Bed load sediment transport rate measuring method based on multi-layer sediment sound signal attenuation correction of Doppler flow velocity profiler

Abstract

The invention discloses a bed load sediment transport rate measurement method based on multi-layer sediment acoustic signal attenuation correction of a Doppler velocity profiler, which comprises the following steps: sampling sediment on the surface of a riverbed in an overtopping area of a to-be-measured river reach, and measuring sediment gradation to obtain the median particle size of the bed sediment; obtaining flow measurement data, and extracting ship speed data from the flow measurement data; calculating a riverbed movement speed according to the ship speed data; filtering the riverbed movement speed data, and calculating a characteristic value of the filtered riverbed movement speed data; respectively calculating the vertical projection area ratio of bed load according to the filtered riverbed movement speed data characteristic values; calculating a dimensionless sediment particle size according to the median particle size of the bed sand; calculating the thickness of a bed load layer according to the dimensionless sediment particle size; calculating the volume concentration of the bed load according to the vertical projection area ratio of the bed load and the thickness of the bed load layer; calculating a multi-layer sediment sound signal attenuation correction coefficient according to the bed load volume concentration; and calculating the bed load sediment transport rate according to the multi-layer sediment sound signal attenuation correction coefficient. The bed load sediment transport rate can be accurately and effectively measured.

Description

Technical Field

[0001] The invention relates to a bed load sediment transport rate measurement method based on attenuation correction of multi-layer sediment acoustic signals of a Doppler velocity profiler, and belongs to the technical field of hydraulics and river dynamics. Background Art

[0002] River sediment can be divided into bed sediment, suspended load and bed load according to its movement mode. The movement model and measurement technology of suspended load are relatively mature, while the movement law of bed load is still an important problem in river dynamics. Since the development of sediment movement mechanics in the early 20th century, the problem of bed load movement has become a research focus of the international academic community. Although bed load accounts for a small proportion of the total sediment carried by a river, it interacts closely with the riverbed, affecting the scouring and silting of the riverbed and playing a key role in the evolution of river morphology. The bed load sediment transport rate directly determines the river type, which is of great significance to water-sediment balance, river morphological stability, and the design and management of river engineering. Classic bed load transport rate formulas, such as the Meyer-Peter and Müller formulas and the Einstein formula, were proposed based on a large number of experiments or theoretical analyses and have become the basis for bed load research. In recent years, data mining methods have also shown great potential in the prediction of bed load transport rate. Methods such as Bagging, M5P and random forest have all shown high accuracy. In addition, with the development of computer technology, numerical simulation methods of bed load movement have been widely used, and combining data-driven models with traditional mechanical analysis has become an important direction for bed load research.

[0003] The measurement of bed load sediment transport rate is an important part of hydrological measurement, and its measurement data provides basic support for the study of river morphological evolution, sediment disaster prevention and control, etc. Since the 20th century, the international bed load measurement technology has been continuously developing, and international academic conferences have also specifically discussed the technical issues of bed load measurement. Bed load measurement methods can be divided into direct measurement and indirect measurement methods. The direct measurement of bed load is to obtain riverbed sediment samples through sedimentation tanks and samplers, or to calculate the change of sediment flux by measuring the movement of riverbed sand waves; the indirect measurement of bed load is to use detection devices arranged in the riverbed to record the signals generated by the natural movement of bed load sediment, mainly including Swiss vibration plates, Japanese sound tubes and hydrophones, and analyze the acoustic or vibration signals generated by bed load sediment through physical principles to establish the relationship between bed load motion parameters and measurement signals. However, there are many difficulties in bed load measurement. Due to the turbulent water flow and the different sizes of bed load particles, the existing measurement technology is difficult to effectively capture its movement law. Traditional bedload measurement methods, such as the sampler method and the pit method, have high accuracy, but are complex to operate and have low sampling efficiency, making it difficult to meet the data requirements of high temporal and spatial resolution. In recent years, the development of new sensors such as hydrophones and Swiss vibration plates has made progress in long-term continuous monitoring of bedload, but the deployment cost of these technologies is high and their applicability in complex river environments is still limited. Therefore, the development of high temporal and spatial resolution bedload measurement technology has become a current research hotspot.

[0004] Acoustic Doppler current profiler (ADCP) is often used to measure water velocity. Its measurement principle is to emit pulse sound waves into the water through four acoustic wave probes arranged in a certain pattern, receive the sound waves scattered by the bed load in the water, and calculate the water movement speed based on the Doppler frequency shift of the reflected signal. Its bottom tracking function can emit bottom sound waves. In recent years, it has been proven to have the potential to measure bed load sediment transport rate with high temporal and spatial resolution, and is the frontier direction of bed load measurement technology. However, due to the multi-layer attenuation of the acoustic signal in natural sediment, the bed load velocity measured by the acoustic Doppler current profiler will be affected, and the bed load sediment transport rate measured by the acoustic Doppler current profiler has a large number of errors. At present, there is no accurate bed load sediment transport rate measurement method based on the acoustic Doppler current profiler, which seriously restricts the development of bed load measurement technology. Summary of the invention

[0005] In order to overcome the defects in the prior art, the present invention aims to provide a method for measuring bed load transport rate based on attenuation correction of multi-layer sediment acoustic signals of a Doppler current profiler.

[0006] The present invention provides a technical solution to solve the above technical problems: a method for measuring bed load sediment transport rate based on attenuation correction of multi-layer sediment acoustic signals of Doppler current profiler, comprising the following steps:

[0007] In the floodplain area of ​​the river section to be measured, the sediment on the riverbed surface is sampled and the sediment gradation is measured to obtain the median particle size of the bed sand;

[0008] Select a measuring point, use ADCP and a matching unmanned boat equipped with DGPS to perform fixed-point bottom-tracking current measurement, obtain current measurement data, and extract the bottom tracking ship speed from the current measurement data;

[0009] Calculate the speed of riverbed movement based on bottom-tracking ship speed;

[0010] Filtering the riverbed movement speed data, and calculating the characteristic value of the filtered riverbed movement speed data;

[0011] The vertical projection area ratio of bed load is calculated according to the characteristic values ​​of the filtered riverbed movement velocity data;

[0012] The dimensionless sediment particle size was calculated based on the median particle size of the bed sand;

[0013] Calculate the bedload thickness based on dimensionless sediment particle size;

[0014] The bed load volume concentration is calculated based on the bed load vertical projection area ratio and bed load layer thickness;

[0015] Calculate the attenuation correction coefficient of multi-layer sediment acoustic signal according to the volume concentration of bed load;

[0016] The bed load transport rate is calculated based on the attenuation correction coefficient of the multi-layer sediment acoustic signal.

[0017] A further technical solution is to turn off the ADCP intelligent pulse function in the fixed-point bottom current measurement, use 3MHz fixed frequency sound waves for measurement, and turn on the comprehensive track function. According to the DGPS signal, ensure that the side ship position is always at the selected measuring point, and perform bottom tracking ship speed measurement with a measurement time of more than 3 minutes.

[0018] A further technical solution is that the calculation formula for the riverbed movement speed is:

[0019] v a =-v BT

[0020] Where: v a is the velocity of the riverbed, m / s; v BT is the bottom tracking ship speed, m / s.

[0021] A further technical solution is that the filtering of riverbed movement speed data includes:

[0022] Remove all negative riverbed velocity data;

[0023] Calculate the standard deviation of the remaining riverbed movement velocity data;

[0024] The riverbed movement velocity data with a value higher than three times the standard deviation were removed;

[0025] The riverbed movement velocity data with a value less than the ADCP bottom tracking measurement threshold of 0.001 were removed.

[0026] A further technical solution is that the calculation formula of the vertical projection area ratio of the bed load is:

[0027]

[0028] Where: c p is the vertical projection area ratio of bed load, %; is the average value of riverbed movement velocity data, m / s; v astd is the standard deviation of riverbed velocity data, m / s; P f is the noise data percentage of riverbed movement velocity data, %.

[0029] A further technical solution is that the calculation formula of the dimensionless sediment particle size is:

[0030]

[0031] Where: D * is the dimensionless sediment particle size; D 50 is the median particle size of sediment; s is the specific gravity of sediment bed load; ν is the kinematic viscosity coefficient of the liquid.

[0032] A further technical solution is that the calculation formula for the thickness of the bed load layer is:

[0033]

[0034] Where: τ sk is the shear stress of water flow; τ c is the critical starting shear stress; δ is the thickness of the bedload layer.

[0035] A further technical solution is that the calculation formula for the bed load volume concentration is:

[0036]

[0037] Where: c v is the bedload volume concentration; c p is the vertical projection area ratio of bed load, %.

[0038] A further technical solution is that the calculation formula of the multi-layer sediment sound signal attenuation correction coefficient is:

[0039]

[0040] Where: k is the attenuation correction coefficient of multi-layer sediment acoustic signal; is the average value of riverbed movement velocity data, m / s; v astd is the standard deviation of riverbed movement velocity data, m / s.

[0041] A further technical solution is that the calculation formula of the bed load sediment transport rate is:

[0042]

[0043] Where: g b is the bed load transport rate per unit width, kg / m / min; is the average value of riverbed movement velocity data, m / s; ρ s is the bed load density, kg / m 3 .

[0044] The present invention has the following beneficial effects:

[0045] 1. The present invention can continuously measure the bed load sediment transport rate for a long time, has high measurement efficiency and temporal and spatial resolution, and realizes effective and continuous measurement of the bed load sediment transport rate in a convenient and simple way;

[0046] 2. The present invention does not interfere with the flow field of the river and can accurately measure the distribution of bed load and sediment transport rate in the river;

[0047] 3. The present invention is easy to operate, has low measurement and calibration costs, and can measure bed load and sediment transport rate without requiring a large amount of manpower. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 for Figure 1 It is a flow chart of the method for measuring bed load sediment transport rate based on attenuation correction of multi-layer sediment acoustic signal of Doppler current profiler of the present invention;

[0049] Figure 2 This is a comparison chart of the bed load transport rate measurement results from a simulation test for bed load transport rate measurement. DETAILED DESCRIPTION

[0050] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0051] like Figure 1 As shown, a method for measuring bed load sediment transport rate based on attenuation correction of multi-layer sediment acoustic signals of a Doppler current profiler of the present invention comprises the following steps:

[0052] Step 1: Select sampling points in the floodplain area of ​​the measured river section and use a standard bedload sampler (such as HS differential pressure sampler) to sample the sediment on the riverbed surface. To ensure the reliability of the data, repeat sampling is performed at each sampling point. The collected sediment samples are dried, sieved and analyzed after removing moisture, and the gradation of the sediment is calculated by weighing method to determine the median particle size D of the bed sand. 50 m;

[0053] Step 2. Select a measuring point with a water depth greater than 40 cm in the central area of ​​the measured river section to ensure that the location of the measuring point can fully represent the water flow characteristics of the river section. Use cables to fix the ADCP to the measuring vessel or bracket, and ensure that the ADCP is installed stably to avoid external interference. Keep the measuring vessel or bracket stable at the measuring point, perform fixed-point bottom-tracking flow measurement, and the measurement time should be no less than 6 minutes to ensure the integrity and accuracy of the data. During this period, the ADCP continuously records the bottom tracking ship speed to ensure that the file format is correct and the data is complete;

[0054] Step 3. Use the data processing software provided with ADCP to open the current measurement file saved in step 2, and ensure that the software version matches and can read the data normally. Export the bottom tracking ship speed data in the data processing toolbox. Select "Bottom Tracking Reference" for the ship track reference to ensure that the exported data has high accuracy. Export the measurement time, water depth, bottom tracking ship speed and other data as a custom file and save it in the specified directory, ensuring that the file name is clear and convenient for subsequent processing;

[0055] Step 4: Read the bottom tracking ship speed data generated in step 3 to ensure that the data file is complete and undamaged. Use Matlab to open the "bottom track" array in the bottom tracking ship speed data, find the "BT Vel" field, obtain the bottom tracking ship speed components in different directions measured by ADCP, and use the bottom tracking ship speed in the flow direction to calculate the riverbed movement speed;

[0056] v a =-v BT

[0057] Where: v a is the velocity of the riverbed, m / s; v BT is the bottom tracking ship speed, m / s;

[0058] Step 5: Filter the riverbed movement speed calculated in step 4 to remove unreasonable noise data;

[0059] Specifically, the following steps are included: 1) removing all negative riverbed velocity data; 2) calculating the standard deviation of the remaining riverbed velocity data; 3) removing riverbed velocity data with a value higher than three times the standard deviation; and 4) removing riverbed velocity data with a value less than the ADCP bottom tracking measurement threshold of 0.001 m / s.

[0060] Step 6, calculating the average value, standard deviation, and noise data percentage of the filtered riverbed movement speed data obtained in step 5 as the characteristic value of the riverbed movement speed data;

[0061] Step 7: Use the characteristic value of the riverbed movement velocity data obtained in step 6 to calculate the vertical projection area ratio c of the bedload p ;

[0062]

[0063] Where: c p is the vertical projection area ratio of bed load, %; is the average value of riverbed movement velocity data, m / s; v astd is the standard deviation of riverbed velocity data, m / s; P f is the noise data percentage of riverbed movement velocity data, %;

[0064] Step 8, calculating the dimensionless sediment particle size according to the median particle size of the bed sand;

[0065]

[0066] Where: D * is the dimensionless sediment particle size; D 50 is the median particle size of sediment; s is the specific gravity of sediment bed load; ν is the kinematic viscosity coefficient of the liquid;

[0067] Step 9, calculating the bedload thickness based on the dimensionless sediment particle size;

[0068]

[0069] Where: τ sk is the shear stress of water flow; τ c is the critical starting shear stress; δ is the thickness of the bedrock layer;

[0070] Step 10, calculating the bed load volume concentration according to the bed load vertical projection area ratio and the bed load layer thickness;

[0071]

[0072] Where: c v is the bedload volume concentration; c p is the vertical projection area ratio of bed load, %;

[0073] Step 11, calculating the multi-layer sediment acoustic signal attenuation correction coefficient according to the bed load layer thickness and bed load volume concentration;

[0074]

[0075] Where: k is the attenuation correction coefficient of multi-layer sediment acoustic signal; is the average value of riverbed movement velocity data, m / s; v astd is the standard deviation of riverbed movement velocity data, m / s;

[0076] Step 12, calculating the bed load sediment transport rate according to the riverbed movement velocity, bed load volume concentration, and multi-layer sediment acoustic signal attenuation correction coefficient;

[0077]

[0078] Where: g b is the bed load transport rate per unit width, kg / m / min; is the average value of riverbed movement velocity data, m / s; ρ s is the bed load density, kg / m 3 .

[0079] Example

[0080] Steps 4 to 12 are used to calculate the attenuation correction coefficient of the multi-layer sediment acoustic signal of the bed load and the bed load sediment transport rate. The results are compared in the attached Figure 2 It can be seen that the bed load transport rate calculated by the present invention is basically consistent with the actual value, the scatter points are distributed near the 1:1 line, and the errors of most data points are also within one order of magnitude. Therefore, it is explained that the bed load transport rate measurement method based on the attenuation correction of the multi-layer sediment acoustic signal of the Doppler current profiler meets the actual needs, has high feasibility, and can provide a new idea for the existing bed load transport rate measurement.

[0081] The above description is not intended to limit the present invention in any form. Although the present invention has been disclosed through the above embodiments, it is not intended to limit the present invention. Any technician familiar with the profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are within the scope of the technical solution of the present invention.

Claims

1. A method for measuring bed load sediment transport rate based on attenuation correction of multi-layer sediment acoustic signal of Doppler current profiler, characterized in that: The following steps are involved: In the floodplain area of ​​the river section to be measured, the sediment on the riverbed surface is sampled and the sediment gradation is measured to obtain the median particle size of the bed sand; Select a measuring point, use ADCP and a matching unmanned boat equipped with DGPS to perform fixed-point bottom-tracking current measurement, obtain current measurement data, and extract the bottom tracking ship speed from the current measurement data; Calculate the speed of riverbed movement based on bottom-tracking ship speed; Filtering the riverbed movement speed data, and calculating the characteristic value of the filtered riverbed movement speed data; The vertical projection area ratio of bed load is calculated according to the characteristic values ​​of the filtered riverbed movement velocity data; The dimensionless sediment particle size was calculated based on the median particle size of the bed sand; Calculate the bedload thickness based on dimensionless sediment particle size; The bed load volume concentration is calculated based on the bed load vertical projection area ratio and bed load layer thickness; Calculate the attenuation correction coefficient of multi-layer sediment acoustic signal according to the bed load volume concentration; The bed load transport rate is calculated based on the attenuation correction coefficient of the multi-layer sediment acoustic signal.

2. The method for measuring bed load sediment transport rate based on attenuation correction of multi-layer sediment acoustic signal of Doppler current profiler according to claim 1 is characterized in that: In the fixed-point bottom current measurement, the ADCP intelligent pulse function is turned off, 3MHz fixed frequency sound waves are used for measurement, and the comprehensive track function is turned on. According to the DGPS signal, it is ensured that the side ship position is always at the selected measuring point, and the bottom tracking ship speed measurement is performed, and the measurement time is more than 3 minutes.

3. The method for measuring bed load sediment transport rate based on attenuation correction of multi-layer sediment acoustic signal of Doppler current profiler according to claim 1 is characterized in that: The calculation formula of the riverbed movement speed is: v a =-v BT Where: v a is the velocity of the riverbed, m / s; v BT is the bottom tracking ship speed, m / s.

4. A method for measuring bed load transport rate based on attenuation correction of multi-layer sediment acoustic signal of Doppler current profiler according to claim 1, characterized in that: The filtered riverbed movement speed data includes: Remove all negative riverbed velocity data; Calculate the standard deviation of the remaining riverbed movement velocity data; The riverbed movement velocity data with a value higher than three times the standard deviation were removed; The riverbed movement velocity data with a value less than the ADCP bottom tracking measurement threshold of 0.001 were removed.

5. The method for measuring bed load transport rate based on attenuation correction of multi-layer sediment acoustic signal of Doppler current profiler according to claim 1 is characterized in that: The calculation formula of the vertical projection area ratio of the bed load is: Where: c p is the vertical projection area ratio of bed load, %; is the average value of riverbed movement velocity data, m / s; v astd is the standard deviation of riverbed velocity data, m / s; P f is the noise data percentage of riverbed movement velocity data, %.

6. The method for measuring bed load transport rate based on attenuation correction of multi-layer sediment acoustic signal of Doppler current profiler according to claim 1 is characterized in that: The calculation formula of the dimensionless sediment particle size is: Where: D * is the dimensionless sediment particle size; D 50 is the median particle size of sediment; s is the specific gravity of sediment bed load; ν is the kinematic viscosity coefficient of the liquid.

7. The method for measuring bed load sediment transport rate based on attenuation correction of multi-layer sediment acoustic signal of Doppler current profiler according to claim 6 is characterized in that: The calculation formula of the bed load thickness is: Where: τ sk is the shear stress of water flow; τ c is the critical starting shear stress; δ is the thickness of the bedload layer.

8. The method for measuring bed load transport rate based on attenuation correction of multi-layer sediment acoustic signal of Doppler current profiler according to claim 7 is characterized in that: The calculation formula of the bed load volume concentration is: Where: c v is the bedload volume concentration; c p is the vertical projection area ratio of bed load, %.

9. The method for measuring bed load sediment transport rate based on attenuation correction of multi-layer sediment acoustic signal of Doppler current profiler according to claim 8 is characterized in that: The calculation formula of the multi-layer sediment sound signal attenuation correction coefficient is: Where: k is the attenuation correction coefficient of multi-layer sediment acoustic signal; is the average value of riverbed movement velocity data, m / s; v astd is the standard deviation of riverbed movement velocity data, m / s.

10. The method for measuring bed load transport rate based on attenuation correction of multi-layer sediment acoustic signal of Doppler current profiler according to claim 9, characterized in that: The calculation formula of the bed load transport rate is: Where: g b is the bed load transport rate per unit width, kg / m / min; is the average value of riverbed movement velocity data, m / s; ρ s is the bed load density, kg / m 3 .

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