A pipeless exploration data inland waterlogging risk distribution evaluation method

Abstract

The application discloses a pipe-free survey data inland waterlogging risk distribution evaluation method, focuses on proposing a minimum calculation unit drawing method, a waterlogging total amount calculation method and a waterlogging diffusion to inland waterlogging distribution method, and mainly comprises the following steps: drawing a sub-water catchment area and an "equal flow time surface" based on rainwater catchment characteristics, combining drainage zoning planning, roads, pipe network outlet distribution and the like; proposing that the waterlogging total amount of the sub-water catchment area is equal to the total amount of precipitation in the area minus the total amount of infiltration, the total amount of pipe network water storage and the total amount of pipe network water delivery, each of which is calculated by using a rainstorm intensity formula, a trapezoidal method, a design flow formula based on a specification, a generalized pipe network water storage length, an "equal flow time surface" catchment method, a deviation principle, a farthest path principle and "three key times"; reconstructing a terrain of a research area, forming a waterlogging "diffusion range" with a sequence row and column number and an elevation and a "diffusion base point" with a lowest elevation and a waterlogging amount based on a certain rule range and sequencing; diffusing outward with the base point as a center; obtaining a waterlogging range and a waterlogging water level by using a bisection iteration method combined with a waterlogging amount error; and then obtaining an inland waterlogging risk distribution area.

Description

Technical Field

[0001] This invention relates to urban flooding risk assessment technology, specifically to a method for assessing the distribution of urban flooding risk in plain cities without available survey data. Background Technology

[0002] With the acceleration of urbanization, the urban population and impervious area are increasing rapidly, river channels are narrowing, flood storage and detention areas are shrinking, and flood discharge capacity is decreasing. Coupled with low standards and slow construction and upgrading of drainage facilities, urban vulnerability to flooding disasters is increasing. Furthermore, influenced by both human activities and natural factors, global warming, El Niño, and La Niña have led to a significant increase in extreme weather events. The total amount, frequency, intensity, and duration of heavy rainfall are continuously rising, further aggravating the disaster risk of extreme weather events. This exacerbates the severity and difficulty of urban flooding disasters, triggering secondary disasters affecting lifelines and causing greater damage to people and the socio-economic situation.

[0003] Conducting urban flooding risk assessments is one of the means to prevent urban flooding disasters. Currently, there are two main methods for urban flooding risk analysis: traditional numerical simulation methods based on physical equations and emerging machine learning algorithms based on large data sources. However, both methods are severely hampered by the availability of high-precision data. The construction, calibration, and validation of conventional urban flooding models require a large amount of reliable drainage system survey data, high-precision topographic data, land use data, river cross-section data, meteorological and hydrological data, inundation range, inundation depth, and inundation duration. Machine learning requires long-term accumulated hydrological and inundation data. However, due to varying local economic foundations, survey data, data management systems, and data granularity, different problems arise in practical applications, making it difficult for some cities to successfully advance urban flooding risk assessments.

[0004] Therefore, how to quickly assess the risk of urban flooding before a rainstorm occurs, especially in cities lacking complete drainage network data and with poor economic foundations, has practical significance and application prospects in the field of urban flood disaster prediction, early warning, and urban disaster prevention and mitigation. Summary of the Invention

[0005] In view of the above-mentioned shortcomings in the prior art, the method for assessing urban flooding risk distribution in plain cities without drainage network data provided by the present invention solves the problem that the existing technology makes it difficult to carry out urban flooding risk assessment in some cities when complete drainage network data is lacking.

[0006] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0007] A method for assessing the risk distribution of urban flooding in plains cities without available survey data is provided, comprising the following steps:

[0008] S1. Obtain the urban planning map of the city to be evaluated, divide it into multiple sub-catchment areas, and divide it into multiple "iso-flow surfaces" according to the street distribution within the sub-catchment areas;

[0009] S2. Reconstruct the terrain of the city to be evaluated, then draw the minimum bounding rectangle of the sub-catchment area, and create fishing nets and points; assign values ​​to the reconstructed terrain and the highest elevation inside and outside the sub-catchment area respectively, forming a water accumulation "diffusion range" file with ordered row and column numbers and elevation point attributes;

[0010] S3. Calculate the total precipitation and total infiltration in the sub-catchment area at any given time; determine the water storage length and pipe diameter of the drainage network, and calculate the total water storage of the drainage network accordingly.

[0011] S4. Based on the water catchment time of the "isochronous surface" in the sub-catchment area, determine its net rainfall process, and then calculate the runoff flow process of the sub-catchment area. Determine the runoff start time, the start time of water accumulation, and the maximum water accumulation time. Based on the three times, calculate the total water transfer of the sub-catchment area.

[0012] S5. Calculate the maximum total water accumulation based on the formula for total water accumulation and the time of maximum water accumulation; calculate the total water accumulation at any time based on the runoff flow process of the sub-catchment area.

[0013] S6. Based on the topography of the sub-catchment area before filling the depression, select the lowest elevation point in the sub-catchment area, and combine it with the calculated total water volume to form a water "diffusion baseline point" file that includes ordered row and column numbers, elevation and water volume;

[0014] S7. Using the diffusion base point as the center, the water spreads outward within the range of the "diffusion range" file. During the diffusion, the actual water level after diffusion is calculated by combining the bisection iteration method with the water volume error. The water range and water level are obtained, and then the water depth is obtained. Finally, the distribution area of ​​urban flooding risk is obtained.

[0015] Furthermore, step S1 further includes:

[0016] S11. Obtain the city planning map of the city to be evaluated and divide it into multiple watershed areas;

[0017] S12. Based on the distribution of the city's dual drainage network, waterways, and main streets, each catchment area is divided into multiple sub-basins.

[0018] S13. Based on the distribution of drainage outlets at the end of the drainage network in the sub-basin, the sub-basin is divided into multiple sub-catchment areas, and based on the street distribution within the sub-catchment areas, it is divided into multiple "iso-flow time surfaces".

[0019] Step S2 further includes:

[0020] S14. The sub-catchment area is divided into grids, and the terrain is reconstructed by using ground topographic data, filling depressions, raising the elevation of unflooded areas, and terrain fusion.

[0021] S15. Draw the minimum bounding rectangle of the sub-catchment area, and create a fishing net and points; assign values ​​to the sub-catchment area and its interior and exterior using reconstructed terrain and highest elevation respectively, forming a water accumulation "diffusion range" file with ordered row and column numbers and elevation point attributes.

[0022] The beneficial effects of the above technical solution are as follows: The above method mainly proposes a method for drawing the minimum construction range "sub-catchment area" and the minimum calculation unit "isoflow temporal surface". On the one hand, its minimum calculation unit is larger than the grid unit of conventional numerical model construction, which improves the calculation speed; on the other hand, it can quickly avoid the complexity and data acquisition difficulties of drawing sub-catchment areas required by conventional numerical models, which require high-precision terrain and distribution of all drainage pipe networks and rainwater grates in the initial stage. Instead, it draws efficiently based on the characteristics of the runoff, combined with factors such as drainage zones, road width, dual drainage pipe networks, and distribution of drainage outlets at the end of the drainage pipe network, with lower calculation and data acquisition costs. This is also a key link in breaking down the study area into a whole for efficient calculation, and plays a foundational role in quickly assessing the risk of urban flooding.

[0023] Furthermore, methods for calculating the total precipitation within a sub-catchment area include:

[0024] Rainfall data for the sub-catchment area was obtained using meteorological bureau data or rainstorm intensity formulas, and rainfall sequences at the same time intervals were extracted to construct a rainfall sequence, which includes rainfall time and rainfall intensity.

[0025] Based on the rainfall sequence, the rainfall intensity at any given time can be obtained by interpolation:

[0026]

[0027] Where p(t) x ) for t x Rainfall intensity at any given time, mm / h; t x For any time interval, h; t ID For any given time, the closest to t in the rainfall sequence x And compared to t x The moment of light rainfall is h; Δt is the time interval, h; p(t) ID ) and p(t ID +Δt) are respectively t ID and t ID +Δt, rainfall intensity, mm / h;

[0028] Calculate the total precipitation in the sub-catchment area at any given time:

[0029]

[0030] Wherein, P(t) x ) for t x Total precipitation at any given time, m 3 p(t) and p(t+Δt) are the rainfall intensities at times t and t+Δt, respectively, in mm / h; x0 is the first moment of the rainfall sequence; S is the area of ​​the sub-catchment area, in m³. 2 .

[0031] The beneficial effects of the above technical solution are as follows: Rainfall sequences are generally obtained from meteorological bureaus or calculated using rainstorm intensity formulas. The conventional form of rainfall sequences is generally based on a certain time step and is formed in conjunction with the corresponding rainfall intensity. In order to meet actual needs, this solution proposes a method for calculating rainfall intensity and total rainfall at any time, mainly to provide a basis for calculating the total water accumulation at any time in the later period.

[0032] Furthermore, methods for calculating the total infiltration volume of sub-catchment areas include:

[0033] Calculate the infiltration rate at time t based on the steady-state infiltration rate and the initial infiltration rate:

[0034] f(t) = f c +(f0―f c )*e ―kt

[0035] Where f(t) is the infiltration rate at time t, mm / h; f c The infiltration rate is set to a stable infiltration rate (mm / h); f0 is the initial infiltration rate (mm / h); and k is the infiltration attenuation coefficient.

[0036] Calculate the infiltration rate at any given time:

[0037]

[0038] Where, f(t) x ) for t x Infiltration rate at time t, mm / h; f(t) ID +Δt) and f(t) ID ) are respectively t ID +Δt and t ID Infiltration rate at any given time;

[0039] Based on the infiltration rate f(t) and f(t) x ), calculate the total infiltration at any given time:

[0040]

[0041] Wherein F(t) x ) for t x The total amount of infiltration at time m 3 f(t+Δt) is the infiltration rate at time t+Δt, in mm / h.

[0042] The beneficial effects of the above technical solution are as follows: The infiltration process is generally obtained through the Horton formula or empirical values. Its conventional form is generally based on a certain time step and combined with the corresponding infiltration intensity. In order to meet actual needs, this solution proposes a method for calculating the infiltration intensity and total infiltration at any time, mainly to provide a basis for calculating the total water accumulation at any time in the later stage.

[0043] Furthermore, methods for calculating the total water storage capacity of the drainage network include:

[0044] Based on the area of ​​the sub-catchment area, calculate the design flow rate of the rainwater in the drainage network designed for the sub-catchment area:

[0045] Q s =3600qψS

[0046] Among them, Q s Design flow rate for rainwater, m 3 / h; q is the design rainfall intensity, m3 / (m2·s); ψ is the comprehensive runoff coefficient; S is the area of ​​the sub-catchment area, m 2 ;

[0047] Calculate the diameter of the drainage network based on the design flow rate of rainwater in the drainage network:

[0048]

[0049] Where d is the diameter of the rainwater pipe, in meters; v is the design flow velocity of the pipe, in meters per second, which, according to the specifications, ranges from 0.75 m / s to 5 m / s.

[0050] When drainage network data is lacking for a sub-catchment area, the sub-catchment area is generalized into several "iso-flow time surfaces" along the main road, and the length of the water storage network is generalized as the sum of the straight-line distance from the end of the drainage network outlet to the farthest "iso-flow time surface" and the main road within the sub-catchment area.

[0051] Calculate the total water storage capacity of the drainage network based on the pipe diameter and the length of the water storage pipes:

[0052]

[0053] Among them, V s The water storage capacity of the drainage network is expressed in m. 3 L represents the pipe length, in meters (m).

[0054] The beneficial effects of the above technical solution are as follows: Current methods for simplifying water accumulation calculations generally neglect the water storage capacity of pipe networks. To further improve the accuracy of water accumulation calculations, this solution considers the water storage capacity of pipe networks, which is directly related to pipe diameter and storage length. Considering the difficulty in obtaining pipe network data in research areas without such data, this solution uses the design flow formula in the standard and the flow velocity within a typical plain urban pipe network to further derive the pipe diameter. Based on the general rules of pipe network layout and combined with road network distribution, this solution proposes a method for generalizing the pipe network storage length, obtaining a relatively difficult-to-determine variable through generalization, thus providing a simpler way to calculate pipe network storage capacity. Significant improvements have been achieved in terms of generalization method, calculation accuracy, and calculation efficiency.

[0055] Furthermore, step S4 further includes:

[0056] Based on the initial loss and subsequent loss method, the net rainfall process is calculated within the same time interval:

[0057]

[0058] Where R is the net rainfall depth (mm); p is the rainfall intensity (mm / h); and I0 is the initial loss (mm). P' is the average post-drop rate, mm / h; P′ is the rainfall that does not generate runoff in the later stages, mm; t R It is the duration of over-osmosis, i.e., the duration of runoff, in hours;

[0059] Based on the ratio of longitudinal depth in the confluence direction, calculate the net rainfall process for each offset "isotropic surface":

[0060]

[0061] in, for Take the integer T i Δt is the time when the i-th "isotropic surface" converges to the drainage outlet, t; Δt is the net rainfall sequence time interval, t; For the integer value; y = T i modΔt is The modulo operator is the remainder value. R is the coefficient; i,t R is the net rainfall depth at time t of the i-th "isotropic surface", in mm; t-xΔt and R t-(1+x)Δt The net rainfall depths, in mm, are calculated using the initial and subsequent loss methods at times t―xΔt and t―(1+x)Δt, respectively.

[0062] The process of calculating the runoff flow rate of the sub-catchment area:

[0063]

[0064] Among them, Qt Let m be the runoff flow rate at time t. 3 / h;R t R t―1 R t―2 and R t―(n―1) The net rainfall amounts, in mm, are given at times t, t-1, t-2, and t-(n-1); f1, f2, f3, f n The runoff areas for the 1st, 2nd, 3rd, and nth isocurrent time zones are respectively, m 2 n represents the total number of medium-flow time zones in the sub-catchment area; L i Let t be the runoff length of the i-th "isotropic surface", in meters; i,1 t represents the time it takes for surface runoff from the i-th "isotropic surface" to reach the storm drain grate, ranging from 0.15 to 0.25 hours; i,2 , h, represents the time it takes for rainwater from the i-th "isotropic surface" to reach the drain outlet in the drainage network; v is the flow velocity of water in the drainage network, m / s.

[0065] According to the objective function Q t =Q s Determine the start time t of the abortion. f Time t for water accumulation to begin a Maximum water accumulation time t m Q s The design flow rate of rainwater for the drainage network is given in m. 3 / h;

[0066] Based on runoff flow rate Q t and the time t when water begins to accumulate a Calculate the total water transport volume of the drainage network:

[0067]

[0068] Among them, V c (t) represents the total water transfer volume at time t, m 3 ;t f The time of onset of abortion is h; t a The time from the start of water accumulation is h; t x Let h be any time interval; Δt be the time interval, h; Q t+Δt Let m be the runoff flow rate at time t+Δt. 3 / h.

[0069] The beneficial effects of the above technical solution are as follows: This solution can calculate the total water conveyance of the pipeline network in the study area through the above method. In the existing technology, the more accurate method requires the construction of a large amount of basic high-precision data such as topography, remote sensing images, pipe diameter, pipe length, well depth, rain grate, and drainage outlet to construct a flood model of the study area. The flow process and pipeline water conveyance capacity are calculated by simulating the process. This method involves a lot of data, a complex process, and high time cost for model construction.

[0070] This scheme proposes comparing the runoff process of a sub-catchment area with the design flow rate, identifying "three key times," and using the maximum water accumulation time as a boundary to calculate the water delivery volume through time discrimination. The key to runoff calculation lies in introducing the concepts and methods of "isoflow timelines" and "isoflow time surfaces" from hydrology, and incorporating the differences in the actual confluence time of the "isoflow time surfaces" in the study area for offsetting, thus quickly obtaining the runoff process. This ingenious transformation efficiently calculates the runoff process and the total water delivery volume of the pipeline network with relatively low data and time costs, despite computational complexity, making it one of the key elements in calculating the total water accumulation in the study area.

[0071] Furthermore, the time t when the water accumulation is at its maximum is calculated. m The corresponding maximum total water accumulation:

[0072] V(t=t m )=P(t m )-F(t m )-V c (t m )-V s

[0073] Where, V(t=t) m ) for t m The maximum total water accumulation at time t; P(t) m ) for t m Rainfall at any given time, in m 3 ;F(t) m ) for t m Infiltration rate at time m 3 V c (t m ) for t m Total amount delivered at any time, m 3 V s The water storage capacity of the water supply network is m. 3 .

[0074] Furthermore, at time t, the local surface water level decreased to 0. e When the following formula is satisfied:

[0075] Function: V wl (t)=P(t)-F(t)-V c (t)-Vs

[0076] Objective function:

[0077] Constraint: t ≥ t m

[0078] Among them, V wl (t) represents the water accumulation at time t, in m. 3 P(t) represents the precipitation at time t, in meters. 3 F(t) represents the infiltration rate at time t, m 3 V c (t) represents the total amount transported at time t, m 3 ;

[0079] Based on the time t when the surface water level drops to 0. e The formula satisfies the condition to calculate the total water accumulation V at any given time. wl (t):

[0080]

[0081] Wherein, P(t) f ) for t f Rainfall at any given time, in m 3 .

[0082] The beneficial effects of the above technical solution are as follows: The usual method for calculating the water volume at any given time requires constructing a high-precision numerical waterlogging model and adjusting the calculation step size. In order to solve the problem of calculating this water volume value without constructing a high-precision numerical waterlogging model, this solution proposes to calculate the time when the water volume is 0 by calculating the objective function. By comparing any given time with "four key moments" (i.e., the time when runoff begins, the time when water accumulation begins, the time when water accumulation is at its maximum, and the time when water accumulation is 0), the corresponding water volume is calculated according to the proposed corresponding water volume calculation formula. This ingeniously transforms an extremely complex calculation process into a piecewise function that distinguishes between key moments, greatly reducing the calculation difficulty and complexity.

[0083] Furthermore, step S7 further includes:

[0084] S71. Based on the total water accumulation and the area of ​​each cell grid, calculate the maximum water depth elevation z of the grid corresponding to the diffusion base point. max The ground elevation corresponding to its grid is taken as the minimum water depth elevation z0;

[0085] S72. Determine if there exists an elevation z in all grids outside the diffusion base point that is less than the elevation z obtained by accumulating water volume into the grid of the diffusion base point. max If the grid is correct, proceed to step S73; otherwise, proceed to step S77.

[0086] S73. Using the corresponding grid as the calculation unit, and employing the bisection method, calculate the trial water depth elevation z for each calculation unit in the i-th cycle. mid The total water accumulation V is obtained by summing the volumes of all grids within the diffusion range. mid :

[0087] S74, Determine z mid The corresponding |F(z) mid If ε is true, proceed to step S76; otherwise, proceed to step S75. ε is the preset precision, and F(·) is the formula for the difference between the calculated water volume and the trial water volume.

[0088] S75. Calculate F(z) using the difference formula. max If F(z) max ) and F(z mid ) with the same number, update order z max =z mid If F(z) max ) and F(z mid If the signs are opposite, then let the ground elevation of the diffusion base point be z0 = z mid Then return to step S72.

[0089] S76. Calculate the water depth z of the i-th diffusion ring. i Update z max =z i After updating i = i + 1, return to step S72;

[0090] S77. The area corresponding to the diffusion base point and all rings of grids satisfying the judgment condition in step S72 is defined as the water accumulation range. The z-axis corresponding to each ring within the diffusion base point and water accumulation range... max As the water level;

[0091] S78. Subtract the elevation from the water level of the grid to obtain the water depth of each grid. Based on the water accumulation range of all sub-catchment areas and the water depth of their corresponding grids, the distribution area of ​​urban flooding risk is obtained.

[0092] Furthermore, the formula for the difference between the calculated water volume and the trial water volume is as follows:

[0093]

[0094] z max =V wl (t) / S+z0,Z mid =(Z0+Z) max ) / 2

[0095] Where F(z) is the difference between the actual water volume and the calculated water volume, m 3 Vwl (t) represents the water accumulation at time t, in m. 3 ;z mid,n The grid elevations within the diffusion range are less than the calculated water depth elevation; S is the area of ​​a single grid cell, in meters. 3 .

[0096] The beneficial effects of this invention are as follows: This scheme mainly utilizes the nodal water accumulation diffusion method to determine the diffusion base point, diffusion range, and total water volume. The diffusion of nodal water volume to the inundation range and depth is mathematically considered active inundation. Calculating the inundation range of active inundation is relatively complex, and the seed propagation method is widely used. When spreading outward from the seed, one-dimensional hydrodynamics, two-dimensional hydrodynamics, and the water surface balance method can be used. For plain cities with relatively small topographic relief, the water surface balance method is more suitable. When water accumulates at the nodal points and diffuses outward, issues such as superposition and water exchange occur, undoubtedly increasing the computational complexity. To avoid this situation, this scheme requires identifying the scope of "sub-catchment areas" where there is no water exchange in the initial stage. In conjunction with the subsequent calculation of runoff, a method for drawing the smallest computational unit is proposed. This method is mainly based on the characteristics of rainwater runoff, combined with drainage zoning planning, road and pipe network outlet distribution, etc., to draw sub-catchment areas and "isoflow time surfaces." On the one hand, this avoids water exchange and improves calculation speed; on the other hand, it quickly avoids the complexity and data acquisition difficulties required for drawing sub-catchment areas in conventional numerical models, which necessitate high-precision topography and the distribution of all drainage pipe networks and rainwater grates across the entire area. Instead, it achieves this with lower computational and data acquisition costs. This is also the crucial first step in breaking down the study area into a single, efficient unit for calculation.

[0097] To improve computational efficiency, the "diffusion range" needs to be ordered. Therefore, a topographic reconstruction of the study area is proposed, including improving building topography, constructing a minimum bounding rectangle, creating fishing nets and points, etc., ultimately forming a data file of water accumulation "diffusion range" points with ordered row and column numbers and elevations. Similarly, "diffusion base points" with ordered row and column numbers, minimum elevation points, and total water accumulation are obtained. Following the water balance method of active inundation, the water accumulates outward from the diffusion base point within the "diffusion range" file, using a bisection iterative method and satisfying the error between the trial water accumulation and the calculated water accumulation volume, until the water level in the outer circle is no lower than the equilibrium water level, thus obtaining the water accumulation range and water level of the urban flooding.

[0098] This solution, through the aforementioned method, can accurately determine the distribution area of ​​urban flooding risk even without pipeline survey data. This invention can help plain cities, especially those lacking official data and with poor economic foundations, to conduct scientific, efficient, highly accurate, and reusable urban flooding risk assessments, avoiding unnecessary waste of manpower, material resources, and time. Attached Figure Description

[0099] Figure 1 This is a flowchart of a method for assessing the risk distribution of urban flooding in plains cities without available survey data.

[0100] Figure 2 This is a schematic diagram showing the division of the catchment area.

[0101] Figure 3 This is a schematic diagram of the sub-basin division.

[0102] Figure 4 This is a schematic diagram showing the division of the Zihuishui area.

[0103] Figure 5 This is a schematic diagram of the division of the equal current time zone.

[0104] Figure 6 This is a grid topographic map of the Zihui area.

[0105] Figure 7 This is a schematic diagram showing the distribution of the houses.

[0106] Figure 8 This is a schematic diagram of the partially reconstructed Zihui area.

[0107] Figure 9 The diagrams illustrate the process of constructing the diffusion range, where (a) is a diagram of the minimum bounding rectangle; (b) is a diagram of the grid formed by drawing; (c) is a diagram of the point file of the grid; (d) is a diagram of the point attribute file with X row, Y column, and Z height attributes; and (e) is a diagram where each point is assigned attribute values, namely X / Y / Z.

[0108] Figure 10 This is a schematic diagram of the diffusion base points and attribute files of the Zihui area.

[0109] Figure 11 This is a schematic diagram of the catchment area.

[0110] Figure 12 Schematic diagram of runoff process curve

[0111] Figure 13 A visual diagram illustrating the flooding situation of a single sub-catchment area.

[0112] Figure 14 A visualization of the flooding situation in the city to be assessed. Detailed Implementation

[0113] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0114] refer to Figure 1 , Figure 1 A flowchart illustrating the method for assessing the risk distribution of urban flooding in plains areas without available survey data is shown; for example... Figure 1 As shown, the method S includes steps S1 to S7.

[0115] In step S1, the city planning map of the city to be evaluated is obtained and divided into multiple sub-catchment areas. Based on the street distribution within the sub-catchment areas, they are further divided into multiple "iso-flow surfaces".

[0116] In one embodiment of the present invention, step S1 further includes:

[0117] S11. Obtain the city planning map of the city to be evaluated and divide it into multiple catchment areas; for easier understanding, please refer to... Figure 2 Taking the first ring road of a certain city as an example, the blue border line is the river channel, which is divided into 4 water catchment areas according to the plan.

[0118] S12. Based on the city's dual drainage network, river distribution, and main street distribution, each catchment area is divided into multiple sub-basins. A schematic diagram of a sub-basin can be found here. Figure 3 The green area represents the dual drainage network, river distribution, and main street conditions.

[0119] S13. Based on the distribution of drainage outlets at the end of the drainage network in the sub-basin, the sub-basin is divided into multiple sub-catchment areas, and based on the street distribution within each sub-catchment area, it is further divided into multiple "isotropic flow surfaces"; Figure 3 Taking sub-basin 2 as an example, it has two drainage outlets. Based on their distribution, two sub-catchment areas within this region are drawn, forming... Figure 4 A schematic diagram of the Zihuishui area; different isocurrent time zones are drawn based on the streets within the Zihuishui area; Figure 4 Taking sub-catchment area 2 of sub-basin 2 as an example, four "isotropic time zones" within this area are drawn according to the street distribution. See the attached diagram for details. Figure 5 The isocurrent time zone is also called the isocurrent time surface.

[0120] In step S2, the terrain of the city to be evaluated is reconstructed, then the minimum bounding rectangle of the sub-catchment area is drawn, and fishing nets and points are created; the reconstructed terrain and the highest elevation are assigned to the sub-catchment area inside and outside, respectively, to form a water accumulation "diffusion range" file with ordered row and column numbers and elevation point attributes;

[0121] The detailed implementation process of step S2 is as follows:

[0122] S14. The sub-catchment area is divided into grids, and the terrain is reconstructed using ground topographic data, filling depressions, raising the elevation of unflooded areas, and terrain fusion; the detailed implementation process is as follows:

[0123] Interpolate the elevation data points in the Zihui area and perform cut and fill operations to create a raster topographic distribution map of the Zihui area; for example... Figure 6 As shown, taking the sub-catchment area 2 of sub-basin 2 as an example, the elevation scatter points are first interpolated and then filled and cut to form a grid topographic distribution map of the sub-catchment area, with an elevation range of 490.623 to 498.912m.

[0124] The elevation of buildings in the Zihui area is raised to a predetermined height and integrated with the original grid terrain of the Zihui area to form the reconstructed terrain of the Zihui area; the distribution diagram of the buildings can be referenced. Figure 7 The building elevation was raised to 600m and integrated with the original grid terrain to create a reconstructed terrain for the Zihui area. For details, please refer to [reference needed]. Figure 8 The reconstructed schematic diagram shows an elevation range of 490.623 to 600m.

[0125] S15. Draw the minimum bounding rectangle of the sub-catchment area, and create a fishing net and points; assign values ​​to the sub-catchment area and its interior and exterior using reconstructed terrain and highest elevation respectively, forming a water accumulation "diffusion range" file with ordered row and column numbers and elevation point attributes.

[0126] like Figure 9 As shown in (a) to (e), taking sub-catchment area 2 of sub-basin 2 as an example, the tool in ArcGIS software is used to calculate the Minimum Bounding Geometry to obtain the minimum bounding rectangle of each sub-catchment area; then the tool in ArcGIS is used to calculate Create Fishnet and create Label Points; then, combined with the raster formed by the DEM data of the sub-catchment area, the point data with coordinates and elevations within the minimum bounding rectangle of the sub-catchment area can be obtained by calling Extract Values ​​to points in ArcGIS, and finally a "diffusion range" file containing X / Y / Z attributes is formed.

[0127] In step S3, the total precipitation and total infiltration in the sub-catchment area at any given time are calculated; the water storage length and pipe diameter of the drainage network are determined, and the total water storage of the drainage network is calculated accordingly.

[0128] In one embodiment of the present invention, the method for calculating the total precipitation within a sub-catchment area includes:

[0129] Rainfall data for the sub-catchment area was obtained using meteorological bureau data or rainfall intensity formulas, and rainfall sequences at the same time intervals were extracted to construct a rainfall sequence, which includes rainfall time and intensity. For example, a rainfall sequence with a 10-minute interval is shown in the table below:

[0130]

[0131] Based on the rainfall sequence, the rainfall intensity at any given time can be obtained by interpolation:

[0132]

[0133] Where p(t) x ) for t x Rainfall intensity at any given time, mm / h; t x For any time interval, h; t ID For any given time, the closest to t in the rainfall sequence x And compared to t x The moment of light rainfall is h; Δt is the time interval, h; p(t) ID ) and p(t ID +Δt) are respectively t ID and t ID +Δt, rainfall intensity, mm / h;

[0134] Calculate the total precipitation in the sub-catchment area at any given time:

[0135]

[0136] Wherein, P(t) x ) for t x Total precipitation at any given time, m 3 p(t) and p(t+Δt) are the rainfall intensities at times t and t+Δt, respectively, in mm / h; x0 is the first moment of the rainfall sequence; S is the area of ​​the sub-catchment area, in m³. 2 .

[0137] During implementation, the preferred method for calculating the total infiltration volume of the sub-catchment area in this scheme includes:

[0138] Calculate the infiltration rate at time t based on the steady-state infiltration rate and the initial infiltration rate:

[0139] f(t) = fc +(f0―f c )*e ―kt

[0140] Where f(t) is the infiltration rate at time t, mm / h; f c The infiltration rate is set to a stable infiltration rate (mm / h); f0 is the initial infiltration rate (mm / h); and k is the infiltration attenuation coefficient.

[0141] Calculate the infiltration rate at any given time:

[0142]

[0143] Where, f(t) x ) for t x Infiltration rate at time t, mm / h; f(t) ID +Δt) and f(t) ID ) are respectively t ID +Δt and t ID Infiltration rate at any given time;

[0144] Based on the infiltration rate f(t) and f(t) x ), calculate the total infiltration at any given time:

[0145]

[0146] Wherein F(t) x ) for t x The total amount of infiltration at time m 3 f(t+Δt) is the infiltration rate at time t+Δt, in mm / h.

[0147] During implementation, the preferred method for calculating the water storage capacity of the drainage network in this scheme includes:

[0148] Based on the area of ​​the sub-catchment area, calculate the design flow rate of the rainwater in the drainage network designed for the sub-catchment area:

[0149] Q s =3600qψS

[0150] Among them, Q s Design flow rate for rainwater, m 3 / h; q is the design rainfall intensity, m3 / (m2·s); ψ is the comprehensive runoff coefficient; S is the area of ​​the sub-catchment area, m 2 ;

[0151] Calculate the diameter of the drainage network based on the design flow rate of rainwater in the drainage network:

[0152]

[0153] Where d is the diameter of the rainwater pipe, in meters; v is the design flow velocity of the pipe, in meters per second, which, according to the specifications, ranges from 0.75 m / s to 5 m / s.

[0154] When drainage network data is lacking for a sub-catchment area, the sub-catchment area is generalized along the main roads into several "isoflow time surfaces" regions. The length of the water storage network is generalized as the sum of the straight-line distance from the end of the drainage network outlet to the farthest "isoflow time surface" and the main roads within the sub-catchment area; Figure 11 In the diagram, the pipe length L = L + l1 + l2.

[0155] Calculate the total water storage capacity of the drainage network based on the pipe diameter and the length of the water storage pipes:

[0156]

[0157] Among them, V s The water storage capacity of the drainage network is expressed in m. 3 L represents the pipe length in meters; v ranges from 0.75 m / s to 5 m / s, and should be selected according to specifications and local conditions; Q s The design flow rate of the pipe network drainage is calculated with reference to the "Outdoor Drainage Design Standard" (GB 50014-2021).

[0158] In step S4, the net rainfall process is determined based on the water collection time of the "isochronous surface" in the sub-catchment area, and then the runoff flow process of the sub-catchment area is calculated to determine the runoff start time, the start time of water accumulation, the maximum water accumulation time, and the total water transfer of the sub-catchment area based on the three times.

[0159] In one embodiment of the present invention, step S4 further includes:

[0160] Based on the initial loss and subsequent loss method, the net rainfall process is calculated within the same time interval:

[0161] R = pΔt―I0―ft R ―P′

[0162] Where R is the net rainfall depth (mm); p is the rainfall intensity (mm / h); I0 is the initial loss (mm); f is the average subsequent loss rate (mm / h); P′ is the rainfall that does not generate runoff in the later period (mm); t R It is the duration of over-osmosis, i.e., the duration of runoff, in hours;

[0163] Based on the ratio of longitudinal depth in the confluence direction, calculate the net rainfall process for each offset "isotropic surface":

[0164]

[0165] in, for Take the integer T i Δt is the time when the i-th "isotropic surface" converges to the drainage outlet, t; Δt is the net rainfall sequence time interval, t; For the integer value; y = T i modΔt is The modulo operator is the remainder value. R is the coefficient; i,t R is the net rainfall depth at time t of the i-th "isotropic surface", in mm; t-xΔt and R t-(1+x)Δt The net rainfall depths, in mm, are calculated using the initial and subsequent loss methods at times t―xΔt and t―(1+x)Δt, respectively.

[0166] The process of calculating the runoff flow rate of the sub-catchment area:

[0167]

[0168] Among them, Q t Let m be the runoff flow rate at time t. 3 / h;R t R t―1 R t―2 and R t―(n―1) The net rainfall amounts, in mm, are given at times t, t-1, t-2, and t-(n-1); f1, f2, f3, f n The runoff areas for the 1st, 2nd, 3rd, and nth isocurrent time zones are respectively, m 2 n represents the total number of medium-flow time zones in the sub-catchment area; L i Let t be the runoff length of the i-th "isotropic surface", in meters; i,1 t represents the time it takes for surface runoff from the i-th "isotropic surface" to reach the storm drain grate, ranging from 0.15 to 0.25 hours; i,2 , h, represents the time it takes for rainwater from the i-th "isotropic surface" to reach the drain outlet in the drainage network; v is the flow velocity of water in the drainage network, m / s.

[0169] According to the objective function Q t =Q s Determine the start time t of the abortion. f Time t for water accumulation to begin a Maximum water accumulation time t m Q s The design flow rate of rainwater for the drainage network is given in m. 3 / h; Specifically, net rainfall is obtained through the initial loss and subsequent loss method, and then combined with a generalized "isochoric flow curve" to obtain the runoff process of the catchment area. This process curve is compared with the design flow of the drainage network. A schematic diagram of the runoff process curve is shown below. Figure 12 As shown Figure 12 The intersection of these three points represents three key times: the start time of the flow (t). fGenerally, this occurs 5 to 15 minutes after the start of rainfall, at the first moment when the runoff equals the design flow rate of the pipe network; this is the start of water accumulation time t. a The second time when the runoff equals the design flow rate of the pipe network, i.e., the time of maximum water accumulation t. m .

[0170] Based on runoff flow rate Q t and the time t when water begins to accumulate a Calculate the total water transport volume of the drainage network:

[0171]

[0172] Among them, V c (t) represents the total water transfer volume at time t, m 3 ;t f The time of onset of abortion is h; t a The time from the start of water accumulation is h; t x Let h be any time interval; Δt be the time interval, h; Q t+Δt Let m be the runoff flow rate at time t+Δt. 3 / h.

[0173] In step S5, the maximum total water accumulation is calculated based on the formula for total water accumulation and the time of maximum water accumulation; the total water accumulation at any time is calculated based on the runoff flow process of the sub-catchment area.

[0174] Among them, the time t at which the water accumulation is maximum is calculated. m The expression for the corresponding maximum total water volume is:

[0175] V(t=t m )=P(t m )-F(t m )-V c (t m )-V s

[0176] Where, V(t=t) m ) for t m The maximum total water accumulation at time t; P(t) m ) for t m Rainfall at any given time, in m 3 ;F(t) m ) for t m Infiltration rate at time m 3 V c (t m ) for t m Total amount delivered at any time, m 3 V s The water storage capacity of the water supply network is m. 3 .

[0177] When the local surface water level drops to 0 at time t e When the following formula is satisfied:

[0178] Function: V wl (t)=P(t)-F(t)-V c (t)-V s

[0179] Objective function:

[0180] Constraint: t ≥ t m

[0181] Among them, V wl (t) represents the water accumulation at time t, in m. 3 P(t) represents the precipitation at time t, in meters. 3 F(t) represents the infiltration rate at time t, m 3 V c (t) represents the total amount transported at time t, m 3 ;

[0182] Based on the time t when the surface water level drops to 0. e The formula satisfies the condition to calculate the total water accumulation V at any given time. wl (t):

[0183]

[0184] Wherein, P(t) f ) for t f Rainfall at any given time, in m 3 .

[0185] In step S6, the lowest elevation point in the sub-catchment area is selected based on the topography before filling the depression. Combined with the calculated total water volume, a water "diffusion baseline" file is generated, including ordered row and column numbers, elevation, and water volume. The "diffusion baseline" is the lowest point in the sub-catchment area. The lowest elevation point in the sub-catchment area is selected, and a "diffusion baseline" file containing X, Y, Z1, and TotalwaterV (horizontal sorting, vertical sorting, elevation, and water volume) attributes is ultimately generated. The X and Y attribute information is obtained from the nearest point in the "diffusion range"; Z1 is the elevation value after filling the depression; and TotalwaterV is the maximum water volume V (t = t). m ).

[0186] like Figure 10As shown, taking sub-catchment area 2 of sub-basin 2 as an example, the lowest point of each sub-catchment area is obtained before filling the depressions in the sub-catchment area. The X and Y codes of the diffusion base points are obtained from the nearest point in the "Diffusion Range" file. The elevation of the diffusion base points is the elevation after filling the depressions, ultimately forming a "Diffusion Base Point" file containing X, Y, Z1, and maximum water accumulation attributes. Figure 10 The red triangle in the middle is the lowest point of the Zihui area, with attribute information of 126,148,492.0145m.

[0187] In step S7, the water spreads outward from the diffusion base point within the "diffusion range" file. During diffusion, the actual water level after diffusion is calculated using the bisection iteration method combined with the water volume error, thus obtaining the water accumulation range and water level, and then the water depth, ultimately obtaining the distribution area of ​​urban flooding risk.

[0188] In step S7, it is necessary to first construct the formula and objective function for the difference between the calculated water volume and the trial water volume:

[0189]

[0190] Objective function |F(z) mid )|<ε,ε=0.001

[0191] Where F(z) is the difference between the actual water volume and the calculated water volume, m 3 V wl (t) represents the water accumulation at time t, in m. 3 ;z mid,n The grid elevations within the diffusion range are less than the calculated water depth elevation; S is the area of ​​a single grid cell, in meters. 3 z0 is the ground elevation of the diffusion baseline, in meters; z max The elevation z is the result of the water accumulation at the diffusion base point grid. max =V wl (t) / S+z0,m;z mid To calculate the water depth and elevation, Z mid =(Z0+Z) max ) / 2, m; ε is the preset precision.

[0192] Following the construction of the difference formula and objective function, the preferred step S7 of this scheme further includes:

[0193] S71. Based on the total water accumulation and the area of ​​each cell grid, calculate the maximum water depth elevation z of the grid corresponding to the diffusion base point. max The ground elevation corresponding to its grid is taken as the minimum water depth elevation z0;

[0194] S72. Determine if there exists an elevation z in all grids outside the diffusion base point that is less than the elevation z obtained by accumulating water volume into the grid of the diffusion base point. max If the grid is correct, proceed to step S73; otherwise, proceed to step S77.

[0195] S73. Using the corresponding grid as the calculation unit, and employing the bisection method, calculate the trial water depth elevation z for each calculation unit in the i-th cycle. mid The total water accumulation V is obtained by summing the volumes of all grids within the diffusion range. mid :

[0196] S74, Determine z mid The corresponding |F(z) mid If ε is true, proceed to step S76; otherwise, proceed to step S75. ε is the preset precision, and F(·) is the formula for the difference between the calculated water volume and the trial water volume.

[0197] S75. Calculate F(z) using the difference formula. max If F(z) max ) and F(z mid ) with the same number, update order z max =z mid If F(z) max ) and F(z mid If the signs are opposite, then let the ground elevation of the diffusion base point be z0 = z mid Then return to step S72.

[0198] S76. Calculate the water depth z of the i-th diffusion ring. i Update z max =z i After updating i = i + 1, return to step S72;

[0199] S77. The area corresponding to the diffusion base point and all rings of grids satisfying the judgment condition in step S72 is defined as the water accumulation range. The z-axis corresponding to each ring within the diffusion base point and water accumulation range... max As the water level;

[0200] S78. Subtract the elevation from the water level of each raster to obtain the water depth of each raster. Based on the water accumulation range of all sub-catchment areas and the water depth of their corresponding raster cells, the distribution area of ​​urban flooding risk is obtained. This is then loaded and displayed in ArcGIS to form a visualization view. Figure 13 This is a visual diagram illustrating the flooding situation of a single sub-catchment area. Figure 14 A visualization of the flooding situation in the city to be assessed.

[0201] This solution, through the aforementioned methods (S71-S78), can realize the maximum total water accumulation and the water accumulation at any given time in the study area, thus obtaining the most crucial element of this invention. The previous solution clarified the moment of maximum water accumulation. Using the formula that the total water accumulation in a sub-catchment area equals the total precipitation within its region minus the total infiltration, the total water storage in the pipe network, and the total water transported by the pipe network, the maximum total water accumulation can be further calculated.

[0202] The usual method for calculating the water volume at any given moment requires building a high-precision numerical flooding model and adjusting the calculation step size. To address the issue of calculating this water volume without a high-precision numerical flooding model, this solution proposes a calculation objective function to determine the moment when the water volume is 0. By comparing any given moment with four key moments (i.e., the start of runoff, the start of water accumulation, the moment of maximum water accumulation, and the moment when the water volume is 0), the corresponding water volume is calculated according to the proposed water volume calculation formula. This ingeniously transforms a highly complex calculation process into a piecewise function that uses key moments for discrimination, greatly reducing the computational difficulty and complexity.

[0203] The diffusion of accumulated water from nodes to the inundation range and depth is mathematically considered active inundation. Calculating the inundation range of active inundation is complex, and the seed-spreading method is widely used. When spreading outward from the seed node, one-dimensional hydrodynamics, two-dimensional hydrodynamics, and the water surface balance method can be used. For plain cities with relatively small topographic relief, the water surface balance method is more preferred. The outward diffusion of accumulated water from nodes can lead to issues such as superposition and water exchange, undoubtedly increasing computational complexity. To avoid this, this scheme initially maps out "sub-catchment areas" where there is no water exchange. Using the lowest point in a sub-catchment area as the diffusion base point, and based on the calculated total accumulated water volume and assumed water depth, diffusion proceeds outward from the base point. The water depth of each diffusion ring is calculated using a bisection method until the difference between the inundated water volume and the actual water volume meets the required accuracy. Diffusion continues until no area in the outer ring has an elevation lower than the previous diffusion depth. Each catchment area only needs to start diffusion from a single base point, significantly reducing computational complexity and time.

[0204] In summary, this scheme allows for the rapid determination of the design flow rate and pipeline length of drainage networks in areas lacking pipeline survey data before urban rainstorms occur. This enables the rapid determination of the water storage and transmission capacity of the drainage network, facilitating the identification of flood-prone areas during impending rainstorms and enabling a rapid assessment of urban flooding risks. Consequently, it allows management personnel to issue timely flood risk warnings.

Claims

1. A method for assessing the distribution of urban flooding risk in plains cities without available survey data, characterized in that, Including the following steps: S1. Obtain the urban planning map of the city to be evaluated, divide it into multiple sub-catchment areas, and divide it into multiple "iso-flow surfaces" according to the street distribution within the sub-catchment areas; S2. Reconstruct the terrain of the city to be evaluated, then draw the minimum bounding rectangle of the sub-catchment area, and create fishing nets and points; assign values ​​to the reconstructed terrain and the highest elevation inside and outside the sub-catchment area respectively, forming a water accumulation "diffusion range" file with ordered row and column numbers and elevation point attributes; S3. Calculate the total precipitation and total infiltration in the sub-catchment area at any given time; determine the water storage length and pipe diameter of the drainage network, and calculate the total water storage of the drainage network accordingly. S4. Based on the water catchment time of the "isochronous surface" in the sub-catchment area, determine its net rainfall process, and then calculate the runoff flow process of the sub-catchment area. Determine the runoff start time, the start time of water accumulation, and the maximum water accumulation time. Based on the three times, calculate the total water transfer of the sub-catchment area. S5. Calculate the maximum total water accumulation based on the formula for total water accumulation and the time of maximum water accumulation; calculate the total water accumulation at any time based on the runoff flow process of the sub-catchment area. S6. Based on the topography of the sub-catchment area before filling the depression, select the lowest elevation point in the sub-catchment area, and combine it with the calculated total water volume to form a water "diffusion baseline point" file that includes ordered row and column numbers, elevation and water volume; S7. Using the diffusion base point as the center, the water spreads outward within the range of the "diffusion range" file. During the diffusion, the bisection iterative method is used in combination with the water volume error to calculate the actual water level after diffusion, thereby obtaining the water accumulation range and water level, then the water accumulation depth, and finally the distribution area of ​​urban flooding risk. Step S7 further includes: S71. Based on the total water accumulation and the area of ​​each cell grid, calculate the maximum water depth elevation of the grid corresponding to the diffusion base point. The ground elevation corresponding to its grid is taken as the minimum water depth elevation. ; S72. Determine if there exists an elevation among all grids in the i-th ring outside the diffusion base point that is less than the elevation obtained by accumulating water volume into the grid at the diffusion base point. If the grid is correct, proceed to step S73; otherwise, proceed to step S77. S73. Using the corresponding grid as the calculation unit, and employing the bisection method, calculate the trial water depth and elevation for each calculation unit in the i-th cycle. The total water accumulation is obtained by summing the volumes of all grids within the diffusion range. : S74, Judgment corresponding Check if the condition is met. If yes, proceed to step S76; otherwise, proceed to step S75. To preset the accuracy, The formula for calculating the difference between the accumulated water volume and the trial accumulated water volume; S75. Calculate using the difference formula. ,like and Same number, update order = ,like and If the signs are opposite, then the ground elevation of the diffusion base point will be... = Then return to step S72; S76. Calculate the water depth z of the i-th diffusion ring. i ,renew = z i After updating i=i+1, return to step S72; S77. The area corresponding to the diffusion base point and all the ring grids that satisfy the judgment condition in step S72 is taken as the water accumulation range. The diffusion base point and the area corresponding to each ring grid within the water accumulation range are defined as follows: As the water level; S78. Subtract the elevation from the water level of the grid to obtain the water depth of each grid. Based on the water accumulation range of all sub-catchment areas and the water depth of their corresponding grids, the distribution area of ​​urban flooding risk is obtained.

2. The method for assessing the risk distribution of urban flooding in plains areas without access to survey data as described in claim 1, characterized in that, Step S1 further includes: S11. Obtain the city planning map of the city to be evaluated and divide it into multiple watershed areas; S12. Based on the distribution of the city's dual drainage network, waterways, and main streets, each catchment area is divided into multiple sub-basins. S13. Based on the distribution of drainage outlets at the end of the drainage network in the sub-basin, the sub-basin is divided into multiple sub-catchment areas, and based on the street distribution within the sub-catchment areas, it is divided into multiple "iso-flow time surfaces"; Step S2 further includes: S14. The sub-catchment area is divided into grids, and the terrain is reconstructed by using ground topographic data, filling depressions, raising the elevation of unflooded areas, and terrain fusion. S15. Draw the minimum bounding rectangle of the sub-catchment area, and create a fishing net and points; assign values ​​to the sub-catchment area and its interior and exterior using reconstructed terrain and highest elevation respectively, forming a water accumulation "diffusion range" file with ordered row and column numbers and elevation point attributes.

3. The method for assessing the risk distribution of urban flooding in plains areas without access to survey data as described in claim 1, characterized in that, Methods for calculating the total precipitation within a sub-catchment area include: Rainfall data for the sub-catchment area was obtained using meteorological bureau data or rainstorm intensity formulas, and rainfall sequences at the same time intervals were extracted to construct a rainfall sequence, which includes rainfall time and rainfall intensity. Based on the rainfall sequence, the rainfall intensity at any given time can be obtained by interpolation: in, for Rainfall intensity at any given time, in mm / h; For any time interval, h; For any given moment, the closest in the rainfall sequence And compared The duration of light rainfall is h; The time interval is h; and They are respectively and Rainfall intensity, mm / h; Calculate the total precipitation in the sub-catchment area at any given time: in, for Total precipitation at any given time, m 3 ; and t and Rainfall intensity at any given time, in mm / h; This is the first moment in the rainfall sequence; For the area of ​​the Zihuishui area, m 2 .

4. The method for assessing the risk distribution of urban flooding in plains areas without access to survey data as described in claim 3, characterized in that, Methods for calculating the total infiltration volume of a sub-catchment area include: Calculate the infiltration rate at time t based on the steady-state infiltration rate and the initial infiltration rate: in, Let be the infiltration rate at time t, in mm / h; To stabilize the infiltration rate, mm / h; The initial infiltration rate is expressed in mm / h. This is the infiltration attenuation coefficient; Calculate the infiltration rate at any given time: in, for Infiltration rate at any given time, mm / h; and They are respectively and Infiltration rate at any given time; According to the infiltration rate and Calculate the total amount of infiltration at any given time: in, for The total amount of infiltration at time m 3 ; for Infiltration rate at any given time, mm / h.

5. The method for assessing the risk distribution of urban flooding in plains areas without access to survey data as described in claim 1, characterized in that, Methods for calculating the total water storage capacity of a drainage network include: Based on the area of ​​the sub-catchment area, calculate the design flow rate of the rainwater in the drainage network designed for the sub-catchment area: in, Design flow rate for rainwater, m 3 / h; To design the intensity of a rainstorm, m3 / (m2·s); This is the comprehensive runoff coefficient; For the area of ​​the Zihuishui area, m 2 ; Calculate the diameter of the drainage network based on the design flow rate of rainwater in the drainage network: in, Where is the diameter of the rainwater pipe, in meters (m); The design flow velocity for the pipeline, in m / s, is within the range of 0.75 m / s to 5 m / s according to the specifications. When drainage network data is lacking for a sub-catchment area, the sub-catchment area is generalized into several "iso-flow time surfaces" along the main road. The length of the water storage network is generalized as the sum of the straight-line distance from the end of the drainage network outlet to the farthest "iso-flow time surface" and the main road within the sub-catchment area. Calculate the total water storage capacity of the drainage network based on the pipe diameter and the length of the water storage pipes: in, The water storage capacity of the drainage network is expressed in m. 3 ; The length of the pipe is in meters (m).

6. The method for assessing the risk distribution of urban flooding in plains areas without access to survey data as described in claim 5, characterized in that, Step S4 further includes: Based on the initial loss and subsequent loss method, the net rainfall process is calculated within the same time interval: in, The net rainfall depth was [mm]. The rainfall intensity was [mm / h]. This is the initial loss, in mm; It is the average post-loss rate, in mm / h; This refers to the rainfall that does not generate runoff later in the season, measured in mm. It is the duration of over-osmosis, i.e., the duration of runoff, in hours; Based on the ratio of longitudinal depth in the confluence direction, calculate the net rainfall process for each offset "isotropic surface": in, for Take the integer. It is the time t when the i-th "isotropic surface" converges to the drain outlet; It is the net rainfall sequence time interval, t; For integer values; for The modulo operator is the remainder value. For coefficients; Let be the net rainfall depth at time t for the i-th "isotropic surface", in mm; and They are respectively and Net rain depth calculated using the initial loss and subsequent loss method at all times, in mm; The process of calculating the runoff flow rate of the sub-catchment area: in, Let m be the runoff flow rate at time t. 3 / h; , , and Let be the net rainfall at times t, t-1, t-2, and t-(n-1), respectively, in mm; , , , These are the runoff areas for the 1st, 2nd, 3rd, and nth isocurrent time zones, respectively. n represents the total number of medium-flow time zones in the sub-catchment area; Let be the runoff length of the i-th "isotropic surface", in meters. The time it takes for the surface runoff at the i-th "isotropic surface" to converge to the storm drain grate is taken as 0.15~0.25h; denoted as h, where h is the time it takes for rainwater from the i-th "isotropic surface" to reach the drain outlet in the drainage network; v is the flow velocity of water in the drainage network, in m / s. According to the objective function Determine the start time of abortion Time of start of water accumulation and the maximum time of water accumulation , The design flow rate of rainwater in the drainage network is given in m. 3 / h; According to runoff flow and the time when water started to accumulate Calculate the total water transport volume of the drainage network: in, Let m be the total water transport volume at time t. 3 ; The time of onset of abortion, in hours (h). The time from the start of water accumulation is in hours (h). For any time interval, h; The time interval is h; for Runoff flow rate at time m 3 / h.

7. The method for assessing the risk distribution of urban flooding in plains areas without access to survey data as described in claim 6, characterized in that, Calculate the moment of maximum water accumulation The expression for the corresponding maximum total water volume is: in, for The maximum total water accumulation at any given moment; for Rainfall at any given time, in m 3 ; for Infiltration rate at time m 3 ; for Total amount delivered at any time, m 3 ; The water storage capacity of the water supply network is m. 3 .

8. The method for assessing the risk distribution of urban flooding in plains areas without access to survey data as described in claim 6, characterized in that, When the local surface water level drops to 0 When the following formula is satisfied: in, Let m be the water volume at time t. 3 ; Let m be the precipitation at time t. 3 ; Let m be the amount of infiltration at time t. 3 ; Let m be the total amount transported at time t. 3 ; When the surface water level drops to 0 The formula satisfies the condition to calculate the total water accumulation at any given time. : in, for Rainfall at any given time, in m 3 .

9. The method for assessing the risk distribution of urban flooding in plains areas without access to survey data as described in claim 1, characterized in that, The formula for the difference between the calculated water volume and the trial water volume is: function ， in, The difference between the actual water volume and the calculated water volume, in m 3 ; Let m be the water volume at time t. 3 ; The grid elevations within the diffusion range are smaller than the calculated water depth elevations; m is the area of ​​a single grid cell. 3 .

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