JP2001349884A - Soil water sampling method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a soil water sampling apparatus which enables the sampling of soil water in the environment as intact, without changing it at a sampling point, and moreover, the quantitative measurement thereof. SOLUTION: A porous plate 14 is buried at a location where soil water is sampled, while a first tentiometer probe 42 is buried right on it and a second tentiometer 43 near the outside thereof. The porous plate 41 is connected to an external suction bottle 45. When a pore water pressure P1 detected by the first tentiometer probe 42 is higher than the pore water pressure P2 detected by the second tentiometer probe 43, the pressure inside the suction bottle 45 is lowered to suck water into the suction bottle 45 from the porous plate 41, thereby sampling the soil water. Otherwise, the inside of the suction bottle 45 is communicated with the atmospheric air to stop the suction. For the porous plate 41 which can be used is a porcelain porous plate used conventionally for a water retention test or the like of soil.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for automatically collecting vertical infiltrated water in order to analyze the quality of water that vertically penetrates soil such as mountains and residential areas, and to measure the amount of the water. .

[0002]

2. Description of the Related Art The process by which rainwater and irrigation water penetrates the surface soil in an unsaturated manner is closely related to landslide disasters and environmental pollution. For example, surface landslides on mountain slopes are caused by rainwater seeping through surface soil and raising groundwater levels. For this reason, it is extremely important to accurately know the temporal change in the amount of unsaturated permeation in predicting the occurrence of a disaster. It also monitors groundwater contamination due to the application of fertilizers and pesticides in fields, plantations and golf courses, as well as soil and groundwater contamination due to factory effluents, and elucidates the functions of forests to purify rainwater and improve river water quality. It is indispensable to know exactly the quantity and quality of water that is unsaturatedly penetrating the surface soil.

[0003] However, at present, sufficient knowledge has not been obtained regarding this unsaturated permeation process. As one of the causes, it is possible to point out a problem with the method of collecting soil water. In other words, although the movement of dissolved substances in soil is closely related to the movement of soil water, the method of sampling unsaturated soil water currently used is compared with the theory of unsaturated permeation of soil water. Therefore, it is difficult to accurately determine the amount of movement of water and substances dissolved in water under natural conditions.

[0004] Normally, sampling of unsaturated soil water is performed by a method of extracting a solution in a soil sample by centrifugation or the like, but this not only disturbs the site but also makes continuous sampling impossible. is there. As a non-destructive alternative to this, (1) an impermeable plate is buried in the soil layer, and the permeated water accumulated on the upper surface is drained by gravity (Fig. 1)
(A)), (2) An impermeable bottomed column is buried in the soil layer, and water vertically penetrating the inside is drained by gravity (FIG. 1 (b)). Capillary suction of water on the permeable plate or the bottom of the column with glass fiber or nylon (Fig. 1 (c), (d)), (4) Embed a porous cup in the soil layer, Devices such as for aspirating water (FIG. 2) have been developed and marketed.

However, since the methods (1) and (2) are tension-free, they cannot be collected unless the soil water on the plate becomes saturated. Further, in the method (1), the water diffuses to the peripheral portion where the water is dried, and therefore, it is not possible to accurately measure the vertical penetration amount. On the other hand, in the case of (4), since water is suctioned by applying tension, there is a possibility that the target point may be in a drier environment, and quantitative measurement of the amount of permeated water is impossible. The method of (3) is an improvement over the problems of (1) and (2) in that the water cannot be collected unless the soil water on the plate or the bottom of the column becomes saturated. Since only the suction pressure is continuously applied, it is impossible to control the water sampling according to the amount of permeated water or the wetness of the soil, and the environment at the water sampling point cannot be kept equal to the surrounding environment. Regarding the relationship with the surrounding environment, in the method shown in FIGS. 1B and 1D, since the column is isolated from the surroundings, the influence is neglected in the soil where the plant roots are set up. There is also a problem.

[0006]

SUMMARY OF THE INVENTION Briye, USA
Devised an equilibrium pressure lysimeter to prevent such disturbances at the sampling points ("An equilibrium tension lysimeter").
lysimeter for measuring drainage through soil ", So
il Science Society of America Journal, May-June, 1
999). That is, a water sampling box 30 provided with a stainless steel plate (perforated plate) 31 having a large number of micropores (diameter 0.2 μm) provided on the upper part.
(FIG. 3) is buried in the soil, and a pore pressure gauge is provided in the soil immediately above the perforated plate and in the surrounding soil. Then, the suction pressure at the lower part of the perforated plate 31 is adjusted so that the values of these two pore water pressures match and the soil moisture condition of the portion where the water sampling box 30 is buried becomes equal to the surrounding natural soil cross section. In addition,
The suction pressure in the water sampling box 30 by the suction pump is manually adjusted so as to be lower than the pore water pressure in the surrounding natural soil section by 5 kPa (kilopascal), and the constant pressure is continuously applied. This can lead to over-watering,
Conversely, the amount of water taken is prevented from becoming too small.

In the equilibrium pressure lysimeter developed by Briai et al., The suction pressure of a pump for water sampling is manually set so as to be lower by 5 kPa than the inter-soil water pressure measured on a natural soil section as a control. , Its set pressure is kept constant. Here, no clear basis for the value of 5 kPa is given.

[0008] Soil water is sucked through the perforated plate 31, but since the perforated plate 31 has resistance to water permeability, a water pressure difference occurs above and below the perforated plate 31 at the time of water sampling. Since this pressure difference depends on the velocity of water passing through the perforated plate 31,
If a pressure difference of 5 kPa is set uniformly, it becomes impossible to maintain the soil pore water pressure at the soil water sampling point equal to the pore water pressure of the natural soil profile. As a result, it is conceivable that the amount of water itself may be different from the actual amount of permeation.

The present invention has been made in order to solve such a problem, and an object of the present invention is to collect soil water in the same state without changing the environment of a sampling point, and furthermore, to collect the soil water. An object of the present invention is to provide a soil water sampling device capable of quantitative measurement.

[0010]

Means for Solving the Problems To solve the above problems, the method for collecting soil water according to the present invention comprises the steps of: a) burying a porous plate at a soil water collection point and directly placing a first tensiometer on the soil plate; A probe is embedded with a second tensiometer probe near the outside thereof, b) a porous plate is connected to an external suction bottle, and c) a pore water pressure P detected by the first tensiometer probe.
When 1 is higher than the pore water pressure P2 detected by the second tensiometer probe, the pressure inside the suction bottle is reduced to suck water from the porous plate into the suction bottle, and otherwise, the inside of the suction bottle is exposed to the atmosphere. The suction is stopped in communication.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION As a porous plate, a porous plate made of porcelain conventionally used for a soil water retention test or the like (for example, Pressure Plasmid manufactured by US Soilmoisture Equipment Co., Ltd.)
te Cells 0675 series) can be used. This ceramic porous plate for the water retention test is approximately 26 cm in diameter and thickness
Although it is about 0.8 cm in size and various pore sizes are prepared according to the test purpose, when used in the soil water sampling method according to the present invention, a 0.5 Bar or 1 Bar high
It is desirable to use a flow type (large hole).

As a tensiometer, a tensiometer conventionally used for measuring pore water pressure of soil (for example, Tenkiometer DIK-3150 manufactured by Daiki Rika Kogyo Co., Ltd.)
Etc.) can be used. However, only the probe (the sensing part or the sensor part) is essentially used in the present invention.

[0013]

FIG. 4 shows a specific example of the soil water sampling method according to the present invention.
This will be described with reference to FIG. First, as shown in FIG. 4, the porous plate 41 is buried in the target soil. The depth is set according to the purpose of water sampling and the thickness of the unsaturated soil layer at the site, but in general,
About 10-100cm is appropriate. Then, the first and second tensiometer probes 42 and 43 are buried immediately above and near the same depth. A suction port 41 a is provided in the porous plate 41, and a suction tube 44 is connected to the suction port 41 a to guide the suction tube 45 to an external suction bottle 45.

As shown in FIG. 5, the suction bottle 45 is sealed with a stopper, and the inside thereof can be depressurized by a suction pump 46.
Electromagnetic relief valve 47 between suction pump 46 and suction bottle 45
Is provided. Relays 48 and 49 are provided between the suction pump 46 and the electromagnetic relief valve 47 and their power supply 50, respectively, and their operations are controlled by a controller 51. The suction bottle 45 is further provided with a pressure gauge 52 for detecting the pressure inside the suction bottle 45 and a load cell balance 53 for measuring the overall weight, and these are also connected to the controller 51. The first and second tensiometer probes 4
2 and 43 are also connected to the controller 51 so that pressures at both positions can be detected.

A small-capacity measuring cup 55 is provided immediately below the outlet of the suction tube 44 guided from the porous plate 41 in the suction bottle 45. An EC meter probe 56 for measuring the electric conductivity (EC) of water therein is inserted into the measuring cup 55, and the probe 56 is also connected to the controller 51. A general personal computer may be used as the controller 51, but it may be configured as a dedicated device using a microcomputer.

The outline of the control by the controller 51 is as shown in FIG. The controller 51 operates for a predetermined time (for example, 3
Every second) the signal P from the first tensiometer probe 42
a, The signal Pb from the second tensiometer probe 43 and the signal Pc from the pressure gauge 52 are taken in (step S1).
0). Among them, the pressure Pa directly above the porous plate 41 detected by the first tensiometer probe 42 and the pressure Pb of the natural soil beside it are compared (S11), and the pressure Pa directly above the porous plate 41 is lower. In this case, the suction pump 46 is stopped (S12). In this case, it is next checked whether or not the pressure Pc in the suction bottle 45 is -10 cm or less in terms of a head pressure (hereinafter, all pressures are indicated by a relative head pressure based on the atmospheric pressure) (S13). . When Pc <−10 cm, the relief valve 47 is opened (S14), and the inside of the suction bottle 45 is brought close to the atmospheric pressure. Thereby, the suction of the soil water from the porous plate 41 to the suction bottle 45 is stopped. If Pc is higher than -10 cm, the relief valve 47 is closed (S15), and this processing ends. More than S10
Steps S15 to S15 are performed when the pore water pressure Pa at the soil water sampling point is lower than the surrounding pore water pressure Pb (which is relatively dry than the surroundings).

If the determination in step S11 is no, that is, if the pore water pressure Pa at the soil water sampling point is higher than the surrounding pore water pressure Pb (wet than the surrounding water), the process proceeds to step S16, and suction is performed. The pressure Pc in the bottle 45 is -450
Check if it is less than cm. If the pressure Pc in the suction bottle 45 is already -450 cm or less (high vacuum), the suction pump is stopped (S17), and the process ends.
In this case, the soil water is sucked from the porous plate toward the suction bottle 45 by the low pressure (vacuum) in the suction bottle 45. The pressure of -450 cm here is a value in consideration of the pressure resistance of the suction bottle 45.

If the pressure Pc in the suction bottle 45 is -450 cm or more, it is determined whether or not the suction pump is currently stopped (S18). When the suction pump 46 is stopped, it is further checked whether or not the pressure Pc in the suction bottle 45 is -400 cm or more (S19).
7 is released (S20), and the pressure in the suction bottle 45 is increased. Then, it is checked whether or not the pressure Pc in the suction bottle 45 is equal to or more than -300 cm (S21). This is to quickly increase the value of Pc to -300 cm or more by opening the relief valve 47. When the value of Pc reaches -300 cm, the process proceeds to S22, where the relief valve 47
Is closed, and the suction pump 46 is operated (S23).

In the processing from step S16 to step S23, the operating range of the suction pump 46 is set between -300 cm and -450 cm. When the suction pump 46 reaches -450 cm, the suction pump 46 is stopped. When the pressure Pc in the suction bottle 45 rises to -400 cm, the relief valve 47 is opened, and the pressure Pc in the suction bottle 45 is released.
At a stretch to -300 cm, which is the suction pump operation start pressure.

If the suction pump 46 is operating in step S18, the process proceeds to step S21, where the pressure Pc in the suction bottle 45 is
Check if is not less than -300cm. Pc is -300c
If it is not less than m, the relief valve 47 is closed (S22), and the suction pump operation (S23) is continued. After a while, when the pressure in the suction bottle 45 falls to -300 cm or less, the process proceeds from S21 to S24, but the state of the relief valve closing and the operation of the suction pump are similarly maintained. Then, when Pa <Pb (S11) or when Pc <−450 cm (S16), the suction pump 46 is stopped (S12 or S17).

By the above processing, the pore water pressure around the porous plate 41 is always kept almost the same as that of the surrounding environment.
Soil water is collected under natural conditions. The collected soil water once enters the measuring cup 55, where its electric conductivity is measured by the EC meter probe 56. The measured value is recorded in a storage device provided in the controller 51 (or connected to the outside). In addition, since the weight of the entire suction bottle 45 is constantly measured by the load cell balance 53, data on the amount of sucked soil water is collected with time, and is also recorded in the storage device of the controller 51.

As described above, the soil water sampling apparatus according to the present embodiment enables accurate determination of vertical infiltration water, and also enables measurement of the characteristics of the collected soil water at each time. In the above embodiment, the electric conductivity is mentioned as an example of measuring the sampled water, but other than that, the measurement of the component concentration and the like is also possible.

The above apparatus was installed in a field in a deciduous forest zone in the experimental forest headquarters attached to Kyoto University. Porous plate 41 at depth 30
cm, and place the tensiometer probes 42 and 43 directly above it at a depth of 30 cm and at a depth of 20 cm (the above is called a water sampling section), and near that, at a depth of 30 cm and 20 cm (the above is called a natural cross section) ).

FIG. 7A does not perform the above control,
When the suction pump 46 is stopped, the tensiometer probe 42 having a 30 cm deep water sampling cross section and a natural cross section,
Pore pressure measurement results by 43 (and rainfall during that time)
FIG. FIG. 7B shows both tensiometer probes 42 and 4 when the control as shown in FIG. 6 is performed.
3 is a graph showing the measurement results of pore water pressure (and the amount of rainfall during that time) according to No. 3. Comparison between the graphs (a) and (b) shows that the apparatus and control according to the present invention maintain the pore water pressure on the porous plate 41 to be substantially the same as the surrounding natural environment. Understand.

FIG. 8 shows the precipitation (a) during the water sampling period shown in FIG. 7 (b), the depths of 20 cm and 30 cm in the water sampling section and the natural section.
3 is a graph of pore water pressures (b) and (c), an integrated rainfall amount, and an integrated water collection amount (d). By comparing the graphs (a), (b) and (c), it can be seen that the pore water pressure of the soil has increased in response to the rain event, but the value near the porous plate 41 is different from the value of the surrounding environment. It is kept almost the same.
In addition, the same environment is maintained in the upper part (20 cm), and it has been proved that the disturbance of the sampling target place due to the installation of this device is minimized. In addition, it can be seen from the graph (d) that the amount of water withdrawal is increasing for each rainfall event.
The amount of water sampled by this device is 46.4 mm, compared to 73.5 mm.
About 63% of the rainfall is collected by this device. Considering the loss due to evapotranspiration, it is considered that the water sampling amount is almost reasonable.

FIG. 9 is a graph of the amount of collected water and the electrical conductivity of the collected water during another collection period. It can be seen that the electrical conductivity (EC) decreases as the amount of permeated water increases during rainfall. The reason for this is that the amount of ions eluted is small because the contact time of the permeated water during rainfall with the soil particles is short.

[0027]

According to the method of the present invention, since only the porous plate is buried in the soil, compared with the method of Brai et al., In which a large box is buried, there is less disturbance of the soil at the measurement target site. Installation is easy.

In the method of Briai et al., The space below the perforated plate is suctioned by a pump so that the pressure is always at a predetermined pressure. However, as described above, the equilibrium pressure lysimeter developed by Briai et al. The water is sucked through the plate, but since the perforated plate has resistance to water permeation, a water pressure difference occurs between the upper and lower portions of the perforated plate at the time of water sampling. Since this pressure difference depends on the speed of water passing through the perforated plate, if a pressure difference of 5 kPa is set uniformly, maintain the soil pore water pressure at the soil water sampling point equal to the pore water pressure of the natural soil profile. Becomes impossible.
As a result, it is conceivable that the water sampling amount itself is different from the actual permeation amount. In contrast, in the method according to the present invention,
Directly compares the soil pore water pressure directly above the porous plate with the soil pore water pressure near the outside of the porous plate.Suction is performed by operating the suction pump only when both do not match, and when both match, the relief valve is opened and suction is performed. The operation to reduce the pressure to zero is performed. Thus, when the amount of permeated water is large, a larger pressure difference is applied to the upper and lower portions of the porous plate, and when the amount of permeated water is small, the pressure difference is small (when the amount of permeated water is zero, the pressure difference is also zero). As a result, both pore water pressures are always kept equal, and an amount of water equal to the actual amount of permeated water is collected.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an installation example of a conventional tension-free lysimeter.

FIG. 2 is an explanatory view showing an installation example of a conventional tension lysimeter.

FIG. 3 is a perspective view showing a configuration of an equilibrium pressure lysimeter prototyped by Briy et al.

FIG. 4 is a schematic configuration diagram of a soil water sampling device according to the present invention.

FIG. 5 is a configuration diagram of one embodiment of a soil water sampling device of the present invention.

FIG. 6 is a control flowchart of the soil water sampling apparatus according to the embodiment.

FIG. 7 is a graph comparing the change in pore water pressure when the soil water sampling device of the embodiment is operated and when it is not operated.

FIG. 8 is a graph of rainfall, pore water pressure measured by the soil water sampling apparatus of the example, and water sampling.

FIG. 9 is a graph of the water sampling amount and the electric conductivity measurement results obtained by the soil water sampling device of the example.

[Explanation of symbols]

 41 ... Porous plate 41a ... Suction port 42 ... First tensiometer probe 43 ... Second tensiometer probe 44 ... Suction tube 45 ... Suction bottle 46 ... Suction pump 47 ... Electromagnetic relief valve 48, 49 ... Relay 50 ... Power supply 51 ... Controller 52 ... pressure gauge 53 ... load cell balance 55 ... measuring cup 56 ... EC meter probe

Claims (2)

[Claims] 1. A) A porous plate is buried in a soil water sampling point, and a first tensiometer probe is placed immediately above the porous plate.
A second tensiometer probe is embedded in the vicinity of the outside, respectively, b) a porous plate is connected to an external suction bottle, and c) a pore water pressure P detected by the first tensiometer probe.
When 1 is higher than the pore water pressure P2 detected by the second tensiometer probe, the pressure inside the suction bottle is reduced to suck water from the porous plate into the suction bottle, and otherwise, the inside of the suction bottle is exposed to the atmosphere. A method for collecting soil water, comprising: communicating and stopping suction. 2. a) a porous plate to be buried at the soil water sampling point; b) first and second tensiometer probes respectively buried directly above and near the outside of the porous plate; c) the porous plate A suction bottle connected to the plate; d) a suction pump for sucking air inside the suction bottle; e) a relief valve for communicating or shutting off the suction bottle and the atmosphere; f) detection by the first tensiometer probe. When the pressure P1 becomes higher than the pressure P2 detected by the second tensiometer probe, the suction pump is operated, and when not, the relief valve is opened to control the interior of the suction bottle to communicate with the atmosphere. A soil water sampling device comprising: