A new method for flood risk assessment

Abstract

The application provides a new flood risk assessment method, which comprises the following steps: obtaining a flood risk factor; the risk factor comprises a maximum submerged water depth, a maximum flow rate and a submerged duration; and calculating a risk degree R value in a submerged range corresponding to a preset flood occurrence frequency by constructing a GIS grid algorithm, so as to expand a calculation domain of each frequency flood risk factor to the submerged range, thereby the flood risk assessment can be performed on the maximum submerged range. The GIS grid algorithm is constructed to expand the submerged range of all frequency floods to the maximum submerged range in the calculation domain, so that the risk degree R value in the maximum submerged range can be calculated, thereby the flood risk assessment can be performed on the maximum submerged range, and the region ignored by the traditional algorithm is corrected.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of natural disaster monitoring, and particularly relates to a new flood risk assessment method. BACKGROUND

[0002] The flood disaster risk census is an important part of the national comprehensive risk census of natural disasters. Among them, more than 60% of the land area and more than 90% of the population of a country are threatened by floods to varying degrees. Important cities, important infrastructure and major grain producing areas are mainly distributed along the rivers and coastal areas, and the population distribution and productivity layout are highly overlapped with the flood risk area, so it is crucial to do well in the flood disaster census and assess the flood inundation risk.

[0003] The frequency of assessing the flood inundation risk is: 5-year, 10-year, 20-year, 50-year, 100-year, etc. However, in the current method for assessing the flood inundation risk, only the minimum value domain (5-year) is used to assess the flood inundation risk, and the assessment corresponding to the minimum maximum inundation range is ignored. SUMMARY

[0004] The present application aims to solve the defects in the prior art and provide a new flood risk assessment method.

[0005] A new flood risk assessment method comprises:

[0006] Obtaining a flood risk factor; the risk factor comprises: maximum inundation water depth, maximum flow rate, inundation duration;

[0007] The risk factor is calculated by constructing a GIS grid algorithm, and the frequency of each flood risk factor is expanded to the inundation range corresponding to the preset flood occurrence frequency, so as to calculate the inundation risk R value, thereby the maximum inundation range can be assessed.

[0008] Further, the new flood risk assessment method as described above, the flood occurrence frequency comprises: 5-year, 10-year, 20-year, 50-year, 100-year.

[0009] Further, the new flood risk assessment method as described above, the inundation range corresponding to the preset flood occurrence frequency is the inundation range corresponding to the 100-year.

[0010] Further, the new flood risk assessment method as described above, the calculation of the subsequent risk factor on the flood risk degree comprises:

[0011] The risk factor is gridded;

[0012] input the gridded risk factors into a flood inundation risk degree evaluation model, which is:

[0013]

[0014] wherein pi is the probability corresponding to the flood occurrence frequency of the ith year, and Hi is the maximum inundation water depth corresponding to the flood occurrence frequency of the ith year.

[0015] Further, the new flood risk evaluation method as described above further comprises preprocessing the risk factor data, and when the maximum inundation water depth corresponding to the flood occurrence frequency of 5 years is processed, the maximum inundation water depth within the inundation range of 5 years is taken as the original value, and the corresponding inundation water depth H is taken as a "0" value when the inundation range corresponding to the flood occurrence frequency of more than 5 years and less than 100 years is exceeded.

[0016] The present application provides a new flood risk evaluation method, which is a modification of the traditional flood risk evaluation method. The traditional flood risk evaluation is to calculate the risk degree R value (risk evaluation requires R value) according to a given formula using the flood risk factors (maximum inundation water depth, maximum flow rate, inundation duration) of 5 years, 10 years, 20 years, 50 years and 100 years. However, because the inundation range of 5 years is less than that of 10 years, which is less than that of 20 years, which is less than that of 50 years, which is less than that of 100 years in practice, the risk degree R value within the inundation range of 5 years can be calculated only when the calculation domain is limited in the GIS using the above-mentioned given formula, and thus the risk evaluation cannot be performed on the regions outside the inundation range of more than 5 years. The present application expands the inundation range of all frequency floods to the maximum inundation range (here, 100 years) on the calculation domain by constructing a GIS gridding algorithm, so that the risk degree R value within the maximum inundation range can be calculated, and thus the flood risk evaluation can be performed according to the maximum inundation range, which modifies the regions ignored by the traditional algorithm. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a topological relationship diagram of the inundation ranges of different frequency floods;

[0018] Figure 2 is a topological relationship diagram of the maximum inundation water depth of 5 years;

[0019] Figure 3 is a topological relationship diagram of the maximum inundation water depth of 10 years;

[0020] Figure 4 is a topological relationship diagram of the maximum inundation water depth of 20 years;

[0021] Figure 5 is a topological relationship diagram of the maximum inundation water depth of 50 years;

[0022] Figure 6Topological graph of maximum inundation water depth of 100-year frequency;

[0023] Figure 7 R-value result graph of the existing risk degree assessment method;

[0024] Figure 8 Topological graph of maximum inundation water depth of 5-year frequency obtained by the method of the application;

[0025] Figure 9 Topological graph of maximum inundation water depth of 10-year frequency obtained by the method of the application;

[0026] Figure 10 Topological graph of maximum inundation water depth of 20-year frequency obtained by the method of the application;

[0027] Figure 11 Topological graph of maximum inundation water depth of 50-year frequency obtained by the method of the application;

[0028] Figure 12 Topological graph of maximum inundation water depth of 100-year frequency obtained by the method of the application;

[0029] Figure 13 R-value result graph of the risk degree assessment method obtained by the method of the application; DETAILED DESCRIPTION

[0030] In order to make the objects, technical solutions and advantages of the application clearer, the technical solutions in the application are described clearly and completely below. Obviously, the described embodiments are some of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.

[0031] The waterlogging disaster census is one of the basic and main tasks of the first national comprehensive disaster risk census, and the flood risk assessment zoning is the most technically demanding and largest task in the waterlogging disaster census. The basis of the flood risk zoning is the inundation analysis and assessment results of each flood frequency (5-year frequency, 10-year frequency, 20-year frequency, 50-year frequency, 100-year frequency, etc.), the flood risk R value is calculated according to the unified technical requirements of the Ministry of Water Resources, and then the inundation risk zoning and prevention zoning are carried out according to the R value. The inundation risk R value expressed by the grid data is calculated by using the calculation formula specified by the technical requirements for each grid point according to the three elements (maximum inundation water depth, maximum flow rate and inundation duration) of the flood risk of each frequency. Since the inundation ranges of different frequencies are different, errors are prone to occur in the calculation of the risk R value. The application uses the grid calculator in the spatial analysis tool set of ArcGIS to calculate the risk R value.

[0032] The flood risk analysis is mainly based on surveying and mapping results (including section surveying and mapping and submerged area DEM surveying and mapping), and the submerged calculation is carried out according to the hydrological analysis results, so that the evaluation results are obtained. The maximum submerged water depth is taken as the evaluation factor, the grid calculator of ArcGIS is used to calculate the risk value R, and the operation method of other risk evaluation factors is similar.

[0033] Firstly, data is acquired

[0034] The maximum submerged water depth grid data of the evaluation area (5-year, 10-year, 20-year, 50-year, 100-year, etc.) is acquired, in order to express concisely, the following file naming is carried out: 5-year maximum submerged water depth H5, 10-year maximum submerged water depth H10, 20-year maximum submerged water depth H20, 50-year maximum submerged water depth H50, 100-year maximum submerged water depth H100. The corresponding ArcGIS data organization is as follows:

[0035] The submerged ranges of different frequency floods need to meet the topological relationship: H5 < H10 < H20 < H50 < H100, as shown in the following figure: Figures 1-6

[0036] Risk value R calculation principle

[0037] The flood submerged risk value R is calculated by the following formula:

[0038] (1)

[0039] Wherein, pi is the probability corresponding to the flood occurrence frequency of the ith year (the probability corresponding to the flood occurrence frequency of 5 years is 0.2, the probability corresponding to the flood occurrence frequency of 10 years is 0.1, the probability corresponding to the flood occurrence frequency of 20 years is 0.05, the probability corresponding to the flood occurrence frequency of 50 years is 0.02, and the probability corresponding to the flood occurrence frequency of 100 years is 0.01), and the maximum submerged water depth corresponding to the flood occurrence frequency of the ith year.

[0040] In ArcGIS, first, the water depth grid data of the five frequencies used in the above formula is loaded, and then the grid calculator in the spatial analysis tool is used for calculation, the calculation expression is: ("H5.tif" + "H10.tif") / 2 × 0.1 + ("H10.tif" + "H20.tif") / 2 × 0.05 + ("H20.tif" + "H50.tif") / 2 × 0.03 + ("H50.tif" + "H100.tif") / 2 × 0.01, and the output file is R.tif, here, the.tif is a grid picture file with a coordinate system, and the calculation result is as shown in the following figure: Figure 7

[0041] Data preprocessing ​​

[0042] From Figure 1 It can be seen that the inundation range of different frequencies is increased with the decrease of flood frequency, that is, the 100-year flood inundation range is larger than the 50-year flood inundation range, the 50-year flood inundation range is larger than the 20-year flood inundation range, and so on. If the maximum water depth grid results of each frequency are directly calculated by the ArcGIS grid calculator, the calculation domain is determined by the minimum range (5-year), and the inundation range corresponding to more than 5 years cannot be obtained, so the risk degree R value corresponding to more than 5 years cannot be correctly evaluated. In order to obtain the maximum inundation range covering the 100-year, it is necessary to preprocess the inundation ranges of other frequency floods (5-year, 10-year, 20-year, 50-year) participating in the calculation.

[0043] Therefore, in order to make the 5 frequency floods (5-year, 10-year, 20-year, 50-year, 100-year) participating in the calculation of the risk degree R value have the same inundation range, so that the finally calculated risk degree R value covers the maximum range (100-year inundation range), the present application adopts formula 1 to calculate the risk degree R value, the maximum value of pi is designed as the probability corresponding to the 100-year, and Hi is designed as a certain preset value, in the embodiment of the present application, Hi generates a 0-value grid data (grid data is one of the most commonly used data formats in geographic information system, which uses a number of grids to approximate the real ground relief or water depth and other quantities that change with different spatial positions. The 0-value grid here is a grid data generated by setting the 100-year flood inundation depth to 0, and the range format is the same as H100.tif, only the value is 0), so that the part of the inundation water depth exceeding 5 years (or 10 years, 20 years, 50 years) but less than 100 years is "0", so as not to affect the calculation result of the risk degree R value in quantity. The grid size is equal to the 100-year, and the present application adopts H100.tif grid multiplied by "0" to obtain, the grid calculator formula is: "H100.tif" x 0.0, and the output file is H0.tif.

[0044] Then, other frequency flood (5-year, 10-year, 20-year, 50-year) inundation range is added to this 0-value grid to get 5 equal range grid files, so that the inundation range of each frequency flood is equal, to objectively evaluate the flood risk degree beyond 5-year. The specific ArcGIS grid calculation formula is: Con (Is Null ("H5.tif"), "H0.tif", "H5.tif") (5-year inundation range is taken 5-year flood inundation depth H5, and the outside part is taken the "0" value grid H0 constructed above), output is the corrected 5-year maximum water depth grid H5_Rev.tif, and H10, H20, H50 is repeated 3 times, to get all the corrected 4 maximum inundation depth grid H5_Rev.tif, H10_Rev.tif, H20_Rev.tif, H50_Rev.tif. The results are as follows Figures 8-12 .

[0045] Comparison Figures 1-6 With Figures 8-12 It can be seen that, under the premise of keeping the maximum inundation water depth result unchanged, the corrected maximum water depth inundation grid range is consistent with 100-year, so that the corrected risk degree R value calculation can be carried out.

[0046] Risk degree R value calculation

[0047] According to Figures 8-12 The corrected maximum water depth grid, the corrected risk degree R value can be calculated again by using the grid calculator:

[0048] The calculation expression is:

[0049] ("H5_Rev.tif" + "H10_Rev.tif") / 2 × 0.1 + ("H10_Rev.tif" + "H20_Rev.tif") / 2 × 0.05 + ("H20_Rev.tif" + "H50_Rev.tif") / 2 × 0.03 + ("H50_Rev.tif" + "H100.tif") / 2 × 0.01, here Tif is a grid picture file with coordinate system, this calculation expression is the specific expression of formula 1 in the grid calculator, only the calculation parameter is the corrected maximum inundation water depth grid, and the output file is R_rev.tif, the calculation result is as follows Figure 13 .

[0050] From Figure 13 It can be seen that the risk degree outside the 5-year inundation range is not zero, and the risk degree value of the point in the figure is 0.0126, which is Figure 7Completely different, the improved risk degree R value conforms to the actual situation.

[0051] The method provided by the application makes up the defect that the traditional calculation can only calculate according to the minimum value range (5 years once), opens up a road for the risk degree R value calculation of the entire maximum possible inundation range (100 years once), and lays a foundation for correctly performing regional flood risk zoning and prevention zoning.

[0052] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A novel flood risk assessment method, characterized in that, include: Obtain flood risk factors; The risk factors include: maximum inundation depth, maximum flow velocity, and inundation duration; By constructing a GIS grid algorithm for the risk factors, the calculation domain of each frequency flood risk factor is extended to the inundation range corresponding to the preset flood occurrence frequency. Then, the inundation risk R value is calculated, thereby enabling flood risk assessment of the maximum inundation range. The flood occurrence frequencies include: once every 5 years, once every 10 years, once every 20 years, once every 50 years, and once every 100 years. The inundation range corresponding to the preset flood occurrence frequency is the inundation range corresponding to a 100-year return period. The calculation of flood risk level based on risk factors includes: The risk elements are gridded; The gridded risk elements are input into the flood inundation risk assessment model, which is as follows: Where pi is the probability corresponding to the frequency of a flood occurring once in the i-th year, and Hi is the maximum inundation depth corresponding to the frequency of a flood occurring once in the i-th year. It also includes preprocessing the risk factor data. When processing the maximum inundation depth in the case of a flood occurrence frequency of once every 5 years, the maximum inundation depth within the 5-year flood range is taken as the original value. For the flood range that exceeds the 5-year flood but is less than the 100-year flood, the corresponding inundation depth H is taken as "0". Obtain the maximum inundation depth grid data for the assessment area, where the maximum inundation depth for a 5-year return period is H5, the maximum inundation depth for a 10-year return period is H10, the maximum inundation depth for a 20-year return period is H20, the maximum inundation depth for a 50-year return period is H50, and the maximum inundation depth for a 100-year return period is H100. In ArcGIS, first load the water depth grid data for the five frequencies used, and then use the grid calculator in the spatial analysis tools to perform the calculation. The calculation expression is as follows: The output file is R.tif, calculated as ("H5.tif"+"H10.tif") / 2×0.1+("H10.tif"+"H20.tif") / 2×0.05+("H20.tif"+"H50.tif") / 2×0.03+("H50.tif"+"H100.tif") / 2×0.

01. The maximum value of pi is designed to correspond to the probability of a 100-year flood. A 0-value grid data is generated for Hi, and the size of the grid is equal to that of a 100-year flood. The 0-value grid is a grid data that is regenerated by setting the inundation depth of the 100-year flood to 0. The formula for the grid calculator is: H100.tif × 0.0, and the output file is H0.tif; Adding a 0 value to the inundation range for 5-year, 10-year, 20-year, and 50-year flood events will result in 5 grid files with equal ranges. The output is the corrected 5-year flood return maximum water depth grid H5_Rev.tif. Repeat this process 3 times for H10, H20, and H50 to obtain all four corrected maximum flood depth grids: H5_Rev.tif, H10_Rev.tif, H20_Rev.tif, and H50_Rev.tif. Therefore, while keeping the maximum inundation depth unchanged, the range of the maximum inundation grid after correction is consistent with the 100-year return period, so the risk R value after correction can be calculated. The calculation expression is: ("H5_Rev.tif" + "H10_Rev.tif") / 2 × 0.1 + ("H10_Rev.tif" + "H20_Rev.tif") / 2 × 0.05 + ("H20_Rev.tif" + "H50_Rev.tif") / 2 × 0.03 + ("H50_Rev.tif" + "H100.tif") / 2 × 0.01。

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