Method for quickly calculating design flood of small watershed at any global position

Abstract

The invention provides a global arbitrary position small watershed design flood rapid calculation method, and relates to the technical field of hydrology and water resource technologies, a to-be-calculated design flood area is defined as a target point, a watershed characteristic parameter, a rainstorm statistical parameter and a runoff statistical parameter of the target point are acquired, and a target watershed reasoning formula is combined to calculate the design flood of the small watershed. Calculating each frequency design flood of the small watershed; the process of obtaining the drainage basin characteristic parameters comprises the steps of generating a target area water system and a drainage basin boundary vector data set based on DEM data, obtaining a drainage basin boundary above a target point according to the target area through the water system and the drainage basin boundary vector data set, and obtaining the drainage basin characteristic parameters through the drainage basin boundary above the target point. According to the method, the global sub-basin boundary data set and the global water system data set are subjected to spatial index establishment, so that second-level extraction of basin boundaries above any global section point is realized, and the flood analysis efficiency is greatly improved.

Description

Technical Field

[0001] The invention relates to the technical field of hydrology and water resources, and in particular to a method for quickly calculating a design flood for a small watershed at any position in the world. Background Art

[0002] The analysis and calculation of design floods in small watersheds is an important foundation for engineering construction and disaster prevention and mitigation. It is of great significance to ensure the flood control safety standards of water conservancy, hydropower, transportation, municipal engineering and other projects, and to guide the scale and investment decisions of projects. Design flood analysis can be used to assess flood risks, guide flood prevention warnings and emergency responses, and reduce the loss of life and property caused by flood disasters. It is of great value to the rational use of water resources, protection of water ecological environment, promotion of sustainable development of watersheds, and guarantee of regional economic and social development. The main calculation methods for design flood of small watershed include inference formula method, regional experience formula method, historical flood analysis method and comprehensive instantaneous unit line method. The inference formula method is relatively mature in the analysis and calculation of rainstorm flood in areas without data. It is one of the main methods for deriving the design flood peak flow. The inference formula method directly calculates the flood peak at the outlet of the watershed by summarizing the flow conditions of the watershed. The main calculation parameters of the inference formula for design flood of small watershed include watershed area (F), river length (L), main river gradient (J) and other watershed characteristic parameters and design rainstorm (P). If the above parameters are known, the design flood of the small watershed can be quickly calculated in combination with regional experience parameters. The invention patent with the publication number CN112231907A discloses a method for calculating the spatiotemporal distribution of design floods in a watershed. When analyzing and calculating the design floods in small watersheds in areas without data, the watershed boundaries and river systems of the small watersheds are often manually drawn based on the topographic map or generated with the help of GIS software, and then the main watershed characteristic parameters of the watershed are analyzed and calculated. Then, the rainstorm experience atlas of the area where the design watershed is located is consulted to obtain the rainstorm statistical parameters, and then the design rainstorm is calculated by the rainstorm statistical parameters. Finally, the design flood results of the watershed outlet section are calculated using the inference formula and the unit line method. This method requires manual consultation of the rainstorm atlas of the area, and generally calculates the rainstorm statistical parameters based on the center of gravity of the watershed. The work efficiency is extremely low and there is a certain degree of subjectivity. The values ​​taken by different designers lack uniformity. In addition, the above-mentioned watershed characteristic parameter analysis and rainstorm analysis processes are relatively independent, and only the design flood of a single small watershed can be calculated each time. The flexibility and efficiency are low, and it is impossible to respond quickly when a large-scale small watershed design flood analysis and calculation is required. In the context of smart water conservancy construction and the improvement of flash flood disaster prevention and control capabilities, the traditional small watershed design flood calculation method has problems such as low efficiency, strong subjectivity, and lack of uniformity; especially when a large-scale small watershed design flood analysis is required, the existing method requires manual consultation of rainstorm atlases and calculation of watershed characteristic parameters one by one, and each link is relatively independent and cannot meet the needs of rapid response; therefore, a method for rapid calculation of design floods for small watersheds at any location in the world is developed to realize automatic extraction of watershed characteristic parameters, intelligent acquisition of rainstorm parameters, and rapid calculation of design floods, which has important practical significance and application value for improving the ability to forecast and warn of flash flood disasters and supporting smart water conservancy construction. Summary of the invention

[0003] The present invention provides a method for quickly calculating the design flood of a small watershed at any location in the world, aiming to solve at least one technical problem existing in the prior art mentioned in the background technology.

[0004] The present invention provides the following technical solutions to achieve the above objectives: A method for quickly calculating design flood of a small watershed at any location in the world includes the following steps: S1. Establish water system vector dataset V_Str and basin boundary vector dataset V_Bou based on global DEM dataset; S2, record the coordinates of any small watershed outlet as the target point, and use the target point as the starting point to count the watershed boundaries above the target point; S3. Based on the basin boundary above the target point, generate basin characteristic parameters, rainstorm statistical parameters and runoff statistical parameters; S4. Based on the basin characteristic parameters, rainstorm statistical parameters and runoff statistical parameters, combined with the target basin inference formula, calculate the design flood of each frequency of the small basin; Furthermore, the step S1 includes the following steps: S1.1 Prepare the global DEM dataset, use remote sensing images or other water system data extracted to correct the original DEM data, ensure the hydrological logic correctness of the DEM data, and obtain the corrected DEM dataset Adj_DEM; S1.2 After performing depression-filling calculation on the corrected DEM dataset Adj_DEM, the flow direction and cumulative flow tools of GIS software are used to generate the global flow direction raster dataset R_Dir and the cumulative flow raster dataset R_Acc; S1.3 Based on the global flow direction raster dataset R_Dir and the cumulative flow raster dataset R_Acc, the global water system vector dataset V_Str and the basin boundary vector dataset V_Bou are generated through GIS software. When generating the basin boundary, the minimum sub-basin area threshold is set to obtain the sub-basin boundary vector dataset V_Bou and water system vector dataset V_Riv above the area threshold.

[0005] Furthermore, the step S2 includes the following steps: S2.1 adds a unique ID value Reach_ID to each vector river section of the generated water system vector dataset V_Str, and records the ID values ​​of all upstream river sections in the attributes of each vector river section; S2.2 In the generated sub-basin boundary V_Bou, assign the ID value of the corresponding river section to the sub-basin; S2.3 obtains the coordinates of any small watershed outlet, and quickly locates the sub-watershed through spatial query according to the coordinates of the target point, and queries upstream along the river section where the sub-watershed is located, finds all upstream river sections according to the IDs of all upstream river sections, locates all upstream sub-watersheds at the same time, and merges them to generate the upstream watershed boundary V_Up_Bou1; S2.4 Based on the sub-basin boundary V_Target_SubBou where the target point is located, the spatial analysis tool is used to clip the global flow direction grid dataset R_Dir to obtain the flow direction grid data R_Target_Dir within the sub-basin boundary V_Target_SubBou where the target point is located; S2.5 According to the flow direction grid data R_Target_Dir and the coordinates of the target point in the sub-basin boundary V_Target_SubBou, all upstream areas of the sub-basin V_Target_SubBou that flow to the target point are tracked, thereby determining the sub-basin grids above the target point within the sub-basin V_Target_SubBou and generating the vector boundary V_Target_Bou; S2.6 merges the vector boundary V_Target_Bou in S2.5 with the upstream watershed boundary V_Up_Bou1 generated in S2.3 to generate the watershed boundary V_Up_Bou above any small watershed target point.

[0006] Furthermore, the step S3 includes: S3.1 The steps to generate watershed characteristic parameters are as follows: S3.1.1 Based on the basin boundary V_Up_Bou above any small watershed target point, obtain the statistical basin area F; S3.1.2 Based on the global flow direction grid dataset R_Dir, the water flow length tool of GIS software is used to generate the global maximum river length grid dataset R_Len. The dataset R_Len contains the maximum upstream river length value at any grid in the world. S3.1.3 Based on the corrected DEM dataset Adj_DEM, the flow direction raster dataset R_Dir and the accumulated flow raster dataset R_Acc as input data, use the distance tool of the GIS software to generate the global height difference raster dataset R_Diff. The dataset R_Diff contains the height difference between the source of the maximum upstream river length at any grid in the world and this grid; S3.1.4 Based on the global height difference raster dataset R_Diff and the global maximum river length raster dataset R_Len, obtain the gradient raster dataset R_J of the maximum river length above any target point in the world, R_J=R_Diff / R_Len; S3.2 The steps to generate heavy rain statistical parameters are as follows: S3.2.1 Prepare and rasterize the contour maps of rainstorm statistical parameters such as the mean value of rainstorm and Cv value in different periods in different regions around the world, and generate the global rainstorm statistical parameter raster dataset R_Storm_P; the dataset R_Storm_P contains the rainstorm statistical parameter values ​​at any grid position around the world; S3.2.2 Using the basin boundary V_Up_Bou above any small watershed target point as a mask, use the spatial analysis tool to cut the rainstorm statistical parameter grid dataset R_Storm_P to obtain the rainstorm statistical parameter grid dataset R_Up_Bou_Storm_P in any small watershed, and obtain the average rainstorm statistical parameter value of any small watershed after averaging; S3.3 The steps to generate runoff statistics are as follows: S3.3.1 Prepare and rasterize the contour maps of runoff parameters for different regions around the world, and generate the raster datasets R_P of runoff parameters for different regions around the world; S3.3.2 Take the basin boundary V_Up_Bou above any small watershed target point as a mask, and use the spatial analysis tool to cut the runoff parameter raster dataset R_P in S3.3.1 to obtain the runoff parameter raster dataset R_Up_Bou_P in any small watershed, and then average it to obtain the average runoff parameter value of any small watershed.

[0007] Furthermore, the step S4 comprises: S4.1 Based on the average rainstorm statistical parameter value of any small watershed, the design rainstorm value of different frequencies in any small watershed is calculated by frequency analysis method; S4.2 Based on the average runoff parameter value of any small watershed, combined with the design rainstorm values ​​of different frequencies, the runoff parameter values ​​of any small watershed with different frequencies are calculated; S4.3 Based on the basin characteristic parameter values, design rainstorm values ​​and runoff parameter values, combined with the target basin inference formula, calculate the design flood and process of each frequency in any small basin in the world.

[0008] A design flood calculation system, configured with a program module for executing the above method, comprises: A watershed parameter generation module is used to establish a water system vector dataset V_Str and a watershed boundary vector dataset V_Bou and to count the watershed boundary V_Up_Bou above any small watershed target point, and to generate watershed parameters based on the watershed boundary V_Up_Bou above any small watershed target point; The rainstorm statistical parameter generation module is used to generate the global rainstorm statistical parameter grid dataset R_Storm_P, and generate the rainstorm statistical parameters based on the basin boundary V_Up_Bou above any small watershed target point; The module for generating runoff statistics parameters is used to generate the runoff parameters grid dataset R_P in different regions around the world, and generate runoff statistics parameters based on the basin boundary V_Up_Bou above any small watershed target point; The design flood calculation module calls the basin parameters, rainstorm statistical parameters and runoff statistical parameters and calculates the design flood of each frequency according to the target basin reasoning formula. Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention provides a method for extracting basin boundaries above any global river section point. The global sub-basin boundary dataset and global water system dataset are prepared in advance and spatial index is established. At the same time, global flow direction and cumulative flow raster data are prepared. The efficiency of basin boundary extraction is greatly improved through pre-generation of datasets, and the basin boundary above any global section point can be extracted in seconds. The basin boundary result is obtained immediately after the point is drawn. Specifically, it is embodied in: (1) When obtaining the watershed boundary above the target river section point, there is no need to perform spatial analysis steps such as filling, flow direction, accumulated flow, river network generation, river network classification, and watershed generation each time. Instead, the relevant data sets prepared in advance can be directly applied, greatly improving the analysis efficiency. (2) By establishing a spatial index, this method can quickly locate the sub-basin where the target river section point is located and all upstream sub-basins according to the coordinates of the target river section point. By merging, the upstream basin boundary of the sub-basin can be quickly obtained; (3) For the catchment boundary above the target section point in the sub-basin, this method only needs to analyze and traverse the flow direction raster dataset within the local sub-basin. There is no need to analyze and calculate all the flow direction raster datasets above the section point. After obtaining the catchment boundary above the point in the local sub-basin, it can be quickly obtained by merging it with all the sub-basins upstream of the sub-basin to obtain the catchment boundary above the target point.

[0009] 2. The method for quickly calculating the design flood of a small watershed at any location in the world described in the present invention prepares in advance the world's largest river length raster dataset and the global river channel elevation difference raster dataset. According to the coordinates of the target river section point, the maximum river length, main river channel gradient and other watershed characteristic parameters can be quickly queried and extracted, without the need for analysis and extraction each time, which greatly improves the analysis and calculation efficiency.

[0010] 3. The method for quickly calculating the design flood of a small watershed at any location in the world described in the present invention prepares in advance a global rainstorm and runoff parameter raster data set, and prepares in advance the inference formulas and related empirical parameters for each global region. The design flood of any watershed can be quickly calculated through the watershed characteristic parameters obtained above.

[0011] 4. The method for rapid calculation of design floods for small watersheds at any location in the world described in the present invention can be developed into an application through a B / S architecture, which can realize one-click calculation of design floods for small watersheds at any location in the world, greatly improving the efficiency of small watershed flood analysis and calculation, and meeting practical needs such as rapid analysis of mountain torrent disasters and construction of smart water conservancy platforms. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 Schematic diagram of the river section ID value assignment operation of the present invention Figure 1 ; Figure 2 Schematic diagram of the river section ID value assignment operation of the present invention Figure 2 ; Figure 3 This is a schematic diagram of target point positioning of the present invention; Figure 4 This is a schematic diagram of positioning the upstream sub-basin of the target point of the present invention; Figure 5 This is a schematic diagram of the merger of the sub-basins upstream of the target point of the present invention; Figure 6 Schematic diagram of target point clipping flow direction grid data of the present invention Figure 1 ; Figure 7 Schematic diagram of target point clipping flow direction grid data of the present invention Figure 2 ; Figure 8 Generate a schematic diagram for the vector boundary V_Target_Bou of the present invention; Fig. 9 This is a schematic diagram of the watershed boundary merging of the present invention. Figure 1 ; Fig.10 This is a schematic diagram of the watershed boundary merging of the present invention. Figure 2 ; Fig.11 A schematic diagram for generating a maximum river length raster dataset of the present invention; Fig.12A schematic diagram for generating a global height difference raster dataset of the present invention; Fig.13 It is a flow chart of the present invention; Fig.14 This is a schematic diagram of the rapid extraction of watershed characteristic parameters of the present invention. DETAILED DESCRIPTION

[0013] To facilitate the understanding of the present invention, the present application will be described more comprehensively below with reference to the relevant drawings; the drawings show preferred embodiments of the present invention, but the present invention can be implemented in many different forms and is not limited to the embodiments described herein; on the contrary, the purpose of providing these embodiments is to enable a more thorough and comprehensive understanding of the disclosed content of the present invention.

[0014] It should be noted that the terms “vertical”, “horizontal”, “up”, “down”, “left”, “right” and similar expressions used in this document are only for illustrative purposes and do not represent the only implementation method.

[0015] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which the present invention belongs; the terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention; the term "and / or" used herein includes any and all combinations of one or more related listed items.

[0016] Embodiment. A method for quickly calculating design floods for small watersheds at any location in the world, such as Fig.13 , 14 As shown, the following steps are included: S1. Establish water system vector dataset V_Str and basin boundary vector dataset V_Bou based on global DEM dataset; S2, record the coordinates of any small watershed outlet as the target point, and use the target point as the starting point to count the watershed boundaries above the target point; S3. Based on the basin boundary above the target point, generate basin characteristic parameters, rainstorm statistical parameters and runoff statistical parameters; S4. Based on the basin characteristic parameters, rainstorm statistical parameters and runoff statistical parameters, combined with the target basin inference formula, calculate the design flood of each frequency of the small basin; The step S1 comprises the following steps: S1.1 Prepare the global DEM dataset, use remote sensing images or other water system data extracted to correct the original DEM data, ensure the hydrological logic correctness of the DEM data, and obtain the corrected DEM dataset Adj_DEM; S1.2 After performing depression-filling calculation on the corrected DEM dataset Adj_DEM, the flow direction and cumulative flow tools of GIS software are used to generate the global flow direction raster dataset R_Dir and the cumulative flow raster dataset R_Acc; S1.3 Based on the global flow direction raster dataset R_Dir and the cumulative flow raster dataset R_Acc, the global water system vector dataset V_Str and the basin boundary vector dataset V_Bou are generated through GIS software. When generating the basin boundary, the minimum sub-basin area threshold is set to obtain the sub-basin boundary vector dataset V_Bou and water system vector dataset V_Riv above the area threshold.

[0017] The step S2 comprises the following steps: S2.1 adds a unique ID value Reach_ID to each vector river section of the generated water system vector dataset V_Str, and records the ID values ​​of all upstream river sections in the attributes of each vector river section; S2.2 In the generated sub-basin boundary V_Bou, assign the ID value of the corresponding river section to the sub-basin; S2.3 obtains the coordinates of any small watershed outlet, and quickly locates the sub-watershed through spatial query according to the coordinates of the target point, and queries upstream along the river section where the sub-watershed is located, finds all upstream river sections according to the IDs of all upstream river sections, locates all upstream sub-watersheds at the same time, and merges them to generate the upstream watershed boundary V_Up_Bou1; S2.4 Based on the sub-basin boundary V_Target_SubBou where the target point is located, the spatial analysis tool is used to clip the global flow direction grid dataset R_Dir to obtain the flow direction grid data R_Target_Dir within the sub-basin boundary V_Target_SubBou where the target point is located; S2.5 According to the flow direction grid data R_Target_Dir and the coordinates of the target point in the sub-basin boundary V_Target_SubBou, all upstream areas of the sub-basin V_Target_SubBou that flow to the target point are tracked, thereby determining the sub-basin grids above the target point within the sub-basin V_Target_SubBou and generating the vector boundary V_Target_Bou; S2.6 merges the vector boundary V_Target_Bou in S2.5 with the upstream watershed boundary V_Up_Bou1 generated in S2.3 to generate the watershed boundary V_Up_Bou above any small watershed target point.

[0018] Through the aforementioned steps S1 and S2, when it is necessary to obtain the basin boundary above the target river section point, there is no need to perform the spatial analysis steps such as filling, flow direction, cumulative flow, river network generation, river network classification, and basin generation each time, but directly apply the relevant data sets prepared in advance, which greatly improves the analysis efficiency; at the same time, the sub-basin where the target river section point is located and all upstream sub-basins can be quickly located through the coordinates of the target river section point, and the basin boundary upstream of the sub-basin can be obtained by merging; The step S3 comprises: S3.1 The steps to generate watershed characteristic parameters are as follows: S3.1.1 Based on the basin boundary V_Up_Bou above any small watershed target point, obtain the statistical basin area F; S3.1.2 Based on the global flow direction grid dataset R_Dir, the water flow length tool of GIS software is used to generate the global maximum river length grid dataset R_Len. The dataset R_Len contains the maximum upstream river length value at any grid in the world. S3.1.3 Based on the corrected DEM dataset Adj_DEM, the flow direction raster dataset R_Dir and the accumulated flow raster dataset R_Acc as input data, use the distance tool of the GIS software to generate the global height difference raster dataset R_Diff. The dataset R_Diff contains the height difference between the source of the maximum upstream river length at any grid in the world and this grid; S3.1.4 Based on the global height difference raster dataset R_Diff and the global maximum river length raster dataset R_Len, obtain the gradient raster dataset R_J of the maximum river length above any target point in the world, R_J=R_Diff / R_Len; S3.2 The steps to generate heavy rain statistical parameters are as follows: S3.2.1 Prepare and rasterize the contour maps of rainstorm statistical parameters such as the mean value of rainstorm and Cv value in different periods in different regions around the world, and generate the global rainstorm statistical parameter raster dataset R_Storm_P; the dataset R_Storm_P contains the rainstorm statistical parameter values ​​at any grid position around the world; S3.2.2 Using the basin boundary V_Up_Bou above any small watershed target point as a mask, use the spatial analysis tool to cut the rainstorm statistical parameter grid dataset R_Storm_P to obtain the rainstorm statistical parameter grid dataset R_Up_Bou_Storm_P in any small watershed, and obtain the average rainstorm statistical parameter value of any small watershed after averaging; S3.3 The steps to generate runoff statistics are as follows: S3.3.1 Prepare and rasterize the contour maps of runoff parameters for different regions around the world, and generate the raster datasets R_P of runoff parameters for different regions around the world; S3.3.2 Take the basin boundary V_Up_Bou above any small watershed target point as a mask, and use the spatial analysis tool to cut the runoff parameter raster dataset R_P in S3.3.1 to obtain the runoff parameter raster dataset R_Up_Bou_P in any small watershed, and then average it to obtain the average runoff parameter value of any small watershed.

[0019] The step S4 comprises: S4.1 Based on the average rainstorm statistical parameter value of any small watershed, the design rainstorm value of different frequencies in any small watershed is calculated by frequency analysis method; S4.2 Based on the average runoff parameter value of any small watershed, combined with the design rainstorm values ​​of different frequencies, the runoff parameter values ​​of any small watershed with different frequencies are calculated; S4.3 Based on the basin characteristic parameter values, design rainstorm values ​​and runoff parameter values, combined with the target basin reasoning formula, calculate the design flood and process of each frequency of any small basin in the world; the target basin reasoning formula adopts the reasoning formula method commonly used in the prior art, which was proposed by Irish engineer TJMulvaney in 1851. Later, scientists from various countries improved the reasoning formula according to the characteristics of their own basins. The specific reasoning formula has been published in "Engineering Hydrology"; Through the above steps, compared with the prior art, a method for generating watershed parameters, rainstorm statistical parameters and runoff statistical parameters is provided, which eliminates the subjectivity of manual calculation of the above parameters and ensures the uniformity of the calculation process.

[0020] A design flood calculation system, configured with a program module for executing the above method, comprises: A watershed parameter generation module is used to establish a water system vector dataset V_Str and a watershed boundary vector dataset V_Bou and to count the watershed boundary V_Up_Bou above any small watershed target point, and to generate watershed parameters based on the watershed boundary V_Up_Bou above any small watershed target point; The rainstorm statistical parameter generation module is used to generate the global rainstorm statistical parameter grid dataset R_Storm_P, and generate the rainstorm statistical parameters based on the basin boundary V_Up_Bou above any small watershed target point; The module for generating runoff statistics parameters is used to generate the runoff parameters grid dataset R_P in different regions around the world, and generate runoff statistics parameters based on the basin boundary V_Up_Bou above any small watershed target point; The design flood calculation module calls the basin parameters, rainstorm statistical parameters and runoff statistical parameters and calculates the design flood of each frequency according to the target basin inference formula. This application has been used in engineering examples. The steps for rapid analysis and calculation of design floods in small basins at any location in the world are as follows; 1. Generation of watershed characteristic parameters Step 1: Generate the global flow direction raster dataset R_Dir, the cumulative flow raster dataset R_Acc, the water system vector dataset V_Str, and the watershed boundary vector dataset V_Bou: Prepare the global DEM dataset, use remote sensing images or other water system data extracted to correct the original DEM data, ensure the hydrological logic correctness of the DEM data, and obtain the corrected DEM dataset Adj_DEM; After the corrected DEM dataset Adj_DEM is filled with depressions, the flow direction and cumulative flow tools of GIS software are used to generate the global flow direction raster dataset R_Dir and the cumulative flow raster dataset R_Acc. Based on the flow direction raster dataset R_Dir and the cumulative flow raster dataset R_Acc, the global water system V_Str and basin boundary V_Bou data are generated through GIS software. When generating basin boundaries, the minimum sub-basin area threshold (such as 0.5km²) is set to obtain the sub-basin boundary vector dataset V_Bou and water system vector dataset V_Riv above the area threshold; Step 2: Preprocess the water system vector dataset V_Str and the basin boundary vector dataset V_Bou: Add a unique ID value Reach_ID to each vector river section of the generated water system vector dataset V_Str, and record the ID values ​​of all upstream river sections in the attributes of each vector river section; In the generated sub-basin boundary V_Bou, assign the river section ID value to the sub-basin; Figure 1 , 2 As shown; Step 3: Get the coordinates of any small watershed outlet, quickly locate the sub-watershed through spatial query according to the target point coordinates, and query upstream along the river section where the sub-watershed is located, find all upstream river sections according to the IDs of all upstream river sections, locate all upstream sub-watersheds at the same time, and merge them to generate the upstream watershed boundary V_Up_Bou1; Figure 3 , 4 and 5; Step 4: According to the sub-basin boundary V_Target_SubBou where the target point is located, use the spatial analysis tool to clip the flow direction grid dataset R_Dir to obtain the flow direction grid data R_Target_Dir within the sub-basin boundary V_Target_SubBou where the target point is located; Figure 6 , 7 As shown; Step 5: According to the flow direction grid data R_Target_Dir and the target point coordinates in the sub-basin boundary V_Target_SubBou, track all upstream areas of the sub-basin V_Target_SubBou that flow to the target point, thereby determining the sub-basin grids above the target point within the sub-basin V_Target_SubBou and generating the vector boundary V_Target_Bou; Figure 8 As shown; Step 6: Merge the vector boundary V_Target_Bou in step 5 with the upstream watershed boundary generated in step 3 to generate the watershed boundary V_Up_Bou above the target point of any small watershed, and calculate the watershed area F; Fig. 9 , 10 As shown; Step 7: Based on the global flow direction grid dataset R_Dir generated in step 1, use the water flow length tool of GIS software to generate the global maximum river length grid dataset R_Len. The data set R_Len contains the maximum upstream river length value at any grid in the world; Fig.11 As shown; Step 8: Using the corrected DEM dataset Adj_DEM, flow direction grid dataset R_Dir and cumulative flow grid dataset R_Acc in step 1 as input data, use the distance tool of GIS software to generate the global height difference grid dataset R_Diff. The dataset R_Diff contains the height difference between the upstream maximum river length source and the current grid at any grid in the world; Fig.12 As shown; Step 9: Use the raster calculator tool to calculate the gradient raster dataset R_J of the maximum river length above any target point in the world, R_J=R_Diff / R_Len; 2. Generation of heavy rain statistical parameters Step 10: Prepare and rasterize the heavy rain statistical parameter contour maps such as the mean value and Cv value of heavy rain in different time periods such as 10min, 30min, 1h, 3h, 6h, and 12h in various regions around the world (such as Guizhou Province) to generate the global heavy rain statistical parameter grid dataset R_Storm_P; the dataset R_Storm_P contains the heavy rain statistical parameter values ​​at any grid position around the world; Step 11: Using the boundary V_Up_Bou above any small watershed target point as a mask, use the spatial analysis tool to cut the heavy rain statistical parameter grid dataset R_Storm_P obtained in step 10 to obtain the heavy rain statistical parameter grid dataset R_Up_Bou_Storm_P in any small watershed, and then average the heavy rain statistical parameter value in any small watershed; 3. Generation of statistical parameters of runoff generation and convergence Step 12: Prepare and rasterize the contour maps of runoff parameters in various regions around the world (such as Guizhou Province) to generate raster datasets of runoff parameters in different regions around the world R_P; Step 13: Using the boundary V_Up_Bou above any small watershed target point as a mask, use the spatial analysis tool to cut the runoff parameter grid dataset R_P in step 12 to obtain the runoff parameter grid dataset R_Up_Bou_P in any small watershed, and then average it to obtain the average runoff parameter value of any small watershed; 4. Design flood analysis and calculation Step 14: Based on the average rainstorm statistical parameter value of any small watershed obtained in step 11, the design rainstorm value of different frequencies of any small watershed is calculated by using the frequency analysis method; Step 15: Based on the average runoff parameter value of any small watershed obtained in step 13, combined with the design rainstorm values ​​of different frequencies, the runoff parameter values ​​of any small watershed with different frequencies are calculated; Step 16: Based on the basin characteristic parameter values, design rainstorm values ​​and runoff parameter values ​​obtained in 1, 2 and 3, combined with the target basin inference formula, calculate the design flood and process of each frequency for any small basin in the world.

[0021] Obviously, the above is only a part of the embodiments of the present invention, not all of the embodiments. The above embodiments are not intended to limit the present invention. For those skilled in the art, the present invention may have various changes and variations. Any combination, modification, equivalent replacement, improvement and all other embodiments that can be made by those of ordinary skill in the art within the spirit and principle of the present invention should be within the protection scope of the present invention.

Claims

1. A method for rapid calculation of design flood of small watersheds at any location in the world, characterized by: The following steps are involved: S1. Establish water system vector dataset V_Str and basin boundary vector dataset V_Bou based on global DEM dataset; S2, record the coordinates of any small watershed outlet as the target point, and use the target point as the starting point to count the watershed boundaries above the target point through the water system vector dataset V_Str and the watershed boundary vector dataset V_Bou; S3. Based on the basin boundary above the target point, generate basin characteristic parameters, rainstorm statistical parameters and runoff statistical parameters; S4. Based on the basin characteristic parameters, rainstorm statistical parameters and runoff statistical parameters, combined with the target basin inference formula, calculate the design flood of each frequency in the small basin.

2. The method for rapid calculation of design flood of small watershed at any position in the world according to claim 1 is characterized by: The step S1 comprises the following steps: S1.1 Prepare the global DEM dataset, use remote sensing images or other water system data extracted to correct the original DEM data, ensure the hydrological logic correctness of the DEM data, and obtain the corrected DEM dataset Adj_DEM; S1.2 After performing depression-filling calculation on the corrected DEM dataset Adj_DEM, the flow direction and cumulative flow tools of GIS software are used to generate the global flow direction raster dataset R_Dir and the cumulative flow raster dataset R_Acc; S1.3 Based on the global flow direction raster dataset R_Dir and the cumulative flow raster dataset R_Acc, the global water system vector dataset V_Str and the basin boundary vector dataset V_Bou are generated through GIS software. When generating the basin boundary, the minimum sub-basin area threshold is set to obtain the sub-basin boundary vector dataset V_Bou and water system vector dataset V_Riv above the area threshold.

3. The method for rapid calculation of design flood of small watershed at any position in the world according to claim 2 is characterized by: The step S2 comprises the following steps: S2.1 adds a unique ID value Reach_ID to each vector river section of the generated water system vector dataset V_Str, and records the ID values ​​of all upstream river sections in the attributes of each vector river section; S2.2 In the generated sub-basin boundary V_Bou, assign the ID value of the corresponding river section to the sub-basin; S2.3 obtains the coordinates of any small watershed outlet, and quickly locates the sub-watershed through spatial query according to the coordinates of the target point, and queries upstream along the river section where the sub-watershed is located, finds all upstream river sections according to the IDs of all upstream river sections, locates all upstream sub-watersheds at the same time, and merges them to generate the upstream watershed boundary V_Up_Bou1; S2.4 Based on the sub-basin boundary V_Target_SubBou where the target point is located, the spatial analysis tool is used to clip the global flow direction grid dataset R_Dir to obtain the flow direction grid data R_Target_Dir within the sub-basin boundary V_Target_SubBou where the target point is located; S2.5 According to the flow direction grid data R_Target_Dir and the coordinates of the target point in the sub-basin boundary V_Target_SubBou, all upstream areas of the sub-basin V_Target_SubBou that flow to the target point are tracked, thereby determining the sub-basin grids above the target point within the sub-basin V_Target_SubBou and generating the vector boundary V_Target_Bou; S2.6 merges the vector boundary V_Target_Bou in S2.5 with the upstream watershed boundary V_Up_Bou1 generated in S2.3 to generate the watershed boundary V_Up_Bou above any small watershed target point.

4. The method for rapid calculation of design flood of small watershed at any position in the world according to claim 3 is characterized by: The step S3 comprises: S3.1 The steps to generate watershed characteristic parameters are as follows: S3.1.1 Based on the basin boundary V_Up_Bou above any small watershed target point, obtain the statistical basin area F; S3.1.2 Based on the global flow direction grid dataset R_Dir, the water flow length tool of GIS software is used to generate the global maximum river length grid dataset R_Len. The dataset R_Len contains the maximum upstream river length value at any grid in the world. S3.1.3 Based on the corrected DEM dataset Adj_DEM, the flow direction raster dataset R_Dir and the accumulated flow raster dataset R_Acc as input data, use the distance tool of the GIS software to generate the global height difference raster dataset R_Diff. The dataset R_Diff contains the height difference between the source of the maximum upstream river length at any grid in the world and this grid; S3.1.4 Based on the global height difference raster dataset R_Diff and the global maximum river length raster dataset R_Len, obtain the gradient raster dataset R_J of the maximum river length above any target point in the world, R_J=R_Diff / R_Len; S3.2 The steps to generate heavy rain statistical parameters are as follows: S3.2.1 Prepare and rasterize the contour maps of rainstorm statistical parameters such as the mean value of rainstorm and Cv value in different periods in different regions around the world, and generate the global rainstorm statistical parameter raster dataset R_Storm_P; the dataset R_Storm_P contains the rainstorm statistical parameter values ​​at any grid position around the world; S3.2.2 Using the basin boundary V_Up_Bou above any small watershed target point as a mask, use the spatial analysis tool to cut the rainstorm statistical parameter grid dataset R_Storm_P to obtain the rainstorm statistical parameter grid dataset R_Up_Bou_Storm_P in any small watershed, and obtain the average rainstorm statistical parameter value of any small watershed after averaging; S3.3 The steps to generate runoff statistics are as follows: S3.3.1 Prepare and rasterize contour maps of runoff parameters for different regions around the world to generate raster datasets of runoff parameters for different regions around the world R_P; S3.3.2 Take the basin boundary V_Up_Bou above any small watershed target point as a mask, and use the spatial analysis tool to cut the runoff parameter raster dataset R_P in S3.3.1 to obtain the runoff parameter raster dataset R_Up_Bou_P in any small watershed, and then average it to obtain the average runoff parameter value of any small watershed.

5. The method for rapid calculation of design flood of small watershed at any position in the world according to claim 4 is characterized by: The step S4 comprises: S4.1 Based on the average rainstorm statistical parameter value of any small watershed, the design rainstorm value of different frequencies in any small watershed is calculated by frequency analysis method; S4.2 Based on the average runoff parameter value of any small watershed, combined with the design rainstorm values ​​of different frequencies, the runoff parameter values ​​of any small watershed with different frequencies are calculated; S4.3 Based on the basin characteristic parameter values, design rainstorm values ​​and runoff parameter values, combined with the target basin inference formula, calculate the design flood and process of each frequency in any small basin in the world.

6. A design flood calculation system, characterized in that: A program module configured to execute the method according to any one of claims 1 to 5, comprising: A watershed parameter generation module is used to establish a water system vector dataset V_Str and a watershed boundary vector dataset V_Bou and to count the watershed boundary V_Up_Bou above any small watershed target point, and to generate watershed parameters based on the watershed boundary V_Up_Bou above any small watershed target point; The rainstorm statistical parameter generation module is used to generate the global rainstorm statistical parameter grid dataset R_Storm_P, and generate the rainstorm statistical parameters based on the basin boundary V_Up_Bou above any small watershed target point; The module for generating runoff statistics parameters is used to generate the runoff parameters grid dataset R_P in different regions around the world, and generate runoff statistics parameters based on the basin boundary V_Up_Bou above any small watershed target point; The design flood calculation module calls the basin parameters, rainstorm statistical parameters and runoff statistical parameters and calculates the design floods of each frequency according to the target basin inference formula.

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