Method for predicting variation trend of non-point source pollutant in-river quantity after comprehensive regulation of drainage basin

Abstract

The invention discloses a method for predicting the change trend of the non-point source pollutant river entering amount after comprehensive treatment of a drainage basin. The emission of various pollutants in each drainage basin is continuously increased, and the problem of non-point source pollution is increasingly prominent. Basic data of a drainage basin are collected; sub-basin division and hydrological response unit generation; establishing a non-point source pollution SWAT model; carrying out model sensitivity analysis, model calibration and non-point source pollutant river entering quantity calculation; analyzing the non-point source pollutant river entering amount and the change trend thereof; according to the trend analysis result, the implementation effect of the non-point source pollution treatment measures is evaluated, and according to the evaluation result, the drainage basin non-point source pollution comprehensive treatment measures are optimized. The method provides a scientific basis for the design and construction of the comprehensive treatment project of the watershed environment.

Description

TECHNICAL FIELD

[0002] The application belongs to the technical field of water ecological protection and environmental governance, and particularly relates to a method for predicting the change trend of non-point source pollutant inflow into a river after comprehensive treatment of a river basin. BACKGROUND

[0004] In order to protect water resources and ecological environment, China has introduced a series of policy documents such as the Water Pollution Control Action Plan, which clearly defines the goals and tasks of non-point source pollution control in river basins. However, after the completion of the comprehensive treatment of the river basin, it is difficult to predict the actual inflow of non-point source pollutants into the river, reasonably assess the impact of various engineering measures on the inflow of non-point source pollutants, and predict the change trend of the inflow of non-point source pollutants. SUMMARY

[0005] In order to make up for the shortcomings of the prior art, the application provides a method for predicting the change trend of non-point source pollutant inflow into a river after comprehensive treatment of a river basin, so as to overcome the problem that the prior art is difficult to accurately and quantitatively evaluate the reduction effect of the comprehensive treatment engineering of the river basin on the inflow of non-point source pollutants, and to provide a scientific basis for the design and construction of the comprehensive treatment engineering of the river basin.

[0006] In order to achieve the above-mentioned purpose, the technical scheme adopted by the application is as follows: A method for predicting the change trend of non-point source pollutant inflow into a river after comprehensive treatment of a river basin, comprising the following steps: Step 1: Collecting basic data of the river basin; Step 2: Sub-basin division and hydrological response unit generation; Step 3: Establishing a non-point source pollution SWAT model; Step 4: Model sensitivity analysis, model calibration and non-point source pollutant inflow calculation; Step 5: Analysis of non-point source pollutant inflow and its change trend; Step 6: According to the trend analysis result, evaluating the implementation effect of the non-point source pollution control measure, and optimizing the comprehensive treatment measure of the non-point source pollution of the river basin according to the evaluation result.

[0007] Further, in step 1, the basic data includes model construction basic data and pollution source data.

[0008] Further, in step 2, the sub-basin division is specifically as follows: The SWAT model extracts the river system of the basin based on the digital elevation map, and then sets the basin inlet, basin outlet and river threshold area in the SWAT model according to the actual situation of the research area, and then divides the entire basin into a plurality of small sub-basins using the SWAT model.

[0009] Further, the step two, the hydrological response unit is divided into specific for: The spatial data required by the model is input and reclassified, the minimum threshold of land use area, the minimum threshold of soil area and slope are set, and after model calculation, each sub-basin is divided into several hydrological response units.

[0010] Further, the step three of non-point source pollution SWAT model is established specifically: Step 3.1: point source pollutant input Step 3.2: agricultural non-point source pollutant input The agricultural crops, fertilizer amount, fertilizer time and irrigation time in the study area are simulated by manually adding farmland management data in the SWAT model cultivation database to simulate the crop rotation process, so as to simulate the process of pollutants such as fertilizers and pesticides into the river; Step 3.3: livestock and poultry breeding pollutant input Step 3.4: rural life non-point source pollutant input Step 3.5: after inputting the data required by the SWAT water quality simulation model into the model and establishing the model database, running the model, outputting the preliminary results of the model.

[0011] Further, the step four is specifically: Step 4.1: model sensitivity analysis Sensitivity analysis software is used to analyze the sensitivity of the model; Step 4.2: parameter calibration ParaSol method is used to calibrate the model, when the relative error of the model simulation result is ≤20%, the coefficient of determination is ≥0.6, and the Nash coefficient is ≥0.5, the model simulation result is feasible; Step 4.3: non-point source pollution into river calculation Keep the input data and running parameters of the model unchanged, cancel the input of point source pollutants, and run the model again to finally get the daily non-point source pollutant into river.

[0012] Further, the step five is specifically: Step 5.1: when there is no watershed comprehensive treatment engineering measure, the overall change trend of non-point source pollution into river; Step 5.2: analysis of non-point source pollution into river and change trend after implementation of engineering measures.

[0013] Further, the step 5.1 is specifically: When there is no comprehensive management measure in the basin, according to the daily non-point source pollutant inflow data calculated by the SWAT model, the M-K non-parametric test method is used to analyze the change trend of the non-point source pollution inflow at the basin outlet section; according to the calculated Zc and alpha value, the overall change trend of the non-point source pollution inflow is obtained when there is no comprehensive management measure such as the basin comprehensive management project.

[0014] Further, the step 5.2 is specifically: Various engineering management measures are input into the SWAT model by modifying the parameters of the SWAT model, and the daily inflow of non-point source pollutants under the engineering management measures is calculated; the M-K non-parametric test method is used to analyze the trend of the non-point source pollution inflow data at the basin outlet section. According to the calculated Zc and alpha value, the overall change trend of the non-point source pollution inflow is obtained when there is a comprehensive management measure such as the basin comprehensive management project; by comparing the inflow of non-point source pollutants before and after the engineering management and the change trend thereof, the management effect of the related engineering is evaluated, so as to provide relevant basis for the design and construction of subsequent comprehensive management engineering of the basin.

[0015] The beneficial effects of the present application are: 1) The coupling model combining the SWAT non-point source pollution model and the Mann-Kendall (M-K) trend analysis model is adopted in the present application, which solves the problem that it is difficult to predict the actual inflow of non-point source pollutants and reasonably evaluate the increasing and decreasing change trend effect of various engineering measures on the inflow of non-point source pollutants after the completion of the comprehensive management engineering of the basin; 2) The evaluation result of the present application can be applied to the design and construction of the non-point source pollution control engineering of the comprehensive ecological management measure of the basin, and provides a scientific basis for the design and construction of the comprehensive environmental management engineering of the basin. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 The operation flowchart of the present application is shown in the figure; Figure 2 The farmland management measure setting diagram is shown in the figure; Figure 3 The pollution change trend judgment basis diagram is shown in the figure. DETAILED DESCRIPTION

[0017] The present application will be described in detail below in combination with specific embodiments.

[0018] The present application is based on the coupling model of the SWAT non-point source pollution model and the Mann-Kendall (M-K) trend analysis method, and proposes a method for predicting the change trend of the non-point source pollution inflow after the comprehensive management of the basin, and the evaluation result can be applied to the design and construction of the non-point source pollution control engineering of the comprehensive ecological management measure of the basin, and provides a scientific basis for the design and construction of the comprehensive environmental management engineering of the basin.

[0019] Taking a water system management project in the Weihe River Basin of Shaanxi Province as an example, the water system management mainly involves water environment management and agricultural non-point source pollution management, and the change trend of non-point source pollutant inflow into the river before and after management is analyzed.

[0020] As shown in Figure 1 The present application comprises the following steps: Step 1: Collecting basin basic data; the basic data includes model construction basic data and pollution source data; The model construction basic data includes surface elevation data (DEM elevation data), land use type data, soil classification data, watershed river system data, hydrological data (daily flow, daily river sediment discharge), measured river water quality monitoring data, meteorological monitoring data (daily temperature, daily precipitation, daily wind speed, daily humidity, daily solar radiation), soil physical and chemical parameters, etc.; the pollution source data includes agricultural planting management information (planting crop types, planting methods, irrigation time, fertilization time and fertilization amount), pollution source data (point source emission data, livestock and poultry breeding data, rural domestic sewage discharge data, etc.).

[0021] ①Model construction basic data: SRTM DEM UTM-03 China DEM digital elevation map provided by the National Qinghai-Tibet Plateau Scientific Data Center is used, with a resolution of 30x30m. ARCGIS software is used to fill the DEM, analyze the flow direction, generate river network and other series of operations.

[0022] ②Land use data: National Land Use Data in 2000, 2010, 2015 and 2020 from the Chinese Academy of Sciences Environmental Science Data Center, with a scale of 1:100,000.

[0023] ③Soil data: Soil data from the website of the Food and Agriculture Organization of the United Nations (FAO), with a resolution of 1km x 1km. The soil database includes soil space and soil physical and chemical data.

[0024] ④Meteorological database construction. Meteorological data includes daily average humidity, daily precipitation, daily average radiation, daily maximum and minimum temperature, and daily average wind speed, which are used for simulating daily river flow and sediment yield in SWAT model. Meteorological data is from the China Atmospheric Assimilation Driving Database.

[0025] ⑤Hydrological and water quality data The hydrological (river flow) and water quality data are used to calibrate the results of the SWAT model, and are not directly input into the database of the model.

[0026] Step 2: Sub-basin division and hydrological response unit generation; ①Sub-basin division is as follows: The SWAT model extracts the basin water system based on a digital elevation map (DEM), and then sets the basin inlet, basin outlet and river threshold area in the SWAT model according to the actual situation of the research region, and then divides the entire basin into a plurality of small sub-basins according to certain parameters by using the SWAT model, so as to facilitate the calculation and analysis of the model.

[0027] ② The hydrological response unit is divided into: The hydrological response unit is a further subdivided calculation based on the division of the sub-basin, and is the smallest calculation unit with the same land use, soil type and the like. The model will perform independent operation on each hydrological response unit.

[0028] The spatial data required by the model is input and reclassified, and the minimum threshold of the land use area, the minimum threshold of the soil area and the slope are set. After model calculation, each sub-basin is divided into a plurality of hydrological response units.

[0029] Step three: the establishment of the non-point source pollution SWAT model, specifically including the following steps: Step 3.1: point source pollution input The point source discharge data in the basin is added to the corresponding river section in the corresponding sub-basin in the form of daily average discharge; Step 3.2: agricultural non-point source pollution input The research region mainly adopts winter wheat and summer corn rotation, accounting for 80% of the total planting area, and the rest is vegetable planting. The crop planting, fertilizer amount, fertilizer time and irrigation time in the research region are manually added to the SWAT model management database (.mgt) to simulate the crop rotation process, so as to simulate the process of pollution substances such as fertilizers and pesticides into the river, as shown in Figure 2 ; Step 3.3: livestock and poultry breeding pollutant input According to related research, the excrement produced by scattered livestock and poultry breeding in the basin is basically returned to the field in the form of fertilizer, so the total nitrogen and total phosphorus produced by livestock and poultry breeding in the research region are added to the database in the form of fertilizer in the SWAT model, and the total nitrogen and total phosphorus produced by livestock and poultry breeding in each sub-basin are calculated.

[0030] In this embodiment, the total nitrogen and total phosphorus produced by livestock and poultry breeding in the research region are added to the database in the form of fertilizer in the SWAT model, and the total nitrogen and total phosphorus produced by livestock and poultry breeding in each sub-basin are calculated.

[0031] Step 3.4: rural life non-point source pollution input The rural life pollutants are usually directly discharged into soil or water body, and generally, the rural population determines the rural life pollutant production amount. The rural life pollutant amount is input into the SWAT model in the form of daily average amount of rural town land and cultivated land, and the total nitrogen amount and the total phosphorus amount generated by rural life in each sub-basin are calculated.

[0032] Step 3.5: running the model, outputting the preliminary results of the model.

[0033] After inputting the data required by the SWAT water quality simulation model into the model and establishing the model database, the model is run, and the preliminary results of the model are output.

[0034] Step four: model sensitivity analysis, model calibration and non-point source pollutant calculation, specifically: The preliminary calculation results of the model deviate greatly from the actual values, so it is necessary to find out the parameters that greatly affect the model and modify these parameters one by one, so as to calibrate the model and make the model simulation results match the actual water quality data.

[0035] Step 4.1: model sensitivity analysis Sensitivity analysis software is used to analyze the sensitivity of the model, and the t-Stat value represents the sensitivity of the parameter, and the greater the absolute value of the numerical value, the greater the sensitivity, and the P-Value value represents the significance of the parameter, and the closer the numerical value to 0, the more significant; the present application respectively carries out sensitivity analysis on the runoff, total nitrogen and total phosphorus as output, and finally obtains the sensitivity analysis results and the sensitive parameters of the model; Step 4.2: parameter calibration Parameter calibration is to assign initial values to the selected sensitive parameters, bring the parameter set into the model for calculation, and then compare the calculation results with the measured data. If the difference between the calculation results and the measured data meets the requirements, the parameter value at this time is taken as the final parameter of the model. If the difference between the calculation results and the measured data cannot meet the requirements, the parameter set is re-assigned and calculated, and the calculation results are compared with the measured data again until the requirements are met.

[0036] The ParaSol method is used to calibrate the model, and when the relative error of the model simulation results is ≤20%, the determination coefficient is ≥0.6, and the Nash coefficient is ≥0.5, the model simulation results are feasible; Among them: Relative error - the relative error refers to the ratio of the absolute error caused by measurement to the measured (conventional) true value multiplied by 100% to obtain a numerical value expressed in percentage.

[0037] Coefficient of determination - similar to the correlation coefficient, it is a numerical characteristic of the relationship between a random variable and multiple random variables, and is used to reflect the reliability of the regression model to explain the change of the dependent variable.

[0038] Nash coefficient - is an index for evaluating the performance of hydrological models or other prediction models, with a value range of (-∞, 1), the closer to 1, the better the prediction effect of the model.

[0039] Step 4.3: Calculation of non-point source pollution into river Keep the input data and running parameters of the model unchanged, cancel the input of point source pollutants, and re-run the model to finally obtain the daily non-point source pollutant load into the river.

[0040] Step five: Analysis of non-point source pollution into river and its trend (M-K analysis), specifically: Step 5.1: Overall trend of non-point source pollution into river without comprehensive management measures in the basin, specifically: Without comprehensive management measures in the basin, according to the daily (monthly) non-point source pollutant load into the river calculated by the SWAT model, the M-K non-parametric test method is used to analyze the monthly data of non-point source pollution into the river at the basin outlet (taking total nitrogen and total phosphorus as examples); According to the calculated Zc and α values (statistical variables calculated by the model, used to judge the trend of the sequence), the overall trend of non-point source pollution into the river without comprehensive management measures such as basin comprehensive management is obtained.

[0041] Step 5.2: Analysis of non-point source pollution into river and its trend after the implementation of engineering measures, specifically: Various engineering management measures are input into the SWAT model by modifying the model parameters (such as FET-SURFACE (surface fertilization depth parameter), FER-KG (fertilization amount parameter), USLE-P (water and soil conservation factor parameter), and CN2 (runoff curve parameter)), and the daily non-point source pollutant load into the river under engineering management measures is calculated; The M-K non-parametric test method is used to analyze the trend of non-point source pollution into the river at the basin outlet. According to the calculated Zc and α values, the overall trend of non-point source pollution into the river with comprehensive management measures such as basin comprehensive management is obtained; By comparing the non-point source pollutant load and its trend before and after the implementation of engineering management measures, the management effect of related engineering is evaluated, so as to provide relevant basis for the design and construction of subsequent comprehensive management engineering in the basin.

[0042] The calculation method of M-K test method is: (1≤k<j≤n) In the formula: Sgn(X ji -X ki ) is a characteristic function, wherein the random sequence S i (i=1, 2, 3..., n) is subject to a normal distribution, and the standard deviation of S i is: In the formula: m is the number of the same number in the sequence; t i is the number of the digits in the i-th group.

[0043] For the statistical variable Z c > 0, it indicates that the non-point source pollution has an upward trend; Z c < 0, it indicates a downward trend; Z c = 0, it indicates no change trend; and α is a significance parameter; and the specific as shown in Figure 3 .

[0044] Step six: according to the trend analysis result, evaluating the implementation effect of the non-point source pollution treatment measure, and optimizing the comprehensive treatment measure of the non-point source pollution in the basin according to the evaluation result.

[0045] The content of the application is not limited to the examples listed, and any equivalent transformation of the technical solution of the application by a person skilled in the art by reading the specification of the application is covered by the claims of the application.

Claims

1. A method for predicting the trend of non-point source pollutant into river after the comprehensive improvement of river basin, characterized in that: It comprises the following steps: Step one: Collecting the basic data of the basin; Step two: Sub-basin division and hydrological response unit generation; Step three: Establishing the non-point source pollution SWAT model; Step four: Model sensitivity analysis, model calibration and non-point source pollution load calculation; Step five: Non-point source pollution load and its trend analysis; Step six: According to the trend analysis results, the implementation effect of non-point source pollution control measures is evaluated, and according to the evaluation results, the comprehensive treatment measures of non-point source pollution in the basin are optimized.

2. The method for predicting the variation trend of non-point source pollutants into river after integrated regulation of a river basin according to claim 1, characterized in that: In step one, the basic data includes model construction basic data and pollution source data.

3. The method for predicting the variation trend of non-point source pollutants into river after integrated regulation of a river basin according to claim 2, characterized in that: In step two, the sub-basin division is specifically as follows: The SWAT model extracts the basin water system based on the digital elevation map, and then sets the basin entrance, basin exit and river threshold area in the SWAT model according to the actual situation of the research area, and then divides the whole basin into several small sub-basins using the SWAT model.

4. The method for predicting the variation trend of non-point source pollutants into river after integrated regulation of a river basin according to claim 3, characterized in that: In step two, the hydrological response unit division is specifically as follows: The spatial data required by the model is input and reclassified, the minimum threshold of land use area, soil area and slope is set, and after model calculation, each sub-basin is divided into several hydrological response units.

5. The method for predicting the variation trend of non-point source pollutants into river after comprehensive harnessing of river basin according to claim 4, characterized in that: In step three, the non-point source pollution SWAT model is established specifically as follows: Step 3.1: Point source pollution input Step 3.2: Agricultural non-point source pollution input The research area agricultural crops, fertilizer amount, fertilizer time and irrigation time are simulated through manual addition of farmland management data in the SWAT model to simulate the process of crop rotation, to simulate the process of fertilizer and pesticide pollution into river; Step 3.3: Livestock and poultry breeding pollution input Step 3.4: Rural life non-point source pollution input Step 3.5: After inputting the data required by the SWAT water quality simulation model into the model and establishing the model database, the model is run to output the preliminary results of the model.

6. The method for predicting the variation trend of non-point source pollutants into river after comprehensive harnessing of river basin according to claim 5, characterized in that: Step four is specifically as follows: Step 4.1: Model sensitivity analysis Sensitivity analysis software is used to analyze the sensitivity of the model; Step 4.2: Parameter calibration ParaSol method is used to calibrate the model, when the relative error of the model simulation result is ≤20%, the coefficient of determination is ≥0.6, and the Nash coefficient is ≥0.5, the model simulation result is feasible; Step 4.3: Non-point source pollution load calculation Keep the input data and running parameters of the model unchanged, cancel the input of point source pollution, and run the model again to finally get the daily non-point source pollution load.

7. The method for predicting the variation trend of non-point source pollutants into river after integrated regulation of a river basin according to claim 6, characterized in that: Step five is specifically as follows: Step 5.1: The overall trend of non-point source pollution load without comprehensive treatment measures in the basin; Step 5.2: Non-point source pollution load and trend analysis after the implementation of engineering measures.

8. The method for predicting the variation trend of non-point source pollutants into river after integrated regulation of a river basin according to claim 7, characterized in that: Step 5.1 is specifically as follows: When there is no comprehensive management measure, the daily non-point source pollutant quantity into river is calculated by SWAT model, and the variation trend of non-point source pollution quantity into river at the outlet section of the basin is analyzed by M-K nonparametric test method; according to the calculated Zc and α values, the overall variation trend of non-point source pollution quantity into river without comprehensive management measures is obtained.

9. The method for predicting the variation trend of non-point source pollutants into river after integrated regulation of a river basin according to claim 8, characterized in that: The step 5.2 is specifically: Various engineering management measures are input into the SWAT model by modifying the parameters of the SWAT model, and the daily non-point source pollutant quantity into river under the engineering management measures is calculated; the trend of non-point source pollution quantity into river at the outlet section of the basin is analyzed by M-K nonparametric test method; according to the calculated Zc and α values, the overall variation trend of non-point source pollution quantity into river with comprehensive management measures is obtained; The non-point source pollutant quantity into river and its variation trend before and after the engineering management are compared, the management effect of the related engineering is evaluated, and relevant basis is provided for the design and construction of subsequent comprehensive management engineering of the basin.

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