Distributed ditch and pond wetland water surface rate calculation method based on graph theory, estimation system, equipment and readable storage medium

Abstract

The invention discloses a method for calculating the water surface rate of a distributed ditch-pond wetland based on a graph theory in the technical field of water resource management. The method comprises the following steps: 1) investigating a distributed ditch-pond system and forming a ditch-pond topological structure; 2) establishing a graph theory model of a distributed ditch-pond wetland based on the ditch-pond topological structure, and generating an adjacent matrix of the graph theory model; 3) constructing the flow weight of the adjacent matrix based on the production and confluence relationship of the ditch-pond network; 4) quantifying the pollutant reduction weight of the adjacent matrix based on a distributed first-order dynamic process of pollutants; 5) according to the graph theory model of the ditch-pond network and the flow and pollutant reduction weight thereof, by taking small watershed effluent water quality up-to-standard discharge as a target, iterating the ditch-pond area water surface rate to search for the minimum ditch-pond system water surface area meeting the water quality up-to-standard discharge requirement, and estimating the ditch-pond wetland water surface rate; aiming at how to quantify the characteristics of the drainage ditch-pond system, the distribution characteristics of the ditch-pond wetland are introduced into wetland water surface rate estimation, and the ditch-pond system can be protected.

Description

Technical Field

[0001] The invention relates to the technical field of water resource management and environmental engineering, and in particular to a distributed ditch pond wetland water surface rate estimation model based on graph theory. Background Art

[0002] Agriculture is well developed and the water system is rich in plain river network areas. Under the combined influence of natural topography and human farming, farmland and drainage ditch and pond systems coexist. The drainage ditch and pond system around farmland is not only a channel for agricultural drainage, but also a wetland system that can remove pollutant loads in drainage and then improve the outlet water quality of farmland small watersheds. Therefore, the drainage ditch and pond wetland system has multiple service functions such as drainage environment ecology. In order to more reasonably develop and protect the ditch and pond wetland system, it is necessary to develop a more reasonable method to quantify the minimum wetland water surface area.

[0003] Traditionally, drainage system design is mainly based on optimal drainage. In recent years, attention has gradually been paid to the ecological and environmental functions of drainage ditch and pond systems. In addition, as a complex network system, how to quantify its characteristics is one of the key and difficult points of research. Currently, the ditch and pond wetland system is mainly considered as a whole, and there are few studies that incorporate the distribution characteristics of ditch and pond wetlands into the estimation of wetland water surface rate. Therefore, proposing a method to estimate the minimum wetland water surface area is of great significance for protecting the ditch and pond system and quantifying its characteristics. Summary of the invention

[0004] The present invention aims at how to quantify the characteristics of drainage ditch and pond systems, incorporates the distribution characteristics of ditch and pond wetlands into the estimation of wetland water surface rate, and proposes a method for estimating the minimum wetland water surface area, which is of great significance for protecting the ditch and pond system and quantifying its characteristics.

[0005] The object of the present invention is achieved by: a distributed ditch pond wetland water surface rate calculation method based on graph theory, comprising the following steps:

[0006] Step 1) Investigate the distributed ditch-pond system and form a ditch-pond topology;

[0007] Step 2) establishing a graph theory model of the distributed ditch and pond wetland based on the ditch and pond topological structure, and generating its adjacency matrix;

[0008] Step 3) constructing the flow weight of the adjacency matrix based on the flow generation and confluence relationship of the ditch and pond network;

[0009] Step 4) quantifying the pollutant reduction weight of the adjacency matrix based on the distributed first-order dynamics of the pollutants;

[0010] Step 5) Based on the graph theory model of the ditch-pond network and its flow and pollutant reduction weights, with the goal of meeting the discharge quality standards for the outflow of the small watershed, the ditch-pond area water surface ratio is iterated to search for the minimum ditch-pond system water surface area that meets the water quality discharge requirements, and the ditch-pond wetland water surface ratio is estimated.

[0011] Furthermore, step 2) specifically includes: based on the obtained ditch and pond topological structure data, the water flow network of the ditch and pond wetland system is generalized and constructed into a directed graph model, in which nodes serve as representatives of each ditch and pond, and edges are used to characterize the connectivity and water flow paths between the ditches and ponds. By using the matrix representation method in graph theory, an adjacency matrix is ​​generated, thereby accurately describing the connection relationship, water flow direction and potential circulation path of the ditch and pond network in mathematical form.

[0012] Furthermore, step 3) specifically includes: considering the flow generation and confluence relationship of the ditch and pond network, assigning the farmland flow generation to the corresponding edge in the adjacency matrix as the flow weight q i,j , accurately reflects the changing characteristics of the water flow size and direction between ditches and ponds. The calculation process is as follows:

[0013]

[0014] In the formula, q i,j is the flow from the i-th ditch-pond wetland unit to the j-th ditch-pond unit, m 3 / day;q i,j,m is the flow rate contributed by the mth farmland flow-producing area during the process of the flow from the ith ditch-pond wetland unit to the jth ditch-pond unit, m 3 / day;q i,n is the flow rate of the nth ditch and pond unit upstream of the i-th ditch and pond wetland unit, m 3 / day; M and N are the total number of farmland and upstream units of the i-th ditch and pond unit, respectively; M = 0 means that there is no farmland inflow to the unit, and N = 0 means that there is no upstream inflow unit to the unit;

[0015] Among them, farmland output q i,j,m It is estimated by multiplying the estimated farmland area by the farmland drainage flux. The calculation process is as follows:

[0016] q i,j,m =α i,j h0*A i,m

[0017] Where h0 is the farmland yield flow, which is approximately estimated by the annual yield flow measured in the field, and m 3 / day; A i,j,m is the area of ​​the mth farmland runoff area in the i-th ditch-pond wetland unit, m 2 ; α i,jis the distribution coefficient of farmland runoff in the process of flowing from the i-th ditch and pond wetland unit to the j-th ditch and pond unit; when the ditch and pond unit i has only one downstream unit j, the distribution coefficient is 1.

[0018] Furthermore, step 4) specifically includes: based on the distributed first-order kinetic process of pollutants in the ditch and pond wetlands, considering factors such as the input concentration of pollutants, the hydraulic retention time of the ditch and pond, the degradation coefficient of pollutants and the sedimentation rate, a mathematical model of pollutant concentration changes is established, the reduction coefficient of each ditch and pond for specific pollutants is calculated, and it is assigned to the corresponding edge in the adjacency matrix as the pollutant reduction weight ω i,j , quantitatively describe the pollutant reduction capacity of ditch pond wetlands, the calculation process is as follows:

[0019]

[0020] In the formula, C t,i,j is the pollutant concentration at the end of the period from the i-th ditch-pond wetland unit to the j-th ditch-pond wetland unit, mg L -1 ; The calculation process is as follows:

[0021]

[0022] In the formula, k is the first-order reduction coefficient of pollutants, day -1 ;t h,i is the hydraulic retention time from the i-th ditch-pond wetland unit to the j-th ditch-pond wetland unit, day;

[0023] C 0,i is the initial pollutant concentration of the i-th ditch, pond and wetland unit in the time period, mg L -1 ; The calculation process is as follows:

[0024]

[0025] In the formula, C a is the field pollutant output concentration predicted by the farmland model, mg L -1 ; C t,i,n is the pollutant concentration at the end of the period in the nth ditch and pond unit upstream of the i-th ditch and pond wetland unit, mg L -1 ;

[0026] The final output concentration of the pollutant is the ratio of the remaining pollutant load to the total flow, C t , the calculation process is as follows:

[0027]

[0028] In the formula, C tis the total outflow concentration of the ditch and pond network, mg / L; M0 is the initial load entering the ditch and pond network, kg; ΔM is the pollutant load reduced by the ditch and pond network, kg; L is the total number of ditch and pond network units.

[0029] Further, step 5) specifically includes: taking the discharge of the outflow water quality of the small watershed meeting the standard as the goal, establishing constraint conditions, and using the trial calculation iteration method to adjust and optimize the water surface ratio of the ditch and pond area; in each iteration, using the established graph theory model, flow weight and pollutant reduction weight, calculate the transmission and reduction process of pollutants in the ditch and pond network, and predict the outflow water quality of the small watershed; based on the calculation results, determine whether the outflow water quality meets the predetermined water quality standard, if not, adjust the ditch and pond water surface ratio according to the optimization algorithm and enter the next iteration;

[0030] Furthermore, the calculation process of the ditch, pond and wetland water surface ratio ε required for water quality to meet the discharge standard is as follows:

[0031]

[0032] Where ε is the wetland water surface ratio, %; μ is the ditch and pond area adjustment coefficient.

[0033] A distributed ditch pond wetland water surface rate estimation system based on graph theory is used to implement the above calculation method, including:

[0034] Data collection module, used to investigate and obtain the topological structure and hydraulic connection data of the distributed ditch-pond wetland system;

[0035] A graph theory model building module, used to build a graph theory model of the ditch pond wetland system based on the information obtained by the data acquisition module;

[0036] Adjacency matrix building module, used to generate adjacency matrix describing flow weights and pollutant reduction weights of ditch-pond wetland system;

[0037] The iterative optimization module is used to search for the optimal water surface area of ​​the ditch-pond wetland system that meets the water quality requirements through an iterative algorithm.

[0038] A computer device comprises a memory and a processor, wherein the memory stores a computer program, and wherein the computing method is implemented when the processor executes the computer program.

[0039] A computer-readable storage medium stores a computer program, which implements the computing method when executed by a processor.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] Traditional studies on ditch and pond wetlands often treat them as a whole, ignoring their individual characteristics. This invention proposes an estimation model by comprehensively considering the complex interactions between farmland and drainage ditch and pond systems in the southern plain river network area, and combining graph theory generalization with iterative adjustment analysis. This model can comprehensively consider the complex relationship between the plain river network and drainage ditch and pond, and more reasonably estimate the minimum wetland area. In addition, the ditch and pond wetland water surface rate estimation proposed in this invention is of great significance for coping with the construction of high-standard farmland, and the pond wetland water surface area has important reference value for the agricultural production and ecological environmental service functions of irrigation areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] 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.

[0043] Figure 1 This is an overall flow chart of the distributed ditch pond wetland water surface rate calculation method based on graph theory in Example 1.

[0044] Figure 2 This is a drainage ditch and pond distribution and drainage direction diagram of the distributed ditch and pond wetland water surface rate calculation method based on graph theory in Example 1.

[0045] Figure 3 This is the drainage ditch and pond flow network analysis and drainage classification diagram of the distributed ditch and pond wetland water surface rate calculation method based on graph theory in Example 1.

[0046] Figure 4 This is a comparison diagram of the ditch pond wetland areas under different ditch pond structures and water quality targets in Example 1. DETAILED DESCRIPTION

[0047] 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.

[0048] Example 1

[0049] Reference Figure 1 to Figure 4 , which is the first embodiment of the present invention, provides a distributed ditch pond wetland water surface rate estimation based on graph theory. In order to verify the beneficial effects of the present invention, scientific demonstration is carried out through simulation experiments.

[0050] Specifically, the farmland drainage ditch ponds at the experimental base of Yangzhou Farmland Water Conservancy Science Research Station located in Jiangdu District, Yangzhou City, Jiangsu Province were selected as a case analysis.

[0051] According to field measurement data, the average concentration of ammonia nitrogen in the field was determined to be 2.34 mg N / L, and the drainage volume was 116.2 cm / year;

[0052] In order to evaluate the impact of distributed ditch-pond structure on ditch-pond water surface ratio, we considered the centralized ditch-pond wetland system as a whole as the control group (Zou Jiarong et al., 2022) and calculated the estimation model of the distributed ditch-pond wetland water surface ratio (distributed, this patent document).

[0053] The centralized ditch-pond wetland system considers the ditch-pond as a whole, and the degradation process of pollutants is expressed by the first-order reaction equation. Assuming that the water quality control goal of the small watershed is to reduce the concentration of pollutants in the drainage to c t , the hydraulic retention time required in the treatment wetland (t h ,h)The calculation process is as follows:

[0054] t h =-ln(c t / c0) / r)

[0055] Where c t is the target concentration, mg / L; c0 is the initial concentration, mg / L; r is the pollutant degradation constant.

[0056] The corresponding wetland area required for treatment (A w ,hm 2 )The calculation process is as follows:

[0057] A w =Qt h / h

[0058] Where h is the wetland water depth, m.

[0059] The calculation process of the area ratio (ε) of wetland to farmland to be treated is as follows:

[0060]

[0061] Where A f is the farmland area, hm 2 ;H d The average water depth drained onto the farmland area, m.

[0062] S1: Investigate the current status of the distributed ditch and pond system.

[0063] Specifically, ditch and pond data are obtained based on a systematic survey of the current status of ditches and ponds, including using unmanned aerial photography technology, GPS and other technologies to conduct on-site surveys of the actual conditions of ditches and ponds, determine the boundaries, shapes, water depths and connectivity of ditches and ponds, and collect information such as water flow channels.

[0064] S2: Establish a graph theory model of distributed ditch-pond wetlands based on the ditch-pond topological structure and generate its adjacency matrix.

[0065] Furthermore, each ditch and pond represents a node, and the water flow connection paths between the ditches and ponds represent edges, thus constructing a directed graph model of the ditch and pond wetland system.

[0066] Furthermore, the directionality of water flow is determined by elevation difference and hydraulic gradient, ensuring that the path of water flow is consistent with the natural hydrodynamic process. In the constructed graph model, the directed edges between nodes reflect the actual flow direction of water flow. The adjacency matrix is ​​used to mathematically express the connectivity between nodes and quantitatively represent the transmission path and intensity of water flow in the ditch pond wetland system.

[0067] S3: Construct the flow weight of the adjacency matrix based on the runoff relationship of the ditch and pond network.

[0068] Furthermore, hydrological, meteorological and topographic data in the study area are collected. These data include: rainfall and rainfall intensity, topography and slope, soil type, etc. Based on the above collected data, data processing and analysis are carried out to calculate the runoff of each ditch and pond and the flow from one ditch to another.

[0069] The main flow channels of water in the ditch and pond network are determined by terrain slope analysis. These channels include inflow channels and outflow channels. After the flow channels between the ditches and ponds are determined, the farmland flow is assigned to the corresponding edge in the adjacency matrix as the flow weight q i,j , the calculation process is as follows:

[0070]

[0071] In the formula, q i,j is the flow from the i-th ditch-pond wetland unit to the j-th ditch-pond unit, in m 3 / day(same below);q i,j,m is the flow rate contributed by the mth farmland flow-producing area during the process of the flow from the ith ditch-pond wetland unit to the jth ditch-pond unit, m 3 / day;q i,n is the flow rate of the nth ditch and pond unit upstream of the i-th ditch and pond wetland unit, m 3 / day; M and N are the total number of farmland and upstream units of the ith ditch and pond unit, respectively. M = 0 means that there is no farmland inflow to the unit, and N = 0 means that there is no upstream inflow unit to the unit.

[0072] Among them, farmland output q i,j,m It is estimated by multiplying the estimated farmland area by the farmland drainage flux. The calculation process is as follows:

[0073] q i,j,m =α i,j h0*A i,m

[0074] Where h0 is the farmland production flow, which is approximately estimated by the annual production flow measured in the field, m / day; A i,j,m is the area of ​​the mth farmland runoff area in the i-th ditch-pond wetland unit, m 2 ; α i,j is the distribution coefficient of farmland runoff from the i-th ditch-pond wetland unit to the j-th ditch-pond unit; when the ditch-pond unit i has only one downstream unit j, the distribution coefficient is 1.

[0075] S4: Quantifying the pollutant reduction weights of the adjacency matrix based on the distributed first-order dynamics of pollutants.

[0076] On each connected path (i.e., water flow channel between nodes) in the ditch and pond network, its pollutant reduction weight will be determined based on the reduction efficiency of the upstream node and the flow characteristics of the water flow in the path. The contribution of the upstream node to the reduction of downstream pollutants is determined by the comprehensive reduction capacity of each ditch and pond that the water flows through on the path. By analyzing these connected paths, the reduction of pollutant concentration changes on each path can be obtained.

[0077] For the pollutant reduction process of each unit in the ditch and pond wetland network, the pollutant reduction weight ω of the node in the adjacency matrix can be used. i,j To quantify the pollutant reduction capacity of the ditch-pond wetland network, the calculation process is as follows:

[0078]

[0079] In the formula, C t,i,j is the pollutant concentration at the end of the period from the i-th ditch-pond wetland unit to the j-th ditch-pond wetland unit, mg L -1 ; C 0,i is the initial pollutant concentration of the i-th ditch, pond and wetland unit in the time period, mg L -1 .

[0080] S4.2: For the initial concentration of pollutants in the ith ditch, pond and wetland unit, we assume that all farmland runoff and upstream runoff are fully mixed instantaneously at the beginning of the period, so the initial concentration of pollutants C 0,i , the calculation process is as follows:

[0081]

[0082] In the formula, C a is the field pollutant output concentration predicted by the farmland model, mg L -1 ; C t,i,n is the pollutant concentration at the end of the period in the nth ditch and pond unit upstream of the i-th ditch and pond wetland unit, mg L -1 .

[0083] S4.3: After the pollutants are fully mixed, their reduction process can be quantified according to the distributed first-order kinetic process, that is, the pollutant concentration C at the end of the i-th unit period t,i,j , the calculation process is as follows:

[0084]

[0085] In the formula, k is the first-order reduction coefficient of pollutants, day -1 ;t h,i is the hydraulic retention time from the i-th ditch-pond wetland unit to the j-th ditch-pond wetland unit, day.

[0086] S4.4: The hydraulic retention time is calculated as follows:

[0087]

[0088] In the formula, h i is the water depth of the ditch unit, m; A′ i is the area of ​​the ditch unit, m 2 .

[0089] S4.5: For a distributed network of gullies, ponds and wetlands, the final output concentration of a pollutant is the ratio of the residual pollutant load to the total flow, C t , the calculation process is as follows:

[0090]

[0091] In the formula, C t is the total outflow concentration of the ditch and pond network, mg / L; M0 is the initial load entering the ditch and pond network, kg; ΔM is the pollutant load reduced by the ditch and pond network, kg; L is the total number of ditch and pond network units.

[0092] It should be noted that for each connection path between ditches and ponds, a corresponding reduction weight is assigned based on the reduction of pollutants on the path. The larger the weight, the better the effect of pollutant reduction on the path. Conversely, the smaller the weight, the relatively poor reduction effect on the path. The reduction weight of each connection path reflects the contribution of different paths in the ditch and pond system to the overall pollutant reduction.

[0093] S5: Based on the graph theory model of the ditch-pond network and its flow and pollutant reduction weights, the ditch-pond area water surface ratio is iterated to search for the minimum ditch-pond system water surface area that meets the water quality discharge requirements.

[0094] Furthermore, with the goal of achieving standard discharge of outflow water quality in small agricultural watersheds, the water surface ratio of the ditch-pond wetland system is iteratively adjusted for different water quality standards (Class III, Class IV, Class V water quality) to search for the minimum wetland water surface area that meets the water quality standards. The initial calculated pollutant concentration at the outlet is compared with the predetermined water quality standard. If it meets the water quality standard, it means that the initial area configuration has met the water quality requirements and the iteration ends. If it does not meet the water quality standard, the area water surface ratio of the ditch-pond needs to be adjusted to further reduce the pollutant concentration.

[0095] Each time the area water surface ratio of the ditch and pond is adjusted, the hydraulic retention time of each ditch and pond is recalculated, and the pollutant reduction efficiency is updated. Combined with the new area water surface ratio, flow weight, and reduction weight, the transmission process of pollutants in the ditch and pond network is simulated again to calculate the new outlet pollutant concentration. When the outlet pollutant concentration meets the water quality standard, or the adjusted area water surface ratio changes little, the iterative process converges and the optimization calculation ends.

[0096] S6: Determine the minimum water surface area of ​​the ditch and pond system that meets the water quality requirements.

[0097] Further: After the iteration process is completed, the minimum ditch and pond water surface area is obtained, and the optimal area water surface ratio of each ditch and pond is calculated, and the ditch and pond wetland water surface ratio ε required for water quality to meet the discharge standard is calculated. The calculation process is as follows:

[0098]

[0099] Where ε is the wetland water surface ratio, %; μ is the ditch and pond area adjustment coefficient.

[0100] S7: The simulation results show the difference in water surface rate requirements between distributed and lumped ditch-pond wetland systems under different water quality targets.

[0101] The results show that for Class III water quality targets (1 mg / L), the water surface rate requirement of the distributed system reaches 52.1%, which is significantly higher than the 32.9% of the lumped system. Under Class IV water quality targets (1.5 mg / L), the distributed system requires a water surface rate of 22.6%, while the lumped system only requires 17.2%. When it comes to Class V water quality targets (2 mg / L), the water surface rate requirements of the distributed and lumped systems are close, at 6.8% and 6.1%, respectively.

[0102] It is further explained that as water quality targets increase, the wetland area required for the distributed system is significantly higher than that of the lumped system. This is mainly because the distributed ditch-pond wetland system is affected by the hydraulic connection between ditches and ponds during the pollutant reduction process, and the reduction efficiency is relatively low (about 70-90% of the lumped system), so a larger water surface area is required to compensate for the difference in purification efficiency. The gap between the distributed and lumped systems gradually decreases as the water quality targets decrease, mainly because the purification capacity of the distributed ditch-pond wetlands decreases under low water quality targets, which is not obvious under low water quality targets.

[0103] This embodiment also provides a distributed ditch pond wetland water surface rate based on graph theory, including a data acquisition module for investigating and obtaining the topological structure and hydraulic connection data of the distributed ditch pond wetland system; a graph theory model construction module for constructing a graph theory model of the ditch pond wetland system according to the information obtained by the data acquisition module; an adjacency matrix construction module for generating an adjacency matrix describing the flow weight and pollutant reduction weight of the ditch pond wetland system; and an iterative optimization module for searching for the optimal ditch pond wetland system water surface area that meets the water quality requirements through an iterative algorithm.

[0104] This embodiment also provides a computer device, which is suitable for estimating the water surface rate of distributed ditch, pond and wetland in agricultural areas, including a memory and a processor; the memory is used to store computer-executable instructions, and the processor is used to execute computer-executable instructions to achieve the estimation of the water surface rate of distributed ditch, pond and wetland in agricultural areas as proposed in the above embodiment.

[0105] The computer device is a terminal system, including a central processing unit (CPU), memory, communication interface, display and input device connected through a system bus. The processor is used to perform calculation and control functions. The memory is divided into non-volatile storage media and internal memory, the former is used to store operating systems and computer programs, and the latter provides support for the operation of these programs. The communication interface is used to communicate with external terminals via wired or wireless means, and wireless communication can be achieved through WiFi, mobile networks, NFC (near field communication) or other technologies. The display can be a liquid crystal display or an electronic ink display, and the input device includes a touch layer, physical buttons, trackballs, touchpads, or external keyboards, touchpads or mice.

[0106] The present embodiment also provides a storage medium having a computer program stored thereon, which, when executed by a processor, implements the following steps: investigating a distributed ditch-pond system and forming its topological structure; establishing a graph theory model of a distributed ditch-pond wetland based on the ditch-pond topological structure and generating its adjacency matrix; constructing the flow weight of the adjacency matrix based on the flow generation and confluence relationship of the ditch-pond network; quantifying the pollutant reduction weight of the adjacency matrix based on the distributed first-order kinetic process of pollutants; and, based on the graph theory model of the ditch-pond network and its flow and pollutant reduction weights, iterating the ditch-pond area water surface ratio to search for the minimum ditch-pond system water surface area that meets the water quality discharge requirements, with the goal of meeting the discharge standards for the outflow of small watersheds.

[0107] In summary, considering the complex interaction between farmland and drainage ditch and pond systems in the plain river network areas of the south, and combining graph theory models and iterative adjustment analysis, an effective estimation model is proposed, which can comprehensively analyze the complex hydraulic relationship between the plain river network and the drainage ditch and pond system, and reasonably estimate the minimum wetland water surface area. This invention not only improves the scientific nature of wetland system design, but also provides a reliable decision-making basis for agricultural production and ecological environmental services in irrigation areas. In addition, the present invention has important application value in dealing with water quality control issues in the construction of high-standard farmland, and helps to optimize the allocation of water resources and achieve environmental protection goals.

[0108] The above embodiments are only used to help understand the method and core idea of ​​the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A distributed ditch and pond wetland water surface rate calculation method based on graph theory, characterized in that: The following steps are involved: Step 1) Investigate the distributed ditch-pond system and form a ditch-pond topology; Step 2) establishing a graph theory model of the distributed ditch and pond wetland based on the ditch and pond topological structure, and generating its adjacency matrix; Step 3) constructing the flow weight of the adjacency matrix based on the flow generation and confluence relationship of the ditch and pond network; Step 4) quantifying the pollutant reduction weight of the adjacency matrix based on the distributed first-order dynamics of the pollutants; Step 5) Based on the graph theory model of the ditch-pond network and its flow and pollutant reduction weights, with the goal of meeting the discharge quality standards for the outflow of the small watershed, the ditch-pond area water surface ratio is iterated to search for the minimum ditch-pond system water surface area that meets the water quality discharge requirements, and the ditch-pond wetland water surface ratio is estimated.

2. The method for calculating the water surface rate of a distributed ditch and pond wetland based on graph theory according to claim 1 is characterized in that: Step 2) specifically includes: based on the obtained ditch and pond topological structure data, the water flow network of the ditch and pond wetland system is generalized and constructed into a directed graph model, in which nodes serve as representatives of each ditch and pond, and edges are used to characterize the connectivity and water flow paths between the ditches and ponds. By using the matrix representation method in graph theory, an adjacency matrix is ​​generated, thereby accurately describing the connection relationship, water flow direction and potential circulation path of the ditch and pond network in mathematical form.

3. The method for calculating the water surface rate of a distributed ditch and pond wetland based on graph theory according to claim 2 is characterized in that: Step 3) specifically includes: considering the relationship between the flow generation and confluence of the ditch and pond network, assigning the farmland flow to the corresponding edge in the adjacency matrix as the flow weight q i,j , accurately reflects the changing characteristics of the water flow size and direction between ditches and ponds. The calculation process is as follows: In the formula, q i,j is the flow from the i-th ditch-pond wetland unit to the j-th ditch-pond unit, m 3 / day;q i,j,m is the flow rate contributed by the mth farmland flow-producing area during the process of the flow from the ith ditch-pond wetland unit to the jth ditch-pond unit, m 3 / day;q i,n is the flow rate of the nth ditch and pond unit upstream of the i-th ditch and pond wetland unit, m 3 / day; M and N are the total number of farmland and upstream units of the i-th ditch and pond unit, respectively; M = 0 means that there is no farmland inflow to the unit, and N = 0 means that there is no upstream inflow unit to the unit; Among them, farmland output q i,j,m It is estimated by multiplying the estimated farmland area by the farmland drainage flux. The calculation process is as follows: q i,j,m =α i,j h0*A i,m Where h0 is the farmland yield flow, which is approximately estimated by the annual yield flow measured in the field, and m 3 / day; A i,j,m is the area of ​​the mth farmland runoff area in the i-th ditch-pond wetland unit, m 2 ; α i,j is the distribution coefficient of farmland runoff in the process of flowing from the i-th ditch and pond wetland unit to the j-th ditch and pond unit; when the ditch and pond unit i has only one downstream unit j, the distribution coefficient is 1.

4. The method for calculating the water surface rate of a distributed ditch and pond wetland based on graph theory according to claim 3 is characterized in that: Step 4) specifically includes: based on the distributed first-order kinetic process of pollutants in ditch ponds and wetlands, considering factors such as the input concentration of pollutants, the hydraulic retention time of ditch ponds, the degradation coefficient of pollutants and the sedimentation rate, a mathematical model of pollutant concentration changes is established, the reduction coefficient of each ditch pond for specific pollutants is calculated, and it is assigned to the corresponding edge in the adjacency matrix as the pollutant reduction weight ω i,j , quantitatively describe the pollutant reduction capacity of ditch pond wetlands, the calculation process is as follows: In the formula, C t,i,j is the pollutant concentration at the end of the period from the i-th ditch-pond wetland unit to the j-th ditch-pond wetland unit, mgL -1 ; The calculation process is as follows: In the formula, k is the first-order reduction coefficient of pollutants, day -1 ;t h,i is the hydraulic retention time from the i-th ditch-pond wetland unit to the j-th ditch-pond wetland unit, day; C 0,i is the initial pollutant concentration of the i-th ditch, pond and wetland unit in the period, mgL -1 ; The calculation process is as follows: In the formula, C a is the field pollutant output concentration predicted by the farmland model, mgL -1 ; C t,i,n is the pollutant concentration at the end of the period in the nth ditch and pond unit upstream of the i-th ditch and pond wetland unit, mgL -1 ; The final output concentration of the pollutant is the ratio of the remaining pollutant load to the total flow, C t , the calculation process is as follows: In the formula, C t is the total outflow concentration of the ditch and pond network, mg / L; M0 is the initial load entering the ditch and pond network, kg; ΔM is the pollutant load reduced by the ditch and pond network, kg; L is the total number of ditch and pond network units.

5. The method for calculating the water surface rate of a distributed ditch and pond wetland based on graph theory according to claim 4 is characterized in that: Step 5) specifically includes: taking the discharge of small watershed outflow water quality meeting the standard as the goal, establishing constraint conditions, and using the trial and error iteration method to adjust and optimize the water surface ratio of the ditch and pond area; in each iteration, using the established graph theory model, flow weights and pollutant reduction weights, calculate the transmission and reduction process of pollutants in the ditch and pond network, and predict the outflow water quality of the small watershed; based on the calculation results, determine whether the outflow water quality meets the predetermined water quality standard. If not, adjust the ditch and pond water surface ratio according to the optimization algorithm and enter the next iteration.

6. The method for calculating the water surface rate of a distributed ditch and pond wetland based on graph theory according to claim 5 is characterized in that: in: The calculation process of the ditch, pond and wetland water surface ratio ε required for water quality to meet the discharge standards is as follows: Where ε is the wetland water surface ratio, %; μ is the ditch and pond area adjustment coefficient.

7. A distributed ditch pond wetland water surface rate estimation system based on graph theory, used to implement the calculation method described in any one of claims 1 to 6, characterized in that: include: Data collection module, used to investigate and obtain the topological structure and hydraulic connection data of the distributed ditch-pond wetland system; A graph theory model building module, used to build a graph theory model of the ditch pond wetland system based on the information obtained by the data acquisition module; Adjacency matrix building module, used to generate adjacency matrix describing flow weights and pollutant reduction weights of ditch-pond wetland system; The iterative optimization module is used to search for the optimal water surface area of ​​the ditch-pond wetland system that meets the water quality requirements through an iterative algorithm.

8. A computer device comprising a memory and a processor, characterized in that: The memory stores a computer program, wherein: when the processor executes the computer program, the computing method according to any one of claims 1 to 6 is implemented.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the computing method according to any one of claims 1 to 6 is implemented.

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