Hydrological connectivity assessment method suitable for tidal creek water system in flood tide stage

Abstract

The invention discloses a tidal creek water system hydrological communication evaluation method suitable for a flood tide stage, and relates to the technical field of water conservancy projects. Comprising an image processing stage and a communication simulation stage. Wherein the image processing stage comprises the following steps: generating a tidal creek network tif file through a high-resolution remote sensing image; extracting the boundary and the central axis of the tidal creek network; generating a tidal creek central axis node file and a midpoint file; extracting the average width of the tidal creek network segments; the communication simulation stage comprises the following steps: defining a traffic package; generating a weighted adjacent matrix of the tidal creek network; calculating a weighted out-degree matrix of the adjacent matrix and a corresponding Laplacian matrix; and calculating a connectivity index. The hydrological communication condition of the tidal creek water system is effectively evaluated.

Description

Technical Field

[0001] The invention relates to the technical field of water conservancy engineering, and more particularly to a method for evaluating hydrological connectivity of tidal ditch water systems during high tide. Background Art

[0002] The hydrological connectivity of tidal channel water systems controls important ecological processes such as the exchange of materials and energy between the ocean and tidal flats, which in turn affects the health and stability of the intertidal ecosystem. During high tide, the tide flows from the ocean to the intertidal zone, carrying relevant nutrients, organisms and sediment to the tidal flats, playing an important role in the health and stability of the tidal flat ecosystem.

[0003] Therefore, evaluating the hydrological connectivity of tidal ditch water systems during high tide is crucial to understanding the status of tidal flat ecosystems. The present invention solves the problem of evaluating the hydrological connectivity of tidal ditch water systems during high tide. The prior art involves multiple concentrated inland water bodies in hydrological connectivity evaluation methods, and coastal wetlands mainly focus on vertical hydrological connectivity of tidal flats, while there are few methods for evaluating the hydrological connectivity of tidal ditch water systems. Foreign related research mainly evaluates the distribution of water during high tide in tidal ditch water systems by placing dye balls. This method is not only time-consuming and labor-intensive, but also difficult to recover dye balls due to the influence of external factors (wind and waves, fishing boat tracks), making it difficult to effectively evaluate the hydrological connectivity of tidal ditch water systems.

[0004] Therefore, it is an urgent problem for those skilled in the art to propose a method for evaluating the hydrological connectivity of tidal ditch water systems during high tide to solve the difficulties existing in the prior art. Summary of the invention

[0005] In view of this, the present invention provides a method for evaluating the hydrological connectivity of a tidal ditch water system during high tide, which is used to solve the technical problems existing in the prior art.

[0006] In order to achieve the above object, the present invention provides the following technical solutions: A method for evaluating hydrological connectivity of tidal ditch water systems during high tide, comprising the following steps: S1, an image processing stage and S2, a connectivity simulation stage; wherein: S1, the image processing stage includes: S11, generate tidal channel network tif files through high-resolution remote sensing images; S12, extract the boundary and central axis of the tidal channel network; S13, generating a node file and a midpoint file of the tidal channel central axis; S14, extract the average width of the tidal channel network segments; S2, the connectivity simulation phase includes: S21, define traffic packages; S22, generating a weighted adjacency matrix of the tidal channel network; S23, calculating the weighted out-degree matrix of the adjacency matrix and the corresponding Laplace matrix; S24. Calculate the connectivity index.

[0007] Optionally, the specific content of the tidal channel network tif file generated by high-resolution remote sensing images in S11 is: Obtain high-resolution remote sensing images of the tidal channel network in the study area; Perform image processing on the acquired remote sensing images; Through band operation, the normalized water index of the tidal channel network area is calculated and a water index image is generated; Reclassify the water index image and perform binarization processing on the water index image; By binarizing the image, a tidal channel network tif file is generated.

[0008] Optionally, the specific content of extracting the boundary and central axis of the tidal channel network in S12 is: Through the generated tif file of the tidal channel network, the ArcScan module is used to extract the initial files of the boundary shp file and the central axis shp file of the tidal channel network; By comparing with the original image, the generated boundary and center axis shp files are adjusted to generate the final boundary shp files and center axis shp files of the tidal channel network.

[0009] Optionally, the specific contents of the tidal channel central axis node file and the midpoint file generated in S13 are: According to the central axis shp file of the tidal ditch network, the segment node shp file and the midpoint shp file of the tidal ditch are extracted through the GIS feature module, and the nodes are numbered according to the order in which the tidal water flows through each node and the direction of the tidal water during the high tide stage.

[0010] Optionally, the specific content of extracting the average width of the tidal gully network fragment in S14 is: The ArcGIS nearest neighbor analysis tool was used to perform statistics on the midpoint shp file and the boundary shp file to obtain the distance from the midpoint to the tidal ditch boundary. Twice the distance from the midpoint to the tidal ditch boundary was the average width of the tidal ditch segment. The width attribute was assigned to the attribute table of the central axis shp file through the union tool.

[0011] Optionally, the specific content of the traffic package defined in S21 is: Flow Parcel: A single flow parcel enters the system from the top and propagates downstream until it reaches the junction of a tidal creek.

[0012] Optionally, the specific content of the weighted adjacency matrix of the tidal channel network generated in S22 is: Add a floating point field in the attributes of the central axis shp file and name it weight; According to the flow direction of the tide and the average width of the tidal ditch segments, the proportion of the tidal flow of each tidal ditch segment after the tidal ditch bifurcates is calculated and assigned to the weight field; Generate central axis node shp file and central axis shp file; According to the spectral graph theory, a directed graph of tidal channel network is constructed; The weighted adjacency matrix of the tidal gully network directed graph was generated using GIS spatial connection tools.

[0013] Optionally, the specific contents of the weighted out-degree matrix and the corresponding Laplace matrix of the adjacency matrix calculated in S23 are: The weighted out-degree matrix is ​​a diagonal matrix. The element Dii on the diagonal represents the degree of node i, which is the sum of the values ​​of each column of the corresponding weighted adjacency matrix. The calculation formula is: ; ; The calculation formula of the Laplace matrix is: ; in, is the weighted out-degree matrix, is the Laplace matrix, is the weighted adjacency matrix, For Node i The out-degree, For the matrix W Middle i Row, No. j The corresponding value of the column.

[0014] Optionally, the specific content of calculating the connectivity index in S24 is: The connectivity within the subnet is determined by the steady-state flow F, and the connectivity index between subnets is characterized by the sharing index, which is calculated as follows: ; in, For subnet S i The number of nodes in For Node v To the exit i The proportion of the flow discharged.

[0015] It can be seen from the above technical solution that, compared with the prior art, the present invention discloses a method for evaluating the hydrological connectivity of tidal ditch water systems during high tide, which has the following beneficial effects: the model simulates the flow characteristics of tidal water in the tidal ditch during high tide by constructing a connectivity framework, which saves time and effort, and the evaluation is reliable. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0017] Figure 1 A flow chart of a method for evaluating hydrological connectivity of tidal ditch water systems during high tide provided by the present invention; Figure 2 A steady flow pattern diagram of a tidal creek provided in an embodiment of the present invention; wherein 2a is a steady flow pattern diagram in 1984; 2b is a steady flow pattern diagram in 2009; 2c is a steady flow pattern diagram in 2017; Figure 3 A hydrological connectivity characteristic diagram of a tidal ditch provided in an embodiment of the present invention; wherein 3a is a hydrological connectivity characteristic change diagram within a subnet, and 3b is a hydrological connectivity characteristic change diagram between subnets. DETAILED DESCRIPTION

[0018] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] See also Figure 1 As shown, the present invention discloses a method for evaluating hydrological connectivity of tidal ditch water systems during high tide, comprising the following steps: S1, an image processing stage and S2, a connectivity simulation stage; wherein, S1, the image processing stage includes: S11, generate tidal channel network tif files through high-resolution remote sensing images; S12, extract the boundary and central axis of the tidal channel network; S13, generating a node file and a midpoint file of the tidal channel central axis; S14, extract the average width of the tidal channel network segments; S2, the connectivity simulation phase includes: S21, define traffic packages; S22, generating a weighted adjacency matrix of the tidal channel network; S23, calculating the weighted out-degree matrix of the adjacency matrix and the corresponding Laplace matrix; S24. Calculate the connectivity index.

[0020] Furthermore, the specific content of the tidal gully network tif file generated by high-resolution remote sensing images in S11 is: Obtain high-resolution remote sensing images of the tidal channel network in the study area; Specifically, for example, the Gaofen-2 remote sensing image has a spatial resolution of 0.3m.

[0021] Perform image processing on the acquired remote sensing images; Specifically, it includes atmospheric correction, geometric correction, image cropping and other processing.

[0022] Through band operation, the normalized water index of the tidal channel network area is calculated and a water index image is generated; Specifically, the calculation formula of the normalized water index (NDWI) is: .

[0023] Reclassify the water index image and perform binarization processing on the water index image; Specifically, the water index image is reclassified, and values ​​greater than 0 are assigned to 1, and values ​​less than zero are assigned to 0.

[0024] By binarizing the image, a tidal channel network tif file is generated.

[0025] Furthermore, the specific contents of extracting the boundary and central axis of the tidal channel network in S12 are as follows: Through the generated tif file of the tidal channel network, the ArcScan module is used to extract the initial files of the boundary shp file and the central axis shp file of the tidal channel network; By comparing with the original image, the generated boundary and center axis shp files are adjusted to generate the final boundary shp files and center axis shp files of the tidal channel network.

[0026] Furthermore, the specific contents of the tidal channel central axis node file and the midpoint file generated in S13 are: According to the central axis shp file of the tidal ditch network, the segment node (endpoint) shp file and the midpoint shp file of the tidal ditch are extracted through the GIS feature module, and the nodes are numbered according to the order in which the tidal water flows through each node and the direction of the tidal water during the high tide stage.

[0027] Specifically, the node that flows through first is assigned a value of 1, and so on, to ensure that the node number that flows through after the tide is greater than the change that flows through first.

[0028] Furthermore, the specific content of extracting the average width of the tidal gully network fragment in S14 is: The ArcGIS nearest neighbor analysis tool was used to perform statistics on the midpoint shp file and the boundary shp file to obtain the distance from the midpoint to the tidal ditch boundary. Twice the distance from the midpoint to the tidal ditch boundary was the average width of the tidal ditch segment. The width attribute was assigned to the attribute table of the central axis shp file through the union tool.

[0029] Furthermore, the specific content of the traffic package defined in S21 is: Flow Parcel: A single flow parcel (sediment, water, or nutrients) enters a system from the top and propagates downstream until it reaches the junction of a tidal channel.

[0030] Specifically, the next possible path is randomly determined, and the probability of choosing a specific path depends on the width of the tidal channel network or any other suitable feature. A single flow package is randomly directed along the delta tidal channel network. It is assumed that the water flow in the tidal channel is defined by a large number of independent flow packages, which are independently directed along the tidal channel network. In general, a tidal channel network has one entry point and multiple exit points, so it corresponds to multiple transmission paths, that is, multiple subnets.

[0031] Furthermore, the specific content of the weighted adjacency matrix of the tidal channel network generated in S22 is: Add a floating point field in the attributes of the central axis shp file and name it weight; According to the flow direction of the tide and the average width of the tidal ditch segments, the proportion of the tidal flow of each tidal ditch segment after the tidal ditch bifurcates is calculated and assigned to the weight field; Generate central axis node shp file and central axis shp file; According to the spectral graph theory, a directed graph of tidal channel network is constructed; The weighted adjacency matrix of the tidal gully network directed graph was generated using GIS spatial connection tools.

[0032] Furthermore, the specific contents of the weighted out-degree matrix and the corresponding Laplace matrix of the adjacency matrix calculated in S23 are: The weighted out-degree matrix is ​​a diagonal matrix. The element Dii on the diagonal represents the degree of node i, which is the sum of the values ​​of each column of the corresponding weighted adjacency matrix. The calculation formula is: ; ; The calculation formula of the Laplace matrix is: ; in, is the weighted out-degree matrix, is the Laplace matrix, is the weighted adjacency matrix, For Node i The out-degree, For the matrix W Middle i Row, No. j The corresponding value of the column.

[0033] Furthermore, the specific content of calculating the connectivity index in S24 is: The connectivity within the subnet is determined by the steady-state flow F, and the connectivity index between subnets is characterized by the sharing index, which is calculated as follows: ; in, For subnet S i The number of nodes in For Node v To the exit i The proportion of the flow discharged.

[0034] Specifically, note that 1- For Node v To other exports j The proportion of the discharged flow, j ≠ i Based on this index, the traffic sharing between the egress subnet and other egress subnets can be captured. If the subnets are completely independent, then =1, all traffic in the subnet eventually flows to the egress i , this situation corresponds to FSI i ≈ 0. On the other hand, if the traffic of the nodes contained in the subnet is shared with many other inter-subnet traffic, , only a small part of the traffic flows to the corresponding outlet. In this case, the corresponding FSI i ≈1, Determined by subnet.

[0035] In a specific embodiment, the above method is used to evaluate the evolution of the hydrological connectivity of the Yellow River Delta tidal channel network. The spatiotemporal pattern of the connectivity of the tidal channel network is shown in Figure 2As shown in 2a-2c in Figure 2, in terms of spatial performance, tidal channels of different levels carry different flows, with larger flows on the main tidal channel and smaller flows on the tributaries at the end of the tidal channel. In addition, from the flow at the exit point of the tidal channel, there is no preferred exit path for the tidal channel. For the hydrological connectivity law within the tidal channel network, see Figure 3 As shown in Figure 3a, the steady flow in the subnet remained stable in 2009, but showed an increasing trend after 2009. Figure 3 As shown in Figure 3b, the connectivity characteristics between subnets showed a stable trend in 2009, and then showed a downward trend after 2009.

[0036] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0037] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for assessing hydrological connectivity of tidal ditch water systems during high tide, characterized in that: The following steps are involved: S1, image processing stage and S2, connectivity simulation stage; where S1, the image processing stage includes: S11, generate tidal channel network tif files through high-resolution remote sensing images; S12, extract the boundary and central axis of the tidal channel network; S13, generating a node file and a midpoint file of the tidal channel central axis; S14, extract the average width of the tidal channel network segments; S2, the connectivity simulation phase includes: S21, define traffic packages; S22, generating a weighted adjacency matrix of the tidal channel network; S23, calculating the weighted out-degree matrix of the adjacency matrix and the corresponding Laplace matrix; S24. Calculate the connectivity index.

2. A method for evaluating hydrological connectivity of tidal ditch water systems during high tide according to claim 1, characterized in that: The specific contents of the tidal channel network tif file generated by S11 using high-resolution remote sensing images are as follows: Obtain high-resolution remote sensing images of the tidal channel network in the study area; Perform image processing on the acquired remote sensing images; Through band operation, the normalized water index of the tidal channel network area is calculated and a water index image is generated; Reclassify the water index image and perform binarization processing on the water index image; By binarizing the image, a tidal channel network tif file is generated.

3. A method for evaluating hydrological connectivity of tidal ditch water systems during high tide according to claim 2, characterized in that: The specific contents of extracting the boundary and central axis of the tidal channel network in S12 are as follows: Through the generated tif file of the tidal channel network, the ArcScan module is used to extract the initial files of the boundary shp file and the central axis shp file of the tidal channel network; By comparing with the original image, the generated boundary and center axis shp files are adjusted to generate the final boundary shp files and center axis shp files of the tidal channel network.

4. A method for evaluating hydrological connectivity of tidal ditch water systems during high tide according to claim 3, characterized in that: The specific contents of the node file and midpoint file of the tidal channel center axis generated in S13 are as follows: According to the central axis shp file of the tidal ditch network, the segment node shp file and the midpoint shp file of the tidal ditch are extracted through the GIS feature module, and the nodes are numbered according to the order in which the tidal water flows through each node and the direction of the tidal water during the high tide stage.

5. A method for evaluating hydrological connectivity of tidal ditch water systems during high tide according to claim 1 or 4, characterized in that: The specific content of extracting the average width of the tidal channel network fragments in S14 is: The ArcGIS nearest neighbor analysis tool was used to perform statistics on the midpoint shp file and the boundary shp file to obtain the distance from the midpoint to the tidal ditch boundary. Twice the distance from the midpoint to the tidal ditch boundary was the average width of the tidal ditch segment. The width attribute was assigned to the attribute table of the central axis shp file through the union tool.

6. A method for evaluating hydrological connectivity of tidal ditch water systems during high tide according to claim 1, characterized in that: The specific contents of the traffic package defined in S21 are: Flow Parcel: A single flow parcel enters the system from the top and propagates downstream until it reaches the junction of a tidal creek.

7. A method for evaluating hydrological connectivity of tidal ditch water systems during high tide according to claim 5, characterized in that: The specific content of the weighted adjacency matrix for generating the tidal channel network in S22 is: Add a floating point field in the attributes of the central axis shp file and name it weight; According to the flow direction of the tide and the average width of the tidal ditch segments, the proportion of the tidal flow of each tidal ditch segment after the tidal ditch bifurcates is calculated and assigned to the weight field; Generate central axis node shp file and central axis shp file; According to the spectral graph theory, a directed graph of tidal channel network is constructed; The weighted adjacency matrix of the tidal gully network directed graph was generated using GIS spatial connection tools.

8. The method for evaluating the hydrological connectivity of tidal ditch water systems during high tide according to claim 1, characterized in that: The specific contents of the weighted out-degree matrix and the corresponding Laplace matrix of the adjacency matrix calculated in S23 are: The weighted out-degree matrix is ​​a diagonal matrix. The element Dii on the diagonal represents the degree of node i, which is the sum of the values ​​of each column of the corresponding weighted adjacency matrix. The calculation formula is: ； ； The calculation formula of the Laplace matrix is: ; in, is the weighted out-degree matrix, is the Laplace matrix, is the weighted adjacency matrix, For Node i The out-degree, For the matrix W Middle i Row, No. j The corresponding value of the column.

9. A method for evaluating hydrological connectivity of tidal ditch water systems during high tide according to claim 1, characterized in that: The specific content of calculating the connectivity index in S24 is: The connectivity within the subnet is determined by the steady-state flow F, and the connectivity index between subnets is characterized by the sharing index, which is calculated as follows: ； in, For subnet S i The number of nodes in For Node v To the exit i The proportion of the flow discharged.

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