A method for processing watershed depressions based on digital elevation model (DEM)

Abstract

A method for processing watershed depressions based on a digital elevation model (DEM) involves logging into a geospatial data cloud network platform to obtain the target watershed's digital elevation data (DEM) as the raw data for watershed simulation. The digital elevation data is then imported into a BTOPMC grid-distributed hydrological model system, and the original DEM data is filled and processed to generate a digital elevation data file. Based on the filled-in elevation data file, the flow direction on each grid in the target watershed is obtained to generate a watershed grid flow direction data file, and the presence of convection grids is checked and captured. Based on the filled-in elevation and watershed grid flow direction data files, the captured convection grids are used as dredging sources, dredged using a formula, and generated a dredged elevation data file. Based on the catchment area data, an appropriate threshold is determined to extract watershed water system features. The watershed boundaries are mapped using ArcGIS software, and dredged river channels are marked to form a river network. This method improves the accuracy of watershed water system feature extraction and belongs to the field of geoscience.

Description

Technical Field

[0001] The invention relates to a water system extraction method of a digital elevation model (DEM), belongs to the field of geology, and particularly relates to a method for processing watershed depressions based on a digital elevation model (DEM). Background Art

[0002] River networks in watersheds are a crucial component of hydrological simulations and resource management plans. Extracting watershed characteristics, a foundational step in visualizing hydrological and other Earth surface motion simulations, typically involves extracting topographic information from a watershed digital elevation model (DEM). This process then determines flow paths and forms river networks. This is the first step in visualizing flow paths and clarifying the topological relationships within a watershed and within river networks. DEM data, particularly raster DEMs, are widely used in the hydrological field due to their ease of acquisition and simple, efficient computational processing.

[0003] In the process of generating digital river networks, due to differences in data collection systems, methods, resolution, and human intervention, river network extraction results often cannot fully reproduce the natural watershed distribution and flow paths. This includes depressions or small plains that exist naturally or are formed during data collection, leading to convection, circulation, and cross-flow. In actual watersheds, such conditions often manifest as reciprocating flow near the watershed outlet. The same grid area may experience different tidal patterns, such as high and low tides, and resting tides, at different time periods. Watershed hydrological simulations generally require that river grids have a single direction to form a complete water system network.

[0004] Researchers have found that directly using existing DEM data for depression-plain areas can easily lead to discontinuous river networks. Locally encrypting and modifying DEM data can effectively enhance the ability to extract watershed information. A common approach is to raise the grid elevation above the watershed elevation to create a slope, forcing water in the depression to flow in a specific direction, generating runoff. However, using only depression-filling techniques to process DEM data can result in overfilling, creating new depressions, alternating tides, and elevated river banks, creating artificial "surface rivers." Summary of the Invention

[0005] In response to the technical problems existing in the prior art, the purpose of the present invention is to provide a method for processing watershed depressions based on the digital elevation model (DEM), analyze and dredge the study area after filling, and extract the watershed characteristics, and improve the extraction accuracy and efficiency by comparing with the measured watershed map.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for processing watershed depressions based on a digital elevation model (DEM) includes the following steps:

[0008] (1) Log in to the geospatial data cloud network platform to obtain the target watershed digital elevation data DEM, and rename the obtained ASCII format digital elevation data to basin.dem as the original data for watershed simulation;

[0009] (2) Import the obtained digital elevation data basin.dem into the BTOPMC grid distributed hydrological model system, use the model system to fill the original DEM data, and generate the digital elevation data file basin.fil after filling;

[0010] (3) Based on the fill elevation data file basin.fil, obtain the water flow direction of each grid in the target basin, generate the basin grid flow direction data file baisn.fd, and check and capture the convection grid;

[0011] (4) Based on the fill elevation data file basin.fil and the basin grid flow direction data file basin.fd, the captured convection grid is used as the dredging source, and the dredging process is performed using the formula to generate the dredging elevation data file basin.drg;

[0012] (5) Based on the catchment area data basin.facc, the appropriate threshold is determined to extract the basin water system characteristics, and the basin range is drawn and the dredged river channels are marked using ArcGIS software to form a river network system.

[0013] As a preferred embodiment, the relevant raster data files generated in step (2) include a grid one-dimensional number file basin.gn, a grid side length and area file, and a depression-filling related data file; wherein the grid side length and area file includes the unit grid latitudinal length basin.dx, the unit grid longitudinal length basin.dy, and the unit grid area basin.1ga; the depression-filling related data file includes the depression-filling height data basin.dhv and the elevation data after depression-filling basin.fil.

[0014] As a preferred method, in step (3), based on the fill elevation data file, the D8 unidirectional flow method is used to mark the grid water flow direction, such as Figure 2 As shown, the target watershed flow direction data file basin.fd is obtained.

[0015] As a preferred embodiment, in step (4), based on the filling elevation data file, the watershed flow direction data file and the captured convection grid, after the filling process is completed, the traversed water flow path grids are checked, and if the elevation of the inflow grid A is the smallest or the elevation of the grid B with the largest slope is the same as that of the inflow grid A, dredging is performed on the inflow grid A, and the elevation of the contour river channel is reduced using a formula.

[0016] As a preferred method, the depressions in the study basin are processed, the extraction of basin water system characteristics is optimized, and the extracted basin water system is compared with the field measured basin map.

[0017] As a preferred embodiment, in step (5), basin water system characteristics are extracted based on the catchment area data basin.facc, and the data management tool in ArcGIS software is used to draw the basin range and mark the dredged river channel in ASCII format to form a river network system that is more in line with reality.

[0018] As a preferred method, the terrain module of the BTOPMC grid distributed hydrological model system adopts the most widely used method proposed by Jenson and Domingue to determine the flow direction in flat areas, that is, first find the cells adjacent to the cells with flow direction, then determine the flow direction of the adjacent cell grids, and repeat until all flat area cells are traversed to generate the basin flow direction file basin.fd.

[0019] As a preferred method, in order to improve the accuracy of watershed water system feature extraction and ensure the effectiveness of hydrological simulation, the dredging depth is calculated using the formula:

[0020]

[0021] drg_dem(i,j)=fil_dem(i,j)-drg(i,j)

[0022] Among them, h0 is a constant that is not greater than the elevation resolution, i, j are the two-dimensional grid numbers, drg(i,j) is the dredging depth, fil_dem(i,j) is the grid elevation before dredging after filling, drg_dem(i,j) is the grid elevation after dredging, s i , s j is the grid side length, which is the actual calculated geodetic length of the longitude and latitude grid side. In particular, when a DEM based on a coordinate system with length as the unit and a grid aspect ratio of 1 is used, such as Hydro1kDEM,

[0023] If the water flow direction is oblique flow, that is, fd=1,3,5,7, then If the water flow direction is east-west or north-south, that is, fd = 2, 4, 6, 8, then

[0024] In general, the present invention has the following advantages:

[0025] In the above scheme, the digital elevation model of the study area is obtained and preliminarily filled, the nodes of reciprocating flow are marked, and potential river channels are found. On this basis, the bionic dredging method is used to lower the elevation of the contour river channels downstream of the water nodes, so that the surrounding water flows naturally into the river channel, avoiding excessive filling, ground rivers and other phenomena, thereby further improving the accuracy of watershed water system feature extraction. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A flow chart of a large-scale distributed hydrological simulation method provided in an embodiment of the present invention.

[0027] Figure 2 Schematic diagram of water flow direction.

[0028] Figure 3-Figure 8 The process and results of local dredging in the Mekong River Basin, including: Figure 3 is the initial local elevation (mekong.dem), Figure 4 It is the local elevation after filling. Figure 5 is the initial elevation water flow direction and mark (mekong.fd), Figure 6 For dredging elevation water flow direction and marking (mekong.fd), Figure 7 Marks the elevation and water flow direction after dredging (mekong.drg). Figure 8 To obtain a local river network.

[0029] Figure 9 The dredging process and results for the entire Mekong River basin. DETAILED DESCRIPTION

[0030] The present invention will be further described in detail below with reference to specific implementation methods.

[0031] The digital river network extraction method of the terrain module based on the BTOPMC model system of the present invention includes:

[0032] (1) Log in to the geospatial data cloud network platform to obtain the target watershed digital elevation data (DEM), mosaic the obtained data, and add administrative regions as reference;

[0033] (2) Using the BTOPMC grid distributed hydrological model system to perform preliminary coordinate system processing and depression filling processing on the original DEM data to generate relevant raster data files;

[0034] (3) Based on the fill elevation data file, the water flow direction on each grid of the target watershed is obtained, and the water flow direction data file (baisn.fd) is generated to capture the water nodes where reciprocating flow occurs;

[0035] (4) Based on the basin filling data file, the water flow direction file and the captured water nodes, dredging is performed to generate a dredging data file (basin.drg);

[0036] (5) Based on the river network data, the characteristics of the watershed are extracted, the watershed range is drawn, the dredged river channels are marked, and the river network is formed.

[0037] In this embodiment, the Mekong River Basin is taken as an example, and the details are as follows:

[0038] (1) Log in to the geospatial data cloud network platform to obtain the Hydro1k DEM, mosaic the obtained data, and add administrative regions as reference.

[0039] In this example, using the Mekong River Basin as an example, select the coordinate system parameters according to the prompts. Select the Lambert Azimuthal Equal-Area projection corresponding to the Hydro1k DEM, with the projection center set to the Asian projection center (N45°, E100°), and the Clarke 1866 AUTHALIC SPHERE datum. Convert the data obtained above into an ASCII file, rename it to mekong.dem, and import it into the BTOPMC grid distributed hydrological model system.

[0040] (2) The BTOPMC grid distributed hydrological model system is used to perform preliminary coordinate system processing on the original DEM data mekong.dem. The specific operation is to enter the command line according to the prompts in the path CBTOPMC / BSHELL / y_1_preprocess.sh environment to perform depression filling processing and generate relevant raster data files.

[0041] The required parameters include the original data storage path, the name of the study basin, the total flow direction of the basin (including four options: 1: upper left to lower right, 2: upper right to lower left, 3: lower right to upper left, 4: lower left to upper right), flow direction selection priority (1: maximum slope, 2: minimum elevation), and river width model (the system provides 1: Zhong Xiangning river width model, 2: Altunin river width model, 3: Lu1 river width model, and 4: Lu2 river width model).

[0042] In this example, based on the actual situation of the study basin, the general flow direction of the Mekong River basin is from upper left to lower right, so the parameter is selected as 1; the flow direction prioritizes the minimum elevation grid, so the parameter is selected as 2; the river width model is the Zhongxiangning River width model, so the parameter is selected as 4. The command line is as follows:

[0043] . / y_1_preprocess.sh~ / mekong / LA1k mekong 1 2 4

[0044] In this embodiment, the terrain module of the BTOPMC model system traverses the watershed grid and performs depression filling according to the imported watershed digital elevation model data (mekong.dem) and the setting of the coordinate system parameters, and generates a depression filling depth file (mekong.dhv) and a post-filling elevation file (mekong.fil).

[0045] (3) Based on the fill elevation data file mekong.fil, obtain the water flow direction on each grid of the target watershed, generate the watershed grid flow direction data file mekong.fd, and check and capture the convection grid.

[0046] In this embodiment, the terrain module of the BTOPMC model system determines the flow direction in the flat area. The most widely used method is the one proposed by Jenson and Domingue. The expression method is as follows: Figure 2 First, find the cells adjacent to the cells with flow direction, determine the flow direction of these cells, repeat this process to go through all the flat area cells, and finally check whether there is a convection flow direction.

[0047] (4) Based on the fill elevation data file mekong.fil and the watershed grid flow direction data file mekong.fd, the captured convection grid is used as the dredging source, and the dredging process is performed using the formula to generate the dredging elevation data file mekong.drg.

[0048] In this embodiment, river dredging is divided into four stages:

[0049] 1) Identify incorrect runoff paths;

[0050] 2) Grid marking and flow direction verification and confirmation;

[0051] 3) Grid dredging, judging whether downstream grids need to continue dredging until the river outlet;

[0052] 4) Check whether the old flow path needs to be further dredged due to the connection with other grid flow paths.

[0053] In this embodiment, the dredging depth is calculated using the formula:

[0054]

[0055] drg_dem(i,j)=fil_dem(i,j)-drg(i,j)

[0056] Among them, h0 is 0.01m, i, j are the two-dimensional grid numbers, drg(i,j) is the dredging depth, fil_dem(i,j) is the grid elevation before dredging after filling, drg_dem(i,j) is the grid elevation after dredging, si , s j is the mesh side length.

[0057] In this embodiment, the Hydro1k DEM with length as the unit and a grid length and width of 1 km is used.

[0058] When the water flow direction is oblique flow, that is, fd=1, 3, 5, 7, then

[0059] When the water flow direction is east-west or north-south, that is, fd = 2, 4, 6, 8, then

[0060] Due to limited space, this example only uses a 7km×7km area in the Mekong River Basin as an example of the calculation process. Figure 7 shown.

[0061] (5) Based on the backflow area data (mekong.facc), the watershed water system characteristics are extracted. The specific operation is to use Excel software to filter all cells in mekong.facc that exceed the threshold, regenerate the ASCII format file, and use the conversion tools in ArcGIS software - from ASCII to raster - from raster to line to draw the watershed in the form of vector lines to form a river network. The dredged river part is emphasized with gray shadow, as shown in the following example. Figure 8 shown.

[0062] In this embodiment, it is assumed that each grid has 1 unit of water volume. According to the natural law that water flows from high to low, the water volume value flowing through each grid is calculated according to the distribution of topographic water flow direction, and the distribution of the watershed area of ​​the target basin can be obtained. After obtaining the watershed area distribution, the numbers are extracted based on the reasonable source watershed area threshold. Since the data obtained in this embodiment is a part of the basin, the grid number threshold is set to 1. If the Mekong River network needs to be fully displayed, a larger threshold needs to be set. The specific operation is to use Excel software to filter out grids with more than 1000 in mekong.facc, and repeat the above step (5) to use ArcGIS to export the vector digital river network. The result is as follows: Figure 9 As shown, for ease of viewing, the basin boundary line (gray dotted line) is embedded, and the dredged river channel part is emphasized with gray shading.

[0063] In this embodiment, the terrain module of the BTOPMC model system is programmed in C language under the Linux system. The parameters involved are introduced in detail in the system, and there are cases for reference.

[0064] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for processing watershed depressions based on a digital elevation model (DEM), characterized in that: The following steps are involved: (1) Log in to the geospatial data cloud network platform to obtain the target watershed digital elevation data DEM, and rename the obtained ASCII format digital elevation data to basin.dem as the original data for watershed simulation; (2) Import the obtained digital elevation data basin.dem into the BTOPMC grid distributed hydrological model system, use the model system to fill the original DEM data, and generate the digital elevation data file basin.fil after filling; (3) Based on the fill elevation data file basin.fil, obtain the water flow direction of each grid in the target watershed, generate the watershed grid flow direction data file baisn.fd, and check and capture the convection grid; (4) Based on the fill elevation data file basin.fil and the basin grid flow direction data file basin.fd, the captured convection grid is used as the dredging source, and the dredging process is performed using the formula to generate the dredging elevation data file basin.drg; in order to improve the accuracy of the basin water system feature extraction and ensure the effectiveness of the hydrological simulation, the dredging depth is calculated using the formula. drg_dem(i,j)=fil_dem(i,j)-drg(i,j) Among them, h0 is a constant that is not greater than the elevation resolution, i, j are the two-dimensional grid numbers, drg(i,j) is the dredging depth, fil_dem(i,j) is the grid elevation before dredging after filling, drg_dem(i,j) is the grid elevation after dredging, s i , s j is the grid side length, which is the actual calculated geodesic length of the longitude and latitude grid side; (5) Based on the catchment area data basin.facc, the appropriate threshold is determined to extract the characteristics of the watershed system. The watershed range is drawn and the dredged river channels are marked using ArcGIS software to form a river network system.

2. The method for processing watershed depressions based on a digital elevation model (DEM) according to claim 1, characterized in that: The relevant raster data files generated in step (2) include the grid one-dimensional number file basin.gn, the grid side length and area file, and the basin filling related data file; The grid side length and area files include the unit grid latitudinal length basin.dx, the unit grid longitudinal length basin.dy, and the unit grid area basin.1ga; the filling-related data files include the filling height data basin.dhv and the elevation data after filling basin.fil.

3. The method for processing watershed depressions based on a digital elevation model (DEM) according to claim 1, characterized in that: In step (3), based on the fill elevation data file, the D8 unidirectional flow method is used to mark the grid water flow direction and obtain the target basin flow direction data file basin.fd.

4. The method for processing watershed depressions based on a digital elevation model (DEM) according to claim 1, characterized in that: In step (4), based on the filling elevation data file, the watershed flow direction data file and the captured convection grid, after the filling process is completed, the traversed water flow path grids are checked. If the elevation of the inflow grid A is the smallest or the elevation of the grid B with the largest slope is the same as it, dredging is performed on the inflow grid A, and the elevation of the contour river channel is reduced using the formula.

5. The method for processing watershed depressions based on a digital elevation model (DEM) according to claim 1, characterized in that: The depressions in the study basin were processed, the extraction of basin water system characteristics was optimized, and the extracted basin water system was compared with the field measured basin map.

6. The method for processing watershed depressions based on a digital elevation model (DEM) according to claim 1, characterized in that: In step (5), basin water system characteristics are extracted based on the catchment area data basin.facc, and the data management tool in ArcGIS software is used to draw the basin range and mark the dredged river channel in ASCII format to form a river network system that is more in line with reality.

7. The method for processing watershed depressions based on a digital elevation model (DEM) according to claim 2, characterized in that: The terrain module of the BTOPMC grid distributed hydrological model system adopts the most widely used method to determine the flow direction in flat areas, which is proposed by Jenson and Domingue. That is, first find the cells adjacent to the cells with flow direction, then determine the flow direction of the adjacent cell grids, and repeat until all flat area cells are traversed to generate the basin flow direction file basin.fd.

8. The method for processing watershed depressions based on a digital elevation model (DEM) according to claim 4, characterized in that: When using the Hydro1k DEM, a DEM based on a coordinate system with length as the unit and a grid aspect ratio of 1, If the water flow direction is oblique flow, that is, fd = 1, 3, 5, 7, then If the water flow direction is east-west or north-south, that is, fd = 2, 4, 6, 8, then

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