A bed load discharge measurement method based on Doppler current profiler multi-layer sediment sound signal attenuation correction

Abstract

The application discloses a kind of based on Doppler flow velocity profiler multilayer sediment sound signal attenuation correction's bed load sediment transport rate measurement method, comprising: in the floodplain area of the river reach to be measured, the bed surface of sediment is sampled, and the bed material gradation is measured, and the median size of bed sand is obtained;Obtain flow data, and extract ship speed data from flow data;According to ship speed data, calculate riverbed movement speed;Filter riverbed movement speed data, and calculate the eigenvalue of filtered riverbed movement speed data;According to the eigenvalue of filtered riverbed movement speed data, respectively calculate bed load vertical projection area ratio;According to bed sand median size, calculate dimensionless sediment particle size;According to dimensionless sediment particle size, calculate bed load layer thickness;According to bed load vertical projection area ratio and bed load layer thickness, calculate bed load volume concentration;According to bed load volume concentration, calculate multilayer sediment sound signal attenuation correction coefficient;According to multilayer sediment sound signal attenuation correction coefficient, calculate bed load sediment transport rate.The application accurately and effectively measures bed load sediment transport rate.

Description

Technical Field

[0001] The invention relates to a bed load 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 based on its movement pattern. While the movement models and measurement techniques for suspended load are relatively mature, the movement patterns of bed load remain a significant challenge in river dynamics. Since the development of sediment mechanics in the early 20th century, bed load movement has become a key research focus in international academia. Although bed load accounts for a relatively small proportion of a river's total sediment load, it interacts closely with the riverbed, influencing scouring and deposition, and playing a key role in the evolution of river morphology. The bed load transport rate directly determines the river type, and 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 foundation of bed load research. In recent years, data mining methods have also shown great potential in bed load transport rate prediction. Methods such as bagging, M5P, and random forest have all shown high accuracy. In addition, with the development of computer technology, numerical simulation methods for bed load movement have been widely used. Combining data-driven models with traditional mechanical analysis has become an important direction in bed load research.

[0003] Measuring bedload transport rates is a crucial component of hydrological surveying. Its data provide fundamental support for research on river morphological evolution and sediment disaster prevention. Since the 20th century, bedload measurement technology has continuously advanced internationally, with international academic conferences dedicated to discussing the technical aspects of bedload measurement. Bedload measurement methods can be categorized as direct or indirect. Direct bedload measurement involves obtaining sediment samples from the riverbed using sediment traps and samplers, or by measuring the movement of sand waves on the riverbed to calculate changes in sediment flux. Indirect bedload measurement uses detection devices placed in the riverbed to record signals generated by the natural movement of bedload, primarily including Swiss vibrating plates, Japanese acoustic tubes, and hydrophones. Physical principles are used to analyze the acoustic or vibration signals generated by the bedload to establish a relationship between bedload motion parameters and the measured signals. However, bedload measurement presents numerous challenges. Due to the turbulent flow and the varying particle sizes of bedload, existing measurement techniques struggle to effectively capture its motion patterns. Traditional bedload measurement methods, such as samplers and pits, while highly accurate, are complex to operate, have low sampling efficiency, and are unable to meet the demands for high-temporal and spatial resolution data. While recent developments in new sensors, such as hydrophones and Swiss vibrating plates, have made progress in long-term, continuous bedload monitoring, these technologies are expensive to deploy and their applicability in complex river environments remains limited. Therefore, developing bedload measurement technologies with high temporal and spatial resolution has become a current research hotspot.

[0004] Acoustic Doppler Current Profilers (ADCPs) are commonly used to measure water velocity. Their measurement principle involves transmitting pulsed sound waves into the water through four regularly arranged acoustic probes. The probes then receive the sound waves scattered by the bedload in the water, and calculate the water velocity based on the Doppler frequency shift of the reflected signal. Their bottom-tracking function, which allows them to emit sound waves probing the bottom, has recently been demonstrated to have the potential to measure bedload transport rates with high temporal and spatial resolution, making them a cutting-edge area in bedload measurement technology. However, due to the multi-layer attenuation of acoustic signals in natural sediments, bedload velocities measured by ADCPs are affected, resulting in significant errors in the resulting bedload transport rates. Currently, there is no accurate method for measuring bedload transport rates using ADCPs, which has severely hampered the development of bedload 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 solves the above technical problems and provides a technical solution: a method for measuring bed load transport rate based on attenuation correction of multi-layer sediment acoustic signals of a Doppler current profiler, comprising the following steps:

[0007] Sampling the sediment on the riverbed surface in the floodplain area of ​​the river section to be measured, and measuring the sediment gradation to obtain the median particle size of the bed sediment;

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

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

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

[0011] The vertical projection area ratio of bed load was calculated based on the characteristic values ​​of the filtered riverbed velocity data;

[0012] Calculate the dimensionless sediment particle size 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 bed load volume concentration;

[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 integrated track function. According to the DGPS signal, ensure that the side ship position is always at the selected measuring point, perform bottom tracking ship speed measurement, and the measurement time is 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 riverbed movement speed, 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 for 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 percentage of riverbed movement velocity data, %.

[0029] A further technical solution is that the calculation formula for 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 bed load 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 bed load 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 for 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 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 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 channel;

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

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

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

[0050] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

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

[0052] Step 1: Select sampling points in the floodplain area of ​​the measured river section and use a standard bed load sampler (such as the 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 sediment gradation is calculated by weighing to determine the median particle size D of the bed sand. 50 m;

[0053] Step 2: Select a measuring point in the center of the measured river section with a water depth greater than 40 cm, ensuring that the measuring point location fully represents the flow characteristics of the river section. Use a cable to secure the ADCP to the survey vessel or bracket, and ensure that the ADCP is mounted securely to avoid external interference. Keep the survey vessel or bracket stable at the measuring point and perform a fixed-point bottom-tracking flow measurement for at least 6 minutes to ensure data integrity and accuracy. During this time, the ADCP continuously records the bottom-tracking vessel speed to ensure the file format is correct and the data is complete.

[0054] Step 3. Use the data processing software provided with the ADCP to open the current measurement file saved in Step 2. 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. Ensure 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 and ensure that the data file is complete and undamaged. Use Matlab to open the "bottom track" array in the bottom tracking ship speed data, search for the "BT Vel" field, obtain the bottom tracking ship speed components in different directions measured by the ADCP, and use the bottom tracking ship speed in the flow direction to calculate the riverbed movement velocity.

[0056] v a =-v BT

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

[0058] Step 5: Filter the riverbed movement velocity 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 lower than the ADCP bottom tracking measurement threshold of 0.001 m / s.

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

[0061] Step 7, calculate the vertical projection area ratio c of the bed load using the riverbed movement velocity data characteristic value obtained in step 6 p ;

[0062]

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

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

[0065]

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

[0067] Step 9, calculate the bed load layer thickness according to the dimensionless sediment particle size;

[0068]

[0069] In the formula: τ sk is the shear stress of the flow; τ c is the critical starting shear stress; δ is the bed load layer thickness;

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

[0071]

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

[0073] Step 11, calculate the multi-layer sediment sound signal attenuation correction coefficient according to the bed load layer thickness and the 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: Calculate the bed load transport rate based on 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] Use steps 4 to 12 to calculate the attenuation correction coefficient of the bedload multi-layer sediment acoustic signal and the bedload 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 shown 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 does not 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 use the technical content disclosed above to make some changes or modifications to equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any simple modifications, 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 transport rate based on attenuation correction of multi-layer sediment acoustic signals of Doppler current profiler, characterized in that: The following steps are involved: Sampling the sediment on the riverbed surface in the floodplain area of ​​the river section to be measured, and measuring the sediment gradation to obtain the median particle size of the bed sediment; Select a measuring point and use ADCP and a matching unmanned vessel equipped with DGPS to conduct fixed-point bottom-tracking current measurement to obtain current measurement data, and extract the bottom tracking ship speed from the current measurement data; Calculate the riverbed movement speed based on the bottom-tracking ship speed; Filtering the riverbed movement velocity data and calculating characteristic values ​​of the filtered riverbed movement velocity data, wherein the characteristic values ​​include the mean value, standard deviation, and noise data percentage of the riverbed movement velocity data; The vertical projection area ratio of bed load is calculated based on the characteristic value of the filtered riverbed movement velocity data; Calculate the dimensionless sediment particle size 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 multi-layer sediment acoustic signal attenuation correction coefficient based on the bed load thickness, riverbed movement velocity, and 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 transport rate based on attenuation correction of multi-layer sediment acoustic signals 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 integrated track function is turned on. According to the DGPS signal, the side ship position is ensured to always be at the selected measuring point, and bottom tracking ship speed measurement is performed, and the measurement time is more than 3 minutes.

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

4. The method for measuring bed load transport rate based on attenuation correction of multi-layer sediment acoustic signals of Doppler current profiler according to claim 1 is 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 signals of Doppler current profiler according to claim 1 is characterized in that: The calculation formula for 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 percentage of riverbed movement velocity data, %.

6. The method for measuring bed load transport rate based on attenuation correction of multi-layer sediment acoustic signals of Doppler current profiler according to claim 1, 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 transport rate based on attenuation correction of multi-layer sediment acoustic signals of Doppler current profiler according to claim 6, characterized in that: The calculation formula for the bed load thickness is: Where: τ sk is the water shear stress; τ c is the critical starting shear stress; δ is the thickness of the bed load layer.

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

9. The method for measuring bed load transport rate based on attenuation correction of multi-layer sediment acoustic signals of Doppler current profiler according to claim 8, 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; is the riverbed movement speed, 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 signals of Doppler current profiler according to claim 9, characterized in that: The calculation formula for 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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