Urban rainfall runoff process simulation method considering LID facility
By coupling two-dimensional hydrodynamic and one-dimensional pipe network models, the problem of insufficient accuracy of traditional models in urban rainfall runoff processes is solved, realizing efficient and accurate simulation of LID facilities and providing a quantitative analysis tool for sponge city construction.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-25
- Publication Date
- 2026-03-10
AI Technical Summary
Existing hydrological and hydrodynamic models struggle to accurately obtain key parameters such as flow velocity when simulating urban rainfall runoff, especially in densely built-up urban areas with complex underlying surfaces. This leads to reduced simulation accuracy and affects the reliability of urban flooding processes.
By employing a coupled two-dimensional hydrodynamic numerical model and a one-dimensional pipe network model, basic data and land use classification of the study area are obtained, the location and area of LID facilities are constructed, physical and geometric parameters are set, infiltration rate and overflow rainwater volume are calculated, and the models are coupled to simulate the runoff process of LID facilities.
It achieves high-precision simulation of LID facilities in urban rainfall runoff processes, systematically evaluates their regulation effect, provides quantitative analysis tools for sponge city construction, and improves the computational efficiency and accuracy of the model.
Smart Images
Figure CN121637883A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of numerical simulation technology of urban rainfall and hydrology and hydrodynamics. Specifically, this invention relates to a method for simulating urban rainfall-runoff processes considering LID facilities. Background Technology
[0002] Climate change and rapid urbanization are exacerbating the risk of urban flooding. Global warming is leading to more frequent extreme rainfall events, while urban expansion is increasing impervious surfaces and damaging natural water systems, all of which are putting immense pressure on urban drainage systems and drastically reducing their flood control capacity. To address urban flooding, my country is actively exploring solutions, among which the concept of "sponge cities" has received considerable attention.
[0003] The concept of "sponge city," proposed in 2013, aims to create a "resilient" urban water system by utilizing low-impact development (LID) facilities to achieve natural rainwater storage, infiltration, and purification. This concept integrates traditional and green engineering technologies, adopting a multi-scale governance model encompassing watershed, region, and community levels. It combines engineering measures such as pipeline renovation with non-engineering methods like disaster early warning to comprehensively enhance urban flood control and drainage capabilities. Numerical simulation technology has provided crucial support for the planning and construction of sponge cities.
[0004] Currently, simulations of low-impact development (LID) facilities primarily employ hydrological models. These models simulate hydrological responses by simplifying the natural water cycle and mainly fall into three categories: empirical models, which establish input-output relationships based on statistical connections and are computationally simple but lack physical mechanisms; mechanistic models, which strictly adhere to physical laws but have high parameter requirements and are computationally complex; and conceptual models, which use a semi-empirical, semi-theoretical approach as a compromise. A common problem with these models is their insufficient description of dynamic hydraulic processes, making it difficult to accurately obtain key parameters such as flow velocity. In densely built-up urban areas with complex underlying surfaces, simulation accuracy significantly decreases. The inherent limitations of hydrological models can affect the reliability of simulation results for urban flooding processes, including LID measures.
[0005] Hydrodynamic models offer significant advantages in flood simulation: one-dimensional models are suitable for pipe network calculations but insufficient for surface runoff simulation; three-dimensional models offer high accuracy but are computationally complex; two-dimensional models strike a balance between accuracy and efficiency, becoming the mainstream tool, with their finite volume method particularly adept at handling discontinuous flow problems. However, existing models often simplify runoff generation processes and neglect key hydrological mechanisms such as infiltration, affecting the accuracy of water volume calculations. With the advancement of sponge city construction, there is an urgent need to develop new models that can couple hydrological and hydrodynamic processes, accurately simulating surface runoff generation and confluence and pipe network-surface coupling processes, while also considering the impact of human activities, providing reliable support for planning and design. Summary of the Invention
[0006] The purpose of this invention is to provide a method for simulating urban rainfall-runoff processes that takes into account LID facilities, which solves the problems of inaccurate runoff calculation in traditional full hydrodynamic models and the inability of traditional hydrological models to obtain hydraulic variables such as flow velocity.
[0007] The technical solution adopted in this invention is a simulation method for urban rainfall runoff processes considering LID facilities, as detailed below: S1. Obtain basic data of the study area, classify land use, and determine the location and area of LID facilities; S2. Construct a two-dimensional hydrodynamic numerical model and a one-dimensional pipe network model for the study area, respectively, and couple the two models to obtain a coupled model. S3. Select an appropriate calculation method based on the research object and terrain data, set the physical and geometric parameters of the LID facility, and select whether to set the location node and pipeline parameters of the LID facility based on the calculation method. S4. Calculate the water depth based on the infiltration rate, compare the water depth with the outlet weir height of the LID facility, further calculate the overflow rainwater volume, input the calculated overflow rainwater into the coupled model, and perform pipeline hydrodynamic process calculation. Other areas on the surface are calculated using a two-dimensional hydrodynamic model. S5. Repeat S4 until the simulation ends, and output the LID simulation results, 2D surface simulation results, and 1D pipeline simulation results.
[0008] The invention is further characterized by: In S1, basic data of the study area are obtained by interpolation of measured elevation points or by UAV-borne lidar. The basic data of the study area includes hydrological and meteorological data, rainfall data, surface topography data, land use data, etc., and the types, numbers, locations and corresponding geometric parameters of LIDs contained in the study area are statistically analyzed. The land use classification in S1 is as follows: based on natural attributes, it is divided into roads, green spaces, buildings, and underground spaces, and the Manning coefficient and infiltration rate are determined for each land use type.
[0009] The specific method for S2 is as follows: S2.1 First, the basic data of the study area is processed to form the input parameters required for modeling; S2.2. By dividing the study area into structured grid cells, a two-dimensional hydrodynamic numerical model of the study area is constructed. The two-dimensional hydrodynamic model is calculated using two-dimensional shallow water equations. ; ; Where t represents time, in seconds; For variable vectors; Water depth, in meters (m). qx and q y They are respectively x and y The unit width flow rate in both directions, in meters. 2 / s; F and G 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; i For infiltration source terms; 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; S2.3 Construct a one-dimensional pipeline network model, which is obtained through the one-dimensional Saint-Venant equation:
[0010]
[0011] in, A This refers to the cross-sectional area of the pipe, in meters (m²). 2 ; Q This refers to the pipe flow rate, measured in meters (m³). 3 / s; t represents time, in seconds; s The distance along the flow path for a fixed cross-section, in meters; g This is the acceleration due to gravity, measured in m / s². 2 ; u Flow velocity, in m / s; h The average water depth across the cross-section is expressed in meters (m). S 0 represents the slope gradient at the bottom. S f For the friction ratio decrease; S2.4. Based on the relative relationship between the location, elevation, and two-dimensional surface of the rainwater inlet, the two-dimensional model and the one-dimensional model are coupled to obtain a one-dimensional and two-dimensional coupled model.
[0012] The specific method for S3 is as follows: S3.1 Determine whether the research object is the runoff control process of a single LID facility or the urban stormwater process that includes LID facilities; S3.2 If the research object is the runoff control process of a single LID facility, then select the LID single unit or LID single unit unitization method: if the LID range is greater than the accuracy of a two-dimensional grid unit, then set the LID as a single facility; if the LID range is less than the accuracy of a two-dimensional grid unit, then process it as a single unit of LID, that is, set it according to the actual proportion of the LID facility, and specify the overflow pipe outlet when there is an overflow pipe. S3.3 If the research object is an urban stormwater process that includes LID facilities, it shall be handled according to the method of coupling LID effect with stormwater process, and the settings shall be made according to the actual proportion of LID facilities. When there is an overflow pipe, the overflow pipe outlet shall be specified, and the overflow pipe and the stormwater pipe network shall be connected.
[0013] The specific method for setting LID as a single facility in S3.2 is as follows: the inner boundary treatment method based on water balance is used to calculate the flow over the weir. Corresponding grids are selected upstream and downstream of the overflow weir. The flow over the weir is calculated by the weir flow formula in the upstream grid. The h on the grid is used as the head over the weir. In the same time step, the increase in water volume on the downstream grid is equal to the decrease in water volume on the corresponding upstream grid to achieve water balance. The finite volume method of Godunov scheme is used to spatially discretize and solve the two-dimensional shallow water equation to calculate the stormwater process outside the inner boundary. The weir flow formula used is:
[0014] In the formula: and These are two parameters, taking values of 1.6566 and 1.5 respectively, whose magnitudes depend on the inlet type and its geometry; The water head above the weir is expressed in meters (m). The efficiency coefficient represents the inlet blockage level. It has a value of 1 and varies between 0 and 1, where 0 represents complete blockage and 1 represents no blockage.
[0015] The specific method for setting LID as a single unit in S3.2 is as follows: set the location node and pipeline parameters of the LID facility, set the physical and geometric parameters of the LID facility, change the flow calculation method of the node where the LID facility is located, and when calculating the flow of the node where the LID facility is located, determine the difference between the surface water depth around the LID facility and the inlet weir height of the LID facility. When the water depth is less than the inlet weir height, the node does not receive water. When the water depth is greater than the inlet weir height, the node receives water using the weir flow formula. The head above the weir is the surface water depth minus the inlet weir height.
[0016] The specific method for coupling the LID effect with the stormwater process in S3.3 is as follows: the typical LID integrated control effect is coupled with the urban pipe network model. The surface runoff generation and runoff of the model follows the Green-Ampt model to calculate the infiltration process. The Hargreaves method governing equations and the planar two-dimensional shallow water equations are used for calculation. The pipe network hydrodynamic process follows the dynamic wave method, that is, the complete one-dimensional Saint-Venant equations are solved using a one-dimensional hydrodynamic model, or its simplified form, namely diffusion waves and motion waves. The finite difference method is its main numerical solution method.
[0017] The physical and geometric parameters of the LID facility in S4 include the inlet weir height and width, radius, confluence ratio, runoff coefficient, infiltration rate, and the outlet overflow weir height and width.
[0018] The specific method for S5 is as follows: S5.1 Water entering the LID range infiltrates according to the actual infiltration rate of the facility to obtain the water depth result; S5.2 Compare the obtained water depth with the outlet weir height of the LID facility. If the water depth after infiltration is greater than the outlet weir height, calculate the flow rate entering the pipeline according to the weir flow formula. This part of the overflow rainwater is the water that the LID facility has not controlled. S5.3 Input the calculated overflow rainwater into the coupled model to calculate the hydrodynamic process of the pipe network. For other areas on the surface, a two-dimensional hydrodynamic model is used for calculation.
[0019] In S5.1, for the simulation calculation of LID facilities, the overflow process at the inlet and outlet of a single facility should be considered during the detailed simulation of a single LID facility. If the size of the computational grid is larger than the size of a single LID facility, then a two-dimensional grid is generalized as an LID facility; if the LID region is larger than a single two-dimensional grid, then a region is generalized as an LID facility. The calculations were performed using the actual area of the LID facility, while the infiltration model was calculated using the Green-Ampt model, and coupled with the pipeline network model based on the actual layout of the overflow outlets.
[0020] The beneficial effects of this invention are: (1) This invention considers a method for simulating urban rainfall runoff processes using LID (Light Identification and Discharge) facilities. By coupling a two-dimensional surface hydrological model and a one-dimensional pipe network model, it systematically evaluates the regulatory effects of LID measures such as bioretention ponds and rain gardens on urban stormwater. This method first integrates multi-source data on the study area, including hydrological and meteorological data, topographic data, land use data, and LID facility characteristics, to construct a refined numerical model system. For different types of LID facilities, a differentiated modeling strategy is adopted. During model operation, the infiltration process of LID units is calculated first. When the accumulated water exceeds the design capacity, the overflow is calculated using the weir flow formula and input into the pipe network system. Finally, multi-dimensional evaluation indicators such as LID regulation efficiency, surface water accumulation characteristics, and pipe network operation status are output. This method can provide a quantitative analysis tool for sponge city construction, urban flood control, and drainage system optimization. (2) The present invention considers the urban rainfall-runoff process simulation method of LID facilities. The proposed model not only overcomes the problem of inaccurate runoff calculation in traditional full hydrodynamic models, but also makes up for the lack of hydraulic variables such as flow velocity in traditional hydrological models. In the LID simulation calculation, the hydrodynamic process of runoff regulation of various facilities is fully considered, including the calculation of individual LID units and LID unitization, and the coupling of LID effects with the rain-flood process. The calculation accuracy is higher than that of the nonlinear reservoir method of traditional hydrological models, and the calculation process is more reasonable.
[0021] (3) This model can be applied not only to the simulation study of runoff regulation law of single LID facilities, but also to the planning, design and effect evaluation stage of typical sponge communities. It is an effective tool for exploring sponge city construction and can be reliably applied to the simulation study of sponge city stormwater process. (4) This invention constructs an LID runoff regulation simulation method, enriches the simulation content of the entire process of urban flooding, constructs an efficient and high-precision coupled model of the entire process of urban flooding, realizes GPU-accelerated computing of the entire process, innovates the asynchronous coupling algorithm, and further improves the computational efficiency of the coupled model. Attached Figure Description
[0022] Figure 1 This is a flowchart illustrating the urban rainfall-runoff process simulation method of the present invention, which takes into account LID facilities. Figure 2 This is a schematic diagram of the LID (Large Identification and Reduction) intra-unit boundary treatment method in the urban rainfall runoff process simulation method of the present invention, which considers LID facilities. Figure 3 This is a schematic diagram of the LID generalization process of the urban rainfall runoff process simulation method considering LID facilities in this invention; Figure 4 This is a schematic diagram of the computational region in Embodiment 1 of the simulation method of the present invention; Figure 5This refers to the rainfall event on August 20, 2017, in Embodiment 1 of the simulation method of this invention. Figure 6 This is a comparison diagram of the water flow growth process of a rain garden unit in Embodiment 1 of the simulation method of the present invention; Figure 7 This is a location map of Tianfu Heyuan residential area in Embodiment 2 of the simulation method of the present invention; Figure 8 This is a diagram of the pipeline network layout in the study area of Embodiment 2 of the simulation method of the present invention; Figure 9 This is a comparison chart of the simulated and measured results of the flow process at the community outlet in Embodiment 2 of the simulation method of the present invention. Detailed Implementation
[0023] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.
[0024] This invention considers a method for simulating urban rainfall-runoff processes in LID facilities, such as... Figure 1 As shown, the details are as follows: S1. Obtain basic data of the study area, classify land use, and determine the location and area of LID facilities; Specifically, basic data of the study area is obtained by interpolation of measured elevation points or by using UAV-borne lidar. The basic data of the study area includes hydrological and meteorological data, rainfall data, surface topography, land use data, etc., and the types, numbers, locations and corresponding geometric parameters of LIDs contained in the study area are statistically analyzed. The land use classification is as follows: based on natural attributes, it is divided into roads, green spaces, buildings, and underground spaces, and the Manning coefficient and infiltration rate are determined for each land use type.
[0025] S2. The study area is divided into structured grid cells, and a two-dimensional hydrological and hydrodynamic numerical model of the study area is constructed. Based on the pipe network data, the topological relationship between rainwater nodes and pipes is established, and a one-dimensional pipe network model is constructed. The two-dimensional model and the one-dimensional model are coupled according to the relationship between the rainwater inlet location and the two-dimensional surface to obtain a coupled model. The specific method is as follows: S2.1 First, the basic data of the study area is processed to form the input parameters required for modeling; S2.2. By dividing the study area into structured grid cells, a two-dimensional hydrodynamic numerical model of the study area is constructed. The two-dimensional hydrodynamic model is calculated using two-dimensional shallow water equations. ; ; Where t represents time, in seconds; 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; F and G 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; i For infiltration source terms; 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; S2.3 Construct a one-dimensional pipeline network model, which is obtained through the one-dimensional Saint-Venant equation:
[0026]
[0027] in, A This refers to the cross-sectional area of the pipe, in meters (m²). 2 ; Q This refers to the pipe flow rate, measured in meters (m³). 3 / s; t represents time, in seconds; s The distance along the flow path for a fixed cross-section, in meters; g This is the acceleration due to gravity, measured in m / s². 2 ; u Flow velocity, in m / s; h The average water depth across the cross-section is expressed in meters (m). S 0 represents the slope gradient at the bottom. S f For the friction ratio decrease; S2.4. Based on the relative relationship between the location, elevation, and two-dimensional surface of the rainwater inlet, the two-dimensional model and the one-dimensional model are coupled to obtain a one-dimensional and two-dimensional coupled model.
[0028] S3. Based on the research object and topographic data, select an appropriate calculation method and set the physical and geometric parameters of the LID facility, including the inlet weir height and width, radius, runoff ratio, runoff coefficient, infiltration rate, and the outlet overflow weir height and width; and determine whether to set the location node and pipeline parameters of the LID facility according to the calculation method. The study area is the size of the catchment area that can be controlled by the bioretention measures; the specific method is as follows: S3.1 Determine whether the research object is the runoff control process of a single LID facility or the urban stormwater process that includes LID facilities; S3.2 If the research object is the runoff control process of a single LID facility, then select the LID single unit or LID single unit unitization method: if the LID range is greater than the accuracy of a two-dimensional grid unit, then set the LID as a single facility; if the LID range is less than the accuracy of a two-dimensional grid unit, then process it as a single unit of LID, that is, set it according to the actual proportion of the LID facility, and specify the overflow pipe outlet when there is an overflow pipe. All calculations used the actual LID area, while the infiltration model employed the Green-Ampt model, coupled with the pipe network model based on the actual overflow outlet layout. For LID measures with overflow outlets, such as rain gardens, vegetated swales, and bioretention systems, key parameters such as infiltration parameters, overflow outlet height, and weir coefficient needed to be set. Specifically, in the LID hydrodynamic process simulation, taking a rain garden as an example, some rainwater infiltrates into the ground through the interior of the rain garden pool. Rainwater exceeding the infiltration capacity accumulates in the pool, overflowing at the outlet when it reaches the overflow height of the rain garden.
[0029] The specific method for setting LID as a single facility is as follows: The weir flow is calculated using an inner boundary treatment method based on water balance, such as... Figure 2 As shown, corresponding grids are selected upstream and downstream of the overflow weir. The flow rate over the weir is calculated by the weir flow formula in the upstream grid. The h on the grid is taken as the head above the weir. In the same time step, the increase in water volume on the downstream grid is equal to the decrease in water volume on the corresponding upstream grid to achieve water balance. The two-dimensional shallow water equation is solved by spatial discretization using the Godunov scheme finite volume method to calculate the rainwater process outside the inner boundary. The weir flow formula used is:
[0030] In the formula: and These are two parameters, taking values of 1.6566 and 1.5 respectively, whose magnitudes depend on the inlet type and its geometry; The water head above the weir is expressed in meters (m). The efficiency coefficient represents the inlet blockage level. It has a value of 1 and varies between 0 and 1, where 0 represents complete blockage and 1 represents no blockage.
[0031] like Figure 3 As shown, the specific method for setting LID as a single LID unit is as follows: set the location node and pipeline parameters of the LID facility, set the physical and geometric parameters of the LID facility, change the flow calculation method of the node where the LID facility is located, and when calculating the flow of the node where the LID facility is located, determine the difference between the surface water depth around the LID facility and the inlet weir height of the LID facility. When the water depth is less than the inlet weir height, the node does not receive water. When the water depth is greater than the inlet weir height, the node receives water using the weir flow formula. The head above the weir is the surface water depth minus the inlet weir height.
[0032] S3.3 If the research object is an urban stormwater process that includes LID facilities, it shall be handled according to the method of coupling LID effect with stormwater process, and the settings shall be made according to the actual proportion of LID facilities. When there is an overflow pipe, the overflow pipe outlet shall be specified, and the overflow pipe and the stormwater pipe network shall be connected.
[0033] The specific method for coupling the LID effect with the stormwater process is as follows: the typical LID integrated control effect is coupled with the urban pipe network model. The surface runoff generation and runoff of the model follows the Green-Ampt model to calculate the infiltration process. The Hargreaves method governing equations and the planar two-dimensional shallow water equations are used for calculation (the method is the same as S2.2). The pipe network hydrodynamic process follows the dynamic wave method, that is, the complete one-dimensional Saint-Venant equations are solved using a one-dimensional hydrodynamic model (the method is the same as S2.3), or its simplified form, namely diffusion waves and motion waves. The finite difference method is its main numerical solution method.
[0034] Water entering the LID range first infiltrates according to the infiltration rate of the bioretention measures, and the infiltration model adopted is the Green-Ampt model.
[0035] S4. Calculate the water depth based on the infiltration rate and compare the water depth with the outlet weir height of the LID facility. If the water depth after infiltration is greater than the outlet weir height, calculate the flow rate entering the pipeline according to the weir flow formula. This part of the water is the water that the LID cannot control. Further calculations of overflow rainwater volume were performed, and the calculated overflow rainwater was input into the coupled model to perform hydrodynamic process calculations of the pipe network. Two-dimensional hydrodynamic models were used to calculate other areas of the surface. S5. Repeat S4 until the simulation ends, and output the LID simulation results, 2D surface simulation results, and 1D pipeline network simulation results. The specific method is as follows: S5.1 Water entering the LID range infiltrates according to the actual infiltration rate of the facility to obtain the water depth result; For LID facility simulation calculations, the overflow process at the inlet and outlet of a single LID facility should be considered during the detailed simulation of the individual facility. If the size of the computational grid is larger than the size of a single LID facility, then a two-dimensional grid is generalized as an LID facility; if the LID region is larger than a single two-dimensional grid, then a region is generalized as an LID facility. The calculations were performed using the actual area of the LID facility, while the infiltration model was calculated using the Green-Ampt model, and coupled with the pipeline network model based on the actual layout of the overflow outlets.
[0036] S5.2 Compare the obtained water depth with the outlet weir height of the LID facility. If the water depth after infiltration is greater than the outlet weir height, calculate the flow rate entering the pipeline according to the weir flow formula. This part of the overflow rainwater is the water that the LID facility has not controlled. S5.3 Input the calculated overflow rainwater into the coupled model to calculate the hydrodynamic process of the pipe network. For other areas on the surface, a two-dimensional hydrodynamic model is used for calculation.
[0037] This invention systematically evaluates the regulatory effects of LID (Low-Intensity Detection) facilities, such as bioretention ponds, on urban stormwater runoff by coupling a two-dimensional surface hydrological model and a one-dimensional pipe network model. The method first integrates multi-source data on the study area, including hydrological and meteorological data, topographic data, land use data, and LID facility characteristics, to construct a refined numerical model system. The two-dimensional surface model uses a structured grid to simulate surface runoff and water accumulation processes, while the one-dimensional pipe network model calculates the hydraulic characteristics of the pipes based on the pipe network topology. The two models are dynamically coupled through stormwater inlets.
[0038] Bioretention facilities achieve refined simulation through parameterized infiltration, retention, and overflow processes. During model runtime, the infiltration process of LID (Low Infiltration Intake) units is calculated first. When the accumulated water exceeds the design capacity, the overflow rate is calculated using the weir flow formula and input into the pipe network system. Finally, multi-dimensional evaluation indicators such as LID regulation efficiency, surface water accumulation characteristics, and pipe network operational status are output. This method can provide a quantitative analysis tool for sponge city construction, urban flood control, and drainage system optimization.
[0039] This invention discloses a method for simulating urban rainfall-runoff processes considering LID (Low-Intensity Detection) facilities. By coupling a two-dimensional surface hydrological model and a one-dimensional pipe network model, it systematically evaluates the regulatory effects of LID measures such as bioretention ponds on urban stormwater. The method first integrates multi-source data on the study area, including hydrological and meteorological data, topographic data, land use data, and LID facility characteristics, to construct a refined numerical model system. The two-dimensional surface model uses a structured grid to simulate surface runoff and water accumulation processes, while the one-dimensional pipe network model calculates the hydraulic characteristics of the pipes based on the pipe network topology. The two models are dynamically coupled through stormwater inlets. Bioretention facilities are simulated with refined parameters for infiltration, retention, and overflow processes. During model operation, the infiltration process of LID units is calculated first. When the accumulated water exceeds the design capacity, the overflow rate is calculated using the weir flow formula and input into the pipe network system. Finally, multi-dimensional evaluation indicators such as LID regulation efficiency, surface water accumulation characteristics, and pipe network operation status are output. This method can provide a quantitative analysis tool for sponge city construction, urban flood control, and drainage system optimization.
[0040] Example 1 The computational accuracy of the coupled model was verified by selecting an actual rain garden and its catchment area within its control range as the research object. Since the accuracy of actual terrain data acquisition cannot meet the accuracy requirements of LID unit simulation calculation, the coupled model method was adopted to study the runoff process of LID unit units.
[0041] Figure 4 This is a schematic diagram of the study area, where node 1 represents the node where the rain garden is located, node 2 represents the outlet node, grid 3 is the normal terrain grid, and the water flow direction is marked inside the blue pipe.
[0042] Figure 5 The simulation was conducted for a rainfall event on August 20, 2017, with a duration of 5700 s and a simulation duration of 6900 s. The infiltration rate measured using the double-ring infiltration method was 90 mm / h. Due to the short rainfall duration, evaporation was negligible. The influence of shrubs and grasses around the rain garden and within the pool on the flow rate was considered, with a Manning coefficient of 0.24. The study area consisted of 81 square grid cells with a size of 5 m. It was assumed that the outflow boundary was an open boundary and the remaining boundaries were closed boundaries, and the Courant number was set to 0.5 during the model calculation.
[0043] Comparison of simulation results and measured results of the rain garden outlet water volume growth process, for example Figure 6 As shown in the figure, the simulation results and the measured results show a good fit in terms of water volume growth trends. The calculated RMSE value is 0.3446, which is less than half the standard deviation of the simulation value (0.5808). Therefore, this coupled model can be reliably applied to the simulation calculation of LID (Low-Intensity Flow) unit-based runoff regulation processes.
[0044] Example 2 This embodiment selects Tianfu Heyuan Community in Fengxi New City, Xixian New Area, Shaanxi Province as the research object, and its location map is shown below. Figure 7 The study area is a typical sponge city community, including various LID (Low Infiltration and Diffusion) facilities, comprehensive pipeline network data, and monitoring equipment, providing complete input data for model validation. The model input data includes community topographic data, land use data, rainfall data, infiltration data, and pipeline network data. The study area is 76,422 m². 2 The topographic accuracy is 1m. Infiltration and Manning parameters are shown in Table 1 below. Infiltration data were obtained using the double-ring infiltration method. Manning parameters under different land use conditions are referenced in the literature. The pipe network distribution map for this community is provided by [reference needed]. Figure 8 As shown, it contains 51 nodes, two outlets, and 49 pipes. Rainfall data is as follows: Figure 5 .
[0045] Table 1 Values of different land use parameters
[0046] The process of monitoring the flow at the community exit is compared with the simulation results, such as... Figure 9 As shown, the simulated flow rate process matches the measured flow rate process trend well. The calculated RMSE value is 0.2460, which is less than half of the standard deviation of the simulated value (0.5297). This proves that the coupled model is reliable in the simulation application of LID runoff regulation process at the community scale.
[0047] Example 3 This embodiment considers a method for simulating urban rainfall-runoff processes in LID (Low-Intensity Discharge) facilities, as detailed below: S1. Obtain basic data of the study area, classify land use, and determine the location and area of LID facilities; S2. Construct a two-dimensional hydrodynamic numerical model and a one-dimensional pipe network model for the study area, respectively, and couple the two models to obtain a coupled model. S3. Select an appropriate calculation method based on the research object and terrain data, set the physical and geometric parameters of the LID facility, and select whether to set the location node and pipeline parameters of the LID facility based on the calculation method. S4. Calculate the water depth based on the infiltration rate, compare the water depth with the outlet weir height of the LID facility, further calculate the overflow rainwater volume, input the calculated overflow rainwater into the coupled model, and perform pipeline hydrodynamic process calculation. Other areas on the surface are calculated using a two-dimensional hydrodynamic model. S5. Repeat S4 until the simulation ends, and output the LID simulation results, 2D surface simulation results, and 1D pipeline simulation results.
[0048] Furthermore, in S1, basic data of the study area is obtained by interpolation of measured elevation points or by using UAV-borne lidar. The basic data of the study area includes hydrological and meteorological data, rainfall data, surface topography data, land use data, etc., and the types, numbers, locations and corresponding geometric parameters of LIDs contained in the study area are statistically analyzed. The land use classification in S1 is as follows: based on natural attributes, it is divided into roads, green spaces, buildings, and underground spaces, and the Manning coefficient and infiltration rate are determined for each land use type.
[0049] Example 4 This embodiment considers a method for simulating urban rainfall-runoff processes using LID facilities. Further, the specific method for S2 is as follows: S2.1 First, the basic data of the study area is processed to form the input parameters required for modeling; S2.2. By dividing the study area into structured grid cells, a two-dimensional hydrodynamic numerical model of the study area is constructed. The two-dimensional hydrodynamic model is calculated using two-dimensional shallow water equations. ; ; Where t represents time, in seconds; 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; F and G 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; i For infiltration source terms; 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; S2.3 Construct a one-dimensional pipeline network model, which is obtained through the one-dimensional Saint-Venant equation:
[0050]
[0051] in, A This refers to the cross-sectional area of the pipe, in meters (m²). 2 ; Q This refers to the pipe flow rate, measured in meters (m³). 3 / s; t represents time, in seconds; s The distance along the flow path for a fixed cross-section, in meters; g This is the acceleration due to gravity, measured in m / s². 2 ; u Flow velocity, in m / s; h The average water depth across the cross-section is expressed in meters (m). S 0 represents the slope gradient at the bottom. S f For the friction ratio decrease; S2.4. Based on the relative relationship between the location, elevation, and two-dimensional surface of the rainwater inlet, the two-dimensional model and the one-dimensional model are coupled to obtain a one-dimensional and two-dimensional coupled model.
[0052] Example 5 This embodiment considers a method for simulating urban rainfall-runoff processes using LID facilities. Further, the specific method in S3 is as follows: S3.1 Determine whether the research object is the runoff control process of a single LID facility or the urban stormwater process that includes LID facilities; S3.2 If the research object is the runoff control process of a single LID facility, then select the LID single unit or LID single unit unitization method: if the LID range is greater than the accuracy of a two-dimensional grid unit, then set the LID as a single facility; if the LID range is less than the accuracy of a two-dimensional grid unit, then process it as a single unit of LID, that is, set it according to the actual proportion of the LID facility, and specify the overflow pipe outlet when there is an overflow pipe. S3.3 If the research object is an urban stormwater process that includes LID facilities, it shall be handled according to the method of coupling LID effect with stormwater process, and the settings shall be made according to the actual proportion of LID facilities. When there is an overflow pipe, the overflow pipe outlet shall be specified, and the overflow pipe and the stormwater pipe network shall be connected.
[0053] Example 6 This embodiment considers the urban rainfall runoff process simulation method of LID facilities. Further, in S3.2, the specific method of setting LID as a single facility is as follows: the inner boundary treatment method based on water balance is used to calculate the flow over the weir. Corresponding grids are selected at the upstream and downstream of the overflow weir. The flow over the weir is calculated by the weir flow formula in the upstream grid. The h on the grid is used as the head on the weir. In the same time step, the increase in water volume on the downstream grid is equal to the decrease in water volume on the corresponding upstream grid to achieve water balance. The finite volume method of Godunov format is used to spatially discretize and solve the two-dimensional shallow water equation to calculate the rainwater process outside the inner boundary. The weir flow formula used is:
[0054] In the formula: and These are two parameters, taking values of 1.6566 and 1.5 respectively, whose magnitudes depend on the inlet type and its geometry; The water head above the weir is expressed in meters (m). The efficiency coefficient represents the inlet blockage level. It has a value of 1 and varies between 0 and 1, where 0 represents complete blockage and 1 represents no blockage.
[0055] The specific method for setting LID as a single unit in S3.2 is as follows: set the location node and pipeline parameters of the LID facility, set the physical and geometric parameters of the LID facility, change the flow calculation method of the node where the LID facility is located, and when calculating the flow of the node where the LID facility is located, determine the difference between the surface water depth around the LID facility and the inlet weir height of the LID facility. When the water depth is less than the inlet weir height, the node does not receive water. When the water depth is greater than the inlet weir height, the node receives water using the weir flow formula. The head above the weir is the surface water depth minus the inlet weir height.
[0056] The specific method for coupling the LID effect with the stormwater process in S3.3 is as follows: the typical LID integrated control effect is coupled with the urban pipe network model. The surface runoff generation and runoff of the model follows the Green-Ampt model to calculate the infiltration process. The Hargreaves method governing equations and the planar two-dimensional shallow water equations are used for calculation. The pipe network hydrodynamic process follows the dynamic wave method, that is, the complete one-dimensional Saint-Venant equations are solved using a one-dimensional hydrodynamic model, or its simplified form, namely diffusion waves and motion waves. The finite difference method is its main numerical solution method.
[0057] Example 7 This embodiment considers a method for simulating urban rainfall runoff processes using LID facilities. Furthermore, in S4, the physical and geometric parameters of the LID facilities include the inlet weir height and width, radius, runoff ratio, runoff coefficient, infiltration rate, and the outlet overflow weir height and width.
[0058] Example 8 This embodiment considers a method for simulating urban rainfall-runoff processes using LID facilities. Further, the specific method in S5 is as follows: S5.1 Water entering the LID range infiltrates according to the actual infiltration rate of the facility to obtain the water depth result; S5.2 Compare the obtained water depth with the outlet weir height of the LID facility. If the water depth after infiltration is greater than the outlet weir height, calculate the flow rate entering the pipeline according to the weir flow formula. This part of the overflow rainwater is the water that the LID facility has not controlled. S5.3 Input the calculated overflow rainwater into the coupled model to calculate the hydrodynamic process of the pipe network. For other areas on the surface, a two-dimensional hydrodynamic model is used for calculation.
[0059] In S5.1, for the simulation calculation of LID facilities, the overflow process at the inlet and outlet of a single facility should be considered during the detailed simulation of a single LID facility. If the size of the computational grid is larger than the size of a single LID facility, then a two-dimensional grid is generalized as an LID facility; if the LID region is larger than a single two-dimensional grid, then a region is generalized as an LID facility. The calculations were performed using the actual area of the LID facility, while the infiltration model was calculated using the Green-Ampt model, and coupled with the pipeline network model based on the actual layout of the overflow outlets.
Claims
1. A method for simulating urban rainfall runoff processes considering LID facilities, characterized by, Specifically as follows: S1, obtain basic data of the study area, and perform land use classification to determine the position and area of LID facilities; S2, construct a two-dimensional water dynamic numerical model and a one-dimensional pipe network model of the study area respectively, couple the two models to obtain a coupled model; S3, select a suitable calculation method according to the research object and topographic data, set the physical and geometric parameters of the LID facilities, and select whether to set the node and pipe parameters at the position of the LID facilities according to the calculation method; S4, calculate the water depth according to the infiltration rate, compare the water depth with the weir height of the LID facility outlet, further calculate the overflow rainwater, input the calculated overflow rainwater into the coupled model, and perform pipe network water dynamic process calculation, and the two-dimensional water dynamic model is used for calculation in other areas of the ground surface; S5, repeat S4 until the simulation is completed, and output the LID simulation results, two-dimensional ground simulation results, and one-dimensional pipe network simulation results.
2. The urban rainfall runoff process simulation method considering LID facilities according to claim 1, characterized by, In S1, the basic data of the study area is obtained by interpolation of measured elevation points or by unmanned aerial laser radar, and the basic data of the study area includes hydro-meteorological, rainfall, ground topography, land use and other data of the study area, and the types, number, position and corresponding geometric parameters of the LID contained in the study area are counted; In S1, the land use classification is specifically: according to the natural properties, it is divided into roads, green lands, houses and underground spaces, and the Manning coefficient and infiltration rate of each land use type are determined.
3. The urban rainfall runoff process simulation method considering LID facilities according to claim 1, characterized by, The specific method of S2 is as follows: S2.1, first process the basic data of the study area to form the input parameters required for modeling; S2.2, construct a two-dimensional water dynamic numerical model of the study area by dividing the study area into structured grid cells, and the two-dimensional water dynamic model is calculated by two-dimensional shallow water equation: ； ； where t is time in s; is a variable vector; is water depth in m; q x and q y are x and y single-width flow in two directions in m 2 / s; F and G are x and y flux vectors in directions; g is the gravitational acceleration in m / s 2 ; u and v are x and y flow velocities in directions in m / s; is a source term vector; i is an infiltration source term; z b is the riverbed bottom elevation in m; is the Chezy coefficient, where n is the Manning coefficient; S2.3, construct a one-dimensional pipe network model, which is calculated by one-dimensional Saint-Venant equation: wherein A A is the cross-sectional area of the pipe, in m 2 ; Q Q is the flow rate of the pipe, in m 3 / s; t is time, in s; s L is the distance along the flow path of the fixed cross-section, in m; g g is the acceleration due to gravity, in m / s 2 ; u v is the flow velocity, in m / s; h h is the average water depth over the cross-section, in m; S 0 is the bed slope gradient; S f is the frictional slope gradient; S2.4, according to the relative relationship between the rainwater inlet position, elevation and two-dimensional ground, the two-dimensional model and the one-dimensional model are coupled to obtain a one-dimensional and two-dimensional coupled model.
4. The urban rainfall runoff process simulation method considering LID facilities according to claim 1, characterized by, The specific method of S3 is as follows: S3.1, determine whether the research object is a single LID facility runoff control process or a city rainwater process containing LID facilities; S3.2, if the research object is a single LID facility runoff control process, select LID monomer or LID monomer unit processing method: if the LID range is greater than one two-dimensional grid cell accuracy, set the LID as a single facility; if the LID range is less than one two-dimensional grid cell accuracy, unitize the LID according to the actual proportion of the LID facility, and specify the overflow pipe outlet if there is an overflow pipe; S3.3, if the research object is a city rainwater process containing LID facilities, process according to the method of coupling LID action and rainwater process, set according to the actual proportion of the LID facility, and specify the overflow pipe outlet if there is an overflow pipe, and the overflow pipe and the rainwater pipe network are in communication.
5. The urban rainfall runoff process simulation method considering LID facilities according to claim 4, characterized by, The specific method of setting LID as a single facility in S3.2 is: calculating over weir flow by using an internal boundary processing method based on water balance, selecting corresponding grids on the upstream and downstream of the overflow weir respectively, calculating the over weir flow of the upstream weir front grid according to the weir flow formula, taking h on the grid as the weir head, and in the same time step, the water volume increased on the downstream grid is equal to the water volume reduced on the corresponding upstream grid to achieve water balance, and calculating the rain and flood process outside the internal boundary by using the finite volume method of Godunov format for spatial discrete solution of two-dimensional shallow water equation; The weir flow formula used is: wherein: and are two parameters, respectively equal to 1.6566 and 1.5, whose value depends on the type of inlet and its geometry; is the weir head, unit m; is the efficiency coefficient, which indicates the inlet clogging condition, value equal to 1, whose value varies between 0 and 1, where 0 indicates complete clogging and 1 indicates no clogging.
6. The urban rainfall runoff process simulation method considering LID facilities according to claim 4, wherein, The specific method of setting LID as a single unit in S3.2 is: setting the node and pipe parameters where the LID facility is located, setting the physical and geometric parameters of the LID facility, and changing the flow calculation method of the node where the LID facility is located. When calculating the flow of the node where the LID facility is located, it is judged whether the surface water depth around the LID facility is less than the height of the LID facility inlet weir. When the water depth is less than the height of the inlet weir, the node does not enter water. When the water depth is greater than the height of the inlet weir, the node enters water according to the weir flow formula, and the weir head is the surface water depth minus the height of the inlet weir.
7. The urban rainfall runoff process simulation method considering LID facilities according to claim 4, characterized by, The specific method of coupling LID effect with rain and flood process in S3.3 is: coupling the typical LID comprehensive control effect with the urban pipe network model, the model surface runoff and infiltration follows the Green-Ampt model to calculate the infiltration process, the Hargreaves method control equation and the planar two-dimensional shallow water equation calculation method, the pipe network hydrodynamic process follows the dynamic wave method, that is, a one-dimensional hydrodynamic model is used to solve the complete one-dimensional Saint-Venant equation set, or its simplified form, that is, the diffusion wave and the motion wave, and the finite difference method is the main numerical solution method.
8. The method of claim 1, wherein the LID facility is considered in the urban rainfall runoff process simulation. The physical and geometric parameters of the LID facility in S4 include the height and width of the inlet weir, the radius, the convergence ratio, the runoff coefficient, the infiltration rate, the height and width of the outlet overflow weir, etc.
9. The method of claim 1, wherein the LID facility is considered in the urban rainfall runoff process simulation. The specific method of S5 is as follows: S5.1, the water entering the LID range is infiltrated according to the actual infiltration rate of the facility, and the water depth result is obtained; S5.2, compare the obtained water depth with the outlet weir height of the LID facility. When the water depth after infiltration is greater than the outlet weir height, calculate the flow size entering the pipe according to the weir flow formula, and this part of the overflow rainwater is the water that the LID facility has not controlled; S5.3, input the calculated overflow rainwater into the coupling model to calculate the pipe network hydrodynamic process, and the two-dimensional hydrodynamic model is used to calculate the other areas on the ground.
10. The method of claim 9, wherein the LID facility is considered in the urban rainfall runoff process simulation. In S5.1, the LID facility simulation calculation is considered in the single facility simulation process of the LID facility, and the overflow process at the inlet and outlet of the single facility is considered; If the size of the calculation grid is greater than the size of a single LID facility, a two-dimensional grid is generalized as a LID facility, and if the LID area is greater than a single two-dimensional grid, a piece of area is generalized as a LID facility. The actual area of LID facilities is used in the calculation process, and the Green-Ampt model is used in the infiltration model. The actual layout of the overflow port is coupled with the pipe network model.