沙漠研究 24-1, 245-248 (2014)
Ἃ₍◊✲ 24-1, 245 - 248 (2014)
Journal of Arid Land Studies
Journal of Arid Land Studies－ DT11 Refereed Paper －㸫DT11 Refereed Paper㸫

Simple Method of Shallow Groundwater Exploration by Groundwater
Aeration Sound in Semi-Arid Grassland
Takayuki KAWAI*1), Yasuyuki TADA 2), Masato SHINODA 3), Ryota TSUCHIYA 4),
Toshihiro MORII 5), Tetsuya SUZUKI 5) and Khuut TSEEDULAM 6)
Abstract: The groundwater aeration sound (GAS) has been focused to identify the groundwater path point in the field of slope
disaster science. This study aimed to develop a new exploration technique of groundwater level using the GAS, which is suitable forharsh natural environments and to verify the measurement accuracy of the exploration method. In addition this study was aimed totarget free groundwater and perched water. The GAS is the kind of elastic wave generated in the vicinity of the saturated /unsaturated boundary. We have developed a device that can collect this small wave from the ground surface. The total weight ofthe device is 0.9 kg, making it highly portable and workable. On the assumption that there is a relevance of GAS and groundwaterlevels, we conducted a survey using the existing wells in the dry grasslands of Mongolia. Results indicated that a logarithmic
relationship between the GAS and groundwater levels. It was found that the groundwater level could be estimated easily bymeasuring the GAS value from the surface. Furthermore, the correlation of GAS level and groundwater level showed different
trends in each geological condition.
Key Words: Groundwater aeration sound, Groundwater level, Shallow groundwater exploration

1. Introduction
About 40% of the total land area of the earth is arid andsemi-arid area (Middleton et al., 1997). Many of the water
resources in this arid area are dependent on groundwater(Cesare, 2001). In recent years, the depletion of groundwater
resources due to excessive pumping has been a major concern.
For sustainable use of groundwater, a detailed determination oflocal groundwater environment is urgently needed. However,significant time and budget are necessary to measure this factor
using existing technologies such as geophysical explorationand observation wells. In addition, the field measurement in aharsh drylands natural environment is extremely difficult
because the measuring methods are difficult (e.g., transport ofheavy equipment and exploration drilling operations.)
We focused our attention on the groundwater aeration
sound which has been attracting attention for utility in slope
disaster science. The purpose of this study is to develop a
new exploration technique of groundwater assessment using
the groundwater aeration sound which is suitable for drylands
and to verify the measurement accuracy of the exploration
method. In addition, this study targets free groundwater andperched water.
* Corresponding Author: kawai@agr.niigata-u.ac.jp

Fig. 1. Pattern diagrams of soil pore and arise of elastic wave.

2. Materials and Methods
2.1. Groundwater aeration soundThe moving speed of groundwater is projected among themass transfer phenomena under the ground. Therefore, air
movement in the soil pore occurs frequently by the wake ofgroundwater movement in the vicinity of the saturated /unsaturated boundary. This soil air pushes the pore water
through the soil gap and the water screen is popped (Fig. 1).
At that time, the elastic wave is generated. Tada et al. (2005)
named Groundwater Aeration Sound (GAS) as that complex
wave of this elastic wave and various friction sounds.
It was revealed that spring water and pipe flow occurs at
㸦Received, September 11th, 2013; Accepted, January 10th, 2014㸧

2-8050 Igarashi, Nishi-ku, Niigata city, Japan
1) Natural Hazards and Disaster Recovery Research Institute, Niigata Univ., Japan4) Iga Research Institute, Mie Univ., Japan

2) Forestry and Forest Products Research Institute, Japan

5) Faculty of Agriculture, Niigata Univ., Japan

3) Arid Land Research Center, Tottori Univ., Japan

6) Mongolian Univ. of Science and Technology, Mongolia

246

Headphone
Headphone
RecorderRecorder123

Hydrostat
Level meter

Measurement
point4Pickup

Groundwaterflow sound

Ground surface

Groundwater level( deep )( shallow )Fig. 2. Measuring device and measurement of Groundwater aeration sound. 1. Headphone, 2. Acceleration pickup sensor, 3. Vibration isolation
plate, 4. Level meter.

the high GAS point in natural slopes by Tada et al. (2006).
This observation may suggest that GAS can be applied to field
groundwater exploration.
2.2. Measuring device of groundwater aeration soundThe GAS measuring device consists of headphone,acceleration pickup sensor with needle, vibration isolation plate,and level meter with an amplifying system and filteringfunctions (Fig. 2). The functions of each part are as follows:
1) Headphone: The measurer can hear and confirm an
actual groundwater aeration sound in the field.
2) Acceleration pickup sensor: A sensor to capture weak
vibration with a stainless needle of ĳ0.8×18 cm in thepickup sensor to prevent external noise such as winds.
3) Vibration isolation plate: This plate prevents various
vibrations above ground surface.
4) Level meter: This part consist of amplification circuit,filter circuit and level meter. The weak sound captured by
the pickup sensor is magnified by the amplification circuit.
Wind noises are removed by the filter circuit. The filter
function can flexibly correspond to various noises in thefield. The level meter directs the sound level of thegroundwater aeration sound.
The total weight of the device is 0.9 kg with highportability and workability. The measurement method simply
requires inserting a needle into the ground surface and to obtaina single sample takes about 5 - 10 minutes. Figure 2 gives anoverview of the measurement using the GAS device. The
exploration is performed by one person to avoid noise, probing

Ulan Bator
Bayan - Unjuul

Fig. 3. Shallow well points in Bayan - Unjuul.

at regular intervals along the survey line.
recorded by the external device as needed.

The GAS is

2.3. Field survey
Tada et al. (2006) suggested that the waveform intension ofGAS is formed by the distance from the aeration source point.
The first point to be considered is whether this result is also
adapted to natural groundwater that flows under threedimensions. Therefore, we determined the relationship247

122Groundwater level ( m -GL )Groundwater level ( m -GL )) 10LGm 8(leve 6lreta 4wdnu 2orG
0

121
3

108
6
4
2
0

0

100200

Plain area
Mountainous area0

between groundwater level and GAS level in the drygrasslands of Mongolia.
The study site was Bayan Unjuul, located about 130 km
south of Ulan Bator (Fig. 3). There are many shallow wells
used by nomadic people around the Bayan Unjuul area. The
water level of these wells is about 1 - 10 m. Then, wemeasured GAS level at the same time as the measurement ofgroundwater level from the surface.
Based on preliminary data, the measurement frequency is
800 Hz for the upper limit and 200 Hz for lower limit. The
measurement period was from August 24th to September 3rdof 2010. There was no precipitation during this period.
Figure 3 showed the measurement points of wells. The
total number of wells for the survey was 39, located in both theplains and mountainous area. The water level in each well
was measured by a contact type water level measure. The
copper wire is contained in this measure and a buzzer sounds
when the head reaches to the water surface.

3. Results and Discussion
The actual measured groundwater level from the surface
ranged from 0.21 - 11.95 m (- G.L.).
Figure 4 shows the correlation between the groundwaterlevel and GAS level. A trend in the data was observed thatGAS level became stronger as the groundwater became more
shallow. The relationship between GAS and groundwaterlevel was observed up to 9.4 m. This result suggested that thegroundwater aeration sound survey method gave an accurate
estimation of groundwater level up to 10 m depth.
We derived an equation to estimate the round groundwater

100150200

Groundwater aeration level

Groundwater aeration level
Fig. 4. Relation between groundwater level and GAS level. Gas isdimensionless number. Line 1 is the expression of logarithmic
approximation. Lines 2 and 3 are the range of error with amargin of plus or minus 2 m of groundwater level.
is a well insand dune andare wells in weathering granite.

50Fig. 5. Relation between groundwater level and GAS level of eachphysical feature.

level from GAS level. Incidentally, the data of 87.67 (GASlevel) and 11.95 m (groundwater level) were not used for thecalculation. The estimation equation was able to approximate
the natural logarithm and the coefficient of determination was
0.4384 and average estimation error was 1.30 m. This result
was sufficiently accurate to estimate the approximate
groundwater level in the field. From these results, it wasshown that the GAS data which were collected with thedeveloped device was useful to estimate the groundwater level.
Figure 5 shows two groups of plots by dividing theapproximate physical features by the same result as Figure 4.
Although divided into mountains and plains, there was no
significant difference in the trend of the two groups.
On the other hand, we noticed a large estimation error.
For example, such data outside the line of the estimated error
lines (Line 2 and 3 in Fig. 4) show that the range of error with amargin of plus or minus 2 m of groundwater level. The pointof groundwater level was relatively deep despite large GASlevels, and was due to the geological condition that thegroundwater flow was relatively fast, such as with sand dunes
and weathering granite. Conversely, the point of groundwaterlevel was relatively shallow despite the GAS level being small
and was associated with the geological condition that thegroundwater flow seems to be slow, such as near the small lake,or basalt. The estimate equation of groundwater level may
change with groundwater flow velocities. From these results,
it was shown that the groundwater aeration sound has atendency to be influenced by different geological conditions.

4. Conclusion
In this research, we proposed a new exploration method toestimate the groundwater level by Groundwater Aeration

248Sound. We adapted this method to dry grasslands andobtained the following results.
1. The sound collection device that was developed islightweight and is suitable for measurements in dry land.
2. A correlation was observed for groundwater level and theGAS level, and it was possible to approximate the naturallogarithm.
3. The coefficient of determination for estimate equation was0.4384 and average estimation error was 1.30 m. Theresults showed that the GAS was effective in exploration ofshallow groundwater in the field.
4. The GAS can estimate the groundwater level toapproximately 10 m deep under the conditions of arid land.
5. There was a difference in GAS distribution depending on
geological conditions.
Accumulated data for eachgeological condition were desirable.

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