A method for analyzing river pollution input in plain river network areas based on a basin hydrological and water quality model

Abstract

A method for analyzing river pollution in plain river network areas based on a watershed hydrological and water quality model, belonging to the technical field of comprehensive water environment treatment; aiming at the complex hydrological characteristics and the problem that pollution sources are difficult to trace in plain river network areas, through river channel topological relationship sorting, sub-watershed division, watershed hydrological and water quality model construction, pollution load calculation and pollution source composition analysis, accurate analysis of river pollutants is achieved; the specific technical steps include river channel screening and topological relationship sorting, sub-watershed division based on ArcSWAT, watershed hydrological and water quality model building and simulation, pollution load calculation and pollution source identification; this method can reasonably divide the watershed, simulate the scouring and river entry process of pollutants, improve the accuracy of pollution source analysis, significantly improve the treatment efficiency, achieve accurate tracing and quantitative analysis of pollutants in plain river network areas, and provide strong data support and theoretical basis for the precise comprehensive treatment of water environment.

Description

Technical Field

[0001] The present invention relates to the technical field of comprehensive water environment treatment, and particularly relates to a method for analyzing river pollution in plain river network areas based on a basin hydrological and water quality model. Background Art

[0002] At present, the concept of water environment treatment has gradually changed from the traditional idea mainly based on "end treatment" to a water pollution treatment mode of "source control, process interruption, and end treatment" for the whole process prevention and control. The comprehensive treatment of the basin water environment has become the main direction of water pollution treatment. With the continuous advancement of the comprehensive water environment treatment work, the number of comprehensive water environment treatment projects in the basin is increasing day by day. However, from the perspective of the implementation effect of the projects, most projects do not fully combine the current pollution situation and pollution characteristics of the basin for in-depth technical analysis, resulting in the phenomenon of applying a unified treatment plan template in multiple projects. This is not only uneconomical but also greatly reduces the actual application effect.

[0003] In order to improve the treatment efficiency, it is necessary to formulate a more targeted and effective comprehensive treatment plan in combination with the regional status quo. Formulating such a plan requires a comprehensive understanding of the basin situation, including pollution sources, the proportion of various pollution sources, the pollution load generated in different regions, and the pollution characteristics of the river. However, the types of basin pollution are complex and diverse, the discharge paths are numerous, and it is often difficult to directly trace the water body pollution sources, and these problems are particularly prominent in plain river network areas.

[0004] In plain river network areas, the terrain is flat, the river network is densely intertwined, the water system is complex, and dikes are usually built to form their own enclosures. Control facilities such as sluices and pumps are often installed on the river channels, making the water flow largely artificially controlled, and the pollution in the same polder area may flow into different water bodies. Due to these complex hydrological characteristics, it is often difficult to accurately calculate the pollution load entering an important water body when conducting statistical analysis of river pollutants in plain river network areas.

[0005] Traditional analysis means are unable to cope with the complex situation in plain river network areas and cannot meet the needs of precise pollution control. Therefore, it is necessary to use numerical simulation technology to simulate the water environment, hydrology, and water quality processes of the whole basin for a long time. Through the detailed description of the basin, complex water environment problems can be made analyzable and calculable, so as to provide a strong guiding basis for the design of comprehensive water environment treatment plans.

[0006] However, current watershed models are more often applied to dendritic river systems with large topographic undulations, where the water flow direction is from top to bottom and not affected by human regulation. In these areas, it is relatively easy to identify the current river system and reasonable catchment areas that conform to the current situation using model software based on elevation data. However, in plain river network areas, due to the flat terrain and significant human influence among river systems, it is difficult to directly divide the river system and reasonable catchment areas that conform to the actual situation using existing watershed model software.

[0007] In summary, there are many unreasonable aspects in directly using existing watershed models to construct hydrological and water quality models for plain river network areas. There is an urgent need to establish a more applicable method for analyzing pollution entering rivers at the watershed level in plain river network areas to address the current technical challenges and limitations of existing technical methods. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a method for analyzing pollution entering rivers in plain river network areas based on a watershed hydrological and water quality model, so as to solve the technical problems in water pollution control under the complex hydrological characteristics of plain river network areas. Specifically, at present, due to the flat terrain, dense and intertwined river networks, complex water systems and significant human regulation in plain river network areas, traditional pollution analysis methods are difficult to accurately calculate the pollution load entering important water bodies, thus affecting the accuracy and effectiveness of water environment governance. By providing a method for analyzing pollution entering rivers in plain river network areas based on a watershed hydrological and water quality model, the present invention aims to overcome the limitations in the prior art that are unable to accurately trace the source and calculate the pollution load in plain river network areas.

[0009] To solve the above technical problems, the technical solution adopted by the present invention is as follows: A method for analyzing pollution entering rivers in plain river network areas based on a watershed hydrological and water quality model, comprising the following steps:

[0010] Step1: Based on project objectives, requirements and demands, combined with river system data, image maps, and planning data, conduct river channel screening to select the key river channels to be simulated and depicted, and sort out the river channel topological relationship in combination with data such as gate-pump scheduling rules, polder area planning, and current river system status;

[0011] Step2: Conduct sub-catchment area division, and reasonably divide the plain river network area according to the principles of large watershed division, sub-region division, and hierarchical division to obtain reasonable catchment areas;

[0012] Step3: Combine land use and soil type data to conduct hydrological response unit division, which serves as the smallest calculation unit of the model;

[0013] Step 4: Combine data such as meteorological data, agricultural planting data, livestock and poultry breeding, aquaculture, industrial pollution, and the tail water of sewage treatment plants. Based on the sub-watershed partitions and hydrological response units divided in Step 2 - Step 3, extract information such as area, slope, river depth, width, length, and slope, and build a watershed hydrological and water quality model;

[0014] Step 5: Use the built watershed hydrological and water quality model to simulate processes such as water infiltration, evaporation, overland flow, and pollutant scouring, degradation, sedimentation, and river entry. Combine real-time monitoring data for model parameter calibration;

[0015] Step 6: According to the model results, statistically analyze the total river entry load, the composition and proportion of pollution sources, and identify key pollution areas.

[0016] In the preferred solution, the specific method for reasonable partitioning in Step 2 includes: for areas with polder areas, use the polder area as the catchment unit, and set the outlet position of the catchment partition according to the location of the drainage pumping station; if the polder area is large and there are multiple rivers inside, further cut it into smaller catchment units according to elevation data; the partitioning of the remaining catchment areas is carried out by combining automatic and manual methods based on elevation data and river network conditions; during the partitioning process, if an aquaculture fish pond or lake is encountered, it is divided into separate catchment partitions respectively.

[0017] In the preferred solution, during the partitioning of the sub-watershed partitions in Step 2, it also involves cutting the fish ponds spanning two polder areas into sub-watersheds according to the specific location of the aquaculture fish ponds and the boundaries of the polder areas.

[0018] In the preferred solution, the LSPC (Loading Simulation Program C, watershed modeling system) watershed hydrological and water quality model is used in Step 5 to simulate losses or increases in various migration processes such as water infiltration, evaporation, scouring, degradation, and sedimentation of water volume and load.

[0019] In the preferred solution, the watershed hydrological and water quality model in Step 5 includes a rainfall-runoff calculation model and a pollutant scouring calculation model. Among them, the rainfall-runoff calculation model uses the Chezy-Manning equation and an empirical expression of the relationship between outflow depth and retention volume to calculate the overland flow; the pollutant scouring calculation model is used to calculate the scouring amount of surface pollutants.

[0020] In the preferred solution, the model parameter calibration process in Step 5 includes using hydrological and water quality monitoring data for parameter adjustment to ensure the accuracy and reliability of the model.

[0021] A method for analyzing river entry pollution in plain river network areas based on a watershed hydrological and water quality model provided by the present invention has the following beneficial effects:

[0022] 1. The present invention solves the technical problems in water pollution control under the complex hydrological characteristics in the plain river network area, and overcomes the limitations in the prior art that cannot accurately trace the source and calculate the pollution load in the plain river network area;

[0023] 2. Considering the hydrological characteristics of the plain river network area, the present invention establishes a method of "large watershed division, sub-region division, and hierarchical division" for dividing sub-catchment areas. It fully considers the complexity of the flat terrain, polder area scheduling, crisscrossing river networks, and many lakes and marshes in the plain river network area, reasonably divides the catchment areas, and ensures that the surface runoff and pollutant convergence paths are reasonable, coming from the same catchment area and flowing into the same river, guaranteeing the rationality and correctness of the basin model simulation;

[0024] 3. Based on ArcSWAT (ArcGIS for Soil and Water Assessment Tool, a basin hydrological model and environmental simulation software), the present invention can perform automatic division of catchment areas in combination with elevation data and the current situation of water systems. At the same time, it can be manually adjusted according to the regional situation, without the need for additional operation tools, and can directly output the input format required by the basin hydrological and water quality model, with convenient operation;

[0025] 4. Based on the basin hydrological and water quality model, the present invention fully considers the scouring and river entry processes of pollutants on land, can reasonably simulate the process of pollutant generation - river entry, and can achieve accurate source tracing;

[0026] 5. By reasonably dividing the catchment areas and constructing a basin hydrological and water quality model, the present invention can accurately simulate the hydrological and water quality processes in the plain river network area, realize accurate source tracing of pollutants and accurate calculation of pollution load;

[0027] 6. The present invention provides scientific data support and theoretical basis for the comprehensive water environment management project, helps to formulate targeted treatment plans, and thus improves the treatment efficiency and effect;

[0028] 7. Based on ArcSWAT, the present invention performs automatic zoning in combination with elevation data and the current situation of water systems, and at the same time supports manual adjustment, with simple operation and high universality;

[0029] 8. By providing a method for analyzing river - entering pollution in the plain river network area based on the basin hydrological and water quality model, the present invention significantly improves the accuracy of pollution analysis and treatment efficiency, and provides strong support for the comprehensive water environment management;

[0030] 9. The present invention realizes accurate source tracing and quantitative analysis of pollutants in the plain river network area, and provides strong data support and theoretical basis for the precise comprehensive management of the water environment. Description of the Drawings

[0031] The present invention will be further described below in conjunction with the drawings and embodiments:

[0032] Figure 1 is the working process diagram of the present invention;

[0033] Figure 2 is the schematic diagram of the sub - catchment area division result of the present invention;

[0034] Figure 3 is the pollution space distribution map of the present invention. Detailed Embodiment

[0035] The technical solutions in the present invention will be further described below in conjunction with the drawings and embodiments:

[0036] Embodiment 1

[0037] As Figure 1 shown, a method for analyzing the pollution entering rivers in plain river network areas based on a basin hydrological and water quality model includes the following steps:

[0038] Step1: Based on the project objectives, requirements, and demands, combined with water system data, image maps, and planning data, conduct river channel screening to select the key river channels to be simulated and characterized. Combine data such as sluice - pump scheduling rules, polder area planning, and water system status to sort out the river channel topological relationship;

[0039] Step2: Conduct sub - catchment area division. Adopt the principles of large - basin division, sub - area division, and hierarchical division to reasonably divide the plain river network area and obtain a reasonable catchment area division;

[0040] Step3: Combine land use and soil type data to conduct hydrological response unit division, which serves as the smallest calculation unit of the model;

[0041] Step4: Combine meteorological data, agricultural planting data, livestock and poultry breeding, aquaculture, industrial pollution, sewage treatment plant effluent and other data. Based on the sub - catchment area and hydrological response unit divided in Step2 - Step3, extract information such as area, slope, river channel depth, width, length, and slope, and build a basin hydrological and water quality model;

[0042] Step5: Use the established basin hydrological and water quality model to simulate processes such as water infiltration, evaporation, overland flow, and pollutant scouring, degradation, sedimentation, and entry into rivers. Combine real - time monitoring data to calibrate the model parameters;

[0043] Step6: According to the model results, statistically analyze the total pollution load entering rivers, the composition and proportion of pollution sources, and identify key pollution areas.

[0044] In this embodiment, the specific method for reasonable division in Step 2 includes: for areas with polder areas, taking the polder area as the catchment unit, setting the outlet position of the catchment sub - area according to the location of the drainage pumping station; if the polder area is large and there are multiple rivers inside, it is further cut into smaller catchment units according to the elevation data; the division of the remaining catchment areas is carried out by combining automatic and manual methods according to the elevation data and the river network situation; during the division process, if there are aquaculture fish ponds or lakes, they are respectively divided as separate catchment sub - areas.

[0045] Furthermore, during the division process of the sub - catchment areas in Step 2, it also involves cutting the sub - basins of the fish ponds that straddle two polder areas according to the specific location of the aquaculture fish ponds and the polder boundaries.

[0046] Furthermore, in Step 5, the LSPC (Loading Simulation Program C, Watershed Modeling System) watershed hydrological and water quality model is adopted for the watershed hydrological and water quality model to simulate the losses or increases in various migration processes such as infiltration, evaporation, scouring, degradation, and sedimentation of water volume and load.

[0047] Furthermore, the watershed hydrological and water quality model in Step 5 includes a rainfall - runoff calculation model and a pollutant scouring calculation model. Among them, the rainfall - runoff calculation model uses the Chezy - Manning equation and an empirical expression of the relationship between the outflow depth and the retention volume to calculate the slope surface flow; the pollutant scouring calculation model is used to calculate the scouring amount of surface pollutants.

[0048] Furthermore, the model parameter calibration process in Step 5 includes using hydrological and water quality monitoring data for parameter adjustment to ensure the accuracy and reliability of the model.

[0049] Furthermore, the construction of the watershed hydrological and water quality model in Step 5 specifically includes the following steps:

[0050] Step5.1: Use the land use type map and soil type map to divide the hydrological response units, and calculate the area of various hydrological response units in each sub - catchment area.

[0051] Step5.2: Extract the characteristic values and parameters required for the watershed hydrological and water quality model, including the river channel length, slope, flow direction, width, depth, the area and slope of the catchment sub - area, the underlying surface type, the types of agricultural crops and fertilization amount, the types and quantities of livestock and poultry farming, aquaculture information, the location information of pollution sources, the altitude of the meteorological station and meteorological data.

[0052] Step5.3: Make meteorological files, point source files, and flow boundary input files.

[0053] Step5.4: Build a watershed hydrological and water quality model and calibrate the model in combination with hydrological and water quality monitoring data;

[0054] Step5.5: Construct a rainfall-runoff calculation model. Using the Chezy-Manning equation and the empirical expression of the relationship between the outflow depth and the retention volume, the calculation formula for overland flow outflow is:

[0055] (1)

[0056] (2)

[0057] (3)

[0058] (4)

[0059] (5)

[0060] (6)

[0061] (7)

[0062] Among them, is the surface outflow; is the time step, 60 is the time, unit: second; is the average surface retention volume within the simulation time interval; is the equilibrium surface retention volume under the current supply; is the moisture supply rate of overland flow; is the potential surface retention volume; is the initial surface storage; is the initial surface starting storage; is the overland Manning coefficient; is the overland length; is the overland slope, 、 are intermediate variables;

[0063] Equation (1) represents the situation of increasing overland flow, and equation (2) represents the situation where the surface water volume is in equilibrium or the overland flow decreases;

[0064] Construct a pollutant wash-off calculation model. The calculation formula for surface pollutant wash-off is:

[0065] (8)

[0066] (9)

[0067] Among them, is the amount of pollutants washed off from the surface; is the amount of pollutant storage available on the surface for direct flushing by overland flow; is the sensitivity parameter between pollutant amount and washoff; is the amount of pollutant storage available on the previous surface for direct flushing by overland flow; is dry deposition or total deposition flux; is the rainfall; is the atmospheric wet deposition concentration.

[0068] Example 2

[0069] In another preferred embodiment, based on the above embodiment 1, Figure 1 As shown in the figure, a method for analyzing river inflow pollution in plain river network areas based on the basin hydrological and water quality model is proposed. This technology is based on the basin hydrological and water quality model, combined with ArcSWAT to divide sub-catchment areas, and follows the division principles of "large basin division, sub-area division, and hierarchical division". It can reasonably divide the plain river network area into sub-catchment areas and build a basin hydrological and water quality model. It can reasonably simulate regional pollution sources, calculate river inflow loads, identify the composition and proportion of pollution sources, and identify key pollution areas, providing support for precise governance and control decisions of basin waters.

[0070] The method comprises the following steps:

[0071] S1. Sorting out river channel topological relationships

[0072] Based on project goals, needs, and requirements, river channels were screened using water system data, image maps, and planning information to identify key river channels for simulation. River channel topology was then analyzed using data on sluice and pump scheduling rules, polder area planning, and the current state of the water system to determine the location of pollution.

[0073] S2. Subcatchment division

[0074] The watershed division is based on ArcSWAT. The division principle is "large watershed division, sub-area division, and hierarchical division". The specific division method is as follows:

[0075] For areas with polders, the polder area is used as a catchment unit. The discharge of water from the polder area into the river network is influenced by the drainage station, and the outlet location of the catchment sub-area is determined based on the location of the drainage station into the river network. If the polder area is large and contains multiple rivers, the polder area can be further divided into smaller catchment units based on the elevation data within the polder area and the river network within the polder area. The outlet location of the sub-basin is defined by the location of the drainage station.

[0076] The remaining area of the catchment area is divided automatically + manually based on elevation data and river network conditions. During the division process, if an aquaculture fishpond is encountered, the fishpond is divided as a separate catchment area. If a fishpond straddles two polder areas, the sub-basin is cut according to the polder boundary. Lakes are also divided as separate catchment areas.

[0077] S3. Division of Hydrological Response Units

[0078] Combined with land use and soil type data, hydrological response units are divided as the smallest computational units of the model.

[0079] S4. Construction of Watershed Model

[0080] Based on the catchment area division and river network topological relationship, a watershed hydrological and water quality model is constructed. This model depicts the process of non-point source scouring into the river, expresses the formation and emission processes of various pollution sources, and simulates the temporal and spatial variation processes of COD (Chemical Oxygen Demand), ammonia nitrogen, total nitrogen, and total phosphorus. The specific steps are as follows:

[0081] Use the land use type map and soil type map to divide hydrological response units as the smallest computational units of the model, and calculate the areas of various hydrological response units in each sub-catchment area.

[0082] Extract the characteristic values and parameters required for the watershed hydrological and water quality model, including river length, slope, flow direction, width, depth, catchment area, slope, underlying surface type, agricultural planting types and fertilization amounts, livestock and poultry breeding types and quantities, aquaculture information, pollution source location information, elevation of meteorological stations and meteorological data, etc.

[0083] Make meteorological files, point source files, and flow boundary input files.

[0084] Build a watershed hydrological and water quality model and calibrate the model in combination with hydrological and water quality monitoring data.

[0085] S5. Pollution Load Simulation and Analysis

[0086] Use the established watershed hydrological and water quality model to simulate processes such as water infiltration, water diversion, evaporation, overland flow, and pollutant scouring, degradation, sedimentation, and entry into the river. The specific calculation models include the following:

[0087] Construct a rainfall-runoff calculation model. Using the Chezy-Manning equation and the empirical expression of the relationship between outflow depth and retention volume, the overland flow outflow calculation formula is as follows:

[0088] (1)

[0089] (2)

[0090] (3)

[0091] (4)

[0092] (5)

[0093] (6)

[0094] (7)

[0095] Among them, is surface runoff; is the time step, 60 is the time, unit: second; is the average surface retention within the simulation time interval; is the equilibrium surface retention under the current supply; is the water supply rate of overland flow; is the potential surface retention; is the initial surface storage; is the initial surface starting storage; is the overland Manning coefficient; is the overland length; is the overland slope, , are intermediate variables;

[0096] Equation (1) represents the situation of increasing overland flow, and Equation (2) represents the equilibrium state of surface water volume or decreasing overland flow;

[0097] Construct a pollutant wash-off calculation model, surface pollutant wash-off calculation formula:

[0098] (8)

[0099] (9)

[0100] Among them, is the amount of pollutants washed off from the surface; is the storage of pollutants on the surface that can be directly washed off by overland flow; is the sensitivity parameter between the amount of pollutants and wash-off; is the previous storage of pollutants on the surface that can be directly washed off by overland flow; is the dry deposition or total deposition flux; is the rainfall; is the atmospheric wet deposition concentration.

[0101] S6. Pollution Analysis

[0102] Combined with the gate-pump scheduling rules, statistically analyze the river inflow loads and their proportions of various pollution sources, and analyze the pollution characteristics in the region. Taking a certain region as an example, after reasonably dividing the sub-catchment areas (such as Figure 2 shown), based on the divided catchment areas, build a regional river basin hydrological and water quality model. Through the model simulation of the scouring and river inflow processes of pollutants, depict the spatio-temporal variation process of the land hydrological and water quality. Obtain the river inflow loads (see Table 1) and the spatial distribution of pollution loads in the study area (such as Figure 3 ), and identify the key pollution sources and key pollution areas.

[0103] Through the above specific implementation manners, the present application realizes the accurate source tracing and quantitative analysis of pollutants in the plain river network area, providing strong data support and theoretical basis for the comprehensive treatment of water environment.

[0104] Table 1 Pollution load statistics

[0105]

[0106] In the preferred solution, the specific method for reasonable division in Step 2 includes: for areas with polder areas, taking the polder area as the catchment unit, and setting the outlet position of the catchment area according to the location of the drainage pumping station; if the polder area is large and there are multiple rivers inside, further cut it into smaller catchment units according to the elevation data; the division of the remaining regional catchment areas is carried out by combining automatic and manual methods according to the elevation data and the river network situation; during the division process, if an aquaculture fish pond or a lake is encountered, they are respectively divided as separate catchment areas; the above settings ensure the independence of each catchment area and the convenience of management; at the same time, use GIS (Geographic Information System) technology to assist in the analysis, accurately simulate the water flow path, optimize the layout of the drainage system, and improve the overall drainage efficiency and flood control ability.

[0107] In the preferred solution, during the division process of the sub-catchment areas in Step 2, it also involves cutting the fish ponds straddling two polder areas according to the specific location of the aquaculture fish ponds and the polder area boundaries; the above settings ensure the accuracy of the sub-catchment areas, effectively avoiding confusion and omission in water resource management; at the same time, for special terrains and fish pond layouts, adopt customized division strategies to improve the water resource utilization efficiency.

[0108] In the preferred solution, in Step 5, the watershed hydrological and water quality model adopts the LSPC (Loading Simulation Program C, watershed modeling system) watershed hydrological and water quality model to simulate losses or increases in various migration processes such as infiltration, evaporation, scouring, degradation, and sedimentation of water volume and load; the above settings can accurately capture the dynamic changes of hydrology and water quality in the watershed, providing a scientific basis for water resource management and environmental protection; at the same time, this model also has high flexibility and can adjust parameters according to actual needs to ensure the accuracy and practicality of simulation results.

[0109] In the preferred solution, the watershed hydrological and water quality model in Step 5 includes a rainfall-runoff calculation model and a pollutant scouring calculation model. Among them, the rainfall-runoff calculation model uses the Chezy-Manning equation and an empirical expression of the relationship between outflow depth and retention volume to calculate the slope surface flow; the pollutant scouring calculation model is used to calculate the scouring amount of surface pollutants; the above settings can comprehensively simulate the hydrological cycle and water quality change process in the watershed, improve the decision-making support ability for water resource management and environmental protection, and ensure the data accuracy and the effectiveness of model prediction.

[0110] In the preferred solution, the model parameter calibration process in Step 5 includes using hydrological and water quality monitoring data to adjust parameters to ensure the accuracy and reliability of the model; the above settings also include verifying the calibrated model, testing its prediction ability through an independent data set, further adjusting and optimizing parameters until the established standards are met, and finally locking the optimal parameter combination to provide a solid foundation for subsequent applications.

[0111] In summary, the present invention provides a method for analyzing river pollution in plain river network areas based on a basin hydrological and water quality model, which solves the technical problems in water pollution control under the complex hydrological characteristics of plain river network areas, and overcomes the limitations of the prior art in terms of inaccurate source tracing and pollution load accounting in plain river network areas; considering the hydrological characteristics of plain river network areas, the present invention establishes a method of "large basin division, sub-region division, and hierarchical division" for dividing sub-catchment areas, fully taking into account the complexity of flat terrain, polder area scheduling, dense river network, and numerous lakes and marshes in plain river network areas, reasonably dividing the catchment areas, ensuring that the surface runoff and pollutant convergence paths are reasonable, coming from the same catchment area and flowing into the same river, and ensuring the rationality and correctness of basin model simulation; based on ArcSWAT, the present invention can perform automatic division of catchment areas in combination with elevation data and the current water system status, and can be manually adjusted according to the regional status at the same time, without the need for additional operation tools, and can directly output the input format required by the basin hydrological and water quality model, with convenient operation; based on the basin hydrological and water quality model, the present invention fully considers the scouring and river entry processes of pollutants on land, can reasonably simulate the process of pollutant generation-river entry, and can achieve accurate source tracing; by reasonably dividing the catchment areas and constructing a basin hydrological and water quality model, the present invention can accurately simulate the hydrological and water quality processes in plain river network areas, achieve accurate source tracing of pollutants and accurate accounting of pollution loads; the present invention provides scientific data support and theoretical basis for water environment comprehensive treatment projects, helps to formulate targeted treatment plans, and thus improves the treatment efficiency and effect; based on ArcSWAT, the present invention performs automatic zoning in combination with elevation data and the current water system status, and supports manual adjustment at the same time, with simple operation and high universality; by providing a method for analyzing river pollution in plain river network areas based on a basin hydrological and water quality model, the present invention significantly improves the accuracy of pollution analysis and treatment efficiency, and provides strong support for water environment comprehensive treatment.

Claims

1. A method for analyzing river pollution in plain river network areas based on a basin hydrological and water quality model, characterized in that, The method includes the following steps: Step1: Based on the project objectives, requirements, and specifications, combine water system data, image maps, and planning data to screen river channels, select key river channels to be simulated and depicted, and sort out the river channel topological relationship in combination with the gate-pump scheduling rules, polder area planning, and water system status data; Step2: Conduct sub-catchment area division. Adopt the principles of large river basin division, sub-region division, and hierarchical division to reasonably divide the plain river network area and obtain reasonable catchment areas; Step3: Combine land use and soil type data to divide hydrological response units, which serve as the smallest calculation units of the model; Step4: Combine meteorological data, agricultural planting data, livestock and poultry breeding, aquaculture, industrial pollution, and wastewater treatment plant effluent data. Based on the sub-catchment areas and hydrological response units divided in Step2~Step3, extract information such as area, slope, river channel depth, width, length, and slope, and build a basin hydrological and water quality model; Step5: Use the established basin hydrological and water quality model to simulate the processes of water infiltration, evaporation, overland flow, and pollutant scour, degradation, sedimentation, and river entry. Combine real-time monitoring data to calibrate the model parameters. The specific steps are as follows: Step5.1: Use land use type maps and soil type maps to divide hydrological response units and calculate the areas of various hydrological response units in each sub-catchment area; Step5.2: Extract the characteristic values and parameters required by the basin hydrological and water quality model, including river channel length, slope, flow direction, width, depth, the area and slope of the catchment area, underlying surface type, agricultural planting types and fertilization amounts, livestock and poultry breeding types and quantities, aquaculture information, pollutant source location information, elevation of meteorological stations, and meteorological data; Step5.3: Produce meteorological files, point source files, and flow boundary input files; Step5.4: Build a basin hydrological and water quality model and calibrate the model in combination with hydrological and water quality monitoring data; Step5.5: Build a rainfall-runoff calculation model. Use the Chezy-Manning equation and the empirical expression of the relationship between outflow depth and retention volume. The overland flow calculation formula on the slope: （1）； （2）； （3）； （4）； （5）； （6）； （7）； Among them, is surface runoff; is the time step; is the average surface retention within the simulation time interval; is the equilibrium surface retention under the current supply; is the water supply rate of overland flow; is the potential surface retention; is the initial surface storage; is the initial surface starting storage; is the overland Manning coefficient; is the overland length; is the overland slope, 、 are intermediate variables; Equation (1) represents the situation of increasing overland flow, and Equation (2) represents the situation where the surface water volume is in balance or the overland flow decreases; Build a pollutant scour calculation model. The surface pollutant scour calculation formula: （8）； （9）； wherein, is the amount of pollutants washed from the ground surface; is the storage amount of pollutants on the ground surface available for direct scouring by overland flow; is the sensitivity parameter between the amount of pollutants and scouring; is the previous storage amount of pollutants on the ground surface available for direct scouring by overland flow; is the dry deposition or total deposition flux; is the rainfall; is the atmospheric wet deposition concentration; Step6: According to the model results, statistically analyze the total river entry load, pollutant source composition and proportion, and identify key pollution areas.

2. The method for analyzing the pollution entering rivers in the plain river network area based on the basin hydrological and water quality model according to claim 1, characterized in that, The specific method of reasonable division in Step2 includes: for areas with polders, use the polder as the catchment unit and set the catchment area outlet location according to the position of the drainage pumping station; if the polder is large and there are multiple rivers inside, further cut it into smaller catchment units according to elevation data; for the remaining area catchment area division, it is divided automatically and manually in combination with elevation data and river network conditions; during the division process, if an aquaculture fish pond or lake is encountered, it is divided into separate catchment areas respectively.

3. A method for analyzing pollution entering rivers in plain river network areas based on a basin hydrological and water quality model according to claim 1, characterized in that: In the process of dividing the sub-catchment areas in Step 2, it also involves cutting the fish ponds that straddle two polder areas according to the specific locations of the aquaculture fish ponds and the boundaries of the polder areas.

4. A method for analyzing pollution entering rivers in plain river network areas based on a basin hydrological and water quality model according to claim 1, characterized in that: In Step 5, the LSPC watershed hydrological and water quality model is adopted as the watershed hydrological and water quality model to simulate the losses or increases in various migration processes such as infiltration, evaporation, scouring, degradation, and sedimentation of water volume and load.

5. A method for analyzing pollution entering rivers in plain river network areas based on a basin hydrological and water quality model according to claim 1, characterized in that: In Step 5, the watershed hydrological and water quality model includes a rainfall-runoff calculation model and a pollutant scouring calculation model. Among them, the rainfall-runoff calculation model uses the Chezy-Manning equation and an empirical expression of the relationship between the outflow depth and the retention volume to calculate the overland flow. The pollutant scouring calculation model is used to calculate the scouring amount of surface pollutants.

6. The method for analyzing pollution entering river in plain river network area based on basin hydrological and water quality model according to claim 1, characterized in that: In Step 5, the model parameter calibration process includes using hydrological and water quality monitoring data for parameter adjustment to ensure the accuracy and reliability of the model.

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