DEM-based determination method for flood calculation parameters designed by Huai Shanghai method

Abstract

The invention discloses a DEM-based determination method for design flood calculation parameters of a Huai Shanghai method, and the method comprises the steps: obtaining a target drainage basin and peripheral DEM data, calculating the water flow direction of each grid through a D8 algorithm, and generating a flow direction grid; determining a main stream position according to the flow direction grid; matching a net rain time period according to the drainage basin area A, and calculating net rain intensity i when net rain in the time period is 20mm; identifying the underlying surface type in combination with a satellite image, and matching the roughness values to form a roughness grid; estimating the flow velocity of each grid through a dynamic wave method; determining an isochrone; constructing an L-B curve and a tau-B curve; and determining core parameters of the Huai Shangshi method. The method has the advantages that the isochrone is determined based on the DEM, the isochrone calculation method is improved, the isochrone determination precision is improved, the L-B curve is reasonably determined, then standard, automatic and high-precision acquisition of seven core parameters of the Huai Shangzhou method is achieved, and the parameter determination efficiency and quality are improved.

Description

Technical Field

[0001] This invention relates to the field of flood calculation technology in water conservancy engineering design, and is particularly applicable to the method for determining flood calculation parameters based on the Huaihe River method using DEM. Background Technology

[0002] The Huaihe River method, a classic design flood calculation method, is based on analyzing unit hydrograph parameters using isochrones. This is combined with regional comprehensive parameters to calculate the unit hydrograph peak duration and peak discharge, thereby determining the unit hydrograph. Finally, it is combined with net rainfall data to deduce the flood hydrograph at the watershed outlet. In this method, isochrones are used to determine the effective location of the peak flow surface; the accurate determination of the isochrones directly determines the accuracy of the unit hydrograph calculation. Therefore, isochrones are not only a direct representation of the watershed's runoff time field but also a key spatial parameter for transforming the spatiotemporally distributed net rainfall into a time-series discharge process.

[0003] However, the traditional method for determining isochrones in the Huaihe River basin has significant drawbacks, limiting its accuracy and automated application. First, traditional methods typically assume uniform flow velocity at all points within the basin, neglecting the spatial heterogeneity of flow velocity caused by factors such as topography, river networks, and land use. This leads to discrepancies between the isochrones reflecting the actual confluence times and the actual conditions. Second, isochrones often rely on hand-drawn sketches based on experience, resulting in a highly subjective and inefficient process, and making it difficult to accurately measure the isochrone area, leading to accumulated errors in parameter acquisition. More critically, even if the isochrones are determined, there is a lack of standardized and automated conversion algorithms for transforming them into discretized parameters suitable for computer programming (such as a matching array of the area of ​​each isochrone block and its corresponding confluence time). These problems make traditional methods unsuitable for the demands of modern hydrological simulation systems for efficient, objective, and reproducible calculations. Therefore, a technical solution based on digital topography and velocity fields, capable of automated isochrone extraction and parameter analysis, is urgently needed. Summary of the Invention

[0004] The purpose of this invention is to provide a method for determining the design flood calculation parameters based on the DEM method in the Huaihe River Basin, in order to solve the problems of complex determination of isochrones and low efficiency and accuracy of parameter calculation in the Huaihe River Basin method.

[0005] To achieve the above objectives, the method for determining design flood calculation parameters based on the DEM method in the Huaihe River Basin, as described in this invention, includes the following steps: S1, Construct flow direction grid; acquire DEM data of the target watershed and surrounding area, use the D8 algorithm to calculate the flow direction of each grid, and generate flow direction grid; S2, determine the basin area and main stream; determine the watershed watershed boundary based on the flow direction grid, delineate the basin area above the control section, and calculate the basin area A; calculate the cumulative runoff based on the flow direction grid, extract the area where the cumulative runoff is greater than the threshold, and determine the location of the main stream; S3, determine the net rainfall intensity; match the net rainfall period according to the watershed area A, and calculate the net rainfall intensity i when the net rainfall is 20mm in the period; S4, calculate roughness; combine satellite imagery to identify the underlying surface type, and match roughness values ​​to form a roughness grid; S5, Calculate the grid velocity; Based on DEM data, roughness grid, and net rainfall intensity, estimate the velocity of each grid using the dynamic wave method; S6, determine the isochrones; calculate the runoff time in each grid based on the grid velocity, then use the GIS runoff path tool to calculate the runoff time from each grid to the watershed outlet, and extract the isochrones according to the specified isochrone intervals; S7, construct the L~B curve and τ~B curve; calculate the catchment area and river length between adjacent isochrones, and then calculate the catchment width B between adjacent isochrones; analyze the average isochrone of two adjacent isochrones; measure the length L of the main stream and the confluence time τ between the intersection of the average isochrone and the main stream and the catchment outlet; calculate the catchment width B and the main stream length L in sequence, and draw the L~B curve and τ~B curve; S8, determine the core parameters of the Huaihe River flood control method; determine the effective area A of the flood peak based on the L~B curve and τ~B curve. v This allows for the determination of the main river length L within the effective area of ​​the flood peak. AV The effective area of ​​the flood peak and the width of the catchment area B AV Average slope S of the main stream within the effective area of ​​the flood peak AV The length L of the main stream from the furthest effective area of ​​the flood peak to the outflow section. x Corresponding to L x The average gradient of the river channel S Lx .

[0006] Furthermore, in step S1, the DEM data is denoised using median filtering, and the inverse distance weighted interpolation method is used to fill the data-free areas, and GIS tools are used to perform depression filling calculations.

[0007] Furthermore, in step S2, the cumulative flow threshold is set to 100-500 flow direction grids, which is adjusted according to the actual size of the watershed.

[0008] Further, in step S4, the underlying surface types include cultivated land, forest land, grassland, urban construction land, and waterways; the roughness ratio n of the cultivated land is 0.03~0.05; the roughness ratio n of the forest land is 0.05~0.08; the roughness ratio n of the grassland is 0.04~0.06; the roughness ratio n of the urban construction land is 0.02~0.03; and the roughness ratio n of the waterway is 0.025~0.035.

[0009] Further, in step S2, determining the location of the main stream specifically involves extracting the region where the cumulative confluence volume is greater than a preset cumulative confluence volume threshold, vectorizing it into the main and tributary river lines, and then extracting the location of the main stream.

[0010] Furthermore, in step S4, high-resolution satellite imagery and a supervised classification algorithm are used to identify the underlying surface type, classifying each raster and labeling the corresponding roughness value.

[0011] Further, step S6 specifically involves using the confluence path calculation tool in the GIS software, inputting the latitude and longitude coordinates of the watershed outlet section as the confluence endpoint; calculating the time for each grid to travel along the confluence path to the outlet section based on the grid velocity and the distance between grids, and summing these to obtain the total confluence time for each grid; using the "contour generation" tool in the GIS software, inputting the total confluence time for each grid, setting the contour interval, and generating isochrones; deleting invalid isochrones outside the watershed boundary, and using the "smoothing tool" in the GIS to process the inflection points of the isochrones to ensure that the isochrones continuously and completely cover the watershed above the control section, and that the spacing between adjacent isochrones is uniform, conforming to the distribution pattern of confluence time.

[0012] Furthermore, in step S7, the "grid mask" tool in the GIS software is used to extract the watershed between adjacent isochrones to obtain the watershed area between adjacent isochrones; the length of the main stream between adjacent isochrones is measured; that is, the river segment length; the watershed width = watershed area / river segment length; the average isochrone of two adjacent isochrones is analyzed, and the length of the main stream from the intersection of the average isochrone and the main stream to the watershed outlet is measured. The L~B curve is plotted with the main stream length as the abscissa and the watershed width as the ordinate.

[0013] The advantages of this invention are that it determines the isothermal timelines based on the DEM digital elevation model, improves the isothermal timeline calculation method, increases the accuracy of isothermal timeline determination, and reasonably determines the L~B curve, thereby achieving the standardization, automation, and high-precision acquisition of the seven core parameters of the Huaihe River method, and improving the efficiency and quality of parameter determination. Attached Figure Description

[0014] Figure 1 is a flowchart of the method described in this invention.

[0015] Figure 2 This is a schematic diagram illustrating the determination of the effective area location of the flood peak in the method described in this invention.

[0016] Figure 3 This is a schematic diagram illustrating the determination of the effective area of ​​the flood peak in the method described in this invention.

[0017] Figure 4 This is a schematic diagram of DEM data for a certain watershed in Embodiment 2 of the present invention.

[0018] Figure 5 This is a schematic diagram of the flow direction grid calculation results in Embodiment 2 of the present invention.

[0019] Figure 6 This is a schematic diagram of the watershed and river channel extraction results in Embodiment 2 of the present invention.

[0020] Figure 7 This is a schematic diagram of the result of drawing the flow time line in Embodiment 2 of the present invention.

[0021] Figure 8 This is a schematic diagram of the L~B relationship curve in Embodiment 2 of the present invention.

[0022] Figure 9 This is a schematic diagram of the τ~B relationship curve in Embodiment 2 of the present invention.

[0023] Figure 10 This is a schematic diagram of the effective area location of the flood peak determined in Embodiment 2 of the present invention. Detailed Implementation

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0025] Example 1 The method for determining the design flood calculation parameters based on DEM in the Huaihe River method described in this invention, such as... Figure 1 As shown, it includes the following steps: S1. Construct a flow direction raster. Acquire DEM data for the target watershed and surrounding areas, prioritizing a 30m grid resolution; if the watershed area is small, a 10m resolution can be used. Use median filtering to remove noise points (such as isolated high-value or low-value rasters) from the DEM data to avoid errors in flow direction calculation. Use inverse distance weighted interpolation to fill data-free areas and perform depression-filling calculations using GIS tools to ensure the DEM data is free of depressions and breaks, meeting the needs of subsequent hydrological analysis. In the GIS software, use the D8 algorithm tool to compare the elevation values ​​of each raster with its eight adjacent raster units (top, bottom, left, right, upper left, upper right, lower left, lower right). Determine the flow direction of the raster with the largest elevation difference, where 1 represents east, 2 southeast, 4 south, 8 southwest, 16 west, 32 northwest, 64 north, and 128 northeast, thus generating the flow direction raster.

[0026] S2: Determine the catchment area and main stream; determine the catchment outlet based on the location of water conservancy projects; calculate the cumulative runoff volume based on the flow direction grid. The cumulative runoff volume reflects the upstream catchment area of ​​each grid, measured in grid numbers. Set a threshold for the cumulative runoff volume, typically 100-500 flow direction grids, adjusted according to the actual size of the catchment area. Extract the areas where the cumulative runoff volume exceeds the threshold; these are the river channel grids, vectorized into tributary river lines, and then used to determine the location of the main stream line.

[0027] Then, the watershed boundary determined by the flow direction grid is used to delineate the complete watershed area above the control section; The number and area of ​​effective flow direction grids within the complete watershed above the control section are statistically analyzed, and the watershed area above the control section is calculated to obtain the watershed area parameter A.

[0028] S3, determine the net rainfall intensity; match the net rainfall period according to the watershed area A, and calculate the net rainfall intensity i when the net rainfall is 20mm during that period. Specifically... When 200km 2 ≤A≤300km 2 The clear rainfall period is 1-2 hours; When 300 km 2 ≤A≤1000 km 2 The net rainfall period is 2-4 hours. When 1000 km 2 ≤A≤5000 km 2 The net rainfall period is 4-8 hours. Given that the standard value of net rainfall during the period calculated by the Huaihe River method is 20 mm, the net rainfall intensity i (mm / h) is calculated according to the formula i = 20 / t (t is the net rainfall period, unit: h). For example, when the net rainfall period is t = 2h, the net rainfall intensity is i = 10 mm / h.

[0029] S4, calculate the roughness; combine satellite imagery to identify the underlying surface type, and match the roughness values ​​to form a roughness grid.

[0030] High-resolution satellite imagery (such as GF-2 and Landsat-8 imagery) and supervised classification algorithms are used to identify the underlying surface type of the watershed. Each raster is classified and its corresponding roughness value is marked to form a roughness raster.

[0031] The underlying surface types include cultivated land, forest land, grassland, urban construction land, and waterways. The roughness coefficient n of the cultivated land is 0.03~0.05; the roughness coefficient n of the forest land is 0.05~0.08; the roughness coefficient n of the grassland is 0.04~0.06; the roughness coefficient n of the urban construction land is 0.02~0.03; and the roughness coefficient n of the waterway is 0.025~0.035.

[0032] S5, Calculate the grid velocity; based on DEM data, grid roughness, and net rainfall intensity, estimate the velocity of each grid using the dynamic wave method. Alternatively, other techniques can be used to pre-calculate the grid velocity under different rainfall intensities within the watershed.

[0033] S6, determine the isochrones; calculate the runoff time in each grid cell based on the grid velocity, then use the GIS runoff path tool to calculate the runoff time from each grid cell to the watershed outlet, and extract the isochrones according to the specified isochrone intervals.

[0034] Specifically, in GIS software, a flow path calculation tool (such as ArcGIS's "Flow Path" tool) is called, and the latitude and longitude coordinates of the watershed outlet section are input as the flow endpoint; the length of each grid along the flow path to the outlet section is calculated using the grid flow velocity as the weight. This length is numerically equal to the total flow time (in hours) from each grid to the outlet section, generating a flow time grid; in GIS software, the "contour generation" tool is called, the total flow time of each grid is input, and the contour interval is set (such as 0.1h, 0.2h, 0.3h, etc.) to generate isochronous lines.

[0035] Invalid isohyet lines outside the watershed boundary are deleted from the generated isohyet lines. The "smoothing tool" in GIS is used to process the inflection points of the isohyet lines to ensure that the isohyet lines continuously and completely cover the watershed above the control section, and that the spacing between adjacent isohyet lines is uniform, which conforms to the distribution law of confluence time.

[0036] S7. Construct the L~B curve and τ~B curve. From the watershed outlet upstream, for each isohyet, use the "raster mask" tool in GIS software to extract the watershed area between adjacent isohyets, obtaining the watershed area between them. Measure the length of the main stream between adjacent isohyets, i.e., the river segment length. Calculate the watershed width B between adjacent isohyets. Watershed width B = watershed area / river segment length. Analyze the average isohyets of two adjacent lines, measure the length of the main stream from the intersection of the isohyet and the main stream to the watershed outlet, and plot the L~B curve with the main stream length as the x-axis and the watershed width as the y-axis. Plot the τ~B curve with the confluence time τ as the x-axis and the watershed width B as the y-axis.

[0037] S8, determine the core parameters of the Huaihe River method; based on the τ~B curve, determine the location of the maximum basin width B, and select two isochrones on the left and right sides of the basin width B according to the rules, denoted as τ1 and τ2, thus determining the effective area location of the flood peak. For example... Figure 2 As shown.

[0038] Based on the location of the effective flood peak area on the L~B curve, determine the length of the main stream from the intersection of isochrone τ1 and the main stream to the outlet of the basin, L1 and L2. Integrate the basin width between L1 and L2 on the L~B curve to determine the effective flood peak area A. v .like Figure 3 As shown.

[0039] The effective area of ​​the flood peak and the width of the catchment area B AV =A V / L AV The average catchment width of the effective area for responding to flood peaks. L AV =L2- L1.

[0040] Calculate A V The weighted average slope of the corresponding main stream section is the average slope S of the main stream within the effective area of ​​the flood peak. AV .

[0041] The length of the main stream from the intersection of the isohyetal line τ2 and the main stream to the outlet of the basin is the length of the main stream L2 from the furthest point of the effective area of ​​the flood peak to the outlet section. x .

[0042] Corresponding to L x The average gradient of the river channel S Lx That is, the length L of the main stream from the starting point of the main stream to the furthest point of the effective area of ​​the flood peak to the outflow section. x The average gradient of the main stream within the section.

[0043] Example 2 Based on the DEM data of a certain watershed obtained from the open platform, the parameters for the comprehensive unit line method in the Huaihe River Basin were extracted and calculated. This watershed is located in the non-mainstream and Huainan areas within Henan Province.

[0044] 1. Data Acquisition and Preprocessing DEM data of a watershed is obtained from an open platform, preprocessed using geographic information processing tools, and the final data result is as follows. Figure 4 As shown.

[0045] 2. Flow direction grid calculation Based on the preprocessed DEM data, the D8 algorithm was used to calculate the raster flow direction, where 1 represents east, 2 represents southeast, 4 represents south, 8 represents southwest, 16 represents west, 32 represents northwest, 64 represents north, and 128 represents northeast. The calculation results are as follows: Figure 5 As shown.

[0046] 3. Watershed division Based on the flow direction grid calculated in the previous step, cumulative flow grid calculation and catchment area delineation are performed to obtain the catchment area above a certain control section, the main stream, and the catchment area A. In this calculation, the catchment area A is 602 km². 2 .like Figure 6 The image shown is a schematic diagram of the river channel extraction results for this watershed.

[0047] 4. Calculation of grid flow velocity and convergence time Based on the grid flow direction and velocity, the grid runoff duration is calculated, and isothermal lines at 1-hour intervals are extracted. The isothermal line plotting results are as follows: Figure 7 As shown.

[0048] 5. Calculation of parameters for the Huaihe River method Based on the isohyets calculated in the previous step and the watershed characteristic parameter analysis, the average width of the watershed between two adjacent confluence timelines was calculated, as shown in Table 1. L~B and τ~B curves were then plotted according to the table relationships. Figure 8 and Figure 9 As shown. According to the calculation rules of the Huaihe River Basin method, this area is located in other areas outside the Huaihe River main stream and Huainan. The ratio of the runoff duration covered by the effective area AV of the flood peak to the runoff duration of the area furthest from the effective area of ​​the flood peak should be 1 / 2. According to the τ~B relationship curve, the runoff duration of the effective area of ​​the flood peak should be in the range of 2.5~5.0h, combined with the isochrones. Figure 4 The effective area and location of the flood peak, i.e., A, are obtained. V 252km 2 ,See Figure 10 The diagram shows the location of the effective area of ​​the flood peak. Calculate the length L of the main river within the effective area of ​​the flood peak. AVThe effective area of ​​the flood peak is 13.7 km, and the width of the drainage basin B is... AV The length is 18.4 km, and the average slope S of the main stream within the effective area of ​​the flood peak is... AV The effective area of ​​the flood peak is 1 / 58, and the length of the main stream from the furthest point of the effective flood peak to the outflow section, Lx, is 35.7 km, corresponding to an average channel gradient S of Lx. Lx The value is 1 / 123. At this point, all the parameters required for the comprehensive unit line method in the Huaihe River Basin of Henan Province have been calculated.

[0049] Table 1. Relationship between L~B and τ~B .

Claims

1. A method for determining design flood calculation parameters based on DEM in the Huaihe River method, characterized in that, Includes the following steps: S1, Construct flow direction grid; acquire DEM data of the target watershed and surrounding area, use the D8 algorithm to calculate the flow direction of each grid, and generate flow direction grid; S2, determine the basin area and main stream; determine the watershed watershed boundary based on the flow direction grid, delineate the basin area above the control section, and calculate the basin area A; calculate the cumulative runoff based on the flow direction grid, extract the area where the cumulative runoff is greater than the threshold, and determine the location of the main stream; S3, determine the net rainfall intensity; match the net rainfall period with the watershed area A, and calculate the net rainfall intensity when the net rainfall is 20mm during that period. i ; S4, calculate roughness; combine satellite imagery to identify the underlying surface type, and match roughness values ​​to form a roughness grid; S5, Calculate the grid velocity; Based on DEM data, roughness grid, and net rainfall intensity, estimate the velocity of each grid using the dynamic wave method; S6, determine the isochrones; calculate the runoff time in each grid based on the grid velocity, then use the GIS runoff path tool to calculate the runoff time from each grid to the watershed outlet, and extract the isochrones according to the specified isochrone intervals; S7. Construct the L~B curve and τ~B curve; calculate the catchment area and river length between adjacent isochrones, and then calculate the catchment width between adjacent isochrones. B Analyze the average isochrones of two adjacent isochrones, and measure the length of the main stream from the intersection of the average isochrone and the main stream to the watershed outlet. L And the confluence time τ; calculate the basin width in sequence. B and the length of the main stream L ,draw L~B curves and τ~B curve; S8, determine the core parameters of the Huaihe River flood control method; determine the effective area A of the flood peak based on the L~B curve and τ~B curve. v This allows for the determination of the main river length L within the effective area of ​​the flood peak. AV The effective area of ​​the flood peak and the width of the catchment area B AV Average slope S of the main stream within the effective area of ​​the flood peak AV The length L of the main stream from the furthest effective area of ​​the flood peak to the outflow section. x Corresponding to L x The average gradient of the river channel S Lx .

2. The method for determining the design flood calculation parameters based on DEM in the Huaihe River Basin method according to claim 1, characterized in that: In step S1, the DEM data is denoised using median filtering, and the inverse distance weighted interpolation method is used to fill the data-free areas. GIS tools are also used to perform depression filling calculations.

3. The method for determining the design flood calculation parameters based on DEM in the Huaihe River Basin method according to claim 1, characterized in that: In step S2, the cumulative flow threshold is set to 100-500 flow direction grids, which is adjusted according to the actual size of the watershed.

4. The method for determining the calculation parameters of the Huaihe River flood based on DEM according to claim 1, characterized in that: In step S4, the underlying surface types include cultivated land, forest land, grassland, urban construction land, and waterways; the roughness ratio n of cultivated land is 0.03~0.05; the roughness ratio n of forest land is 0.05~0.08; the roughness ratio n of grassland is 0.04~0.06; the roughness ratio n of urban construction land is 0.02~0.03; and the roughness ratio n of waterways is 0.025~0.

035.

5. The method for determining the design flood calculation parameters based on DEM in the Huaihe River Basin according to claim 1, characterized in that: In step S2, determining the location of the main stream involves extracting regions where the cumulative confluence volume exceeds a preset threshold, vectorizing these regions into tributary river lines, and then extracting the location of the main stream.

6. The method for determining the design flood calculation parameters based on DEM in the Huaihe River Basin method according to claim 1, characterized in that: In step S4, high-resolution satellite imagery and a supervised classification algorithm are used to identify the underlying surface type. Each raster is classified and its corresponding roughness value is labeled.

7. The method for determining the design flood calculation parameters based on DEM in the Huaihe River Basin according to claim 1, characterized in that: Step S6 involves using the confluence path calculation tool in the GIS software, inputting the latitude and longitude coordinates of the watershed outlet section as the confluence endpoint; calculating the time for each grid cell to travel along the confluence path to the outlet section based on the grid velocity and the distance between grid cells, and summing these to obtain the total confluence time for each grid cell; using the "contour generation" tool in the GIS software, inputting the total confluence time for each grid cell, setting the contour interval, and generating isochrones; deleting invalid isochrones outside the watershed boundary, and using the "smoothing tool" in the GIS software to process the inflection points of the isochrones to ensure that the isochrones continuously and completely cover the watershed above the control section, and that the spacing between adjacent isochrones is uniform, conforming to the distribution pattern of confluence time.

8. The method for determining the design flood calculation parameters based on DEM in the Huaihe River Basin method according to claim 1, characterized in that: In step S7, the "raster mask" tool in the GIS software is used to extract the watershed between adjacent isochrones to obtain the watershed area between adjacent isochrones; the length of the main stream between adjacent isochrones is measured; that is, the river segment length; the watershed width = watershed area / river segment length; the average isochrone of two adjacent isochrones is analyzed, and the length of the main stream from the intersection of the average isochrone and the main stream to the watershed outlet is measured. The L~B curve is plotted with the main stream length as the abscissa and the watershed width as the ordinate.

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