Method for determining urban inundation area of short duration heavy rainfall

Abstract

The application provides a calculation method for a short-duration heavy rainfall urban inundation area, and belongs to the technical field of urban waterlogging inundation calculation.The application simplifies a city ground water convergence process, divides a complex flow field into a plurality of unit sub-catchment areas, calculates the ground water amount in a unit, sequentially calculates the ground water amount in each catchment area, and further obtains the ground water amount of the whole flow field.The application converts the ground water amount into a ground surface inundation range according to the water level-topography and other surface features of the flow field, has few model parameters, a fast calculation process and strong principle universality, and can be comprehensively promoted.

Description

Technical Field

[0001] This invention belongs to the field of urban stormwater and flood calculation, specifically combining passive inundation calculation with urban pipeline dynamic flow and watershed topography DEM model. Background Technology

[0002] Many areas have complex terrain, incomplete data on underground drainage systems, and inadequate rainstorm and flood monitoring facilities. The resurvey work is enormous, time-consuming, and labor-intensive, making it difficult to apply general urban rainstorm and flood forecasting and early warning systems. It is impossible to quickly and accurately determine the inundation and water accumulation in the area, and people cannot directly identify the disaster situation and fall into flood-prone areas.

[0003] Short-duration heavy rainfall primarily generates surface runoff directly or flows into downstream rivers through drainage networks, causing rapid flooding. On one hand, with urbanization, the proportion of paved surfaces increases, altering underlying surface conditions, slowing infiltration rates, and reducing the amount of infiltrated water. On the other hand, drainage pipes can only withstand floods within their design lifespan. During floods exceeding standard levels, increased pipe pressure, coupled with rising river levels creating a backwater effect, exacerbates overflow pressure in pipe manholes, leading to surface flooding. This, combined with the accumulated surface water, ultimately results in regional flooding. Urban flooding severely impacts people's travel and can even cause injuries or fatalities.

[0004] It is evident that, given the scarcity of regional drainage network data, rapidly establishing a short-duration urban heavy rainfall forecasting and early warning system to determine the distribution of inundation depth and water accumulation within the basin is crucial for helping the public identify flood-affected areas, prevent and mitigate disasters, and assisting relevant management departments in identifying disaster situations, conducting rescue and relief operations, and reducing casualties. Summary of the Invention

[0005] To address the aforementioned problems, this invention proposes a method for determining urban inundation areas during short-duration heavy rainfall. First, the surface water volume of the watershed is determined. Then, based on topographic features, the accumulated water is converted into an inundation area for display. The sources of surface water in the watershed are generalized, including both drainage network overflow and water directly formed by rainfall. Specifically, a drainage network system is quickly established based on the regional road network, and the watershed is discretized into several sub-catchments. Urban stormwater flood models are established for each sub-catchment to calculate the pipe overflow. The surface water volume directly formed by rainfall in each sub-catchment is determined using the principle of passive inundation. These are then superimposed and summarized to obtain the overall surface water volume of the watershed. Finally, the accumulated water volume is converted into an inundation area based on surface features. The specific determination method is as follows:

[0006] S1. To quickly determine the urban surface water volume and thus the flood inundation area, it is first necessary to collect and preprocess basic watershed data, including watershed rainfall and comprehensive geographical data.

[0007] (1) Preprocessing of rainfall data:

[0008] The rainfall duration sequence was determined using a rainfall intensity formula, and the water distribution pattern of the watershed rainfall was generalized. The surface water generated by rainfall mainly consists of the water remaining after deducting vegetation interception, depression filling, evaporation, infiltration, and the water carrying capacity of urban pipe networks. Due to the short rainfall duration, rapid urban runoff, and relatively low vegetation cover, the watershed evaporation and vegetation interception are negligible during the flood process. Therefore, the rainfall distribution process can be generalized as follows: [The text abruptly ends here, so the translation stops as well.] Within the time period t from 0 to T1, the rainfall P1 is initially allocated, with surface water accounting for K1 and water infiltration accounting for K2, where K1+K2=1; that is, the surface water in the initial allocation is K1P1. The surface water K1P1 is then redistributed, with the underground pipe network receiving K3, and the remaining water remaining on the surface. That is, K1K3P1 flows to the underground pipe network, and K1(1-K3)P1 of water remains on the surface.

[0009] (2) Geographic information data preprocessing:

[0010] Integrated geographic information of a watershed is the geographical foundation for determining the relationship between surface water and inundation extent. The distribution patterns of inundation areas vary across different regions due to differences in geographical distribution. Preliminary processing mainly includes processing data such as watershed topography, DEM elevation, river network distribution, water level-water volume relationship, land use type, BeiDou high-resolution satellite imagery, street conditions, and road network elevation. A powerful geographic information processing platform is used to determine parameters such as watershed vegetation cover, surface undulation and slope, infiltration, and the relationship between surface water volume and water level changes.

[0011] S2. Constructing an Underground Drainage Network: Roads are the core and backbone of a city. To avoid the impact of buildings in non-road areas, underground pipelines are generally laid along roads. This layout allows for simultaneous construction and is more advantageous from an investment and construction perspective. Therefore, for watersheds lacking drainage network data, underground pipelines are established based on the distribution of regional roads. The pipe shape is generally circular. The pipe diameter is determined comprehensively based on local drainage requirements, design specifications, and reference to the design standards of underground pipeline networks in similar cities. The burial elevation and length of the pipelines are determined by combining road elevation and ground undulations, thereby constructing a rough underground drainage network for the watershed.

[0012] S3. Watershed Discretization:

[0013] The watershed is divided into multiple sub-catchments, and each sub-catchment is analyzed separately to determine the surface water volume. It is assumed that the entire watershed is subject to passive inundation, a condition applicable to geographically flat areas with relatively simple topography, where connectivity between regions is not considered; that is, any area will be submerged as long as its elevation falls below the inundation elevation. The surface water within each individual sub-catchment is solely determined by rainfall, with no flow between sub-catchments or between sub-catchments.

[0014] S4. Analyze the surface water volume on a single sub-catchment:

[0015] According to the aforementioned rainfall allocation rules, rainfall within a short duration is distributed proportionally, with the amount of water directly retained on the ground being K1(1-K3)P1 (corresponding to water volume w1). A single sub-catchment area contains several underground pipe sections and i collection well nodes. The first rainfall period... The overflow of each node is as follows Then the nodal overflow generated by all nodes within the sub-catchment area is w2= That is, the overflow volume of the underground pipe network within the sub-catchment area ds to the surface through the collection well node is w2= Then the time period of this sub-catchment area. The amount of water generated in the inland area is:

[0016]

[0017] S5. Similarly, we can obtain the time period. The surface water volumes of the other sub-catchments S2, S3, ... Sn are W2, W3, ..., Wn, respectively. n The total surface water volume of the entire watershed is the sum of the surface water volumes of all its sub-catchments. That is, when the sub-catchment of the watershed is sufficiently divided, a sub-catchment with an area of ​​ds is in If the surface water volume generated during the time period is dw, then the total surface water volume of the watershed during the time period dt is... .

[0018] S6. Determine the total surface water volume of the watershed:

[0019] If a watershed is divided into n sub-catchments, then the total surface water volume of the watershed is the sum of the surface water volumes of all sub-catchments:

[0020] (1) Time period (T=T1 time)

[0021] The surface water volume of n sub-catchments is: , , , ..., ,

[0022] The total surface water volume of the entire watershed is:

[0023] At time T1, the surface water level in the basin was: =

[0024] That is when Time, that is, during a period of time Inside, t ranges from 0 to (T ranges from 0 to T1), the total catchment area is S, divided into several sub-catchments ds, and the water accumulation in each sub-catchment ds is d. Then the time period Within the basin, the total water volume is:

[0025] W= =

[0026] (2) Time period (Time T = T2)

[0027] The surface water volume of n sub-catchments is: , , , ..., ,

[0028] The total surface water volume of the entire watershed is:

[0029] The surface water level in the basin at time T2 is: = +

[0030] That is, during the time period T from T1 to T2, when Time, that is, during a period of time Within (t from T1 to T2), the water accumulation on each sub-catchment ds is d. Then the time period Within the basin, the water volume is:

[0031] W= =

[0032] Then, during the time period T from 0 to T2, the total surface water volume of the entire watershed is:

[0033] W= =

[0034] And so on...

[0035] (m) time period (T=T) m time)

[0036] The surface water volume of n sub-catchments is: , , , ..., ,

[0037] The total surface water volume of the entire watershed is:

[0038] T m The surface water level in the basin at that time was: = + +…+

[0039] That is, T ranges from 0 to T m During the specified period, the total surface water volume of the entire watershed was:

[0040] W= =

[0041] Calculate time periods sequentially , , ..., Water volume of the basin area , , ..., The results are accumulated for each time period to calculate the value of each time period. Surface water volume corresponding to the watershed (m=1, 2, ...), thus obtaining the time series of surface water accumulation. ~ That is, by integrating the total surface water volume of the watershed over different time periods, the change in water volume over time can be obtained: W = = .

[0042] S7. Visualization of watershed inundation extent:

[0043] Based on the surface features of the watershed, the water level-topography correspondence (Z~A~W) is determined. The surface water volume W of the watershed at time T corresponds to the surface inundation water level Z and the inundation range A. Using geographic information processing visualization technology, the surface water volume of the watershed at each time is transformed into a cloud map display of the inundation area of ​​the watershed. Attached Figure Description

[0044] Figure 1 This is a flowchart illustrating the present invention;

[0045] Figure 2 This is a schematic diagram of the structure of the method for determining the surface water volume of a watershed according to the present invention;

[0046] Figure 3 This is a schematic diagram of the watershed discretization into sub-catchment areas according to the present invention;

[0047] Figure 4 This is an example of a watershed land use classification map;

[0048] Figure 5 This is a satellite image of the drainage network distribution in the watershed (including the road network) as an example.

[0049] Figure 6 This is a watershed sub-catchment division map of an example;

[0050] Figure 7 This is a river system distribution map of the example area;

[0051] Figure 8 This is the 20-year return period rainstorm curve for the river basin in the example;

[0052] Figure 9 This is a map showing the inundation range of the watershed under different inundation water levels in the implementation examples. Detailed Implementation

[0053] The method of determining the present invention will be described below with reference to the accompanying drawings in the embodiments of the present invention.

[0054] like Figure 1 The process shown and Figure 2 The structure shown:

[0055] (1) Process the basic geographic files of the covered area using a geographic information system platform. First, collect the DEM digital elevation raster files (30m resolution) of the covered area from the geospatial data cloud. Vector files of 30m resolution and administrative divisions were used to extract land use classification data (30m resolution) for the region from the Global Land Cover website. 30m), such as Figure 4 Using BeiDou high-precision remote sensing imagery to obtain high-resolution regional satellite images and road network satellite images, such as... Figure 5 Through basic geographic information processing, considering the road network distribution and regional geographical conditions, drainage pipe networks are established along both sides of the main roads. Then, based on the pipe network and drainage nodes, the area is divided into several sub-catchment zones, such as... Figure 3 and Figure 6 As shown, complete the vector file of the watershed and export it, then convert the format file.

[0056] (2) Based on the model file after preliminary processing and format conversion, a regional rainstorm and flood model is established. Hydrological data and literature officially published by the local water resources bureau are consulted, and the rainfall duration process lines for different years are quickly determined using the rainstorm intensity formula, such as... Figure 8 Improve and run the rainstorm and flood model of the watershed, and extract the overflow of each node at each time step from the calculation results file.

[0057] (3) The extracted overflow from each node is superimposed with the amount of rainfall that falls directly to the ground. Based on the topographic features of the region, the inundation range and water depth corresponding to different surface water volumes are determined, such as... Figure 9 As shown.

Claims

1. A method for determining urban inundation areas caused by short-duration heavy rainfall, characterized in that, Includes the following steps: S1. Collect basic data on the watershed and preprocess it; Including basin rainfall and comprehensive geographical data; (1) Preprocessing of rainfall data: The rainfall duration sequence was determined using the rainfall intensity formula, and the water distribution pattern of rainfall in the watershed was generalized. The rainfall distribution process can be summarized as: a rainfall period Within the time period t from 0 to T1, the rainfall P1 is initially allocated, with surface water accounting for K1 and water infiltration accounting for K2, where K1+K2=1; that is, the surface water in the initial allocation is K1P1; the surface water K1P1 is then redistributed, with the underground pipe network receiving K3, and the remaining water remaining on the surface, that is, K1K3P1 flows to the underground pipe network, and K1(1-K3)P1 water is retained on the surface; (2) Geographic information data preprocessing: Preliminary processing includes processing watershed topography, DEM elevation, river network distribution, water level-water volume relationship, land use type, BeiDou high-resolution satellite imagery, street conditions, and road network elevation data to determine the relationship between watershed vegetation cover, surface slope, infiltration parameters, and surface water volume with water level changes. S2. Construct underground drainage network: For watersheds lacking drainage network data, establish underground pipelines based on the distribution of regional roads to construct the watershed's underground drainage network; S3. Watershed Discretization: The watershed is divided into multiple sub-catchments, and each sub-catchment is analyzed separately to determine the surface water volume. It is assumed that the watershed is entirely subject to passive flooding, which is applicable to geographically flat areas with relatively simple topographical structures and where connectivity between regions is not considered. In other words, any area will be flooded as long as its elevation is below the flooding elevation. The surface water in all individual sub-catchments is only related to rainfall, and there is no mutual flow within or between individual sub-catchments. S4. Analyze the surface water volume on a single sub-catchment: Based on the aforementioned rainfall distribution pattern, rainfall within a short duration is distributed according to a certain proportion, with the amount of water directly retained on the ground being K1(1-K3)P1, corresponding to the water volume w1; within a single sub-catchment area, there are several underground pipe sections and i collection well nodes, and the first rainfall period... The overflow of each node is as follows Then the nodal overflow generated by all nodes within the sub-catchment area is w2= That is, the overflow volume of the underground pipe network within the sub-catchment area ds to the surface through the collection well node is w2= Then the time period of this sub-catchment area The amount of surface water generated internally is: ， S5. Similarly, within the time period... The surface water volumes of the other sub-catchments S2, S3, ... Sn are W2, W3, ..., Wn, respectively. n The total surface water volume of the entire watershed is the sum of the surface water volumes of all its sub-catchments. That is, when the sub-catchment of the watershed is sufficiently divided, a sub-catchment with an area of ​​ds is in If the surface water volume generated during the time period is dw, then the total surface water volume of the watershed during the time period dt is... ; S6. Determine the total surface water volume of the watershed: If a watershed is divided into n sub-catchments, then the total surface water volume of the watershed is the sum of the surface water volumes of all sub-catchments: (1) Time period At time T=T1, The surface water volume of n sub-catchments is: , , , ..., , The total surface water volume of the entire watershed is: , At time T1, the surface water level in the basin was... = , That is when Time, that is, during a period of time Inside, t ranges from 0 to Let T range from 0 to T1, and the total catchment area be S, divided into several sub-catchments ds. The water accumulation in each sub-catchment ds is d. Then the time period Within the basin, the total water volume is: W= = ， (2) Time period At time T=T2, The surface water volume of n sub-catchments is: , , , ..., , The total surface water volume of the entire watershed is: , The surface water level in the basin at time T2 is: = + , That is, during the time period T from T1 to T2, when Time, that is, during a period of time Within, t ranges from T1 to T2, and the water accumulation on each sub-catchment ds is d. Then the time period Within the basin, the water volume is: W= = ， Then, during the time period T from 0 to T2, the total surface water volume of the entire watershed is, W= = ， And so on; m time period T=T m time; The surface water volume of n sub-catchments is: , , , ..., , The total surface water volume of the entire watershed is: , T m The surface water level in the basin at that time was: = + +…+ , That is, T ranges from 0 to T m During the specified period, the total surface water volume of the entire watershed was: W= = ， Calculate time periods sequentially , , ..., Water volume of the basin area , , ..., The results are accumulated for each time period to calculate the value of each time period. Surface water volume corresponding to the watershed m=1,2,…, thus obtaining the time series of surface water accumulation. ~ That is, by integrating the total surface water volume of the watershed over different time periods, the change in water volume over time can be obtained: W= = ； S7. Visualization of watershed inundation extent: Based on the surface characteristics of the watershed, the surface water volume W at time T corresponds to the inundation level Z and the inundation range A. Using geographic information visualization processing technology, the surface water volume of the watershed at each time is transformed into a cloud map display of the inundation area of ​​the watershed.

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