A method for calculating the flow capacity of a compound river channel

Abstract

A method for calculating the flow capacity of a compound river channel includes a region division unit that divides the compound river channel into regions to determine different regions, a flow velocity measurement unit that measures the instantaneous flow velocity of each region section to calculate the measured value of the average flow velocity of the section; a flow velocity calculation unit that determines the analytical solution of the control equation of different regions of the compound river channel based on the depth-averaged Navier-Stokes equation and obtains the calculated value of the average flow velocity of the section; a result comparison unit that compares the measured value of the average flow velocity of the section with the calculated value of the average flow velocity of the section to obtain the accuracy of the calculation method. The present invention first simplifies the analytical solution form of the complex flow velocity distribution to more accurately and quickly calculate the average flow velocity of the flow section of the compound river channel; secondly, it can also be used to calculate the average flow velocity of the flow section of the compound river channel, which can provide support for river ecological protection, river material transport and pollution prevention.

Description

Technical Field

[0001] The invention relates to the technical field of hydraulics and river dynamics, and in particular to a method for calculating the flow capacity of a compound river channel. Background Art

[0002] Natural rivers usually appear as a complex river channel with a main channel and beach as the main components, and vegetation grows extensively on the beach and slopes in the complex river channel. Vegetated beach can stabilize the slopes, and while satisfying the need for vegetation ecological restoration, it can also ensure the flood discharge capacity of the main channel. It is the main form of river ecological corridors, so the water flow movement under the vegetated beach complex river channel is the focus of current river dynamics research.

[0003] According to the calculation method of velocity distribution, it can be divided into two categories: numerical solution model and analytical solution model. The numerical solution model is to establish a grid of the flow field and use different discrete formats to calculate the refined water flow movement. However, this method has the disadvantages of large amount of calculation and long time consumption. The analytical solution model can obtain the display expression of velocity distribution by solving the water flow control equation under different test conditions. The advantage is that it has a clear calculation method and is more convenient and faster than the numerical solution model. However, due to the complex form of the analytical solution of velocity distribution, its integral form is still difficult to determine, which is not conducive to the calculation of velocity distribution.

[0004] Therefore, due to the limitations of existing technology, people cannot solve it. Summary of the invention

[0005] (I) Purpose of the invention: In order to solve the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a method for calculating the flow capacity of a compound river channel, which can quickly and accurately simulate the average flow velocity of the measured section, and the result can provide a theoretical basis for the planning and design of vegetated ecological corridors and flood control measures.

[0006] (II) Technical solution: In order to solve the above technical problems, the present technical solution provides a method for calculating the flow capacity of a compound river channel, which is applied to a compound river channel flow capacity calculation system, including a region division unit, a flow velocity measurement unit, a flow velocity calculation unit and a result comparison unit, specifically including:

[0007] Step 1, determine different areas of the compound river channel, and measure the instantaneous flow velocity of the cross section of each area, and calculate the measured value of the average flow velocity of the cross section according to the instantaneous flow velocity of each area;

[0008] Step 2: Determine the analytical solutions of the governing equations for different regions of the compound river channel based on the depth-averaged Navier-Stokes equations;

[0009] Step 3: According to the analytical solution of the control equations of different regions of the compound river channel, the average flow velocity of the cross section is calculated;

[0010] Step 4: Draw a conclusion based on the comparison between the measured value of the average flow velocity of the cross section and the calculated value of the average flow velocity of the cross section.

[0011] Preferably, the step 1 is specifically:

[0012] Step 101, dividing the composite river channel with beach vegetation into a main channel area, a slope area, and a beach area;

[0013] Step 102: Under the uniform flow state, measure the instantaneous flow velocity in different areas respectively to obtain the measured value of the cross-sectional average flow velocity.

[0014] Preferably, the composite river channel with beach vegetation is divided into a main channel area, a side slope area and a side beach area from the center outwards;

[0015] The main trough area is a non-vegetated area, which is a flat area without slope in the river channel, and its two end boundaries are the side wall and the position where the slope begins; the slope area also belongs to the non-vegetated area, and the location of the slope area is in the sloped part between the beach area and the main trough area, and the boundary of the slope area is controlled by the boundary between the main trough area and the beach area; the beach area is an area with vegetation growth, and its two end boundaries are the other side wall and the junction with the non-vegetated area.

[0016] Preferably, under uniform flow conditions, the water depth averaged Navier-Stokes equation is used, and the Darcy-Weisbach friction coefficient and eddy viscosity theory are applied to calculate the main trough area, the slope area, and the beach area, respectively, to obtain an analytical solution to the control equation.

[0017] Preferably, the main tank area: Linear slope area,

[0018] For the vegetated beach areas,

[0019] Where: H is the water depth of the main channel area;

[0020] Y is the water depth function of the slope area: Y = H-(yb) / s, ρ is the density of water; g is the acceleration of gravity; S0 is the slope of the bed; x, y, z are respectively along the direction of water flow (longitudinal), the direction of river width (lateral), and the direction of water depth (vertical); u′, v′, w′ are respectively the wave speeds in the x, y, and z directions; C D is the drag coefficient; λ = m D is the vegetation coefficient; m is the vegetation density (plants / m 2 ), D is the diameter of the vegetation; s is the slope gradient; f is the Darcy-Weisbach friction coefficient, ξ xyis the eddy viscosity, ζ is the eddy viscosity coefficient; A1, C1, A2, C2, A3, and C3 are all constants.

[0021] Preferably, the step 3 is specifically:

[0022] Step 301, based on the analytical solution of flow velocity distribution in different regions, obtain the average flow velocity of the cross section in different regions;

[0023] Step 302: According to the cross-sectional average flow velocities in different regions, a calculated value of the cross-sectional average flow velocity in a simple analytical solution integral form is determined.

[0024] Preferably, the calculation method of the cross-sectional average flow velocity of the main channel area, the slope area and the beach area is:

[0025] Main tank area:

[0026] Slope area:

[0027] Beach area:

[0028] Where: y 11 and 12 Respectively represent the left and right boundary positions of the main groove area; y 21 and 22 Respectively represent the left and right boundary positions of the slope area; y 31 and 32 They respectively represent the left and right boundary positions of the beach area.

[0029] Preferably, As a method of calculating the average flow velocity of a section;

[0030] Main tank area:

[0031] Slope area:

[0032] Beach area:

[0033] Preferably, the average flow velocity of the cross section is:

[0034] Preferably, the average absolute error and the average relative error of the measured value of the average flow velocity of the section and the calculated value of the average flow velocity of the section are calculated, thereby evaluating the degree of fit between the calculated value of the average flow velocity of the compound river flow section and the measured value, and drawing a conclusion;

[0035] The smaller the absolute error between the actual measured value of the cross-sectional average flow velocity and the calculated value of the cross-sectional average flow velocity, and the average relative error between the actual measured value of the cross-sectional average flow velocity and the calculated value of the cross-sectional average flow velocity is less than or equal to the first threshold, then the calculation method described in the present invention is more accurate; conversely, the larger the absolute error between the actual measured value of the cross-sectional average flow velocity and the calculated value of the cross-sectional average flow velocity, and the average relative error between the actual measured value of the cross-sectional average flow velocity and the calculated value of the cross-sectional average flow velocity is greater than the first threshold, then the calculation method described in the present invention is more rough.

[0036] (III) Beneficial effects: The method for calculating the flow capacity of a compound river channel of the present invention first simplifies the analytical solution form of complex velocity distribution to more accurately and quickly calculate the average flow velocity of the flow section of the compound river channel; secondly, it can also be used to calculate the average flow velocity of the flow section of the compound river channel, which can provide support for river ecological protection, river material transport and pollution control. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is a flow chart of the steps of the present invention;

[0038] Figure 2 It is a specific step flow chart of step 1 of the present invention;

[0039] Figure 3 It is a schematic diagram of the compound river channel lateral line of the present invention;

[0040] Figure 4 It is a specific step flow chart of step 3 of the present invention;

[0041] Figure 5 This is a diagram showing the range of y values ​​in the present invention;

[0042] Figure 6 It is a result comparison fitting diagram of the first set of test data of the present invention;

[0043] Figure 7 is a result comparison fitting diagram of the second set of test data of the present invention;

[0044] Figure 8 is a result comparison fitting diagram of the third group of test data of the present invention;

[0045] Fig. 9 is a result comparison and fitting diagram of the fourth group of test data of the present invention;

[0046] Fig.10 is a result comparison and fitting diagram of the fifth group of test data of the present invention;

[0047] Fig.11 It is a result comparison fitting diagram of the sixth group of test data of the present invention. DETAILED DESCRIPTION

[0048] The present invention is further described in detail below in conjunction with preferred embodiments. More details are elaborated in the following description to facilitate a full understanding of the present invention. However, the present invention can obviously be implemented in a variety of other ways different from the description. Those skilled in the art can make similar generalizations and deductions based on actual application situations without violating the connotation of the present invention. Therefore, the protection scope of the present invention should not be limited by the content of this specific embodiment.

[0049] The accompanying drawings are schematic diagrams of embodiments of the present invention. It should be noted that the drawings are only examples and are not drawn to scale, and should not be used to limit the actual protection scope of the present invention.

[0050] A method for calculating the flow capacity of a compound river channel is applied to a compound river channel flow capacity calculation system, and includes a region division unit, a flow velocity measurement unit, a flow velocity calculation unit, and a result comparison unit. The region division unit divides the compound river channel into regions, and obtains the main channel area, the slope area, and the beach area in sequence from the center to the river bank. The flow velocity measurement unit measures the flow velocity of each region to obtain the corresponding measured value of the average flow velocity of the cross section. The flow velocity calculation unit determines the analytical solution of the control equation of different regions, and obtains the corresponding calculated value of the average flow velocity of the cross section according to the analytical solution of the control equation. The result comparison unit solves the average relative error and the average absolute error according to the measured value of the average flow velocity of the cross section and the calculated value of the average flow velocity of the cross section, so as to obtain the accuracy of the calculation method.

[0051] like Figure 1 As shown, the following steps are included:

[0052] Step 1: The area division unit divides the compound river channel into regions to determine different regions of the compound river channel. The velocity measurement unit measures the instantaneous velocity of the cross section of each region, and calculates the measured value of the average flow velocity of the cross section based on the instantaneous velocity of each region.

[0053] Step 2: The velocity calculation unit determines the analytical solutions of the control equations for different regions of the compound river channel based on the depth-averaged Navier-Stokes equation.

[0054] Step 3: The velocity calculation unit calculates the average velocity of the cross section based on the analytical solution of the control equations of different regions of the compound river channel.

[0055] Step 4: The result comparison unit compares the measured value of the cross-sectional average flow velocity with the calculated value of the cross-sectional average flow velocity to obtain the accuracy of the calculation method.

[0056] More specifically, Figure 2 As shown, the step 1 is specifically as follows:

[0057] Step 101, the regional division unit divides the composite river channel with beach vegetation into a main channel area, a slope area, and a beach area.

[0058] like Figure 3 As shown, the composite river channel with beach vegetation is divided into the main channel area, the slope area and the beach area from the center to the outside. The beach area is an area with vegetation growth, and its two end boundaries are the side wall and the junction with the non-vegetated area. The main channel area belongs to the non-vegetated area, which is a flat area with no slope in the river channel, and its two end boundaries are the side wall on the other side and the position where the slope begins. The slope area also belongs to the non-vegetated area, which appears as a sloped part in the composite river channel. The slope area is located between the beach area and the main channel area, and the boundary is controlled by the boundary between the main channel area and the slope area.

[0059] Step 102: Under the uniform flow state, the flow velocity measurement unit measures the instantaneous flow velocity in different areas respectively to obtain the measured value of the cross-sectional average flow velocity.

[0060] When the water flow maintains a constant uniform flow, the instantaneous flow velocity is measured for the main channel area, the slope area and the beach area of ​​the compound river channel respectively. After data processing, the collected instantaneous flow velocity is weighted averaged for the main channel area, the slope area and the beach area of ​​the compound river channel to obtain the measured value of the cross-sectional average flow velocity of the compound river channel.

[0061] It should be noted that the sampling frequency and sampling time interval are constant when measuring flow rate. After a measurement is completed, it can be modified, but during the same measurement process, the sampling frequency and sampling time interval cannot be changed.

[0062] More specifically, the step 2 is as follows:

[0063] The velocity calculation unit determines the average Navier-Stokes equation of water depth in a composite river channel with vegetation on the beach under uniform flow conditions. The Darcy-Weisbach friction coefficient and eddy viscosity theory are applied to calculate the main channel area, the slope area, and the beach area, respectively, and obtain the analytical solution of the control equation, as shown in formula (1), formula (4) and formula (8):

[0064] For the main tank area:

[0065]

[0066] Where: H is the water depth of the main channel area;

[0067]

[0068]

[0069] For linear slope regions,

[0070]

[0071] in:

[0072]

[0073]

[0074] Y is the water depth function of the slope area: Y = H-(yb) / s (7).

[0075] For the beach areas with vegetation,

[0076]

[0077] in:

[0078]

[0079]

[0080] Where ρ is the density of water; g is the acceleration of gravity; S0 is the slope of the bed; x, y, and z are the direction of water flow (longitudinal), river width (lateral), and water depth (vertical), respectively; u′, v′, and w′ are the wave velocities in the x, y, and z directions, respectively; C D is the drag coefficient; λ = m D is the vegetation coefficient; m is the vegetation density (plants / m 2 ), D is the diameter of the vegetation; s is the slope; f is the Darcy-Weisbach friction coefficient, ξ xy is the eddy viscosity, ζ is the eddy viscosity coefficient; A1, C1, A2, C2, A3, and C3 are all constants.

[0081] More specifically, Figure 4 As shown, the step 3 is specifically as follows:

[0082] Step 301: As shown in formula (11), the velocity calculation unit obtains the average cross-sectional velocity of different regions based on the velocity distribution analytical solution of different regions.

[0083]

[0084] Wherein: y1 and y2 represent the boundary positions of each area respectively; the value range of y1 and y2 needs to fall within the actual boundary range. In the actual test process, it is determined by the leftmost and rightmost ends of the measured points in each area.

[0085] As shown in formula (12), formula (13) and formula (14), they are the calculation methods of the cross-sectional average flow velocity in the main channel area, slope area and beach area respectively.

[0086] Main tank area:

[0087] Slope area:

[0088] Beach area:

[0089] like Figure 5 As shown, where: y 11 and 12 Respectively represent the left and right boundary positions of the main groove area; y 21 and 22 Respectively represent the left and right boundary positions of the slope area; y 31 and 32 They respectively represent the left and right boundary positions of the beach area.

[0090] Step 302: The velocity calculation unit determines a cross-sectional average velocity calculation value having a simple analytical solution integral form according to the cross-sectional average velocity in different regions.

[0091] In order to simplify the integral form of the velocity distribution analytical solution, the present invention proposes to As a method to calculate the average flow velocity of a section.

[0092] Main tank area:

[0093]

[0094] Slope area:

[0095]

[0096] Beach area:

[0097]

[0098] Average flow velocity in section:

[0099]

[0100] More specifically, the step 4 is as follows:

[0101] As shown in formula (19) and formula (20), the result comparison unit calculates the average absolute error and the average relative error between the measured value of the cross-sectional average flow velocity and the calculated value of the cross-sectional average flow velocity, thereby evaluating the degree of fit between the calculated value of the average flow velocity of the compound river flow section and the measured value, and obtaining the accuracy of the calculation method described in the present invention.

[0102] As shown in formula (19), the mean absolute error expression is:

[0103]

[0104] As shown in formula (20), the average relative error expression is:

[0105]

[0106] Generally speaking, the smaller the absolute error between the actual measured value of the cross-sectional average flow velocity and the calculated value of the cross-sectional average flow velocity, the more accurate the calculation method described in the present invention is; conversely, the larger the absolute error between the actual measured value of the cross-sectional average flow velocity and the calculated value of the cross-sectional average flow velocity, the rougher the calculation method described in the present invention is.

[0107] More preferably, the absolute error is the difference between the predicted value and the measured value, and in theory, the smaller the better. However, since some values ​​are small in themselves, the difference will also be small, so the present invention introduces relative error for further verification. If the average relative error of the measured value of the average flow velocity of the section and the calculated value of the average flow velocity of the section described in the present invention is less than or equal to the first threshold value, it indicates that the measured value and the predicted value are in good agreement, and the calculation method described in the present invention is more accurate. Conversely, if the average relative error of the measured value of the average flow velocity of the section and the calculated value of the average flow velocity of the section is greater than the first threshold value, it indicates that the calculation method described in the present invention is more rough.

[0108] The first threshold value of the present invention is gradually refined in the actual application of the calculation method of the present invention. The first threshold value of the present invention is 10%.

[0109] The following is a detailed introduction in conjunction with specific embodiments:

[0110] First, the first preferred embodiment is carried out in a rectangular test water tank of the Institute of Water Ecology and Environment of China Institute of Water Resources and Hydropower Research, the model of which is: length × width × depth = 10m × 1.0m × 1.0m. The bottom of the rectangular test water tank is paved with a PVC template, the wall of the rectangular test water tank is made of glass, and the rectangular test water tank is divided into three areas in the horizontal direction: the main tank, the slope, and the beach. The width of the main tank area is 0.4m, the height and width of the slope area are both 0.2m, and the height and width of the beach area are 0.2m and 0.4m respectively.

[0111] The rectangular test water tank is a circulating water tank, and the water flow is kept in a constant uniform flow condition by controlling the upstream valve and the downstream tailgate, so that the water level in the rectangular test water tank meets the requirements. The present invention uses simulated vegetation of short grass and sedge as the research object to simulate the composite river channel of beach vegetation. The parameters of the test are shown in Table 1, and 3 groups of test data are obtained respectively. The instantaneous flow velocity of the rectangular test water tank is measured by an acoustic Doppler velocity meter ADV (Acoustic Doppler Velocimetry), and the measured value of the average flow velocity of the cross section is obtained by the measured instantaneous flow velocity.

[0112] The acoustic Doppler flow meter is based on the Doppler principle and adopts a remote measurement method to measure a sampling point at a certain distance from the probe.

[0113] The second preferred embodiment test was carried out in the State Key Laboratory of Hydraulics and Mountain River Development and Protection of Sichuan University. The test flume is 16m long, 0.3m wide and 0.4m high. And the parameters of the test are shown in Table 1, and 3 groups of test data are obtained respectively. The front section of the test flume is provided with a water inlet valve. After the water flows through the triangular weir (the actual flow rate is read), it enters the still water pool and finally flows into the test flume. A probe that can slide back and forth is arranged at the center of the test flume. The probe can read the water depth along the test flume. A flat gate is provided at the tail of the test flume. The water level is controlled by adjusting the opening of the flat gate to obtain a uniform flow. When the water surface gradient and the bed slope read by the probe are less than or equal to 2%, the water flow is considered to be a uniform flow. A Doppler sound velocity three-dimensional flowmeter (ADV) measuring bracket is installed on the guide rail of the test water tank. The Doppler sound velocity three-dimensional flowmeter produced by Sontek is used to collect flow velocity data. The sampling frequency and sampling time interval at each measuring point are 50Hz and 30s (sometimes greater than 30s). Therefore, each measuring point has at least 1500 instantaneous flow velocity data. The original flow velocity data is processed by supporting software, and the actual measured value of the cross-section average flow velocity is finally obtained.

[0114] Table 1 Test parameters

[0115]

[0116] The average absolute error and average relative error of the six tests were calculated, as shown in Table 2. The error analysis of the predicted cross-sectional average flow velocity calculation value and the measured cross-sectional average flow velocity actual value was performed to verify the accuracy of the method. Figure 6 to Figure 11 As shown in the figure, the hollow circle represents the main trough area; the octagon represents the slope area; the cross represents the beach area; the pentagon represents the cross section, which is the weighted average of the main trough area, the slope area and the beach area.

[0117] Table 2 Comparison of measured and calculated values ​​under different working conditions

[0118]

[0119] It can be seen from the average absolute error and average relative error of different working conditions in Table 2 that the calculated value of the average flow velocity of the section obtained by the compound river flow capacity calculation method proposed in the present invention is well matched with the measured value of the average flow velocity of the section, indicating that the calculation method described in the present invention is reliable, and provides a theoretical method for facilitating the calculation of the average flow velocity of the flow section and accurately describing the pollutant transport process.

[0120] The present invention provides a method for calculating the flow capacity of a compound river channel. Firstly, the method simplifies the analytical solution form of the complex velocity distribution, and more accurately and quickly calculates the average velocity of the compound river channel flow section. Secondly, the method can also be used to calculate the average velocity of the compound river channel flow section, which can provide support for river ecological protection, river material transport and pollution prevention.

[0121] The above content is an explanation of the preferred embodiments of the present invention, which can help those skilled in the art to more fully understand the technical solution of the present invention. However, these embodiments are merely illustrative, and it cannot be determined that the specific implementation methods of the present invention are limited to the description of these embodiments. For ordinary technicians in the technical field to which the present invention belongs, without departing from the concept of the present invention, several simple deductions and transformations can be made, which should be regarded as belonging to the protection scope of the present invention.

Claims

1. A method for calculating the flow capacity of a compound river channel, characterized in that: The invention is applied to a compound river flow capacity calculation system, comprising a region division unit, a flow velocity measurement unit, a flow velocity calculation unit and a result comparison unit. The calculation method specifically comprises: Step 1: The area division unit divides the compound river channel into regions to determine different regions of the compound river channel. The flow velocity measurement unit measures the instantaneous flow velocity of each section of each region, and calculates the measured value of the average flow velocity of the section according to the instantaneous flow velocity of each region. Step 2, the velocity calculation unit determines the analytical solutions of the control equations in different areas of the compound river channel according to the depth-averaged Navier-Stokes equation; the velocity calculation unit determines the depth-averaged Navier-Stokes equation under uniform flow conditions, and applies the Darcy-Weisbach friction coefficient and eddy viscosity theory to calculate the main channel area, slope area, and beach area, respectively, to obtain the analytical solutions of the control equations; main channel area: Linear slope area, For the vegetated beach areas, Where: H is the water depth of the main channel area; Y is the water depth in the slope area: Y = H-(yb) / s, ρ is the density of water; g is the acceleration of gravity; S0 is the slope of the bed; x, y, z are the direction of water flow, river width, and water depth respectively; u′, v′, w′ are the wave speeds in the x, y, and z directions respectively; C D is the drag coefficient; λ = m·D is the vegetation coefficient; m is the vegetation density, D is the vegetation diameter; s is the slope; f is the Darcy-Weisbach friction coefficient, ξ xy is the eddy viscosity, ζ is the eddy viscosity coefficient; A1, C1, A2, C2, A3, C3 are all constants; Step 3, the velocity calculation unit calculates the average velocity of the cross section according to the analytical solution of the control equations of different regions of the compound river channel; Step 4: The result comparison unit compares the measured value of the cross-sectional average flow velocity with the calculated value of the cross-sectional average flow velocity to obtain the accuracy of the calculation method.

2. A method for calculating the flow capacity of a compound river according to claim 1, characterized in that: The step 1 is specifically as follows: Step 101, the regional division unit divides the composite river channel with beach vegetation into a main channel area, a slope area, and a beach area; Step 102: Under the uniform flow state, the flow velocity measurement unit measures the instantaneous flow velocity in different areas respectively to obtain the measured value of the cross-sectional average flow velocity.

3. A method for calculating the flow capacity of a compound river according to claim 2, characterized in that: The composite river channel with beach vegetation is divided into the main channel area, the side slope area and the side beach area from the center to the outside. The main trough area is a non-vegetated area, which is a flat area without slope in the river channel, and its two end boundaries are the side wall and the position where the slope begins; the slope area also belongs to the non-vegetated area, and the location of the slope area is in the sloped part between the beach area and the main trough area, and the boundary of the slope area is controlled by the boundary between the main trough area and the beach area; the beach area is an area with vegetation growth, and its two end boundaries are the other side wall and the junction with the non-vegetated area.

4. A method for calculating the flow capacity of a compound river according to claim 1, characterized in that: The step 3 is specifically as follows: Step 301, the velocity calculation unit obtains the average flow velocity of the sections in different areas based on the velocity distribution analytical solution in different areas; Step 302: The velocity calculation unit determines a cross-sectional average velocity calculation value having a simple analytical solution integral form according to the cross-sectional average velocity in different regions.

5. A method for calculating the flow capacity of a compound river according to claim 4, characterized in that: Calculation method of average flow velocity in the main channel area, slope area and beach area: Main channel area: Slope area: Beach area: Where: y 11 and 12 Respectively represent the left and right boundary positions of the main groove area; y 21 and 22 Respectively represent the left and right boundary positions of the slope area; y 31 and 32 They respectively represent the left and right boundary positions of the beach area.

6. A method for calculating the flow capacity of a compound river according to claim 5, characterized in that: Will As a method of calculating the average flow velocity of the section; Main trough area: Slope area: Beach area:

7. A method for calculating the flow capacity of a compound river according to claim 6, characterized in that: Average flow velocity in section:

8. A method for calculating the flow capacity of a compound river according to claim 1, characterized in that: Results The average absolute error and average relative error of the measured value of the average flow velocity of the unit calculation section and the calculated value of the average flow velocity of the section were compared, and the fitting degree between the calculated value and the measured value of the average flow velocity of the compound river flow section was evaluated, and a conclusion was drawn; The smaller the absolute error between the actual measured value of the cross-sectional average flow velocity and the calculated value of the cross-sectional average flow velocity, and the average relative error between the actual measured value of the cross-sectional average flow velocity and the calculated value of the cross-sectional average flow velocity is less than or equal to the first threshold, then the more accurate the calculation method is; conversely, the larger the absolute error between the actual measured value of the cross-sectional average flow velocity and the calculated value of the cross-sectional average flow velocity, and the average relative error between the actual measured value of the cross-sectional average flow velocity and the calculated value of the cross-sectional average flow velocity is greater than the first threshold, then the more rough the calculation method is.

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