Determination method and device of leg sediment thrust-suspension ratio

Abstract

The invention belongs to the technical field of water conservancy projects, and particularly relates to a method and a device for determining a leg sediment thrust-suspension ratio. The method comprises the following steps: S1, establishing a tributary inlet mathematical model and carrying out similarity verification; s2, obtaining the particle size of bed sand, the particle size of suspended sand and the sand content of a water body; s3, determining the leg sediment pushing-suspending ratio according to the tributary convergence inlet mathematical model, the convergence tributary bed sand particle size, the suspended sand particle size and the water body sand content, and determining the leg sediment pushing-suspending ratio through the method when the data of suspending inhibition and pushing inhibition cannot be obtained according to historical data information.

Description

Technical Field

[0001] The invention belongs to the technical field of water conservancy projects, and in particular relates to a method and a device for determining a section sediment thrust-suspension ratio. Background Art

[0002] The sediment load-to-suspension ratio refers to the ratio of the load to the suspended sediment in a certain section of a river. The load-to-suspension ratio is an important parameter in sediment kinematics, used to describe the movement and transport characteristics of sediment in a river. The load-to-suspension ratio is defined as: ,in, The t represents the load-to-suspension ratio, where T represents the amount of bedload flowing through a specific section, and S represents the amount of suspended sediment flowing through a specific section. The sediment load-to-suspension ratio is affected by a variety of factors, including: Riverbank slope: The amount and rate of riverbank collapse increase with increasing riverbank slope. Most of the collapsed material begins to move after entering the river channel, accounting for 89.85% to 93.6% of the total collapse, resulting in a load-to-suspension ratio of 9.23% to 11.23%; Water velocity: Sediment must overcome gravity, frictional resistance, and interparticle cohesion to transition from static to dynamic, while these forces are not overcome when transitioning from dynamic to static. Sediment particle size: Sediments of different particle sizes exhibit different motion characteristics in water flow, which affects the calculation of the load-to-suspension ratio. The load-to-suspension ratio has important applications in river and coastal engineering. In river engineering, the load-to-suspension ratio can help understand sediment transport and deposition processes and optimize river management and flood control measures. In coastal engineering, the study of thrust-to-overhang ratio is of great significance for port construction and waterway maintenance, especially in silty sandy coastal areas. The calculation and prediction of thrust-to-overhang ratio is crucial to prevent port siltation and ensure the smooth flow of waterways.

[0003] During the design process of the Pinglu Canal, the Shaping River Mouth-Madao Hub section was a data-free area, and it was impossible to obtain data on overhang and push restraint based on historical data, making it impossible to carry out subsequent design work. Summary of the Invention

[0004] In order to overcome the problem that it is impossible to obtain the data of overhang suppression and push suppression based on historical data in the Shaping River Estuary-Madao Hub section, obtain other relevant parameters and conditions, and fit the sediment push-suspension ratio of this section, a method and device for determining the sediment push-suspension ratio of this section are proposed.

[0005] In order to achieve the above objectives, the following technical solutions are proposed: A method for determining the sediment thrust-suspension ratio of a section includes the following steps: S1, establish a mathematical model of the tributary inlet and perform similarity verification; S2, obtain the bed sand particle size, suspended sand particle size and water sediment content of the inflow tributary; S3. Determine the sediment push-to-suspend ratio of the section based on the mathematical model of the tributary confluence, the bed sand particle size of the confluence tributary, the suspended sediment particle size and the sediment content of the water body.

[0006] As a preferred solution, in step S1, the control equations in the mathematical model of the tributary confluence include a two-dimensional sediment continuity equation, a two-dimensional riverbed deformation equation, a bed load transport rate equation, and a suspended load transport rate equation.

[0007] As a preferred solution, in step S1, the suspended sediment equilibrium concentration is expressed as c E It is expressed as follows:

[0008] As a preferred option, the steps of similarity verification include: selecting a river section with a similar riverbed composition to the target section, and extracting historical topography and water level data of the similar river section; determining the verification scope, and conducting similarity verification of the riverbed scouring and silting volume, scouring and silting location, and scouring and silting thickness; selecting the daily average flow and daily average sediment content data measured in the engineering river section during the same period as the basis for dynamic bed verification, and conducting similarity judgment with the water and sediment processes in the historical topography and water level data.

[0009] As a preferred solution, in step S2, the bed sand particle size is obtained by grouping the bed sand composition of the project river section according to the particle grading curve of the riverbed sediment sampling, and determining the number of groups and the particle size range in each group.

[0010] As a preferred solution, in step S2, the suspended sediment particle size is determined by grouping the suspended sediment particle size composition of the project river section according to the suspended sediment particle grading table, and determining the number of groups and the particle size range in each group.

[0011] As a preferred solution, step S3 includes: first, calculating the thrust-overhang ratio of the main river channel of this river section based on the thrust-overhang ratio results adopted by other hydropower hubs in the same region; second, determining the intensity of the bed sediment movement at the confluence based on the bed sand particle size and suspended sand particle size of the influent tributary; finally, estimating the thrust-overhang ratio of the influent tributary.

[0012] Based on the same concept, a device for determining the sediment thrust-suspension ratio of a flight section is also proposed, comprising at least one processor and a memory communicatively connected to the at least one processor; the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor so that the at least one processor can execute any of the above-described methods for determining the sediment thrust-suspension ratio of a flight section.

[0013] The solution of the present invention has the following beneficial effects: when the suspension suppression and thrust suppression data cannot be obtained based on historical data, the method of the present invention can be used to determine the suspension and thrust ratio of the section. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1It is a flow chart of a method for determining the sediment thrust-suspension ratio of a section; Figure 2 This is a flow chart of the project river section from July 10, 2020 to October 15, 2021; Figure 3 This is a diagram of the sediment inflow process in the project river section from July 10, 2020 to October 15, 2021; Figure 4 It is to verify the comparison between the terrain calculated by the river model and the measured terrain Figure 1 ; Figure 5 It is to verify the comparison between the terrain calculated by the river model and the measured terrain Figure 2 ; Figure 6 It is a particle gradation curve of riverbed sediment sampling. DETAILED DESCRIPTION

[0015] The present invention will be further described in detail below in conjunction with test examples and specific embodiments. However, this should not be understood as limiting the scope of the present invention to the following embodiments, and all technologies implemented based on the present invention fall within the scope of the present invention.

[0016] Example 1 A method for determining the sediment thrust-suspension ratio of a section, the flow chart is as follows Figure 1 As shown, the following steps are included: S1, establish a mathematical model of the tributary inlet and perform similarity verification; S2, obtain the bed sand particle size, suspended sand particle size and water sediment content of the inflow tributary; S3. Determine the sediment push-to-suspend ratio of the section based on the mathematical model of the tributary confluence, the bed sand particle size of the confluence tributary, the suspended sediment particle size and the sediment content of the water body.

[0017] In step S1, the control equations in the mathematical model of the tributary confluence include a two-dimensional sediment continuity equation, a two-dimensional riverbed deformation equation, a bed load transport rate equation, and a suspended load transport rate equation.

[0018] (1) Plane two-dimensional sediment continuity equation:

[0019] in, The force of water flow carrying sand.

[0020] (2) Two-dimensional riverbed deformation equation:

[0021] Where, , It can be calculated by the theoretical formula, namely: , , is the Karman coefficient. It is necessary to calibrate using measured data.

[0022] (3) Bedload transport rate equation: The Van-Rijn bed load transport rate formula is used.

[0023]

[0024] Where T is the dimensionless transport parameter, ; Critical starting flow rate

[0025] Effective starting flow rate ; Bed resistance coefficient ; is the critical shields constant (approximately equal to 0.06), which can be selected using Table 1; is the dimensionless sediment particle size, ; v is the kinematic viscosity of water, which is 10-6m 2 / s.

[0026] The values of Shields constant are shown in Table 1: Table 1 Shields constant values

[0027] (3) Suspended sediment transport rate equation: Suspended sediment transport will be produced when the following conditions are met.

[0028]

[0029]

[0030] The suspended matter volume concentration at a height a from the bed surface is calculated as follows:

[0031]

[0032] Adoption coefficient Convert the water diffusion coefficient into the suspended sediment diffusion coefficient:

[0033] Van Rijn defined a correction factor for the sediment concentration profile :

[0034] Where, is the saturated sediment concentration. When the suspended sediment concentration exceeds Sediment deposition will occur when the above correction factor is used, and the Rose suspended sediment index Z is calculated as follows:

[0035] Depth-integrated suspended sediment transport rate for:

[0036] In the formula ; The suspended sediment equilibrium concentration cE can be calculated using the approximate formula shown in Table 2.

[0037] Table 2 Suspended sediment equilibrium concentration c E Calculation formula

[0038] The bed sand composition of the model simulated river section is basically fine sand, medium-coarse sand, gravel sand and pebbles, with less clay sand. The Van Rijn formula has good adaptability for the corresponding simulation.

[0039] The study section lacks historically measured topographic data and multi-year runoff and sediment data, making it difficult to validate a two-dimensional sediment mathematical model for this section. Therefore, the report uses existing historical topographic and water level data from the adjacent Xijiang River mainstream and the Rongjiang River mainstream of the Xijiang River system as a basis for similarity validation of the two-dimensional sediment mathematical model, aiming to demonstrate the degree of similarity and adaptability of the two-dimensional sediment mathematical model.

[0040] The two-dimensional sediment model verification includes the two-dimensional sediment model verification of the Rongjiang mainstream section of the Xijiang River system and the two-dimensional sediment model verification of the Xijiang mainstream section.

[0041] Verification of the two-dimensional sediment model for the Rongjiang mainstream of the Xijiang River system: (1) Verify river section selection The validation river section was selected from the Rongjiang (Liujiang) mainstream in Xiucaizhou, Liucheng County, Liuzhou City, Guangxi Zhuang Autonomous Region, 48.5 km upstream from the Rongjiang Guding Hydropower Station and 17.5 km downstream from the Dapu Hydropower Station. The sediment in this section is primarily suspended sediment, and the median particle size of the riverbed is approximately 1.6 mm, similar to the riverbed composition of the study section. The report also collected river channel topography data from two field measurements of the validation river section in October 2021 and July 2020, as well as daily average flow and daily average sediment concentration data measured in the engineering section during the same period. This data is sufficient for sediment model validation.

[0042] (2) Verification scope The report verifies the similarity of the riverbed erosion and deposition volume, erosion and deposition location, and erosion and deposition thickness of the sediment model. The calculation range of the erosion and deposition verification determines that the verification river section is approximately 3 km long.

[0043] (3) Verification period and water and sand conditions The river channel topography data measured twice on-site in October 2021 and July 2020, and the daily average flow and daily average sediment content data measured in the engineering river section during the same period were used as the basis for dynamic bed verification. That is, the measured topography in July 2020 was used as the initial topography, and the water and sediment process of the engineering river section between July 10, 2020 and October 15, 2021 was simulated. The similarity of the riverbed scouring and deposition of the mathematical model was tested by comparing with the measured topography in July 2020.

[0044] The flow process of the project river section from July 10, 2020 to October 15, 2021 is shown in the following table: Figure 2 , see the process of coming to Sha Figure 3 .

[0045] (3) Verification results Through verification simulation, the model parameters were repeatedly adjusted, and finally the requirements of scouring and deposition similar to the prototype riverbed were achieved. The verification results of the sediment mathematical model are briefly described as follows: ① Verification of scouring and silting volume Based on the two measured riverbed topographic maps of the verification section in July 2020 and October 2021, the scour volume in the main channel of this section (about 3.0 km upstream and downstream of the bridge) during the verification period was calculated to be 47.81×104m 3 The amount of scattered sedimentation is 1.73×104m 3 The scour volume of the main channel calculated by numerical model of the same river section is 36.12×104m 3 The sedimentation volume is 1.32×104m 3 The relative errors of scour and sedimentation between the model and the prototype were 24.47% and 25.84%, respectively, which met the requirements of relevant regulations.

[0046] Table 3 Comparison of scouring and silting volume in the verified river section

[0047] ②Verification of scour and silt distribution Figure 4 This is a comparison of the topography calculated by the numerical model and the measured topography of the river section. As can be seen from the figure, the scouring and silting areas calculated by the numerical model are basically consistent with the original riverbed. From the measured results of the topographic map, the overall riverbed evolution of the verified river section showed overall scouring from July 10, 2020 to October 15, 2021 (see Figure 4(a) The main scouring areas are concentrated in the main channel of the river section. There are also sporadic scouring patches on the banks of both sides. There are also a small amount of micro-silting areas between the scouring blocks. From the verification of the water-sediment mathematical model (see Figure 4 (b)) is consistent with the measured results. The river channel as a whole is eroded, and the erosion area extends from the main channel to both banks.

[0048] The verification of riverbed erosion and deposition similarity shows that the model's erosion and deposition volume, erosion and deposition depth, and erosion and deposition location are relatively close to those of the prototype, and the model can basically reproduce the water and sediment movement and river channel evolution of the project section.

[0049] Verification of the two-dimensional sediment model for the main stream of the Xijiang River: (1) Verify river section selection The validation section was selected for the Santan reach of the Xijiang River, located in Changgang Town, Fengkai County, Zhaoqing City, Guangdong Province. This section, characterized by suspended sediment load and a median bed size of approximately 1.5 mm, is similar in composition to the study section. The report also collected river channel topography data from two field measurements of the validation section, conducted in June 2013 and June 2014, as well as daily average flow and sediment concentration data from the engineering section during the same period. This data was sufficient for sediment model validation.

[0050] (2) Verification scope The report verifies the similarity of the riverbed erosion and deposition volume, erosion and deposition locations, and erosion and deposition thickness of the sediment model. The calculation range of the erosion and deposition verification is determined to be a river section of approximately 5.1 km upstream and downstream of the Santan River section.

[0051] (3) Verification period and water and sand conditions The dynamic bed validation model was based on river channel topography data from two field measurements in June 2013 and June 2014, along with daily average flow and sediment concentration data from the validation section during the same period. Using the June 2013 measured topography as the initial topography, the model simulated the flow and sediment processes in the validation section between June 2013 and June 2014. The similarity of the mathematical model's riverbed erosion and deposition patterns was verified by comparing it to the June 2013 measured topography. The flow and sediment processes in the validation section from June 2013 to June 2014 are shown in Table 4.

[0052] Table 4 Water and sediment process of the verified river section from June 2013 to June 2014

[0053] (3) Verification results Through verification simulation, the model parameters were repeatedly adjusted, and finally the requirements of scouring and deposition similar to the prototype riverbed were achieved. The verification results of the sediment mathematical model are briefly described as follows: ① Verification of scouring and silting volume Based on the two measured riverbed topography maps of the model validation section in June 2013 and June 2014, the scour volume in the main channel of the 5.1 km long river section near the Santan bend in Changgang Town during the validation period was calculated to be 95.3×10 4 m 3 The amount of siltation on both sides of the river is 87.3×10 4 m 3 The scouring capacity of the main channel calculated by mathematical model of the same river section is 81.9×10 4 m 3 The sedimentation volume is 75.2×10 4 m 3 (See Table 5.) The relative errors in scour and sedimentation between the model and the prototype were 14.06% and 13.86%, respectively, meeting the requirements of relevant regulations.

[0054] Table 5 Comparison of scouring and silting volume in the verified river section

[0055] ②Verification of scour and silt distribution Figure 5 This figure compares the topography calculated by the numerical model with the measured topography for the validation river section. As can be seen, the simulated scour and sedimentation locations are largely consistent with the original riverbed. Sediment accumulation in this validation river section is concentrated within the spur dikes on the left bank and the spur dikes on the right bank. Scour occurs throughout the main channel of the validation river section. Verification of riverbed scour and sedimentation similarity demonstrates that the model's scour and sedimentation volume, depth, and locations are fairly similar to those of the prototype, demonstrating that the model is generally able to replicate the water and sediment movement and river channel evolution of the projected river section.

[0056] In step S2, the bed sand particle size is obtained by grouping the bed sand composition of the project river section according to the particle gradation curve of the riverbed sediment sampling, and determining the number of groups and the particle size range in each group.

[0057] The sediment of Pinglu Canal mainly comes from the sediment inflow of tributaries on both sides of the river, mainly involving the Qin River Basin and Shaping River and its tributary Shizi River. The bed load and riverbed sand particle size are selected according to the riverbed sand particle size of Shaping River section measured on August 23, 2022. In order to more accurately simulate the sediment movement of the river section, the bed sand composition of the project river section is grouped according to the above-mentioned sediment gradation curve. The sediment particles are divided into 8 groups in total, with a particle size range of 0.01mm~8mm. Figure 6 The particle gradation curve of the riverbed sediment (bed load) sampling in the Shaping River section, the average particle size and proportion of each group of bed sediment are shown in Table 6.

[0058] Table 6 Bed load (bed sand) particle size grouping

[0059] At the same time, the eco-lab module in mike21 was used to successively calculate the sediment movement in the study section under 8 groups of sediment particle size conditions, and the sediment scouring and deposition results were calculated according to the combination of sediment particle size ratios, thereby more comprehensively reflecting the sediment scouring and deposition conditions in the engineering section.

[0060] In step S2, the suspended sediment particle size is obtained by grouping the suspended sediment particle size composition of the project river section according to the suspended sediment particle gradation table, and determining the number of groups and the particle size range in each group.

[0061] The suspended sediment particle grading work in the Yujiang River Basin began in 1966. The suspended sediment particle grading of the Nanning Hydrological Station is shown in Table 7.

[0062] Table 7 Suspended sediment particle size distribution at Nanning Hydrological Station

[0063] To more accurately simulate sediment movement in the river section, the suspended sediment particle size composition of the project river section was grouped according to the aforementioned sediment gradation. Sediment particles were divided into eight groups, ranging in size from 0.0025 mm to 0.25 mm. The average particle size and proportion of suspended sediment in each group are shown in Table 8.

[0064] Table 8 Suspended sediment particle size grouping

[0065] At the same time, the eco-lab module in mike21 was used to successively calculate the sediment movement in the study section under each group of sediment particle size conditions, and the sediment scouring and deposition results were calculated according to the combination of sediment particle size ratios, thereby more comprehensively reflecting the scouring and deposition of suspended sediment in the engineering section.

[0066] Furthermore, in step S3, the determination of the sediment push-suspension ratio includes the determination of the sediment push-suspension ratio of the main channel and the sediment push-suspension ratio of the tributary inflow.

[0067] The determination of the sediment suspension ratio in the main river channel (taking the sediment suspension ratio of the Yujiang River in the Xijin Reservoir as an example) includes the following: According to the Preliminary Design Report on the Second Line Ship Lock of Xijin Water Conservancy Hub, there is no measured data on bed load at any hydrological station in the Yujiang River Basin. The calculation of bed load and sediment transport at the Xijin dam site is mainly based on the results of the bed load ratio measured for some projects in the Guangxi Zhuang Autonomous Region.

[0068] According to the actual measurement results of bed load carried out during the design of the Baise Water Conservancy Project on Youjiang River, the annual bed load transport accounts for 6.9% of the annual suspended load transport; the actual measurement results of bed load transport carried out during the design of the Tonggutan Hydropower Station on Xunjiang River show that the annual bed load transport accounts for 2.46% of the annual suspended load transport; when the Tianshengqiao Second-level Hydropower Station was designed in 1966, the bed load was tested at the Bajie Special Hydrological Station for less than a year, and the annual bed load transport accounted for 3% of the annual suspended load transport.

[0069] With reference to the above three hydropower hubs’ overhang ratio results and combined with the topography of the basin where Xijin Reservoir is located, the overhang ratio of Yujiang River to sand in Xijin Reservoir was calculated as 3%.

[0070] The determination of the sediment push-and-suspension ratio of tributaries includes the following: Given the lack of measured sediment data for the Shaping and Shizi rivers, the main tributaries of the project section, it is difficult to determine the inferred suspension ratio of sediment entering the tributaries based on measured data. The Guangxi Hydrological Atlas also lacks a clear description or estimation method for the inferred suspension ratio of mountain rivers in the region. However, based on field surveys of bed sediment, suspended sediment particle size, and water sediment content in the Pinglu Canal's confluence tributaries, a mathematical model of the tributary confluences was established. Hydrological sediment analysis within the physical model indicates that the confluence tributaries of the Pinglu Canal's runoff section all have sandy riverbeds with fine median bed sediment particle size, resulting in minimal bedload movement at the confluences. Based on the inferred suspension ratio of sediment entering the Yujiang River near the Xijin Reservoir, a preliminary empirical estimate of the inferred suspension ratio for major tributaries such as the Shaping and Shizi rivers is 3%.

[0071] Finally, it should be noted that the embodiments described in detail above are only the best practices of the invention and cannot be used to limit the scope of rights of the invention. Equivalent replacement of the technical solutions recorded in the aforementioned embodiments does not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the invention, and they should all be included in the scope of the claims and description of the invention.

Claims

1. A method for determining the sediment thrust-suspension ratio of a section, characterized in that: The following steps are involved: S1, establish a mathematical model of the tributary inlet and perform similarity verification; S2, obtain the bed sand particle size, suspended sand particle size and water sediment content of the inflow tributary; S3. Determine the sediment push-to-suspend ratio of the section based on the mathematical model of the tributary confluence, the bed sand particle size of the confluence tributary, the suspended sediment particle size and the sediment content of the water body.

2. The method for determining the thrust-suspension ratio of a section of sediment according to claim 1, characterized in that: In step S1, the control equations in the mathematical model of the tributary confluence include a two-dimensional sediment continuity equation, a two-dimensional riverbed deformation equation, a bed load transport rate equation, and a suspended load transport rate equation.

3. The method for determining the sediment thrust-suspension ratio of a section according to claim 2, characterized in that: In step S1, the suspended sediment equilibrium concentration is expressed as c E It is expressed as follows: 。 4. The method for determining the sediment thrust-suspension ratio of a section according to claim 2, wherein: The steps of similarity verification include: selecting a river section with a similar riverbed composition to the target section, and extracting the historical topography and water level data of the similar river section; determining the verification scope, and conducting similarity verification of the riverbed scouring and silting volume, scouring and silting location, and scouring and silting thickness; selecting the daily average flow and daily average sediment content data measured in the engineering river section during the same period as the basis for dynamic bed verification, and making similarity judgments with the water and sediment processes in the historical topography and water level data.

5. The method for determining the thrust-suspension ratio of a section of sediment according to claim 1, characterized in that: In step S2, the bed sand particle size is obtained by grouping the bed sand composition of the project river section according to the particle gradation curve of the riverbed sediment sampling, and determining the number of groups and the particle size range in each group.

6. The method for determining the section sediment thrust-suspension ratio according to claim 1, characterized in that: In step S2, the suspended sediment particle size is obtained by grouping the suspended sediment particle size composition of the project river section according to the suspended sediment particle gradation table, and determining the number of groups and the particle size range in each group.

7. The method for determining the section sediment thrust-suspension ratio according to claim 1, characterized in that: Step S3 includes: first, calculating the load-overhang ratio of the main channel of this river section based on the load-overhang ratio results adopted by other hydropower hubs in the same region; second, determining the intensity of bedload movement at the confluence based on the bed sand particle size and suspended sand particle size of the inflowing tributary; finally, estimating the load-overhang ratio of the inflowing tributary.

8. A device for determining the thrust-suspension ratio of a section of sediment, characterized in that: The invention comprises at least one processor and a memory in communication with the at least one processor; the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor so that the at least one processor can execute a method for determining the sediment thrust-suspension ratio of a section according to any one of claims 1 to 7.

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