CN112242003A - City sub-catchment area division method considering land type and flow direction - Google Patents
City sub-catchment area division method considering land type and flow direction Download PDFInfo
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Abstract
The invention discloses a method for dividing urban sub-catchment areas considering the land types and the flow direction, which comprises the following steps of S1, preliminarily dividing an urban research area into a plurality of primary catchment areas by taking a main river with an actual drainage function of a drainage basin as a dividing boundary according to the natural topography condition of the urban research area and the confluence relation among rivers; and S2, according to the division result of the primary catchment areas, taking primary and secondary trunk roads with drainage pipes distributed on two sides and a main channel with a drainage function as division boundaries, dividing each primary catchment area into units with relatively independent medium sizes, and acquiring a plurality of secondary catchment areas. The advantages are that: the analysis requirement of regional large-scale ponding is fully considered, the regional large-scale catchment area division is realized by utilizing the iteration determination algorithm, the regional large-scale catchment area division method is suitable for the regional large-scale catchment area fine division, the division result is consistent with the real land class distribution, and the method has good feasibility.
Description
Technical Field
The invention relates to the technical field of catchment area division, in particular to a city sub-catchment area division method considering the land type and the flow direction.
Background
In recent years, with the aggravation of global climate change and the rapid development of urbanization, urban inland inundation disasters are frequent and wide, the life and property safety of urban public infrastructure and residents is seriously threatened, and the importance of increasing urban rainstorm flood management and forecasting and early warning is increased. The catchment area division is used as an important link and a key step of urban rainstorm flood early warning, and the rationality of the division greatly influences the accuracy of rainstorm waterlogging prediction. Therefore, how to accurately and reasonably determine the boundary of the catchment area has important significance for realizing better urban waterlogging disaster management and prediction.
The catchment area division method mainly comprises a hydrological analysis method based on a Digital Elevation Model (DEM) and a geometric method based on nodes. The hydrological analysis method based on the DEM generally extracts the flow direction of a basin by means of the DEM and based on algorithms such as D8 and the like, and then divides a catchment area; however, when the method is applied to a flat terrain region, the flow direction of water flow is consistent to generate a parallel pseudo river channel, and the extracted catchment region boundary has great difference with the actual situation, so that a RIDEM model is provided for truly reflecting the distribution of the catchment region in the flat city region. The hydrological analysis method based on the DEM fully considers the influence of natural terrains on the flow direction of water flow, but neglects the effect of an urban internal drainage system and a pipe network on confluence. Node-based geometric squareThe method has the main idea that a water catchment area is determined by using a Voronio algorithm based on the spatial distribution of rainwater wells in drainage pipelines, and the method is simple and feasible and fully considers the evacuation effect of artificial drainage facilities on urban accumulated water; however, since this method is based only on a geometric method, natural topographic conditions are not considered in the dividing process, which tends to cause the confluent flow direction in the sub-flow domain to be different from the actual flow direction. Before about 2015, most studies have focused on a single method for catchment division, but urban drainage is a combination of drainage pipe systems and terrain, and in recent years, some scholars try to combine the two methods for catchment division. Such as Huang et al (2019), combine two methods, surrounding a small scale (less than 10 km) in the region2) Based on a Voronoi graph algorithm, a catchment area division method comprehensively considering a natural DEM and an artificial rainwater well is provided.
However, although the existing latest method (the two methods are combined to divide the catchment area) comprehensively considers the natural surface catchment nodes and the catch basins, the catch basins in the city are not uniformly distributed, and when a catch basin Voronoi diagram is established, the areas with too low catch basin density are directly divided by overlapping the natural catchment nodes with different functions from the catch basins, so that the division result is easy to have great uncertainty; in addition, rainwater wells in urban central areas are generally high in density, which has little influence on small-scale research in the areas, however, when the rainwater wells are applied to large-scale research in the areas, the division results cannot be practically applied due to the excessive number of polygons. In addition, when the latest method is used for catchment areas, the catchment areas are simply and geometrically divided mainly through a Voronio algorithm, so that the division result of the microscopic catchment areas and the real surface runoff of the complex underlying surface have deviation, and the same building is divided into a plurality of catchment areas.
Disclosure of Invention
The invention aims to provide a method for dividing a sub-catchment area of a city by considering the land type and the flow direction, thereby solving the problems in the prior art.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a method for dividing the sub-catchment area of city in consideration of land class and flow direction includes such steps as providing a water tank,
s1, preliminarily dividing the urban research area into a plurality of primary catchment areas by taking a main river with an actual drainage function of a basin as a dividing boundary according to the natural topography of the urban research area and the confluence relation among rivers;
s2, according to the division result of the primary catchment areas, taking primary and secondary trunk roads with drainage pipes distributed on two sides and a main channel with a drainage function as division boundaries, dividing each primary catchment area into units with relatively independent medium sizes, and obtaining a plurality of secondary catchment areas;
s3, carrying out flow direction analysis on the corrected DEM of the urban research area, determining a main flow direction and a water converging point, and dividing each secondary water converging area based on the main flow direction and the water converging point to obtain a primary tertiary water converging area;
and S4, establishing a three-level catchment area fine division iterative algorithm by combining the surface type of the urban research area, and finely dividing the primary three-level catchment area to obtain a three-level fine sub-catchment area.
Preferably, in step S3, the modified DEM of the urban area of interest is obtained by,
Ea＝Ei+H
wherein E isaCorrection of DEM elevation values for urban research areas, EiThe original DEM elevation value of the urban research area is shown, and H is the height of the corresponding building.
Preferably, step S3 specifically includes the following steps,
s31, filling and digging the corrected DEM of the urban research area by using a hydrological analysis tool, sequentially calculating the elevation difference of the DEM of the center grid of the corrected DEM of the urban research area to the eight directions of the east, south, west, north, southeast, northeast, southwest and northwest of the periphery based on a D8 algorithm, and determining the descending direction with the largest difference as the water flow direction of the center grid;
s32, calculating the number of grids on the upstream of the central grid, through which water flows, and determining the water catchment amount of the grids, and connecting the grids with the water catchment amount higher than the water catchment threshold value to form a water catchment ridge line, wherein the junction point of the water catchment ridge line is the water catchment point;
and S33, dividing all grids contained in the catchment ridgelines with the same flow direction into the same independent catchment area by taking the catchment point as a starting point, namely obtaining a primary three-level catchment area.
Preferably, step S4 specifically includes the following steps,
s41, calculating and acquiring the area of each land type map spot by superposing the ground surface types of the primary three-level catchment area and the urban research area;
s42, calculating the ratio of the area of a certain geographical pattern spot to the total area of the primary three-level catchment area where the geographical pattern spot is located, judging the size relation between the ratio and the area ratio threshold of the geographical pattern spot, if the ratio is larger than or equal to the area ratio threshold of the geographical pattern spot and the number of rainwater wells existing within the preset distance threshold of the periphery of the geographical pattern spot is larger than 0, determining that the geographical pattern spot is a single sub-catchment area, and dividing the geographical pattern spot into sub-catchment areas separately to obtain three-level fine sub-catchment areas; if the ratio is smaller than the area ratio threshold of the land type pattern spots, the land type pattern spots are mixed sub-catchment areas, topological association and combination are carried out on the land type pattern spots and the adjacent land type pattern spots, and three-level fine sub-catchment areas are obtained;
and S43, repeating the step S42, traversing all the ground type map spots until the area of all the three-level fine sub-catchment areas is larger than or equal to the area ratio threshold of the ground type map spots or the number of catch basins existing in the single ground type map spots is larger than 0 or the flow directions of the adjacent ground type map spots are different, ending iteration, and finishing the division of the three-level fine sub-catchment areas.
Preferably, the surface types include lawns, forests, arable land, wastelands, buildings, and square roads; the sub-catchment areas comprise lawn sub-catchment areas, forest sub-catchment areas, building sub-catchment areas and square sub-catchment areas.
Preferably, the rule function for topologically associating and merging the geographical class pattern spot and the adjacent geographical class pattern spots is expressed as,
Merge(i,j)＝f(AreaSNeiij,Rainwaterij,Directionij,SemNeiij)
wherein i is 1,2, …, m is groundThe total number of pattern-like patches; j is 1,2, …, n, n is the total number of adjacent ground class patches j of the ground class patch i; AreaSNeiijThe area ratio of the adjacent land type image spots j of the land type image spot i, the DirectionijThe included angle between the flow direction of the geo-graphic spot i and the flow direction of the adjacent geo-graphic spot j is RainwaterijSemNei is the number of catch basins and catch basins between the geographical pattern spot i and the adjacent geographical pattern spot jijThe semantic proximity of the land type image spot i and the adjacent land type image spot j is obtained;
the semantic proximity mathematical model is expressed as
Wherein L isiAnd LjThe land type corresponding to the land type image spot i and the adjacent land type image spot j respectively, and x is equal to LiNumber of ground class categories with semantic proximity, Distance (L)i,Lj) Is a position in the semantic neighborhood class set;
the topological association and merging rule function of the geographic class spot i and the adjacent geographic class spot j is expressed as:
wherein, delta is a land pattern spot area ratio threshold; w is a1And w2Respectively representing the weight of the corresponding index.
The invention has the beneficial effects that: 1. when the method is used for catchment areas, the dual functions of urban macroscopic natural terrains and artificial construction drainage facilities on drainage are considered, and the influence of real surface type distribution on surface runoff is also fully considered, so that the catchment area division is more consistent with the real drainage scene. 2. The accuracy of catchment area division is improved, and through threshold value setting and iteration, the problem that catchment area division is too fine and broken to cause practical application to the hydrological model under the large scale in the area is still solved. 3. The analysis requirement of regional large-scale ponding is fully considered, the regional large-scale catchment area division is realized by utilizing the iteration determination algorithm, the regional large-scale catchment area division method is suitable for the regional large-scale catchment area fine division, the division result is consistent with the real land class distribution, and the method has good feasibility. 4. The method can reflect the spatial heterogeneity of the large-scale catchment units in the area, and is obviously superior to the existing catchment area division method in the aspects of keeping the distribution with real land types and the consistency of the surface flow direction.
Drawings
FIG. 1 is a flow chart illustrating a partitioning method according to an embodiment of the present invention;
FIG. 2 is a schematic diagram illustrating a division of a primary catchment area according to an embodiment of the present disclosure;
FIG. 3 is a schematic diagram illustrating the division of a secondary catchment area according to an embodiment of the present disclosure;
FIG. 4 is a schematic illustration of a building height based DEM correction in an embodiment of the present invention;
FIG. 5 is a schematic diagram of the preliminary three-level catchment area division based on the flow direction in the embodiment of the present invention;
FIG. 6 is a schematic diagram of a single catchment area and a mixed catchment area according to an embodiment of the present disclosure;
FIG. 7 is a schematic diagram of three-level fine sub-catchment areas and an upstream-downstream relationship according to an embodiment of the present disclosure;
FIG. 8 is a diagram illustrating a result of dividing a catchment area of an urban research area according to an embodiment of the present invention;
FIG. 9 is a schematic diagram of comparing the flow directions of the original DEM and the corrected DEM in the embodiment of the invention
FIG. 10 is a schematic diagram showing the comparison between the Huang (2019) partition method and the partition method according to the present invention;
fig. 11 is a schematic diagram illustrating that the dividing method of the present invention is adopted to divide different flow direction fields into different catchment areas 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.
Example one
As shown in fig. 1, in the present embodiment, a method for dividing a sub-catchment area of a city considering land type and flow direction is provided, which includes the following steps,
s1, preliminarily dividing the urban research area into a plurality of primary catchment areas by taking a main river with an actual drainage function of a basin as a dividing boundary according to the natural topography of the urban research area and the confluence relation among rivers;
s2, according to the division result of the primary catchment areas, taking primary and secondary trunk roads with drainage pipes distributed on two sides and a main channel with a drainage function as division boundaries, dividing each primary catchment area into units with relatively independent medium sizes, and obtaining a plurality of secondary catchment areas;
s3, carrying out flow direction analysis on the corrected DEM of the urban research area, determining a main flow direction and a water converging point, and dividing each secondary water converging area based on the main flow direction and the water converging point to obtain a primary tertiary water converging area;
and S4, establishing a three-level catchment area fine division iterative algorithm by combining the surface type of the urban research area, and finely dividing the primary three-level catchment area to obtain a three-level fine sub-catchment area.
In the embodiment, the invention provides a dividing method for realizing accurate division of a large-scale catchment area in an area, aiming at the problems that the existing dividing method is different from the actual earth surface type distribution and a large-scale catchment area dividing method in an adaptive area is lacked. The method comprises the steps of firstly, carrying out preliminary catchment area division on an area based on distribution such as terrain, main canals and pipe networks, and then according to a preliminary division result, realizing the accurate division of the catchment area with large scale by establishing a catchment area fine division iterative algorithm. Specifically, the dividing method comprises three parts, namely macroscopic scale first-level catchment area division based on natural topography, secondary catchment area division based on main canals and pipe networks, and microscopic scale third-level catchment area division based on land types and flow directions. The following describes the division process for the above three parts.
First, based on the natural topography the macro scale first grade catchment area division (the specific division process can refer to figure 2)
The partial content corresponds to step S1 in the dividing method; the urban first-level drainage system is responsible for draining rainstorm and waterlogging water of a large area to the outside of a river and generally consists of a main river network in the area. The main river network integrally divides the urban area to form a plurality of independent natural catchment blocks. Based on the situation, the primary catchment area division is mainly based on the urban natural topography situation and the convergence relation among regional rivers, a main river (Stream-M) with an actual drainage function of a drainage basin is used as a division boundary, the area is preliminarily divided into a plurality of catchment areas, and the divided catchment areas are ensured to accord with the main river division characteristics under the urban natural topography. As shown in fig. 2, the main river of the urban research area is a dividing boundary, and the urban research area can be divided into A, B, C, D, E five First Level-sinks (FL sinks).
Secondly, dividing a secondary catchment area based on a main canal and a pipe network (the specific dividing process can refer to figure 3)
The partial content corresponds to step S2 in the dividing method; the influence of urban terrain and ground feature factors is fully considered in the division of the primary catchment area, but the natural terrain of the city is changed in the construction process, and the urban catchment characteristics are influenced by the macroscopic terrain and are limited and guided by the artificial construction drainage system. Compared with natural surface runoff, the surface runoff in urban areas has strong spatial heterogeneity, and the runoff flow direction can be generally changed under the influence of an artificial impervious surface. The urban secondary drainage system is responsible for draining rainwater in areas such as urban streets into a main river network and generally comprises a rainwater pipe network or an artificial main canal and the like. The underground pipe networks distributed on two sides of the primary and secondary main roads are often main channels for surface runoff and underground drainage of local areas, have functions similar to natural river channels or drainage main channels, and play an important role in the local drainage process. The invention provides a secondary catchment area dividing method (SL catch) based on a drainage main channel and a pipe network, which mainly divides a research area into units with relatively independent medium scales according to a main channel and a secondary main channel with drainage pipes distributed on two sides and a main channel with a drainage function as dividing bases. Because most of the drainage pipe networks are buried at two sides of the main and secondary trunk roads, the division result of the secondary catchment area is mainly embodied as the division of the main and secondary trunk roads and the branch water system. Fig. 3 shows the secondary catchment area division of the primary catchment area C, and the secondary catchment area division of the main canals and the pipe network can effectively ensure the uniformity of the subsequent catchment area division.
Third, micro-scale three-level catchment area division based on land type and flow direction
The partial content corresponds to steps S3 and S4 in the dividing method. The three-level sub-catchment area is the minimum unit for constructing the hydrological model, and the dividing accuracy of the three-level sub-catchment area directly influences the precision of an analysis result. In order to ensure that the catchment area division result is consistent with the real land type, the invention combines the terrain flow direction and the fine land utilization type to carry out three-level catchment area division. Firstly, based on a modified DEM, utilizing a D8 algorithm to perform flow Direction analysis, determining a main flow Direction, and dividing a secondary catchment area based on the main flow Direction to obtain a primary tertiary catchment area (D-B catch); and then, establishing a three-level catchment area fine division iterative algorithm by combining the surface type, and finely dividing the D-B catch to finally obtain the catchment area with the minimum unit. The specific third part comprises the following contents:
1. correcting DEM (refer to figure 4 for the specific correction process)
The surface runoff process and the runoff direction in urban areas are determined by the terrain and are influenced by factors such as buildings, roads, main canals and the like. The invention refines and corrects the original DEM in consideration of the influence of the urban underlay on a path flow path, and has the basic idea that different ground feature information influencing a confluence path is merged into the DEM, and the water catchment capacity of grids is changed by artificially increasing or reducing a certain height or proportion of the elevation value of grid points of the DEM containing the ground feature information, so that the aim of reflecting the space state of a drainage system is fulfilled. Because the influence of roads and main canals on the runoff is fully considered when the secondary catchment area is divided, the influence of building distribution on the runoff is only considered when the DEM is corrected.
Then, in step S3, a modified DEM of the urban area of interest is obtained by,
Ea＝Ei+H
wherein，EaCorrection of DEM elevation values for urban research areas, EiThe original DEM elevation value of the urban research area is shown, and H is the height of the corresponding building.
2. Flow direction-based three-level catchment area preliminary division (the specific division process can refer to FIG. 5)
The partial content corresponds to the content of step S3, and specifically includes
S31, analyzing the flow direction; filling and digging the corrected DEM of the urban research area by using an ArcGIS hydrological analysis tool, sequentially calculating the elevation difference of the DEM of the center grid of the corrected DEM of the urban research area to the eight directions of the surrounding east, south, west, north, southeast, northeast, southwest and northwest based on a D8 algorithm, and determining the descending direction with the largest difference as the water flow direction of the center grid;
s32, extracting a catchment point; calculating the number of grids at the upstream of the central grid, which the water flow of the grids passes through, determining the water catchment amount of the grids, and connecting the grids with the water catchment amount higher than the water catchment threshold value to form a water catchment ridge line, wherein the junction point of the water catchment ridge line is a water catchment point; in the flow direction extraction, the confluence threshold can influence the selection result of the main water flow and the branch flow, so that the optimal confluence threshold 1000 is selected through multiple experiments.
S33, dividing a primary third-level catchment area; and dividing all grids contained in the catchment ridgelines with the same flow direction into the same independent catchment area by taking the catchment point as a starting point, namely obtaining a primary third-level catchment area (D-B catch).
3. Three-level catchment area fine division based on land class (refer to fig. 6 and 7 for concrete division process)
In order to reflect the distribution of the urban catchment area more truly, the method combines the high-precision land utilization type data and rainwater well distribution data to establish a catchment area fine division iterative algorithm, and finely divides the D-B catch catchment area to obtain a minimum catchment unit (S-catch), namely a three-level fine sub-catchment area. Specifically, the following contents are included
S41, overlapping the primary third-level catchment area and the city research areaTable type, calculating Area of each land type pattern spoti(ii) a Where i represents the ith terrain-like spot. The landmark types mainly include 6 types, lawn, forest, farmland, wasteland, building and square road.
S42, calculating Area of certain map spotiThe ratio of the area of the primary three-level catchment area D-B catch to the area of the area AreaShareiJudging the size relation between the ratio and a ground type pattern spot area ratio threshold, if the ratio is greater than or equal to the ground type pattern spot area ratio threshold and the number of rainwater wells existing within the preset distance threshold around the ground type pattern spot is greater than 0, then the ground type pattern spot is a single sub-catchment area, and the ground type pattern spot is divided into sub-catchment areas separately to obtain three-level fine sub-catchment areas; if the ratio is smaller than the area ratio threshold of the land type pattern spots, the land type pattern spots are mixed sub-catchment areas, topological association and combination are carried out on the land type pattern spots and the adjacent land type pattern spots, and three-level fine sub-catchment areas are obtained; wherein the Area of the ground pattern spotiThe ratio of the area of the primary three-level catchment area D-B catch to the area of the area AreaShareiThe formula for calculating (a) is as follows,
wherein m is the total number of the land type pattern spots, and Area is the total Area of the catchment Area of the primary third-level catchment Area D-B catch where the ith land type pattern spot is located. The preset distance threshold may be set to 100 meters.
Based on area ShareiAnd determining a single catchment area and a mixed catchment area. In order to avoid that the sub-catchment areas in the area are divided into too small areas to influence the operation of a subsequent hydrological model, the area ratio threshold delta of the terrain-like pattern is defined in the invention, and when the area is shapediWhen the number of rainwater wells within 50m of the periphery is more than 0, the map spot i of the land is a single sub-catchment area (such as an area A in figure 6), and the sub-catchment areas need to be divided independently, wherein the sub-catchment areas comprise a lawn sub-catchment area, a forest sub-catchment area, a building sub-catchment area and a square sub-catchment area; the invention combines the actual situation of the research area with a large number of experiments to ensureThe area occupying threshold δ of the map-like patch of the localization is 0.15. If AreaShareiIf the area is less than delta, the geographical map spot i and the adjacent geographical map spot j are subjected to topological association and merging to form a mixed catchment area (such as an area B in the figure 6).
And S43, repeating the step S42, traversing all the ground type map spots until the area of all the three-level fine sub-catchment areas is larger than or equal to the area ratio threshold of the ground type map spots or the number of catch basins existing in the single ground type map spots is larger than 0 or the flow directions of the adjacent ground type map spots are different, ending iteration, and finishing the division of the three-level fine sub-catchment areas.
In this embodiment, the rule function for topologically associating and merging the geographical map spots and the neighboring geographical map spots is expressed as,
Merge(i,j)＝f(AreaSNeiij,Rainwaterij,Directionij,SemNeiij)
wherein i is 1,2, …, m is the total number of the map spots; j is 1,2, …, n, n is the total number of adjacent ground class patches j of the ground class patch i; AreaSNeiijThe area ratio of the adjacent land type image spots j of the land type image spot i, the DirectionijThe included angle between the flow direction of the geo-graphic spot i and the flow direction of the adjacent geo-graphic spot j is RainwaterijSemNei is the number of catch basins and catch basins between the geographical pattern spot i and the adjacent geographical pattern spot jijThe semantic proximity of the land type image spot i and the adjacent land type image spot j is obtained;
the semantic proximity mathematical model is expressed as
Wherein L isiAnd LjThe land type corresponding to the land type image spot i and the adjacent land type image spot j respectively, and x is equal to LiNumber of ground class categories with semantic proximity, Distance (L)i,Lj) Is a position in the semantic neighborhood class set; the semantic positions in the invention are arranged according to lawns, woods, square roads, buildings, cultivated lands and wastelands, and the semantic distance between adjacent elements is regulated to be 1 unit, such as lawns and broadside fieldsThe semantic location of the field road is 2 units.
The topological association and merging rule function of the geographic class spot i and the adjacent geographic class spot j is expressed as:
wherein, delta is a land pattern spot area ratio threshold; w is a1And w2Respectively representing the weight of the corresponding index; the weight assignment uses objective weight assignment CRITIC.
In this embodiment, after the dividing method is executed, the upstream and downstream relationships of the sub-catchment areas are added according to the water flow direction in the S-catch catchment area, so as to provide information for the subsequent calculation of the hydrological model. The dividing method not only improves the dividing precision of the catchment area, but also solves the problem that the catchment area cannot be practically applied to the hydrological model due to too fine division under large scale in the area through threshold setting and iteration.
Example two
The invention relates to a method for dividing a catchment area by taking the eastern region of the eastern campsite of the eastern campcity as an experimental sample area, wherein the area of the catchment area is 44 square kilometers, and the method belongs to a large-scale area for the research of the catchment area division. The east-Ying region is located in the northeast of Shandong province and is a central region of east-Ying city, the east-Ying region spans the east longitude 118 degrees 12 '42' to 118 degrees 59 '52', the northern latitude 37 degrees 14 '13' to 37 degrees 31 '57', the east-endanger Bohai sea and the West-Yihuang river and mainly comprises two parts, namely the east city and the West city, wherein the east city built-up region is a main test region of the invention. The mid-latitude of the east campsite is affected by the continental Asia and the western Pacific, belongs to the continental monsoon climate in the warm zone, the rainfall is mostly concentrated in summer and accounts for 65% of the annual rainfall, and the urban landscaping is very easy to suffer from inland inundation disasters in summer. The terrain of a research area is flat, the average height of the ground is 6-8 meters, the area is an area with developed urbanization and suburbs of farmlands, and multiple land utilization types coexist.
The test data adopted by the invention mainly comprises: (1) basic geographic data: land use types, road vector data, water system vector data, 0.05m high-resolution remote sensing images and 0.5m resolution DEM data, and are from the natural resource bureau in the Dongying city. (2) Pipe network data: data such as pipelines (15151), inspection wells (15791), discharge ports (147) in main cities of the eastern camp city are from the gas station of the eastern camp city.
1. Overall catchment area division result
FIG. 8 shows the result of dividing the first, second and third grade fine catchment areas of the east-rural areas by the method of the present invention. Wherein, fig. 8(a) shows the division result of the primary and secondary catchment areas; FIG. 8(b) shows the result of dividing the three-level fine sub-catchment areas; the water catchment area is divided into regular boundaries, the distribution of the water catchment area is consistent with the distribution of the boundaries of rivers, road networks, drainage pipe networks and buildings in the research area, and the method not only considers the dual functions of urban macroscopic natural terrains and artificial construction drainage facilities on drainage, but also fully considers the influence of real surface type distribution on surface runoff, so that the water catchment area division is more consistent with the real drainage situation.
The divided catchment areas of the invention comprise 4 primary catchment areas, 111 secondary catchment areas and 804 tertiary minimum catchment areas, wherein the maximum catchment area is 72.86hm2Minimum area of 0.28hm2. It should be noted that the catchment area unit with a large area is mainly of land utilization type such as water system pool, wetland and the like, and the area range of other catchment units except for the special land types is 0.28hm2～25.63hm2And the root mean square difference is 3.18, which shows that the overall geometric shape of the catchment area divided by the method is more uniform. The divided catchment areas are relatively small in the central urban area and relatively large in the urban and rural boundary area, and the indication shows that the spatial heterogeneity of surface runoff is reflected to a certain extent by the catchment areas divided by the method. Furthermore, the present invention is directed to 44km2The large-scale catchment area in the area is moderate in dividing quantity and can be directly and practically applied to a subsequent hydrological model.
2. Local area method comparison and discussion
In order to verify the reliability of the method in more detail, namely the catchment area division result is consistent with the real land type and runoff, the flow direction analysis result of the original DEM and the corrected DEM by using the land type, Huang et al (2019) and the catchment area division result of the method are compared by using a Voronio algorithm.
(1) Comparison of original DEM and corrected DEM flow direction
In order to more clearly reflect the influence of the original DEM and the corrected DEM on the flow direction, the invention selects an area containing artificial facilities as a comparison area, for example, FIG. 9(a) shows the flow direction generated based on the original DEM, and FIG. 9(b) shows the flow direction generated based on the terrain-based corrected DEM. It is obvious from the black frame of the figure that the flow direction based on the original DEM directly passes through the interior of the building and is not consistent with the real surface runoff, which is mainly because the height of the building is not considered by the original DEM, the blocking effect of the building on the surface runoff can not be reflected. And because the ground surface height corresponding to the artificial building area is increased based on the DEM after the land type correction, the blocking effect of the building on the surface runoff can be well reflected, and the flow direction extraction effect is more consistent with the actual runoff. However, it should be noted that when the flow direction analysis is performed, the DEM correction is not performed on other artificial facilities such as roads, and this is because it is considered that the drainage pipe network is generally buried under the trunk road, and when the secondary catchment area is divided, the catchment area is fully divided by fully combining the roads and the pipe network, so that the DEM correction is not performed on the road area in the flow direction analysis.
(2) Water catchment division based on Voronio algorithm is compared with the method of the invention
Considering that the research area of the invention is larger, the quantity of rainwater wells is larger, and the dividing of the catchment area by using the Huang et al (2019) method is easy to cause the breakdown of a computer, the invention selects 1.6km in the urban research area2And carrying out result comparison analysis on the subareas. As shown in fig. 10(a), which is a catchment area divided by the Huang et al (2019) method, it can be seen that at least one catch basin or natural catchment point in each catchment area is used as a drainage point, which illustrates that the method effectively takes account of the influence of the natural earth surface and artificial drainage facilities on earth surface confluence. However, as can be seen from the enlarged black and white areas, the division method is very easy to divide the same building, forest surface and other irregularities into a plurality of catchment areas, resulting in the division result and realityThe distribution of the real land types is inconsistent; and the rainwater wells are not uniformly distributed, so that the divided catchment area units are irregular in geometric shape. Furthermore, although Huang et al (2019) considers natural catchment points (with flow direction characteristics) as dividing nodes, simple Voronio subdivision still easily causes the phenomenon of different surface flow directions in the same catchment area, which all cause deviation of catchment units from real surface runoff.
Fig. 10(b) shows the catchment areas divided based on the method of the present invention, and it is obvious that the positions of the catchment areas are the same as those of the Huang et al (2019), and each catchment area has a drainage point corresponding to a rainwater well or a pipeline, which shows that the dividing result can represent a real urban drainage situation. The difference is that the catchment areas divided based on the method are consistent with the main rivers and the main road boundaries in the areas, and the same land types which are continuously distributed are basically not divided into a plurality of catchment areas, so that the consistency of the distribution of the complex underlying surface and the real land types is effectively ensured. Meanwhile, the method also accurately considers the real flow direction of the earth surface, even if two earth classes are adjacent, the earth surface flow direction is regularly divided into two different catchment areas (such as two plots in fig. 11, the general flow directions of the plots are opposite directions, and the white arrows indicate) due to different earth surface flow directions. In addition, by setting the area threshold of the land pattern spots and considering factors such as catch basins among the land pattern spots, the divided catchment area units have regular geometric shapes and can reflect the spatial heterogeneity of surface runoff; the iterative determination method can also effectively solve the problem that the catchment area division is too fine and broken to be practically applied to the hydrological model under the large scale of the area. Table 1 shows the inventive method in comparison to the Huang et al (2019) catchment division method.
TABLE 1 comparison of catchment area division methods
3. Conclusion
Catchment area division is a precondition and a key link for urban rainstorm flood early warning, and the accuracy of division has great significance for high-precision prediction of urban rainstorm waterloggingIt has important meaning. In the existing method, although the influence of natural terrains and artificial pipelines on the catchment area can be comprehensively considered, the deviation between the division result and the real surface distribution of the complex underlying surface is easily caused in the fine catchment area by simply using a Voronio algorithm; in addition, the existing method for dividing the multi-focus area small-scale catchment area is lack of a large-scale catchment area dividing method suitable for different areas. Therefore, the invention provides a sub-catchment area dividing method considering the land type and the flow direction around the large scale of the area, which not only comprehensively considers the distribution of natural terrains, artificial pipelines and the like, but also effectively improves the consistency of the catchment area dividing precision and the real earth surface by considering the constraint rules of land type pattern spots, the flow direction and the like. In addition, the method fully considers the analysis requirement of the regional large-scale accumulated water, and realizes the division of the regional large-scale catchment area by using an iteration determination algorithm. Passing through the large scale of Dongying City (44 km)2) The actual data verification and comparative analysis are carried out, and the main conclusion is as follows:
(1) in the aspect of dividing the whole catchment area, 804 fine catchment areas are divided by the method, the whole catchment area is regular in geometric shape and is matched with natural rivers, artificial road networks, drainage pipe networks and building boundary distribution, and the method fully considers the influence of nature and artificial facilities on surface runoff; in addition, in the divided catchment areas, except for ground surface types such as a water system pool, a wetland and the like, the root mean square difference of the areas of other catchment units is 3.18, and the area of the catchment area in the central urban area is smaller than that in the suburban area, which shows that the method not only can reflect the spatial heterogeneity of large-scale catchment units in the area, but also can ensure that the overall geometric shapes of the catchment units are uniform.
(2) In the aspect of local comparison, the positions of the catchment area units divided by the method are approximately the same as those of the Huang et al (2019), each catchment area can contain at least one drainage point corresponding to a rainwater well or a catchment point, and the dividing result can reflect real urban drainage conditions. But the method of the invention is obviously superior to the existing catchment area division method in the aspects of keeping the consistency with the real land type distribution and the surface flow direction.
The method provided by the invention is suitable for finely dividing the large-scale catchment area in the area, and the dividing result is consistent with the real land type distribution, so that the method has good feasibility. In addition, in order to ensure that the method is suitable for large-scale areas, the method of the invention sets a land area ratio threshold parameter, and sets a land threshold value to be 0.15 according to the characteristics of the research area.
By adopting the technical scheme disclosed by the invention, the following beneficial effects are obtained:
the invention provides a method for dividing a sub-catchment area of an urban in consideration of land types and flow directions. The accuracy of catchment area division is improved, and through threshold value setting and iteration, the problem that catchment area division is too fine and broken to cause practical application to the hydrological model under the large scale in the area is still solved. The analysis requirement of regional large-scale ponding is fully considered, the regional large-scale catchment area division is realized by utilizing the iteration determination algorithm, the regional large-scale catchment area division method is suitable for the regional large-scale catchment area fine division, the division result is consistent with the real land class distribution, and the method has good feasibility. The method can reflect the spatial heterogeneity of the large-scale catchment units in the area, and is obviously superior to the existing catchment area division method in the aspects of keeping the distribution with real land types and the consistency of the surface flow direction.
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 (6)
1. A method for dividing a city sub-catchment area considering the land type and the flow direction is characterized in that: comprises the following steps of (a) carrying out,
s1, preliminarily dividing the urban research area into a plurality of primary catchment areas by taking a main river with an actual drainage function of a basin as a dividing boundary according to the natural topography of the urban research area and the confluence relation among rivers;
s2, according to the division result of the primary catchment areas, taking primary and secondary trunk roads with drainage pipes distributed on two sides and a main channel with a drainage function as division boundaries, dividing each primary catchment area into units with relatively independent medium sizes, and obtaining a plurality of secondary catchment areas;
s3, carrying out flow direction analysis on the corrected DEM of the urban research area, determining a main flow direction and a water converging point, and dividing each secondary water converging area based on the main flow direction and the water converging point to obtain a primary tertiary water converging area;
and S4, establishing a three-level catchment area fine division iterative algorithm by combining the surface type of the urban research area, and finely dividing the primary three-level catchment area to obtain a three-level fine sub-catchment area.
2. The method for dividing the urban sub-catchment area according to claim 1, wherein the method comprises the following steps: in step S3, a modified DEM of the urban research area is obtained by,
Ea＝Ei+H
wherein E isaCorrection of DEM elevation values for urban research areas, EiThe original DEM elevation value of the urban research area is shown, and H is the height of the corresponding building.
3. The method for dividing the urban sub-catchment area according to claim 1, wherein the method comprises the following steps: the step S3 specifically includes the following contents,
s31, filling and digging the corrected DEM of the urban research area by using a hydrological analysis tool, sequentially calculating the elevation difference of the DEM of the center grid of the corrected DEM of the urban research area to the eight directions of the east, south, west, north, southeast, northeast, southwest and northwest of the periphery based on a D8 algorithm, and determining the descending direction with the largest difference as the water flow direction of the center grid;
s32, calculating the number of grids on the upstream of the central grid, through which water flows, and determining the water catchment amount of the grids, and connecting the grids with the water catchment amount higher than the water catchment threshold value to form a water catchment ridge line, wherein the junction point of the water catchment ridge line is the water catchment point;
and S33, dividing all grids contained in the catchment ridgelines with the same flow direction into the same independent catchment area by taking the catchment point as a starting point, namely obtaining a primary three-level catchment area.
4. The method for dividing the urban sub-catchment area according to claim 3, wherein the method comprises the following steps: the step S4 specifically includes the following contents,
s41, calculating and acquiring the area of each land type map spot by superposing the ground surface types of the primary three-level catchment area and the urban research area;
s42, calculating the ratio of the area of a certain geographical pattern spot to the total area of the primary three-level catchment area where the geographical pattern spot is located, judging the size relation between the ratio and the area ratio threshold of the geographical pattern spot, if the ratio is larger than or equal to the area ratio threshold of the geographical pattern spot and the number of rainwater wells existing within the preset distance threshold of the periphery of the geographical pattern spot is larger than 0, determining that the geographical pattern spot is a single sub-catchment area, and dividing the geographical pattern spot into sub-catchment areas separately to obtain three-level fine sub-catchment areas; if the ratio is smaller than the area ratio threshold of the land type pattern spots, the land type pattern spots are mixed sub-catchment areas, topological association and combination are carried out on the land type pattern spots and the adjacent land type pattern spots, and three-level fine sub-catchment areas are obtained;
and S43, repeating the step S42, traversing all the ground type map spots until the area of all the three-level fine sub-catchment areas is larger than or equal to the area ratio threshold of the ground type map spots or the number of catch basins existing in the single ground type map spots is larger than 0 or the flow directions of the adjacent ground type map spots are different, ending iteration, and finishing the division of the three-level fine sub-catchment areas.
5. The method for dividing the urban sub-catchment area according to claim 4, wherein the method comprises the following steps: the surface types comprise lawns, forests, cultivated lands, wastelands, buildings and square roads; the sub-catchment areas comprise lawn sub-catchment areas, forest sub-catchment areas, building sub-catchment areas and square sub-catchment areas.
6. The method for dividing the urban sub-catchment area according to claim 4, wherein the method comprises the following steps: the rule function expression of topological association and combination of the geographical map spots and the adjacent geographical map spots is as follows,
Merge(i,j)＝f(AreaSNeiij,Rainwaterij,Directionij,SemNeiij)
wherein i is 1,2, …, m is the total number of the map spots; j is 1,2, …, n, n is the total number of adjacent ground class patches j of the ground class patch i; AreaSNeiijThe area ratio of the adjacent land type image spots j of the land type image spot i, the DirectionijThe included angle between the flow direction of the geo-graphic spot i and the flow direction of the adjacent geo-graphic spot j is RainwaterijSemNei is the number of catch basins and catch basins between the geographical pattern spot i and the adjacent geographical pattern spot jijThe semantic proximity of the land type image spot i and the adjacent land type image spot j is obtained;
the semantic proximity mathematical model is expressed as
Wherein L isiAnd LjThe land type corresponding to the land type image spot i and the adjacent land type image spot j respectively, and x is equal to LiNumber of ground class categories with semantic proximity, Distance (L)i,Lj) Is a position in the semantic neighborhood class set;
the topological association and merging rule function of the geographic class spot i and the adjacent geographic class spot j is expressed as:
wherein, delta is a land pattern spot area ratio threshold; w is a1And w2Respectively representing the weight of the corresponding index.
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