Method for analyzing and evaluating influence of dredging depth and dredging width on flow capacity of harbor branch

Abstract

The invention discloses a method for analyzing and evaluating the influence of dredging depth and dredging width on the port branch flow capacity. The method comprises the following steps that 1, a bifurcated river plane two-dimensional hydrodynamic mathematical model where a dredging port branch is located is established; 2, carrying out mathematical model calibration verification; 3, a desilting section desilting depth and desilting width combination scheme is prepared; 4, carrying out river hydrodynamic numerical simulation analysis under different desilting section depth and desilting section width combination schemes; 5, introducing a design standard flood lower harbor branch distribution ratio eta to represent the flow capacity of the dredging harbor branch, and analyzing and evaluating the influence of the dredging depth and the dredging width on the flow capacity; the method for analyzing and evaluating the influence of the dredging depth and the dredging width on the flow capacity of the harbor branch based on the numerical simulation means and mathematical analysis is provided for solving the problems existing in an existing common method, the calculation process is simple and clear, the conformity of the calculation result and the actual situation is high, and therefore the method has good application prospects. The method has good convenience, operability and reliability.

Description

Technical Field

[0001] The invention relates to the technical field of water conservancy analysis, and in particular to an analysis and evaluation method for the influence of dredging depth and dredging width on the flow capacity of a branch. Background Art

[0002] River dredging and regulation projects usually need to determine the flow capacity of the regulated river, or determine the dredging cross-sectional area of ​​the river according to the designed flow capacity of the river. The dredging cross-section is usually designed to be trapezoidal, and there are different combinations of dredging depth and width under the same dredging cross-sectional area. Therefore, it is of practical significance to analyze the impact of dredging depth and width on flow capacity and then reasonably select the dredging cross-section. In order to analyze and determine the impact of dredging cross-section on flow capacity, a common method is to use the open channel uniform flow formula to estimate the discharge under different dredging depth and width combinations, that is, based on hydraulic parameters such as flow cross-sectional area, wetted perimeter, hydraulic radius, roughness, and river slope, the Manning formula is used to calculate the discharge. Due to the complex boundary conditions of multi-branched rivers, their hydraulic parameters such as flow cross-sectional area, wetted perimeter, hydraulic radius, roughness, and river slope are not fixed values, and the water flows between branches often affect each other. Therefore, the use of the Manning formula applicable to open channel uniform flow to calculate the branch discharge after the implementation of the multi-branched river dredging project and analyze the flow capacity has great limitations. The calculation process is often complicated, and the calculation results will also have a large deviation from the actual situation.

[0003] Based on this, the present invention designs a method for analyzing and evaluating the impact of dredging depth and dredging width on the flow capacity of harbor branches to solve the above problems. Summary of the invention

[0004] The purpose of the present invention is to provide a method for analyzing and evaluating the influence of dredging depth and dredging width on the flow capacity of a harbor, so as to solve the problems raised in the above-mentioned background technology.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for analyzing and evaluating the influence of dredging depth and dredging width on the flow capacity of a harbor, comprising the following steps: The following steps are involved: (1) Establish a two-dimensional hydrodynamic mathematical model of the branch river where the dredging port is located: Collect data on the river's topography, geology, hydrology, riverbed, shoreline, river-related structures, operation and management of major water projects, and related research results, and establish a two-dimensional hydrodynamic mathematical model for bifurcated rivers; (2) Conduct calibration and verification of mathematical models: The model is verified using measured hydrological data, which mainly includes the flow and diversion ratio of each branch, water level, flow velocity, and flow direction; the difference between the calculated value and the measured value of each hydrological station meets the error requirements mainly by adjusting the grid file, model roughness, and initial water level field boundary; (3) Formulate a combination plan for the dredging depth and dredging width of the dredging section: A trapezoidal desilting section is used; the slope ratio i of the slopes on both sides of the excavated channel is determined according to the geological conditions of the river channel and the requirements for slope stability, i≤i0, where i0 is the maximum slope ratio that meets the requirements for slope stability; assuming that the minimum distance between the levees on both sides of the regulated river section is B0, the bottom width B of the desilting section, the desilting depth H, and the slope ratio i of the slopes on both sides of the excavated channel of the desilting section should satisfy the relationship in formula 4; B+2H / i+△B≤B0 (Formula 4) Where: B0 is the minimum distance between the embankment foots on both sides of the river section under regulation / m; B is the bottom width of the dredging section / m; H is the dredging depth / m; i is the slope ratio of the excavated river channel of the dredging section; △B is the safe distance between the embankment foots / m; The dredging depth H can be taken as the difference between the average riverbed elevation Z0 in the dredging area and the bottom elevation Z of the dredging section, that is, H=Z0-Z; the bottom elevation Z of the dredging section can be selected in a value range according to the distribution of the bottom elevation of the main river channel of the dredged branch that is similar to the dredged branch in the bifurcated river; (4) Conduct numerical simulation analysis of river hydrodynamics under different combinations of dredging section depths and dredging section widths: Using the verified two-dimensional hydrodynamic mathematical model of the bifurcated river in the above step 2, the hydrodynamic numerical simulation calculation under the design standard flood is carried out, and the flood discharge of each branch of the bifurcated river under each scheme is counted. The flood discharge of the desilted branch is recorded as Q, and the flood discharge of other branches is recorded as Q1, Q2, ..., Qn-1 (n is a natural number, and n ≥ 3). The diversion ratio η of the desilted branch of each scheme is calculated. The diversion ratio η is expressed by Formula 5: (Formula 5); (6) The diversion ratio η of the branch under the design standard flood is introduced to represent the flow capacity of the desilted branch. By establishing the relationship between the desilting depth H and the desilting width B on the diversion ratio η of the desilted branch, the influence of the desilting depth and the desilting width on the flow capacity is analyzed and evaluated: According to the results of hydrodynamic numerical simulation calculation and analysis, EXCEL or MATLAB software is used to perform statistical analysis of the diversion ratio η under various combinations of dredging depth H and dredging width B, and a fitting relationship is established for the influence of dredging depth H and dredging width B on the diversion ratio η of the dredged harbor. Based on the established influence relationship between dredging depth H and dredging width B on the diversion ratio η of the dredged harbor, the influence of dredging depth and dredging width on the flow capacity can be analyzed and evaluated.

[0006] Preferably, the hydrodynamic mathematical model in step (1) is based on Mike21 software and Navier-Stokes equations based on incompressibility and uniform distribution of Reynolds values, and is subject to the Boussinesq assumption and the assumption of hydrostatic pressure; The two-dimensional non-steady shallow water equations are: (Formula 1) (Formula 2) (Formula 3) Where: For time; is the Cartesian coordinate system coordinate; is the water level; is the still water depth; is the total water depth; They are The velocity component in the direction; , are the average flow velocities in the x and y directions based on the water depth; Pa is the local atmospheric pressure; is the density of water at standard temperature and pressure; , Along Shear stress in the direction; , Along Bottom shear stress in the direction; is the Coriolis force coefficient, , is the Earth's rotation angular velocity, is the local latitude; is the acceleration due to gravity; is the density of water; are the radiation stress components respectively; is the horizontal viscous stress term, is the source-sink term, The source-sink flow is Flow velocity in direction.

[0007] Preferably, the scope of the hydrodynamic mathematical model in step (1) is from the section of the controlling hydrological station of the main and tributary rivers or below the dam to the section where the hydrological station or tidal level station is located downstream of the section where the harbor merges; the roughness of the hydrodynamic mathematical model can be determined based on experience, and is preliminarily given in combination with the river channel type, riverbed morphology, riverbed composition, and distribution of river-related structures, and is finally determined through model verification and adjustment; the upper boundary of the hydrodynamic model is set at the starting section of the main and tributary rivers, and the upper boundary adopts the flow rate; the lower boundary of the model is set at the section where the hydrological station or tidal level station is located downstream of the section where the harbor merges, and the lower boundary adopts the water level.

[0008] Preferably, the hydrodynamic mathematical model in step (1) adopts an unstructured triangular grid, and the grid size is determined comprehensively based on the accuracy of the modeled topographic map, the degree of terrain undulation, and the size of important river-related structures. The grid size should be equivalent to the interval between elevation measurement points of the modeled topographic map. The local grid in areas with drastic terrain undulations and important river-related structures should be encrypted, and the scale of the encrypted grid should be equivalent to the scale of the river-related structures.

[0009] Preferably, in step (3), the excavation of the river channel centerline, the connection of the inlet and outlet sections with the original river channel is carried out according to the Code for Design of River Regulation (GB50707-2011).

[0010] Preferably, the error between the model calculation value and the measured value in step (2) should meet the relevant requirements of the "Technical Specifications for Simulation Tests of Water Transport Engineering" (JTS-T 231-2021).

[0011] Preferably, the levee foot safety distance △B in step (3) can be determined according to the Code for Design of Levee Engineering (GB50286-2013), depending on the level of the levee engineering, and with reference to the width of the backwater side levee protection land (Table 13.2.2 of the Code for Design of Levee Engineering (GB50286-2013)). For a dredged river section with a levee level of 1, △B can be 20 to 30 m; for a dredged river section with a levee level of 2 or 3, △B can be 10 to 20 m; for a dredged river section with a levee level of 4 or 5, △B can be 5 to 10 m.

[0012] Compared with the prior art, the beneficial effects of the present invention are: in view of the problems existing in the current commonly used methods, the present invention proposes an analysis and evaluation method for the impact of dredging depth and dredging width on the flow capacity of harbors based on numerical simulation and mathematical analysis. The calculation process is simple and clear, and the calculation results are highly consistent with the actual situation. Therefore, this method has good convenience, operability and reliability.

[0013] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for describing the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0015] Figure 1 A schematic diagram of a bifurcated river according to the present invention; Figure 2 It is the relationship between the branch flow ratio of the present invention and the dredging depth and the bottom width of the dredging section. DETAILED DESCRIPTION

[0016] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0017] Below Figure 1 A bifurcated river is shown as an example for explanation.

[0018] In the figure, River 1 and River 2 are divided into Branch 1, Branch 2 and Branch 3 after they merge at the estuary delta. Branch 1, Branch 2 and Branch 3 are connected to each other by connecting ports.

[0019] In recent years, due to the combined influence of changes in water and sand movement and human activities, the river section about 5 km long below the entrance of Gangcha 2 (the shaded area in the figure) has been seriously silted up, and the flow is almost cut off during the dry season, which seriously affects flood discharge and tidal intake, has an adverse impact on the safety and health of the river, and restricts the high-quality development of the economy and society. Therefore, it is necessary to dredge and regulate the river section about 5 km long below the entrance of Gangcha 2.

[0020] The dredging section for dredging and regulation adopts a trapezoidal shape. According to the geological conditions of the dredged river section and the stability requirements of the dredged excavation section, the slope ratio i on both sides of the dredged excavation channel is 1:5. Based on the unsilted section of the dredged harbor and the main river channel depth of the harbor similar to the dredged harbor in the bifurcated river, the bottom elevation Z of the dredged section is selected to be in the range of -2~-4m. The average riverbed elevation Z0 within the dredged range of the dredged river section is 1m, so the dredging depth range is 3~5m. Combined with formula 4, it is determined that the bottom width of the dredged section in the dredged river section within the dredged depth range of 3~5m should be 40~60m. Within the range of the dredged section depth and the dredged section bottom width, the combination schemes of the dredged section dredging depth and dredged bottom width carried out by the random hydrodynamic numerical simulation calculation are shown in Table 1.

[0021] Based on the hydrodynamic numerical simulation, the diversion ratio of the dredged branch 2 under the design flood condition of 50 years is calculated under various desilting depth and desilting bottom width combinations, see Table 2. According to the data in Table 2, the relationship between the desilting branch diversion ratio η and the desilting depth H and desilting width B is calculated using EXCEL software, and the relevant curves and relationship are fitted, see Figure 2 It can be seen that when the dredged bottom width is 40m, 50m, and 60m, the diversion ratio of the dredged harbor can be expressed by the following formulas 6, 7, and 8 respectively: η1 = 0.0135H + 0.0535 (Equation 6) η2 = 0.0142H + 0.0597 (Equation 7) η3 = 0.0143H + 0.0629 (Equation 8) From Equations 6 to 8, we can deduce the influence of dredging depth and bottom width of dredging section on the flow capacity of harbor branches.

[0022] Table 1 Combination schemes of dredging depth and dredging bottom width for dredging sections proposed by hydrodynamic numerical simulation analysis

[0023] Table 2 Diversion ratio of branch 2 for each combination of dredging depth and dredging bottom width under the design flood condition with a return period of 50 years

[0024] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0025] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementation methods described. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. The method for analyzing and evaluating the impact of dredging depth and dredging width on the flow capacity of a harbor branch is characterized by: The following steps are involved: (1) Establish a two-dimensional hydrodynamic mathematical model of the branch river where the dredging port is located: Collect data on the river's topography, geology, hydrology, riverbed, shoreline, river-related structures, operation and management of major water projects, and related research results, and establish a two-dimensional hydrodynamic mathematical model for bifurcated rivers; (2) Conduct calibration and verification of mathematical models: The model is verified using measured hydrological data, which mainly includes the flow and diversion ratio of each branch, water level, flow velocity, and flow direction; the deviation between the calculated value and the measured value of each hydrological station meets the accuracy requirements mainly by adjusting the grid file, model roughness, and initial water level field boundary; (3) Formulate a combination plan for the dredging depth and dredging width of the dredging section: A trapezoidal desilting section is used; the slope ratio i of the slopes on both sides of the excavated channel is determined according to the geological conditions of the river channel and the requirements for slope stability, i≤i0, i0 is the maximum slope ratio that meets the requirements for slope stability; assuming that the minimum distance between the embankment feet on both sides of the regulated river section is B0, then the bottom width B of the desilting section, the desilting depth H, and the slope ratio i of the slopes on both sides of the excavated channel of the desilting section should satisfy the relationship in formula 4; B+2H / i+△B≤B0 (Formula 4) Where: B0 is the minimum distance between the embankment foots on both sides of the river section under regulation / m; B is the bottom width of the dredging section / m; H is the dredging depth / m; i is the slope ratio of the excavated river channel of the dredging section; △B is the safe distance between the embankment foots / m; The dredging depth H can be taken as the difference between the average riverbed elevation Z0 in the dredging area and the bottom elevation Z of the dredging section, that is, H=Z0-Z; the bottom elevation Z of the dredging section can be selected in a value range according to the distribution of the bottom elevation of the main river channel of the dredged branch that is similar to the dredged branch in the bifurcated river; (4) Conduct numerical simulation analysis of river hydrodynamics under different combinations of dredging section depths and dredging section widths: Using the verified two-dimensional hydrodynamic mathematical model of the bifurcated river in step 2 above, the hydrodynamic numerical simulation calculation under the design standard flood is carried out, and the flood discharge of each branch of the bifurcated river under each scheme is counted. The flood discharge of the dredged branch is recorded as Q, and the flood discharge of other branches is recorded as Q1, Q2, ..., Q n-1 (n is a natural number, and n≥3), calculate the diversion ratio η of the dredging branch for each scheme, and the diversion ratio η is expressed by formula 5 (Formula 5); (5) The diversion ratio η of the branch under the design standard flood is introduced to represent the flow capacity of the desilted branch. By establishing the relationship between the desilting depth H and the desilting width B on the diversion ratio η of the desilted branch, the influence of the desilting depth and the desilting width on the flow capacity is analyzed and evaluated: According to the results of hydrodynamic numerical simulation calculation and analysis, EXCEL or MATLAB software is used to perform statistical analysis of the diversion ratio η under various combinations of dredging depth H and dredging width B, and a fitting relationship is established for the influence of dredging depth H and dredging width B on the diversion ratio η of the dredged harbor. Based on the established influence relationship between dredging depth H and dredging width B on the diversion ratio η of the dredged harbor, the influence of dredging depth and dredging width on the flow capacity can be analyzed and evaluated.

2. The method for analyzing and evaluating the influence of dredging depth and dredging width on the flow capacity of a harbor according to claim 1 is characterized in that: The hydrodynamic mathematical model in step (1) is based on Mike21 software and the Navier-Stokes equations based on incompressibility and uniform distribution of Reynolds values, and is subject to the Boussinesq assumption and the assumption of hydrostatic pressure; The two-dimensional non-steady shallow water equations are: (Formula 1) (Formula 2) (Formula 3) Where: For time; is the Cartesian coordinate system coordinate; is the water level; is the still water depth; is the total water depth; They are The velocity component in the direction; , are the average flow velocities in the x and y directions based on the water depth; Pa is the local atmospheric pressure; is the density of water at standard temperature and pressure; , Along Shear stress in the direction; , Along Bottom shear stress in the direction; is the Coriolis force coefficient, , is the Earth's rotation angular velocity, is the local latitude; is the acceleration due to gravity; is the density of water; are the radiation stress components respectively; is the horizontal viscous stress term, is the source-sink term, The source-sink flow is Flow velocity in direction.

3. The method for analyzing and evaluating the influence of dredging depth and dredging width on the flow capacity of a harbor according to claim 2 is characterized in that: In step (1), the scope of the hydrodynamic mathematical model is from the section of the controlling hydrological station of the main and tributary rivers or the section below the dam to the section where the hydrological station or tidal level station is located downstream of the section where the harbor merges; the roughness of the hydrodynamic mathematical model can be determined based on experience, and is preliminarily given in combination with the river channel type, riverbed morphology, riverbed composition, and distribution of river-related structures, and is finally determined through model verification and adjustment; the upper boundary of the hydrodynamic model is set at the starting section of the main and tributary rivers, and the upper boundary adopts the flow rate; the lower boundary of the model is set at the section where the hydrological station or tidal level station is located downstream of the section where the harbor merges, and the lower boundary adopts the water level.

4. The method for analyzing and evaluating the influence of dredging depth and dredging width on the flow capacity of a harbor according to claim 3 is characterized by: In step (1), the hydrodynamic mathematical model adopts an unstructured triangular grid. The grid size is determined comprehensively based on the accuracy of the modeled topographic map, the degree of terrain undulation, and the size of important river-related structures. The grid size should be equivalent to the interval between elevation measurement points of the modeled topographic map. The local grid in areas with drastic terrain undulations and important river-related structures should be encrypted, and the scale of the encrypted grid should be equivalent to the scale of the river-related structures.

5. The method for analyzing and evaluating the influence of dredging depth and dredging width on the flow capacity of a harbor according to claim 1 is characterized in that: Step (3) excavation of the river channel centerline, the inlet and outlet sections and the connection with the original river channel are implemented in accordance with the "Code for River Regulation Design" (GB50707-2011).

6. The method for analyzing and evaluating the influence of dredging depth and dredging width on the flow capacity of a harbor according to claim 1, characterized in that: The error between the model calculation value and the measured value described in step (2) should meet the relevant requirements of the "Technical Specifications for Simulation Test of Water Transport Engineering" (JTS-T 231-2021).

7. The method for analyzing and evaluating the influence of dredging depth and dredging width on the flow capacity of a harbor according to claim 1 is characterized in that: The safe distance △B of the levee foot in step (3) can be determined according to the Code for Design of Levee Engineering (GB50286-2013), depending on the level of the levee project and the width of the backwater side levee (Table 13.2.2 of the Code for Design of Levee Engineering (GB50286-2013)). For levee level 1 in the desilted river section, △B can be 20-30m; for levee level 2 or 3 in the desilted river section, △B can be 10-20m; for levee level 4 or 5 in the desilted river section, △B can be 5-10m.

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