CN113128009B - Sub-basin unit division method considering mountain area plain landform difference - Google Patents
Sub-basin unit division method considering mountain area plain landform difference Download PDFInfo
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Abstract
The invention discloses a sub-basin unit division method considering mountain plain landform difference, which comprises the steps of calculating the flow direction and confluence cumulant of each grid in a basin, and extracting a simulated river network based on a river network threshold; setting the length of a plain unit, carrying out N × N size aggregation on plain areas and peripheral grids thereof, and setting a plain unit marking serial number for each N × N area; starting from a drainage basin outlet, taking a simulated river network grid as a main trunk, traversing the upstream, dividing a calculation unit according to the encountered grid type, and assigning a unique sub-drainage basin number to the divided unit; determining the flow direction between adjacent plain units and mountain units; and according to the flow direction relation, tracing traversal is started from the river outlet unit, and an upstream and downstream topological relation table of the sub-basin is generated. The advantages are that: the surface and underground water flow mechanisms of different landforms in the watershed are better and more comprehensively described, the hydrological simulation precision of the distributed hydrological model is improved, and theoretical and practical support is provided for the construction and application of the distributed hydrological model in the large-scale watershed.
Description
Technical Field
The invention relates to the technical field of sub-basin unit division, in particular to a sub-basin unit division method considering mountain area plain landform difference.
Background
In the construction application of the large-scale watershed distributed hydrological model, the method for dividing the computing units by adopting the sub-watersheds is a common method. Compared with pure grid unit division, the method has the advantages that hydrologic processes among all computing units can be kept relatively independent, and the number of the computing units is reduced. The sub-watershed division method assumes that the earth surface convergence process and the underground convergence process have the same watershed, and the earth surface and underground runoff production in the sub-watershed division method are converged to the river channel from the watershed and finally flow out of the sub-watershed. The method is suitable for mountainous areas because the underground watershed of the mountainous area is obvious. However, since the terrain is flat, there are no distinct watershed division boundaries between the units and no constant flow direction of surface groundwater, the surface water system is scattered, the flow direction of groundwater is not fixed, and a relatively active water exchange process also exists between the units on the surface and the underground, the terrain is not suitable for division of the computing units by sub-watersheds. For a large-scale drainage basin, a mountain area and a plain area exist in the drainage basin, and if the whole drainage basin is divided into computing units by adopting a single sub-drainage basin, the water circulation process of the plain area in the drainage basin cannot be accurately described; if only grid cells are used for scribing, the number of computing cells becomes very large, which may cause a computing dimension disaster.
Disclosure of Invention
The invention aims to provide a sub-basin unit dividing method considering the difference of mountain plain landforms, so as to solve the problems in the prior art.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a sub-basin unit dividing method considering mountain area plain landform difference comprises the following steps,
s1, calculating the flow direction and confluence cumulant of each grid in the flow field based on DEM data, and extracting a simulated river network based on a set river network threshold;
s2, setting the length of the plain unit, carrying out N × N size aggregation on the plain area and the peripheral grids thereof, and setting the label serial number of the plain unit for each N × N area;
s3, starting from a watershed outlet, taking a simulated river network grid as a backbone, tracing and traversing upwards, dividing a calculation unit according to the encountered grid type, and assigning a unique sub-watershed number to each divided unit, wherein the number is a natural number from 1; the divided units comprise plain units and mountain units;
s4, determining the flow direction between the adjacent plain units and the mountain area units by utilizing the grid flow direction information;
and S5, according to the flow direction relation between the plain unit and the mountain area unit, tracing and traversing from the river outlet unit to generate a sub-basin upstream and downstream topological relation table.
Preferably, the grid flow direction is calculated by using a D8 algorithm, namely, the flow direction of the grid flowing to the grid with the steepest gradient in the peripheral 8 grids is taken as the flow direction of the grid; the sum of the confluence accumulation of the grids is the sum of the upstream all the grids flowing into the current grid.
Preferably, the river network threshold is used for defining whether each grid belongs to a river network grid or a slope grid, and when the confluence accumulation amount of the grids is greater than the river network threshold, the grids are defined as the river network grids, otherwise, the grids are defined as the slope grids; and all the river network grids form a simulated river network, and the river network threshold value needs to ensure that the extracted simulated river network is consistent with the actual river network source in a source head area.
Preferably, step S2 specifically includes the following steps,
s21, setting the length of the plain unit as integral multiple of the length of the grid to ensure that the boundaries of the divided plain unit and the mountain area unit are matched;
s22, starting from the initial row and column of the grid image layer, performing accumulated traversal row by row and column by column according to the step length, checking N rows and N columns of N adjacent grids each time, if the number of the plain grids in the area is more than or equal to that of the mountainous area grids, marking the N rows and N columns as plain units, and setting the same plain unit marking serial numbers for all the grids in the area, wherein the serial numbers are natural numbers starting from 1; and if the number of the plain grids is less than that of the mountainous area grids, no processing is performed.
Preferably, the plain unit is a N × N grid type unit, the mountain unit is a sub-basin type unit determined according to a confluence path, and the plain unit comprises a plain river channel unit with a river channel therein and a plain slope unit without a river channel therein; the mountain area unit comprises a mountain area river channel unit with a river channel in the unit and a mountain area slope unit without a river channel in the unit.
Preferably, in step S3, different encoding processing modes are respectively used for the traceable traversed grids according to the attributes thereof; if the traversal starting grid is a mountain river grid, processing according to a mountain river grid coding mode; if the river channel grid is plain, processing according to a plain grid coding mode; traversing until the river source is finished;
the plain grid coding mode is that,
inquiring the plain unit mark serial number of the current plain grid, and assigning the same sub-basin number to the grids with the plain unit mark serial number equal to the grid plain unit mark serial number in the range of (2N-1) × (2N-1) around the plain unit; if the plain unit has a river channel grid, marking the plain unit as a plain river channel unit, otherwise, marking the plain unit as a plain slope unit;
taking the grid flowing into the plain unit as a starting point, performing traversal search again, and if the flowing grid is a plain grid, processing according to a plain grid coding mode; if the inflowing grid is a mountain river grid, processing according to a mountain river grid coding mode; if the inflowing grids are mountain slope grids, processing according to a mountain slope grid coding mode;
the mountain river grid coding mode is that,
tracing and traversing the river network grid until the grid is marked by an artificial division point, a bifurcation river channel or a plain unit, taking the traversed river network grid as a river reach, and assigning a sub-basin number; taking river channel grids in the river reach as a starting point, tracing slope grids until no upstream inflow grids exist or the upstream inflow grids serve as plain unit marking grids, assigning sub-basin numbers corresponding to the river channel grids to all the converged slope grids, forming a mountain area unit by all the river channel grids and the slope grids, and marking the type of the unit as a mountain area river channel unit;
if plain grids flow in at the upstream of the mountain river channel unit, processing according to a plain grid coding mode by taking each inflow plain grid as a starting point;
the grid coding mode of the hillside surface in the mountainous area is as follows,
and the method comprises the steps of only when the mountainous area slope grids flow into the plain unit grids, the mountainous area slope grid coding mode exists, searching all mountainous area slope grids flowing into the same plain unit, tracing and traversing the mountainous area slope grids flowing upstream by taking the mountainous area slope grids as a starting point until no upstream inflow grids or the upstream inflow grids are plain unit marking grids, classifying the traversed grids into the same mountainous area unit, wherein the sub-basin number of the traversed grids is equal to the sub-basin number of the inflow plain unit plus 1, and marking the unit type as the mountainous area slope unit.
If the upstream inflow grid is terminated as a plain unit in the mountain slope grid tracing traversal process, the encountered plain grid needs to be processed by adopting a plain grid coding mode.
Preferably, in step S4, the river type unit determines the upstream-downstream relationship between the units according to the flow direction of the river grid; the flow direction of the mountain slope unit is a plain unit where the grid of the outlet grid flow direction is located; determining the plain slope unit according to the plain slope unit flow direction determination rule;
the flow direction determining rule of the plain slope unit is that the elevation of the plain slope unit and the elevations of the peripheral units thereof are determined, and the gradient from the plain slope unit to the peripheral units is calculated by utilizing the elevation of the plain slope unit and the elevations of the peripheral units, so that the flow direction of the plain slope unit is the peripheral unit with the steepest flow direction gradient; and the gradient is the distance between the elevation of the plain slope surface unit and the elevation of the peripheral unit subtracted by the elevation of the plain slope surface unit.
Preferably, the elevation of the plain unit is equal to the average of the elevations of all grids in the unit; the elevation of the mountain area unit is the average value of the elevations of all grids directly adjacent to the plain slope surface unit in the mountain area unit.
Preferably, the distance between the plain unit and the peripheral plain unit is represented by centroid point straight line distance, the distance between the upper, lower, left and right adjacent units is 1 plain unit length, and the distance between the diagonal adjacent units is
Length of each plain unit;if the plain unit and the mountain area unit are only adjacent to each other by 1 edge, the length of the plain unit is expressed according to 1 length; if the plain unit and the mountain unit have a plurality of adjacent edges, then press
Individual plain unit length.
Preferably, the generated sub-watershed upstream and downstream topological relation table comprises a current sub-watershed code, a downstream sub-watershed code, an upstream sub-watershed code, a river slope unit mark and a plain mountain unit mark; a sub-basin number equal to 0 indicates no upstream or downstream sub-basins; the river slope unit mark is equal to 0 to indicate a slope, and equal to 1 to indicate a river; the plain mountain unit mark equal to 1 represents a slope, and equal to 0 represents a mountain.
The invention has the beneficial effects that: 1. the method is based on the DEM, considers the landform difference of the plain area of the mountain area, divides and codes the sub-basin, can ensure that the sub-basins obtained by division basically accord with the upstream and downstream relation among all units in the basin of the plain area, can aggregate small grids in the plain area into a large plain unit according to requirements to carry out sub-basin coding, and ensures the accuracy of sub-basin range division. 2. The method can better and more comprehensively depict the surface and underground water flow mechanisms of different landforms in the watershed, improve the hydrological simulation precision of the distributed hydrological model, and provide theoretical and practical support for the construction and application of the distributed hydrological model in the large-scale watershed.
Drawings
Fig. 1 is a schematic flow chart of a sub-basin dividing method according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a watershed to be divided of a plain area in an embodiment of the invention;
FIG. 3 is a schematic diagram of the plain range and plain index number in an embodiment of the present invention;
FIG. 4 is a flow chart of a plain grid coding mode according to an embodiment of the present invention;
FIG. 5 is a schematic flow chart of a mountain river grid coding mode according to an embodiment of the present invention;
FIG. 6 is a schematic flow chart of a mountain slope trellis encoding mode according to an embodiment of the present invention;
FIG. 7 is a schematic flow diagram of the flow direction between the units in the embodiment of the present invention;
FIG. 8 is a diagram illustrating sub-basin partitioning results according to an embodiment of the present invention;
fig. 9 is a representation of the upstream and downstream topological relations of the sub-watershed in the embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to the accompanying drawings. It should be understood that the detailed description and specific examples, while indicating the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.
As shown in fig. 1, the present invention provides a sub-basin unit division method considering mountain area plain landform difference, comprising the following steps,
s1, calculating the flow direction and confluence cumulant of each grid in the flow field based on DEM data, and extracting a simulated river network based on a set river network threshold;
s2, setting the length of the plain unit, carrying out N × N size aggregation on the plain area and the peripheral grids thereof, and setting the label serial number of the plain unit for each N × N area;
s3, starting from a watershed outlet, taking a simulated river network grid as a backbone, tracing and traversing upwards, dividing a calculation unit according to the encountered grid type, and assigning a unique sub-watershed number to each divided unit, wherein the number is a natural number from 1; the divided units comprise plain units and mountain units;
s4, determining the flow direction between the adjacent plain units and the mountain area units by utilizing the grid flow direction information;
and S5, according to the flow direction relation between the plain unit and the mountain area unit, tracing and traversing from the river outlet unit to generate a sub-basin upstream and downstream topological relation table.
In this embodiment, the sub-watershed division method of the present invention specifically includes the above five steps, and the following explains the specific contents of the five steps, respectively.
Firstly, extracting the simulated river network
The part is the content of the step S1, and the specific content of the step S1 is to calculate the flow direction of each grid in the flow domain by using a D8 algorithm based on the DEM data, set a river channel threshold value based on the flow direction calculation for each grid confluence accumulation number, and set the grid with the confluence accumulation number greater than the threshold value as a river network grid, thereby extracting a simulated river network.
The specific process of calculating the flow direction of each grid in the flow domain by adopting the D8 algorithm is to take the flow direction of the grid flowing to the grid with the steepest gradient in the 8 peripheral grids as the flow direction of the grid; the confluence accumulation amount of the grids is calculated as the sum of all the grids flowing into the current grid upstream.
In this embodiment, the river network threshold is used to define whether each grid belongs to a river network grid or a slope grid, and when the confluence cumulant of the grid is greater than the river network threshold, the grid is defined as the river network grid, otherwise, the grid is defined as the slope grid; all the river network grids constitute a simulated river network.
The specific value of the river network threshold is determined by a user, and the river network threshold needs to ensure that the extracted simulated river network is consistent with the actual river network source in a source head area; the value process of the river network threshold value is that the value is gradually increased from small to small through experiments until the extracted simulated river network is consistent with the actual river network source in the source head area.
Setting plain unit mark serial number
This part is the content of step S2, and step S2 includes the following two steps, as shown in fig. 2 and 3;
s21, setting the length of the plain unit as integral multiple of the length of the grid to ensure that the boundaries of the divided plain unit and the mountain area unit are matched;
the length of the plain unit is integral multiple (N times) of the DEM grid length, and the boundary of the divided plain unit is matched with the boundary of the mountain sub-watershed unit; the larger the unit length is, the smaller the number of plain units is, and the smaller the unit length is, the larger the number of plain units is. The length value of the plain unit is determined by user research, and is generally recommended to be 3-10 DEM grid lengths.
S22, starting from the initial row and column of the raster image layer, performing accumulation traversal row by row and column by step length, starting retrieval from the (1,1) raster, wherein the next row of retrieval raster is (N +1,1), the next column of retrieval raster is (1, N +1), and the like; checking N rows and N columns of N-N adjacent grids each time, if the number of the plain grids in the region is larger than or equal to that of the mountainous region grids, marking the N-N region as a plain unit, and setting the same plain unit marking serial numbers for all the grids in the region, wherein the serial numbers are natural numbers starting from 1; and if the number of the plain grids is less than that of the mountainous area grids, no processing is performed.
After the processing in step S2 is finished, a plain cell mark layer can be obtained, in which the grid identified as a plain cell in the layer has a serial number greater than 0, and no data is identified as a mountain area. The plain unit marking layer is mainly used for determining which grids belong to the same plain unit.
Specifically, in step S2, the plain area unit length may be set to be 5 Dem grid lengths, and traversal is performed row by row and column by column from the (1,1) grid according to 5 grid steps to mark the plain area unit. If the number of the plain grids in the range of 5-by-5 to be searched is more than or equal to that of the grids in the mountain area, assigning a plain unit mark serial number to all 25 grids, and if the number of the plain grids is less than that of the grids in the mountain area, assigning 0. The plain unit numbers are natural numbers that increase sequentially from 1.
Thirdly, numbering each unit in sub-basin
This step corresponds to step S3, and in step S3, the plain cells are the N × N lattice cells determined in step S2, the mountain cells are the sub-river basin cells determined from the confluence paths, and if there is a river in the cells, the mountain cells become river cells, and if there is no river, the mountain cells become slope cells. 4 small-class units are formed by intersecting plain units and mountain units; specifically, the plain units comprise plain river channel units with river channels in the units and plain slope units without river channels in the units; the mountain area unit comprises a mountain area river channel unit with a river channel in the unit and a mountain area slope unit without a river channel in the unit.
As shown in fig. 4 to fig. 6, in the present embodiment, the specific execution process of step S3 is to use different encoding processing modes for the traceable and traversed grids according to their attributes; if the traversal starting grid is a mountain river grid, processing according to a mountain river grid coding mode; if the river channel grid is plain, processing according to a plain grid coding mode; traversing until the river source is finished;
the plain grid coding mode is that,
inquiring the plain unit mark serial number of the current plain grid, and assigning the same sub-basin number to the grids with the plain unit mark serial number equal to the grid plain unit mark serial number in the range of (2N-1) × (2N-1) around the plain unit; if the plain unit has a river channel grid, marking the plain unit as a plain river channel unit, otherwise, marking the plain unit as a plain slope unit;
taking the grid flowing into the plain unit as a starting point, performing traversal search again, and if the flowing grid is a plain grid, processing according to a plain grid coding mode; if the inflowing grid is a mountain river grid, processing according to a mountain river grid coding mode; if the inflowing grids are mountain slope grids, processing according to a mountain slope grid coding mode;
the mountain river grid coding mode is that,
tracing and traversing the river network grid until meeting artificial division points (reservoirs, hydrological station position points and the like), a bifurcation river channel or plain unit marked grid, taking the traversed river channel grid as a river reach, and assigning a sub-basin number; taking river channel grids in the river reach as a starting point, tracing slope grids until no upstream inflow grids exist or the upstream inflow grids serve as plain unit marking grids, assigning sub-basin numbers corresponding to the river channel grids to all the converged slope grids, forming a mountain area unit by all the river channel grids and the slope grids, and marking the type of the unit as a mountain area river channel unit;
if plain grids flow in at the upstream of the mountain river channel unit, processing according to a plain grid coding mode by taking each inflow plain grid as a starting point;
the grid coding mode of the hillside surface in the mountainous area is as follows,
and the method comprises the steps of only when the mountainous area slope grids flow into the plain unit grids, the mountainous area slope grid coding mode exists, searching all mountainous area slope grids flowing into the same plain unit, tracing and traversing the mountainous area slope grids flowing upstream by taking the mountainous area slope grids as a starting point until no upstream inflow grids or the upstream inflow grids are plain unit marking grids, classifying the traversed grids into the same mountainous area unit, wherein the sub-basin number of the traversed grids is equal to the sub-basin number of the inflow plain unit plus 1, and marking the unit type as the mountainous area slope unit.
If the upstream inflow grid is terminated as a plain unit in the mountain slope grid tracing traversal process, the encountered plain grid needs to be processed by adopting a plain grid coding mode.
Specifically, step S3 may be performed according to the following procedure, starting from the watershed water outlet, traversing upward tracing with the simulated river network grid as a backbone, and performing computing unit partitioning according to the traversal grid attribute by using different encoding processing modes.
If the grid which starts traversing is a mountain river grid, calling a mountain river grid coding mode, continuously tracing and traversing upwards to find river network grids by taking the grid as a starting point until the grid is marked to be finished by artificial division points, bifurcation river channels and plain units, taking the traversed river grid as a river reach, assigning a sub-basin number, tracing the source and tracing the slope grids by taking each river grid as the starting point until no upstream inflow grid exists or the upstream inflow grid is marked to be the plain unit, assigning the sub-basin number to all slope grids, marking the unit type as a mountain river unit, and starting tracing and finding the next river reach after finishing one river reach.
If the grid at the beginning of traversal is a plain unit marking grid, calling a plain grid coding mode, assigning the same sub-basin number (the number is the front sub-basin number +1) to the grid with the plain unit marking serial number equal to the grid plain unit marking serial number in the range of (2N-1) × (2N-1), if the plain unit has a river channel grid, marking the plain unit as a plain river channel unit, otherwise, marking the plain unit as a plain slope unit; then, the grid flowing into the plain unit is taken as a starting point, traversal searching is carried out again, and if the inflow grid is a plain grid, a plain grid coding mode is recursively called for processing; if the inflow grid is a mountain river grid, recursively calling a mountain river grid coding mode for processing; and if the inflow grid is a mountain slope grid, recursively calling a mountain slope grid coding mode for processing.
Fourthly, determining the flow direction between the adjacent plain units and the mountain area units
This step corresponds to step S4, and as shown in fig. 7, the river type cells in step S4 determine the upstream-downstream relationship between the cells according to the flow direction of the river grid; the flow direction of the mountain slope unit is a plain unit where the grid of the outlet grid flow direction is located; determining the plain slope unit according to the plain slope unit flow direction determination rule;
the flow direction determining rule of the plain slope unit is that the elevation of the plain slope unit and the elevations of the peripheral units thereof are determined, and the gradient from the plain slope unit to the peripheral units is calculated by utilizing the elevation of the plain slope unit and the elevations of the peripheral units, so that the flow direction of the plain slope unit is the peripheral unit with the steepest flow direction gradient; and the gradient is the distance between the elevation of the plain slope surface unit and the elevation of the peripheral unit subtracted by the elevation of the plain slope surface unit.
In this embodiment, the elevation of the plain unit is equal to the average of the elevations of all the grids in the unit; the elevation of the mountain area unit is the average value of the elevations of all grids directly adjacent to the plain slope surface unit in the mountain area unit.
In this embodiment, the distance between the plain unit and the peripheral plain unit is represented by the centroid point linear distance, the distance between the upper, lower, left and right adjacent units is 1 plain unit length, and the distance between the diagonal adjacent units is
Length of each plain unit; if the plain unit and the mountain area unit are only adjacent to each other by 1 edge, the length of the plain unit is expressed according to 1 length; if the plain unit and the mountain unit have a plurality of adjacent edges, then press
Individual plain unit length.
Specifically, step S4 may be performed according to the following procedure, and the flow direction between all cells is determined according to the cell type. Determining the flow direction among the units by the river channel type units according to the topological relation of the river network water systems in the units; the mountain slope unit flows to a plain unit determined in the plain grid coding mode; for a plain slope unit, firstly determining the elevation of the plain slope unit and peripheral units thereof, secondly calculating the gradient from the plain slope unit to the peripheral calculation unit, and finally determining the flow direction of the plain slope unit as the direction from the plain slope unit to the gradient lowest unit, wherein the elevation of the plain slope unit is equal to the average elevation value of DEMs in the unit, and the elevation of a mountain area unit adjacent to the plain slope unit is equal to the average elevation value of a plurality of grids in the mountain area unit and directly adjacent to the plain slope unit.
Fifthly, generating an upstream and downstream topological relation table of the sub-basin
This step corresponds to step S5, and as shown in fig. 8 and 9, the sub-watershed upstream and downstream topological relation table generated in step S5 includes current sub-watershed codes, downstream sub-watershed codes, upstream sub-watershed codes (plural), river slope unit marks, and plain mountain unit marks; wherein a sub-basin number equal to 0 indicates no upstream or downstream sub-basins; the river slope unit mark is equal to 0 to indicate a slope, and equal to 1 to indicate a river; the plain mountain unit mark equal to 1 represents a slope, and equal to 0 represents a mountain.
By adopting the technical scheme disclosed by the invention, the following beneficial effects are obtained:
the invention provides a sub-basin unit dividing method considering mountain area plain landform difference, which is based on DEM and considers mountain area plain region landform difference to divide and encode sub-basins, so that the divided sub-basins can be ensured to basically accord with the upstream and downstream relation among units in a basin with a plain region, small grids in the plain region can be aggregated into a large plain unit according to requirements to carry out sub-basin encoding, and the accuracy of sub-basin range division is ensured. The method can better and more comprehensively depict the surface and underground water flow mechanisms of different landforms in the watershed, improves the hydrological simulation precision of the distributed hydrological model, and provides theoretical and practical support for the construction and application of the distributed hydrological model in the large-scale watershed.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and improvements can be made without departing from the principle of the present invention, and such modifications and improvements should also be considered within the scope of the present invention.
Claims (9)
1. A sub-basin unit division method considering mountain area plain landform difference is characterized by comprising the following steps: comprises the following steps of (a) carrying out,
s1, calculating the flow direction and confluence cumulant of each grid in the flow field based on DEM data, and extracting a simulated river network based on a set river network threshold;
s2, setting the length of the plain unit, carrying out N × N size aggregation on the plain area and the peripheral grids thereof, and setting the label serial number of the plain unit for each N × N area;
s3, starting from a watershed outlet, taking a simulated river network grid as a backbone, tracing and traversing upwards, dividing a calculation unit according to the encountered grid type, and assigning a unique sub-watershed number to each divided unit, wherein the number is a natural number from 1; the divided units comprise plain units and mountain units;
s4, determining the flow direction between the adjacent plain units and the mountain area units by utilizing the grid flow direction information;
s5, according to the flow direction relation between the plain unit and the mountain area unit, tracing and traversing from a river outlet unit to generate a sub-basin upstream and downstream topological relation table;
the step S2 specifically includes the following contents,
s21, setting the length of the plain unit as integral multiple of the length of the grid to ensure that the boundaries of the divided plain unit and the mountain area unit are matched;
s22, starting from the initial row and column of the grid image layer, performing accumulated traversal row by row and column by column according to the step length, checking N rows and N columns of N adjacent grids each time, if the number of the plain grids in the area is more than or equal to that of the mountainous area grids, marking the N rows and N columns as plain units, and setting the same plain unit marking serial numbers for all the grids in the area, wherein the serial numbers are natural numbers starting from 1; and if the number of the plain grids is less than that of the mountainous area grids, no processing is performed.
2. The sub-basin unit partitioning method considering difference in mountain area plain landform according to claim 1, wherein: calculating the grid flow direction by adopting a D8 algorithm, namely taking the flow direction of the grid flowing to the grid with the steepest gradient in the 8 peripheral grids as the flow direction of the grid; the sum of the confluence accumulation of the grids is the sum of the upstream all the grids flowing into the current grid.
3. The sub-basin unit partitioning method considering difference in mountain area plain landform according to claim 1, wherein: the river network threshold value is used for defining that each grid belongs to a river network grid or a slope grid, when the confluence cumulant of the grid is greater than the river network threshold value, the grid is defined as the river network grid, otherwise, the grid is defined as the slope grid; and all the river network grids form a simulated river network, and the river network threshold value needs to ensure that the extracted simulated river network is consistent with the actual river network source in a source head area.
4. The sub-basin unit partitioning method considering difference in mountain area plain landform according to claim 1, wherein: the plain unit is an N-N grid type unit, the mountain area unit is a sub-basin type unit determined according to a confluence path, and the plain unit comprises a plain river channel unit with a river channel in the unit and a plain slope unit without the river channel in the unit; the mountain area unit comprises a mountain area river channel unit with a river channel in the unit and a mountain area slope unit without a river channel in the unit.
5. The method for dividing sub-watershed units according to claim 4, wherein the sub-watershed units are divided according to mountain area plain geomorphic differences, and the method comprises the following steps: in step S3, different encoding processing modes are respectively used for the traceable traversed grids according to their attributes; if the traversal starting grid is a mountain river grid, processing according to a mountain river grid coding mode; if the river channel grid is plain, processing according to a plain grid coding mode; traversing until the river source is finished;
the plain grid coding mode is that,
inquiring the plain unit mark serial number of the current plain grid, and assigning the same sub-basin number to the grids with the plain unit mark serial number equal to the grid plain unit mark serial number in the range of (2N-1) × (2N-1) around the plain unit; if the plain unit has a river channel grid, marking the plain unit as a plain river channel unit, otherwise, marking the plain unit as a plain slope unit;
taking the grid flowing into the plain unit as a starting point, performing traversal search again, and if the flowing grid is a plain grid, processing according to a plain grid coding mode; if the inflowing grid is a mountain river grid, processing according to a mountain river grid coding mode; if the inflowing grids are mountain slope grids, processing according to a mountain slope grid coding mode;
the mountain river grid coding mode is that,
tracing and traversing the river network grid until the grid is marked by an artificial division point, a bifurcation river channel or a plain unit, taking the traversed river network grid as a river reach, and assigning a sub-basin number; taking river channel grids in the river reach as a starting point, tracing slope grids until no upstream inflow grids exist or the upstream inflow grids serve as plain unit marking grids, assigning sub-basin numbers corresponding to the river channel grids to all the converged slope grids, forming a mountain area unit by all the river channel grids and the slope grids, and marking the type of the unit as a mountain area river channel unit;
if plain grids flow in at the upstream of the mountain river channel unit, processing according to a plain grid coding mode by taking each inflow plain grid as a starting point;
the grid coding mode of the hillside surface in the mountainous area is as follows,
only when the mountainous area slope grids flow into the plain unit grids, the mountainous area slope grid coding mode exists, all mountainous area slope grids flowing into the same plain unit need to be searched, the mountainous area slope grids flowing into the upstream are traced and traversed by taking the mountainous area slope grids as a starting point until no upstream inflow grids or the upstream inflow grids are plain unit marking grids, the traversed grids are classified into the same mountainous area unit, the sub-basin number of the traversed grids is equal to the sub-basin number of the inflow plain unit plus 1, and the unit type is marked as a mountainous area slope unit;
if the upstream inflow grid is terminated as a plain unit in the mountain slope grid tracing traversal process, the encountered plain grid needs to be processed by adopting a plain grid coding mode.
6. The method for dividing sub-watershed units considering difference in mountain area plain landforms according to claim 5, wherein: in step S4, determining the upstream and downstream relationship between the cells according to the flow direction of the river grid by the river type cell; the flow direction of the mountain slope unit is a plain unit where the grid of the outlet grid flow direction is located; determining the plain slope unit according to the plain slope unit flow direction determination rule;
the flow direction determining rule of the plain slope unit is that the elevation of the plain slope unit and the elevations of the peripheral units thereof are determined, and the gradient from the plain slope unit to the peripheral units is calculated by utilizing the elevation of the plain slope unit and the elevations of the peripheral units, so that the flow direction of the plain slope unit is the peripheral unit with the steepest flow direction gradient; and the gradient is the distance between the elevation of the plain slope surface unit and the elevation of the peripheral unit subtracted by the elevation of the plain slope surface unit.
7. The method for partitioning sub-watershed units according to claim 6, wherein the sub-watershed units are divided according to the difference of mountain plain landforms, and the method comprises the following steps: the elevation of the plain unit is equal to the average value of the elevations of all grids in the unit; the elevation of the mountain area unit is the average value of the elevations of all grids directly adjacent to the plain slope surface unit in the mountain area unit.
8. The sub-watershed considering difference in mountain plain landform according to claim 6The unit dividing method is characterized in that: the distance between the plain unit and the peripheral plain unit is represented by centroid point straight line distance, the distance between the upper, lower, left and right adjacent units is 1 plain unit length, and the distance between the diagonal adjacent units is
Length of each plain unit; if the plain unit and the mountain area unit are only adjacent to each other by 1 edge, the length of the plain unit is expressed according to 1 length; if the plain unit and the mountain unit have a plurality of adjacent edges, then press
Individual plain unit length.
9. The sub-basin unit partitioning method considering difference in mountain area plain landform according to claim 1, wherein: the generated sub-basin upstream and downstream topological relation table comprises a current sub-basin code, a downstream sub-basin code, an upstream sub-basin code, a river slope unit mark and a plain mountain unit mark; a sub-basin number equal to 0 indicates no upstream or downstream sub-basins; the river slope unit mark is equal to 0 to indicate a slope, and equal to 1 to indicate a river; the plain mountain unit mark equal to 1 represents a slope, and equal to 0 represents a mountain.
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