Urban inland inundation simulation method considering rainwater inlet performance limitation

Abstract

The invention discloses an urban inland inundation simulation method considering rainwater inlet performance limitation. The urban inland inundation simulation method comprises the steps that an irregular reservoir with a bottom orifice and a top overflow weir is added to an SWMM model ground surface inlet, wherein the drainage efficiency of the reservoir is equal to that of a ground surface ponding depression, and the rainwater inlet performance limitation is considered and simulated. According to the method, the performance of the rainwater inlet is considered in flood simulation, and a large amount of flood events caused by insufficient performance of the urban rainwater inlet in the current situation are simulated more accurately, so that a better forecasting effect is brought.

Description

Technical Field

[0001] The invention relates to the field of urban flood numerical simulation and municipal drainage efficiency evaluation, and in particular to an urban waterlogging simulation method that takes into account rainwater inlet performance limitations. Background Art

[0002] Traditionally, insufficient sewer capacity is considered the primary cause of urban flooding. However, recent studies have shown that flood events caused by poor performance of urban stormwater inlets are far more common than capacity issues. For example, urban flood statistics for Guangzhou in 2022 show that about 78% of flood events were caused by insufficient performance of stormwater inlets, rather than sewer capacity issues. Urban stormwater inlets are responsible for the interaction of surface runoff with the drainage system, but their performance is often affected by factors such as blockage, aging, poor design, substandard construction quality, low design standards, and environmental changes. These problems prevent rainwater from entering the drainage system smoothly, leading to ground waterlogging and flooding problems.

[0003] In order to achieve accurate urban flood simulation and prediction, the complex water flow exchange process between surface water and drainage system must be described in detail. However, due to the large number of rainwater inlets, diverse types, uncertain operation conditions and potential random defects, accurate simulation of these processes faces great challenges. In addition, in recent years, with the widespread application of urban drainage design concepts such as sponge city (SCP), low impact development (LID) and green infrastructure (GI), the complexity of rainwater inlet systems has continued to increase, which has further affected the accuracy of urban flood simulation. Therefore, it has become an inevitable trend to consider the performance of rainwater inlets in flood simulation models.

[0004] The Storm Flood Management Model (SWMM) is a typical traditional model that does not consider the impact of stormwater inlet performance on urban flood formation. In view of this shortcoming, the present invention solves the problem that SWMM fails to incorporate stormwater inlet performance limitations in simulation by improving its modeling method. Summary of the invention

[0005] The purpose of the present invention is to provide an urban flooding simulation method taking into account the performance limitations of rainwater inlets, including an improved SWMM model. The improved SWMM model includes adding an irregular water storage tank with a bottom orifice and a top overflow weir at the surface inlet of the SWMM model, whose drainage efficiency is equivalent to that of a surface water pond, to achieve consideration and simulation of the performance limitations of rainwater inlets.

[0006] Furthermore, the specific steps of the method are as follows:

[0007] Step 1: Draw independent drainage units and watershed areas for urban waterlogging points by referring to the method of drawing watershed boundaries for reservoirs in natural watersheds;

[0008] Step 2: Draw a water depth-area / volume curve for the depression where the waterlogging point is located. Based on DEM, use ARCGIS software to draw a waterlogging curve for the urban waterlogging point.

[0009] Step 3: Model the drainage facilities covered by the surface outside the catchment area of ​​the water accumulation point in the target drainage unit according to the standard modeling method of the stormwater management model SWMM;

[0010] Step 4: For the drainage facilities in the area covered by the waterlogging point catchment area, the improved SWMM model is used to model the waterlogging point and its catchment area. The waterlogging point and its catchment area are modeled as a surface water storage unit with a bottom orifice and a top overflow weir, a manhole connected to the orifice, an underground drainage pipe connected to the manhole, and a catchment area connected to the storage unit.

[0011] Step 5: Model calibration, including adjusting model parameters so that the model output is accurately aligned with the observed data. SWMM parameters are divided into measurable parameters and unmeasurable parameters. In addition to the unmeasurable parameters when using the standard modeling process, the parameters that need to be calibrated also include the bottom orifice, top overflow weir, surface water storage unit, inspection well, underground drainage pipe and catchment area generalized in the improved method.

[0012] Furthermore, the specific steps for drawing the catchment area of ​​the independent drainage unit and water accumulation point in step 1 are as follows:

[0013] Step 1: Use the large-small-medium division method. First, the entire basin is initially controlled by the natural water system to prevent boundary errors caused by premature artificial division.

[0014] Step 2: Use the Watershed Delineator module in ArcSWAT to subdivide the natural water system into smaller plots based on the natural terrain. Each small watershed defines the watershed range, runoff path within the watershed, and outlet.

[0015] Step 3: According to the runoff direction and the direction of the outlet, the small watersheds that discharge into the same pipe or road and finally discharge into the same drainage outlet are merged into medium watersheds. These medium watersheds are the results of the independent drainage unit division, which are divided into low-risk drainage units without waterlogging points and high-risk drainage units with waterlogging points;

[0016] Step 4: The high-risk drainage units containing waterlogging points are further subdivided to create a catchment area for each waterlogging point, and the small watersheds with runoff directions pointing to the same surface waterlogging point are merged to form the catchment area of ​​the area;

[0017] Furthermore, the specific steps of using ARCGIS software to draw waterlogging curves for urban waterlogging points in step 2 are as follows:

[0018] Step 1: In the ArcMap toolbar, click "ArcToolbox", select the "Contour" tool, open the contour generation dialog box, and set the height interval of the generated contour lines. When generating a contour line every 0.1 meters, enter "0.1";

[0019] Step 2. After setting the parameters, click "OK" to run the tool. GIS will calculate and generate contour lines based on the DEM data.

[0020] Step 3. Use the generated contour lines to draw contour surfaces to obtain a set of elevation-area data, and convert the elevation-area into water depth-area data based on the elevation of the lowest point of the water accumulation point. Use the platform volume calculation formula to convert the water depth-area data into water depth-volume data, which is the water depth-volume curve of the water accumulation point.

[0021] Furthermore, the specific steps of modeling the improved SWMM model in step 4 are as follows:

[0022] Step 1: In the SWMM model, each stormwater inlet has its own catchment area. However, since it is very challenging to accurately measure the performance of each inlet, all stormwater inlets within the depression catchment area are combined into a large stormwater inlet with equivalent drainage capacity to all actual stormwater inlets.

[0023] Step 2: This large rainwater inlet is located at the bottom of the surface water storage tank, represented by the drainage hole at the bottom of the surface water storage tank. An overflow weir is set on the top of the water storage tank to simulate the overflow dynamics of water flow after the water accumulation depression is full. The entire catchment area of ​​the depression where the water accumulation point is located is regarded as a sub-catchment area connected to this large rainwater inlet;

[0024] Step 3: The surface reservoir represents a water-logged depression. It is an irregularly shaped reservoir defined by the depth-area curve parameters. The rainfall in this subcatchment area will be stored in the reservoir through the orifices. Some water enters the underground drainage system through the large stormwater inlet of SWMM, while the runoff that does not enter the underground drainage system due to insufficient inlet capacity remains in the surface reservoir, forming surface water.

[0025] Furthermore, the measurable parameters in the standard modeling step in step five include subcatchment, pipe length, slope and cross-sectional shape, which do not require calibration, while the unmeasurable parameters include roughness and permeability coefficient, which require calibration. All parameters in the improved SWMM model step require calibration, including subcatchment, surface water storage, orifice, weir, manhole and drainage pipe.

[0026] The present invention has the following advantages: by incorporating considerations of rainwater inlet performance into flood simulation, the present invention provides a more accurate simulation of flood events that are currently widespread and are caused by insufficient urban rainwater inlet performance, thereby bringing about better forecasting results.

[0027] The present invention can directly simulate the flood model without coupling with the surface model, thereby reducing the complexity of the model.

[0028] The present invention greatly improves the running speed of the model by simplifying the drainage infrastructure of the surface flood-prone depression, thereby reducing the demand for computing resources.

[0029] The present invention can simulate the flow exchange process of surface and underground drainage facilities in the waterlogged area while simulating urban floods, so as to obtain comprehensive performance data of the drainage facilities in this area, thereby reducing the workload of model updating and the difficulty of model updating. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is the result of the small watershed division of the present invention;

[0031] Figure 2 It is the independent drainage unit / medium watershed division result map of the present invention;

[0032] Figure 3 It is a water accumulation point and water catchment area division result diagram of the present invention;

[0033] Figure 4 It is a generalized schematic diagram of the drainage infrastructure in the water collection area of ​​the water accumulation point of the present invention;

[0034] Figure 5 Two flow path diagrams of runoff formed by urban waterlogging of the present invention;

[0035] Figure 6 A diagram of model objects and their connection structures for model visualization of the present invention;

[0036] Figure 7 This is a surface flood simulation result diagram of the present invention on April 23, 2022;

[0037] Figure 8 This is a surface flood simulation result diagram of the present invention on June 7, 2022;

[0038] Fig. 9 It is a simulation result diagram of underground pipeline capacity utilization on April 23, 2022 of the present invention;

[0039] Fig.10 This is a simulation result diagram of the underground pipeline capacity utilization on June 7, 2022 of the present invention. DETAILED DESCRIPTION

[0040] In this embodiment, a waterlogging point at Tianhe North Road, Tianhe District, Guangzhou City is taken as an example to perform simulation, and the specific steps are as follows:

[0041] Step 1: Divide the target waterlogging point into independent drainage units and the watershed area of ​​the waterlogging point. The specific results are as follows: Figure 1 and Figure 2 As shown;

[0042] Step 2: Calculate the water depth-area / volume curve of the waterlogging point. The specific results are shown in Table 1.

[0043] Step 3: The surface outside the catchment area of ​​the water accumulation point within the target drainage unit, such as Figure 2 As shown, the covered drainage facilities are modeled according to the standard modeling method provided in the Stormwater Management Model SWMM User Manual (Version 5.2);

[0044] Step 4: For water accumulation points and water catchment areas, Figure 2 The drainage facilities in the covered area are modeled. The flood-prone area and its catchment area are modeled as a surface water storage unit with a bottom orifice and a top overflow weir, a manhole connected to the orifice, an underground drainage pipe connected to the manhole, and a catchment area connected to the storage unit. The specific connection structure of the visualization object is generalized as follows Figure 3 As shown, the model entities are Figure 6 ;

[0045] Step 5: Calibrate the model. See the specific results. Figure 7 , Figure 8 , Fig. 9 and Fig.10 The simulation results in the figure show that the Nash efficiency coefficient (NSE) of the simulated flood process on April 23 and June 7, 2022 is 0.90, 0.83, and the relative error (RE) of the simulated flood peak is 0.47%, 0.27%. According to the "Hydrological Information Forecast Specification", the simulation accuracy reaches Class B and above. The simulation results of underground pipeline utilization are NSE of 0.76, 0.33, and the RE of the simulated flood peak is 1.64%, 1.45%.

[0046] In this embodiment, how to read the model output results: at any given moment, the depth, volume and inundation range of the surface flood can be expressed by the storage depth and volume of the surface water storage unit in the model, and the corresponding area obtained by linear interpolation of the water depth-area curve according to the storage depth.

[0047] It is worth noting that when the manhole connected to the bottom orifice of the ground storage unit is overloaded and overflows, since SWMM does not provide a container for this overflow, the overflowing water cannot enter the storage unit directly through the bottom hole. Therefore, it is necessary to perform a manual correction to take into account its impact on the water accumulation in the storage unit. This includes recalculating the amount of water accumulated in the storage unit from the time the manhole began to overflow, and interpolating the storage curve to obtain the corrected water depth corresponding to the new water accumulation. The correction process is divided into two stages: accumulation stage and return stage.

[0048] (1) Accumulation stage: From the beginning to the end of the overflow at the intersection, the accumulated overflow at the intersection is directly added to the existing water volume of the storage unit as the corrected water volume, and then the new water depth is determined by linear interpolation of the water depth-volume curve.

[0049] (2) Backflow stage: When the overflow process of the inspection well connected to the bottom orifice of the ground storage unit ends, the underground drainage pipe has residual capacity to accept new surface runoff. Therefore, the influence of the increased water depth of the overflow water on the orifice drainage flow must be considered. According to the following formulas (1) and (2) for calculating the orifice flow, the water depth of the surface water storage tank is the only parameter that affects the bottom orifice drainage flow. A simplified method is to directly use formula (3) to calculate the corrected bottom orifice flow Q ′ t , subtract the corrected drainage volume Q from the water accumulation in the previous period ′ t ×t to obtain the corrected water volume of the current period, and then use the corrected water volume to interpolate in the water depth-volume curve to obtain the corrected water depth. This process is repeated in each subsequent calculation period until the corrected water depth is equal to the initial depth calculated by the model and the correction is stopped.

[0050]

[0051]

[0052] Among them, Q t is the flow rate through the orifice at time t, which is equal to the model output value, Q'' t is the corrected flow rate through the orifice at time t, C d and C ′ d is the flow coefficient (dimensionless) of the original simulation and correction of the model. Its value is related to the shape of the orifice plate and the fluid properties. It is usually determined by experiments. The shape and fluid properties do not change during the flow correction calculation, so the two are equal. In the example, it is taken as 0.65. A 0,t-1 and A ′ 0,t-1 is the original and corrected opening area, both are submerged outflow, so they are equal, g is the gravitational acceleration (unit: m / s2 ), the standard value is 9.81m / s 2 ,h t-1 and h′ t-1 It is the water level difference between the upstream and downstream of the orifice, which is equal to the water accumulation depth.

[0053] Table 1 Water depth-volume curves of waterlogging points calculated using DEM

[0054] Although the specific embodiments of the present invention are described in detail in conjunction with the accompanying drawings, it should not be understood as limiting the scope of protection of the present invention. Within the scope described in the claims, various modifications and variations that can be made by those skilled in the art without creative work still belong to the scope of protection of the present invention.

[0055] Table 1

[0056]

Claims

1. A method for simulating urban flooding considering stormwater inlet performance limitations, including an improved SWMM model, characterized in that: The improved SWMM model includes adding an irregular water storage tank with a bottom orifice and a top overflow weir at the surface inlet of the SWMM model, whose drainage efficiency is equivalent to that of a surface pond, to realize the consideration and simulation of the performance limitation of the stormwater inlet.

2. The urban flooding simulation method considering rainwater inlet performance limitation as claimed in claim 1, characterized in that: The specific steps of the method are as follows: Step 1: Draw independent drainage units and watershed areas for urban waterlogging points by referring to the method of drawing watershed boundaries for reservoirs in natural watersheds; Step 2: Draw a water depth-area / volume curve for the depression where the waterlogging point is located. Based on DEM, use ARCGIS software to draw a waterlogging curve for the urban waterlogging point. Step 3: Model the drainage facilities covered by the surface outside the catchment area of ​​the water accumulation point in the target drainage unit according to the standard modeling method of the stormwater management model SWMM; Step 4: For the drainage facilities in the area covered by the waterlogging point catchment area, the improved SWMM model is used to model the waterlogging point and its catchment area. The waterlogging point and its catchment area are modeled as a surface water storage unit with a bottom orifice and a top overflow weir, a manhole connected to the orifice, an underground drainage pipe connected to the manhole, and a catchment area connected to the storage unit. Step 5: Model calibration, including adjusting model parameters so that the model output is accurately aligned with the observed data. SWMM parameters are divided into measurable parameters and unmeasurable parameters. In addition to the unmeasurable parameters when using the standard modeling process, the parameters that need to be calibrated also include the bottom orifice, top overflow weir, surface water storage unit, inspection well, underground drainage pipe and catchment area generalized in the improved method.

3. The urban flooding simulation method considering rainwater inlet performance limitation as claimed in claim 2, characterized in that: The specific steps of drawing the catchment area of ​​independent drainage units and water accumulation points in step 1 are as follows: Step 1: Use the large-small-medium division method. First, the entire basin is initially controlled by the natural water system to prevent boundary errors caused by premature artificial division. Step 2: Use the Watershed Delineator module in ArcSWAT to subdivide the natural water system into smaller plots based on the natural terrain. Each small watershed defines the watershed range, runoff path within the watershed, and outlet. Step 3: According to the runoff direction and the direction of the outlet, the small watersheds that discharge into the same pipe or road and finally discharge into the same drainage outlet are merged into medium watersheds. These medium watersheds are the results of the independent drainage unit division, which are divided into low-risk drainage units without waterlogging points and high-risk drainage units with waterlogging points; Step 4: The high-risk drainage units containing waterlogging points are further subdivided to create a catchment area for each waterlogging point, and the small watersheds with runoff directions pointing to the same surface waterlogging point are merged to form the catchment area of ​​the area.

4. The urban waterlogging simulation method considering rainwater inlet performance limitation as claimed in claim 2, characterized in that: The specific steps of using ARCGIS software to draw a waterlogging curve for urban waterlogging points in step 2 are as follows: Step 1: In the ArcMap toolbar, click "ArcToolbox", select the "Contour" tool, open the Contour Generation dialog box, and set the height interval for generating contour lines. When generating a contour line every 0.1 meter, enter "0.1"; Step 2. After setting the parameters, click "OK" to run the tool. GIS will calculate and generate contour lines based on the DEM data. Step 3. Use the generated contour lines to draw contour surfaces to obtain a set of elevation-area data, and convert the elevation-area into water depth-area data based on the elevation of the lowest point of the water accumulation point. Use the platform volume calculation formula to convert the water depth-area data into water depth-volume data, which is the water depth-volume curve of the water accumulation point.

5. The urban waterlogging simulation method considering rainwater inlet performance limitation as claimed in claim 2, characterized in that: The specific steps of the improved SWMM model in step 4 are as follows: Step 1: In the SWMM model, each stormwater inlet has its own catchment area. However, since it is very challenging to accurately measure the performance of each inlet, all stormwater inlets within the depression catchment area are combined into a large stormwater inlet with equivalent drainage capacity to all actual stormwater inlets. Step 2: This large rainwater inlet is located at the bottom of the surface water storage tank, represented by the drainage hole at the bottom of the surface water storage tank. An overflow weir is set on the top of the water storage tank to simulate the overflow dynamics of water flow after the water accumulation depression is full. The entire catchment area of ​​the depression where the water accumulation point is located is regarded as a sub-catchment area connected to this large rainwater inlet; Step 3: The surface reservoir represents a water-logged depression. It is an irregularly shaped reservoir defined by the depth-area curve parameters. The rainfall in this subcatchment area will be stored in the reservoir through the orifices. Some water enters the underground drainage system through the large stormwater inlet of SWMM, while the runoff that does not enter the underground drainage system due to insufficient inlet capacity remains in the surface reservoir, forming surface water.

6. The urban waterlogging simulation method considering rainwater inlet performance limitation as claimed in claim 2, characterized in that: The measurable parameters in the standard modeling step in step five include sub-catchment area, pipe length, slope and cross-sectional shape, which do not require calibration. The unmeasurable parameters include roughness and permeability coefficient, etc., which require calibration. The improvement is that all parameters in the SWMM model step need to be calibrated, including sub-catchment area, surface water tank, orifice, weir, inspection well and drainage pipe.

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