/green side is adhered to the inner wall of the sand tank B, the dissolved oxygen membrane 20 is placed for 12 hours after the adhesion is finished, the glue is completely dried, if the dissolved oxygen membrane 20 comes from the same batch, only one sensor needs to be calibrated according to the specification, and each sensor does not need to be calibrated independently;

2) and filling the sand tank: the gauze is stuck on the permeable plates 6 at the two sides of the middle part subchamber B1 in advance to prevent the medium particles from blocking the permeable holes; according to the actual field riverbed sediment and aquifer structure, selecting the field riverbed sediment and an aqueous medium as filling media of the simulation tank, and simultaneously filling according to the natural volume weight of the field riverbed sediment and the aquifer medium; the siltation layer 7 is compacted once every 5cm of height is filled, so that gap cracks and the like are avoided, and priority flow is prevented from being generated, so that the medium in the simulation tank is close to the riverbed sediment and aquifer medium in a natural state to the maximum extent;

3) and arranging a pressure transmitter: all electrodes are connected to a data collector 18 and calibrated. Setting the electrode arrangement depth in advance, synchronously embedding a pressure transmitter into the arrangement hole 17 of the pressure sensor on the side wall of the experimental groove in the filling process of the sand groove B, and filling other parts of the sand groove B with a medium after arranging the electrode with a certain depth to avoid forming a larger pore in the sand groove B to cause preferential flow and further cause measurement errors;

4) and water saturation of the sand tank: after the sand tank B is filled, a water inlet hole 11 at the bottom of a water inlet area is connected with a liquid supply tank 1 through a guide pipe 3, the speed of a water pump 2 is controlled, and water is slowly fed by ultrapure water from bottom to top, wherein the ultrapure water is water which is fed with argon for a period of time and ensures that the oxygen concentration is less than 0.2mg/L, when the groundwater sampling hole 10 flows out, a water stop clamp at the position is closed, the water head in the sand tank B rises by 5cm every time, water is continuously supplied after the water head in the sand tank B is stabilized, the air in the sand tank B is completely exhausted, and the water supply is continuously performed after the sand tank B is saturated with water;

5) and injecting a tracer: connecting a sand tank B with a water supply system A and a drainage system E, fixing the height of a first water outlet hole 5 of the sand tank B, adjusting the height of a second water outlet hole 16 of the sand tank B to control the seepage hydraulic gradient of river water, taking NaCl as an example as a tracer, preparing NaCl solution with preset concentration under the conditions of given river water level and drainage water level, and introducing the NaCl solution into a seepage tank at a preset speed by using a water pump 2;

6) collecting, testing and processing samples: after the tracer is injected, the sampling and testing work can be started, the sampling time interval is selected according to the seepage speed, the seepage speed is obtained by calculating the amount of water discharged from the second water outlet 16 of the sand tank B, the seepage speed is high, the set sampling time interval is small, otherwise, the time interval can be increased; after the sample is collected, measuring the conductivity until the conductivities in the pore water sampling hole 8 and the underground water sampling hole 10 reach the peak value and are stable and unchanged; processing the acquired data to respectively obtain concentration change conditions of different positions at the same time and different times at the same position, drawing a concentration contour map, observing tracer migration conditions and determining distribution ranges of a dispersion zone, a transition zone and a convection zone;

7) and washing the sand tank: after the experiment is finished, deionized water is used for replacing a tracer solution and continuously introduced into the sand tank B, the introduction speed is controlled by the water pump 2, and the conductivity of the seepage liquid of the pore water sampling hole 8 and the underground water sampling hole 10 is detected until the conductivity data is reduced to be below a background value, which indicates that the washing process is finished;

8) injecting and monitoring experimental water: in the experimental process, a seepage water source is configured according to the actually measured river water chemical index, the configured seepage solution is used for replacing deionized water and is led into a sand tank B, the height of a first water outlet hole 5 of the sand tank B is fixed, and the height of a second water outlet hole 16 of the sand tank B is adjusted to control the seepage speed of the river water;

9) and collecting and testing samples: in the experimental process, the dissolved oxygen membrane 20 is used for monitoring the oxygen concentration in the sand tank B in real time, setting the sampling frequency and testing the concentration of related indexes, the seepage velocity and other related index change rules are synchronously monitored in the experimental process, and meanwhile, the change rules of related indexes of the simulated river water and the simulated water outlet are tested; and after the experiment is finished, collecting sediment medium samples in a layering position, and testing the change rule of the relevant indexes.

In the method, the solution used in the experiment is configured according to the actually measured river water chemical index in the field, humic acid is selected as an electron donor, the concentration is set to be 30mg/L, and sodium sulfate and potassium nitrate are used for respectively adjusting SO₄ ^2-And NO₃ ^-The concentration is 50mg/L and 2.8 mg/L; the gauze meshes adhered on the two sides of the permeable plate 6 can be selected as 100 meshes, the thickness of the deposit layer 7 is respectively set to be 2cm, 3cm and 5cm, and the average particle size of the deposit layer 7 is set to be 20 mu m. The dissolved oxygen membrane 20 and the electrode layout are shown in fig. 1 and fig. 2, respectively; setting a left water head difference and a right water head difference of the sand tank B according to experiment requirements; the pressure recording time interval is set to 5 seconds, the irradiation time interval of the dissolved oxygen membrane is set to 1d, and the same sample is tested repeatedly for three times to ensure the accuracy of the result.