JP2876021B2 - Sediment transport phenomena analysis method - Google Patents

Description

[Detailed Description of the Invention] [Object of the Invention] The present invention provides a method for analyzing sediment transport phenomena, in particular, detection of occurrence, approach or passage of a sudden sediment transport phenomenon such as debris flow, and measurement of the amount of sediment transport by flowing water. About the method. Generally, the sediment transport phenomenon in mountain rivers is very complicated.Therefore, in order to formulate an erosion control plan and disaster prevention measures against sudden landslides such as debris flows, the occurrence, approach, or approach of sediment transport phenomena in the field It is essential to detect passage and monitor sediment transport. The biggest complicating factors in sediment transport in mountain rivers are the discontinuity of sediment production and the very wide range of particle size distribution of the produced sediment. From a macro perspective, the sedimentation phenomenon in mountain rivers can be understood as a process in which the amount of sediment suddenly produced by debris flow and its wide particle size distribution is classified and dispersed as sediment in the river channel. This classification / dispersion process means that the movement form and the amount of sedimentation of sediment vary depending on the particle size, and that the conditions of the riverway change every moment as a result of erosion and deposition of the riverway. This indicates that it is necessary to evaluate changes in shape and form, changes in riverbed material, changes in sediment transport, and changes in flow resistance as a system. As mentioned above,
The phenomena that characterize mountainous rivers are sudden sediment movement caused by debris flow, formation and destruction of armor coat, accompanying deformation and deformation of the riverbed, and fluctuations in flow channels. Show. Since there is no one-to-one correspondence between sediment transport and hydraulics, sediment transport phenomena including sediment transport, including detection of sudden sediment movement, approach or passage, and measurement of sediment transport Is an urgent problem in sabo engineering. [Prior art] As a method of analyzing sedimentation phenomena, surveys on sediment production have been conducted by aerial photo interpretation and site reconnaissance, while on the other hand, river cross-section surveys or sedimentation fluctuation surveys of sabo dams, storage dams, etc. And calculate the amount of sediment transport by calculating the sediment balance using those results.
There is also known a method of detecting generation and passage by attaching a wire to a mountain stream where a debris flow or the like will be generated and passing by cutting the debris flow or the like. However, since the method based on the sediment balance calculation is measured at time intervals of several months to one year to several years, it is not possible to obtain the total amount of sediment discharged from one flood or the sedimentary volume that changes every moment during a flood. That is, the method using a wire has a problem in that there is a malfunction caused by rock fall other than the movement of earth and sand or cutting of the wire by a large animal. Also, in mountain rapid rivers that require sabo works, (a) rapid flooding (b) large flow velocity (c) large particle size range of gravel and large amount of sediment ( D) It is difficult to accurately measure sediment transport because of the dangers involved in the observation and measurement work during floods, and there is no known method to make this possible. [Constitution of the Invention] The present invention provides a method for indirectly analyzing the sediment transport phenomenon by capturing the sediment transport phenomenon using acoustic media. That is, the present invention provides an acoustic sensor comprising a tubular body having a predetermined acoustic characteristic by selecting a material and dimensions so as to have selectivity with respect to the sound caused by quicksand, and an acoustoelectric signal converter stored therein. Is installed in the sediment transport area, and the electrical signal extracted from the acoustic electrical signal converter is signal-processed by a predetermined method to detect the occurrence, approach or passage of the sediment transport phenomenon, or to measure the amount of sediment transport. To provide a method for analyzing sediment transport phenomenon. By using a tubular body having selectivity to the sound emitted when the quicksand hits the tubular body, the amount of quicksand passing through the cross-section where the tubular body is installed can be accurately measured. Similarly, as a tubular body, the sound generated by the collision of quicksand between the quicksand and the quicksand area floor and transmitted through the air or the ground to reach the tubular body, and / or when quicksand collides with the tubular body The use of a tubular body having selectivity for the sound generated at the time of occurrence makes it possible to accurately detect the occurrence, approach, or passage of the sediment movement phenomenon. By arranging a plurality of tubular bodies side by side in the transverse direction of the water flow, it is possible to measure the sediment flow distribution in the transverse direction, so that it is possible to improve the accuracy of the sediment flow measurement. In addition, by arranging a plurality of pieces in the longitudinal direction of the water flow in the same manner, the accuracy of measuring the amount of sediment can be further improved. Examples of processing to be added to the extracted electric signal include processing for obtaining an amplitude spectrum distribution representing the type of sound, processing for measuring the number of pulses having an amplitude equal to or greater than a certain threshold indicating the moment of a collision, and amplitude corresponding to sediment density. And a process for performing a causal law analysis for obtaining a causal law between signals obtained when a plurality of tubular bodies are installed in the longitudinal direction of the water flow. From the process of obtaining the amplitude spectrum distribution, it is possible to know the occurrence, approach or passage of sediment movement development and the presence of sediment in running water, and to perform the measurement process of the number of pulses exceeding a certain threshold, the amplitude distribution shape, and the causality analysis The amount of quicksand can be obtained from the treatment. Embodiment FIG. 1 is a perspective view schematically showing one embodiment (an experimental example) of an electric signal extracting device for carrying out the method of the present invention. This experiment was performed as an example of the method for measuring the amount of sediment transport by the above-described method. A small microphone (2) is placed in an iron pipe (1) of an appropriate diameter, and both ends are sealed with a sound absorbing material (3, 3). About half of this pipe is buried in the riverbed (4), and the amount of relatively large particles (bedload) moving near the riverbed is measured by analyzing the sound of the pipe when it hits the stream or sediment. I do. The arrow is the direction of the water flow. It should be noted that increasing the number of signals obtained by arranging a plurality of pipes shown in FIG.
It is expected to improve the accuracy of estimation and increase the number of items to be estimated. In addition, it is desirable to install the pipe on a fixed floor in order to keep the installation conditions constant. Since this method estimates the state of the object being struck from the difference in sound emitted when the object strikes the pipe, it is difficult to deduce the estimation rule from physical phenomena theoretically. Empirical estimation rules need to be established. Also, of course, during a flood, since the flow is turbulent and irregular, the resulting signal is expected to have various irregularities. For example, the signal obtained from the microphone satisfies the steady-state ergodicity, running water belongs to the Gaussian stochastic process, and sedimentation belongs to the Poisson stochastic process when the sedimentation amount is small (when the number of collisions is small), and the sedimentation amount When it is large (when the number of collisions is large), it can be considered that it belongs to the Gaussian stochastic process like the flowing water. Then, the signal is processed as a signal of a water flow represented by a Gaussian stochastic process plus a signal (innovation) generated when a quicksand (stone) collides. The collision of quicksand with the pipe (innovation) can be considered to follow a Poisson stochastic process when the number of collisions is small, and to follow a Gaussian distribution when the number of collisions is large. From the above, the parameters for sediment transport estimation are summarized as follows. Estimated items Parameter (a) Separation of running water and quicksand (stone) Spectral distribution (b) Stone size Amplitude value (c) Number of stone impacts, sedimentation volume Amplitude distribution, amplitude spectrum distribution, sound attenuation characteristics, certain threshold The pulse number analysis described above is performed by a computer using A / D conversion of the output from the microphone as a digital signal. Whether the output is directly A / D-converted or analog-recorded once and then A / D-converted depends on experimental conditions or installation conditions. There are various methods for spectrum analysis. For example, MEM (maximum entropy method) can be used. An experiment was conducted by installing four pipes having different outer diameters and wall thicknesses as shown in the following table in a water channel having a width of 30.7 cm, a total length of 12 m, and a slope of 2.2 mm. Of these, the outer diameter is approximately matched to the maximum and average particle size of the sand used in the experiment. The interval between the pipes was set to be 10 times the particle size, and the pipes were installed so that the upper half was exposed on the fixed bed. Outer diameter (mm) 10.0 30.0 Length (cm) 30.0 30.0 Wall thickness (mm) 1.0 2.0 1.0 2.0 The natural frequency of the primary mode in the radial direction of a cylindrical closed tube of length l and radius a is 0.61 c / a, circle It is expressed as 0.298 c / a in the circumferential direction and 3c / 4l in the axial direction. On the other hand, volume V, surface area A
The reverberation energy density in the room is ε / ε ₀ = e ^{-13.6t / T}
The reverberation time T is represented by T = 0.16 V / αA. Where α
Is a constant. For a pipe with an outer diameter of 30 mm and a length of 30 cm,
The natural frequency of the axial first mode is about 700 Hz, the natural frequency of the circumferential first mode is about 8 kHz, and the natural frequency of the radial first mode is about 20 kHz. By combining the pipe material, the pipe diameter, the length, and the sound absorbing material, it is possible to manufacture a pipe having predetermined acoustic characteristics, reverberation characteristics, and quicksand impact conditions (number of times). The experiment was conducted by first changing the amount of running water and the amount of sediment transported on a fixed bed. The waveforms of the obtained electric signals are shown in FIGS. Table 1 shows the relationship between the experimental conditions and the waveform chart numbers. The results of MEM analysis of the electrical signals of Experiment Nos. 1 to 3 are shown in FIGS. 6, 7 (a) and 8 (a), respectively. Also experiment
The amplitude distributions of the electrical signals Nos. 2 to 3 are shown in FIGS. 7 (b) and 8 (b), respectively. The following can be understood from these data. (B) Separation of running water and sediment: In the case of only flowing water, various sequestration components are included [Fig. 6], but when running sand (stone) hits, around 700 Hz, which corresponds to the natural frequency in the axial direction, [FIG. 7 (a) and FIG. 8 (a)]. (B) Size of quicksand (stone) An experiment was conducted in which stones of different weights were run one by one in the same manner as in Experiment No. 4, and the peak values of the stone weight and amplitude were compared. I came to. In this experiment, about 15g,
When the particle size was 22 mm or more, the peak value of the amplitude became larger as the stone became heavier. (C) Number of stone collisions and amount of sedimentation If the collision circuit of stones is set as a threshold to three times the variance obtained from the amplitude distribution in the case of only running water, and counted with the number of pulses exceeding that, Fig. 3 4, the number of collisions is almost 4 to 5 times / sec in both cases. If all of the quicksand has the same size (weight) and hits all the pipes, the weight per quicksand is 16g-20g, the particle size is 22.6mm-24.4mm, and the average of the quicksand used in the experiment It will show a value larger than the particle size (about 1 cm) but smaller than the maximum particle size (about 3 cm). From this experiment, it was confirmed that if the material, shape, and microphone of the pipe were selected so that the number of collisions could be counted, the amount of sediment could be measured by appropriately setting the threshold even if the concentration of sediment was different. We were able to. If the distribution form of the number of collisions per second is obtained (sampling number 44), the result is as shown in FIG. In the figure, the solid line A corresponds to Experiment No. 2 and the broken line B corresponds to Experiment No. 3. If the amount of sedimentation is the same even if the concentration of sedimentation is different, it can be seen that the distribution has a Poisson-like distribution form, which is useful data for measuring the amount of sedimentation. On the other hand, from the amplitude distributions in the case where the sediment concentration is low and in the case where the sediment concentration is high shown in FIGS. 7 (a) and 8 (a), it is found that the higher the sediment concentration, the larger the spread of the amplitude distribution. In addition, it will be a powerful data for measuring sediment transport. In the above analysis example, a tubular body is installed horizontally in the watershed,
It is an example of a method for measuring the amount of sediment transported by converting the acoustic signal generated when quicksand collides into an electrical signal and processing the signal. When the transmitted sound signal is converted to an electric signal and processed,
In the case of detecting approach or passage, the analysis can be performed in the same manner. Further, by installing a plurality of tubular bodies and performing a multidimensional analysis or a time series causal analysis as a signal processing method, a more detailed and effective analysis can be performed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory view showing one embodiment of the method of the present invention. (1) Pipes (quick sand collides with this pipe) (2) Microphone (converts acoustic signals into electrical signals) (3,3) Sound absorbing material (fills both ends with sound absorbing material to speed up sound attenuation) ( 4) Fixed floor on which pipes are installed (arrows indicate flow direction) FIG. 2: Waveform diagram showing an example of an electric signal in the case of flowing water only. FIG. 3: Waveform diagram showing an example of an electric signal when the flow rate is 20 / sec and the amount of sediment transport is 4873 g / min (volume concentration of the sediment transport 0.15%) (arrows indicate the time of the impact of the sediment transport). FIG. 4: Waveform diagram showing an example of an electric signal when the flow rate is 10 / sec and the amount of sediment transported is 4873 g / min (volume concentration of the sediment transported 0.31%) (arrows indicate the time of the impact of the sediment transport). FIG. 5: Waveform diagram showing an example of an electric signal at the time of collision of one stone (59.3 g) (enlarged in the time axis direction). Fig. 6: Spectrum distribution diagram of amplitude in case of only running water (20 / sec). FIG. 7: (a) Spectral distribution diagram of amplitude at a flow rate of 20 / sec and a sediment load of 4873 g / min (volume density of quicksand 0.31%). (B) Distribution diagram of amplitude. FIG. 8: (a) Amplitude spectrum distribution diagram when flow rate is 10 / sec and sediment flow is 4873 g / min (volume density of sediment transport 0.31%). (B) Distribution diagram of amplitude. FIG. 9 is an explanatory diagram showing a relationship between a peak amplitude value of a signal and a stone weight at the time of collision of one quicksand. FIG. 10 is an explanatory diagram showing the distribution of the number of collisions per second.

Claims (1)

(57) [Claims] When detecting the amount of sediment transported per unit time for the sediment passing through a cross section or a part of an arbitrary point along the river channel, the material and dimensions should be selected so that they have selectivity to the sound generated when the sediment hits. An acoustic sensor consisting of a tubular body having a selected and predetermined acoustic characteristic and an acousto-electric signal converter housed inside the tubular body is mounted on the river cross section or on a part of the floor so that the major axis of the tubular body is in the water flow direction. And a portion exposed to the fixed floor to selectively minimize the effect of acoustics generated when quicksand collide with quicksand and the quicksand area floor. The acoustic signal generated inside the tubular body is converted into an electric signal by an acoustic-electrical signal converter, and the converted electric signal is subjected to statistical signal processing such as processing for determining the distribution form of the amplitude or the like. Causality analysis Of processing, or to perform the process of measuring the number of pulses having an amplitude of more than a certain threshold, quicksand phenomenon analysis method characterized by. 2. The method according to the above item (1), wherein a plurality of tubular bodies are installed in the water current transverse direction in order to measure the transverse distribution of the amount of sediment transport. 3. The method according to the above item (1), wherein a plurality of tubular bodies are installed in the longitudinal direction of the water flow in order to measure the amount of quicksand with high accuracy. 4. When detecting the occurrence, approach or passage of sediment transport phenomena in rivers, selectivity should be given to the sound transmitted through the ground generated by the sediment transport by river sediment or by the collision of quick sediment with the bed of the quick sediment area. An acoustic sensor consisting of a tubular body having predetermined acoustic characteristics by selecting materials and dimensions and an acoustic-electrical signal converter stored inside the tubular body is installed in the floor of a river channel, and inside the tubular body, The generated acoustic signal is converted into an electric signal by an acoustic-electrical signal converter, and the converted electric signal is subjected to statistical signal processing such as processing for determining the amplitude distribution form or processing such as causality analysis, or to an amplitude exceeding a certain threshold. A method for analyzing sediment transport phenomena, characterized by adding a process of measuring the number of pulses having 5. The method according to the above item (4), wherein a plurality of tubular bodies are installed underground in the sedimentation area in the longitudinal direction of the river channel in order to measure the speed and scale of the sedimentation phenomenon.