Monitoring experiment device and measuring method for underground water-river water exchange flux

Abstract

The invention relates to an underground water-river water exchange flux monitoring experiment device and a measuring method, the underground water-river water exchange flux monitoring experiment device comprises a water tank, the water tank is internally provided with a separator which divides the water tank into an upper part and a lower part and is provided with a water seepage gap, and the upper part, corresponding to the separator, of the water tank is provided with a sand layer with simulated soil and stone; the lower part, corresponding to the separator, of the water tank is a water flow channel; a shaft vertically inserted into the sand layer is also arranged in the water tank; a valve communicated with the interior of the shaft is arranged on the outer surface of the side wall, in the water tank, of the shaft; a water level monitoring device for monitoring the water level in the shaft is arranged on the water tank; a water pump is arranged on the water tank and is communicated with the water flow channel and the water tank through a water pipe respectively. Meanwhile, the invention discloses a method for measuring by using the device. The device is simple, the experiment is convenient, the seepage flux can be calculated through the change of the water level in the shaft, and the device can be used for simulating the water exchange of underground water-river water under different heterogeneous structure conditions.

Description

Technical Field

[0001] The invention relates to the field of hydrogeology, and in particular to a monitoring experimental device and a measuring method for groundwater-river water exchange flux. Background Art

[0002] The eutrophication problem of rivers is increasingly aggravated by the excessive input of nutrients such as nitrogen and phosphorus, which has posed a serious threat to aquatic ecosystems and water quality safety. Excess nutrients lead to rapid reproduction of algae, hypoxia in water bodies, imbalance of aquatic ecosystems, and impact on biodiversity. At the same time, as the main source of water supply in many regions, the water quality safety of rivers is also seriously affected. Especially in arid and semi-arid areas, groundwater is an important channel for nitrogen, phosphorus and other substances to enter rivers, and the role of nutrient load brought by groundwater discharge in the eutrophication process cannot be ignored. Therefore, accurate quantification of groundwater discharge in rivers has become the key to assessing the impact of groundwater on eutrophication.

[0003] In the study of riverbed groundwater discharge, common monitoring methods include seepage meter measurement, water balance, radon mass balance, temperature tracing, numerical simulation, etc. For example, the seepage meter measurement method can directly measure the groundwater flow rate and flux through the riverbed. Lee et al. used this method to study the Han River in South Korea and found that riverbed groundwater discharge contributed significantly to the river water volume. The water balance law infers the groundwater discharge by calculating the difference between precipitation, evaporation and river flow in the basin. Yu Chang et al. used the RCCC-WBM water balance model in the Baihe River Basin in the source area of ​​the Yellow River to simulate the water cycle process in the Baihe River Basin. Radon mass balance technology, as a geochemical method, tracks groundwater flow by analyzing the distribution characteristics of radon isotopes. Chen Hongwei et al. used the Dongting Lake section of the Zijiang River Basin as the object and used radon mass balance technology to explore the groundwater-river water interaction relationship in the region. Temperature tracing tracks the interaction between groundwater and surface water based on water temperature differences. Zhang Shuxun et al. used temperature data to analyze and calculate the groundwater-river water exchange flux in a certain section of the upper reaches of the Heihe River in my country, and analyzed the temporal and spatial differences in their interactions and their influencing mechanisms. In addition, with the development of technology, numerical simulation methods have become more mature. They can comprehensively consider hydrogeological parameters and simulate groundwater flow and its interaction with surface water. Ferguson et al. used the MODFLOW model to conduct simulation studies in the Colorado River Basin in the United States and evaluated the impact of groundwater extraction on river water volume. Although these methods have their own effectiveness, they generally have limitations such as complex operation, inability to accurately monitor, the need for specific geological conditions, or difficulty in achieving long-term continuous observation. Summary of the invention

[0004] In view of the existing deficiencies, the present invention provides a monitoring experimental device and a measuring method for groundwater-river water exchange flux.

[0005] The technical solution adopted by the present invention to solve its technical problems is: a monitoring experimental device for groundwater-river water exchange flux, including a water trough, in which a partition is arranged to divide the water trough into an upper and lower part and provided with a water seepage gap, the upper part of the water trough corresponding to the partition is provided with a sand layer simulating soil and stone, and the lower part of the water trough corresponding to the partition is a water flow channel; a wellbore vertically inserted into the sand layer is also arranged in the water trough; a valve connected to the inside of the wellbore is arranged on the outer surface of the side wall of the wellbore in the water trough; a water level monitoring device for monitoring the water level in the wellbore is arranged on the water trough; a water pump is arranged on the water trough, and the water pump is connected to the water flow channel and the water trough through a water pipe respectively.

[0006] Preferably, the top detachable cover of the water tank is provided with a water tank cover plate, and the water level monitoring device and the water pump are both arranged on the top of the water tank cover plate.

[0007] Preferably, the water level monitoring device comprises a liquid level meter arranged in the wellbore above the sand layer and a controller arranged outside the water tank.

[0008] Preferably, the liquid level gauge is a float type liquid level gauge, and a gap is provided between the front end of the insertion rod of the liquid level gauge and the top surface of the sand layer.

[0009] Preferably, the water tank is a water tank of a barrel-shaped structure, the ratio of the inner diameter to the depth of the water tank is 1:2, and the partition is arranged at a position in the water tank at a certain distance from the bottom of the water tank, and the distance is 4%-5% of the depth of the water tank.

[0010] Preferably, the inner diameter of the wellbore is 11%-12.5% ​​of the inner diameter of the water tank, the length is not less than 2 / 3 of the depth of the water tank, the thickness of the wellbore is 7%-8% of the inner diameter of the wellbore, the valve is arranged at a distance from the top of the wellbore that is 25%-35% of the length of the wellbore, and the valve diameter of the valve is 20%-25% of the inner diameter of the wellbore.

[0011] Preferably, a filter screen is provided on the top of the partition.

[0012] Preferably, the height of the sand layer is greater than half the depth of the water tank.

[0013] A method for monitoring groundwater-river water exchange flux, characterized in that: using any of the monitoring experimental devices described above, the steps are as follows:

[0014] The water tank is filled with water until the water surface is higher than a certain height of the sand layer, and the injected water immerses the valves and water level monitoring devices in the open state;

[0015] Use the water level monitoring device to continuously collect water level change data at a certain frequency. After the water level stabilizes, close the valve until the water level stabilizes again;

[0016] The water level change curve is drawn using the water level change data, where the head change function in the wellbore after the valve is closed is:

[0017]

[0018] Among them, K is the permeability coefficient of the sand layer, L is the distance from the bottom of the wellbore to the top of the sand layer, and H is s (t) is the water level outside the wellbore; the head change function inside the wellbore is differentiated with respect to time t to obtain:

[0019]

[0020] At t=t0, the slope of the curve at the time when the valve is closed is the exchange flux between groundwater and river water.

[0021] Preferably, the frequency is 5-15s / time.

[0022] The beneficial effects of the present invention are as follows: the device is simple, the experiment is convenient, and long-term and large-scale continuous observation can be realized. The seepage flow rate can be calculated by the water level change in the wellbore. The water exchange between groundwater and river water under different heterogeneous structural conditions can be simulated by changing the sand layer structure in the sand trough. Only a wellbore and a water level monitoring device are required to measure the water exchange in the actual site. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a schematic structural diagram of an embodiment of the present invention;

[0024] Figure 2 It is a diagram showing the meanings of various symbols in the function of water head change in the wellbore after the valve is closed in an embodiment of the present invention;

[0025] Figure 3 is a graph showing changes in water level in a wellbore according to an embodiment of the present invention;

[0026] Names and serial numbers of parts in the figure: 1-water tank 10-water tank cover 2-partition 20-filter 3-sand layer 30-water layer 4-water flow channel 5-wellbore 50-wellbore cover 6-valve 7-water level monitoring device 70-liquid level meter 71-controller 700-float 701-rod 8-water pump 80-water pipe. DETAILED DESCRIPTION

[0027] In order to more clearly illustrate the purpose, technical solutions and advantages of the embodiments of the present invention, the present invention will be further described in conjunction with the accompanying drawings and embodiments below for a clear and complete description. Obviously, the described embodiments are partial embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the protection scope of the present invention. In addition, the directional terms mentioned in the present invention, such as "up", "down", "front", "back", "left", "right", "inside", "outside", etc., are only referenced to the directions of the attached diagrams. The directional terms used are for better and clearer explanation and understanding of the present invention, rather than indicating or implying the orientation that the present invention must have, and therefore cannot be understood as limitations on the present invention.

[0028] Embodiments of the present invention Figure 1As shown in, a monitoring experimental device for groundwater-river water exchange flux includes a water tank 1, which is a water tank of a barrel-shaped structure. The ratio of the inner diameter and the depth of the water tank 1 is 1:2. For example, the inner diameter of the water tank 1 is 0.6m and the depth is 1.2m. A partition 2 is provided in the water tank 1 to divide the water tank 1 into two parts, an upper part and an lower part, and a water seepage gap is provided. The partition 2 is made of a PVC board, and the water seepage gap thereon can be a water seepage hole or a water seepage gap that can seep water. The partition 2 is arranged in the water tank 1 at a position with a certain distance from the bottom of the water tank 2, and the size of the distance is 4%-5% of the depth of the water tank 1. When the depth of the water tank 1 is 1.2m, the partition 2 is arranged in the water tank 1 at a height of 50mm from the bottom of the water tank 1. The upper part of the water tank 1 corresponding to the partition 2 is provided with a sand layer 3 simulating soil and stone. The sand layer 3 is formed by laying quartz sand on the top of the partition 2 to simulate different geological structure conditions. At this time, the height of the laid sand layer 3 is greater than half of the depth of the water tank 1. For example, the height of the laid sand layer 3 is 750mm, which makes the measured data more accurate and closer to the actual situation. In order to prevent the quartz sand from falling into the water flow channel 4 through the seepage gap on the partition 2, a filter screen 20 is provided on the top of the partition 2. The lower part of the water tank 1 corresponding to the partition 2 is the water flow channel 4. At this time, a water pipe 80 connected to the water pump 8 can be arranged in the water flow channel 4. At the same time, water inlets and outlets can be arranged on the side wall or the bottom of the water tank 1 corresponding to the water flow channel 4. Inlet and outlet valves or plugs are installed in the water inlets, and the water inlets and outlets facilitate the inlet and outlet of water into the water flow channel 4, as well as the cleaning of the water flow channel 4; a wellbore 5 is also provided in the water tank 1, which is vertically inserted into the sand layer 3. The wellbore 5 is a cylindrical structure component, which is vertically inserted into the sand layer 3 at the axial position of the water tank 1. The inner diameter of the wellbore 5 is 11.0%-12.5% ​​of the inner diameter of the water tank 1, the length of the wellbore 5 is not less than 2 / 3 of the depth of the water tank 1, and the thickness of the wellbore 5 is 7%-8% of the inner diameter of the wellbore 5. When the inner diameter of the water tank 1 is 0.6m and the depth is 1.2m, the inner diameter of the wellbore 5 is set to 70mm, which is 12% of the inner diameter of the water tank 1, and the outer diameter is set to 75mm. At this time, the thickness of the wellbore 5 is 5mm, which is the wellbore 5. 7.14% of the inner diameter of the well 5, the length of the well 5 is 0.8m, that is, 75% of the depth of the water tank 1, and the outer surface of the side wall of the well 5 in the water tank 1 is provided with a valve 6 connected to the inside of the well 5, which means that the valve 6 is in the water tank 1, so that the water layer 30 formed after the subsequent water injection can immerse the valve 6, but the switch part of the valve 6 is exposed to the water surface; at this time, the valve 6 is set at a distance from the top of the well 5 of 25%-35% of the length of the well 5, such as 250mm from the top of the well 5, that is, 31.25% of the length of the well 5, and the valve diameter of the valve 6 is 20%-25% of the inner diameter of the well 5. For example, the valve diameter of the valve 6 is selected to be 15mm, that is, 21.4%, the overall height of the valve 6 is set to 150mm; the water tank 1 is provided with a water level monitoring device 7 for monitoring the water level in the well 5, and the water level monitoring device 7 is used to monitor the change of the water level in the well 5; the water tank 1 is provided with a water pump 8, which is connected to the water flow channel 4 and the inside of the water tank 1 through a water pipe 80. After water is injected into the water tank 1, the water pipe 80 connected to the inside of the water tank 1 is inserted into the water layer 30, and there is a gap between the top of the sand layer 3. The water pump 8 is a peristaltic pump. The peristaltic pump can be used to pump water from the water flow channel 4 and inject it into the water tank 1, which simulates the leakage of river water, or the water in the water tank 1 is pumped out and injected into the water flow channel 4, which generates upward seepage, simulating the discharge of groundwater. .

[0029] Further improvements, such as Figure 1 As shown in the figure, the top of the sink 1 is detachably covered with a sink cover 10, and the water level monitoring device 7 and the water pump 8 are both arranged on the top of the sink cover 10. The top of the sink 1 is closed by the sink cover 10, which also facilitates the arrangement of the water level monitoring device 7 and the water pump 8 and simplifies the structure of the sink 1. The detachable structure of the sink cover 10 on the sink 1 can be a raised ring arranged on the bottom surface of the sink cover 10 along the circumference of the bottom surface of the sink cover 10. The inner diameter of the raised ring is matched with the outer diameter of the sink 1, and the sink 1 can be matched and set in the raised ring. At the same time, a sink cover through hole for the well 5 to pass through is also provided at the center position of the sink cover 10. When the outer diameter of the well 5 is 75 mm, the sink cover through hole is a through hole with a diameter of 75 mm.

[0030] Further improvements, such as Figure 1As shown in , the water level monitoring device 7 includes a liquid level meter 70 arranged in the wellbore 5 above the sand layer 3 and a controller 71 arranged outside the water tank 1. The controller 71 is used to control the liquid level meter 70 to collect water level data, and store and process the collected data. When a water tank cover plate 10 is detachably covered on the top of the water tank 1, the controller 71 is installed on the top of the water tank cover plate 10, and the wellbore 5 is installed in the middle of the water tank cover plate 10 and partially protrudes above the water tank cover plate 10. At the same time, a wellbore cover plate 50 is detachably covered on the top of the wellbore 5. The detachable structure can be the same as the structure of the detachable cover of the water tank cover plate 10 on the water tank 1. Then, a threaded hole is set on the bottom surface of the wellbore cover plate 50, and then the liquid level meter 70 is threadedly installed in the threaded hole. The controller 71 is connected to the liquid level meter 70 through a cable. The liquid level gauge 70 is a float type liquid level gauge, that is, it is mainly composed of a float 700, a rod 701 and corresponding electronic control parts. The float 700 is a non-contact magnetic float. After the liquid level gauge 70 is placed in the wellbore 5, the front end of the rod 701 is immersed in water but does not contact the sand layer, that is, there is a gap between the front end of the rod 701 of the liquid level gauge 70 and the top surface of the sand layer 3. When the liquid level meter 70 is threadedly connected to the shaft cover plate 50, an external thread is provided at the end of the plug rod 701 of the liquid level meter 70 for threaded connection with the threaded hole on the shaft cover plate 50, which facilitates the installation of the liquid level meter 70. For example, the diameter of the external threaded part at the end of the plug rod 701 of the liquid level meter 70 is set to 18mm, the plug rod 701 is 364.3mm long, and a magnetostrictive wire is installed in the plug rod 701, which is 364.3mm long. The front end and the end of the plug rod 701 are respectively provided with blind areas of 63.5mm and 50.8mm in length, and an external thread of 24mm in length and 18mm in diameter is also provided at the end. The float 700 is a float with a diameter of 53.6mm mounted on the plug rod 701; the electronic control part is arranged at the top of the shaft cover plate 50, and a Modbus output port is arranged on the electronic control part, and then connected to the controller 71 through a cable; the range of the liquid level meter 70 is 250mm, and the accuracy is 0.01mm.

[0031] A method for monitoring groundwater-river water exchange flux, such as Figure 1 As shown in , using the monitoring experimental device as described in any of the above, the steps are as follows:

[0032] Water is injected into the water tank 1 until the water surface is higher than the sand layer 3 by a certain height to form a water layer 30, and the injected water immerses the valve 6 and the water level monitoring device 7 in the open state; according to the specifications of the water tank 1, the wellbore 5 and the liquid level gauge 70 in the aforementioned embodiment, at this time, the water surface after water injection in the water tank 1 is 200 mm higher than the top surface of the sand layer 3. In the water tank 1, from bottom to top, there are the water flow channel 4, the partition 2, the filter screen 20, the sand layer 3, and the water layer 30. The valve 6 is immersed in water, and the switch of the valve 6 is exposed outside the water surface. In the whole process, the valve 6 is always in the open state, and the front end of the liquid level gauge 70 is immersed in water so that the float 700 floats on the water surface.

[0033] The two ends of the water pipe 80 of the peristaltic pump are respectively connected to the water layer 30 above the sand layer 3 and the water flow channel 4 below. By injecting water into the lower water flow channel 4 and pumping water from the upper water layer 30, upward seepage is generated to simulate the discharge of groundwater; conversely, the leakage of river water is simulated. When in use, first turn on the peristaltic pump, wait for 1-2 hours until the water level stabilizes, and then close the valve 6 to change the water level in the wellbore 5 until the water level stabilizes again. During the whole process, the water level monitoring device 7 is used to continuously collect water level change data at a certain frequency; the controller 71 monitors the water level change through the liquid level meter 70 at a frequency of 10s / time to continuously collect water level data, and stores and processes the collected water level data.

[0034] When processing water level data, the water level change data is used to draw a water level change curve, where the head change function in the wellbore after the valve is closed is:

[0035]

[0036] Where h(r, z, t) is the water head at any position in the wellbore, r is the horizontal distance from any point in the wellbore to the center of the wellbore, z is the vertical distance from any point in the wellbore to the bottom of the wellbore, t is the time, q is the exchange flux between groundwater and river water, K is the permeability coefficient of the sand layer, L is the distance from the bottom of the wellbore to the top of the sand layer, H s (t) is the water level outside the wellbore, such as Figure 2 As shown in ; the head change function in the wellbore is differentiated with respect to time t to obtain:

[0037]

[0038] At t=t0, the moment the valve closes:

[0039]

[0040] The slope of the curve at the time when the valve is closed is the groundwater-river water exchange flux.

[0041] like Figure 3As shown in the figure, the horizontal axis represents time, and the vertical axis represents the water level in the wellbore 5. After the valve 6 is closed, the water level in the wellbore 5 drops and stabilizes after a period of time. The slope of the water level change curve at the moment when the valve 6 is closed (t0) is -0.04, that is, the simulated groundwater-river water exchange flux q = 0.04mm / s, and the flow rate in the wellbore 5 is calculated by Q = qA (A is the cross-sectional area of ​​the wellbore) to be Q = 15.39ml / s, and the actual peristaltic pump flow rate Q0 = 16.6ml / s. It can be seen that the error between the flow rate calculated by the device and the actual flow rate is small, so the groundwater-river water exchange flux measured by the device has a high accuracy.

[0042] Although the present invention has been described in detail above with general descriptions and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements can be made on the basis of the present invention. Therefore, these modifications or improvements made on the basis of not departing from the spirit of the present invention all belong to the scope of protection claimed by the present invention.

Claims

1. A monitoring experimental device for groundwater-river water exchange flux, characterized in that: The invention comprises a water trough, wherein a partition is arranged in the water trough for dividing the water trough into an upper and lower part and having a water seepage gap, the upper part of the water trough corresponding to the partition is provided with a sand layer simulating soil and stone, and the lower part of the water trough corresponding to the partition is a water flow channel; a wellbore is also arranged in the water trough and vertically inserted into the sand layer; a valve connected to the inside of the wellbore is arranged on the outer surface of the side wall of the wellbore in the water trough; a water level monitoring device for monitoring the water level in the wellbore is arranged on the water trough; a water pump is arranged on the water trough, and the water pump is connected to the water flow channel and the water trough through a water pipe respectively.

2. The monitoring experimental device for groundwater-river water exchange flux according to claim 1, characterized in that: The top of the water tank is detachably covered with a water tank cover plate, and the water level monitoring device and the water pump are both arranged on the top of the water tank cover plate.

3. The monitoring experimental device for groundwater-river water exchange flux according to claim 1, characterized in that: The water level monitoring device comprises a liquid level meter arranged in the wellbore and above the sand layer, and a controller arranged outside the water tank.

4. The monitoring experimental device for groundwater-river water exchange flux according to claim 3, characterized in that: The liquid level gauge is a float type liquid level gauge, and a gap is provided between the front end of the insertion rod of the liquid level gauge and the top surface of the sand layer.

5. The monitoring experimental device for groundwater-river water exchange flux according to claim 1, characterized in that: The water tank is a water tank with a barrel-shaped structure, and the ratio of the inner diameter to the depth of the water tank is 1:

2. The partition is arranged at a position in the water tank at a certain distance from the bottom of the water tank, and the size of the distance is 4%-5% of the depth of the water tank.

6. The monitoring experimental device for groundwater-river water exchange flux according to claim 1, characterized in that: The inner diameter of the wellbore is 11%-12.5% ​​of the inner diameter of the water tank, the length is not less than 2 / 3 of the depth of the water tank, the thickness of the wellbore is 7%-8% of the inner diameter of the wellbore, the valve is arranged at a distance from the top of the wellbore that is 25%-35% of the length of the wellbore, and the valve diameter of the valve is 20%-25% of the inner diameter of the wellbore.

7. The monitoring experimental device for groundwater-river water exchange flux according to claim 1, characterized in that: A filter screen is arranged on the top of the partition.

8. The monitoring experimental device for groundwater-river water exchange flux according to claim 1, characterized in that: The height of the sand layer is greater than half of the depth of the water tank.

9. A method for monitoring groundwater-river water exchange flux, characterized in that: Using the monitoring experimental device as described in any one of claims 1 to 8, the steps are as follows: The water tank is filled with water until the water surface is higher than a certain height of the sand layer, and the injected water immerses the valves and water level monitoring devices in the open state; Use the water level monitoring device to continuously collect water level change data at a certain frequency. After the water level stabilizes, close the valve until the water level stabilizes again; The water level change curve is drawn using the water level change data, where the head change function in the wellbore after the valve is closed is: Among them, K is the permeability coefficient of the sand layer, L is the distance from the bottom of the wellbore to the top of the sand layer, and H is s (t) is the water level outside the wellbore; the head change function inside the wellbore is differentiated with respect to time t to obtain: At t=t0, the slope of the curve at the time when the valve is closed is the exchange flux between groundwater and river water.

10. The method for monitoring groundwater-river water exchange flux according to claim 9, characterized in that: The frequency is 5-15s / time.

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