Urban fine pipe network drainage effect simulation method based on nonlinear reservoir method

Abstract

The invention discloses an urban fine pipe network drainage effect simulation method based on a nonlinear reservoir method, and the method comprises the steps: obtaining the rainfall, terrain, underlying surface and trunk pipe network data of a research region, building a two-dimensional hydrodynamic model and a one-dimensional pipe network model based on the obtained data, dividing a control region for each rainwater node, and carrying out the calculation of the control region. Establishing a coupling relationship between a ground surface grid in the control area and a corresponding rainwater node; calculating the rainfall and infiltration process of the research area to judge whether the rainwater nodes overflow or not, if overflow occurs, performing overflow calculation, if overflow does not occur, deducting a certain amount of water from each earth surface grid, counting the water amount, adding the water amount into the corresponding rainwater nodes respectively, and correcting the water amount by adopting a nonlinear reservoir method; and performing data updating according to the calculation result until the set operation time is reached, and outputting the final calculation result of the research area. The problem that the drainage capacity of the pipe network is difficult to generalize in the absence of fine pipe network data in the prior art is solved.

Description

Technical Field

[0001] This invention belongs to the technical field of urban water conservancy numerical simulation methods, specifically relating to a method for simulating the drainage effect of urban fine pipe network based on the nonlinear reservoir method. Background Technology

[0002] In recent years, with the continuous acceleration of urbanization in my country, the high concentration of population, industries, and infrastructure has led to significant changes in the underlying surface characteristics of cities. Furthermore, due to global climate change, extreme rainstorm events are becoming more frequent and intense. High-frequency and high-intensity rainfall has resulted in severe waterlogging on urban roads and in residential areas, widespread traffic congestion and even disruptions, and localized areas experiencing "sea-like" flooding. This not only disrupts the normal operation of cities but also poses a serious threat to the safety of residents' lives and property, as well as the safety of urban infrastructure.

[0003] As a crucial foundation for urban flooding models, drainage networks are often difficult to survey due to their underground location. Detailed network data, especially for residential areas, is frequently scarce, with only coarse data available. Therefore, in the absence of detailed network data, generalizing the drainage capacity of the network has become a major challenge in urban flooding simulation. Summary of the Invention

[0004] The purpose of this invention is to provide a method for simulating the drainage effect of urban fine-grained pipe networks based on the nonlinear reservoir method, which solves the problem in the prior art that it is difficult to generalize the drainage capacity of pipe networks when fine-grained pipe network data is lacking.

[0005] The technical solution adopted in this invention is a method for simulating the drainage effect of urban fine pipe network based on the nonlinear reservoir method. It acquires rainfall, topography, underlying surface and main pipe network data of the study area, constructs a two-dimensional hydrodynamic model and a one-dimensional pipe network model based on the acquired data, divides the control area for each rainwater node, and establishes the coupling relationship between the surface grid and the corresponding rainwater node within the control area. The calculation of rainfall and infiltration processes in the study area determines whether rainwater nodes overflow. If overflow occurs, overflow calculation is performed. If no overflow occurs, a certain amount of water is deducted from each surface grid. This water volume is then counted and added to the corresponding rainwater nodes. The nonlinear reservoir method is used to correct the water volume. The data is then updated based on the calculation results until the set running time is reached, and the final calculation results for the study area are output.

[0006] The invention is further characterized in that, Includes the following steps: Step 1: Collect data on rainfall, topography, underlying surface, and main pipeline network in the study area; determine the location and boundaries of the area; obtain the location, bottom elevation, and burial depth of the main pipeline network nodes; and determine the length and diameter of the main pipeline segments. Based on this, determine the topological relationship between the pipeline segments and the rainwater nodes. Step 2, according to the terrain of the study area, construct a two-dimensional surface water dynamic model based on the grid structure, and calculate the surface runoff by solving the two-dimensional shallow water equation; Step 3, based on the basic attributes and topological relations of the main pipe network, construct a SWMM one-dimensional pipe network model; Step 4, based on the node distribution of the two-dimensional surface water dynamic model and the SWMM one-dimensional pipe network model, define a control area for each rainwater node, and establish a "many-to-one" coupling relationship between all two-dimensional surface grids in each control area and the rainwater node corresponding to the control area, to construct a one-two-dimensional coupling model; Step 5, after the rainfall falls on the ground, the soil infiltration rate is deducted first to calculate the net rainfall; Step 6, based on the water depth of the rainwater node and the water depth of the surface grid, determine whether the rainwater node has overflow, if it has overflow, carry out overflow calculation; if it does not have overflow, deduct a certain amount of net rainfall in the surface grid, and calculate the total inflow water quantity of each control area and flow into the corresponding rainwater node; Step 7, use the nonlinear reservoir method to correct the pipe network confluence process to obtain the water quantity flowing out of the pipe network or flowing into the pipe network; Step 8, according to the overflow water quantity in step 6 or the reduced water quantity on the surface grid, update the surface water depth of the two-dimensional surface water dynamic model, and calculate the surface confluence process; Step 9, according to the water quantity flowing out of the pipe network or flowing into the pipe network in step 7, update the pipe network water quantity of the SWMM one-dimensional pipe network model, calculate the pipe network hydrodynamic process through the updated model, and obtain the node water depth, pipe network water head and flow velocity information of the main pipe network; Step 10, repeat steps 5-9 until the preset time is reached, and output the simulation rainstorm results of the study area.

[0007] The two-dimensional shallow water equation for calculating the surface runoff in step 2 is as follows: ; ; In the formula, t is the time, unit: s; q is the variable vector; h is the water depth, unit: m; q x and q y are the single-width flow rates in x and y directions, respectively, unit: m 2 / s; F and G are the flux vectors in x and y directions, respectively; g is the gravitational acceleration, unit: m / s 2 ;u and v are the flow velocities in x and y directions, respectively, with unit of m / s; S is the source term vector; R is the rainfall infiltration source term; z b is the riverbed bottom elevation, with unit of m; C f is the Chezy coefficient, C f =gn 2 / h 1 / 3 , where n is the Manning coefficient.

[0008] The calculation time step of the coupling model is determined based on the time step of the two-dimensional surface model simulation and the time step of the one-dimensional pipe network model simulation in step 4, as shown in the following formula, . In the formula, is the calculation time step of the coupling model, with unit of s; is the time step of the two-dimensional surface model simulation, with unit of s; is the time step of the one-dimensional pipe network model simulation, with unit of s.

[0009] The calculation formula of the net rainfall in step 5 is shown in the following formula: . In the formula, R is the net rainfall intensity, with unit of mm / h; i is the rainfall intensity, with unit of mm / h; f is the soil infiltration rate, with unit of mm / h; is the stable infiltration rate, with unit of mm / h; f 0 is the initial infiltration rate, with unit of mm / h; t is the time, with unit of s; k d is the attenuation coefficient, with unit of s -1 .

[0010] When the water depth of the rainwater node is greater than the water depth of the surface grid, it is determined as overflow, and the expression of the overflow calculation is shown in the following formula in step 6: . In the formula, Q out is the node overflow flow, with unit of m 3 / s; m1 is the orifice flow coefficient, ranging from [0, 1], and is valued according to specific conditions; A is the node area, with unit of m 2 ; g is the gravitational acceleration, with unit of m / s 2 ; Z2D is the surface grid water depth, unit: m; Z 1D is the rainwater node water depth, unit: m; When the rainwater node water depth is less than the surface grid water depth, it is judged as inflow, and the surface grid rainwater reduction and node inflow are calculated by the following formula: ; In the formula, h old is the initial surface water depth, unit: m; h new1 is the surface water depth when the water has not entered the pipeline after the rainfall occurs, unit: m; h new2 is the surface water depth after the inflow occurs, unit: m; is the equivalent drainage reduction rate of the road, unit: mm / h, which can be determined by rating or empirical value; V jtotal is the inflow of node j, unit: m 3 ; m is the number of grids of the equivalent drainage area corresponding to node j; A cell is the surface grid area, unit: m 2 .

[0011] In step 7, the correction is made by constructing a virtual reservoir for each main rainwater node, so that the surface reduced rainwater first enters the virtual reservoir, and then slowly flows into the rainwater node from the virtual reservoir. The correction formula is as follows: ; In the formula, V old is the water storage before inflow, unit: m³; h j is the water depth of the virtual reservoir after entering the rainwater, unit: m 3 / s; Q in is the inflow, unit: m 3 / s; W j is the generalized width of the Thiessen polygon partition, unit: m; S j is the slope of the Thiessen polygon partition; n j is the Manning roughness coefficient; h min is the water storage depth, unit: m; Q min is the flow threshold, unit: m³ / s.

[0012] The calculation formula of the surface water depth in step 8 is as follows: ; In the formula, Z 2Dnew is the new grid water level considering the calculation of rainwater node overflow or inflow flux at the time step, and the unit is m.

[0013] The expression for calculating the pipe network hydrodynamic process in step 9 is as follows: ; In the formula, x is the distance, and the unit is m; t is the time, and the unit is s; A is the flow area, and the unit is m 3 ; Q is the flow, and the unit is m 3 / s; H is the water head in the pipe, and the unit is m; Z is the bottom elevation in the pipe, and the unit is m; Y is the water depth in the pipe, and the unit is m; S f is the friction term; g is the acceleration of gravity, and the unit is m / s 2 .

[0014] The preset time in step 10 is , until , the simulation rain flood results of the research area are output, t is the current simulation time, is the simulation time step, is the total simulation time.

[0015] The beneficial effects of the present application are: The urban fine pipe network drainage effect simulation method based on the nonlinear reservoir method of the present application deducts a certain amount of rainwater from multiple grids around the nodes of the main pipe network when the water exchange occurs between the one-dimensional pipe network and the two-dimensional ground surface, adds the deducted water to the nodes, and modifies the inflow process of the nodes. The convergence process of rainwater in the pipe network is closer to the actual situation, the rain flood process calculation of the urban fine pipe network data missing area can be realized, the GPU parallel is used for accelerated calculation, the simulation precision and simulation calculation efficiency of the pipe network drainage process in the urban fine pipe network data missing area are improved, and an efficient and reliable simulation method support is provided for the urban flood control and drainage decision. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is the process schematic diagram of the urban fine pipe network drainage effect simulation method based on the nonlinear reservoir method of the present application.

[0017] Figure 2 is the pipe network layout diagram in embodiment 4 of the present application.

[0018] Figure 3is a comparison chart of simulation results and fine pipe network simulation results in embodiment 4 of the present application.

[0019] Figure 4 is a topographic map in embodiment 5 of the present application.

[0020] Figure 5 is a pipe network layout map in embodiment 5 of the present application.

[0021] Figure 6 is a comparison chart of simulation results and fine pipe network simulation results in embodiment 5 of the present application.

[0022] Figure 7 is a topographic map in embodiment 6 of the present application.

[0023] Figure 8 is a pipe network layout map in embodiment 6 of the present application.

[0024] Figure 9 is a comparison chart of simulation results and fine pipe network simulation results in embodiment 6 of the present application. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0026] Embodiment 1 The urban fine pipe network drainage effect simulation method based on the nonlinear reservoir method of the present application, by obtaining rainfall, terrain, underlying surface and main pipe network data of a research area, constructing a two-dimensional water power model and a one-dimensional pipe network model based on the obtained data, dividing a control area for each rainwater node, establishing a coupling relationship between a ground grid in the control area and a corresponding rainwater node; calculating rainfall and infiltration process of the research area to determine whether rainwater nodes overflow, if overflow occurs, performing overflow calculation, if no overflow occurs, deducting a certain amount of water in each ground grid, counting the amount of water and adding it to the corresponding rainwater node respectively, and correcting it by using the nonlinear reservoir method, then updating data according to the calculation results until the set running time is reached, and outputting the final calculation results of the research area.

[0027] Specifically, as shown in Figure 1 the method comprises the following steps: Step 1, collect rainfall, terrain, underlying surface, main pipe network data in the study area, determine the area location and boundary, obtain the main pipe network node position, bottom elevation and burial depth, the length of the main pipe section, the pipe diameter attribute, and determine the topological relationship between the pipe section and the rainwater node on this basis; Step 2, according to the terrain of the study area, a two-dimensional surface water dynamic model based on grid structure is constructed, and surface runoff calculation is carried out by solving two-dimensional shallow water equation; Step 3, based on the basic attributes and topological relationship of the main pipe network, a SWMM one-dimensional pipe network model is constructed; Step 4, based on the node distribution of the two-dimensional surface water dynamic model and the SWMM one-dimensional pipe network model, a control area is drawn for each rainwater node, a "many-to-one" coupling relationship is established between all two-dimensional surface grids in each control area and the rainwater node corresponding to the control area, and a one-two-dimensional coupled model is constructed; Step 5, after the rainfall falls on the ground, the soil infiltration rate is deducted first to calculate the net rainfall; Step 6, based on the water depth of the rainwater node and the water depth of the surface grid, it is judged whether the rainwater node overflows, if it overflows, the overflow calculation is carried out, if it does not overflow, a certain net rainfall is deducted in the surface grid, the total inflow water quantity of each control area is counted and is collected into the corresponding rainwater node; Step 7, the nonlinear reservoir method is used to correct the pipe network confluence process to obtain the water quantity flowing out of the pipe network or flowing into the pipe network; Step 8, according to the overflow water quantity in step 6 or the water quantity reduced on the surface grid, the surface water depth of the two-dimensional surface water dynamic model is updated, and the surface confluence process is calculated; Step 9, according to the water quantity flowing out of the pipe network or flowing into the pipe network in step 7, the pipe network water quantity of the SWMM one-dimensional pipe network model is updated, the pipe network water dynamic process is calculated through the updated model, and the node water depth, pipe network water head and flow velocity information of the main pipe network are obtained; Step 10, repeat steps 5 to 9 until the preset time is reached, and output the simulation rain flood results of the study area; Specifically, the preset time is , until , the simulation rain flood results of the study area are output, t is the current simulation time, is the simulation time step, is the total simulation time.

[0028] Embodiment 2 In the above embodiment 1, the two-dimensional shallow water equation for surface runoff calculation in step 2 of the urban fine pipe network drainage effect simulation method based on the nonlinear reservoir method is specifically as shown in the following formula (1) and formula (2): (1); (2) ; wherein, t is time, unit: s; q is variable vector; h is water depth, unit: m; q x and q y are single-width flow in x and y directions respectively, unit: m 2 / s; F and G are flux vectors in x and y directions respectively; g is gravity acceleration, unit: m / s 2 ; u and v are flow velocities in x and y directions respectively, unit: m / s; S is source term vector; R is rainfall infiltration source term; z b is riverbed bottom elevation, unit: m; C f is Chezy coefficient, C f =gn 2 / h 1 / 3 , wherein n is Manning coefficient.

[0029] Further, the two-dimensional hydrodynamic model of the application adopts finite volume method of Godunov format to perform numerical discretization on two-dimensional shallow water equation, and the mass and momentum flux of water on the interface of control unit is calculated by HLLC approximate Riemann solver.

[0030] Then, the corresponding land use attribute is given to each grid according to different underlying surface types.

[0031] Further, the calculation time step of the coupling model is determined based on the simulation time step of the two-dimensional ground surface model and the simulation time step of the one-dimensional pipe network model in step 4, as shown in the following formula (3) : (3) ; wherein, is the calculation time step of the coupling model, unit: s; is the simulation time step of the two-dimensional ground surface model, unit: s; is the simulation time step of the one-dimensional pipe network model, unit: s.

[0032] Embodiment 3 Based on the above embodiment 2, the calculation formula of net rainfall in step 5 of the urban fine pipe network drainage effect simulation method based on the nonlinear reservoir method of the application is shown in the following formula (4) : (4); wherein, R is the net rainfall intensity, unit mm / h; i is the rainfall intensity, unit mm / h; f is the soil infiltration rate, unit mm / h; is the stable infiltration rate, unit mm / h; f 0 is the initial infiltration rate, unit mm / h; t is time, unit s; k d is the attenuation coefficient, unit s -1 .

[0033] Further, the judgment of the water depth of the rainwater node and the water depth of the ground surface in step 6 is as follows Z 1D is the water depth of the rainwater node, unit m; the following Z 2D is the water depth of the ground surface grid, unit m. If Z 1D >Z 2D is judged as overflow, that is, rainwater overflows from the pipe network to the ground surface, and overflow calculation is performed, and the expression of the overflow calculation is shown in the following formula (5): (5); wherein, Q out is the node overflow flow, unit m 3 / s; m1 is the orifice flow coefficient, range [0, 1], which is valued according to specific conditions; A is the node area, unit m 2 ; g is the gravitational acceleration, unit m / s 2 ; Z 2D is the water depth of the ground surface grid, unit m; Z 1D is the water depth of the rainwater node, unit m; If Z 1D < Z 2D is inflow, that is, rainwater enters the pipe network from the ground surface, and a certain net rainfall is reduced in the grid of the ground surface model, the total water quantity entering the pipe network of each control area is counted and added to the corresponding pipe network node, and the calculation formula is shown in the following formula (6): (6); wherein, h old is the initial water depth of the ground surface, unit m; hnew1 is the surface water depth after the rainfall occurs but before the water enters the pipe, with the unit of m; h new2 is the surface water depth after the inflow occurs, with the unit of m; is the equivalent drainage reduction rate of the road, with the unit of mm / h, which can be determined by rating or empirical value; V jtotal is the inflow of node j, with the unit of m 3 ; m is the number of grids of the equivalent drainage area corresponding to node j; A cell is the surface grid area, with the unit of m 2 .

[0034] Further, the correction in step 7 is to construct a virtual reservoir for each main rainwater node, and the rainwater reduced from the surface after the inflow occurs first enters the virtual reservoir from the surface, and then slowly flows into the rainwater node from the virtual reservoir. In addition, since the missing pipe network has a certain water storage space, when considering the reservoir water storage depth and flow threshold, the pipe network inflow exceeds the corresponding threshold only when the inflow occurs, and the calculation formula is shown in the following formula (7): (7); In the formula, V old is the water storage capacity before the inflow of the reservoir, with the unit of m³; h j is the water depth of the virtual reservoir after the rainwater enters, with the unit of m 3 / s; Q in is the inflow, with the unit of m 3 / s; W j is the generalized width of the Thiessen polygon partition, with the unit of m; S j is the slope of the Thiessen polygon partition; n j is the Manning roughness coefficient; h min is the water storage depth, with the unit of m; Q min is the flow threshold, with the unit of m³ / s.

[0035] Further, the calculation formula of the surface water depth in step 8 is shown in the following formula (8): (8); In the formula, Z 2Dnew is the new grid water level considering the time step of the rainwater node overflow or inflow flux calculation, with the unit of m.

[0036] Further, the expression for calculating the water dynamic process of the pipe network in step 9 is shown in the following formula (9): (9); wherein, x is the distance, in m; t is the time, in s; A is the flow area, in m 3 ; Q is the flow, in m 3 / s; H is the water head in the pipe, in m; Z is the bottom elevation in the pipe, in m; Y is the water depth in the pipe, in m; S f is the friction term; g is the acceleration of gravity, in m / s 2 .

[0037] Example 4 An ideal city example is constructed, and the ideal city research area is 240 m long and 284 m wide. The cross section is composed of a 24 m wide road in the middle and two 130 m wide catchment areas on the sides. The vertical and horizontal slopes of the city area are 0.003 and 0.005, respectively. The road is 0.2 m lower than the two sides of the catchment area, and the slope from the road ridge to the road edge on both sides is 0.02.

[0038] The size of the rainwater well in the designed pipe network is 0.4 m x 0.7 m, the rainwater well interval is 35 m, and the main drainage pipe is laid in the middle of the road. The fine pipe network of the ideal city area includes 63 rainwater nodes, 119 pipe sections and 1 outlet; the main pipe network includes 7 rainwater nodes, 7 pipe sections and 1 outlet, and the pipe network layout is as shown in Figure 2 . The 60 mm / h rainfall is selected to simulate the rainwater process of the ideal city, and the simulation time is 2 h.

[0039] The outlet flow process of the coupling model of the fine pipe network in this example is compared as shown in Figure 3 . The calculated Nash efficiency coefficient is 0.978, and the peak relative error is 6.88%, which is less than 10%, indicating that the simulation effect of this example is good.

[0040] Example 5 This example takes the Glasgow city area in the United Kingdom as an example, and designs a set of fine pipe network and a set of main pipe network for calculating and comparing the rainfall runoff and pipe network drainage process of a small city area.

[0041] The surface grid accuracy of the research area is 1 m x 1 m, and the area is 1000 m x 400 m, as shown in Figure 4As shown. The detailed pipe network model has 208 rainwater nodes, 208 rainwater pipes, and 2 outlets; the main pipe network has 36 rainwater nodes, 36 rainwater pipes, and 2 outlets, as shown. Figure 5 As shown. A simulated urban stormwater process was conducted using a rainfall rate of 60 mm / h for 2 hours.

[0042] Finally, the comparison of the total discharge flow rate process calculation results between this embodiment and the fine pipe network coupling model is as follows: Figure 6 As shown, the calculated Nash efficiency coefficient is 0.895, and the calculated peak relative error is 8.68%, which is less than 10%, indicating that the simulation effect of this embodiment is good.

[0043] Example 6 In this embodiment, the southwest part of Tianfu Heyuan in Fengxi New City, Xixian New Area, Xi'an City is used as an example to calculate and compare the rainfall runoff and pipe network drainage process at the community scale.

[0044] The surface grid accuracy of the study area is 1m×1m, and the area is 6.02 hm². 2 ,like Figure 7 As shown. The detailed pipe network model has 107 rainwater nodes, 107 rainwater pipes, and 2 outlets; the main pipe network has 24 rainwater nodes, 24 rainwater pipes, and 2 outlets, as shown. Figure 8 As shown. A simulated urban stormwater process was conducted using a rainfall rate of 60 mm / h for 2 hours.

[0045] Finally, the comparison of the total discharge flow rate process calculation results between this embodiment and the fine pipe network coupling model is as follows: Figure 9 As shown, the calculated Nash efficiency coefficient is 0.873, and the calculated peak relative error is 3.73%, which is less than 10%, indicating that the simulation effect of this embodiment is good.

[0046] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0047] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for simulating the drainage effect of urban fine-grained pipe networks based on the nonlinear reservoir method, characterized in that, Data on rainfall, topography, underlying surface and main pipe network in the study area were acquired. Based on the acquired data, a two-dimensional hydrodynamic model and a one-dimensional pipe network model were constructed. Control areas were divided for each rainwater node, and the coupling relationship between the surface grid and the corresponding rainwater node within the control area was established. The calculation of rainfall and infiltration processes in the study area determines whether rainwater nodes overflow. If overflow occurs, overflow calculation is performed. If no overflow occurs, a certain amount of water is deducted from each surface grid. This water volume is then counted and added to the corresponding rainwater nodes. The nonlinear reservoir method is used to correct the water volume. The data is then updated based on the calculation results until the set running time is reached, and the final calculation results for the study area are output.

2. The method for simulating urban fine-scale pipe network drainage effects based on the nonlinear reservoir method according to claim 1, characterized in that, Includes the following steps: Step 1: Collect data on rainfall, topography, underlying surface, and main pipeline network in the study area; determine the location and boundaries of the area; obtain the location, bottom elevation, and burial depth of the main pipeline network nodes; and determine the length and diameter of the main pipeline segments. Based on this, determine the topological relationship between the pipeline segments and the rainwater nodes. Step 2: Based on the topography of the study area, construct a two-dimensional surface hydrodynamic model with a grid structure, and calculate surface runoff generation and confluence by solving the two-dimensional shallow water equation; Step 3: Based on the basic attributes and topological relationships of the main pipeline network, construct a one-dimensional SWMM pipeline network model; Step 4: Based on the node distribution of the two-dimensional surface hydrodynamic model and the SWMM one-dimensional pipe network model, a control area is defined for each rainwater node. A "many-to-one" coupling relationship is established between all two-dimensional surface grids in each control area and the corresponding rainwater nodes in that control area to construct a one-dimensional coupling model. Step 5: After the rainfall reaches the ground, first deduct the soil infiltration rate to calculate the net rainfall. Step 6: Determine whether the rainwater node has overflowed based on the water depth of the rainwater node and the water depth of the surface grid. If overflow has occurred, perform overflow calculation. If no overflow occurs, a certain amount of net rainfall is deducted from the surface grid, and the total inflow of water in each control area is counted and collected into the corresponding rainwater node. Step 7: The nonlinear reservoir method is used to correct the flow process of the pipe network to obtain the amount of water flowing out of or into the pipe network. Step 8: Update the surface water depth of the two-dimensional surface hydrodynamic model based on the overflow volume or the water reduction volume on the surface grid in Step 6, and calculate the surface runoff process. Step 9: Based on the water volume flowing out of or into the pipe network in Step 7, update the pipe network water volume of the SWMM one-dimensional pipe network model, calculate the pipe network hydrodynamic process through the updated model, and obtain the water depth, pipe network head and flow velocity information of the main pipe network nodes. Step 10: Repeat steps 5 through 9 until the preset time is reached, and output the simulated rainfall and flood results for the study area.

3. The method for simulating urban fine-scale pipe network drainage effects based on the nonlinear reservoir method according to claim 2, characterized in that, In step 2, the specific formula for solving the two-dimensional shallow water equation to calculate surface runoff generation and confluence is as follows: ； ； In the formula, t Time, in seconds; q For variable vectors; h Water depth, in meters (m). q x and q y These represent the unit width flow rates in the x and y directions, respectively, in meters (m). 2 / s; F and G These are the flux vectors in the x and y directions, respectively; g This is the acceleration due to gravity, measured in m / s². 2 ; u and v These are the flow velocities in the x and y directions, respectively, in m / s; S Source term vector; R For rainfall infiltration source items; z b This is the elevation of the riverbed bottom, in meters (m). C f For the Xie Cai coefficient, C f =gn 2 / h 1 / 3 , where n is the Manning coefficient.

4. The method for simulating urban fine-scale pipe network drainage effects based on the nonlinear reservoir method according to claim 2, characterized in that, In step 4, the computation time step of the coupled model is determined based on the simulation time step of the two-dimensional surface model and the simulation time step of the one-dimensional pipeline network model, as shown in the following formula. ； In the formula, The time step is calculated for the coupled model, in seconds. The time step for the two-dimensional surface model simulation is expressed in seconds. This represents the time step in the one-dimensional pipeline network model simulation, measured in seconds (s).

5. The method for simulating urban fine-scale pipe network drainage effects based on the nonlinear reservoir method according to claim 2, characterized in that, The formula for calculating net rainfall in step 5 is as follows: ； In the formula, R Net rainfall intensity, expressed 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 .

6. The method for simulating urban fine-scale pipe network drainage effects based on the nonlinear reservoir method according to claim 2, characterized in that, In step 6, when the water depth at the rainwater node is greater than the water depth at the surface grid, it is determined to be an overflow. The expression for overflow calculation 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). When the water depth at a rainwater node is less than the water depth at the surface grid, it is considered an inflow. The rainwater reduction at the surface grid and the inflow at the node are calculated using the following formula: ； 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 equivalent drainage reduction rate for roads, expressed in mm / h, 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. 2 .

7. The method for simulating urban fine-scale pipe network drainage effects based on the nonlinear reservoir method according to claim 2, characterized in that, In step 7, the correction involves constructing a virtual reservoir for each main rainwater node, so that the rainwater reduced from the surface first enters the virtual reservoir and then slowly flows from the virtual reservoir into the rainwater node. The correction formula is as follows: ； In the formula, V old This represents the water volume stored in the reservoir before the inflow, in m³. h j The water depth of the virtual reservoir after entering the rainwater, in meters. 3 / s; Q in Inflow rate, in meters (m³) 3 / s; W j The generalized width of the Thiessen polygon partition, in meters; S j The slope for the Thiessen polygon partition; n j This is the Manning roughness coefficient; h min This refers to the water storage depth, expressed in meters (m). Q min This represents the flow rate threshold, measured in m³ / s.

8. The method for simulating the urban fine-scale pipe network drainage effect based on the nonlinear reservoir method according to claim 2, characterized in that, The formula for calculating the surface water depth in step 8 is as follows: ； In the formula, Z 2Dnew The new grid water level is calculated to take into account the overflow or inflow of rainwater nodes at different time steps, and the unit is meters.

9. The method for simulating urban fine-scale pipe network drainage effects based on the nonlinear reservoir method according to claim 2, characterized in that, The expression for calculating the hydrodynamic process of the pipeline network in step 9 is as follows: ； 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 This is the friction term; g is the acceleration due to gravity, in m / s². 2 .

10. The method for simulating urban fine-scale pipe network drainage effects based on the nonlinear reservoir method according to claim 2, characterized in that, The preset time in step 10 is... ,until Output the simulated rainfall and flood results for the study area, where t is the current simulation time. To simulate the time step, To simulate the total duration.

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