Urban rainwater pipe network system reconstruction optimization method

Abstract

This invention discloses a method for optimizing and upgrading urban stormwater drainage systems. The method includes establishing a model input database for the area to be upgraded; establishing a two-dimensional surface hydrodynamic model and a one-dimensional stormwater drainage network hydraulic model; constructing a bidirectional coupled exchange model to simulate the surface runoff confluence and underground drainage transport process; identifying weak links in the system; and implementing drainage zoning optimization, pipe diameter adjustment, and the addition of drainage channels or outlets to address issues such as excessively long drainage paths, excessively large zoning areas, insufficient local discharge outlets, and insufficient pipe diameter capacity. Based on this, multiple low-impact development (LID) facility deployment schemes are constructed and comprehensively evaluated to select the optimal urban stormwater drainage system upgrade scheme. This method can simultaneously identify the operational status of the underground stormwater drainage network and the response to surface water accumulation, improving the accuracy of identifying the urban flooding formation process and key weak links. By considering the optimized system and the deployment of LID facilities in a unified manner, it achieves simultaneous optimization between improving end-of-pipe discharge capacity, reducing emissions at the source, and regulating the process.

Description

Technical Field

[0001] This invention relates to the field of urban flood control optimization and renovation technology, specifically to a method for optimizing and renovating urban stormwater drainage systems. Background Technology

[0002] With the acceleration of urbanization and the frequent occurrence of extreme rainfall events, the impermeable surface area in cities continues to increase, the surface runoff velocity accelerates, and the confluence time shortens. This places an increasing burden on urban stormwater drainage systems, making urban flooding a more prominent problem. As a crucial component of the urban drainage and flood control system, the stormwater drainage network's drainage capacity directly affects road traffic, the safety of residents' lives and property, and the operational safety of urban infrastructure.

[0003] In existing technologies, the analysis and renovation of urban stormwater systems typically employ one-dimensional stormwater network models to simulate and analyze node overflows, pipe overload, and system discharge capacity. Alternatively, two-dimensional surface hydrodynamic models are used to calculate the extent and depth of surface water accumulation. Some studies also use a coupling method of one-dimensional underground pipe networks and two-dimensional surface runoff to simulate urban stormwater processes. Meanwhile, in terms of system renovation, common measures include optimizing pipe network layout, adjusting pipe diameters, adding drainage channels, and implementing low-impact development facilities such as permeable paving, sunken green spaces, rain gardens, and green roofs.

[0004] However, existing technologies still have the following shortcomings: First, existing stormwater pipe network renovations often focus on expanding local pipe sections or improving single nodes, lacking a systematic analysis of the coupling relationship between drainage zones, discharge paths, node load distribution, and surface water accumulation response, making it difficult to effectively solve the systemic waterlogging problem in complex built-up areas; Second, stormwater pipe network renovations and low-impact development facility deployments are mostly designed and evaluated separately, lacking a unified collaborative optimization framework, which easily leads to a disconnect between source reduction and end-of-pipe emissions; Third, existing scheme comparisons often focus on single indicators, such as node overload rate, water accumulation area, or project investment, lacking a comprehensive evaluation method that takes into account water volume control, economic costs, and environmental benefits, which is not conducive to forming a renovation scheme with optimal comprehensive benefits. Summary of the Invention

[0005] The purpose of this invention is to provide a method for the renovation and optimization of urban stormwater pipe network systems. This method can simultaneously identify the operating status of underground stormwater pipe networks and the response of surface water accumulation, thereby improving the accuracy of identifying the formation process and key weak links of urban flooding.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a method for upgrading and optimizing urban stormwater drainage network systems, comprising the following steps:

[0007] Step 1: Establish a model input database for the area to be modified, and unify the data coordinates, resolution, and calculation time step; Step 2: Based on the model input database, construct a two-dimensional hydrodynamic model of the land surface and a one-dimensional hydraulic model of the stormwater pipe network, respectively. Step 3: Couple the two-dimensional surface hydrodynamic model with the one-dimensional stormwater pipe network hydraulic model to construct a two-way coupled exchange model and conduct current working condition simulation. Step 4: Identify the parts of the pipeline system that need to be modified based on the simulation results of the current working conditions, and implement systematic modification and optimization.

[0008] The invention is further characterized by: The model input database includes topographic elevation data, land use type data, design rainfall data, and existing stormwater drainage network data; Topographic elevation data were obtained from CAD measured elevation points in the study area and then interpolated using ArcGIS to generate a digital elevation model (DEM) of a specified resolution. Land use type data includes four types of underlying surfaces: buildings, green spaces, roads, and plazas. Corresponding infiltration rate parameters and Manning roughness parameters are assigned to different underlying surface types. The design rainfall data is based on the storm intensity formula of the area to be transformed, and the design rainfall process lines with different return periods are generated by combining the Chicago rainfall pattern method. The current stormwater pipe network data includes the spatial distribution and attribute parameters of stormwater pipe sections, inspection wells, and discharge outlets, as well as the division range and confluence relationship of the current drainage zones.

[0009] The two-dimensional surface hydrodynamic model is a two-dimensional surface runoff model based on shallow water equations. The surface computational domain is established based on digital elevation model and land use type data to simulate the generation, confluence and water accumulation process of surface runoff. The one-dimensional stormwater pipe network hydraulic model is a one-dimensional pipe network hydraulic model based on the Saint-Venant equation. It is solved using the dynamic wave method and established based on the current stormwater pipe network data. It is used to simulate the water flow movement in the pipe, the nodal head, and the overload state of the pipe section.

[0010] The bidirectional coupled exchange model uses inspection wells as the water exchange interface. It synchronously updates the surface water level and the water level of the pipe network nodes in each calculation time step. It determines the direction and flow rate of water exchange based on the head difference between the surface water level and the water level of the pipe network nodes, realizing real-time joint calculation of surface runoff and underground pipe network drainage. It outputs node overload rate, pipe section overload rate, surface water depth, water accumulation area and total system drainage indicators through current working condition simulation.

[0011] The renovation and optimization include: re-dividing drainage zones in areas with excessively large catchment areas and excessively long drainage paths, and shortening drainage paths; adjusting the pipe diameter of pipe sections with insufficient water conveyance capacity according to design flow rate, flow velocity and fullness requirements; and adding discharge channels or discharge outlets in drainage bottleneck areas to improve the overall drainage capacity and connectivity of the system.

[0012] The pipe diameter adjustment shall comply with the following requirements: the design flow velocity inside the pipe shall be controlled between 0.6m / s and 3.0m / s; the design filling degree for gravity flow rainwater pipes shall not exceed 0.7 when the pipe diameter is ≤300mm, not exceed 0.75 when the pipe diameter is 300mm-600mm, and not exceed 0.8 when the pipe diameter is >600mm; the added discharge channel shall be in the form of a culvert or an open channel, the discharge outlet shall be set in the nearest water body, and the discharge capacity shall match the design drainage flow of the area.

[0013] Different return periods include 1-year, 3-year, 5-year, 10-year and 20-year return periods, and the peak rainfall coefficient of the Chicago rainfall pattern method is 0.3-0.5.

[0014] It also includes constructing multiple low-impact development facility combination layout schemes, coupling each scheme with the renovated pipe network system for simulation, establishing a comprehensive evaluation system from three dimensions: water volume regulation benefits, economic costs, and environmental benefits, and using a multi-index decision-making method to score and rank each scheme, and selecting the urban stormwater pipe network system renovation scheme with the best comprehensive benefits.

[0015] Low impact development facilities include at least two of the following: permeable pavement, green roofs, bioretention ponds, rain gardens, and grassed swales.

[0016] Multi-indicator decision-making methods employ either the analytic hierarchy process (AHP) or the entropy weight method.

[0017] The beneficial effects of this invention are: This invention constructs a two-dimensional surface-one-dimensional underground coupled model, which can simultaneously identify the operational status of underground stormwater pipe networks and the response of surface water accumulation, thereby improving the accuracy of identifying the formation process and key weak links of urban flooding. By considering drainage zoning optimization, pipe diameter adjustment, new discharge channels and the deployment of low-impact development facilities in a unified manner, it can achieve synergistic optimization between improving end-of-pipe discharge capacity and source emission reduction and process regulation. By establishing a comprehensive evaluation framework, it can meet drainage safety objectives while taking into account economic and environmental benefits. Attached Figure Description

[0018] Figure 1 This is a diagram of the rainwater pipe network system before the modification in Embodiment 1 of the present invention; Figure 2 This is a diagram showing the overload situation of the pipeline nodes before the modification in Embodiment 1 of the present invention; Figure 3 This is a diagram showing the overload situation of the pipeline section before the modification in Embodiment 1 of the present invention; Figure 4 This is a diagram of the modified rainwater pipe network system according to Embodiment 1 of the present invention; Figure 5 This is a diagram showing the overload situation of pipeline nodes and pipe sections after the modification in Embodiment 1 of the present invention. Detailed Implementation

[0019] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0020] Example 1 The urban stormwater drainage network system renovation and optimization method provided in this embodiment includes the following steps: Step 1: Establish a model input database for the area to be modified, and unify the data coordinates, resolution, and calculation time step; The model input database includes topographic elevation data, land use type data, design rainfall data, and existing stormwater drainage network data. The topographic elevation data uses CAD-measured elevation points in the study area, which are then interpolated using ArcGIS to generate a digital elevation model (DEM) of a specified resolution. The land use type data includes four types of underlying surfaces: buildings, green spaces, roads, and plazas, with corresponding infiltration rate and Manning roughness parameters assigned according to different underlying surface types. The design rainfall data uses the storm intensity formula officially released by the city where the area to be renovated is located, combined with the Chicago rainfall pattern method to generate design rainfall process lines with different return periods. The peak rainfall coefficient is 0.3-0.5, and the return periods include 1-year, 3-year, 5-year, 10-year, and 20-year return periods. The existing stormwater drainage network data includes the spatial distribution and attribute parameters of stormwater pipe sections, manholes, and outlets, as well as the division range and confluence relationship of the existing drainage zones.

[0021] Step 2: Based on the model input database, construct a two-dimensional hydrodynamic model of the land surface and a one-dimensional hydraulic model of the stormwater pipe network, respectively. Step 3: Couple the two-dimensional surface hydrodynamic model with the one-dimensional stormwater pipe network hydraulic model to construct a two-way coupled exchange model, and use design rainfall driven models with different return periods to conduct current working condition simulation. Step 4: Identify the weak links in the pipeline network system based on the simulation results of the current working conditions, and implement systematic transformation and optimization.

[0022] Example 2 Based on Example 1, the urban stormwater pipe network system renovation and optimization method provided in this example includes step 2; The two-dimensional hydrodynamic model of the surface is a two-dimensional surface runoff model based on shallow water equations. The surface computational domain is established based on the digital elevation model (DEM) and land use type data. The governing equations include the continuity equation and the momentum equation, which are used to simulate the generation, confluence and water accumulation process of surface runoff. The continuity equation is formula (1): (1) x The equation for directional momentum is formula (2): (2) yThe equation for directional momentum is formula (3): (3) In the formula, h This refers to the depth of surface water. u , v They are respectively x , y directional velocity component; g It is the acceleration due to gravity; r Rainfall intensity; f This refers to the amount of infiltration. q e This refers to the exchange flow between the ground surface and the pipeline network. A To calculate the area of ​​a unit; S 0x , S 0y They are respectively x , y Directional surface slope; S fx , S fy They are respectively x , y Directional friction barrier.

[0023] The one-dimensional stormwater pipe network hydraulic model is a one-dimensional pipe network hydraulic model based on the Saint-Venant equation. It is solved using the dynamic wave method and established based on the current stormwater pipe network data. It is used to simulate the water flow motion in the pipe, the nodal head and the overload state of the pipe section. The governing equations include the continuity equation and the momentum equation. The continuity equation is formula (4): (4) The momentum equation is formula (5): (5) In the formula, A p This refers to the cross-sectional area of ​​the pipeline through which water flows. Q The flow rate within the pipe; q i It is a lateral inflow along the path; H For water head; S x For frictional gradient; S 0 represents the slope at the bottom of the pipe.

[0024] Example 3 Based on Example 2, the urban stormwater pipe network system renovation and optimization method provided in this example uses the inspection well as the water exchange interface in step 3. The surface water level and the pipe network node water level are updated synchronously in each calculation time step. The water exchange direction and exchange flow rate are determined according to the head difference between the surface water level and the pipe network node water level, so as to realize the real-time joint calculation of surface runoff and underground pipe network drainage. The node exchange flow rate is calculated using formula (6): (6) In the formula, q v Exchange traffic between nodes; C d For flow coefficient; A 0 represents the effective flow area of ​​the node; g It is the acceleration due to gravity; The difference in water head between surface points and nodes; This is a sign function used to characterize the direction of the exchange; The symbolic function can be represented as: (7) when H 1 (Surface water level) > H At point 2 (node ​​water level), that is... A value >0 indicates that the surface water level is higher than the node water level, and surface runoff enters the underground pipe network through the inspection well node; when H 2> H 1 o'clock, that is <0 indicates that the node water level is higher than the surface water level, and the water in the underground pipe network overflows to the surface through the inspection well node; when the two are equal, no flow exchange occurs at the node.

[0025] The model is driven by different return periods of design rainfall processes. The output of indicators such as node overload rate, pipe section overload rate, surface water depth, water accumulation area, system discharge and surface runoff are simulated under current conditions.

[0026] The principle of the coupled exchange model is as follows: when the surface water level is higher than the manhole node water level, surface runoff enters the underground pipe network through the node; when the node water level is higher than the surface elevation, groundwater overflows to the surface through the node, thus realizing bidirectional exchange between the surface and underground systems. It is used to realize the exchange of inflow and overflow between the surface and underground systems at the manhole nodes, reflecting the real evolution of urban stormwater processes. Through coupled simulation results, areas with insufficient drainage capacity, nodes with long-term overload, key bottleneck pipe sections, areas with unreasonable drainage paths, and high-risk waterlogging areas can be identified within the study area, providing a basis for subsequent renovations. It can improve the discharge capacity of the stormwater pipe network system and reduce peak runoff and waterlogging risks through source reduction and process regulation, avoiding the limitations of simple capacity expansion or simple LID (Limited Area Isolation) deployment.

[0027] Example 4 Based on Example 3, the urban stormwater pipe network system renovation and optimization method provided in this example includes the following steps in step 4: re-dividing drainage zones for areas with excessively large catchment areas and excessively long drainage paths, and shortening drainage paths; adjusting pipe diameters for pipe sections with insufficient water conveyance capacity according to design flow rate, flow velocity and fullness requirements; and adding discharge channels or discharge outlets to drainage bottleneck areas to improve the overall drainage capacity and connectivity of the system.

[0028] The pipe diameter adjustment shall comply with the following requirements: the design flow velocity inside the pipe shall be controlled between 0.6m / s and 3.0m / s; the design filling degree for gravity flow rainwater pipes shall not exceed 0.7 when the pipe diameter is ≤300mm, not exceed 0.75 when the pipe diameter is 300mm-600mm, and not exceed 0.8 when the pipe diameter is >600mm; the added discharge channel shall be in the form of a culvert or an open channel, the discharge outlet shall be set in the nearest water body, and the discharge capacity shall match the design drainage flow of the area.

[0029] Example 5 Based on Example 4, the urban stormwater pipe network system renovation and optimization method provided in this example also includes constructing multiple low-impact development facility combination layout schemes, coupling each scheme with the renovated pipe network system for simulation, establishing a comprehensive evaluation system from three dimensions: water volume regulation benefits, economic costs, and environmental benefits, using a multi-index decision-making method to score and rank each scheme, and selecting the urban stormwater pipe network system renovation scheme with the best comprehensive benefits.

[0030] Low-impact development facilities include at least two of the following: permeable pavement, green roofs, bioretention ponds, rain gardens, and vegetated swales. In the comprehensive evaluation system, water regulation benefits have a weight of 0.4-0.5, economic costs have a weight of 0.3-0.35, and environmental benefits have a weight of 0.15-0.2; the multi-indicator decision-making method employs either the analytic hierarchy process (AHP) or the entropy weight method.

[0031] Example 6 This embodiment uses the built-up area of ​​a small town in Jingwei Subdistrict, Gaoling District, Xi'an City as the study area, with a total area of ​​approximately 10.69 km². 2 It belongs to the temperate semi-humid continental monsoon climate zone, with an average annual temperature of about 13.2℃. Rainfall is mainly concentrated from June to September, characterized by short duration, high intensity, and concentrated peak rainfall. The method of this invention is used for modification and optimization, specifically including the following steps: Step 1: Collect topographic elevation data, land use type data, design rainfall data, and existing stormwater drainage network data of the study area, and unify the coordinates, resolution, and time step to form the model input database.

[0032] The topographic elevation data was generated using CAD-measured elevation points in the study area, and then interpolated using ArcGIS to create a 5m×5m digital elevation model (DEM) consisting of 854,112 grids. Land use type data included four types of underlying surfaces: buildings, green spaces, roads, and plazas, each assigned corresponding infiltration rate and Manning roughness parameters. Design rainfall data was generated based on the Xi'an city rainstorm intensity formula, combined with the Chicago rainfall pattern method, with a comprehensive peak rainfall coefficient of 0.35, a rainfall duration of 120 minutes, a time step of 1 minute, and five return periods (1-year, 2-year, 5-year, 10-year, and 20-year). Existing stormwater drainage network data, such as... Figure 1 As shown, the spatial distribution and attribute information of 60 rainwater pipe sections, 64 inspection wells, 4 discharge outlets, and the existing 4 drainage zones are included; all spatial data adopt the same coordinate reference, the raster resolution is uniformly 5m, and the rainfall input and model calculation time step is uniformly 1min.

[0033] Step 2: Based on the digital elevation model and land use type data, a two-dimensional hydrodynamic model of the surface is established using the GAST model; based on the existing stormwater pipe network data, a one-dimensional stormwater pipe network hydraulic model is established using the SWMM dynamic wave module.

[0034] Step 3: The two-dimensional hydrodynamic model of the surface and the one-dimensional stormwater pipe network hydraulic model are coupled in a two-way coupling manner to construct a coupled exchange model. The inspection well is used as the water exchange interface, and the node exchange flow rate is calculated using formula (6). C d Take 0.62. The simulation results of the current working condition show as follows: Figure 2 and 3 As shown, the overload rates of the pipe sections under 1-year, 2-year, 5-year, 10-year, and 20-year return period rainfall in the study area were 21.88%, 60.94%, 71.88%, 84.38%, and 90.64%, respectively. Under a 2-year return period rainfall, the overload rate of the pipe section reached 90%, with a water accumulation area of ​​456,454 m². 2 The maximum water depth is 0.70m, and the system discharge is 11.567 × 10⁻⁶ m. 4 m 3 This indicates that the existing drainage system is insufficient to meet urban flood control needs. The main weaknesses are a drainage zone with an excessively large catchment area, several pipe sections with insufficient water conveyance capacity, and localized drainage bottlenecks. The entire process of runoff generation, collection, and discharge under design rainfall conditions in the existing stormwater pipe network system illustrates the problems of high peak runoff and delayed drainage in the current system.

[0035] Step 4: Implement renovation and optimization measures targeting weak points. Refine and restructure the original four drainage zones, expand the capacity of pipe sections with insufficient water conveyance in stages, and add connection nodes and discharge channels, such as... Figure 4As shown, after the renovation, the total length of the pipeline network increased from 25656.49m to 27389.94m, the pipe diameter configuration was adjusted from 600-2000mm to 800-2000mm, and the length of high-grade pipes increased (1400mm pipe diameter increased from 374.77m to 4532.45m, 1800mm pipe diameter increased from 2899.86m to 7552.37m, and 2000mm pipe diameter increased from 1274.71m to 6248.02m). A re-simulation was performed after the renovation, as shown below. Figure 5 As shown, under a 2-year return period rainfall condition, the system emissions increase to 14.357 × 10⁻⁶. 4 m 3 The overload rate at nodes decreased to 6.15%, the overload rate at pipe sections decreased to 1.54%, and surface water accumulation exceeding 0.15m was basically eliminated; under a 20-year return period rainfall condition, the system's discharge increased to 38.641 × 10⁻⁶. 4 m 3 The drainage capacity has been significantly improved.

[0036] Step 5, Low Impact Development Facility Layout and Comprehensive Evaluation Data: Based on the goals of an annual runoff volume control rate of no less than 85% and a surface water depth of no more than 0.15m under a 20-year return period rainfall, three low impact development facility combination schemes are constructed, as shown in Table 1: Table 1. Low Impact Development Facility Layout Plan and Evaluation Results

[0037] The three schemes were coupled with the modified urban stormwater drainage network system. Under a design rainfall of 20mm, the annual runoff control rates of the three schemes were 88.50%, 88.56%, and 95.65%, respectively, all exceeding the control targets. Considering the comprehensive water regulation benefits, economic costs, and environmental benefits (with weights of 0.45, 0.32, and 0.18, respectively), the analytic hierarchy process (AHP) was used to calculate the comprehensive score. Scheme 1 scored 0.5048, Scheme 2 scored 0.5670, and Scheme 3 scored 0.5340. Scheme 2 had the best comprehensive benefits and was selected as the final modification scheme. Meanwhile, the economic costs of the three schemes were 486.48 million yuan, 737.47 million yuan, and 847.61 million yuan, respectively. Scheme 3 had the best environmental benefits, but Scheme 2 achieved the best balance between water regulation, economic efficiency, and environmental benefits, making it more suitable for the actual conditions of the study area.

[0038] This invention establishes a two-dimensional hydrodynamic model of the surface and a one-dimensional hydraulic model of the stormwater network based on topographic, land use, design rainfall, existing stormwater pipe network, and low-impact development (LID) facility parameters. A bidirectional coupled exchange model is constructed using manhole nodes as the exchange interface to simulate the surface runoff confluence and underground drainage transport process. Weak links in the system are identified based on indicators such as node overload rate, pipe section overload rate, surface water depth, water accumulation area, and system discharge volume. Drainage zoning optimization, pipe diameter adjustment, and the addition of discharge channels or outlets are implemented to address issues such as excessively long drainage paths, excessively large zoning areas, insufficient local discharge outlets, and insufficient pipe diameter capacity. Based on this, multiple LID facility deployment schemes are constructed, and a comprehensive evaluation is conducted from three dimensions: water volume control benefits, economic costs, and environmental benefits, to select the optimal urban stormwater pipe network system renovation scheme. By constructing a two-dimensional surface-one-dimensional underground coupled model, the operational status of underground stormwater pipe networks and surface water accumulation response can be identified simultaneously, improving the accuracy of identifying the formation process and key weak links of urban flooding. By considering drainage zoning optimization, pipe diameter adjustment, new discharge channels and low-impact development facility deployment in a unified manner, the synergistic optimization between improving end-of-pipe discharge capacity and source emission reduction and process regulation can be achieved. By establishing a comprehensive evaluation framework, economic and environmental benefits can be taken into account while meeting drainage safety objectives.

Claims

1. A method for reconstructing and optimizing an urban stormwater pipe network system, characterized in that, Includes the following steps: Step 1: Establish a model input database for the area to be modified, and unify the data coordinates, resolution, and calculation time step; Step 2: Based on the model input database, construct a two-dimensional hydrodynamic model of the land surface and a one-dimensional hydraulic model of the stormwater pipe network, respectively. Step 3: Couple the two-dimensional surface hydrodynamic model with the one-dimensional stormwater pipe network hydraulic model to construct a two-way coupled exchange model and conduct current working condition simulation. Step 4: Identify the parts of the pipeline system that need to be modified based on the simulation results of the current working conditions, and implement systematic modification and optimization.

2. The method for upgrading and optimizing urban stormwater drainage network systems according to claim 1, characterized in that, The model input database includes topographic elevation data, land use type data, design rainfall data, and existing stormwater drainage network data; Topographic elevation data were obtained from CAD measured elevation points in the study area and then interpolated using ArcGIS to generate a digital elevation model (DEM) of a specified resolution. Land use type data includes four types of underlying surfaces: buildings, green spaces, roads, and plazas. Corresponding infiltration rate parameters and Manning roughness parameters are assigned to different underlying surface types. The design rainfall data is based on the storm intensity formula of the area to be transformed, and the design rainfall process lines with different return periods are generated by combining the Chicago rainfall pattern method. The current stormwater pipe network data includes the spatial distribution and attribute parameters of stormwater pipe sections, inspection wells, and discharge outlets, as well as the division range and confluence relationship of the current drainage zones.

3. The method for upgrading and optimizing urban stormwater drainage network systems according to claim 2, characterized in that, The two-dimensional hydrodynamic model of the surface is a two-dimensional surface runoff model based on the shallow water equation. The surface computational domain is established according to the digital elevation model and land use type data to simulate the generation, confluence and water accumulation process of surface runoff. The one-dimensional stormwater pipe network hydraulic model is a one-dimensional pipe network hydraulic model based on the Saint-Venant equation. It is solved using the dynamic wave method and established based on the current stormwater pipe network data. It is used to simulate the water flow movement in the pipe, the nodal head, and the overload state of the pipe section.

4. The method for upgrading and optimizing urban stormwater drainage network systems according to claim 2, characterized in that, The bidirectional coupled exchange model uses inspection wells as the water exchange interface. It synchronously updates the surface water level and the water level of the pipe network nodes in each calculation time step. It determines the water exchange direction and exchange flow rate based on the head difference between the surface water level and the water level of the pipe network nodes, realizing real-time joint calculation of surface runoff and underground pipe network drainage. It outputs node overload rate, pipe section overload rate, surface water depth, water accumulation area and total system drainage indicators through current working condition simulation.

5. The method for upgrading and optimizing urban stormwater drainage network systems according to claim 2, characterized in that, The modifications and optimizations include: re-dividing drainage zones in areas with excessively large catchment areas and excessively long drainage paths, and shortening drainage paths; adjusting the pipe diameter of pipe sections with insufficient water conveyance capacity according to design flow rate, flow velocity, and filling requirements; and adding discharge channels or outlets in drainage bottleneck areas to improve the overall drainage capacity and connectivity of the system.

6. The method for upgrading and optimizing urban stormwater drainage network systems according to claim 5, characterized in that, The pipe diameter adjustment shall comply with the following requirements: the design flow velocity inside the pipe shall be controlled between 0.6m / s and 3.0m / s; the design filling degree for gravity flow rainwater pipes shall not exceed 0.7 when the pipe diameter is ≤300mm, not exceed 0.75 when the pipe diameter is 300mm-600mm, and not exceed 0.8 when the pipe diameter is >600mm; the added discharge channel shall be in the form of a culvert or an open channel, the discharge outlet shall be set in the nearest water body, and the discharge capacity shall match the design drainage flow of the area.

7. The method for upgrading and optimizing urban stormwater drainage network systems according to claim 2, characterized in that, The different return periods include 1-year, 3-year, 5-year, 10-year and 20-year return periods, and the peak rainfall coefficient of the Chicago rainfall pattern method is 0.3-0.

5.

8. The method for upgrading and optimizing urban stormwater drainage network systems according to claim 2, characterized in that, It also includes constructing multiple low-impact development facility combination layout schemes, coupling each scheme with the renovated pipe network system for simulation, establishing a comprehensive evaluation system from three dimensions: water volume regulation benefits, economic costs, and environmental benefits, and using a multi-index decision-making method to score and rank each scheme, and selecting the urban stormwater pipe network system renovation scheme with the best comprehensive benefits.

9. The method for upgrading and optimizing urban stormwater drainage network systems according to claim 8, characterized in that, The low-impact development facilities include at least two of the following: permeable pavement, green roofs, bioretention ponds, rain gardens, and grassed swales.

10. The method for upgrading and optimizing urban stormwater drainage network systems according to claim 8, characterized in that, The multi-indicator decision-making method adopts either the analytic hierarchy process (AHP) or the entropy weight method.

Images