CN109472868B - A sub-basin division method for inland river basins - Google Patents

Abstract

The invention discloses a sub-basin division method of an inland river basin, which includes: setting the low-lying land or lake center in the inland river basin as its virtual exit point; setting the elevation value at the grid of the virtual exit point in DEM as Null, and obtaining DEM1; draw a vector virtual river network, so that the river network is finally connected to the virtual outlet point, and convert it into a reference river network grid; convert the internal and external boundaries of the inland river basin into a grid; for the reference river network and the internal and external boundaries of the watershed in DEM1 The elevation at the grid position is corrected to obtain DEM2; the simulated river network is extracted from DEM2; the range of the lake is encoded and converted into a grid; the grid of the simulated river network is traced and traversed, and the river network is coded considering the range of the lake; The river network grid is used as the starting point, and the non-river network grid is traced and traversed, and the river network code of the river network grid is set as the code of all non-river network grid sub-watersheds that are imported into the current river network grid. The invention can divide the inland river basin without river outlet into sub-basins, and ensure that the lakes are located in the same sub-basin.

Description

A sub-basin division method for inland river basins

technical field

The invention relates to the field of hydrological models, in particular to a method for dividing sub-basins of inland river basins.

Background technique

In the hydrological model, the conventional method of extracting watersheds and sub-watersheds includes using the hydrological analysis module of GIS (Geographic Information System, geographic information system) software to start from DEM (Digital Elevation Model, digital elevation model) to experience filling, flow direction calculation, and confluence accumulation. Number calculation, simulated river network extraction, sub-watershed division and other steps; the premise that this method can correctly divide the sub-watershed is that there must be one or more watershed outlets that can flow out of the DEM boundary through a series of grids.

For inland river basins, the outlet of the basin is generally located in the center of the basin, and the surrounding grid is much higher, and a large inland river basin is often composed of multiple relatively independent small inflow areas. If the above-mentioned conventional methods are used to extract watersheds and sub-watersheds, the following problems exist:

(1) When filling the sub-basin, the outlet inside the watershed will be filled and flow out of the boundary from the area with a lower boundary. When dividing sub-watersheds, it is easy to get the wrong upstream and downstream confluence relationship and combine multiple independent small internal flows Regions are merged into one region;

(2) For inland river basins, the upper reaches generally originate from mountainous areas with sufficient water and are generally perennial rivers, the middle and lower reaches are generally seasonal rivers, and the end is generally wetlands or tail lakes, whose water is basically used for evaporation It will flow out of the basin; in order to facilitate the analysis of lake water balance, it is necessary to divide the range of the lake into the same sub-basin; the conventional method does not meet the above requirements, and the problem of dividing the lake into multiple sub-basins often occurs;

(3) For the middle and lower reaches of inland river basins, due to the relatively small height difference within the region, the range of sub-basins divided by conventional methods is often quite different from other existing achievements such as water resources planning, so it is not necessary to use them in model simulation analysis. It is easy to unify to the same unit for analysis, and it will lead to abnormal division of boundary areas, making the surrounding non-basin areas be divided into the current watershed or a part of the current watershed is missing.

Contents of the invention

The technical problem to be solved by the present invention is that in the existing conventional methods for extracting watersheds and sub-basins, when sub-basins are divided into inland river basins, there are abnormal confluence relations between the upper and lower reaches of the sub-basins, merging of independent small inland water areas, and lakes Problems such as division into multiple sub-basins and incorrect division of sub-basins.

In order to solve the above-mentioned technical problems, the technical solution adopted in the present invention is to provide a method for sub-basin division of inland river basins, including the following steps:

Step S10, assuming that the local lowest elevation point in the inland river basin or the center of the lake without an outlet is the virtual outlet point of the inland river basin, and the virtual outlet point is used as the end point of the river flow in the inland river basin;

Step S20, use GIS software to empty the grid elevation value of the location of the virtual exit point in the corresponding watershed DEM, and obtain a corrected DEM layer DEM1;

Step S30, draw a virtual river network according to the DEM elevation of the inland river basin and the measured river network information, and make the river network finally connect to a virtual exit point, and convert it into a grid according to the position and size of the DEM grid, Get the reference river grid;

Step S40, converting the collected inland river basin boundary into a grid according to the position and size of the DEM grid;

Step S50, burn the information of the reference river network grid and the boundary grid of the inland river basin into DEM1, and perform elevation correction on the positions of the reference river network grid and the boundary grid of the inland river basin respectively, to obtain the inland river The location of the watershed boundary grid is higher than the original DEM by a certain elevation, and the reference river network grid location elevation is lower than the original DEM by a certain elevation of the corrected DEM layer DEM2;

Step S60, using the hydrological analysis module of GIS software to extract the simulated river network for DEM2;

Step S70, perform unique and non-repetitive lake coding on each lake range in the collected inland river basin, and convert it into a grid according to the position and size of the DEM grid;

Step S80, start from each virtual exit point in turn, trace the source of the simulated river network grid according to the grid flow direction, perform a unique and non-repeated river network code for each river section, and make the simulated river network grid with the same lake code The river network codes of grids are the same;

Step S90, taking each simulated river network grid as a starting point, trace the source of the non-simulated river network grid according to the grid flow direction, find all non-river network grids imported into the current simulated river network grid, and find The sub-watershed code of the non-river network grid is the river network code of the simulated river network grid, and then the inland river basin is divided into sub-watersheds according to the sub-watershed code.

In the above method, the area information of the inland river basin to be divided is collected before setting the virtual exit point;

The area information of the inland river basin to be divided includes the DEM elevation of the inland river basin; the number, range and location information of the lakes in the inland river basin; the boundary information of the inland river basin;

Among them, the inland river basin boundary information includes inner boundary information and outer boundary information; the outer boundary is the boundary that includes the entire inland river basin, and the inner boundary is the boundary of water resource divisions in the inland river basin.

In the above method, in step S10, within the entire inland river basin, when there are multiple independent and unconnected water resource divisions, virtual outlets should be set up in each independent and unconnected water resource division .

In the above method, in step S30, the drawn virtual river network includes two forms:

The first is to extend the existing measured river network to a virtual river network with a virtual outlet;

The second is a virtual river network that is newly drawn according to the DEM elevation and is relatively independent from the measured river network in a large area without a measured river network, so that it is finally connected to a virtual outlet.

In the above method, in step S30, the drawn virtual river network first merges the virtual river network and the measured river network into a linear vector layer, and then combines the linear vector layer according to the position and size of the DEM grid Convert to raster.

In the above method, when drawing the virtual river network, when there is a lake on the river, a virtual river network connecting the upstream and downstream sections is drawn inside the lake.

In the above method, in step S50, according to the information of the reference river network grid and the boundary grid of the inland river basin, the elevation correction is performed on the positions of the reference river network grid and the boundary grid of the inland river basin according to the priority, Specifically:

Increase the DEM1 elevation value at the location of the inland river basin boundary grid by a fixed value; correspondingly, decrease the DEM1 elevation value at the location of the reference river network grid by a fixed value;

If a grid is both an outer boundary grid and a reference river network grid, it will be treated as a boundary grid, and the elevation value of DEM1 at the location will be increased by a fixed value;

If a grid is both an inner boundary grid and a reference river network grid, it will be treated as a river network grid, and the elevation value of DEM1 at the location will be reduced by a fixed value.

In the above method, lake codes and river network codes are continuous natural number codes starting from 1.

In the above method, step S80 is specifically:

Traverse the simulated river network grid according to the grid flow direction, and assign a unique code to each river network grid;

If there is no branched simulated river grid or lake grid, the next river grid code is equal to the river network code of the current grid;

If a bifurcated simulated river network grid or lake grid is encountered, the river network code of the next river network grid is equal to the river network code of the current grid plus 1;

If a lake grid is encountered and the current simulated river network grid also has the same lake code, no matter whether it is bifurcated or not, the river network code of the next simulated river network grid is equal to the river network code of the current simulated river network grid;

Simulated river network grids with the same river network code belong to the same river segment;

After the upstream river traversal of a certain virtual outlet is completed, the source tracing traversal of other virtual outlets is performed. At this time, the initial river network code of the new source tracing traversal is the maximum code of the previous stage plus 1.

Compared with the prior art, the present invention is based on DEM, combined with information such as the measured river network, watershed boundary, lake range, etc., using multiple virtual exit points to extract different sub-watershed ranges, and considering the lake range, River network coding can ensure that the divided sub-basin basically conforms to the upstream and downstream relationship in the inland river basin, and makes a lake only located in one sub-basin, ensuring the correctness of sub-basin division.

Description of drawings

Fig. 1 is the flow chart of the sub-basin division method of a kind of inland river basin provided by the present invention;

Fig. 2 is a schematic diagram of a specific embodiment with two lakes and two partitions in the present invention;

Fig. 3 is a schematic diagram after the virtual exit is set to Fig. 2 in the present invention;

Fig. 4 is the schematic diagram after carrying out virtual river network drawing to Fig. 3 in the present invention;

Fig. 5 is the schematic diagram after carrying out simulation river network extraction to Fig. 4 in the present invention;

Fig. 6 is the schematic diagram after carrying out river network coding to Fig. 5 in the present invention;

FIG. 7 is a schematic diagram of implementing sub-watershed division after sub-watershed encoding is performed on the non-simulated river network grid shown in FIG. 6 in the present invention.

Detailed ways

The invention provides a method for sub-basin division of inland river basins. Based on DEM, combined with information such as measured river networks, basin boundaries, and lake water surface ranges, multiple virtual exit points are used to extract different sub-basin ranges, which can Ensure that the divided sub-basin basically conforms to the upstream and downstream relationship in the inland river basin, and make a lake only in one sub-basin to ensure the correctness of sub-basin division. The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

As shown in Figure 1, a sub-basin division method of an inland river basin provided by the present invention comprises the following steps:

Step S10, assuming that the low-lying land in the inland river basin to be divided (the lowest local elevation point within the entire inland river basin) or the central position of the lake without an outlet is the virtual outlet point of the inland river basin, and the virtual outlet point is used as the inland river basin. The river flows to the end of the river basin;

Before setting the virtual exit point, collect the information of the inland river basin area to be divided, including the DEM elevation of the inland river basin, the number, scope and location information of lakes in the inland river basin, and the boundary of the inland river basin; among them , the boundary information of inland river basins includes inner boundary information and outer boundary information, the outer boundary is the boundary that includes the entire inland river basin (as shown in the outer solid line in Figure 3), and the inner boundary is the boundary of water resources divisions in the inland river basin (as shown in the internal dotted line in Figure 3); then, according to the DEM elevation in each water resource division, set a virtual exit point at the point with the lowest elevation (low-lying land or the center of a lake with no exit); Therefore, it is necessary to set up virtual exit points in the above-mentioned different water resource partitions that are not connected with each other. Therefore, according to the characteristics of the basin, multiple virtual exit points can be set in an inland river basin, and at least one virtual exit point can be set. exit point. As shown in Figure 2, in this embodiment, the collected inland river basin area information includes two lakes (black areas), lake a on the perennial river and lake b at the tail of the river, respectively. There are two lakes in the watershed. The water resource division boundary is the dotted line in Figure 2, which divides the entire inland river basin into two water resource divisions, Division I and Division II; according to the DEM elevation, virtual exits are set up in Division I and Division II respectively Points, as shown in Fig. 3, are respectively circle A and circle B near the boundary of the partition.

Step S20, use GIS software to empty the grid elevation value at the position of the virtual exit point in the DEM of the corresponding watershed (that is, set it to a Null value), and obtain a corrected DEM layer that is hollowed out at the position of the virtual exit point, called DEM1.

Step S30, according to the DEM elevation of the inland river basin and the measured river network (linear vector) information, draw (manually) a virtual river network (linear vector), and make the river network finally connected to a certain virtual exit point, And according to the position and size of the DEM grid, it is converted into a grid, and the reference river network grid is obtained.

In the present invention, the drawn virtual river network includes two forms, one is an extension of the measured river network, that is, extending the measured river network to a certain virtual exit point; For areas without river channels, a new river network that is relatively independent from the measured river network is drawn according to the DEM elevation, so that it is finally connected to a virtual exit point. After the virtual river network is drawn, it needs to be merged with the measured river network into a linear vector layer, and then the merged linear vector layer is converted into a grid according to the position and size of the DEM grid. When there are lakes on the river, it is necessary to draw a virtual river network in the lake to connect the upstream and downstream river sections. Figure 4 is the drawing of the virtual river network for the embodiment shown in Figure 3, a virtual river network is drawn in the lake a on the perennial river to ensure that its upstream and downstream sections are connected, and then according to the DEM elevation, the area of subregion I and subregion II The measured river network is extended to the corresponding virtual exit point; and in order to divide the large area without river channels in the upper left corner of Division II into sub-watersheds, an independent virtual river network is added there and connected to the corresponding virtual exit point B, so that This area can be divided into a sub-basin independently (that is, the No. 2 reach in Figure 6, if the virtual reach is not added, the No. 2 and No. 4 sub-basins in 7 will be merged into one sub-basin).

Step S40, converting the collected inland river basin boundary (linear vector) into a grid according to the DEM grid position and size;

Step S50, burn the grid information of the reference river network grid and the boundary of the inland river basin (including the inner boundary and the outer boundary) into DEM1, and respectively record the positions of the reference river network grid and the boundary grid of the inland river basin Elevation correction is carried out to obtain a corrected DEM layer in which the position of the virtual exit point is hollowed out, the grid position of the boundary of the inland river basin is higher than the original DEM by a certain elevation, and the elevation of the reference river network grid position is lower than the original DEM by a certain elevation, called for DEM2.

In step S50 of the present invention, according to the information of the reference river network grid and the border grid of inland river basins, the elevations of the positions of the reference river network grid, outer boundary grid, and inner boundary grid in DEM1 are corrected according to priority ,Specifically:

Increase the DEM1 elevation value at the location of the inland river basin boundary (inner boundary and outer boundary) grid by a fixed value (for example, 1000m); correspondingly, decrease the DEM1 elevation value at the location of the reference river network grid by a fixed value (e.g. 1000m);

If a grid is both the outer boundary grid and the reference river grid, it will be treated as the outer boundary grid (the elevation value is increased by a fixed value); if a grid is both the inner boundary grid and the reference river grid grid, it is treated as a river network grid (the elevation value is reduced by a fixed value).

Step S60, using the hydrological analysis module of GIS software to extract the simulated river network from DEM2, that is, to obtain the simulated river network through the steps of filling, flow direction calculation, cumulative confluence calculation, threshold setting and extraction of the simulated river network, as shown in Figure 5. The line is the simulated river network extracted from Figure 4; generally, the density of the simulated river network extracted is greater than that of the measured river network, and the length of the rivers is also inconsistent.

Step S70, carry out unique and non-repetitive lake encoding for each lake range (area vector) in the collected inland river basin, and convert it into a grid according to the DEM grid position and size; wherein, the lake encoding is from 1 The first consecutive natural numbers are encoded.

Step S80, starting with each virtual exit point in turn, tracing the source of the simulated river network grid according to the grid flow direction, performing river network codes for each river section, and making the rivers of the simulated river network grids with the same lake code The network codes are the same, that is, the influence of the range of the lake area is considered during the coding process, so that the lake areas of the same code are located in the same sub-basin. In the present invention, step S80 is specifically:

Traverse the simulated river network grid according to the grid flow direction, and assign a unique code to each river network grid;

If there is no branched simulated river grid or lake grid, the next river grid code is equal to the river network code of the current grid;

If a bifurcated simulated river network grid or lake grid is encountered, the river network code of the next river network grid is equal to the river network code of the current grid plus 1;

If a lake grid is encountered and the current simulated river network grid also has the same lake code, no matter whether it is bifurcated or not, the river network code of the next simulated river network grid is equal to the river network code of the current simulated river network grid, In order to make the river network rasters within the same lake range have the same river network code;

The simulated river network grids with the same river network code belong to the same river section, and the river network code of the river section is a continuous natural number code starting from 1;

After the upstream river traversal of a certain virtual outlet is completed, the source tracing traversal of other virtual outlets is performed. At this time, the initial river network code of the new source tracing traversal is the maximum code of the previous stage plus 1.

Taking Fig. 5 as an example, the simulated river network grid shown in Fig. 5 traces the origin from two virtual exit points in turn, first traverses the partition II and then traverses the partition I, and encodes each river section, a total of 18 river sections, As shown in Figure 6; among them, the objects whose river network code is 1 are 4 river sections located in the water body of the tail lake, because these river sections are located in the same lake and have the same lake code, so the river The network codes are the same, and the other river network code objects are individual river sections without bifurcations.

Step S90, taking each simulated river network grid as a starting point, trace the source of the non-simulated river network grid according to the grid flow direction, find all the non-river network grids imported into the current simulated river network grid, and set the search The sub-watershed codes of the obtained non-river network grids are the river network codes of the simulated river network grids, and finally divide the inland river basins into sub-watersheds according to the sub-watershed codes, that is, the same sub-watershed codes are the same sub-watershed, and The sub-basins are coded into different sub-basins, so as to realize the sub-basin division of inland river basins. As shown in Figure 7, a total of 18 sub-basins are obtained.

The present invention is not limited to the above-mentioned best implementation mode, and anyone should know that the structural changes made under the inspiration of the present invention, all technical solutions that are identical or similar to the present invention, all fall within the scope of protection of the present invention Inside.

Claims (8)

1. A method for sub-basin division of an inland river basin, characterized in that, comprising the following steps: Step S10, assuming that the local lowest elevation point in the inland river basin or the center of the lake without an outlet is the virtual outlet point of the inland river basin, and the virtual outlet point is used as the end point of the river flow in the inland river basin; Step S20, use GIS software to empty the grid elevation value of the location of the virtual exit point in the DEM corresponding to the inland river basin, and obtain a corrected DEM layer DEM1; Step S30, draw a virtual river network according to the DEM elevation of the inland river basin and the measured river network information, and make the river network finally connect to a virtual exit point, and convert it into a grid according to the position and size of the DEM grid, Get the reference river grid; Step S40, converting the collected inland river basin boundary into a grid according to the position and size of the DEM grid; Step S50, burn the information of the reference river network grid and the boundary grid of the inland river basin into DEM1, and perform elevation correction on the positions of the reference river network grid and the boundary grid of the inland river basin respectively, to obtain the inland river The location of the watershed boundary grid is higher than the original DEM by a certain elevation, and the reference river network grid location elevation is lower than the original DEM by a certain elevation of the corrected DEM layer DEM2; Step S60, using the hydrological analysis module of GIS software to extract the simulated river network for DEM2; Step S70, perform unique and non-repetitive lake coding on each lake range in the collected inland river basin, and convert it into a grid according to the position and size of the DEM grid; Step S80, start from each virtual exit point in turn, trace the source of the simulated river network grid according to the grid flow direction, perform a unique and non-repeated river network code for each river section, and make the simulated river network grid with the same lake code The river network codes of grids are the same; Step S90, taking each simulated river network grid as a starting point, trace the source of the non-simulated river network grid according to the grid flow direction, find all non-river network grids imported into the current simulated river network grid, and find The sub-watershed code of the non-river network grid is the river network code of the simulated river network grid, and then the inland river basin is divided into sub-watersheds according to the sub-watershed code; Step S80 is specifically: Traverse the simulated river network grid according to the grid flow direction, and assign a unique code to each river network grid; If there is no branched simulated river grid or lake grid, the next river grid code is equal to the river network code of the current grid; If a bifurcated simulated river network grid or lake grid is encountered, the river network code of the next river network grid is equal to the river network code of the current grid plus 1; If a lake grid is encountered and the current simulated river network grid also has the same lake code, no matter whether it is bifurcated or not, the river network code of the next simulated river network grid is equal to the river network code of the current simulated river network grid; Simulated river network grids with the same river network code belong to the same river segment; After the upstream river traversal of a certain virtual outlet is completed, the source tracing traversal of other virtual outlets is performed. At this time, the initial river network code of the new source tracing traversal is the maximum code of the previous stage plus 1. 2. The method according to claim 1, characterized in that before setting the virtual exit point, the area information of the inland river basin to be divided is collected; The area information of the inland river basin to be divided includes the DEM elevation of the inland river basin; the number, range and location information of the lakes in the inland river basin; the boundary information of the inland river basin; Among them, the inland river basin boundary information includes inner boundary information and outer boundary information; the outer boundary is the boundary that includes the entire inland river basin, and the inner boundary is the boundary of water resource divisions in the inland river basin. 3. The method according to claim 2, characterized in that, in step S10, within the entire inland river basin, when there are multiple independent and unconnected water resource divisions, each independent, unconnected Virtual outlets should be set up in the water resource partitions. 4. The method according to claim 2, characterized in that, in step S30, the virtual river network drawn includes two forms: The first is to extend the existing measured river network to a virtual river network with a virtual outlet; The second is a virtual river network that is newly drawn according to the DEM elevation and is relatively independent from the measured river network in a large area without a measured river network, so that it is finally connected to a virtual outlet. 5. The method according to claim 4, characterized in that, in step S30, the drawn virtual river network first merges the virtual river network and the measured river network into a linear vector layer, and then merges the merged linear vector layer The vector layer is converted into a raster according to the position and size of the DEM raster. 6. The method according to claim 4, wherein when drawing the virtual river network, when there is a lake on the river, a virtual river network connecting the upstream and downstream sections is drawn inside the lake. 7. The method according to claim 2, characterized in that, in step S50, according to the reference river network grid and inland river basin boundary grid information, according to the priority of The location of the watershed boundary grid is corrected for elevation, specifically: Increase the DEM1 elevation value at the location of the inland river basin boundary grid by a fixed value; correspondingly, decrease the DEM1 elevation value at the location of the reference river network grid by a fixed value; If a grid is both an outer boundary grid and a reference river network grid, it will be treated as a boundary grid, and the elevation value of DEM1 at the location will be increased by a fixed value; If a grid is both an inner boundary grid and a reference river network grid, it will be treated as a river network grid, and the elevation value of DEM1 at the location will be reduced by a fixed value. 8. The method according to claim 2, characterized in that the lake code and the river network code are continuous natural number codes starting from 1.