A calculation method and system for converting critical flow of beach scouring and silting

Abstract

The application provides a kind of beach scouring and silting conversion critical flow calculation method and system, comprising the following steps: based on the type of beach, initially determine the number of critical flow that target beach has;The research area is gridded, a plane two-dimensional water and sediment mathematical model is established and the parameter is rated and verified;A plurality of groups of typical flow from the minimum flow to the maximum flow are determined in turn;The flow starting capacity and flow sediment carrying capacity of target beach under each typical flow are calculated, and the flow interval of the strong and weak conversion of hydrodynamic force at the beach is judged;Based on the determined flow interval, more detailed water and sediment calculation conditions are divided;The scouring and silting amount at the target beach under each water and sediment condition is calculated, and the critical flow interval that causes the target beach to occur scouring and silting conversion is finally determined.The application reveals the internal mechanism of the beach scouring and silting conversion from the water and sediment dynamic angle, the identification of the critical flow interval based on the dynamic mechanism is more accurate, the hydrological and topographical data required is less than the existing method, and the practicability is stronger.

Description

Technical Field

[0001] This invention belongs to the field of river dynamics technology, specifically relating to a method and system for calculating the critical flow rate for the conversion between scour and sedimentation on riverbanks. Background Technology

[0002] Banks are common geomorphic units in alluvial rivers, and their formation is closely related to river deposition. There are three main types of banks in alluvial rivers: cross banks in straight rivers, convex bank banks in meandering rivers, and distributary banks in braided rivers. The morphological changes of banks caused by flow variability, such as dissection, downstream movement, and siltation, all alter the local river system, thereby affecting flood control, water intake, and navigation safety.

[0003] Under certain water and sediment saturation conditions, hydrodynamic changes caused by flow variability are the main determinant of the morphological changes of riverbanks. Cross-shoals often exist in straight rivers with relatively small width-to-depth ratios. When the upstream flow is low, the main current bends under the pressure of the riverbanks, the flow velocity is low, and the riverbanks are difficult to scour. As the flow gradually increases, due to the limitation of river width, the main current's swaying amplitude is smaller, the overall flow velocity of the river increases, and sediment movement occurs throughout the entire river channel, causing the cross-shoals to migrate freely downstream. Under moderate to low flow conditions, siltation occurs on the convex bank riverbanks under the influence of circulation. However, under flood flow conditions, the main current shifts towards the convex bank riverbanks due to inertia, making the convex bank riverbanks easily cut by the flow, forming gullies. The main stream of a distributary river exhibits displacement under different flow rates. When the upstream flow increases from low-water to flood-water, the main stream gradually shifts from the low-water-prone distributary to the flood-prone distributary. The hydrodynamic force at the distributary banks in the upstream area of ​​the flood-prone distributary continuously increases, and the banks develop from siltation to scouring. Conversely, the hydrodynamic force at the distributary banks in the upstream area of ​​the low-water-prone distributary shows a process of first increasing and then decreasing, and its evolutionary characteristics also change from no scouring to scouring, and then to siltation.

[0004] As flow increases, the scouring and deposition properties of different types of riverbanks change. Free-flowing, cross-flowing riverbanks evolve from non-scouring to scouring; convex bank riverbanks and riverbanks in the upstream distributary area of ​​flood-prone channels evolve from deposition to scouring; and riverbanks in the upstream distributary area of ​​low-flow-prone channels exhibit a more complex pattern, evolving from deposition to scouring and then back to deposition. The flow rate that causes this scouring-deposition transformation of riverbanks can be considered the critical flow rate. Existing studies have largely used statistical methods to demonstrate a positive correlation between the deformation of a single or single type of riverbank and the duration of a certain characteristic flow rate, such as the flat-shoal flow rate (Q=20000~25000 m³ / h) lasting more than 20 days after the Three Gorges Reservoir impoundment. 3The critical flow rate (CFR) is the main cause of scouring on the convex bank of the Jingjiang section of the lower Yangtze River. However, statistical methods lack theoretical analysis of the dynamic mechanisms of the CFR. Furthermore, statistical methods for determining the CFR require extensive experimental data, which significantly limits their application. Summary of the Invention

[0005] In view of the above-mentioned technical conditions and limitations, this invention provides a method for calculating the critical flow rate for the scour-deposition transition of riverbanks. Based on the scour-deposition variation patterns of different types of riverbanks under different flow rates, and combined with a two-dimensional water and sediment mathematical model of the river channel, the critical flow rate for the scour-deposition transition of riverbanks can be accurately calculated.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] A method for calculating the critical flow rate for scour and sedimentation transition on riverbanks includes the following steps:

[0008] Step 1. Based on the location of the target beach and the upstream and downstream river conditions, classify the beach types and make a preliminary judgment on the number of critical flow rates of the target beach;

[0009] Step 2. Grid the study area containing the target beach, establish a two-dimensional planar water and sediment mathematical model, and calibrate and verify the parameters;

[0010] Step 3. Based on the multi-year flow history of the study area, determine multiple typical flow groups from the lowest flow to the highest flow in sequence;

[0011] Step 4. Select the initial topography, use a two-dimensional planar hydro-sediment mathematical model to calculate the water flow initiation capacity and sediment carrying capacity at the target beach under various typical flow rates, draw the graph of the changes of the two with the flow rate, and determine the flow range in which the hydrodynamic strength changes.

[0012] Step 5. Based on the flow range where the hydrodynamic intensity changes as determined in Step 4, further refine the water and sediment calculation conditions;

[0013] Step 6. Select the initial topography, use a two-dimensional planar water and sediment mathematical model to calculate the scouring and deposition volume at the target beach under various water and sediment conditions, draw a graph showing the change of scouring and deposition volume with flow rate, verify the accuracy of the number of critical flow rates initially determined in Step 1, and finally determine the critical flow range that causes the target beach to undergo scouring and deposition conversion.

[0014] Furthermore, step 1 is implemented as follows:

[0015] The study area, including the target bar, was morphologically analyzed. The target bar types were categorized into four types, and the number of critical discharges at each target bar was preliminarily determined, including:

[0016] (1) Straight river type alternating side beach: During the process of increasing flow, there is a critical flow that causes it to develop from non-scouring to scouring;

[0017] (2) Meandering river convex bank beach: During the process of increasing flow, there is a critical flow that causes it to develop from siltation to scouring;

[0018] (3) The flood of the diverted river type tends to the upstream area of ​​the diverted river: During the process of increasing flow, there is a critical flow that causes it to develop from siltation to scouring;

[0019] (4) The low water level of the branch river type tends to be on the upstream side beach of the branch: During the process of increasing flow, there are two critical flow rates that cause it to develop from no scouring to scouring and then to siltation.

[0020] Furthermore, step 2 is implemented as follows:

[0021] Step 21. Based on the boundary of the study area and the left and right bank boundary lines, generate a two-dimensional body-fitted orthogonal curve mesh containing the target beach area;

[0022] Step 22. Collect measured topographic data and corresponding hydrological data of the study area during the same time period, and determine the inlet flow, sediment concentration and outlet water level of the two-dimensional planar water and sediment mathematical model;

[0023] Step 23. Initialize the roughness value of the study area, calculate the frictional water level and cross-sectional velocity of the study area under the roughness value using a two-dimensional planar water and sediment mathematical model, and compare it with the measured values. If they do not match, adjust the roughness value from downstream to upstream and repeat the calculation until the calculated frictional water level and cross-sectional velocity match the measured values.

[0024] Step 24. Initialize the sediment parameters of the study area. Calculate the scour and deposition distribution and scour and deposition volume of the study area under these sediment parameters using a two-dimensional planar water and sediment mathematical model. Compare the results with the measured values. If they do not match, adjust the sediment parameters and repeat the calculation until the calculated scour and deposition distribution and scour and deposition volume match the measured values.

[0025] Furthermore, step 3 is implemented as follows:

[0026] Step 31. Collect the daily average water level and flow rate data measured at the nearest hydrological station in the study area, and plot the water level-flow rate relationship curve;

[0027] Step 32. Divide the flow range from the lowest to the highest flow in the study area into several typical flow rates, including low flow, multi-year average flow, flood flow, multi-year average flood flow, and flood flow.

[0028] Step 33. For runoff river sections, calculate the water level of hydrological stations under each typical flow rate using the water level-flow relationship curve, deduce the outlet water level according to the water surface gradient, and determine multiple sets of typical flow calculation conditions; for tidal river sections, select the tidal range tidal pattern corresponding to each typical flow rate at 85% cumulative frequency as the outlet water level process, and determine multiple sets of typical flow calculation conditions.

[0029] Furthermore, step 4 is implemented as follows:

[0030] Step 41. Calculate the flow velocity at the target beach under various typical flow conditions using a two-dimensional planar water-sediment mathematical model. and water depth Calculate the water flow initiation capacity at the target beach. and the force of water flow carrying sand ;

[0031] Step 42. Plot the changes in water flow initiation capacity and sediment carrying capacity as a function of flow rate, based on the water flow initiation capacity. The flow range from less than 1 to greater than 1 is considered the range where the hydrodynamic force at the beach changes from weak to strong, based on the sediment-carrying capacity of the water flow. The flow range from increasing to decreasing is considered the flow range where the hydrodynamic force at the beach changes from strong to weak;

[0032] Furthermore, in step 4, the water flow initiation capability is... , This is the starting flow rate.

[0033] Furthermore, step 5 is implemented as follows:

[0034] Step 51. Collect the daily average flow and sediment concentration data measured at the nearest hydrological station in the study area, and plot the flow-sediment concentration relationship curve;

[0035] Step 52. Based on the flow ranges from weak to strong and from strong to weak hydrodynamics at the beach determined in Step 42, more detailed flow levels are divided. Typical flow calculation conditions are determined in the manner described in Step 33. The sediment concentration at each hydrological station under each typical flow is calculated using the flow-sediment concentration relationship curve described in Step 51, and multiple sets of water and sediment calculation conditions are determined.

[0036] Furthermore, step 6 is implemented as follows:

[0037] Step 61. Calculate the scouring and deposition at the target beach under various water and sediment conditions using a two-dimensional planar water and sediment mathematical model. The scouring and deposition of a unit grid is the product of the scouring and deposition change value of the unit grid and its area. The scouring and deposition at the target beach is the sum of the scouring and deposition of the unit grids included in the beach area.

[0038] Step 62. Plot the change of scour and sedimentation volume with flow rate to verify the accuracy of the number of critical flow rates determined in Step 1. The flow range in which the scour and sedimentation volume changes from a positive value to a negative value can be regarded as the critical flow range in which the beach transitions from sedimentation to scour. The flow range in which the scour and sedimentation volume changes from a negative value to a positive value can be regarded as the critical flow range in which the beach transitions from scour to sedimentation.

[0039] Furthermore, the aforementioned two-dimensional planar water and sediment mathematical model is as follows:

[0040] (1) Equation of continuity of water flow:

[0041]

[0042] (2) Equations of water flow

[0043] Directional momentum equation:

[0044]

[0045]

[0046] Directional momentum equation:

[0047]

[0048]

[0049] In the formula: These are the coordinates of two orthogonal curves in an orthogonal curvilinear coordinate system; For time; They are respectively directional flow velocity; Water level; For water depth; It is the acceleration due to gravity; The coefficient for thanking talent; They are respectively Lamé coefficient in direction; These represent turbulent stresses in different directions. The first subscript indicates the direction of the outward normal to the surface where the stress is located, and the second subscript indicates the direction of the stress.

[0050] (3) Equation for non-uniform suspended sediment transport:

[0051]

[0052]

[0053] In the formula, , , , For the first The sediment concentration recovery saturation coefficient, settling velocity, water flow sediment carrying capacity, and suspended sediment volumetric sediment concentration of the group were determined. Indicates the sediment diffusion coefficient; Represent the Prandtl-Schmidt number;

[0054] (4) Non-uniform bedload sediment transport equation:

[0055]

[0056]

[0057] In the formula: , For the first Group bedload recovery saturation coefficient, sediment settling velocity; , These are, respectively, bedload transport rate and bedload saturation transport rate;

[0058] (5) Equation of riverbed deformation:

[0059]

[0060] In the formula: Number of particle size groups for bedloaded and suspended sediments respectively; The dry density of the bed sand; This refers to the elevation of the bed surface.

[0061] On the other hand, the present invention provides a calculation system for the critical flow rate of scour and sedimentation conversion on riverbanks, comprising:

[0062] The barn type classification module is used to classify bar types based on the location of the target bar and the upstream and downstream river conditions, and to preliminarily determine the number of critical flow rates of the target bar.

[0063] Mathematical model building module. It is used to grid the research area containing the target beach, establish a two-dimensional planar water and sediment mathematical model, and calibrate and verify the parameters;

[0064] Typical Flow Determination Module. It is used to determine multiple sets of typical flows from the lowest flow to the highest flow based on the multi-year flow process of the study area.

[0065] The initial interval determination module is used to select the initial terrain, use a two-dimensional planar hydro-sediment mathematical model to calculate the water flow initiation capacity and sediment carrying capacity at the target beach under various typical flow rates, draw the changes of the two with the flow rate, and determine the flow rate interval where the hydrodynamic strength changes.

[0066] The water and sediment calculation condition delineation module is used to delineate more detailed water and sediment calculation conditions based on a defined flow range.

[0067] The final critical flow range determination module is used to select the initial topography, calculate the scouring and deposition volume at the target beach under various water and sediment conditions using a two-dimensional planar water and sediment mathematical model, plot the change of scouring and deposition volume with flow rate, verify the accuracy of the preliminary judgment of the number of critical flow rates, and finally determine the critical flow range that causes the target beach to undergo scouring and deposition.

[0068] Compared with existing technologies, this invention has the following advantages: the model construction greatly restores the actual landform and scouring and deposition process of the beach, and reveals the intrinsic mechanism of scouring and deposition transformation of the beach from the perspective of hydrodynamics, namely, the different trends of hydrodynamics and sediment load as the flow rate increases. The identification of the critical flow range based on the dynamic mechanism is more accurate, and the hydrological and topographic data required by this method are easier to collect than those of existing methods, making it more practical. Attached Figure Description

[0069] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0070] Figure 1 This is a flowchart of the method described in this invention.

[0071] Figure 2 This is a riverbed map of the Sanyi Bridge in an embodiment of the present invention.

[0072] Figure 3 This is a graph showing the trend of the diversion ratio of the left branch of Luocheng Island as a function of flow rate.

[0073] Figure 4 The following are the verification results of the two-dimensional planar water and sediment mathematical model: (a) and (b) are the verification of water level in the left and right branches of Luochengzhou, (c) and (d) are the verification of flow velocity in the left and right branches of Luochengzhou, and (e) and (f) are the verification of riverbed scouring and deposition distribution.

[0074] Figure 5 This represents the inlet tidal level process of the model under flat-shoal flow.

[0075] Figure 6 The graph shows the changing trends of the water flow initiation capacity (a) and the water flow sediment carrying capacity (b) at the Sanyi Bridge beach with the flow rate.

[0076] Figure 7 The curve showing the flow-sediment content relationship at the Datong Hydrological Station.

[0077] Figure 8 This is a graph showing the trend of sedimentation and erosion on the beach near Sanyi Bridge as a function of flow rate. Detailed Implementation

[0078] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0079] Example 1

[0080] like Figure 1 As shown, this invention provides a method for calculating the critical flow rate for the conversion between scour and sedimentation on riverbanks, comprising the following steps:

[0081] Step 1. Based on the location of the target beach and the upstream and downstream river conditions, classify the beach types and make a preliminary judgment on the number of critical flow rates of the target beach;

[0082] Step 2. Grid the study area containing the target beach, establish a two-dimensional planar water and sediment mathematical model, and calibrate and verify the parameters;

[0083] Step 3. Based on the multi-year flow history of the study area, determine multiple typical flow groups from the lowest flow to the highest flow in sequence;

[0084] Step 4. Select the initial topography, use a two-dimensional planar hydro-sediment mathematical model to calculate the water flow initiation capacity and sediment carrying capacity at the target beach under various typical flow rates, draw the graph of the changes of the two with the flow rate, and determine the flow range in which the hydrodynamic strength changes.

[0085] Step 5. Based on the flow range determined in Step 4, further refine the water and sediment calculation conditions;

[0086] Step 6. Select the initial topography, use a two-dimensional planar water and sediment mathematical model to calculate the scouring and deposition volume at the target beach under various water and sediment conditions, draw a graph showing the change of scouring and deposition volume with flow rate, verify the accuracy of the number of critical flow rates determined based on Step 1, and finally determine the critical flow range that causes the target beach to undergo scouring and deposition conversion.

[0087] The implementation method of step 1 is as follows:

[0088] We collected data on the river channel plan morphology of the study area, including the target beach, and classified the target beach types into the following four categories to preliminarily determine the number of critical flows that the target beach may have.

[0089] Straight river type alternating slopes: There exists a critical flow rate during the process of increasing flow. This causes it to evolve from non-scouring to scouring;

[0090] For meandering riverbanks with convex banks: there exists a critical flow rate during the process of increasing flow. This causes it to evolve from siltation to erosion.

[0091] Distributary floods tend to occur along the upstream banks of the distributary: as the flow increases, there exists a critical flow rate. This causes it to evolve from siltation to erosion.

[0092] In the low-water tendency of the branching river type, there are two critical flow rates in the upstream area of ​​the branching channel: during the process of increasing flow, there are two critical flow rates. and This causes it to progress from non-flushing to erosion and then to siltation.

[0093] The implementation method of step 2 is as follows:

[0094] Step 21. Based on the boundary of the study area and the left and right bank boundary lines, generate a two-dimensional body-fitted orthogonal curve mesh containing the target beach area;

[0095] Step 22. Collect measured topographic data and corresponding hydrological data of the study area during the same time period, and determine the inlet flow, sediment concentration and outlet water level of the two-dimensional planar water and sediment mathematical model;

[0096] Step 23. Initialize the roughness value of the study area, calculate the frictional water level and cross-sectional velocity of the study area under the roughness value using a two-dimensional planar water and sediment mathematical model, and compare it with the measured values. If they do not match, adjust the roughness value from downstream to upstream and repeat the calculation until the calculated frictional water level and cross-sectional velocity match the measured values.

[0097] Step 24. Initialize the sediment parameters of the study area. Calculate the scour and deposition distribution and scour and deposition volume of the study area under these sediment parameters using a two-dimensional water and sediment mathematical model. Compare the results with the measured values. If they do not match, adjust the sediment parameters and repeat the calculation until the calculated scour and deposition distribution and scour and deposition volume match the actual values.

[0098] The implementation method of step 3 is as follows:

[0099] Step 31. Collect the daily average water level and flow rate data measured at the nearest hydrological station in the study area, and plot the water level-flow rate relationship curve;

[0100] Step 32. Divide the flow range from the lowest to the highest flow in the study area into several typical flow types, such as low-water flow, multi-year average flow, flood flow, multi-year average flood flow, and flood flow.

[0101] Step 33. For runoff river sections, calculate the water level of hydrological stations under each typical flow rate using the water level-flow relationship curve, deduce the outlet water level according to the water surface gradient, and determine multiple sets of typical flow calculation conditions; for tidal river sections, select the tidal range tidal pattern corresponding to each typical flow rate at 85% cumulative frequency as the model outlet water level process, and determine multiple sets of typical flow calculation conditions.

[0102] The implementation method of step 4 is as follows:

[0103] Step 41. Calculate the flow velocity at the target beach under various typical flow conditions using a two-dimensional planar water-sediment mathematical model. and water depth Calculate the water flow initiation capacity at the target beach. and the force of water flow carrying sand ;

[0104] Define the water flow starting capacity as , The starting flow velocity is calculated using the following formula:

[0105]

[0106] In the formula: The particle size of the sediment For the density of water, This refers to sediment density. For runoff river sections, the sediment-carrying capacity of the water flow is... For tidal river sections, the force of water flow carrying sediment is... .

[0107] Step 42. Plot the changes in water flow initiation capacity and sediment carrying capacity as a function of flow rate, based on the water flow initiation capacity. The flow range from less than 1 to greater than 1 is considered the range where the hydrodynamic force at the beach changes from weak to strong, based on the sediment-carrying capacity of the water flow. The flow range from increasing to decreasing is considered the flow range where the hydrodynamic force at the beach changes from strong to weak.

[0108] The implementation method of step 5 is as follows:

[0109] Step 51. Collect the daily average flow and sediment concentration data measured at the nearest hydrological station in the study area, and plot the flow-sediment concentration relationship curve;

[0110] Step 52. Based on the flow ranges from weak to strong and from strong to weak hydrodynamics at the beach determined in Step 42, more detailed flow levels are divided. Typical flow calculation conditions are determined in the manner described in Step 33. The sediment concentration at each hydrological station under each typical flow is calculated using the flow-sediment concentration relationship curve described in Step 51, and multiple sets of water and sediment calculation conditions are determined.

[0111] The implementation method of step 6 is as follows:

[0112] Step 61. Calculate the scouring and deposition volume at the target beach under various water and sediment conditions using a two-dimensional planar water and sediment mathematical model. The scouring and deposition volume of a single grid cell is the product of the scouring and deposition change value of the single grid cell and its area. The scouring and deposition volume at the target beach is the sum of the scouring and deposition volumes of all grid cells included within the beach area.

[0113] Step 62. Plot the change of scour and sedimentation volume with flow rate to verify the accuracy of the number of critical flow rates initially determined in Step 1. The flow range in which the scour and sedimentation volume changes from positive to negative can be regarded as the critical flow range in which the beach transitions from sedimentation to scour, and the flow range in which the scour and sedimentation volume changes from negative to positive can be regarded as the critical flow range in which the beach transitions from scour to sedimentation.

[0114] The basic equations of the two-dimensional planar water-sediment mathematical model are as follows:

[0115] (1) Equation of continuity of water flow:

[0116]

[0117] (2) Equations of water flow

[0118] Directional momentum equation:

[0119]

[0120]

[0121] Directional momentum equation:

[0122]

[0123]

[0124] In the formula: These are the coordinates of two orthogonal curves in an orthogonal curvilinear coordinate system; For time; for directional flow velocity; Water level; For water depth; It is the acceleration due to gravity; The coefficient for thanking talent; They are respectively Lamé coefficient in direction; These represent turbulent stresses in different directions. The first subscript indicates the direction of the outward normal to the surface where the stress is located; the second subscript indicates the direction of the stress.

[0125]

[0126]

[0127] and Represents horizontal Cartesian coordinates. Represents the turbulent viscosity coefficient. , Indicates coefficient; Represents turbulent kinetic energy; This represents the rate of turbulent kinetic energy dissipation.

[0128] (3) Equation for non-uniform suspended sediment transport:

[0129]

[0130]

[0131] In the formula, , , , For the first The recovery saturation coefficient, settling velocity, sediment-carrying capacity of water flow, and volumetric sediment content of suspended sediment were determined. Indicates the sediment diffusion coefficient; This represents the Prandtl-Schmidt number.

[0132] Water flow carrying sand and sinking speed The results were obtained using Zhang Ruijin's formula:

[0133]

[0134]

[0135] In the formula: if runoff is the main driving force in the study area, If the study area is primarily driven by tidal currents, ; The sand-carrying capacity coefficient; For the first Average particle size of sediment in the group Because of the water depth, These are water flow and sediment density, respectively. These are respectively the density of water flow and the density of sediment. It represents the viscosity coefficient of water flow.

[0136] The concept of sediment-carrying capacity applies to the entire suspended mass and each group of particle sizes, and the sediment-carrying capacity of each suspended mass group. The calculation adopts the method proposed by Hu Haiming and Li Yitian, which considers the influence of water flow conditions and bed sediment composition. That is, the relationship between bed sediment gradation and group sediment carrying capacity gradation is established through the following formula:

[0137]

[0138]

[0139] In the formula, , These are sand-carrying capacity gradation and bed sand gradation, respectively. is the Kármán constant, set to 0.4 in the model. It is the total number of particle size groups. For vertical turbulence intensity, it is usually taken as , These are parameters related to turbulence intensity and the normal distribution function.

[0140] Therefore, given the known bed sediment composition, after calculating the total sediment-carrying capacity and the sediment-carrying capacity gradation of each group, the sediment-carrying capacity of each group is... It is possible Calculated.

[0141] (4) Non-uniform bedload sediment transport equation:

[0142]

[0143]

[0144] In the formula: , For the first Group bedload recovery saturation coefficient, sediment settling velocity, , The concentrations of bedload transport rate and bedload saturation transport rate converted to full water depth, respectively, can be obtained using the following formula:

[0145]

[0146] The bedload saturation transport rate can be calculated using Dou Guoren's formula:

[0147]

[0148] In the formula: This is an empirical coefficient. These are water flow and sediment density, respectively. The initial velocity of the sediment flow can be calculated using equation (3-1). Grouped bedload saturated sediment transport rate. It is possible Calculated.

[0149] (5) Equation of riverbed deformation:

[0150]

[0151] In the formula: Number of particle size groups for bedloaded and suspended sediments respectively; The dry density of the bed sand; This refers to the elevation of the bed surface.

[0152] The Luochengzhou section of the Yangtze River, approximately 23 km long, is located in the dry season tidal zone. Luochengzhou divides the section into two branches, the left branch being the main branch and the right branch a tributary. The Sanyiqiao beach is located on the left bank of the distributary area of ​​the Luochengzhou branch section (see attached diagram). Figure 2 The Datong Hydrological Station is the closest hydrological station to the Luochengzhou section of the river, and there are no major tributaries flowing into it. Therefore, the inflow and sediment conditions of the Datong Hydrological Station can be used to represent the water and sediment conditions of the Luochengzhou section. The specific implementation steps of this invention will now be explained using the Sanyiqiao beach as an example.

[0153] Step 1: Meandering rivers generally exhibit the hydrodynamic characteristic of meandering during low water flow and straightening during high water flow, indicating that the left branch of the Luochengzhou section tends towards the distributary during low water flow. Furthermore, the diversion ratio of the left branch of Luochengzhou decreases with increasing flow (see appendix). Figure 3 Therefore, the Sanyi Bridge shoal is a branch channel diversion area with low water flow. It can be preliminarily determined that there are two critical flow rates during the process of increasing flow. and This caused the beach near Sanyi Bridge to change from being non-eroded to being eroded and then to silted up.

[0154] Step Two: The Luochengzhou section is located in a tidal section. The inlet of the two-dimensional planar hydro-sediment mathematical model is selected at Guazhou Town in the Hechangzhou waterway, a section largely unaffected by tidal currents. The outlet is selected at Jiangyin Station, which has long-term tidal level records. The model uses a body-fitted orthogonal curve grid with a total of 1370×160 nodes. The grid spacing in the direction of water flow is 40m~90m, and the grid spacing perpendicular to the direction of water flow is 10m~50m. The roughness value is calibrated and verified using topographic and water level data from February 2021, and the sediment parameters are calibrated and verified using data from April 2019 to February 2021. The particle size distribution of suspended sediment and bed sediment is divided into six groups: 0.002mm, 0.008mm, 0.016mm, 0.031mm, 0.125mm, and 0.25mm. The proportion of each particle size component is obtained by weighted average of the measured data from April 2019. The verification results of water level, flow velocity, and riverbed scouring and deposition distribution are attached. Figure 4 Overall, the water level, flow velocity, and river channel change trends calculated by the two-dimensional planar hydro-sediment model are in good agreement with the measured results, and can reasonably simulate the recent geomorphological evolution of the Sanyiqiao beach.

[0155] Step 3: The flow range of Datong Hydrological Station starts from the low water flow (16500 m³ / h). 3 / s increased to flood flow (85400 m³ / s) 3 / s), therefore, 6 typical flow rates were set: Q1 low water flow rate (16500 m³ / s). 3 / s), Q2 multi-year average flow (28500m³) 3 / s), Q3 beach flow (45000 m³ / s) 3 / s), Q4 multi-year average flood flow (57500 m³ / s) 3 / s), Q5 flood flow (70000m³) 3 / s) and Q6 flood flow (85400 m³ / s) 3 / s). The inlet flow rate of the two-dimensional planar water and sediment mathematical model can be assumed to be a steady flow, while the outlet water level process adopts the 85% cumulative frequency tidal range spring tide pattern under various typical flow rates at the Jiangyin hydrological station. The daily tidal range at the Jiangyin hydrological station from 2014 to 2021 was calculated and frequency sorted to obtain the corresponding tidal level processes under the above six typical flow rates. (See attached...) Figure 5 The flat beach flow rate (45000 m³) is given. 3 The downstream tidal process corresponding to / s).

[0156] Step 4: Calculate the water flow initiation capacity at the Sanyi Bridge beach under various typical flow rates using a two-dimensional planar hydro-sediment mathematical model. With the force of water flow carrying sand , attached Figure 6 The trends of both parameters with flow rate were plotted. As the flow rate increases, both the initiation capacity of the water flow and the sediment-carrying capacity at the Sanyi Bridge beach show a trend of first increasing and then decreasing. When the flow rate is 16500 m³ / s... 3 When the flow rate is 28500 m³ / s, the water flow initiation capacity is less than 1, and the silt at the Sanyi Bridge beach cannot be stirred. 3 When the flow rate is / s, the initiation capacity of the water flow is greater than 1, and the sediment at the Sanyi Bridge beach begins to move. This indicates that the flow range where the hydrodynamic force at the Sanyi Bridge beach changes from weak to strong is between 16500 and 28500 m³ / s. 3 / s. When the flow rate is 28500m 3 / s increased to 57000m 3 / s, the initiation capacity of the water flow and the sediment-carrying capacity of the water flow continuously increase with the flow rate. When the flow rate increases from 57500 m³ / s... 3 / s increased to 85400m 3 During the process of [number] seconds, the sediment-carrying capacity of the water flow gradually decreases, with the inflection point located at 57500m. 3 / s and 70000m 3 Between 57,500 and 70,000 m³ / s, it can be seen that the flow range where the hydrodynamic force at the Sanyi Bridge beach changes from strong to weak is located between 57,500 and 70,000 m³ / s. 3 / s. Therefore, it is preliminarily believed that, with the increase of flow rate, there are two flow ranges where the hydrodynamic force at the Sanyi Bridge beach transitions from weak to strong: the flow range from 16500 to 28500 m³ / s. 3 / s, the flow rate transitioning from strong to weak is in the range of 57500~70000m³ / s. 3 / s.

[0157] Step 5: Based on the flow range obtained in Step 4, within the range of 16500~70000m³ 3 Within the / s flow range, nine more detailed typical flow groups are set: QS1 (16500m 3 / s), QS2(20000m 3 / s), QS3 (25000m 3 / s), QS4 (30000m 3 / s), QS5 (40000m 3 / s), QS6 (45000m) 3 / s), QS7 (50000m 3 / s), QS8 (60000m) 3 / s), QS9 (650000m) 3 / s). Based on the daily average flow and sediment concentration data of Datong from 2019 to 2021, a flow-sediment concentration relationship curve was plotted, as shown in the appendix. Figure 7 Based on the flow-sediment concentration relationship curve, the sediment concentration at each typical flow rate was determined: QS1 (0.041 kg / m³). 3 QS2 (0.051kg / m) 3 QS3 (0.066kg / m) 3 ), QS4 (0.082kg / m 3 ), QS5 (0.115kg / m 3 ), QS6 (0.132kg / m 3 ), QS7 (0.149kg / m 3 ), QS8 (0.184kg / m 3 ), QS9 (0.221kg / m 3 ).

[0158] Step Six: Calculate the scouring and sedimentation volume at the Sanyi Bridge beach under typical water and sediment conditions using a two-dimensional planar water and sediment mathematical model, and plot the trend of scouring and sedimentation volume with flow rate (see attached figure). Figure 8 As the flow rate increases, the beach near Sanyi Bridge undergoes a process of erosion, transitioning from scouring to silting. In terms of scouring and silting volume, when the flow rate is less than 20,000 m³ / h... 3 At a flow rate of 25000~45000 m³ / s, the beach surface shows virtually no morphological change. 3Between / s, the Sanyiqiao beach generally exhibits a scouring trend, with the scouring intensity first increasing and then decreasing, reaching a maximum at Q=30000m. 3 The scouring intensity was most significant at / s, scouring 76,000 m³ of sediment. 3 When the upstream flow increases to 50,000 m³ 3 At a flow rate of 65,000 m³ / s, significant siltation occurred in the middle and lower reaches of the Sanyi Bridge shoal, transforming the shoal from a scouring to a silting state. This process continued as the flow rate further increased to 65,000 m³ / s. 3 At a rate of / s, the siltation volume on the beach near Sanyi Bridge increased significantly, with approximately 608,000 m³ of silt deposited. 3 This is 10 to 20 times the amount of sediment scoured at low flow rates. Step six further confirms the judgment of the two critical flow rates obtained in step one and finally clarifies the range of the two critical flow rates. Located at 20000~25000m 3 Between / s, and Located at 45,000~50,000m 3 Between / s.

[0159] Example 2

[0160] This embodiment provides a calculation system for the critical flow rate of scour and sedimentation conversion on riverbanks, including:

[0161] The barn type classification module is used to classify bar types based on the location of the target bar and the upstream and downstream river conditions, and to preliminarily determine the number of critical flow rates of the target bar.

[0162] Mathematical model building module. It is used to grid the research area containing the target beach, establish a two-dimensional planar water and sediment mathematical model, and calibrate and verify the parameters;

[0163] Typical Flow Determination Module. It is used to determine multiple sets of typical flows from the lowest flow to the highest flow based on the multi-year flow process of the study area.

[0164] The initial interval determination module is used to select the initial terrain, use a two-dimensional planar hydro-sediment mathematical model to calculate the water flow initiation capacity and sediment carrying capacity at the target beach under various typical flow rates, draw the changes of the two with the flow rate, and determine the flow rate interval where the hydrodynamic strength changes.

[0165] The water and sediment calculation condition delineation module is used to delineate more detailed water and sediment calculation conditions based on a defined flow range.

[0166] The final critical flow range determination module is used to select the initial topography, calculate the scouring and deposition volume at the target beach under various water and sediment conditions using a two-dimensional planar water and sediment mathematical model, plot the change of scouring and deposition volume with flow rate, verify the accuracy of the preliminary judgment of the number of critical flow rates, and finally determine the critical flow range that causes the target beach to undergo scouring and deposition.

[0167] It should be understood that any parts not described in detail in this specification belong to the prior art.

[0168] It should be understood that the above description of the preferred embodiments is quite detailed, but this should not be construed as limiting the scope of protection of this invention. It is neither necessary nor possible to exhaustively describe all possible implementations. Those skilled in the art, guided by this invention, can make substitutions or modifications without departing from the scope of the claims, all of which fall within the scope of protection of this invention. The scope of protection of this invention should be determined by the appended claims.

Claims

1. A method for calculating the critical flow rate for scour and sedimentation conversion on riverbanks, characterized in that, Includes the following steps: Step 1. Based on the location of the target beach and the upstream and downstream river conditions, classify the beach types, including: straight river type cross beach, meandering river type convex bank beach, braided river type flood-prone area beach in the upstream area of ​​the braided channel and braided river type dry-prone area beach in the upstream area of ​​the braided channel, and preliminarily determine the number of critical flow rates of the target beach. Step 2. Grid the study area containing the target beach, establish a two-dimensional planar hydro-sediment mathematical model, and calibrate and verify the parameters; including: initializing the roughness value of the study area, calculating the frictional water level and cross-sectional velocity of the study area under the roughness value using the two-dimensional planar hydro-sediment mathematical model, comparing it with the measured values, and if they do not match, adjusting the roughness value from downstream to upstream, repeating the calculation until the calculated frictional water level and cross-sectional velocity match the measured values; Step 3. Based on the multi-year flow history of the study area, determine multiple typical flow groups from the lowest flow to the highest flow in sequence; Step 4. Select the initial topography, use a two-dimensional planar hydro-sediment mathematical model to calculate the water flow initiation capacity and sediment carrying capacity at the target beach under various typical flow rates, plot the changes of these two values ​​with flow rate, and determine the flow range where the hydrodynamic strength changes; the implementation method is as follows: Step 41. Calculate the flow velocity at the target beach under various typical flow conditions using a two-dimensional planar water-sediment mathematical model. and water depth Calculate the water flow initiation capacity at the target beach. and the force of water flow carrying sand ; Step 42. Plot the changes in water flow initiation capacity and sediment carrying capacity as a function of flow rate, based on the water flow initiation capacity. The flow range from less than 1 to greater than 1 is considered the range where the hydrodynamic force at the beach changes from weak to strong, based on the sediment-carrying capacity of the water flow. The flow range from increasing to decreasing is considered the flow range where the hydrodynamic force at the beach changes from strong to weak; Step 5. Based on the flow range where the hydrodynamic intensity changes as determined in Step 4, further refine the water and sediment calculation conditions; Step 6. Select the initial topography, use a two-dimensional planar hydro-sediment mathematical model to calculate the scouring and deposition volume at the target beach under various hydro-sediment conditions, plot the scouring and deposition volume as a function of flow rate, verify the accuracy of the number of critical flow rates initially determined in Step 1, and finally determine the critical flow range that causes the target beach to undergo scouring and deposition conversion; the implementation method is as follows: Step 61. Calculate the scouring and deposition at the target beach under various water and sediment conditions using a two-dimensional planar water and sediment mathematical model. The scouring and deposition of a unit grid is the product of the scouring and deposition change value of the unit grid and its area. The scouring and deposition at the target beach is the sum of the scouring and deposition of the unit grids included in the beach area. Step 62. Plot the change of scour and sedimentation volume with flow rate to verify the accuracy of the number of critical flow rates determined in Step 1. The flow range in which the scour and sedimentation volume changes from a positive value to a negative value can be regarded as the critical flow range in which the beach transitions from sedimentation to scour. The flow range in which the scour and sedimentation volume changes from a negative value to a positive value can be regarded as the critical flow range in which the beach transitions from scour to sedimentation.

2. The method for calculating the critical flow rate for scour and sedimentation conversion on a beach according to claim 1, characterized in that, The implementation method of step 1 is as follows: The study area, including the target bar, was morphologically analyzed. The target bar types were categorized into four types, and the number of critical discharges at each target bar was preliminarily determined, including: (1) Straight river type alternating side beach: During the process of increasing flow, there is a critical flow that causes it to develop from non-scouring to scouring; (2) Meandering river convex bank beach: During the process of increasing flow, there is a critical flow that causes it to develop from siltation to scouring; (3) The flood of the diverted river type tends to the upstream area of ​​the diverted river: During the process of increasing flow, there is a critical flow that causes it to develop from siltation to scouring; (4) The low water level of the branch river type tends to be on the upstream side beach of the branch: During the process of increasing flow, there are two critical flow rates that cause it to develop from no scouring to scouring and then to siltation.

3. The method for calculating the critical flow rate for scour and sedimentation conversion on a beach according to claim 2, characterized in that, The implementation method of step 2 is as follows: Step 21. Based on the boundary of the study area and the left and right bank boundary lines, generate a two-dimensional body-fitted orthogonal curve mesh containing the target beach area; Step 22. Collect measured topographic data and corresponding hydrological data of the study area during the same time period, and determine the inlet flow, sediment concentration and outlet water level of the two-dimensional planar water and sediment mathematical model; Step 23. Initialize the roughness value of the study area, calculate the frictional water level and cross-sectional velocity of the study area under the roughness value using a two-dimensional planar water and sediment mathematical model, and compare it with the measured values. If they do not match, adjust the roughness value from downstream to upstream and repeat the calculation until the calculated frictional water level and cross-sectional velocity match the measured values. Step 24. Initialize the sediment parameters of the study area. Calculate the scour and deposition distribution and scour and deposition volume of the study area under these sediment parameters using a two-dimensional planar water and sediment mathematical model. Compare the results with the measured values. If they do not match, adjust the sediment parameters and repeat the calculation until the calculated scour and deposition distribution and scour and deposition volume match the measured values.

4. The method for calculating the critical flow rate for scour and sedimentation conversion on a beach according to claim 3, characterized in that, The implementation method of step 3 is as follows: Step 31. Collect the daily average water level and flow rate data measured at the nearest hydrological station in the study area, and plot the water level-flow rate relationship curve; Step 32. Divide the flow range from the lowest to the highest flow in the study area into several typical flow rates, including low flow, multi-year average flow, flood flow, multi-year average flood flow, and flood flow. Step 33. For runoff river sections, calculate the water level of hydrological stations under each typical flow rate using the water level-flow relationship curve, deduce the outlet water level according to the water surface gradient, and determine multiple sets of typical flow calculation conditions; for tidal river sections, select the tidal range tidal pattern corresponding to each typical flow rate at 85% cumulative frequency as the outlet water level process, and determine multiple sets of typical flow calculation conditions.

5. The method for calculating the critical flow rate for scour and sedimentation conversion on a beach according to claim 1, characterized in that, In step 4, the water flow starting capacity is , This is the starting flow rate.

6. The method for calculating the critical flow rate for scour and sedimentation conversion on a beach according to claim 5, characterized in that, The implementation method of step 5 is as follows: Step 51. Collect the daily average flow and sediment concentration data measured at the nearest hydrological station in the study area, and plot the flow-sediment concentration relationship curve; Step 52. Based on the flow ranges from weak to strong and from strong to weak hydrodynamics at the beach determined in Step 42, more detailed flow levels are divided. Typical flow calculation conditions are determined in the manner described in Step 33. The sediment concentration at each hydrological station under each typical flow is calculated using the flow-sediment concentration relationship curve described in Step 51, and multiple sets of water and sediment calculation conditions are determined.

7. The method for calculating the critical flow rate for scour and sedimentation conversion on a side beach according to claim 1, characterized in that, The aforementioned two-dimensional planar water and sediment mathematical model is as follows: (1) Equation of continuity of water flow: (2) Equations of water flow Directional momentum equation: Directional momentum equation: In the formula: These are the coordinates of two orthogonal curves in an orthogonal curvilinear coordinate system; For time; They are respectively directional flow velocity; Water level; For water depth; It is the acceleration due to gravity; The coefficient for thanking talent; They are respectively Lamé coefficient in direction; These represent turbulent stresses in different directions. The first subscript indicates the direction of the outward normal to the surface where the stress is located, and the second subscript indicates the direction of the stress. (3) Equation for non-uniform suspended sediment transport: In the formula, , , , For the first The sediment concentration recovery saturation coefficient, settling velocity, water flow sediment carrying capacity, and suspended sediment volumetric sediment concentration of the group were determined. Indicates the sediment diffusion coefficient; President Trump Schmidt number; (4) Non-uniform bedload sediment transport equation: In the formula: , For the first Group bedload recovery saturation coefficient, sediment settling velocity; , These are, respectively, bedload transport rate and bedload saturation transport rate; (5) Equation of riverbed deformation: In the formula: Number of particle size groups for bedloaded and suspended sediments respectively; The dry density of the bed sand; This refers to the elevation of the bed surface.

8. A calculation system for the critical flow rate of scour and sedimentation conversion on riverbanks, characterized in that, include: The barn type classification module is used to classify bar types based on the location of the target bar and the upstream and downstream river conditions, and to preliminarily determine the number of critical flow rates of the target bar. Mathematical model building module. It is used to grid the research area containing the target beach, establish a two-dimensional planar water and sediment mathematical model, and calibrate and verify the parameters; Typical Flow Determination Module. It is used to determine multiple sets of typical flows from the lowest flow to the highest flow based on the multi-year flow process of the study area. The initial interval determination module is used to select the initial terrain, use a two-dimensional planar hydro-sediment mathematical model to calculate the water flow initiation capacity and sediment carrying capacity at the target beach under various typical flow rates, draw the changes of the two with the flow rate, and determine the flow rate interval where the hydrodynamic strength changes. The water and sediment calculation condition delineation module is used to delineate more detailed water and sediment calculation conditions based on a defined flow range. The final critical flow range determination module is used to select the initial topography, calculate the scouring and deposition at the target beach under various water and sediment conditions using a two-dimensional planar water and sediment mathematical model, draw a graph of scouring and deposition as a function of flow rate, verify the accuracy of the preliminary judgment of the number of critical flow rates, and finally determine the critical flow range that causes the target beach to undergo scouring and deposition. The system for calculating the critical flow rate for shoal erosion-siltation conversion is used to perform the steps in the method for calculating the critical flow rate for shoal erosion-siltation conversion as described in any one of claims 1-7.

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