JP2003194614A - System and method for detecting water level - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a water level detecting system that can surely detect a water level, and the deposit amount of sludge and sediment of earth and sand in real time. <P>SOLUTION: A vibration frequency characteristic of a piezoelectric element 5 when an excitation signal is impressed to the piezoelectric element 5 for converting an electric signal into a mechanical vibration is detected to determine the change of the vibration frequency characteristic caused by contact of water, the sludge or the sediment of the earth and the sand with the piezoelectric element 5, and the deposit amount of the sludge or the sediment of the earth and sand is detected thereby. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to flood detection on roads and underpasses, water level measurement in lakes and rivers, and sludge,
The present invention relates to a water level detection system and a water level detection method for detecting sedimentation.

[0002]

2. Description of the Related Art Conventionally, in places where the ground is low on roads and underpasses, there are few places where floods and warning systems for warning floods are installed in the event of a typhoon or heavy rain. Road managers often enforce such regulations. Therefore, there is a possibility that the vehicle may be submerged or a water accident may occur. In order to detect flooding on roads and underpasses and to issue flooding alerts, it is necessary to install an alarm system in advance when newly constructing roads or underpasses. By the way, as a sensor used in such an alarm system, there are a float type sensor for measuring the water level and a piezoelectric vibrator. However, the float type sensor does not operate when sand or mud accumulates, so that the periodic maintenance is performed. The piezoelectric vibrator is often used because maintenance is troublesome due to the need for a piezoelectric vibrator.

As a conventional technique using a piezoelectric vibrator, for example, JP-A-63-191027 and JP-A-4-329 are known.
317 and Japanese Patent Laid-Open No. 11-281463. The water level detection device disclosed in Japanese Patent Laid-Open No. 63-191027 is designed to detect the water level by changing the frequency of the acoustic impedance of the piezoelectric vibrator in the air and in the water. JP-A-4-32
In the water level measuring device disclosed in Japanese Patent No. 9317, a piezoelectric vibrator is provided in the water level control cylinder, and the natural frequency that changes according to the volume fluctuation in the water level control cylinder is measured to continuously maintain the water level in the water level control cylinder. It can be measured as a quantity.

The water level detecting ultrasonic level sensor disclosed in Japanese Patent Laid-Open No. 11-281463 includes a piezoelectric oscillation vibrating section for generating ultrasonic waves and a drive control circuit for driving and controlling the piezoelectric oscillation vibrating section. When the liquid comes into contact with the piezoelectric oscillation vibrating portion, a transmission signal from the piezoelectric oscillation vibrating portion propagates through the liquid, and the reflected wave and the reverberation wave of the liquid are received so that the water level can be detected.

Further, as a system capable of accurately detecting the water level of dirty water such as sewage or muddy water, there is disclosed in Japanese Patent Laid-Open No. Hei 5 (1999) -54.
There are those disclosed in Japanese Patent Application Laid-Open No. 209772 and Japanese Patent Application Laid-Open No. 6-147953. Japanese Patent Laid-Open No. 5-209772
The vibrating sediment detecting device disclosed in Japanese Patent Publication provides a vibration plate with a piezoelectric element for excitation and reception in the detection pipe, and applies the output of the oscillation circuit to the piezoelectric element for excitation through a waterproof cable. It was done like this. The vibrating plate and the detection pipe naturally oscillate in a non-contact state with earth and sand, and when sediment accumulates, the vibration is suppressed and the received signal from the piezoelectric element for reception is attenuated. If it continues to decay, it will notify that there was sediment.

The water level monitoring device disclosed in Japanese Unexamined Patent Publication (Kokai) No. 6-147953 is such that the water level is calculated from a signal from a semiconductor pressure detector that detects pressure from changes in electrical characteristics caused by strain of the element. Is.

[0007]

By the way, in the above-mentioned conventional apparatus for detecting the water level and the apparatus for detecting the sediment, those for simply detecting the water level and the sediment (Japanese Patent Laid-Open No. 63-19).
No. 1027, JP-A-11-281463, JP-A-5-
No. 209772), or even if continuous measurement of the water level is possible, one using a pressure detecting means (JP-A-6-14).
No. 7953) does not work unless the water level is high to some extent, or the measurement target is specific (Japanese Patent Laid-Open No. 11-281463).
No.) could not be used to reliably measure water levels on roads, underpasses, lakes and rivers. Moreover, with all of these conventional techniques, the water level, sludge, sediment, etc. cannot be measured in real time, and even if these techniques are combined, it cannot be realized.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a water level detection system and a water level detection method capable of reliably and in real time measuring water levels, sludge, sediment, and the like. .

[0009]

According to a first aspect of the present invention, there is provided a water level detecting system for measuring a vibration frequency characteristic of a piezoelectric element when a vibration signal is applied to the piezoelectric element for converting electrical energy into mechanical energy. It is characterized by comprising a vibration frequency characteristic detecting means for detecting, and a water level detecting means for detecting a water level from a change in the vibration frequency characteristic of the piezoelectric element obtained when the piezoelectric element comes into contact with water.

According to this structure, the vibration frequency characteristic of the piezoelectric element when the excitation signal is applied to the piezoelectric element for converting the electric signal into the mechanical vibration is detected, and the vibration frequency due to the contact of water with the piezoelectric element is detected. Detects water level from changes in characteristics.
Therefore, the water level can be measured in real time. Also, using a piezoelectric element as a sensor element, we are watching the change in vibration frequency characteristics due to contact with water.
It can reliably detect any water level. Moreover, an inexpensive water level detection system can be realized by using the piezoelectric element.

A water level detecting system according to a second aspect of the present invention is the water level detecting system according to the first aspect of the present invention, in which a plurality of piezoelectric elements are arranged so as to come into contact with water with a time difference. And a water level rising speed calculation means for obtaining a water level rising speed from each time difference when the water level is detected by each piezoelectric element of the sensor unit and the arrangement interval of the plurality of piezoelectric elements.

According to this structure, since the rising speed of the water level can be obtained, it is possible to contribute to grasping the urgency of the disaster.
Can provide detailed information such as alerts and evacuation information.

The water level detection system of the present invention according to claim 3 is the water level detection system of the present invention according to claim 1 or 2, wherein the water level detection means is in contact with the piezoelectric element with water, sludge or earth and sand. It is characterized by detecting the accumulation of sludge or sediment based on the difference in the vibration frequency characteristics.

According to this structure, the water level, the sludge, and the sediment can be distinguished from each other based on the difference in vibration frequency characteristics when water, sludge, and sediment contact the piezoelectric element. In other words, the vibration frequency characteristics of the piezoelectric element change depending on the specific gravity and viscosity of the substance in contact with the piezoelectric element. By observing this change, it is possible to identify whether it is water, sludge, or sediment. You can

The water level detection system of the present invention according to claim 4 is the water level detection system of the present invention according to any one of claims 1 to 3, wherein the detection result of the water level detection means or the water level rising speed is used. It is characterized by comprising a transmitting means for transmitting the calculation result of the calculating means.

According to this structure, it is possible to grasp a disaster situation or the like at a remote place and take prompt action.

A water level detection system according to a fifth aspect of the present invention is the water level detection system according to the fourth aspect of the present invention, wherein the transmitting means includes a wireless communication terminal or a telemeter.

According to this structure, information can be transmitted without large-scale communication equipment.

The water level detecting method of the present invention according to claim 6 is
Applying a vibration signal to a piezoelectric element that converts electrical energy into mechanical energy to detect water level, sludge or sediment accumulation from a change in frequency characteristic due to contact of water, sludge or sediment with the piezoelectric element. Characterize.

According to this method, the vibration frequency characteristic of the piezoelectric element when the vibration signal is applied to the piezoelectric element for converting the electric signal into the mechanical vibration is detected, and the vibration frequency due to the contact of water with the piezoelectric element is detected. Detects water level from changes in characteristics.
Therefore, the water level can be measured in real time. Also, using a piezoelectric element as a sensor element, we are watching the change in vibration frequency characteristics due to contact with water.
It can reliably detect any water level. Moreover, an inexpensive water level detection system can be realized by using the piezoelectric element.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a configuration diagram of a water level detection system according to an embodiment of the present invention. In this figure, the water level detection system according to the present embodiment includes a sensor unit 1 and a signal processing unit 2.
And a notification unit 3. The sensor unit 1 includes a plurality of piezoelectric elements 5 having different natural frequencies and a damping material 6 such as foamed rubber material, and the piezoelectric elements 5 are mounted on the damping material 6. Each piezoelectric element 5 is composed of a piezoelectric ceramic 5A and a diaphragm 5B as shown in FIG. The signal processing unit 2 includes a signal processing amplifier 2A, a microcomputer 2B, and a transmitter 2C.

FIG. 3 is a block diagram showing the configuration of the signal processing amplifier 2A of the signal processing unit 2. In this figure, the signal processing amplifier 2A includes a synchronizing signal generator 10, a variable frequency oscillator 11, an amplifier 12, a resistor 13, a differential amplifier 14, a four-quadrant multiplier 15, and a low-pass filter 16. Consists of The signal processing amplifiers 2A are provided in the number corresponding to the number of the piezoelectric elements 5, or only one is provided, and a changeover switch (not shown) for sequentially switching the piezoelectric elements 5 is used. The signal processing amplifier 2A corresponds to the vibration frequency characteristic detecting means. Further, the microcomputer 2B corresponds to the water level detection means and the water level rise speed calculation means. Also, the transmitter 2C
Corresponds to the transmission means.

The sync signal generator 10 generates a sync signal for repeatedly operating the variable frequency oscillator 11.
The variable frequency oscillator 11 generates a sinusoidal electric signal whose frequency continuously changes in a predetermined frequency range (for example, 1 kHz to 20 kHz). That is, every time the sync signal is output from the sync signal generator 10, a sine wave signal is repeatedly generated from the initial frequency (for example, 1 kHz). The amplifier 12 amplifies the sine wave signal generated by the variable frequency oscillator 11 to a level capable of driving the sensor unit 1 and outputs the amplified signal (this output is referred to as a vibration signal Vr).

The resistor 13 is inserted in series between the amplifier 12 and the piezoelectric element 5 of the sensor unit 1, and a voltage corresponding to the current flowing through the piezoelectric element 5 is generated at both ends thereof. Since the current flowing through the piezoelectric element 5 changes in accordance with the change in frequency, the voltage appearing across the resistor 13 reflects the frequency characteristic of the piezoelectric element 5. The differential amplifier 14 amplifies the voltage generated across the resistor 13 and outputs it (this output is referred to as a reception signal Vi). The four-quadrant multiplier 15 includes the excitation signal Vr output from the amplifier 12 and the differential amplifier 1
By multiplying the received signal Vi output from the signal No. 4, the influence of noise on these signals is removed.

The low-pass filter 16 uses the output signal of the four-quadrant multiplier 15 as cos (2ωt + α) described below.
A signal (output voltage Vo) from which + β) has been removed is output.
The output voltage Vo becomes a signal that reflects the frequency characteristic (amplitude and phase) of the piezoelectric element 5 with respect to the frequency change of the vibration signal Vr. At this time, if nothing touches the surface of the piezoelectric element 5, a voltage having a peak at a frequency near the natural frequency of the piezoelectric element 5 appears as shown in FIG. Then, when the surroundings of the piezoelectric element 5 are submerged from this state, the vibration characteristics of the piezoelectric element 5 change, and the position and magnitude of the peak voltage change as shown in FIG. In this way, the water level can be easily detected from the change in the peak voltage. The microcomputer 2B determines air, water, and mud flow based on the output of the signal processing amplifier 2A, and outputs the result to the notification unit 3. That is, since the vibration frequency characteristic of the piezoelectric element 5 changes depending on the specific gravity and the viscosity of the substance in contact with the piezoelectric element 5, the change is compared with the change observed when the microcomputer 2B comes in contact with air, water, or a mud flow. By doing so, the output of the signal processing amplifier 2A can be identified and determined.

Here, the above operating principle will be described below by using mathematical expressions. Here, Vr = Asin
(Ωt + α) and Vi = Bsin (ωt + β). However, A and B are amplitudes, ωt is frequency, and α and β are phase shifts. Vr × Vi = Asin (ωt + α) × Bsin (ωt + β) = AB [cos (β−α) −cos (2ωt + α + β)] / 2 (1)

The portion of cos (β-α) in the equation (1) is a DC component that changes according to the phase difference, and the amplitude component of the received signal Vi is also included here. Also, cos (2ωt +
The part of (α + β) is the original excitation signal Vr and the received signal Vi.
Is a signal having twice the frequency of Since the required frequency characteristic information is the amplitude (magnitude) of the received signal Vi, only cos (β-α) in equation (1) is required. Therefore, the signal is passed through the low-pass filter 16 and cos (2ωt
The component of + α + β) may be removed. In this way, the output voltage Vo has frequency characteristics in the form of voltage.

Next, the operation of the water level detection system having the above structure will be described. The variable frequency oscillator 11 generates a sine wave whose frequency changes in an arbitrary range. The generated sine wave signal is amplified by the amplifier 12 to generate the excitation voltage V
It is input to the sensor unit 1 as r and causes the piezoelectric element 5 to generate mechanical vibration. When mechanical vibration occurs in the piezoelectric element 5, a voltage corresponding to the current flowing in the piezoelectric element 5 is generated across the resistor 13, and this voltage is amplified by the differential amplifier 14 and the reception signal Vi is output. Then, the received signal Vi and the exciting voltage Vr output from the amplifier 12 are multiplied by the four-quadrant multiplier 15, and the output is subjected to the cos (2ωt + α + β) component removal by the low-pass filter 16 to output the output voltage Vo. Is obtained. The amplitude of the received signal Vi can be accurately detected by multiplying the vibration signal Vr and the received signal Vi by the four-quadrant multiplier 15.

Output signal Vo from the low-pass filter 16
Is a signal reflecting the vibration frequency characteristic (amplitude and phase) of the piezoelectric element 5 with respect to the frequency change of the vibration signal Vr,
When nothing touches the surface of the piezoelectric element 5, a voltage having a peak appears at a frequency near the natural frequency of the piezoelectric element 5, as shown in A of FIG. When the surroundings of the piezoelectric element 5 are submerged in this state, the vibration frequency characteristic of the submerged piezoelectric element 5 changes, and the position and magnitude of the peak voltage change as shown in B of FIG. After that, when the piezoelectric element 5 is buried in a fluid of high viscosity such as sludge, its vibration frequency characteristic becomes as shown in C of FIG. In this case, when the viscosity is relatively low, such as earth and sand, the vibration frequency characteristic of the piezoelectric element 5 is as shown in D of FIG.

FIG. 7 is a diagram showing a sensor unit 1 having four piezoelectric elements 5. As shown in this figure, the water level during flooding can be measured by vertically arranging the four piezoelectric elements 5 at regular intervals. FIG. 8 is a view assuming a flooded condition of a road, in which two piezoelectric elements 5 of ch (channel) 3 and ch 4 are immersed in water. The vibration frequency characteristic waveform of each channel at this time is as shown in FIG.
The vibration frequency characteristics of the piezoelectric elements 5 of ch3 and ch4 are ch1.
It can be seen that the vibration frequency characteristics of the piezoelectric elements 5 of ch2 and ch2 change, and that the piezoelectric elements 5 of ch3 and ch4 are respectively submerged in water. Microcomputer 2B of signal processing unit 2
Judges the situation and outputs the information notifying that it was flooded.

On the other hand, FIG. 10 is a diagram showing the vibration frequency characteristic waveform of each channel when the road surface is buried in the mud flow. Since the mud flow has a large vibration impedance as compared with water, the vibration frequency characteristic of the piezoelectric element 5 at that time becomes flat as compared with the case of water. In the example of the vibration frequency characteristic waveform shown in this figure, it can be seen that the portion of the piezoelectric element 5 of ch4 is also buried in the mud flow. In this way, the condition of the mud flow can be grasped and appropriate processing can be taken in the road management facility.

FIG. 11 is a diagram for measuring the velocity of submergence. By measuring the time T1 until the piezoelectric element 5 of ch3 comes into contact with water from the origin when the piezoelectric element 5 of ch4 comes into contact with water from the origin, the submersion speed from the distance interval of the piezoelectric element 5 is measured. (Cm / hour)
Can be asked. This information can contribute to understanding the urgency of the disaster. Hereafter, the submergence speed can be similarly obtained sequentially with the lapse of time.

In FIG. 12, the sensor unit 1 is connected to the tunnel 2
It is an example of being attached to the inside of 0 and the curb 21. In this example, the signal processing unit 2 includes a wireless communication device (not shown) for sending measurement data to a road management facility (not shown). By using a battery such as a rechargeable battery as the power source of the signal processing unit 2, the signal processing unit 2 can be used even in a place where there is no power source facility.

FIG. 13 shows an example in which the sensor unit 1 is attached to the wall surface of the river bank 22. Further, FIG. 14 shows an example of attachment to the wall surface of the pier 23. In the case of a river, the sensor unit 1 needs a length corresponding to that of the river, so that the sensor unit 1 has a long length as shown in FIG.
Will be the number corresponding to it. Needless to say, the piezoelectric elements 5 are attached at regular intervals, but since the number and intervals of the piezoelectric elements 5 are the water level, sludge, and the measurement range and resolution of sediment,
The quantity and interval may be appropriately determined according to the measurement request.

FIGS. 16 and 17 are views showing an example of a method of displaying the measurement result in the notification unit 3, in which the vibration frequency characteristics of each piezoelectric element 5 are judged, and water, sludge and earth and sand are indicated by LED (light emitting diode). ) Color-coded display. In this case, the diode group 25 indicates the water level, the diode group 26 indicates the sludge level, and the diode group 27 indicates the sediment level. The diode group 25 has a number of diodes corresponding to the current water level, the diode group 26 has a number of diodes corresponding to the current sludge level, and the diode group 27 has a number corresponding to the current sediment level. The diode lights up.

In the state shown in FIG. 17, the piezoelectric elements 5 up to the third from the riverbed are in the state of earth and sand, the piezoelectric elements 5 from the fourth to the sixth are in the state of sludge, and the seventh from the seventh. The figure shows a state in which the light emitting diode groups 25, 26, 27 corresponding to the respective numbers up to the ninth piezoelectric element 5 are lit in a water state. In addition, regarding this measurement display, LED
In addition to the color-coded display by, it is possible to display graphs and animations using a numerical display or a personal computer. Since the notification unit 3 is connected to the signal processing unit 2 by wire or wirelessly, it is possible to grasp the water level, sludge, and sediment accumulation at a remote place.

As described above, according to the water level detection system of the present embodiment, the vibration frequency characteristic of the piezoelectric element 5 when the vibration signal is applied to the piezoelectric element 5 for converting the electric signal into the mechanical vibration is detected. Since the change in the vibration frequency characteristic due to the contact of the piezoelectric element 5 with water, sludge, or earth and sand is determined, it is possible to detect the water level, sludge, or sediment. Therefore, when a road or underpass is flooded due to a typhoon or heavy rain, it is possible to quickly contact the management facility, and by taking measures such as blocking traffic, it is possible to prevent water submersion and water accidents. In addition, since sediment and sludge deposits and water levels at the bottom of lakes and rivers can be measured in real time, detailed information such as alerts and evacuation information can be provided.

Further, since the vibration frequency characteristic of the piezoelectric element 5 can be grasped in advance, it is not necessary to set a special reference value at the site. In addition, the piezoelectric element 5, the amplifier 12, the differential amplifier 1
Since the 4- and 4-quadrant multipliers 15 are inexpensive, the device cost can be kept low. Since the sensor unit 1 can be made smaller and thinner, it can be easily attached to the wall of the pier or the sea wall. In addition, the water level, sludge, and sediment deposition information can be sent to the management facility by using packet communication of a mobile phone, etc., and it is possible to provide a simple information system that does not require large-scale equipment.

Although a sine wave having a single frequency range is used in the above embodiment, a plurality of frequency range switching devices (corresponding to the frequency range changing means) (not shown) for switching the frequency range are provided to provide a plurality of frequency ranges. You may make it possible to select the sine wave of a frequency range alternatively. In this case, the variable frequency oscillator 11 has a function of repeatedly generating a sine wave signal in the frequency band of the range switched by the frequency range switch. In this way, by allowing the sine wave of multiple frequency ranges to be selected alternatively, water, sludge,
It is possible to select the optimum frequency range for measurement according to the physical characteristics of the earth and sand, which enables more accurate measurement.

[0040]

As described above, according to the present invention,
Detects the vibration frequency characteristic of the piezoelectric element when a vibration signal is applied to the piezoelectric element that converts an electrical signal into mechanical vibration, and determines the change in the vibration frequency characteristic due to contact of water, sludge, or sand with the piezoelectric element. Since this is done, it is possible to detect the water level, sludge, or sediment accumulation. In addition, since a plurality of piezoelectric elements are provided, it is possible to measure the water level, the increase in the amount of sludge and the amount of sediment accumulation, and the speed of increase, which can contribute to the provision of detailed information such as warning and evacuation information.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a water level detection system according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a piezoelectric element used in the water level detection system according to the present embodiment.

FIG. 3 is a configuration diagram of a signal processing amplifier used in the water level detection system according to the present embodiment.

FIG. 4 is a diagram showing an example of measurement results of the water level detection system according to the present embodiment, which is an output voltage waveform diagram in the case of no flooding.

FIG. 5 is a diagram showing an example of measurement results of the water level detection system according to the present embodiment, which is an output voltage waveform diagram in the presence of flooding.

FIG. 6 is a diagram showing an example of measurement results of the water level detection system according to the present embodiment, which is an output voltage waveform diagram in the process of reaching no flood, having flood, sludge contact, and sediment contact.

FIG. 7 is a configuration diagram of an example of a sensor unit used in the water level detection system according to the present embodiment.

8 is a diagram for explaining detection of a flooded condition on a road by the sensor unit of FIG.

9 is a diagram showing an example of measurement results using the sensor unit of FIG. 7, and is an output voltage waveform diagram in the presence of air and water.

FIG. 10 is a diagram showing an example of measurement results using the sensor unit of FIG. 7, and is an output voltage waveform diagram in the case where air, water, and a mud flow exist.

11 is a diagram showing a submergence velocity measurement diagram using the sensor unit of FIG. 7. FIG.

12 is a diagram showing an example in which the sensor unit of FIG. 7 is attached to a tunnel and a road curb.

FIG. 13 is a view showing how the sensor unit is attached to the seawall.

FIG. 14 is a view showing how the sensor unit is attached to the pier.

FIG. 15 is a configuration diagram of a river sensor unit.

FIG. 16 is a diagram showing a notification example in the notification unit of the water level detection system according to the present embodiment.

FIG. 17 is a diagram showing a notification example in the notification unit of the water level detection system according to the present embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 sensor unit 2 signal processing unit 2A signal processing amplifier (vibration frequency characteristic detection means) 2B microcomputer (water level detection means, water level rise rate calculation means) 2C transmission section (transmission means) 3 notification unit 5 piezoelectric element 5A piezoelectric ceramics 5B diaphragm 6 Damping Material 10 Synchronous Signal Generator 11 Variable Frequency Oscillator 12 Amplifier 13 Resistor 14 Differential Amplifier 15 4 Quadrant Multiplier 16 Low Pass Filter 20 Tunnel 21 Road 22 Revetment 23 Pier 25, 26, 27 Light Emitting Diode Group

Claims (6)

[Claims] 1. A vibration frequency characteristic detecting means for detecting a vibration frequency characteristic of the piezoelectric element when a vibration signal is applied to the piezoelectric element for converting electric energy into mechanical energy.
A water level detection system, comprising: a water level detection unit that detects a water level from a change in vibration frequency characteristics of the piezoelectric element obtained when the piezoelectric element comes into contact with water. 2. A sensor unit in which a plurality of piezoelectric elements are arranged so as to come into contact with water with a time lag, each time difference when each piezoelectric element of the sensor unit detects a water level, and the plurality of piezoelectric elements. 2. The water level detection system according to claim 1, further comprising: a water level increase rate calculation unit that obtains a water level increase rate from the arrangement interval. 3. The water level detection means detects deposition of sludge or sediment based on a difference in vibration frequency characteristics due to contact of water, sludge or sediment with the piezoelectric element. The water level detection system described in 2. 4. The transmission means for transmitting the detection result of the water level detection means or the calculation result of the water level rise speed calculation means, according to claim 1. Water level detection system. 5. The water level detection system according to claim 4, wherein the transmission means includes a wireless communication terminal or a telemeter. 6. The accumulation of water level, sludge or earth and sand from the change in frequency characteristic due to contact of water, sludge or earth and sand to the piezoelectric element by applying a vibration signal to the piezoelectric element for converting electric energy into mechanical energy. A water level detection method characterized by detecting water.