A non-destructive in-situ tracer-based method for measuring net groundwater recharge

Abstract

The present application discloses a method for measuring the net recharge of groundwater in situ and non-destructively based on tracing. The measurement method comprises: A. Excavating the soil of the area to be measured to form a placement hole extending in the horizontal direction, and the placement hole is used to accommodate the tracer to be placed; B. After the tracer is placed, the placement hole is backfilled; C. Multiple soil sampling is performed at predetermined time intervals in the tracer placement area; D. Analysis of the sampled soil regarding the tracer concentration peak contained therein; E. Based on the concentration peak and based on the predetermined time interval, the net leaching amount of groundwater in the area to be measured is calculated according to the following formula. The method and system for measuring the net recharge of groundwater in situ and non-destructively based on tracing provided by the present method ensure the uniformity and consistency of tracer migration on the same horizontal placement surface of the tracer, and avoid the situation where the tracer measurement of the net recharge of groundwater is inaccurate due to the change of the in-situ structure of the soil above the sampling position.

Description

Technical Field

[0001] The present application relates to the technical field of groundwater net recharge, and in particular to a method for measuring groundwater net recharge in situ non-destructively based on tracing. Background Art

[0002] Groundwater resources are an important resource for ensuring water supply in northern my country, and play an important role in industrial and agricultural production and domestic water use. However, excessive development and utilization of groundwater will lead to a significant drop in groundwater levels, forming a regional groundwater drop funnel and causing a series of serious ecological and environmental safety problems, such as water resource depletion, ground subsidence, and saltwater intrusion.

[0003] In order to ensure the balance of regional groundwater extraction and replenishment, it is necessary to accurately evaluate the net groundwater recharge and formulate a reasonable groundwater extraction strategy based on this. However, the groundwater recharge process occurs below the ground, making it difficult to observe directly and measure accurately. In recent years, numerical calculation methods have gradually developed to estimate the net groundwater recharge by calculating the water movement process, but these methods only reflect groundwater recharge through indirect results. The existing methods of burying instruments below the ground to monitor water flux or placing tracers have destroyed the soil structure above the tracer during the installation of the instrument or equipment or the placement of the tracer. The subsequent backfill soil is difficult to reach the original state of the soil, thereby changing the properties of the soil and the characteristics of water movement, making it difficult to accurately reflect the net groundwater recharge.

[0004] In addition, the existing methods for measuring net groundwater recharge are relatively scattered, and no systematic solutions for measuring devices, operating methods, and calculation processes are provided, which makes them lack practicality and difficult to promote and apply. Summary of the invention

[0005] In view of this, the present application provides an in-situ non-destructive groundwater net recharge measurement method based on tracing, which can solve the problem that the net groundwater recharge is difficult to measure accurately.

[0006] The present application provides a method for measuring the in-situ non-destructive groundwater net recharge based on tracing, comprising the following steps:

[0007] A. Excavate the soil of the area to be tested to form a placement hole extending in the horizontal direction, wherein the placement hole is used to accommodate the tracer to be placed;

[0008] B. After the tracer is placed, backfilling the placement hole;

[0009] C. taking soil samples at predetermined time intervals multiple times from the area where the tracer is placed;

[0010] D. analyzing the sampled soil for the tracer concentration peak contained therein;

[0011] E. Calculate the net leaching amount of groundwater in the test area according to the concentration peak and the predetermined time interval according to the following formula:

[0012]

[0013] Among them, Q c is the net leaching amount of groundwater; Δt is the time interval between two adjacent tracer samplings; Δz is the depth of the tracer concentration peak moving downward during the two sampling intervals; v is the speed at which the tracer concentration peak moves downward during the two sampling intervals; θ is the average volumetric moisture content of the soil layer that the tracer concentration peak passes through when moving downward during the Δt time.

[0014] Optionally, in step A, excavating a delivery hole includes:

[0015] The soil of the area to be tested is excavated in the vertical direction to form an operating pit;

[0016] The side wall of the working pit is excavated in the horizontal direction to form the delivery hole.

[0017] Optionally, the depth of the working pit is 2 / 3 of the groundwater depth.

[0018] Optionally, the delivery holes are square planes composed of parallel drilled holes with a distribution interval of 1 cm.

[0019] Optionally, the square delivery hole is 80 cm long along the free surface of the working pit and 60 cm wide from the working pit toward the soil. There are 4 delivery holes in a working pit, each of which is opposite to the other. Their vertical positions are at the depth of the working pit and 1 / 2 of the depth of the working pit from the top surface position of the working pit.

[0020] Optionally, in step B, a marker is buried during the backfilling process, and the marker is 30 cm away from the ground surface.

[0021] Optionally, in step C, the location of the soil sampling is 25 cm away from the working pit from the placement hole.

[0022] Optionally, in step C, the analysis is specifically performed by drying the sampled soil, dispersing it in pure water to obtain a clear liquid, and then measuring the bromide ion concentration of the clear liquid.

[0023] Compared with the prior art, the beneficial effects of this application are:

[0024] 1. This application proposes a tracer-based in-situ non-destructive groundwater net recharge measurement method and system. This method uses a non-destructive method to put the tracer into the soil, and the movement of the tracer reflects the actual groundwater recharge process. This method can significantly avoid the situation where the tracer is inaccurate in measuring the net groundwater recharge due to the destruction of the original soil structure.

[0025] 2. The tracer placement method proposed in this application is a horizontal square uniform placement area. Compared with the traditional tracer drilling placement method, the tracer placement area is more uniform and reasonable, and can ensure the uniform downward migration of the tracer on a horizontal tracer placement surface, thereby greatly reducing the deviation of the tracer test results caused by spatial non-uniformity between different observations. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The technical solution and other beneficial effects of the present application will be made apparent by describing in detail the specific implementation methods of the present application in conjunction with the accompanying drawings.

[0027] Figure 1 A tracer-based in-situ non-destructive groundwater net recharge measurement method and system flow chart involved in the embodiments of the present application;

[0028] Figure 2 A schematic diagram of the measurement position of the net groundwater recharge in the Longsheng well-channel combination area and a schematic diagram of the soil profile of a typical measurement point involved in the embodiments of the present application;

[0029] Figure 3 Schematic diagram of (a) the vertical free surface and the horizontal tracer placement surface of the square pit in the embodiment of the present application, and (b) the operation schematic diagram of the horizontal tracer placement surface;

[0030] Figure 4 This is a schematic diagram of GPS measurement of ground features and measurement of the distance from the ground features to square pit markers in an embodiment of the present application.

[0031] Figure 5 (a) The sampling locations and arrangements of each measuring point in the present application, and (b) a schematic diagram of drilling soil samples;

[0032] Figure 6 Schematic diagram of (a) soil drying, (b) solution filtration and (c) bromide ion concentration measurement in indoor tests in the embodiments of the present application;

[0033] Figure 7 This is a schematic diagram of the comparison of two tracer profile concentration peaks at a typical well irrigation area farmland groundwater net recharge measurement point in the embodiment of the present application. DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0035] In the description of the present application, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present application, "plurality" means two or more, unless otherwise clearly and specifically defined.

[0036] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or mutual communication; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0037] The disclosure below provides many different embodiments or examples to realize the different structures of the present application. In order to simplify the disclosure of the present application, the parts and settings of specific examples are described below. Of course, they are only examples, and the purpose is not to limit the present application. In addition, the present application can repeat reference numbers and / or reference letters in different examples, and this repetition is for the purpose of simplification and clarity, which itself does not indicate the relationship between the various embodiments and / or settings discussed. In addition, the various specific processes and material examples provided by the present application, but those of ordinary skill in the art can appreciate the application of other processes and / or the use of other materials.

[0038] The present application provides a method for measuring the in-situ non-destructive groundwater net recharge based on tracing, comprising the following steps:

[0039] A. Excavate the soil of the area to be tested to form a placement hole extending in the horizontal direction, wherein the placement hole is used to accommodate the tracer to be placed;

[0040] B. After the tracer is placed, the placement hole is backfilled;

[0041] C. taking soil samples at predetermined time intervals multiple times from the area where the tracer is placed;

[0042] D. analyzing the tracer concentration peak contained in the sampled soil;

[0043] E. According to the above concentration peak and based on the above predetermined time interval, the net leaching amount of groundwater in the above test area is calculated according to the following formula:

[0044]

[0045] Among them, Q c is the net leaching amount of groundwater; Δt is the time interval between two adjacent tracer samplings; Δz is the depth of the tracer concentration peak moving downward during the two sampling intervals; v is the speed at which the tracer concentration peak moves downward during the two sampling intervals; θ is the average volumetric moisture content of the soil layer that the tracer concentration peak passes through when moving downward during the Δt time.

[0046] As an exemplary implementation method, in step A, excavating a delivery hole includes:

[0047] The soil of the area to be tested is excavated in the vertical direction to form an operating pit;

[0048] The side wall of the working pit is excavated in the horizontal direction to form the delivery hole.

[0049] As a demonstrative implementation method, the depth of the working pit is 2 / 3 of the groundwater depth.

[0050] As an exemplary implementation, the delivery holes are a square plane composed of parallel drill holes with a distribution interval of 1 cm.

[0051] As a demonstrative implementation method, the square delivery hole is 80 cm long along the free surface of the working pit and 60 cm wide from the working pit toward the soil. There are four delivery holes in a working pit, each of which is opposite to the other. Their vertical positions are respectively at the depth of the working pit and 1 / 2 of the depth of the working pit from the top surface position of the working pit.

[0052] As an exemplary implementation method, in step B, a marker is buried during the backfilling process, and the marker is 30 cm away from the ground surface.

[0053] As a demonstrative implementation method, in step C, the location of the soil sampling is 25 cm away from the working pit from the placement hole.

[0054] As an exemplary implementation method, in step C, the analysis is specifically to dry the sampled soil, disperse it in pure water to obtain a clear liquid, and then measure the bromide ion concentration of the clear liquid.

[0055] Now, the measurement operation process of the present application is described in a common application scenario. It should be noted that this common implementation scheme cannot be used as a basis for understanding the essential feature identification of the technical problem claimed to be solved by the present application, and it is only a demonstration.

[0056] In this embodiment, the net groundwater recharge measurement test in the Longsheng test area of ​​the Hetao Irrigation District in Inner Mongolia, China is used as an example to illustrate the implementation steps. Figure 1 As shown, the present embodiment provides a tracer-based in-situ non-destructive groundwater net recharge measurement method and system, which includes the following steps:

[0057] S1, test location selection and vertical free surface layout.

[0058] This example takes the Longsheng Experimental Area in the Hetao Irrigation District of Inner Mongolia as a typical research area. The arrangement of the measurement locations of the net groundwater recharge is as follows: Figure 2 As shown in the figure, it can be found that there are 7 measurement points for net groundwater recharge in farmland, and 6 measurement points for net groundwater recharge in wasteland. The following part is based on the measurement points for net groundwater recharge in farmland in well irrigation area.

[0059] At the selected groundwater net recharge measurement location, soil work is carried out and a square pit (i.e., working pit) is excavated. The horizontal size of the square pit is 1m×1m, and the vertical depth is 1.1m. The vertical free surfaces around the square pit are leveled. A typical location is selected, and soil ring sampling is performed every 20cm on the vertical free surface to measure soil hydraulic parameters at different depths and record the changes in soil texture along the depth. The schematic diagram of the vertical profile of soil texture is shown in the figure below. Figure 2 shown.

[0060] S2, lateral drilling is performed on the vertical free-surface to obtain the tracer placement area.

[0061] For each vertical open surface, the tracer sampling position is a horizontal plane with a length of 80 cm along the side length of the square working pit and a length of 60 cm perpendicular to the open surface towards the soil at a specified depth on the open surface, such as Figure 3 (a) is shown. To obtain such a horizontal plane, an electric drill is used to perform lateral drilling at a specified depth on each vertical free-air surface. The drill bit is a smooth straight steel bar with a length of 60 cm and a diameter of 1 cm, and one end is ground into a drill bit. During the drilling process, the tracer placement surface is kept horizontal as much as possible, with different holes spaced 1 cm apart, and finally a row of horizontal grid-like holes is formed to obtain placement holes (also called the tracer horizontal placement surface).

[0062] The operation diagram is as follows Figure 3In this experiment, a square pit can get a total of 4 placement holes that are opposite to each other. One group of relative placement holes is vertically set at the depth of the square pit, that is, at a depth of 1.00m for horizontal tracer placement, and the other group of relative placement holes is vertically set at a depth of 0.50m for horizontal tracer placement.

[0063] S3, tracer delivery scheme.

[0064] KBr solution, which is scarce in nature, is selected as the main component of the tracer, and the dosage of each tracer horizontal placement surface is 2L. A 100ml syringe is used as a tracer placement tool. A plastic hose is inserted into the water outlet of the syringe, and the rest of the plastic hose is fixed on a plastic rod. After the tracer begins to be placed, the syringe draws in the tracer solution. The plastic rod with the plastic hose fixed is inserted deep into the borehole, and then slowly pulled outward, while slowly pushing the syringe to inject the solution. When the plastic rod is pulled out of the borehole, the tracer placement of the borehole is completed, and the tracer sampling is carried out in the adjacent borehole. Ensure that the amount of tracer solution injected into each borehole is 50ml. Until all placement holes are sampled.

[0065] S4, backfilling and position determination of the test square pit.

[0066] After all tracer horizontal placement surfaces have been sampled, the test square pit is backfilled. Every 10-20 cm of the square pit is backfilled, the backfilled soil needs to be compacted by using the impact force of the free fall of the rammer. When backfilling to a depth of 30 cm from the ground surface, set the square pit position mark. The marker is a non-corrosive screwdriver. The marker is fixed at the four corners of the square pit, and a plastic stick is placed vertically at each marker position to lead to the surface. Then continue backfilling until the square pit is filled. In the test area, select more than two key features that are difficult to change over time for longitude and latitude measurement and mapping. Then measure the distance from each key feature to the four plastic sticks. GPS measurement of features and distance measurement from features to square pit markers are as follows. Figure 4 shown.

[0067] S5, tracer periodic sampling scheme.

[0068] The tracer was sampled regularly using a manual drill. Four holes were drilled on each side of the test square pit, with each sampling hole spaced 20 cm apart. Sampling was done twice a year in May and October. Figure 5(a) As shown. When sampling, first find the key features around the sampling point according to the figure drawn in step 4, and then use the triangle positioning method to find the corner points of the test pit according to the distance between the features and the corner points of the test square pit, and dig down to 30 cm to find the square pit position marker, so as to obtain the accurate position of the square pit. According to the accurate position of the square pit, the vertical projection surface of the horizontal tracer placement surface is calculated. The horizontal line directly above each tracer horizontal placement surface and 30 cm away from the square pit is the sampling position for all previous times. Soil samples are taken by manual drilling, and samples are taken every 10 cm vertically until the groundwater level. Manually drilled soil samples are as follows: Figure 5 (b) as shown.

[0069] S6, Indoor experimental analysis plan for soil samples.

[0070] Take 60-65g of each soil sample and put it in an oven to dry. Then take 20g of the dried soil and put it in a 250ml Erlenmeyer flask. Add 100ml of pure water at a soil-water ratio of 1:5 to dissolve it. After sufficient shaking, filter it in a 100ml Erlenmeyer flask to obtain a clear solution. Then repeat stirring for 2 minutes in the stirrer of the ion meter, and use an ion meter equipped with a bromide ion electrode to measure the bromide ion concentration. The schematic diagram of soil drying, solution filtration and bromide ion concentration measurement in the indoor experiment is shown in the figure. Figure 6 shown.

[0071] S7, calculation of net groundwater recharge.

[0072] According to the tracer distribution along the depth of the soil profile at the measured sampling point, the tracer concentration peak of each profile is determined. The results are shown in Figure 7 As shown. According to formula 1,

[0073]

[0074] Among them, Q c is the net leaching amount of groundwater; Δt is the time interval between two adjacent tracer samplings; Δz is the depth of the tracer concentration peak moving downward during the two sampling intervals; v is the speed at which the tracer concentration peak moves downward during the two sampling intervals; θ is the average volumetric moisture content of the soil layer that the tracer concentration peak passes through when moving downward during the Δt time.

[0075] The net groundwater recharge at the measuring point of farmland groundwater recharge in the well irrigation area was 33.8 mm / year. The average net groundwater recharge at the 7 measuring points of farmland groundwater recharge in Longsheng area was 36.3 mm / year.

[0076] In summary, this embodiment provides an in-situ non-destructive groundwater net recharge measurement method and system based on tracing. Based on the traditional tracer method for measuring groundwater net recharge, this method proposes a non-destructive tracer placement method to ensure that the sampling area is a horizontal square uniform placement area, ensure the uniformity of tracer migration on the same tracer horizontal placement surface, and avoid the inaccurate tracer measurement of groundwater net recharge caused by changes in the original soil structure above the sampling position.

[0077] The above is only a preferred specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed in the present application should be covered within the protection scope of the present application.

Claims

1. A method for measuring the net recharge of groundwater in situ and non-destructively based on tracing, characterized in that: The following steps are involved: A. Excavate the soil of the area to be tested to form a placement hole extending in the horizontal direction, wherein the placement hole is used to accommodate the tracer to be placed; B. After the tracer is placed, backfilling the placement hole; C. taking soil samples at predetermined time intervals multiple times from the area where the tracer is placed; D. analyzing the sampled soil for the tracer concentration peak contained therein; E. According to the concentration peak and based on the predetermined time interval, the net leaching amount of groundwater in the test area is calculated according to the following formula: in, Q c is the net leaching amount of groundwater; Δ t is the time interval between two adjacent tracer samplings; Δ z is the depth to which the tracer concentration peak moves downward between two sampling intervals; v is the speed at which the tracer concentration peak moves downward between two sampling intervals; θ is Δ t The average volumetric moisture content of the soil layer that the tracer concentration peak passes through when moving downward within a certain period of time; In step A, excavating a delivery hole includes: The soil of the area to be tested is excavated in the vertical direction to form an operating pit; For the vertical free-air surfaces around the working pit, excavate the vertical free-air surfaces along the horizontal direction at the designated depths of the vertical free-air surfaces around the working pit to form a horizontal placement surface; The horizontal placement surface is a square plane composed of parallel drill holes with a distribution interval of 1 cm; The length of the horizontal delivery surface is 80 cm along the free surface of the working pit, and the width is 60 cm from the working pit toward the soil. There are 4 delivery holes in a working pit, each of which is opposite to the other. Their vertical positions are respectively at the depth of the working pit and 1 / 2 of the depth of the working pit from the top surface position of the working pit.

2. The measuring method according to claim 1, characterized in that: In step B, a marker is buried during the backfilling process, and the marker is 30 cm away from the ground surface.

3. The measuring method according to claim 1, characterized in that: In step C, the location of the soil sampling is 25 cm from the placement hole to the working pit.

4. The measuring method according to claim 1, characterized in that: In step C, the analysis is specifically to dry the sampled soil, disperse it in pure water to obtain a clear liquid, and then measure the bromide ion concentration of the clear liquid.

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