Water environment capacity evaluation and pollutant quantitative reduction method based on rain pattern classification

Abstract

The invention discloses a rain pattern classification-based water environment capacity evaluation and pollutant quantitative reduction method, which comprises the following steps of: obtaining modeling data, and constructing a water environment mathematical model; determining pollutants; the concentration and the flow of pollutants discharged by the rainwater pump station under different rain types are collected; the pollutant concentration and flow data are input into the water environment mathematical model, and high-time-precision water quality and water quantity data of the assessment section under different rain patterns are obtained; calculating the water environment capacity under the condition of no rainwater pump station discharge and the water environment capacity under the condition of rainwater pump station discharge; and according to the water environment capacity value, rainwater pump station reduction schemes and corresponding pollutant reduction rates under different rain patterns are given. According to the method, the migration and transformation rule of the water quality of the water body can be reflected more truly, the attenuation effect of the pollutants is fully considered, the relation between the rainwater pump station and the water environment capacity is clarified, a corresponding pollutant quantitative reduction scheme is given, and the method has the advantages of being high in applicability, easy to operate and the like.

Description

Technical Field

[0001] The invention belongs to the field of river water environment management, and in particular relates to a water environment capacity assessment and pollutant quantitative reduction method based on rain type classification. Background Art

[0002] Water environment capacity reflects the ability of water to dilute, purify, migrate and transform pollutants under natural conditions. It is the basis and basis for formulating water discharge standards, controlling total water pollution and achieving water quality goals. The research and application of water environment capacity provides a scientific basis for water environment planning and protection, helps solve the water environment problems facing the country, and is of great significance for protecting the water ecological environment and promoting sustainable economic and social development.

[0003] However, the current calculation formula for water environment capacity is generally based on the average value of various indicators within a certain time range, which has certain limitations in the calculation of time accuracy and cannot accurately calculate the water environment capacity of the study area. At the same time, few studies can clarify the relationship between pump station discharge and water environment capacity, which is not conducive to river water environment management. Summary of the invention

[0004] Purpose of the invention: In order to overcome the shortcomings of the existing technology in time accuracy calculation, a water environment capacity assessment and pollutant quantitative reduction method based on rain type classification is provided, which can comprehensively consider the influence of factors such as rainfall, make up for the shortcomings of conventional water environment capacity calculation methods in time accuracy, and can more truly reflect the migration and transformation laws of water quality, fully consider the attenuation effect of pollutants, clarify the relationship between rainwater pumping stations and water environment capacity, and give corresponding pollutant quantitative reduction plans. It has the advantages of strong applicability and easy operation, is suitable for promotion and use, and provides a certain basis for the scientific research of subsequent overflow pollution reduction plans.

[0005] Technical solution: To achieve the above purpose, the present invention provides a method for water environment capacity assessment and pollutant quantitative reduction based on rain type classification, comprising the following steps:

[0006] S1: Obtain modeling data of corresponding rivers in the specified area and construct corresponding water environment mathematical model;

[0007] S2: Determine the pollutants to be predicted;

[0008] S3: According to the pollutants determined in step S2, the concentration and flow rate of pollutants discharged by the rainwater pumping station under different rain types are collected;

[0009] S4: Input the pollutant concentration and flow data of step S3 into the water environment mathematical model to obtain high-time-precision water quality and water quantity data of the assessment section under different rainfall types;

[0010] S5: Calculate the water environment capacity without rainwater pump station discharge and the water environment capacity with rainwater pump station discharge according to the water quality and water quantity data obtained in step S4;

[0011] S6: Based on the calculated water environment capacity value, the rainwater pump station reduction plan and the corresponding pollutant reduction rate under different rainfall types are given.

[0012] Furthermore, the water environment mathematical model in step S1 includes a hydrodynamic module (HD) and a water quality module (AD). The hydrodynamic model calculation adopts the Saint-Venant equations describing the one-dimensional unsteady flow in the open channel, including the mass conservation equation and the momentum conservation equation, and additionally considers the floodplain and lateral inflow:

[0013]

[0014] Where, formula (1) is the mass conservation equation, formula (2) is the momentum conservation equation; A is the cross-sectional area of ​​the water passage, m 2 ; Q is the flow rate, m 3 / s; t is the time coordinate; x is the distance coordinate; q is the side inflow, m 3 / s; g is the acceleration due to gravity, m / s 2 ; h is the water level, m; C is the Xiecai coefficient, R is the hydraulic radius, m / s.

[0015] The water quality model, namely the advection diffusion module (AD), uses the hydrodynamic conditions generated by the HD module to calculate the soluble and suspended substances in the water body using the advection diffusion equation. The AD module can accurately calculate and simulate the transport process of pollutants. The specific calculation equation is as follows:

[0016]

[0017] Where C is the pollutant concentration, mg / L; t is the time, s; u is the flow velocity, m / s; x is the spatial coordinate along the water flow direction, m; D is the diffusion coefficient, m 2 / s; K is the first-order attenuation coefficient, 1 / d.

[0018] Furthermore, the modeling data in step S1 include a water system map of the study area, river topography data, hydrodynamic and water quality parameters such as pollutant degradation coefficients, hydrological information data, river pollutant concentrations, rainwater pump station discharge and pollutant concentrations.

[0019] Furthermore, the method for determining pollutants in step S2 is: according to the water quality requirements of the key river monitoring sections in the study area and the main exceeding factors of the monitoring sections under the current situation, combined with the "Surface Water Environmental Quality Standard" (GB3838-2002), determine the conventional water quality affecting pollutants.

[0020] Furthermore, in step S3, the drainage flow and water quality data of the rainwater pumping station are input into the model in the form of point source pollution, and the rainfall in the study period is statistically analyzed based on the drainage volume and pollutant emission concentration in the time series, where the rainfall is divided into 6 levels, level 1: 24-hour rainfall is less than 10 mm, level 2: 24-hour rainfall is 10-25 mm, level 3: 24-hour rainfall is 25-50 mm, and level 4: 24-hour rainfall is greater than 50 mm.

[0021] Furthermore, in step S4, before the pollutant concentration and flow data are input into the water environment mathematical model, the parameters of the hydrodynamic module and the water quality module are calibrated and verified, that is, the measured values ​​and simulated values ​​representing the cross-section are compared and analyzed, the corresponding errors are calculated, and the model parameters are continuously adjusted so that the errors are within the required accuracy of the model, which can be used for subsequent model applications; according to the time accuracy requirements for the results, the corresponding accuracy is set through the model output option, and the corresponding time series data is exported.

[0022] Furthermore, the calculation method of the water environment capacity in step S5 is:

[0023]

[0024] Where: For target accuracy (such as d -1 ) flow, m 3 / s; For the target accuracy within the self-computation unit (such as d -1 ) Wastewater discharge, m 3 / s;C s is the limit of the water environment functional area of ​​the calculation unit, mg / L; The target accuracy of the upstream water pollutant in the calculation unit (such as d -1 ) concentration, mg / L; T is the calculation time (depending on the requirements, such as d); W i For the i-th target accuracy (such as d -1 ) calculates the unit water environment capacity, kg / x (i.e., kg / d); W is the water environment capacity value calculated on the basis of the water environment capacity under target accuracy, kg.

[0025] Furthermore, the step S6 is specifically as follows:

[0026] According to step S5, the water environment capacity under different working conditions is calculated, and the difference in water environment capacity with and without rainwater pump station discharge, as well as the pollutant reduction rate under different reduction amounts are calculated, and the reduction plan of rainwater pump stations under different rain types is given. The calculation formula is as follows:

[0027] W0=W2-W1

[0028]

[0029] Where W0 is the water environment capacity difference, kg; W1 is the water environment capacity without rainwater pumping station discharge, kg; W2 is the water environment capacity with rainwater pumping station discharge, kg; η is the pollutant reduction rate, %.

[0030] The step S6 provides a reduction plan for a rainwater pump station under different rain types, specifically: the water environment capacity without rainwater pump station discharge is recorded as W1, and the water environment capacity with rainwater pump station discharge is recorded as W2; the daily water environment capacity of W2 is analyzed. If after the rainwater pump station discharges, W0=W2-W1<0, it means that the rainwater pump station needs to set up a corresponding reduction plan, and the specific reduction amount should be W0, and the reduction rate under different working conditions is given; if after the rainwater pump station discharges, W0=W2-W1>0, it means that the flushing effect of the rainwater pump station has a greater impact on the assessment section, and there is no need to set up a reduction plan.

[0031] Beneficial effects: Compared with the prior art, the present invention proposes for the first time a refined calculation method for the water environment capacity of a river under different rainfall conditions, and gives the relationship between the rainwater pumping station and the water environment capacity, as well as the corresponding reduction plan. This makes up for the lack of time accuracy in conventional water environment capacity calculation methods, can more realistically reflect the migration and transformation laws of water quality, and fully consider the attenuation effect of pollutants. It has the advantages of strong applicability and easy operation, is suitable for promotion and use, and provides a certain basis for the scientific research of subsequent overflow pollution reduction plans. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is an operation flow chart of the method of the present invention;

[0033] Figure 2 This is the verification result diagram of the hydrodynamics and water quality of section A. DETAILED DESCRIPTION

[0034] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. After reading the present invention, various equivalent forms of modifications to the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application.

[0035] like Figure 1 As shown, the present invention provides a method for water environment capacity assessment and pollutant quantitative reduction based on rain type classification, comprising the following steps:

[0036] S1: Obtain the modeling data of the corresponding river in the specified area and construct the corresponding water environment mathematical model:

[0037] Modeling data include the water system map of the study area, river topography data, hydrodynamic and water quality parameters such as pollutant degradation coefficients, hydrological information data, river pollutant concentrations, and rainwater pump station discharge and pollutant concentrations;

[0038] The water environment mathematical model includes a hydrodynamic module (HD) and a water quality module (AD). The hydrodynamic model calculation adopts the Saint-Venant equations describing the one-dimensional unsteady flow in the open channel, including the mass conservation equation and the momentum conservation equation, and additionally considers the floodplain and lateral inflow:

[0039]

[0040] Where, formula (1) is the mass conservation equation, formula (2) is the momentum conservation equation; A is the cross-sectional area of ​​the water passage, m 2 ; Q is the flow rate, m 3 / s; t is the time coordinate; x is the distance coordinate; q is the side inflow, m 3 / s; g is the acceleration due to gravity, m / s 2 ; h is the water level, m; C is the Xiecai coefficient, R is the hydraulic radius, m / s.

[0041] The water quality model, namely the advection diffusion module (AD), uses the hydrodynamic conditions generated by the HD module to calculate the soluble and suspended substances in the water body using the advection diffusion equation. The AD module can accurately calculate and simulate the transport process of pollutants. The specific calculation equation is as follows:

[0042]

[0043] Where C is the pollutant concentration, mg / L; t is the time, s; u is the flow velocity, m / s; x is the spatial coordinate along the water flow direction, m; D is the diffusion coefficient, m 2 / s; K is the first-order attenuation coefficient, 1 / d.

[0044] S2: Identify pollutants to be predicted:

[0045] Based on the water quality requirements of key river monitoring sections in the study area and the main exceeding-standard factors of the monitoring sections under the current situation, combined with the Surface Water Environmental Quality Standard (GB3838-2002), conventional pollutants affecting water quality are determined.

[0046] S3: According to the pollutants determined in step S2, the concentration and flow of pollutants discharged by the rainwater pumping station under different rain types are collected:

[0047] The drainage flow and water quality data of the rainwater pumping station are input into the model in the form of point source pollution. The rainfall in the study period is statistically analyzed based on the drainage volume and pollutant emission concentration in the time series. The rainfall is divided into 6 levels: Level 1: 24-hour rainfall is less than 10 mm, Level 2: 24-hour rainfall is 10-25 mm, Level 3: 24-hour rainfall is 25-50 mm, Level 4: 24-hour rainfall is greater than 50 mm.

[0048] S4: Input the pollutant concentration and flow data of step S3 into the water environment mathematical model to obtain high-precision water quality and water quantity data of the assessment section under different rainfall types:

[0049] Before inputting the pollutant concentration and flow data into the water environment mathematical model, the parameters of the hydrodynamic module and the water quality module are calibrated and verified, that is, the measured values ​​of the representative section are compared and analyzed with the simulated values, the corresponding errors are calculated, and the model parameters are continuously adjusted so that the errors are within the allowable range of the model. Then, the model can be used for simulation calculations of subsequent working conditions.

[0050] According to the time accuracy requirements for the results, set the corresponding accuracy through the model output options and export the corresponding time series data.

[0051] S5: Based on the water quality and water quantity data obtained in step S4, the water environment capacity without rainwater pump station discharge and the water environment capacity with rainwater pump station discharge are calculated:

[0052] According to the required time accuracy, the water environment capacity under different conditions is calculated. A method for finely calculating the water environment capacity based on model simulation data is proposed. The calculation method of the water environment capacity is:

[0053]

[0054] Where: For target accuracy (such as d -1 ) flow, m 3 / s; For the target accuracy within the self-computation unit (such as d -1 ) Wastewater discharge, m 3 / s;C s is the limit of the water environment functional area of ​​the calculation unit, mg / L; The target accuracy of the upstream water pollutant in the calculation unit (such as d -1 ) concentration, mg / L; T is the calculation time (depending on the requirements, such as d); W i For the i-th target accuracy (such as d -1 ) calculates the unit water environment capacity, kg / x (i.e., kg / d); W is the water environment capacity value calculated on the basis of the water environment capacity under target accuracy, kg.

[0055] S6: Based on the calculated water environment capacity value, the rainwater pump station reduction plan and the corresponding pollutant reduction rate under different rainfall types are given:

[0056] According to step S5, the water environment capacity under different working conditions is calculated, and the difference in water environment capacity with and without rainwater pump station discharge, as well as the pollutant reduction rate under different reduction amounts are calculated, and the reduction plan of rainwater pump stations under different rain types is given. The calculation formula is as follows:

[0057] W0=W2-W1

[0058]

[0059] Where W0 is the water environment capacity difference, kg; W1 is the water environment capacity without rainwater pumping station discharge, kg; W2 is the water environment capacity with rainwater pumping station discharge, kg; η is the pollutant reduction rate, %.

[0060] A reduction plan for rainwater pumping stations under different rainfall types is given, specifically: the water environment capacity without rainwater pumping station discharge is recorded as W1, and the water environment capacity with rainwater pumping station discharge is recorded as W2; the daily water environment capacity of W2 is analyzed. If after the rainwater pumping station discharges, W0=W2-W1<0, it means that the rainwater pumping station needs to set up a corresponding reduction plan, and the specific reduction amount should be W0, and the reduction rate under different working conditions is given; if after the rainwater pumping station discharges, W0=W2-W1>0, it means that the scouring effect of the rainwater pumping station has a greater impact on the assessment section, and there is no need to set up a reduction plan.

[0061] Based on the above content, in order to verify the effectiveness and effect of the method of the present invention, the method of the present invention is applied to an example, as follows:

[0062] This embodiment uses data from a river area in Nanjing as an example to calculate the water environment capacity of the assessment section of the river. The area has 1 main stream, 7 tributaries, 5 drainage pumping stations, and 1 rainwater pumping station, of which only 1 rainwater pumping station B will have an impact on the assessment section.

[0063] (1) Constructing a mathematical model of water environment

[0064] Based on the geographical location and longitude and latitude coordinates of the river in the study area, the corresponding one-dimensional river network model is constructed. The measured cross-section data of the river is obtained by ADCP navigation equipment and input into the model cross-section file. According to the hydrological data of the river, the boundary conditions, initial conditions and hydrodynamic parameters of the model are set to construct the corresponding hydrodynamic model. On this basis, the relevant water quality time series data and water quality parameters are input to construct the corresponding water quality model. Among them, the boundary conditions include upstream flow and water quality concentration, tributary flow and water quality concentration, downstream water level and water quality concentration, initial conditions include the initial water level of the upstream river, hydrodynamic parameters include the bottom bed roughness coefficient, and water quality parameters include the pollutant degradation coefficient;

[0065] (2) Determine and calculate pollutants

[0066] Since the water quality requirement of a river assessment section A in Nanjing is to stably meet the surface water environmental quality Class III water standard (GB3838-2002), statistics show that the permanganate index of this assessment section has exceeded the standard in recent years, and the exceeding situation is more serious on rainy days, so it is determined that the pollutant to be calculated is the permanganate index.

[0067] (3) Collect the drainage flow and water quality concentration of rainwater pumping stations under different rainfall patterns

[0068] The drainage water quantity and water quality data of the rainwater pumping stations in the study area in June 2022, as well as the rainfall in June, are statistically collected, and different rainfall amounts are classified to make corresponding tables as shown in Tables 1 and 2. The corresponding data are input into the mathematical model in the form of point sources.

[0069] Table 1. Precipitation and rainfall level classification in a certain place in June 2022

[0070]

[0071]

[0072] Table 2 Discharge flow and water quality of rainwater pump station B in June 2022

[0073] Stormwater pump station start / shutdown time <![CDATA[Displacement (m 3 / s)]]> Drainage water quality (mg / L) 2022 / 6 / 512:00-16:00 2 6.71 2022 / 6 / 1510:00-16:00 2 7.25 2022 / 6 / 2413:00-23:00 2 7.05

[0074] (4) Based on the model simulation results, high-precision (depending on the requirements) water quality and quantity data of the assessment section under different operating models are exported.

[0075] First, the model hydrodynamic and water quality parameters were calibrated and verified. The hydrodynamic and water quality calibration verification results of section A are shown in the attached Figure 2 As shown in (a) and (b) in .

[0076] After calibration and verification of the model's hydrodynamic and water quality parameters, the absolute error between the model's calculated value and the actual value of the water level is 0.009m, and the relative error of the water quality is 26.24%. The errors are within the allowable range, and the model can be used for subsequent simulation calculations.

[0077] In order to accurately reflect the daily difference in water environment capacity, this embodiment selects to export the flow and water quality data of the assessment section every 1 hour.

[0078] (5) Calculate water environment capacity in a refined manner.

[0079] Substitute the time series data derived from the model into the specified formula to calculate the daily and 6-month water environment capacity with and without rainwater pump station discharge, see Tables 3 and 4.

[0080] Table 3 Permanganate index water environment capacity of assessment section A without rainwater pump station discharge

[0081]

[0082]

[0083] Table 4 Permanganate index water environment capacity of assessment section A with rainwater pump station discharge

[0084] date Water environment capacity (kg) date Water environment capacity (kg) 2022 / 6 / 1 -4175.28 2022 / 6 / 17 31560.70 2022 / 6 / 2 -3621.48 2022 / 6 / 18 30059.61 2022 / 6 / 3 -1276.92 2022 / 6 / 19 25976.85 2022 / 6 / 4 1033.38 2022 / 6 / 20 17440.42 2022 / 6 / 5 6713.29 2022 / 6 / 21 8505.49 2022 / 6 / 6 8850.44 2022 / 6 / 22 2646.43 2022 / 6 / 7 13619.60 2022 / 6 / 23 -636.02 2022 / 6 / 8 18235.60 2022 / 6 / 24 3449.87 2022 / 6 / 9 22593.51 2022 / 6 / 25 -11353.35 2022 / 6 / 10 27820.23 2022 / 6 / 26 -8721.05 2022 / 6 / 11 32055.75 2022 / 6 / 27 451.09 2022 / 6 / 12 33782.28 2022 / 6 / 28 7643.52 2022 / 6 / 13 33235.16 2022 / 6 / 29 10665.05 2022 / 6 / 14 32521.12 2022 / 6 / 30 14745.61 2022 / 6 / 15 36484.08 June 2022 421740.45 2022 / 6 / 16 31435.46

[0085] (6) Provide a pump station reduction plan

[0086] The daily water environment capacity difference of the assessment section A in June 2022 under different working conditions was statistically analyzed, and the specific data are shown in Table 5. According to the calculation results, within three days of the pump station opening, the water environment capacity difference W0 was negative, indicating that the opening of the rainwater pump station had an adverse effect on the assessment section, among which the water environment capacity decrease caused by the discharge of the rainwater pump station under level 4 was the most serious, which should be taken seriously.

[0087] According to different water environment capacity differences, different rainwater pump station reduction plans are set up, that is, on June 5, 2022, the rainwater pump station should reduce the permanganate index discharge load by 492.46kg, and the reduction rate of this plan is 6.83%; on June 6, 2022, the rainwater pump station should reduce the permanganate index discharge load by 2.11kg, and the reduction rate of this plan is 0.02%; on June 7, 2022, the rainwater pump station should reduce the permanganate index discharge load by 2.39kg, and the reduction rate of this plan is 0.02%; on June 7, 2022, the rainwater pump station should reduce the permanganate index discharge load by 2.39kg, and the reduction rate of this plan is 0.02%. The station should reduce the permanganate index discharge load by 2.44kg, and the reduction rate of the plan is 0.01%; on June 24, 2022, the rainwater pumping station should reduce the permanganate index discharge load by 1983.75kg, and the reduction rate of the plan is 36.51%; on June 25, 2022, the rainwater pumping station should reduce the permanganate index discharge load by 107.89kg, and the reduction rate of the plan is 0.96%; in June 2022, the rainwater pumping station should reduce the permanganate index discharge load by 3267.29kg, and the reduction rate of the plan is 0.77%.

[0088] Table 5 Difference in water environment capacity of permanganate index in assessment section A

[0089] date Water environment capacity difference (kg) date Water environment capacity difference (kg) 2022 / 6 / 1 0.00 2022 / 6 / 17 2.47 2022 / 6 / 2 0.00 2022 / 6 / 18 1.36 2022 / 6 / 3 0.00 2022 / 6 / 19 0.00 2022 / 6 / 4 0.00 2022 / 6 / 20 0.00 2022 / 6 / 5 -492.46 2022 / 6 / 21 0.00 2022 / 6 / 6 -2.11 2022 / 6 / 22 0.00 2022 / 6 / 7 -2.39 2022 / 6 / 23 0.00 2022 / 6 / 8 -2.44 2022 / 6 / 24 -1983.75 2022 / 6 / 9 0.00 2022 / 6 / 25 -107.89 2022 / 6 / 10 0.00 2022 / 6 / 26 0.00 2022 / 6 / 11 0.00 2022 / 6 / 27 0.00 2022 / 6 / 12 0.00 2022 / 6 / 28 0.00 2022 / 6 / 13 0.00 2022 / 6 / 29 0.00 2022 / 6 / 14 0.00 2022 / 6 / 30 0.00 2022 / 6 / 15 -697.68 June 2022 -3267.29 2022 / 6 / 16 17.61 .

Claims

1. A method for water environment capacity assessment and pollutant quantitative reduction based on rain type classification, characterized in that: The steps include: S1: Obtain modeling data of corresponding rivers in the specified area and construct corresponding water environment mathematical model; S2: Determine the pollutants to be predicted; S3: According to the pollutants determined in step S2, the concentration and flow rate of pollutants discharged by the rainwater pumping station under different rain types are collected; S4: Input the pollutant concentration and flow data of step S3 into the water environment mathematical model to obtain high-time-precision water quality and water quantity data of the assessment section under different rainfall types; S5: Calculate the water environment capacity without rainwater pump station discharge and the water environment capacity with rainwater pump station discharge according to the water quality and water quantity data obtained in step S4; S6: Based on the calculated water environment capacity value, the rainwater pump station reduction plan and the corresponding pollutant reduction rate under different rainfall types are given.

2. The method for water environment capacity assessment and pollutant quantitative reduction based on rain type classification according to claim 1 is characterized in that: The water environment mathematical model in step S1 includes a hydrodynamic module and a water quality module. The hydrodynamic model calculation adopts the Saint-Venant equations describing the one-dimensional unsteady flow in the open channel, including the mass conservation equation and the momentum conservation equation, and additionally considers the floodplain and lateral inflow: Wherein, formula (1) is the mass conservation equation, formula (2) is the momentum conservation equation; A is the cross-sectional area of ​​the water flow; Q is the flow rate; t is the time coordinate; x is the distance coordinate; q is the lateral inflow; g is the gravitational acceleration; h is the water level; C is the Scheer coefficient; and R is the hydraulic radius. The water quality model, namely the convection-diffusion module, uses the hydrodynamic conditions generated by the HD module to calculate the soluble and suspended substances in the water body using the convection-diffusion equation; the AD module calculates and simulates the transport process of pollutants. The specific calculation equation is as follows: Where C is the pollutant concentration; t is time; u is flow velocity; x is the spatial coordinate along the direction of water flow; D is the diffusion coefficient; and K is the first-order attenuation coefficient.

3. The method for water environment capacity assessment and pollutant quantitative reduction based on rain type classification according to claim 2 is characterized in that: The modeling data in step S1 include a water system map of the study area, river terrain data, pollutant degradation coefficients, hydrological information data, river pollutant concentrations, rainwater pump station discharge and pollutant concentrations.

4. The method for water environment capacity assessment and pollutant quantitative reduction based on rain type classification according to claim 1 is characterized in that: The method for determining pollutants in step S2 is: determining conventional water quality-influencing pollutants based on water quality requirements of key river monitoring sections in the study area and major exceeding-standard factors of the monitoring sections under current conditions.

5. The method for water environment capacity assessment and pollutant quantitative reduction based on rain type classification according to claim 1 is characterized in that: The step S3 statistically analyzes the rainfall in the study period based on the time series of drainage and pollutant emission concentration, wherein the rainfall is divided into 6 levels, level 1: 24-hour rainfall is less than 10 mm, level 2: 24-hour rainfall is 10-25 mm, level 3: 24-hour rainfall is 25-50 mm, and level 4: 24-hour rainfall is greater than 50 mm.

6. The method for water environment capacity assessment and pollutant quantitative reduction based on rain type classification according to claim 2 is characterized in that: In step S4, before the pollutant concentration and flow data are input into the water environment mathematical model, the parameters of the hydrodynamic module and the water quality module are calibrated and verified; according to the time accuracy requirements for the results, the corresponding accuracy is set through the model output option, and the corresponding time series data is exported.

7. The method for water environment capacity assessment and pollutant quantitative reduction based on rain type classification according to claim 1 is characterized in that: The calculation method of the water environment capacity in step S5 is: Where: is the flow rate under target accuracy; is the sewage discharge volume under the target accuracy within the self-calculation unit; To calculate the limit of the unit water environment functional area; To calculate the target accuracy concentration of pollutants in the upstream water of the unit; T is the calculation time; W i is the water environment capacity of the calculation unit under the i-th target accuracy; W is the water environment capacity value calculated based on the water environment capacity under the target accuracy.

8. The method for water environment capacity assessment and pollutant quantitative reduction based on rain type classification according to claim 1 is characterized in that: The step S6 is specifically as follows: According to step S5, the water environment capacity under different working conditions is calculated, and the difference in water environment capacity with and without rainwater pump station discharge, as well as the pollutant reduction rate under different reduction amounts are calculated, and the reduction plan of rainwater pump stations under different rain types is given. The calculation formula is as follows: W0=W2--W1 Where W0 is the water environment capacity difference; W1 is the water environment capacity without rainwater pumping station discharge; W2 is the water environment capacity with rainwater pumping station discharge; η is the pollutant reduction rate.

9. The method for water environment capacity assessment and pollutant quantitative reduction based on rain type classification according to claim 8 is characterized in that: The step S6 provides a reduction plan for a rainwater pump station under different rain types, specifically: the water environment capacity without rainwater pump station discharge is recorded as W1, and the water environment capacity with rainwater pump station discharge is recorded as W2; the daily water environment capacity of W2 is analyzed. If after the rainwater pump station discharges, W0=W2-W1<0, it means that the rainwater pump station needs to set up a corresponding reduction plan, and the specific reduction amount should be W0, and the reduction rate under different working conditions is given; if after the rainwater pump station discharges, W0=W2-W1>0, it means that the flushing effect of the rainwater pump station has a greater impact on the assessment section, and there is no need to set up a reduction plan.

Images