A method, system, terminal and medium for dividing hydrological units based on DEM

Abstract

The present invention discloses a method, system, terminal and medium for dividing hydrological units based on DEM. The method comprises: obtaining DEM data of a region to be identified and performing data preprocessing; filling and hydrological analysis on the preprocessed DEM; extracting each surface water body grid and merging them to obtain multiple planar surface water bodies, and identifying the overflow points of each planar surface water body; identifying the river network based on a preset river network cumulative flow threshold, dividing the river network into river sections with the river intersection as the segmentation point, and analyzing the end points of the river sections; taking the overflow points of the planar surface water bodies and the end points of the river sections as the starting points, reversely tracing the confluence areas of the planar surface water bodies and the river sections, and obtaining the boundary range of each hydrological unit; setting the output layer parameters to export the surface hydrological unit division result map. The method can automatically, quickly and accurately identify the surface water unit of a region or a watershed.

Description

Technical Field

[0001] The present invention relates to the field of geographic information technology, and in particular to a method, system, terminal and medium for dividing hydrological units based on DEM. Background Art

[0002] Rivers, lakes, wetlands, and swamps are important components of surface water and are important influencing factors of surface runoff, soil infiltration, and groundwater recharge and discharge. Obtaining the location and hydrological characteristics of surface water bodies such as rivers, lakes, wetlands, and swamps is important for understanding the distribution of water resources and studying the interaction between surface water and groundwater. Dividing the surface into a series of surface water units (i.e., hydrological units) can facilitate the investigation and management of surface water resources and the simulation of groundwater circulation and transformation processes.

[0003] The division of surface hydrological units can be carried out by analyzing the surface digital elevation model (DEM). However, the current method of dividing surface hydrological units requires multiple traversals of the DEM grid. This identification method requires a large amount of computing power and memory, and the identification work is very cumbersome in the actual complex river network and surface water body development area. In addition, the existing technology may identify the wrong surface water body grid, and it is necessary to traverse the DEM data again to eliminate the error. Summary of the invention

[0004] In view of the deficiencies in the background technology, the present invention provides a DEM-based hydrological unit division method, system, terminal and medium, which can automatically, quickly and accurately identify regional or basin surface water units.

[0005] In a first aspect, the present invention provides a method for dividing hydrological units based on DEM, comprising:

[0006] S1: Obtain DEM data of the area or watershed to be identified and perform data preprocessing;

[0007] S2: Fill the preprocessed DEM and perform hydrological analysis on the filled DEM to obtain a non-sag DEM, grid flow direction, and grid confluence;

[0008] S3: Compare the DEM without depression with the initial DEM, extract the surface water body grids and fuse them to obtain multiple surface water bodies, identify the overflow points of each surface water body, and calculate the maximum water storage area and maximum storage capacity of the surface water body;

[0009] S4: Identify the river network based on a preset river network cumulative flow threshold, and divide the river network into river sections with the river intersection as the dividing point, analyze each river section to obtain the end point of the river section, and calculate the length of each river section;

[0010] S5: Taking the overflow point of the surface water body and the end point of the river section as the starting point, reversely trace the confluence area of ​​the surface water body and each river section, obtain the boundary range of each hydrological unit, and calculate the area of ​​the surface water body unit and the area of ​​the river section unit;

[0011] S6: Set the output layer parameters and export the surface hydrological unit division result map.

[0012] Furthermore, in S1, data preprocessing includes mosaicking and clipping the DEM data to obtain the DEM of the area or watershed to be identified; setting the projection coordinate system of the DEM layer to generate the target resolution of the DEM data.

[0013] Furthermore, the specific process of S2 is:

[0014] S21: Fill the preprocessed DEM to the maximum water storage capacity;

[0015] S22: Based on the elevation value of the filled DEM, the slope between each grid and the adjacent grid is calculated, and the direction of the maximum slope is used as the water flow direction of each grid;

[0016] S23: Calculate the cumulative flow of each grid according to the flow direction of the grid water.

[0017] Furthermore, the specific steps of S3 are as follows:

[0018] S31: Compare the non-sag DEM with the initial DEM, subtract the elevation values ​​of each grid before and after filling, and the grid with a non-zero difference is the surface water grid;

[0019] S32: Based on the boundary of each surface water body grid, expand outward at a preset buffer distance to obtain a buffer zone and merge the overlapping grids of the buffer zone, merge the surface water body grids located in the same buffer zone to obtain a planar surface water body; wherein the planar surface water body is a polygon;

[0020] S33: Identify the overflow point of the planar surface water body: if the water flow direction of the surface water body grid points to the outside of the planar surface water body, it indicates that the surface water body grid is the overflow point of the planar surface water body;

[0021] S34: Calculate and obtain the maximum water storage area and the maximum storage capacity of the planar surface water body.

[0022] Furthermore, the specific steps of S4 are:

[0023] S41: Filtering grids whose cumulative flow is greater than or equal to a preset river network cumulative flow threshold, and further filtering grids of non-surface water bodies to obtain a river network;

[0024] S42: Locate the intersection points of rivers in the river network as segmentation points to divide the river network into river segments;

[0025] S43: Analyze the characteristics of each river section, and set the grid with the maximum cumulative flow in each river section as the end point of the river section;

[0026] S44: Calculate the length of each river section, and remove the river channels that are not connected to the surface outlet according to the preset minimum river section length, so as to obtain the river sections that meet the preset standards.

[0027] Furthermore, the hydrological unit includes a planar surface water body unit PBU and a river section unit CBU; wherein the planar surface water body unit PBU includes the confluence area of ​​planar surface water bodies and planar surface water bodies; and the river section unit CBU includes the confluence area of ​​river sections and river sections.

[0028] Furthermore, the area calculation formulas for the planar surface water unit and the river section unit are:

[0029]

[0030] in, is the DEM resolution; It is the area of ​​surface water unit / river section unit; It is the number of grids contained in the surface water unit / river section unit.

[0031] In the second aspect, a hydrological unit division system based on DEM includes:

[0032] Data processing module: used to obtain DEM data of the area to be identified, and perform grid division and data preprocessing; used to fill the preprocessed DEM and perform hydrological analysis on the filled DEM to obtain a non-sag DEM, grid flow direction, and grid confluence;

[0033] Surface water body identification and hydrological unit division module: used to compare the non-depression DEM with the initial DEM, extract the surface water body grids and merge them to obtain multiple planar surface water bodies, identify the overflow points of each planar surface water body, and calculate the maximum water storage area and maximum storage capacity of the planar surface water body; used to identify the river network based on the preset river network cumulative flow threshold, and divide the river network into river sections with the river confluence points as the dividing points, and calculate the length of each river section by analyzing the end points of the river sections; starting from the overflow points of the planar surface water bodies and the end points of the river sections, reversely trace the confluence areas of the planar surface water bodies and each river section, obtain the boundary range of each hydrological unit, and calculate the area of ​​the planar surface water unit and the area of ​​the river section unit;

[0034] Surface hydrological unit output module: used to set output layer parameters and export surface hydrological unit division result map.

[0035] The third invention provides an electronic terminal, comprising a processor and a memory, wherein the memory stores a computer program, and the processor calls the computer program to execute the steps of the method described above.

[0036] In a fourth aspect, the present invention provides a readable storage medium: a computer program is stored, and when the computer program is called by a processor, the steps of the method described above are executed.

[0037] Beneficial Effects

[0038] The present invention proposes a DEM-based hydrological unit division method, system, terminal and medium, wherein the method only needs to obtain DEM data of the area or basin to be identified, so as to automatically, quickly and accurately obtain the surface hydrological units of the area or basin to be identified, and derive the surface hydrological unit division result map, and has a wide range of applications, and can be used in river systems, wetland systems, plateau systems, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0040] Figure 1 is a flow chart of a method for dividing hydrological units based on DEM provided by an embodiment of the present invention;

[0041] Figure 2 It is a flowchart of a program for identifying the overflow point of a planar surface water body and the end point of a river section provided by an embodiment of the present invention;

[0042] Figure 3 It is a schematic diagram of the effect of the hydrological unit identification result of a surface water body provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0043] To make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0044] Example 1

[0045] like Figure 1 As shown, this embodiment provides a method for dividing hydrological units based on DEM, including:

[0046] S1: Obtain the DEM data of the area or watershed to be identified, and perform grid division and data preprocessing. Data preprocessing includes mosaicking and clipping the DEM data to obtain the DEM layer of the area or watershed to be identified; setting the projection coordinate system of the DEM layer to generate the target resolution of the DEM data.

[0047] Specifically, DEM data can be downloaded in raster format (raster is grid) through a dedicated geographic data service platform. After downloading the DEM data, the DEM needs to be preprocessed, including setting the projection coordinate system of the DEM layer and exporting it as a DEM with a target resolution (10m×10m). This embodiment is implemented using ArcGIS's Project projection tool and Export tool. When multiple DEM sheets are involved, graphic mosaicking and clipping are also required to generate the DEM layer of the study area. The specific operation is completed using ArcGIS's Mosaic to New Rater and Clip tools. The DEM layer of the area to be identified is named "sDEM", which is raster data, and the attribute value of each raster represents the surface elevation.

[0048] S2: Fill the preprocessed DEM and perform hydrological analysis on the filled DEM to obtain a non-sag DEM, grid flow direction, and grid confluence. The specific process is as follows:

[0049] S21: Fill the preprocessed DEM to the maximum water storage capacity. Specifically, the filled water is gathered in the sunken grids, and the water level of each sunken grid reaches the elevation of its corresponding overflow point. If there is no sunken grid, no water is stored. In the specific implementation, this embodiment processes the "sDEM" layer by using the Fill function of ArcGIS, and the processing result is raster data. The attribute value of each raster represents the elevation value after filling, and the new layer output after filling is named "sDEM_fill".

[0050] S22: Based on the elevation value of the filled DEM, the slope between each grid and the adjacent grid is calculated, and the direction of the maximum slope is used as the water flow direction of each grid. In specific implementation, this embodiment processes "sDEM_fill" by using the Flow direction function of ArcGIS, and the processing result is raster data. The attribute value of each raster represents the water flow direction. The new layer output after processing is named "sDEM_fdr".

[0051] S23: Calculate the cumulative flow of each grid according to the flow direction of the grid. In the specific implementation, this embodiment processes the "sDEM_fdr" by using the Flow accumulation function of ArcGIS, and the processing result is raster data. The attribute value of each grid represents its cumulative flow, and the new layer output after calculation is named "sDEM_facc".

[0052] S3: Compare the DEM without depressions with the initial DEM, extract the surface water grids and fuse them to obtain multiple surface water bodies, identify the overflow points of each surface water body, and calculate the maximum water storage area and maximum storage capacity of the surface water body. The specific process is as follows:

[0053] S31: Compare the non-depression DEM with the initial DEM, subtract the elevation values ​​before and after each grid is filled, and the grid with a non-zero difference is the surface water body grid. In the specific implementation of this embodiment, the Minus function of ArcGIS is used to subtract the attribute values ​​of the grids corresponding to "sDEM_fill" and "sDEM", and the output result is raster data. The attribute value of each grid represents its highest water storage level; the Con function of ArcGIS is used to set the grid attribute with an attribute value of 0 to "null". The new layer output after processing is named "depRas", which represents the maximum water storage range of the surface water body.

[0054] The surface water body range extracted above is in raster format. To facilitate subsequent operations, ArcGIS Raster to polygon tool is used to convert it into vector layer data named "deppoly0". Since the "Raster to polygon" operation can only merge rasters with overlapping edges, it is still necessary to further merge the diagonally overlapping rasters to obtain the surface water body.

[0055] S32: Based on the boundary of each surface water body network, the buffer zone is expanded outward at a preset buffer distance and the overlapping grids of the buffer zone are merged, and the surface water body grids located in the same buffer zone are merged to obtain a planar surface water body and perform ID identification. In the specific implementation, this embodiment uses the Buffer tool of ArcGIS to perform a buffer analysis on the "deppoly0" layer with a buffer radius of 1m (that is, the preset buffer distance is 1m), and merges the surface water body grids with overlapping buffers. The generated layer is in vector format and is named "deppoly_bf"; since the surface water body polygons in the "deppoly_bf" layer contain buffers, the surface water bodies need to be further extracted; the specific operation is to use the Spatialjoin tool of ArcGIS to spatially link the polygons in the "deppoly0" and "deppoly_bf" layers, and then use the Dissovle tool of ArcGIS to merge the polygons belonging to the same surface surface water body in "deppoly0", and the merged surface surface water body polygons have a unique identification ID; the new layer output after the fusion is named "deppoly".

[0056] S33: Identify the overflow point of the planar surface water body: If the water flow direction of the surface water body grid points to the outside of the planar surface water body, it indicates that the surface water body grid is the overflow point of the planar surface water body. In specific implementation, this embodiment traverses the surface water body grids in the "depRas" layer. If the grid water flow direction points to the outside of the surface water body (that is, the grid is different from the surface water body identification ID pointing to the grid), then the grid is the overflow point of the planar surface water body, and the position of the grid is recorded in an array (Numpyarray). After the traversal is completed, the Numpy array to point tool of ArcGIS is used to generate a vector point layer of the overflow point of the planar surface water body, named "thresPoint".

[0057] S34: Calculate and obtain the maximum water storage area and the maximum storage capacity of the planar surface water body; the specific calculation formula is as follows:

[0058]

[0059]

[0060] in, It is the maximum water storage area of ​​a planar surface water body; is the number of grids contained in the surface water body; is the DEM resolution; It is the maximum water storage capacity of a planar surface water body; is the absolute value of the elevation difference before and after filling the surface water body grid i.

[0061] The flowchart for identifying the overflow point of the surface water body and the end point of the river section is as follows Figure 2 shown.

[0062] S4: Identify the river network based on the preset river network cumulative flow threshold, and divide the river network into river sections with the river intersection as the dividing point, analyze each river section to obtain the end point of the river section, and calculate the length of each river section. The specific steps are:

[0063] S41: Filter the grids whose cumulative runoff is greater than or equal to the preset river network cumulative runoff threshold, and further filter the grids of non-surface water bodies to obtain the river network. The river network is linear. In the specific implementation, this embodiment uses the Con function of ArcGIS to filter the grids whose cumulative runoff exceeds the river network cumulative runoff threshold set by the user, and the new layer output after processing is named "stream0".

[0064] The above-screened rasters include river network rasters and surface water body rasters (i.e., rasters within the surface water body polygon range) whose cumulative flow exceeds the user-set threshold, so further screening is required; the specific operation is to use "deppoly" as a mask and use ArcGIS's Clip Raster tool to clip the "stream0" layer. The output result is a river network raster named "stream".

[0065] S42: Locate the river confluence points in the river network as segmentation points, divide the river network into river segments, and identify each river segment with an ID. In specific implementation, this embodiment uses the StreamLink function of ArcGIS to divide the river network grid into river segments based on the river confluence points, and the output result is a river segment grid named "stream_segment".

[0066] S43: Analyze the characteristics of each river segment, and set the grid with the maximum cumulative flow in each river segment as the end point of the river segment. In specific implementation, this embodiment traverses the river segment grids in the "stream_segment" layer, and if the grid has the maximum cumulative flow in the river segment, the grid is the end point of this river segment, and the position of the grid is recorded.

[0067] S44: Calculate the length of each river segment, and remove the river channel that is not connected to the surface outlet according to the preset minimum river length, so as to obtain the river segment that meets the preset standard, thereby reducing the amount of calculation for subsequent work. In specific implementation, when traversing the river segment grid of the "stream_segment" layer, record the length of each river segment. If the length is less than the minimum river segment length set by the user and the river segment is not connected to the surface outlet, delete the river segment and its end point, and then use ArcGIS's Numpy array to point tool to generate a river segment end point vector point layer named "endPoint".

[0068] S5: Taking the overflow point of the surface water body and the end point of the river section as the starting point, reversely trace the confluence area of ​​the surface surface water body and the river channel, obtain the boundary range of each hydrological unit, calculate the area of ​​the surface surface water body unit and the area of ​​the river section unit, and then. The hydrological unit includes the surface surface water body unit PBU and the river section unit CBU; wherein the surface surface water body unit PBU includes the confluence area of ​​the surface surface water body and the surface surface water body; the river section unit CBU includes the confluence area of ​​the river section and the river section. The calculation formulas for the area of ​​the surface surface water body unit and the area of ​​the river section unit include:

[0069]

[0070] in, is the DEM resolution; It is the area of ​​surface water unit / river section unit; It is the number of grids contained in the surface water unit / river section unit.

[0071] In specific implementation, this embodiment merges the "thresPoint" and "endPoint" layers to generate a "points" vector point layer, and then uses the "watershed" function of ArcGIS to use the vector points in the "points" layer as confluence points. Based on the flow direction of surface water, the confluence area of ​​each confluence point is traced back to divide the surface into a series of hydrological units (surface water body units and river section units); the output layer is raster data, named "hydrologic_units".

[0072] S6: Set the output layer parameters to export the surface hydrological unit division result map.

[0073] In specific implementation, this embodiment exports the surface hydrological unit division result map by using the "deppoly", "points", and "hydrologic_unit" layers to map the surface hydrological unit division result; sets a scale, compass, legend, etc. that meet the standards; uses the Export map tool to set the image resolution (such as 300dpj) and output the "surface hydrological unit division result map". The schematic diagram of the effect of the hydrological unit recognition result of a surface water body is shown in Figure 3 shown.

[0074] Example 2

[0075] This embodiment provides a hydrological unit division system based on DEM, including:

[0076] Data processing module: used to obtain DEM data of the area to be identified, and perform grid division and data preprocessing; used to fill the preprocessed DEM and perform hydrological analysis on the filled DEM to obtain a non-sag DEM, grid flow direction, and grid confluence;

[0077] Surface water body identification and hydrological unit division module: used to compare the non-depression DEM with the initial DEM, extract the surface water body grids and merge them to obtain multiple planar surface water bodies, identify the overflow points of each planar surface water body, and calculate the maximum water storage area and maximum storage capacity of the planar surface water body; used to identify the river network based on the preset river network cumulative flow threshold, and divide the river network into river sections with the river confluence points as the dividing points, and calculate the length of each river section by analyzing the end points of the river sections; starting from the overflow points of the planar surface water bodies and the end points of the river sections, reversely trace the confluence areas of the planar surface water bodies and each river section, obtain the boundary range of each hydrological unit, and calculate the area of ​​the planar surface water unit and the area of ​​the river section unit;

[0078] Surface hydrological unit output module: used to set output layer parameters and export surface hydrological unit division result map.

[0079] Example 3

[0080] This embodiment provides an electronic terminal, including a processor and a memory, wherein the memory stores a computer program, and the processor calls the computer program to execute the steps of the above method.

[0081] Example 3

[0082] This embodiment provides a readable storage medium storing a computer program, and when the computer program is called by a processor, the computer program executes the steps of the above method.

[0083] It can be understood that the same or similar parts of the above embodiments can be referenced to each other, and the contents not described in detail in some embodiments can refer to the same or similar contents in other embodiments.

[0084] It should be understood that in the embodiments of the present invention, the processor may be a central processing unit (CPU), and the processor may also be other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or the processor may also be any conventional processor, etc. The memory may include a read-only memory and a random access memory, and provide instructions and data to the processor. A portion of the memory may also include a non-volatile random access memory. For example, the memory may also store information about the type of device.

[0085] The readable storage medium is a computer-readable storage medium, which may be an internal storage unit of the controller described in any of the foregoing embodiments, such as a hard disk or memory of the controller. The readable storage medium may also be an external storage device of the controller, such as a plug-in hard disk, a smart memory card (Smart Media Card, SMC), a secure digital (Secure Digital, SD) card, a flash card (Flash Card), etc. equipped on the controller. Furthermore, the readable storage medium may also include both an internal storage unit of the controller and an external storage device. The readable storage medium is used to store the computer program and other programs and data required by the controller. The readable storage medium may also be used to temporarily store data that has been output or is to be output.

[0086] Based on this understanding, the technical solution of the present invention, in essence or in other words, the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product, which is stored in a storage medium and includes several instructions for enabling a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned readable storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk, etc., various media that can store program codes.

[0087] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for dividing hydrological units based on DEM, characterized in that: include: S1: Obtain DEM data of the area or watershed to be identified and perform data preprocessing; S2: Fill the preprocessed DEM and perform hydrological analysis on the filled DEM to obtain the non-sag DEM, grid flow direction, and grid confluence; S3: Compare the DEM without depression with the initial DEM, extract the surface water grids and fuse them to obtain multiple surface water bodies, identify the overflow points of each surface water body, and calculate the maximum water storage area and maximum storage capacity of the surface water body. The specific steps are as follows: S31: Compare the non-sag DEM with the initial DEM, subtract the elevation values ​​of each grid before and after filling, and the grid with a non-zero difference is the surface water grid; S32: Based on the boundary of each surface water body grid, expand outward at a preset buffer distance to obtain a buffer zone and merge the overlapping grids of the buffer zone, merge the surface water body grids located in the same buffer zone to obtain a planar surface water body; wherein the planar surface water body is a polygon; S33: Identify the overflow point of the planar surface water body: if the water flow direction of the surface water body grid points to the outside of the planar surface water body, it indicates that the surface water body grid is the overflow point of the planar surface water body; S34: Calculate and obtain the maximum water storage area and the maximum storage capacity of the planar surface water body; S4: Identify the river network based on a preset river network cumulative flow threshold, and divide the river network into river sections with the river intersection as the dividing point, analyze each river section to obtain the end point of the river section, and calculate the length of each river section; S5: Taking the overflow point of the surface water body and the end point of the river section as the starting point, reversely trace the confluence area of ​​the surface water body and each river section, obtain the boundary range of each hydrological unit, and calculate the area of ​​the surface water body unit and the area of ​​the river section unit; S6: Set the output layer parameters and export the surface hydrological unit division result map.

2. The method for dividing hydrological units based on DEM according to claim 1, characterized in that: In S1, data preprocessing includes mosaicking and clipping the DEM data to obtain the DEM of the area or watershed to be identified; setting the projection coordinate system of the DEM layer to generate the target resolution of the DEM data.

3. The method for dividing hydrological units based on DEM according to claim 1, characterized in that: The specific process of S2 is: S21: Fill the preprocessed DEM to the maximum water storage capacity; S22: Based on the elevation value of the filled DEM, the slope between each grid and the adjacent grid is calculated, and the direction of the maximum slope is used as the water flow direction of each grid; S23: Calculate the cumulative flow of each grid according to the flow direction of the grid water.

4. The method for dividing hydrological units based on DEM according to claim 1, characterized in that: The specific steps of S4 are: S41: Filtering grids whose cumulative flow is greater than or equal to a preset river network cumulative flow threshold, and further filtering grids of non-surface water bodies to obtain a river network; S42: Locate the intersection points of rivers in the river network as segmentation points to divide the river network into river segments; S43: Analyze the characteristics of each river section, and set the grid with the maximum cumulative flow in each river section as the end point of the river section; S44: Calculate the length of each river section, and remove the river channels that are not connected to the surface outlet according to the preset minimum river section length, so as to obtain the river sections that meet the preset standards.

5. The method for dividing hydrological units based on DEM according to claim 1, characterized in that: The hydrological unit includes a planar surface water body unit PBU and a river section unit CBU; wherein the planar surface water body unit PBU includes the confluence area of ​​planar surface water bodies and planar surface water bodies; and the river section unit CBU includes the confluence area of ​​river sections and river sections.

6. The method for dividing hydrological units based on DEM according to claim 1, characterized in that: The area calculation formulas for the planar surface water unit and the river section unit are: ； in, is the DEM resolution; It is the area of ​​surface water unit / river section unit; It is the number of grids contained in the surface water unit / river section unit.

7. A hydrological unit division system based on DEM, characterized in that: include: Data processing module: used to obtain DEM data of the area to be identified, and perform grid division and data preprocessing; It is used to fill the preprocessed DEM and perform hydrological analysis on the filled DEM to obtain the non-sag DEM, grid flow direction, and grid confluence; Surface water body identification and hydrological unit division module: used to compare the non-depression DEM with the initial DEM, extract the surface water body grids and merge them to obtain multiple surface water bodies, identify the overflow points of each surface water body, and calculate the maximum water storage area and maximum storage capacity of the surface water body. The specific process is as follows: S31: Compare the non-sag DEM with the initial DEM, subtract the elevation values ​​of each grid before and after filling, and the grid with a non-zero difference is the surface water grid; S32: Based on the boundary of each surface water body grid, expand outward at a preset buffer distance to obtain a buffer zone and merge the overlapping grids of the buffer zone, merge the surface water body grids located in the same buffer zone to obtain a planar surface water body; wherein the planar surface water body is a polygon; S33: Identify the overflow point of the planar surface water body: if the water flow direction of the surface water body grid points to the outside of the planar surface water body, it indicates that the surface water body grid is the overflow point of the planar surface water body; S34: Calculate and obtain the maximum water storage area and the maximum storage capacity of the planar surface water body; The river network is identified based on the preset river network cumulative flow threshold, and the river network is divided into river sections with the river confluence point as the segmentation point. The end point of the river section is obtained by analyzing each river section, and the length of each river section is calculated; the overflow point of the surface surface water body and the end point of the river section are used as the starting point, and the confluence area of ​​the surface surface water body and each river section is traced back to obtain the boundary range of each hydrological unit, and the area of ​​the surface water body unit and the area of ​​the river section unit are calculated; Surface hydrological unit output module: used to set output layer parameters and export surface hydrological unit division result map.

8. An electronic terminal, characterized in that: It comprises a processor and a memory, wherein the memory stores a computer program, and the processor calls the computer program to execute the steps of the method according to any one of claims 1 to 6.

9. A readable storage medium, characterized in that: A computer program is stored, and when the computer program is called by a processor, the computer program is used to execute: the steps of the method according to any one of claims 1 to 6.

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