Method for simulating riverway dam break based on two-dimensional coupled hydrodynamic model

Abstract

The application discloses a river channel breach simulation method based on a two-dimensional coupling water power model, and specifically comprises the following steps: obtaining basic data of a calculation region, establishing a one-dimensional river network model and a two-dimensional surface water power model; coupling the one-dimensional river network model and the two-dimensional surface water power model to obtain a two-dimensional coupling water power model, solving the model, and calculating exchange flow; solving a model breach process, calculating a river channel breach flow process; coupling the breach flow into the model to calculate a breach flood evolution; updating section water depth, flow process, grid water depth and flow velocity in the model; outputting information; repeating until a preset simulation time length is reached, and completing simulation calculation. The method solves the problems of inaccurate calculation of a breach process caused by river flood and complex breach setting, is an effective method for calculating a river flood breach process, and has a clear process and simple operation.

Description

Technical Field

[0001] This invention belongs to the technical field of numerical simulation methods for water environment, specifically relating to a method for simulating river embankment breaches based on a one- or two-dimensional coupled hydrodynamic model. Background Technology

[0002] Floods are severe natural disasters caused by factors such as heavy rainfall, rapid snowmelt, and storm surges. In terms of frequency and impact, floods are among the most widespread disasters threatening human society. To mitigate the impact of floods on human production and daily life, dikes are typically built in flood-prone areas to protect against floodwaters. However, when faced with floods exceeding standard levels, the floodwaters may overflow the top of the dikes, leading to dike breaches and resulting in severe consequences such as casualties, property damage, and ecological destruction. Furthermore, with the continuous changes in global climate, the frequency of extreme weather events, especially heavy rainfall, is increasing, further exacerbating the threat of these natural disasters. Therefore, the study of the disaster-causing process of dike breach floods has always been a research hotspot in the field of water resources.

[0003] While flood disasters are generally difficult to completely eliminate, their losses can be significantly reduced through a series of effective strategies. These include classifying floods based on risk levels, strengthening public education on flood escape procedures, optimizing evacuation routes, and using numerical simulations to predict flood disasters. Among these, flood numerical simulation, as a key means of disaster prevention and mitigation, typically requires collecting hydrological, meteorological, and underlying surface data of the study area, and then developing corresponding numerical models. After parameter calibration and validation, it can provide early predictions of potential flood disasters in the study area, thereby achieving the goal of disaster prevention and mitigation. However, because levee-break flood processes are influenced by various factors such as river flood levels, levee elevations, and breach characteristics, accurate simulation requires a large amount of data, and modeling presents certain challenges. Therefore, there is an urgent need for a method that can rapidly and accurately simulate levee-break flood processes based on one-dimensional river network data, levee data, and simplified two-dimensional surface data to improve flood disaster prediction and defense capabilities. Summary of the Invention

[0004] The purpose of this invention is to provide a method for simulating river breaches based on a one- or two-dimensional coupled hydrodynamic model, thereby solving the problem that existing simulation techniques cannot accurately locate the breach position.

[0005] The technical solution adopted in this invention is a method for simulating river embankment breaches based on a one- or two-dimensional coupled hydrodynamic model, which is implemented according to the following steps:

[0006] S1. Obtain basic data for the calculation area, including one-dimensional river cross-section data, two-dimensional surface DEM data, and underlying surface data;

[0007] S2. Establish a one-dimensional river network model and a two-dimensional surface water dynamics model based on the basic data;

[0008] S3. Couple the one-dimensional river network model and the two-dimensional surface hydrodynamic model to obtain a one-dimensional coupled hydrodynamic model.

[0009] S4. Solve the one- or two-dimensional coupled hydrodynamic model and calculate the exchange flow rate;

[0010] S5. Solve the levee breach process of the one- or two-dimensional coupled hydrodynamic model, and calculate the flow rate of the breach based on the set levee breach type and levee breach location information.

[0011] S6. Couple the breach flow rate into a one- or two-dimensional coupled hydrodynamic model to calculate the evolution of the breach flood.

[0012] S7. Update the cross-sectional water depth, flow process, grid water depth, and flow velocity in the one-dimensional coupled hydrodynamic model;

[0013] S8. Output the water depth, flow velocity and breach flow process information obtained from the one-dimensional river network model, and the surface inundation water depth and inundation range information obtained from the two-dimensional surface hydrodynamic model.

[0014] S9. Repeat S4 to S8 until the preset simulation duration is reached to complete the simulation calculation.

[0015] The invention is further characterized in that,

[0016] In step S2, specifically:

[0017] Read one-dimensional river cross-section data, including cross-section number, cross-section spacing, thallopath elevation, initial water level, topological relationship, initial flow, slope and Manning coefficient, and construct a one-dimensional river network model.

[0018] We read basic data such as DEM raster data, land use type data, and infiltration data to construct a two-dimensional surface water dynamic model.

[0019] In step S3, specifically:

[0020] First, the spatial topological relationship is associated with the one-dimensional river network model, and the region where the river channel grid is located is calculated using the one-dimensional river network model. Second, the grids adjacent to the river channel are determined, referred to as the coupled grids. The coupled grids are considered as the exchange boundary between the two-dimensional surface and the one-dimensional river network, and the water exchange in the one-dimensional and two-dimensional models occurs on the coupled grids. To ensure water conservation, the edges connecting the coupled grids and the river channel grids are set as closed boundaries. At the same time, the water level of the one-dimensional river network is interpolated so that the river water level corresponding to each coupled grid on the coupled boundary is more consistent with the actual river water level variation along the course, ensuring the accuracy of the river water level used in the coupled calculation. The coupling relationship between the one-dimensional river network model and the two-dimensional surface hydrodynamic model is established, and finally a one-dimensional and two-dimensional coupled hydrodynamic model is formed.

[0021] In step S4, specifically:

[0022] First, the one-dimensional river network model and the two-dimensional surface hydrodynamic model are solved according to their respective boundary conditions. Then, based on the river level, levee elevation, and surface water level, the directions of water exchange in the one-dimensional and two-dimensional models are divided into the following four categories: 1) The river level is less than the levee elevation and the surface water level is less than the levee elevation, so there is no water exchange; 2) The river level is less than the levee elevation and the surface water level is greater than the levee elevation, so water flows from the two-dimensional surface into the river; 3) The river level is greater than the levee elevation and the surface water level is less than the levee elevation, so water flows from the river into the two-dimensional surface; 4) The river level is equal to the surface water level and both are greater than the levee elevation, so water exchange still exists, and the direction of water exchange needs to be determined based on the direction of water flow on the coupled grid.

[0023] The exchange quantity is given by the following formula (1):

[0024]

[0025] Among them, Q S The exchange quantity calculated at the coupling boundary of a two-dimensional coupled hydrodynamic model is given in m. 3 / s; b is the weir width in meters; g is the acceleration due to gravity in meters per second. 2 h max =max(Z) R Z G )-Z D h min =min(Z) R Z G )-Z D Z R Z indicates the river water level, in meters (m). G Z represents the surface elevation, in meters (m). D This indicates the elevation of the dike, in meters (m).

[0026] Step S5 specifically includes:

[0027] The input file of the one-dimensional coupled hydrodynamic model reads the elevations of the left and right bank levees at each cross section along the one-dimensional river network model, the levee breach type (instantaneous or gradual breach), the breach direction, the breach elevation, and the breach bottom elevation. Then, the levee breach process is calculated to obtain the flow rate at the breach in the one-dimensional coupled hydrodynamic model.

[0028] The calculation method for instantaneous collapse is as follows: When the water level of a one-dimensional river network section is higher than the breach elevation of a certain side of the dike set for that section, it is considered that the dike on this side will instantly collapse to the set breach bottom elevation, and then the exchange volume is calculated using the following weir flow formula (2):

[0029]

[0030] Among them, Q S The instantaneous flow rate at the breach is expressed in m³ / s. 3 / s; b is the ulcer width, in meters; Z R River water level, in meters (m); Z DIE Z represents the bottom elevation of the breach, in meters (m). DBE The breach elevation is in meters (m); g is the acceleration due to gravity (m / s²). 2 ;

[0031] The calculation method for gradual breach is as follows: When the water level of a one-dimensional river network section is higher than the breach elevation of a certain side of the dike set at that section, it is assumed that the dike on this side will breach in a certain breach manner, and the breach will gradually expand until it stabilizes. Then, the flow process is coupled into the model to calculate the breach process, as shown in Equation (3):

[0032]

[0033] Among them, Q Timeseries The breach flow rate during gradual collapse, expressed in m³. 3 / s;

[0034] Step S6 specifically includes:

[0035] Within the same computation time step, the breach flow obtained in S5 is subtracted from the one-dimensional river network model and added to the corresponding breach location in the two-dimensional surface hydrodynamic model. The evolution of the breach flood is calculated using a coupled one-dimensional and two-dimensional hydrodynamic model, thereby obtaining the inundation range, water depth, and duration of the breach flood on the surface.

[0036] The beneficial effects of this invention are:

[0037] (1) The method of the present invention uses a one-dimensional river network model based on HLL format to simulate the river flood process. Based on the water level of the river section and the corresponding levee elevation, the location of possible breach can be reasonably determined. According to the actual calculation needs, two different breach forms, instantaneous breach or gradual breach, can be selected. Then, the obtained breach flow process is added to the two-dimensional hydrodynamic model to calculate the flood evolution and inundation. Using this method, the flood inundation range in the basin can be obtained quickly when the one-dimensional cross-sectional data is accurate.

[0038] (2) The method of this invention uses a one-dimensional river network model to simulate the river channel, which can accurately and quickly obtain the water depth at any cross-section of the river network. It can also preset the locations of potential levee breaches in the model to calculate river channel breach floods, and can perform conventional flood inundation calculations based on the relative values ​​of river channel flood and levee elevation. Compared to traditional pure one-dimensional calculation methods, this method can accurately calculate the river channel flood process while also obtaining the flood's evolution process on the two-dimensional surface. Compared to pure two-dimensional calculation methods, this method has lower requirements for river channel data, eliminating the need for detailed and difficult-to-obtain river and levee DEM data in two-dimensional models. Therefore, this method is an effective method for calculating the river channel flood breach process. Furthermore, the method of this invention is clear in process and simple to operate, and is of great significance for assessing river channel flood inundation risk and creating flood risk maps. Attached Figure Description

[0039] Figure 1 This is a flowchart of the riverbank breach simulation method based on a one- or two-dimensional coupled hydrodynamic model of the present invention;

[0040] Figure 2 This is a schematic diagram of a one- or two-dimensional coupled hydrodynamic model of an ideal river section in an embodiment of the present invention;

[0041] Figure 3 This is a schematic diagram of the coupling principle of a two-dimensional model in an embodiment of the present invention;

[0042] Figure 4 This is a schematic diagram of the river water surface line change process obtained by model calculation in an embodiment of the present invention;

[0043] Figure 5 This is a schematic diagram illustrating the process of calculating water volume changes in each part in an embodiment of the present invention;

[0044] Figure 6 This is a schematic diagram illustrating the flood breach calculation and surface inundation of a certain river section in an embodiment of the present invention. Detailed Implementation

[0045] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0046] Example 1

[0047] This invention relates to a method for simulating riverbank breaches based on a one- or two-dimensional coupled hydrodynamic model, such as... Figure 1 As shown, please follow these steps:

[0048] S1. Obtain basic data for the calculation area, including one-dimensional river cross-section data, two-dimensional surface DEM data, and underlying surface data.

[0049] S2. Establish corresponding one-dimensional river network models and two-dimensional surface water dynamic models based on basic data;

[0050] S3. Couple the one-dimensional river network model and the two-dimensional surface hydrodynamic model according to the spatial topological relationship to obtain a one-dimensional coupled hydrodynamic model; and set the corresponding boundary conditions.

[0051] S4. Based on the boundary conditions of the one-dimensional river network model and the two-dimensional surface hydrodynamic model, solve the one-dimensional and two-dimensional coupled hydrodynamic model, and calculate the exchange flow of the one-dimensional and two-dimensional coupled hydrodynamic model based on the river level, levee elevation, and surface water level.

[0052] S5. Solve the levee breach process of the one- or two-dimensional coupled hydrodynamic model, and calculate the flow rate of the breach based on the set levee breach type and levee breach location information.

[0053] S6. Couple the breach flow obtained in S5 into a one- or two-dimensional coupled hydrodynamic model to calculate the evolution of the breach flood.

[0054] S7. Update key information such as cross-sectional water depth, flow process, grid water depth, and flow velocity in the one-dimensional coupled hydrodynamic model;

[0055] S8. Output the water depth, flow velocity and breach flow process information obtained from the one-dimensional river network model, and the surface inundation water depth and inundation range information obtained from the two-dimensional surface hydrodynamic model.

[0056] S9. Repeat S4 to S8 until the preset simulation duration is reached to complete the simulation calculation.

[0057] Example 2

[0058] This invention relates to a method for simulating riverbank breaches based on a one- or two-dimensional coupled hydrodynamic model, such as... Figure 1 As shown, please follow these steps:

[0059] S1. Obtain basic data for the calculation area, including one-dimensional river cross-section data, two-dimensional surface DEM data, and underlying surface data.

[0060] S2. Based on the basic data, establish corresponding one-dimensional river network models and two-dimensional surface hydrodynamic models; specifically:

[0061] Read one-dimensional cross-sectional data, including key information and parameters such as cross-section number, cross-section spacing, thallopath elevation, initial water level, topological relationships, initial flow rate, slope, and Manning coefficient, and construct a one-dimensional river network model; the modeling diagram is shown below. Figure 2 As shown;

[0062] Read basic data such as DEM raster data, land use type data, and infiltration data to construct a two-dimensional surface hydrodynamic model; the modeling diagram is shown below. Figure 2 As shown;

[0063] S3. Couple the one-dimensional river network model and the two-dimensional surface hydrodynamic model according to the spatial topological relationship to obtain a coupled one-dimensional and two-dimensional hydrodynamic model; and set the corresponding boundary conditions; the coupling principle diagram is shown below. Figure 3 As shown; specifically:

[0064] First, the spatial topological relationship is associated with the one-dimensional river network model, and the region where the river channel grid is located is calculated using the one-dimensional river network model. Second, the grids adjacent to the river channel (hereinafter referred to as the coupled grids) are determined, and the coupled grids are considered as the exchange boundary between the two-dimensional surface and the one-dimensional river network. The water exchange in the one-dimensional and two-dimensional models occurs on the coupled grids. To ensure water conservation, the edges connecting the coupled grids and the river channel grids are set as closed boundaries. At the same time, the water level of the one-dimensional river network is interpolated so that the river water level corresponding to each coupled grid on the coupled boundary is more consistent with the actual river water level variation along the course, ensuring the accuracy of the river water level used in the coupled calculation. The coupling relationship between the one-dimensional river network model and the two-dimensional surface hydrodynamic model is established, and finally a one-dimensional and two-dimensional coupled hydrodynamic model is formed.

[0065] S4. Based on the boundary conditions of the one-dimensional river network model and the two-dimensional surface hydrodynamic model, solve the coupled one-dimensional and two-dimensional hydrodynamic model, and calculate the exchange flow of the coupled one-dimensional and two-dimensional hydrodynamic model based on the river level, levee elevation, and surface water level; specifically:

[0066] First, the one-dimensional river network model and the two-dimensional surface hydrodynamic model are solved according to their respective boundary conditions. Then, based on the river level, levee elevation, and surface water level, the one-dimensional and two-dimensional water exchange directions are divided into the following four categories: (a) the river level is less than the levee elevation and the surface water level is less than the levee elevation, so there is no water exchange; (b) the river level is less than the levee elevation and the surface water level is greater than the levee elevation, so the water flows from the two-dimensional surface into the river; (c) the river level is greater than the levee elevation and the surface water level is less than the levee elevation, so the water flows from the river into the two-dimensional surface; (d) the river level is equal to the surface water level and both are greater than the levee elevation, so there is still water exchange, and the water exchange direction needs to be determined according to the water flow direction on the coupled grid. The specific exchange volume is shown by the following formula (1):

[0067]

[0068] Among them, Q S The exchange quantity calculated at the coupling boundary of a two-dimensional coupled hydrodynamic model is given in m. 3 / s; b is the weir width in meters (m), which is numerically equal to the grid size in the coupling method of this invention; g is the gravitational acceleration in meters per second (m / s²). 2 h max =max(Z) R Z G )-Z D h min =min(Z) R Z G )-Z D Z R Z indicates the river water level, in meters (m). G Z represents the surface elevation, in meters (m). D This indicates the elevation of the dike, in meters (m).

[0069] S5. Solve the levee breach process of the one- or two-dimensional coupled hydrodynamic model, and calculate the flow rate at the breach based on the set breach type and location information; specifically:

[0070] First, the elevations of the left and right bank levees, the breach type (instantaneous or gradual breach), the breach direction, the breach elevation, and the breach bottom elevation of each cross section of the one-dimensional river network model are read from the input file of the one-dimensional coupled hydrodynamic model. Then, the breach process is calculated. The instantaneous breach is calculated as follows: when the water level of the one-dimensional river network cross section is higher than the breach elevation of a certain side of the levee set for that cross section, it is considered that the levee on this bank has instantly breached to the set breach bottom elevation. Then, the exchange volume is calculated using the following weir flow formula (2):

[0071]

[0072] Among them, Q S The instantaneous flow rate at the breach is expressed in m³ / s. 3 / s; b is the ulcer width, in meters; Z R River water level, in meters (m); Z DIE Z represents the bottom elevation of the breach, in meters (m). DBE The breach elevation is in meters (m); g is the acceleration due to gravity (m / s²). 2 .

[0073] The calculation method for gradual breach is as follows: When the water level of a one-dimensional river network section is higher than the breach elevation of a certain side of the dike set at that section, it is assumed that the dike on this side breaches in a certain breach manner, and the breach gradually expands until it stabilizes. This flow process can be calculated using models such as DB-IAHR, and then the flow process is coupled into the model to calculate the breach process, as shown in equation (3):

[0074]

[0075] Among them, Q Timeseries The breach flow rate during gradual collapse, expressed in m³. 3 / s can be calculated from various breach models;

[0076] By solving this step, the flow rate at the breach in the one- or two-dimensional coupled hydrodynamic model can be obtained.

[0077] S6. Couple the breach flow obtained in S5 into a one- or two-dimensional coupled hydrodynamic model to calculate the evolution of the breach flood, specifically:

[0078] Within the same computation time step, the breach flow obtained in S5 is subtracted from the one-dimensional river network model (according to the principle of water conservation, the amount of water allowed to be subtracted from the one-dimensional river network model within each computation time step shall not exceed the total water volume of the river section at the current moment), and added to the corresponding breach location in the two-dimensional surface hydrodynamic model. The evolution of the breach flood is calculated using a coupled one-dimensional and two-dimensional hydrodynamic model, thereby obtaining the inundation range, water depth, and duration information of the breach flood on the surface.

[0079] S7. Update key information such as cross-sectional water depth, flow process, grid water depth, and flow velocity in the one-dimensional coupled hydrodynamic model;

[0080] S8. Output the water depth, flow velocity and breach flow process information obtained from the one-dimensional river network model, and the surface inundation water depth and inundation range information obtained from the two-dimensional surface hydrodynamic model.

[0081] S9. Repeat S4 to S8 until the preset simulation duration is reached to complete the simulation calculation.

[0082] Example 3

[0083] A small watershed was selected, with an area of ​​about 50 square kilometers and a main channel of about 20 kilometers. The surrounding terrain consists of hills and plains, and there have been several records of small-scale dike breaches.

[0084] One-dimensional river cross-section: 30 cross-sections were measured and data were obtained, with a cross-section spacing of about 500 meters. The elevation of the thalweg point was 20-50 meters, the initial water level was set at 22 meters, the initial flow rate was 5 cubic meters per second during the dry season, the slope was 0.002, and the Manning coefficient was 0.03.

[0085] Two-dimensional surface DEM: generated from satellite imagery, resolution 10 meters, elevation 15-60 meters.

[0086] Underlying surface: 40% arable land, with an infiltration rate of 5 mm / hour; 30% forest land, with an infiltration rate of 8 mm / hour; 20% construction land, with an infiltration rate of 2 mm / hour; and 10% water area.

[0087] Construct a one-dimensional river network model and a two-dimensional surface hydrodynamic model; using the software coupling function, associate the topology, mark the 20-meter-wide coupling grid around the main channel, set closed boundaries, interpolate water levels, and complete the construction of the one-dimensional and two-dimensional coupling models.

[0088] Boundary settings: One-dimensional upstream flow boundary is based on hydrological station data, with a peak flow rate of 50 cubic meters per second during flood season; downstream water level boundary is referenced to the estuary tide level. Two-dimensional boundary is set as a closed boundary or flow boundary based on topography.

[0089] Solution: Start the solver. At a certain moment, the river water level is 23 meters, the surface water level is 24 meters, and the embankment crest elevation is 25 meters. It belongs to type (b). According to formula (1), the weir width is 10 meters. Calculate the exchange volume.

[0090] Solution of the breach process: Assume that the breach at section 15 of the main channel is gradually breached, with a breach elevation of 24 meters and a bottom elevation of 22 meters. The DB-IAHR model is used to calculate the breach flow rate and couple it into the model.

[0091] Evolution of levee breach flood: Based on the conservation of water volume, the breach flow is transferred at corresponding time steps to simulate the changes in the flood inundation range and water depth.

[0092] At the end of each step, key information of the 1D / 2D model is updated to prepare for the next calculation. Data is output to a file every 2 hours for GIS mapping and analysis. The simulation is looped for a preset duration of 24 hours, monitored, and the final results are obtained to provide a basis for flood control.

[0093] Example 4

[0094] Figure 4 This diagram illustrates the river surface change process calculated by the model in this embodiment of the invention. It shows the river surface at the initial calculation time and after the calculation reaches a steady state (60 minutes). As can be seen from the diagram, the slope of the river surface before the breach is consistent with the initial slope, while the slope becomes gentler after the breach. This indicates that water loss occurred at the breach location in the one-dimensional river network model, leading to a reduction in the amount of water flowing downstream, which conforms to the principle of water conservation and the water balance equation. Furthermore, the model simulation results show good agreement with the analytical solution, demonstrating that the model can effectively simulate the breach process.

[0095] Figure 5This is a schematic diagram illustrating the water volume change process of the model in this embodiment of the invention. From the perspective of water conservation, the sum of the water flowing into the plain area through the breach and the water flowing out from the river outlet should equal the total water volume flowing into the river. Figure 5 It can be seen that the sum of the outflowing water volume is equal to the total inflow of water into the river channel, indicating that the coupled model constructed in this paper can maintain water conservation well.

[0096] Example 5

[0097] Figure 6 The present invention sets up a flood breach simulation and surface inundation process for a certain river section. The breach occurs on the left bank at section S3 and on the right bank at section S8. The breach flow processes are different, and the resulting inundation ranges are also different. This shows that the method of the present invention can effectively simulate the flood evolution and inundation process with different breach modes and breach flows.

[0098] Example 6

[0099] This invention presents a method for simulating river levee breaches based on a one-dimensional and two-dimensional coupled hydrodynamic model. Following specific steps, basic data is first acquired, and a one-dimensional river network model and a two-dimensional surface hydrodynamic model are constructed. These are coupled to obtain the one-dimensional and two-dimensional coupled hydrodynamic model. Subsequently, calculations are performed sequentially, including solving for the levee breach process and calculating the evolution of the breach flood. Relevant information is continuously updated and output, and the corresponding steps are repeated until the preset simulation duration is reached to complete the simulation. This method solves the problems of inaccurate calculations of levee breach processes caused by river floods and the complexity of breach design. It is an effective method for calculating river flood levee breach processes. Furthermore, this simulation method is clear in its process and simple to operate, and it is of great significance for assessing river flood inundation risk and creating flood risk maps.

Claims

1. A method for simulating a riverway breach based on a two-dimensional coupled hydrodynamic model, characterized in that, The method is implemented according to the following steps: S1, obtaining calculation area basic data, including one-dimensional river channel section data, two-dimensional ground surface DEM data and underlying surface data; S2, establishing a one-dimensional river network model and a two-dimensional ground surface water dynamic model according to the basic data; S3, coupling the one-dimensional river network model and the two-dimensional ground surface water dynamic model to obtain a one-two-dimensional coupled water dynamic model; S4, solving the one-two-dimensional coupled water dynamic model and calculating exchange flow; S5, solving the one-two-dimensional coupled water dynamic model in a breach process, and calculating a flow process of a river channel breach according to set breach forms and breach position information; specifically: reading left and right bank embankment elevations of each section of the one-dimensional river network model in an input file of the one-two-dimensional coupled water dynamic model, and setting breach forms, breach directions, breach elevations and breach bottom elevations, and then performing breach process calculation to obtain flow at the breach in the one-two-dimensional coupled water dynamic model; the calculation method of instantaneous breach is as follows: when the water level of the one-dimensional river network section is higher than the breach elevation of the embankment on one side of the section, it is considered that the embankment on this side is breached instantaneously to the set breach bottom elevation, and then the exchange is calculated by the following weir flow formula (2): （2） wherein, Q S Q is the breach flow rate, in m 3 / s; b W is the breach width, in m; Z R H is the river stage, in m; Z DIE B is the breach bottom elevation, in m; Z DBE D is the breach crest elevation, in m; g g is the acceleration due to gravity, in m / s 2 ; the calculation method of gradual breach is as follows: when the water level of the one-dimensional river network section is higher than the breach elevation of the embankment on one side of the section, it is considered that the embankment on this side is breached in a certain way, and the breach is gradually expanded until stable, and then the flow process is coupled into the model for breach process calculation, as shown in formula (3): （3）； wherein, Q Timeseries is the breach flow rate in m / s for a breach that is gradually eroding 3 / s; S6, coupling the breach flow into the one-two-dimensional coupled water dynamic model for breach flood evolution calculation; S7, updating the section water depth, flow process, grid water depth and flow velocity in the one-two-dimensional coupled water dynamic model; S8, outputting the water depth, flow velocity and breach flow process information obtained by the one-dimensional river network model and the ground surface inundation depth and inundation range information obtained by the two-dimensional ground surface water dynamic model; S9, repeating S4-S8 until the simulation is completed to a preset simulation time.

2. The river dike break simulation method based on a two-dimensional coupled hydrodynamic model according to claim 1, wherein, In the step S2, specifically: reading one-dimensional river channel section data, including section number, section distance, thalweg elevation, initial water level, topological relationship, initial flow, slope and Manning coefficient, which are key information and parameters of the section, to construct the one-dimensional river network model; reading DEM grid data, land use type data and infiltration data to construct the two-dimensional ground surface water dynamic model.

3. The river dike break simulation method based on a two-dimensional coupled hydrodynamic model according to claim 1, wherein, In the step S3, specifically: Firstly, the spatial topological relationship is associated with the one-dimensional river network model, and the area where the river channel grid is located is calculated by using the one-dimensional river network model; secondly, the grid adjacent to the river channel, hereinafter referred to as the coupling grid, is determined, and the coupling grid is considered as the exchange boundary of the two-dimensional ground and the one-dimensional river network, and the water exchange of the one-dimensional and two-dimensional model occurs on the coupling grid; in order to ensure the water conservation, the coupling grid and the edge connected with the river channel grid are set as a closed boundary, and the water level of the one-dimensional river network is interpolated, so that the river water level corresponding to each coupling grid on the coupling boundary is more in line with the actual river water level along the trend, and the river water level used in the coupling calculation is ensured to be accurate; the coupling relationship between the one-dimensional river network model and the two-dimensional ground water dynamic model is established, and finally the one-dimensional and two-dimensional coupled water dynamic model is formed.

4. The river dike break simulation method based on a two-dimensional coupled hydrodynamic model according to claim 3, wherein, In the step S4, specifically: Firstly, the one-dimensional river network model and the two-dimensional ground water dynamic model are solved according to their respective boundary conditions, and then the one-dimensional and two-dimensional water exchange direction is divided into the following four types according to the river water level, the dike elevation and the ground water level: the river water level is less than the dike elevation and the ground water level is less than the dike elevation, and there is no water exchange; the river water level is less than the dike elevation and the ground water level is greater than the dike elevation, and the water flow enters the river channel from the two-dimensional ground; the river water level is greater than the dike elevation and the ground water level is less than the dike elevation, and the water flow enters the two-dimensional ground from the river channel; the river water level is equal to the ground water level, and both are greater than the dike elevation, at this time, there is still water exchange, and the exchange direction of the water flow needs to be determined according to the water flow direction on the coupling grid.

5. The river dike break simulation method based on a two-dimensional coupled hydrodynamic model according to claim 4, wherein, The exchange amount is shown by the following formula (1): （1） wherein, Q S is the exchange quantity calculated at the coupling boundary of the two-dimensional coupled hydrodynamic model, with the unit of m 3 / s; b is the weir width, with the unit of m; g is the gravity acceleration, with the unit of m / s 2 ; h max = max(Z R , Z G )-Z D ; h min = min(Z R , Z G )-Z D ; Z R represents the river water level, with the unit of m; Z G represents the ground surface elevation, with the unit of m; and Z D represents the dike elevation, with the unit of m.

6. The river dike break simulation method based on a two-dimensional coupled hydrodynamic model according to claim 1, wherein, In the step S6, specifically: In the same calculation time step, the breach flow rate obtained in S5 is subtracted from the one-dimensional river network model and added to the corresponding breach position of the two-dimensional ground water dynamic model, and the one-dimensional and two-dimensional coupled water dynamic model is used for dike breach flood evolution calculation, and then the submergence range, water depth and duration information of the dike breach flood on the ground are obtained.

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