Urban rainfall flood process simulation method combining road equivalent drainage and trunk pipe network

Abstract

The invention discloses an urban rainfall flood process simulation method combining road equivalent drainage and a trunk pipe network, and the method comprises the steps: obtaining the basic data of a research region, building a two-dimensional hydrodynamic model and a one-dimensional pipe network model based on the obtained data, and carrying out the Thiessen polygon partitioning of the research region, establishing a coupling relationship among the rainwater nodes, the earth surface grids and the Thiessen polygon partitions; calculating the rainfall and infiltration process of the research area to judge whether the rainwater node overflows or not, if overflow occurs, performing overflow calculation, if not, discharging the road rainwater in the Thiessen polygon partition corresponding to the rainwater node into the rainwater node, and performing data updating according to the calculation result until the set operation time is reached, and then performing data updating according to the calculation result. And outputting a rainfall flood simulation result of the research area. According to the method, the flood process calculation of the region lacking the urban fine pipe network data is realized, and the simulation precision and the simulation calculation efficiency of the pipe network drainage process of the region lacking the urban fine pipe network data are improved.

Description

Technical Field

[0001] This invention belongs to the technical field of urban water conservancy numerical simulation methods, specifically involving a method for simulating urban stormwater processes by combining equivalent road drainage with main pipeline networks. Background Technology

[0002] Driven by both global warming and rapid urbanization, urban flooding is becoming increasingly prevalent and causing more severe damage, leading to a growing demand for urban flooding simulation and risk assessment. In recent decades, advancements in numerical methods and parallel computing have significantly improved the accuracy and efficiency of urban stormwater models. However, the accuracy requirements for fundamental information such as topographic and pipe network data upon which these models rely are also rising. Nevertheless, achieving accurate stormwater simulation still depends on high-precision topographic and pipe network data.

[0003] Urban drainage networks are the main pathway for stormwater runoff discharge, but because they are mostly distributed underground, data for some areas is difficult to obtain, posing a significant challenge to the accuracy and effectiveness of urban stormwater process simulation. In the absence of detailed network data, how to utilize data from main pipe networks and surface water accumulation to study generalized simulation methods for urban stormwater dynamic processes has become a major challenge in simulating these processes. Summary of the Invention

[0004] The purpose of this invention is to provide a method for simulating urban stormwater processes by combining equivalent road drainage with main pipe networks, enabling the calculation of flood processes in areas lacking detailed urban pipe network data, and improving the simulation accuracy and calculation efficiency of pipe network drainage processes in areas lacking detailed urban pipe network data.

[0005] The technical solution adopted in this invention is to combine the urban stormwater process simulation method of road equivalent drainage and main pipe network, obtain rainfall, topography, image, and main pipe network data of the study area, determine the rainwater nodes and pipe segment data in the main pipe network, construct a two-dimensional hydrodynamic model and a one-dimensional pipe network model based on the acquired data, divide the study area into Thiessen polygon partitions, and establish the coupling relationship between rainwater nodes, surface grid and Thiessen polygon partitions. The system calculates rainfall and infiltration processes in the study area to determine whether rainwater nodes overflow. If overflow occurs, overflow calculations are performed. If no overflow occurs, rainwater from roads in the Thiessen polygon partition corresponding to the rainwater node is discharged into that rainwater node. Data is updated based on the calculation results until the set running time is reached, and the simulated stormwater results for the study area are output.

[0006] The invention is further characterized in that, Specifically, the following steps are included: Step 1: Collect basic data on rainfall, topography, imagery, and main pipeline network in the study area; determine the location, boundaries, and area of ​​the region; determine the location, bottom elevation, and surface elevation of rainwater nodes in the main pipeline network; and determine the length, diameter, and topological relationship between the main pipeline segment and the rainwater node. Step 2: Based on the topography of the study area, construct a two-dimensional hydrodynamic model of GAST with a network structure, and assign corresponding land use attributes to each surface grid. Step 3: Divide the study area into Thiessen polygon partitions based on the location of rainwater nodes in the main pipeline network in Step 1, so that the Thiessen polygon partitions correspond to the rainwater nodes and the surface grid in the GAST two-dimensional hydrodynamic model, respectively. Step 4: Based on the length and diameter of the main pipe section and the topological relationship between the pipe section and the rainwater node, construct the SWMM one-dimensional pipe network model, and establish a one-dimensional coupling relationship based on the rainwater node information obtained in Step 1 and the two-dimensional surface water dynamic model constructed in Step 2 to construct the GAST-SWMM one-dimensional coupling model. Step 5, let The calculation time step of the GAST-SWMM one-dimensional coupled model is given, and the GAST two-dimensional hydrodynamic model is used to calculate the rainfall and infiltration process in the study area. Step 6: Determine whether the rainwater node overflows. If overflow occurs, perform overflow calculation. If no overflow occurs, discharge the rainwater from the road in the Thiessen polygon partition corresponding to the rainwater node into the rainwater node, and use a nonlinear reservoir to correct the amount of water flowing into the rainwater node. Step 7: Calculate the two-dimensional surface water depth based on the overflow volume or the water reduction volume on the road in Step 6, and calculate the surface runoff process. Step 8: Based on the water volume flowing out of or into the pipe network in Step 6, use the SWMM one-dimensional pipe network model to calculate the pipe network hydrodynamic process and obtain the water depth at the main pipe network nodes and the pipe network head and velocity information. Step 9: Update the surface water depth and flow velocity calculated in Step 7, and update the water depth at the main pipeline nodes, pipeline head, and flow velocity calculated in Step 8. Step 10, let Repeat steps 5 through 9 until... Output the simulated rainfall and flood results for the study area.

[0007] In step 2, the GAST two-dimensional hydrodynamic model is calculated by solving the two-dimensional shallow water equations, as shown in the following formulas: ; ; ; In the formula, t represents time, and the unit is seconds (s). For variable vectors; Water depth, in meters (m). q x and q y They are respectively x and y The unit width flow rate in both directions, in meters. 2 / s; and They are respectively x and y Flux vector in the direction; g This is the acceleration due to gravity, measured in m / s². 2 ; u and v They are respectively x and y Flow velocity in the direction, in m / s; Source term vector; For rainfall infiltration source items; z b This is the elevation of the riverbed bottom, in meters (m). For the Xie Cai coefficient, ,in n This is the Manning coefficient.

[0008] In step 2, land use attributes include roads, buildings, green spaces, and impermeable areas.

[0009] In step 5, the rainfall and infiltration processes in the study area are calculated using the following formulas: ; In the formula, R Net rainfall rate, in mm / h; i Rainfall intensity, in mm / h; f Soil infiltration rate, in mm / h; To ensure a stable infiltration rate, the unit is mm / h; f 0 represents the initial infiltration rate, in mm / h; t represents time, in seconds. k d This is the attenuation coefficient, measured in seconds. -1 .

[0010] Step 6 determines whether an overflow has occurred at a rainwater node by comparing the water depth at the rainwater node with the surface water depth. If... Z 1D >Z 2D This is called overflow, which means rainwater overflows from the pipe network to the ground surface; such as Z 1D < Z2D This is the inflow, meaning rainwater is discharged from the surface into the pipe network; among which, Z 1D The water depth at the rainwater node is expressed in meters (m). Z 2D The water depth is represented by the surface grid, in meters (m).

[0011] The node overflow calculation formula in step 6 is as follows: ; In the formula, Q out This refers to node overflow, in meters (m). 3 / s; m1 is the orifice flow coefficient, ranging from [0,1], and its value is determined according to the specific situation; A The area of ​​the node is expressed in meters. 2 ; g This is the acceleration due to gravity, measured in m / s². 2 ; Z 2D The water depth is represented by a grid on the surface, in meters (m). Z 1D The water depth at the rainwater node is expressed in meters (m). The inflow calculation formula for nodes in step 6 is as follows: ; ; In the formula, h old The initial water depth at the surface is expressed in meters (m). h new1 The depth of surface water before the water enters the pipes after rainfall, expressed in meters; h new2 The depth of surface water after the inflow occurs, in meters; The road equivalent drainage reduction rate can be determined through calibration or empirical values. V jtotal The inflow rate of node j, in m. 3 m represents the number of grid cells in the equivalent drainage region corresponding to node j. A cell The area of ​​the surface grid is in square meters (m²). 2 ; Q in Inflow rate, in meters (m³) 3 / s; W The generalized width of the Thiessen polygon partition, in meters; S The slope for the Thiessen polygon partition; n This is the Manning roughness coefficient; d jThe net depth of water accumulation above the area of ​​the Thiessen polygon section, in meters; A j This represents the area of ​​the Thiessen polygon partition.

[0012] The calculation of the two-dimensional surface water depth in step 7 is shown in the following formula: ; In the formula, h new3 To calculate the new grid water level considering the overflow or inflow of rainwater nodes at different time steps, The time step for the simulation is expressed in seconds (s). Q in The inflow rate to the node is expressed in milliseconds (m). 3 / s; Q out This refers to node overflow, in meters (m). 3 / s; W The generalized width of the Thiessen polygon partition, in meters; A cell The area of ​​the surface grid is in square meters (m²). 2 ; Z 2D The grid water level does not take into account the overflow or inflow of rainwater nodes.

[0013] The formula for calculating the hydrodynamic process of the pipeline network in step 8 is shown below: ; In the formula, x The distance is in meters (m). t Time, in seconds; A The cross-sectional area of ​​the flow path is expressed in m². 3 ; Q Flow rate, unit is m 3 / s; H The water head in the pipeline is expressed in meters (m). Z This refers to the elevation of the bottom of the pipe / channel, in meters (m). Y The depth of the pipe / channel is expressed in meters (m). S f The friction slope is g; g is the acceleration due to gravity, in m / s². 2 .

[0014] The beneficial effects of this invention are: This invention combines road equivalent drainage with a trunk pipe network to simulate urban stormwater processes. By utilizing trunk pipe networks, regional rainfall, topography, imagery, and identifying trunk pipe network nodes and segments, the numerical simulation of areas lacking detailed pipe network data more closely approximates actual stormwater processes. It can calculate flood processes in areas lacking detailed urban pipe network data and uses GPU parallel processing to accelerate computation, improving the accuracy and efficiency of pipe network drainage process simulation in areas lacking detailed urban pipe network data, thus providing strong pipe network model support for urban flood control and drainage decisions.

[0015] Meanwhile, when calculating the inflow process of rainwater nodes, this invention discharges rainwater from the roads in the corresponding area into the node to achieve an equivalent fine-grained pipe network drainage capacity, thereby further improving the simulation accuracy in areas lacking fine-grained pipe network data. Attached Figure Description

[0016] Figure 1 This is a flowchart illustrating the urban stormwater process simulation method of the present invention, which combines road equivalent drainage with main pipeline network.

[0017] Figure 2 This is a pipeline layout diagram in Embodiment 2 of the present invention.

[0018] Figure 3 This is a comparison chart of the simulation results and the fine pipeline network simulation results in Embodiment 2 of the present invention.

[0019] Figure 4 This is the topographic map in Embodiment 3 of the present invention.

[0020] Figure 5 This is a pipeline layout diagram in Embodiment 3 of the present invention.

[0021] Figure 6 This is a comparison chart of the simulation results and the fine pipeline network simulation results in Embodiment 3 of the present invention. Detailed Implementation

[0022] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0023] This invention combines road equivalent drainage with a method for simulating urban stormwater processes using main pipe networks. It acquires rainfall, topography, imagery, and main pipe network data for the study area, determines rainwater nodes and pipe segment data in the main pipe network, constructs a two-dimensional hydrodynamic model and a one-dimensional pipe network model based on the acquired data, divides the study area into Thiessen polygon partitions, and establishes the coupling relationship between rainwater nodes, surface grids, and Thiessen polygon partitions. The system calculates rainfall and infiltration processes in the study area to determine whether rainwater nodes overflow. If overflow occurs, overflow calculations are performed. If no overflow occurs, rainwater from roads in the Thiessen polygon partition corresponding to the rainwater node is discharged into that rainwater node. Data is updated based on the calculation results until the set running time is reached, and the simulated stormwater results for the study area are output.

[0024] Example 1 This invention combines equivalent road drainage with a method for simulating urban stormwater processes using main pipe networks, such as... Figure 1 As shown, the specific steps include: Step 1: Collect basic data on rainfall, topography, imagery, and main pipeline network in the study area; determine the location, boundaries, and area of ​​the region; determine the location, bottom elevation, and surface elevation of rainwater nodes in the main pipeline network; and determine the length, diameter, and topological relationship between the main pipeline segment and the rainwater node. Step 2: Based on the topography of the study area, construct a two-dimensional hydrodynamic model of GAST with a network structure. Specifically, the calculation is performed by solving the two-dimensional shallow water equation, as shown in the following formulas (1), (2), and (3): (1); (2); (3); In the formula, t represents time, and the unit is seconds (s). For variable vectors; Water depth, in meters (m). q x and q y They are respectively x and y The unit width flow rate in both directions, in meters. 2 / s; and They are respectively x and y Flux vector in the direction; g This is the acceleration due to gravity, measured in m / s². 2 ; u and v They are respectively x and y Flow velocity in the direction, in m / s; Source term vector; For rainfall infiltration source items; z b This is the elevation of the riverbed bottom, in meters (m). For the Xie Cai coefficient, ,in n This is the Manning coefficient.

[0025] Furthermore, the GAST two-dimensional hydrodynamic model of the present invention applies the dynamic wave method to simulate the flood evolution process and uses the Godunov scheme finite volume method to spatially discretize and solve the two-dimensional shallow water equations.

[0026] Then, based on the images, the land use attributes of roads, buildings, green spaces, and impermeable areas are divided, and the corresponding land use attributes are assigned to each grid. Step 3: Divide the study area into Thiessen polygon partitions based on the location of rainwater nodes in the main pipeline network in Step 1, so that the Thiessen polygon partitions correspond to the rainwater nodes and the surface grid in the GAST two-dimensional hydrodynamic model, respectively. Step 4: Based on the length and diameter of the main pipe section and the topological relationship between the pipe section and the rainwater node, construct the SWMM one-dimensional pipe network model, and establish a one-dimensional coupling relationship based on the rainwater node information obtained in Step 1 and the two-dimensional surface water dynamic model constructed in Step 2 to construct the GAST-SWMM one-dimensional coupling model. Step 5, let , This represents the computation time step of the GAST-SWMM one-dimensional coupled model. The time step for the two-dimensional hydrodynamic model simulation. The time step for the one-dimensional pipe network model simulation is given, and the rainfall and infiltration processes in the study area are calculated using the GAST two-dimensional hydrodynamic model, as shown in the following formula (4): (4); In the formula, R Net rainfall rate, in mm / h; i Rainfall intensity, in mm / h; f Soil infiltration rate, in mm / h; To ensure a stable infiltration rate, the unit is mm / h; f 0 represents the initial infiltration rate, in mm / h; t represents time, in seconds. k d This is the attenuation coefficient, measured in seconds. -1 .

[0027] Step 6: Determine if overflow has occurred at the rainwater node by comparing the water depth at the rainwater node with the surface water depth. The following... Z 1D represents the water depth at the rainwater node, in meters; the following... Z 2D represents the surface water depth in meters (m). If... Z 1 D>Z 2 D This is overflow, which means rainwater overflows from the pipe network to the ground surface. Overflow calculation is performed, and the calculation formula is shown in the following formula (5): (5); In the formula, Qout m1 represents the node overflow rate, in m³ / s; m2 represents the orifice flow coefficient, ranging from [0,1], and its value is determined based on specific circumstances. A The area of ​​the node is expressed in m². g This is the acceleration due to gravity, expressed in m / s². Z 2 D The water depth is represented by a grid on the surface, in meters (m). Z 1 D The water depth at the rainwater node is expressed in meters (m). like Z 1 D < Z 2 D This is the inflow, meaning that rainwater is discharged from the surface into the pipe network, and the rainwater from the roads in the Thiessen polygon partition corresponding to the rainwater node is discharged into the rainwater node. In order to reflect the lag process of regional rainwater confluence to the rainwater node, and to correct the amount of water flowing into the rainwater node using a nonlinear reservoir, the calculation formulas are as follows: Formula (6) and Formula (7): (6); (7); In the formula, hold The initial water depth at the surface is expressed in meters (m). hnew1 The depth of surface water before the water enters the pipes after rainfall, expressed in meters; hnew2 The depth of surface water after the inflow occurs, in meters; The road equivalent drainage reduction rate can be determined through calibration or empirical values. Vjtotal denoted as , where is the inflow volume of node j, in m³; m is the number of grid cells in the equivalent drainage area corresponding to node j. Acell This represents the area of ​​the surface grid, in m2. Qin The inflow rate is expressed in m³ / s. W The generalized width of the Thiessen polygon partition, in meters; S The slope for the Thiessen polygon partition; n This is the Manning roughness coefficient; DJ The net depth of water accumulation above the area of ​​the Thiessen polygon section, in meters; Aj This represents the area of ​​the Thiessen polygon partition.

[0028] Step 7: Calculate the two-dimensional surface water depth based on the overflow volume or the water reduction volume on the road in Step 6, and calculate the surface runoff process. The calculation formula is shown in the following formula (8): (8); In the formula, hnew3 To calculate the new grid water level considering the overflow or inflow of rainwater nodes at different time steps, The time step for the simulation is expressed in seconds (s). Q in The inflow rate to the node is expressed in milliseconds (m). 3 / s; Q out This refers to node overflow, in meters (m). 3 / s; W The generalized width of the Thiessen polygon partition, in meters; A cell The area of ​​the surface grid is in square meters (m²). 2 ; Z 2D The grid water level does not take into account the overflow or inflow of rainwater nodes.

[0029] Step 8: Based on the water volume flowing out of or into the pipe network in Step 6, the SWMM one-dimensional pipe network model is used to calculate the pipe network hydrodynamic process, obtain the water depth at the main pipe network nodes and the pipe network head and velocity information, and the calculation formula is shown in the following formula (9): (9); In the formula, x The distance is in meters (m). t Time, in seconds; A The cross-sectional area of ​​the flow path is expressed in m². 3 ; Q Flow rate, unit is m 3 / s; H The water head in the pipeline is expressed in meters (m). Z This refers to the elevation of the bottom of the pipe / channel, in meters (m). Y The depth of the pipe / channel is expressed in meters (m). S f The friction slope is g; g is the acceleration due to gravity, in m / s². 2 .

[0030] Step 9: Update the surface water depth and flow velocity calculated in Step 7, and update the water depth at the main pipeline nodes, pipeline head, and flow velocity calculated in Step 8. Step 10, let Repeat steps 5 through 9 until... The simulated rainfall and flood results for the study area are output. t To simulate time, To simulate the time step, To simulate the total duration.

[0031] Example 2 An ideal city is constructed as a case study. The study area of ​​this ideal city is 240m long and 284m wide. The cross-section consists of a 24m wide road in the middle and two 130m wide catchment areas on both sides. The vertical and horizontal slopes of the city area are 0.003 and 0.005, respectively. The road is 0.2m lower than the sides of the catchment area, and the slope from the road ridge to the sides is 0.02.

[0032] The storm drains are 0.4m x 0.7m in size, spaced 35m apart, with the main drainage pipes laid in the middle of the road. This ideal urban area's fine-grained pipe network includes 21 storm drain nodes, 1 drainage outlet, and 20 pipe segments; the main pipe network includes 7 storm drain nodes, 1 drainage outlet, and 7 pipe segments. The pipe network layout is as follows: Figure 2 Seven Thiessen polygon partitions were constructed based on the rainwater nodes of the main pipeline network. The simulation lasted for 2 hours.

[0033] The comparison of the calculation results of this embodiment and the fine pipe network coupling model in the discharge flow process is as follows: Figure 3 As shown, the calculated peak error is 9.38%, which is less than 10%, indicating that the simulation effect of this embodiment is good.

[0034] Example 3 This embodiment takes the area west of Longwangmiao River in Lubei District, Tangshan City as an example to calculate the rainfall runoff and drainage process under the fine pipe network in this area. Simultaneously, a generalized main pipe network is used to calculate the rainfall runoff and drainage process under this embodiment. On August 18, 2022, the maximum rainfall intensity in the study area was 91.2 mm / h, with a rainfall duration of 20 hours. Using this rainfall event as the rainfall condition for the model, the urban rainfall runoff and drainage process is simulated using a fine pipe network coupled model and the simulation method of this invention.

[0035] The surface grid in the study area has a resolution of 8m × 8m and contains 253,506 grid cells. Figure 4 As shown. The detailed pipe network model has 1378 rainwater nodes and 1388 rainwater pipes; the main pipe network has 166 rainwater nodes and 169 rainwater pipes, as shown. Figure 5 As shown. Based on the main pipeline network, Thiessen polygon partitions are established, and rainwater nodes and partitions are numbered to ensure a one-to-one correspondence, totaling 166 Thiessen polygon partitions. This embodiment does not consider urban waterways and sets 12 drainage outlets. Coupled simulation is performed using the measured rainfall from August 18, 2022, to simulate a 24-hour urban stormwater runoff process.

[0036] The final comparison of the calculation results of this embodiment and the fine pipe network coupling model in the discharge flow process is as follows: Figure 6 As shown, the calculated Nash efficiency coefficient is 0.85, indicating that the simulation method of the present invention is highly feasible.

Claims

1. A method for simulating urban rainwater flood processes by combining road equivalent drainage and trunk pipe network, characterized in that: Obtain rainfall, topography, images, and trunk pipe network data in the study area, and determine the rainwater nodes and pipe segment data in the trunk pipe network. Based on the acquired data, build a two-dimensional hydrodynamic model, a one-dimensional pipe network model, and divide the study area into Thiessen polygon partitions, and establish the coupling relationship between rainwater nodes, surface grids, and Thiessen polygon partitions; Calculate the rainfall and infiltration process in the study area to determine whether the rainwater node overflows. If overflow occurs, perform overflow calculation. If no overflow occurs, discharge the road rainwater in the Thiessen polygon partition corresponding to the rainwater node into the rainwater node, and update the data according to the calculation results until the set running time is reached, and output the simulated rain and flood results of the study area.

2. The urban rain and flood process simulation method combining road equivalent drainage and trunk pipe network according to claim 1 is characterized in that: The specific steps include: Step 1: Collect basic data on rainfall, topography, images, and trunk pipe networks in the study area, determine the location, boundary, and area of ​​the region, determine the location of rainwater nodes in the trunk pipe network, the bottom elevation and surface elevation of rainwater nodes, and determine the length and diameter of the trunk pipe section and the topological relationship between the pipe section and the rainwater node; Step 2: According to the topography of the study area, a GAST two-dimensional hydrodynamic model based on the network structure is constructed, and corresponding land use attributes are assigned to each surface grid; Step 3, divide the study area into Thiessen polygon partitions according to the locations of the rainwater nodes in the trunk pipe network in step 1, so that the Thiessen polygon partitions correspond to the rainwater nodes and the surface grids in the GAST two-dimensional hydrodynamic model respectively; Step 4: Based on the length and diameter of the main pipe segment and the topological relationship between the pipe segment and the rainwater node, a SWMM one-dimensional pipe network model is constructed, and a one-dimensional and two-dimensional coupling relationship is established according to the rainwater node information obtained in step 1 and the two-dimensional surface water dynamic model constructed in step 2, and a GAST-SWMM one-dimensional and two-dimensional coupling model is constructed; Step 5, let is the calculation time step of the GAST-SWMM one- and two-dimensional coupled model, and the GAST two-dimensional hydrodynamic model is used to calculate the rainfall and infiltration process in the study area; Step 6, determine whether overflow occurs at the rainwater node, and if overflow occurs, perform overflow calculation; If overflow does not occur, the road rainwater in the Thiessen polygon partition corresponding to the rainwater node will be discharged into the rainwater node, and the nonlinear reservoir will be used to correct the amount of water flowing into the rainwater node; Step 7, calculating the two-dimensional surface water depth according to the overflow water volume or the water reduction on the road in step 6, and calculating the surface overland flow process; Step 8: According to the amount of water flowing out of or into the pipe network in step 6, the SWMM one-dimensional pipe network model is used to calculate the pipe network hydrodynamic process, and obtain the water depth of the main pipe network node and the pipe network water head and flow rate information; Step 9, updating the surface water depth and flow velocity calculated in step 7, and updating the main pipeline network node water depth and pipeline network water head and flow velocity calculated in step 8; Step 10, let Repeat steps 5 to 9 until , output the simulated rain and flood results for the study area.

3. The urban rain and flood process simulation method combining road equivalent drainage and trunk pipe network according to claim 2 is characterized in that: The GAST two-dimensional hydrodynamic model in step 2 is calculated by solving the two-dimensional shallow water equation, as shown in the following formula: ； ； ； Where, t is time, unit is s; is a variable vector; is the water depth in m; q x and q y They are x and y Single-width flow in both directions, in m 2 / s; and They are x and y Flux vector in direction; g is the acceleration due to gravity, in m / s 2 ; u and v They are x and y Flow velocity in direction, in m / s; is the source term vector; is the rainfall infiltration source term; z b is the riverbed bottom elevation, in m; is Xie Cai coefficient, ,in n is the Manning coefficient.

4. The urban rain and flood process simulation method combining road equivalent drainage and trunk pipe network according to claim 2 is characterized in that: The land use attributes in step 2 include roads, buildings, green spaces and impervious areas.

5. The urban rain and flood process simulation method combining road equivalent drainage and trunk pipe network according to claim 2 is characterized in that: The rainfall and infiltration process in the study area in step 5 are calculated using the following formula: ； In the formula, R is the net rainfall rate in mm / h; i is the rainfall intensity, in mm / h; f is the soil infiltration rate, in mm / h; is the stable infiltration rate, in mm / h; f 0 is the initial infiltration rate, in mm / h; t is the time, in s; k d is the attenuation coefficient, in s -1 .

6. The urban rain and flood process simulation method combining road equivalent drainage and trunk pipe network according to claim 2 is characterized in that: In step 6, whether overflow occurs at the rainwater node is determined by comparing the water depth at the rainwater node with the surface water depth. Z 1D >Z 2D If the rainwater overflows from the pipe network to the ground surface, Z 1D < Z 2D is the inflow, that is, rainwater is discharged from the surface into the pipe network; Z 1D is the water depth of the rainwater node, in m; Z 2D is the surface grid water depth, in meters.

7. The urban rain and flood process simulation method combining road equivalent drainage and trunk pipe network according to claim 2 is characterized in that: The node overflow calculation formula in step 6 is as follows: ； In the formula, Q out is the node overflow, in m 3 / s; m1 is the hole flow coefficient, ranging from [0,1], and the value is determined according to the specific situation; A is the node area, in m 2 ; g is the acceleration due to gravity, in m / s 2 ; Z 2D is the surface grid water depth, in m; Z 1D is the water depth of the rainwater node, in m; The node inflow calculation formula in step 6 is as follows: ； ； In the formula, h old is the initial surface water depth, in m; h new1 It is the surface water depth before water enters the pipe after rainfall, in meters; h new2 is the surface water depth after the inflow occurs, in meters; is the road equivalent drainage reduction rate, which can be determined by calibration or empirical value; V jtotal is the inflow of node j, in m 3 ; m is the number of grids in the equivalent drainage area corresponding to node j; A cell is the surface grid area, in m 2 ; Q in is the inflow rate, in m 3 / s; W is the generalized width of the Thiessen polygon partition, in meters; S The slope of the Thiessen polygon partition; n is the Manning roughness coefficient; d j is the net water depth above the Thiessen polygon partition area, in meters; A j is the area of ​​the Thiessen polygon partition.

8. The urban rain and flood process simulation method combining road equivalent drainage and trunk pipe network according to claim 2 is characterized in that: The two-dimensional surface water depth is calculated in step 7 as shown in the following formula: ； In the formula, h new3 The new grid water level calculated to account for overflow or inflow flux at the rainwater node for the time step, is the simulation time step, in seconds; Q in is the node inflow, in m 3 / s; Q out is the node overflow, in m 3 / s; W is the generalized width of the Thiessen polygon partition, in meters; A cell is the surface grid area, in m 2 ; Z 2D It is the grid water level without considering the overflow or inflow flow of the rainwater node.

9. The urban rain and flood process simulation method combining road equivalent drainage and trunk pipe network according to claim 2 is characterized in that: The formula for calculating the pipe network hydrodynamic process in step 8 is as follows: ； In the formula, x is the distance in m; t is time, unit is s; A is the cross-sectional area of ​​the flow, in m 3 ; Q is the flow rate, in m 3 / s; H is the water head in the pipe, in m; Z is the invert elevation of the pipe, in m; Y is the water depth of the canal, in m; S f is the friction slope; g is the acceleration due to gravity, in m / s 2 .

Images