A method for evaluating the impact of changing the water intake method on the pollutant concentration in the downstream river channel

Abstract

The present invention discloses a method for evaluating the impact of changing the water intake mode on the pollutant concentration in the downstream river channel. First, classify the impact of water intake activities on pollutants: The first category is no water withdrawal, that is, both the distributed water withdrawal and the concentrated water withdrawal are 0; the second category is only considering the concentrated water withdrawal, that is, the distributed water withdrawal is 0; the third category is both concentrated water withdrawal and distributed water withdrawal; according to different categories, use different formulas to calculate the change rate p of the pollutant concentration at the downstream assessment section after changing the water intake conditions; according to the current pollutant concentration C at the downstream assessment section 现状 and the pollutant concentration limit C of the water function area 考核 to analyze the impact of water intake on the river environment. When C 现状 *(1 - p) does not exceed C 考核 , the impact of changing the water intake mode on the pollutant concentration in the downstream river channel is very small. The present invention uses mass conservation and formula transformation to eliminate the problems of having to consider the catchment area and pollutant input in general calculations, thus greatly reducing the data requirements and the analysis workload.

Description

Technical Field

[0001] The present invention belongs to the technical field of water conservancy projects, and particularly relates to a method for evaluating the impact of changing the water intake mode on the pollutant concentration in the downstream river channel. Background Technique

[0002] The evaluation of the impact degree of water intake on the pollutant concentration in the downstream river is the basis for carrying out the water resources demonstration of planning and construction projects and the environmental impact assessment. The change in the water intake scale involves the number of water function areas and the impact of water intake and withdrawal on other water users and the ecological environment. According to the water discharge situation of construction projects, it can be divided into three categories. For the evaluation of the impact of water intake on the pollutant concentration in the downstream river channel, in order to study the pollution problem of water bodies more accurately and quantitatively, the numerical simulation calculation of water quality has become an important research method. Currently, it is generally to construct a regional pollutant migration and transformation model based on the physical process of pollutant migration and transformation for evaluation. The pollutant migration process is not only related to the characteristics of the pollutant itself but also closely related to external conditions. Therefore, the mathematical description of quantitatively analyzing the migration and transformation laws of each water quality variable and the mutual relationship between influencing factors is the key to the accuracy of the model. However, it requires a large number of measured data and parameters, and the analysis process is complex and the workload is huge. Based on the law of conservation of matter, this paper proposes a relatively simple, practical and efficient analysis method. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for evaluating the impact of changing the water intake mode on the pollutant concentration in the downstream river channel based on the above technical difficulties.

[0004] The purpose of the present invention is achieved as follows:

[0005] A method for evaluating the impact of changing the water intake mode on the pollutant concentration in the downstream river channel includes the following steps:

[0006] 1) Classify according to the impact of water intake activities on pollutants: The first category is no water withdrawal, that is, both the along - route water withdrawal and the centralized water withdrawal are 0; the second category is only considering the centralized water withdrawal, that is, the along - route water withdrawal is 0; the third category is both centralized water withdrawal and along - route water withdrawal;

[0007] 2) For the first category determined in step 1), the method for evaluating the impact of changing the water intake mode on the pollutant concentration in the downstream river channel is as follows: Calculate the change rate p of the pollutant concentration at the downstream assessment section after changing the water intake conditions through the following formula:

[0008]

[0009] In the formula: Q2 is the flow rate at the downstream assessment section, m 3 ;

[0010] Q′0 is the discharge flow at the water intake section, m 3 ;

[0011] The downstream discharge of the water intake section = the flow of the water intake section - the water intake volume;

[0012] C2 is the pollutant concentration at the downstream assessment section, in mg / L;

[0013] C x is the pollutant concentration of the pollutants flowing from the water intake section to the downstream assessment section, in mg / L;

[0014] Among the above symbols, different superscripts represent different water intake methods. Superscript 1 represents water intake method 1, and superscript 2 represents water intake method 2;

[0015] 3) For those determined as the second type in step 1), the method for evaluating the impact of changing the water intake method on the pollutant concentration in the downstream river channel is as follows: Calculate the change rate p of the pollutant concentration at the downstream assessment section after changing the water intake conditions through the following formula:

[0016]

[0017] In the formula: Q 取 is the water intake volume, in m 3 ; η1 is the pipeline water conveyance utilization coefficient, η2 is the water use discharge coefficient, η3 is the sewage treatment loss coefficient; C 退 is the pollutant concentration of the centralized wastewater discharge, in mg / L; other symbols have the same meanings as those in formula (1); among the above symbols, different superscripts represent different water intake methods. Superscript 1 represents water intake method 1, and superscript 2 represents water intake method 2;

[0018] 4) For those determined as the third type in step 1), the method for evaluating the impact of changing the water intake method on the pollutant concentration in the downstream river channel is as follows: Calculate the change rate p of the pollutant concentration at the downstream assessment section after changing the water intake conditions through the following formula:

[0019]

[0020] In the formula:

[0021] q0 is the unit-width flow of seepage return water in the irrigation area, in m3; C q is the pollutant concentration corresponding to the unit-width flow q0 of seepage return water in the irrigation area, in mg / L; L is the length of the drainage ditch, in m; γ is the seepage coefficient, in m / s; A is the cross-sectional area of the river channel, in m 2 ; h2 and h1 are the groundwater depths upstream and downstream of the irrigation area, in m; l is the length of the river channel with seepage in the irrigation area, in m; other symbols have the same meanings as those in formula (1); among the above symbols, different superscripts represent different water intake methods. Superscript 1 represents water intake method 1, and superscript 2 represents water intake method 2;

[0022] 5) Evaluation of the impact of changing the water intake method: According to the pollutant concentration C at the current downstream assessment section现状 Analyze the impact of water intake on the river environment in relation to the pollutant concentration limit C of the water functional area. When C 考核 *(1 - p) does not exceed C 现状 when the water intake method change has little impact on the pollutant concentration in the downstream river section. 考核

[0023] Furthermore, calculate the pollutant concentration C x of the pollutants flowing from the water intake section to the downstream assessment section. The specific formula is as follows:

[0024]

[0025] In the formula: The pollutant concentration C x of the pollutants flowing from the water intake section to the downstream assessment section, mg / L;

[0026] x is the distance from the assessment section to the water intake section, m;

[0027] v is the average flow velocity of the river cross-section under the designed flow rate, m / s;

[0028] C0 is the pollutant concentration before water intake at the water section, mg / L;

[0029] K is the comprehensive attenuation coefficient of pollutants, s -1 .

[0030] Furthermore, the calculation method of v is as follows: Calculate the flow velocity v 上 at the water intake section after water intake from the river and the flow velocity v 下 at the assessment section after water intake; Calculate the average value of v 上 and v 下 to obtain v;

[0031] The calculation method of the flow velocity v 上 at the water intake section after water intake is as follows:

[0032] v 上 = Q′0 / (t * A 上 )

[0033] The calculation method of the flow velocity v 下 at the assessment section after water intake is as follows:

[0034] v 下 = Q2 / (t * A 下 )

[0035] Where: Q′0 is the flow rate after water intake at the water intake section, m 3 ; Q2 is the flow rate after water intake at the assessment section, m 3 ; A 上 is the area of the water intake section, m 2 ; A 下is the cross-sectional area for assessment, m 2 ; t is time, s.

[0036] Furthermore, the pollutants in the downstream river channel are representative pollutants. The main pollutants and the pollutants with the greatest risk of exceeding the standard are selected as representative pollutants according to the monitoring of the downstream assessment cross-section.

[0037] The advantages and beneficial effects of the present invention are as follows:

[0038] Using mass conservation, an implicit solution method is adopted to analyze the impact of water intake on the pollutant concentration in the downstream river channel. (1) Compared with the traditional method, the data requirements and workload are reduced: by using mass conservation and formula transformation, the problems of having to consider the lateral inflow and pollutant input in general calculations are eliminated, thus greatly reducing the data requirements and analysis workload; (2) Efficiency improvement: the reduction in workload means that the efficiency can be greatly improved by using this method; (3) Improved calculation reliability: in the general method, the data requirements are large, there are many error sources, and the reliability is not high; at the same time, by using the method of solving equations simultaneously with different schemes, the problems such as the difference in hydrological conditions between different schemes affecting the reduction of pollutants in the interval are eliminated. (4) Suitable for multi-scheme scenario analysis, with good method adaptability: in the general method, a large amount of measured data is required, and due to the obvious differences in the regional characteristics of the river, the universality of these data is poor, while the data volume of this method is greatly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The present invention will be further described below in conjunction with the drawings and embodiments.

[0040] Figure 1 is the flow chart of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0041] Embodiment 1:

[0042] A method for evaluating the impact of changing the water intake method on the pollutant concentration in the downstream river channel includes the following steps:

[0043] Classify according to the impact of water intake activities on pollutants: The first category is without return flow, that is, both the lateral return flow and the concentrated return flow are 0; the second category is only considering the concentrated return flow, that is, the lateral return flow is 0; the third category is both having concentrated return flow and lateral return flow;

[0044] (1) Without return flow, that is, when both the lateral return flow and the concentrated return flow are 0

[0045] 1. Collect data: The flow rates Q0 and Q′0 before and after water intake at the water intake cross-section, the pollutant concentration C0, the distance x from the assessment cross-section to the water intake cross-section, the flow rate Q2 and the pollutant concentration C2 at the downstream assessment cross-section, and the pollutant concentration limit C of the water function area 考核 , the river bed slope i, and the measured large cross-section A.

[0046] 2. Select representative pollutants. Select the main pollutants and the pollutants with the greatest risk of exceeding the standard as representative pollutants based on the monitoring of the downstream assessment section.

[0047] 3. Calculate the pollutant concentration C of the polluted water flowing from the water intake section to the downstream assessment section. x , and the specific formula is as follows:

[0048]

[0049] In the formula: The pollutant concentration C of the polluted water flowing from the water intake section to the downstream assessment section x , mg / L;

[0050] x is the distance from the assessment section to the water intake section, m;

[0051] v is the average velocity of the river cross-section under the designed flow rate, m / s;

[0052] C0 is the pollutant concentration before water intake at the water intake section, mg / L;

[0053] K is the comprehensive attenuation coefficient of the pollutant, s-1.

[0054] The calculation method of v is: Calculate the velocity v of the water intake section after water intake in the river 上 and the velocity v of the assessment section after water intake 下 ; Calculate the average value of v 上 and v 下 to obtain v;

[0055] The calculation method of the velocity v of the water intake section after water intake 上 is as follows:

[0056] v 上 = Q′0 / (t * A 上 )

[0057] The calculation method of the velocity v of the assessment section after water intake 下 is as follows:

[0058] v 下 = Q2 / (t * A 下 )

[0059] Among them: Q′0 is the flow rate after water intake at the water intake section, m 3 ; Q2 is the flow rate after water intake at the assessment section, m 3 ; A 上 is the area of the water intake section, m 2 ; A 下 is the area of the assessment section, m 2 ; t is the time, s.

[0060] 4. Impact assessment of the change in water intake method: Based on the pollutant concentration C at the downstream assessment section under the current situation 现状 and the pollutant concentration limit C of the water function area 考核 , analyze the impact of water intake on the river environment. When C 现状 *(1 - p) does not exceed C 考核 , the change in the water intake method has little impact on the pollutant concentration in the downstream river channel.

[0061] The method for evaluating the impact of changing the water intake method on the pollutant concentration in the downstream river channel is as follows: Calculate the change rate p of the pollutant concentration at the downstream assessment section after changing the water intake conditions through the following formula:

[0062]

[0063] In the formula: Q2 is the flow at the downstream assessment section, m 3 ;

[0064] Q′0 is the discharged flow at the water intake section, m 3 ;

[0065] The discharged flow at the water intake section = the flow at the water intake section - the water intake volume;

[0066] C2 is the pollutant concentration at the downstream assessment section, mg / L;

[0067] C x is the pollutant concentration of the polluted water flowing from the water intake section to the downstream assessment section, mg / L;

[0068] Among the above symbols, different superscripts represent different water intake methods. Superscript 1 represents water intake method 1, and superscript 2 represents water intake method 2.

[0069] (2) Only consider centralized wastewater discharge, that is, the wastewater discharge along the way is 0

[0070] 1. Collect data: The flow rates Q0 and Q′0, pollutant concentration C0 before and after water intake at the water intake section, the distance x from the assessment section to the water intake section, the water volume and water quality information of the sewage treatment plant, the pipeline water conveyance utilization coefficient η1, the water discharge coefficient η2, the sewage treatment loss coefficient η3, the effluent control standard C 退 of the sewage treatment plant, the flow rate Q2 and pollutant concentration C2 at the downstream assessment section and the pollutant concentration limit C 考核 of the water function area, the river bed slope i, and the measured cross-section A.

[0071] 2. Select representative pollutants. Select the main pollutants and the pollutants with the greatest risk of exceeding the standard as representative pollutants according to the monitoring at the downstream assessment section.

[0072] 3. The method for evaluating the impact of changing the water intake method on the pollutant concentration in the downstream river section is as follows: Calculate the change rate p of the pollutant concentration at the downstream assessment section after changing the water intake conditions through the following formula:

[0073]

[0074] In the formula: Q 取 is the water intake volume, m 3 ; η1 is the pipeline water conveyance utilization coefficient, η2 is the water use discharge coefficient, and η3 is the sewage treatment loss coefficient; C 退 is the pollutant concentration of centralized wastewater discharge, mg / L; other symbols have the same meanings as those in formula (1); different superscripts in the above symbols represent different water intake methods, with superscript 1 representing water intake method 1 and superscript 2 representing water intake method 2.

[0075] 4. Impact assessment of changing the water intake method: Analyze the impact of water intake on the river environment based on the relationship between the pollutant concentration C 现状 at the current downstream assessment section and the pollutant concentration limit C 考核 of the water function area. When C 现状 *(1 - p) does not exceed C 考核 , the impact of changing the water intake method on the pollutant concentration in the downstream river section is very small.

[0076] (III) Both centralized wastewater discharge and in - process wastewater discharge

[0077] 1. Collect data: The flow rates Q0 and Q′ ′0 before and after water intake at the water intake section, the pollutant concentration C0, the distance x from the assessment section to the water intake section, the distance x1 from the centralized wastewater discharge section to the water intake section, the unit - width flow rate q0 of seepage water from the irrigation area and the corresponding pollutant concentration C q , the seepage coefficient γ, the river reach length l, the drainage ditch length L, and the distance x2 from the upstream to the water intake section, the centralized wastewater discharge volume Q 退 , the pollutant concentration C 退 of centralized wastewater discharge, the flow rate Q2 and pollutant concentration C2 at the downstream assessment section, and the pollutant concentration limit C 考核 of the water function area, the river bed slope i, the measured cross - section area A, and the groundwater depth h in the irrigation area.

[0078] 2. Select representative pollutants. Select the main pollutants and the pollutants with the greatest risk of exceeding the standard as representative pollutants based on the monitoring at the downstream assessment section.

[0079] 3. The method for evaluating the impact of changing the water intake method on the pollutant concentration in the downstream river section is as follows: Calculate the change rate p of the pollutant concentration at the downstream assessment section after changing the water intake conditions through the following formula:

[0080]

[0081] In the formula:

[0082] q0 is the unit-width flow rate of seepage return water in the irrigation area, m3; C q is the corresponding pollutant concentration, mg / L; L is the length of the drainage ditch, m; γ is the seepage coefficient, m / s; A is the cross-sectional area of the river, m 2 ; h2 and h1 are the groundwater depths upstream and downstream of the irrigation area, m; l is the length of the seepage channel in the irrigation area, m; the meanings of other symbols are the same as those in formula (1); different superscripts in the above symbols represent different water intake methods, superscript 1 represents water intake method 1, and superscript 2 represents water intake method 2;

[0083] 4. Impact assessment of changing the water intake method: According to the pollutant concentration C 现状 at the downstream assessment section under the current situation and the pollutant concentration limit C 考核 of the water function area, the impact of water intake on the river environment is analyzed. When C 现状 *(1 - p) does not exceed C 考核 , the impact of changing the water intake method on the pollutant concentration in the downstream river channel is very small.

[0084] Derivation process of each formula of the present invention:

[0085] According to the law of mass conservation, there is the following relationship between the total amount of pollutants at the water intake section and the total amount of pollutants at the downstream assessment section:

[0086] Total amount of pollutants at the downstream section = Total amount of pollutants at the water intake section - Reduction amount of pollutants in the interval + Inflow amount of pollutants in the interval

[0087] Q2C2 = Q′0C x + Q q1 C q1 + Q q2 C q2 + Q 退 C 退 + Q 进1 C 进1 + Q 进2 C 进2

[0088] In the formula: Q2 is the flow rate at the downstream assessment section;

[0089] Q′0 is the discharge flow rate at the water intake section; Discharge flow rate at the water intake section = Flow rate at the water intake section - Water intake volume;

[0090] Q q1 is the along - way return water flow rate from the water intake section to the centralized return water section;

[0091] Q q2 is the along - way return water flow rate from the centralized return water section to the downstream assessment section;

[0092] Q 退 is the centralized water discharge volume;

[0093] Q 进1 is the runoff volume flowing into the section between the water intake section and the downstream assessment section;

[0094] Q 进2 is the runoff volume flowing into the section between the water intake section and the downstream assessment section;

[0095] C2 is the pollutant concentration at the downstream assessment section;

[0096] C x is the pollutant concentration of the pollutants flowing from the water intake section to the downstream assessment section;

[0097] C q1 is the pollutant concentration of the pollutants discharged along the way from the water intake section to the centralized water discharge section;

[0098] C q2 is the pollutant concentration of the pollutants discharged along the way from the centralized water discharge section to the downstream assessment section;

[0099] C 退 is the pollutant concentration of the centralized water discharge;

[0100] C 进1 is the pollutant concentration of the runoff flowing into the section between the water intake section and the downstream assessment section;

[0101] C 进2 is the pollutant concentration of the runoff flowing into the section between the water intake section and the downstream assessment section;

[0102] Among them, Q′0C x 、Q q1 C q1 、Q q2 C q2 and Q 退 C 退 are the influence items of water intake activities on pollutants; Q 进1 C 进1 and Q 进2 C 进2 are the influence items of non - water intake activities on pollutants.

[0103] The following relationships exist for different water intake schemes:

[0104]

[0105]

[0106] For the influence items of water intake activities on pollutants, both the total amount of pollutants discharged downstream and the reduction amount of pollutants in the interval change.

[0107] For the impact of non-water intake activities on pollutants, considering the high intensity of human activities, according to the existing methods and relevant evaluation specifications, the workload of data collection, analysis and calculation, modeling, etc. for this part is large, difficult, and inefficient. Since these changing factors are not caused by the water intake of the production and construction project, they are strictly the same under the two water intake scenarios. That is

[0108] Through formula transformation, we can obtain:

[0109]

[0110] Therefore, the impact of changing the water intake conditions on the pollutant concentration at the downstream assessment section can be expressed by the concentration reduction rate as:

[0111]

[0112] Let

[0113] Then the impact of changing the water intake conditions on the pollutant concentration at the downstream assessment section can be expressed by the concentration reduction rate as:

[0114]

[0115] According to the impact of water intake activities on pollutants, it can be divided into three categories. The first category is no return water, that is, both the along-channel return water and the centralized return water are 0; the second category is only considering the centralized return water, that is, the along-channel return water is 0; the third category is both centralized return water and along-channel return water.

[0116] A. No return water, that is, when both the along-channel return water and the centralized return water are 0

[0117] According to the law of conservation of mass, there is the following relationship between the total amount of pollutants at the water intake section and the total amount of pollutants at the downstream assessment section:

[0118] Total amount of pollutants at the downstream section = Total amount of pollutants at the water intake section - Interval pollutant reduction + Interval pollutant inflow

[0119] Q2C2 = Q′0C x +Q q1 C q1 +Q q2 C q2 +Q 退 C 退 +Q 进1 C 进1 +Q 进2 C 进2

[0120] Among them, Q′0C x 、Q q1 Cq1 , Q q2 C q2 and Q 退 C 退 are the impact items of water intake activities on pollutants; Q 进1 C 进1 and Q 进2 C 进2

[0121] are the impact items of non - water intake activities on pollutants.

[0122] The following relationships exist for different water intake schemes:

[0123]

[0124]

[0125] For the impact items of water intake activities on pollutants, both the total amount of pollutants discharged downstream and the reduction amount of pollutants in the interval change. Among them

[0126] For the impact items of non - water intake activities on pollutants, considering that the intensity of human activities is very high, according to the requirements of existing methods and relevant evaluation specifications, the workload of data collection, analysis and calculation, modeling, etc. for this part is large, the difficulty is high, and the efficiency is low. Since these changing factors are not caused by water intake from production and construction projects, they are strictly the same under the conditions of two water intake schemes. That is

[0127] Through formula transformation, it can be obtained that:

[0128]

[0129] Therefore, the impact of changing water intake conditions on the pollutant concentration at the downstream assessment section can be expressed by the concentration reduction rate as:

[0130]

[0131] Let Then the impact of changing water intake conditions on the pollutant concentration at the downstream assessment section can be expressed by the concentration reduction rate as:

[0132]

[0133] Among them, the discharge flow at the water intake section is a known quantity, the flow at the downstream assessment section is a known quantity, and the pollutant concentration of the pollutants flowing from the water intake section to the downstream assessment section. According to the "Regulations for Calculating the Pollutant Assimilation Capacity of Water Areas" (GB / T 25173 - 2010), the one - dimensional river model is selected for analysis, and the pollutant concentration is a known quantity. The concentration reduction rate p is calculated.

[0134] B. Only consider concentrated drawdown, that is, the drawdown along the way is 0

[0135] According to the law of conservation of mass, there is the following relationship between the total amount of pollutants at the water intake section and the total amount of pollutants at the downstream assessment section:

[0136] Total amount of pollutants at the downstream section = Total amount of pollutants at the water intake section - Reduction of pollutants in the interval + Inflow of pollutants in the interval

[0137] Q2C2 = Q′0C x +Q q1 C q1 +Q q2 C q2 +Q 退 C 退 +Q 进1 C 进1 +Q 进2 C 进2

[0138] Among them, Q′0C x 、Q q1 C q1 、Q q2 C q2 and Q 退 C 退 are the impact items of water intake activities on pollutants; Q 进1 C 进1 and Q 进2 C 进2 are the impact items of non - water intake activities on pollutants.

[0139] There is the following relationship for different water intake schemes:

[0140]

[0141]

[0142] For the impact items of water intake activities on pollutants, both the total amount of pollutants discharged downstream and the reduction of pollutants in the interval change. Among them different water intake schemes have no impact on the concentration of pollutants in the drawdown of the sewage treatment plant, that is

[0143] For the impact items of non - water intake activities on pollutants, considering that the intensity of human activities is very high, according to the existing methods and the requirements of relevant evaluation specifications, the workload of data collection, analysis and calculation, modeling, etc. for this part is large, difficult and inefficient. Since these changing factors are not caused by water intake from production and construction projects, they are strictly the same under the conditions of the two water intake schemes. That is

[0144] It can be obtained through formula transformation that:

[0145]

[0146] Therefore, the impact of changing the water intake conditions on the pollutant concentration at the downstream assessment section can be expressed by the concentration reduction rate as:

[0147]

[0148] Among them, the downstream discharge flow is a known quantity, the flow at the downstream assessment section is a known quantity, the water intake at the water intake section is a known quantity, and the pollutant concentration of the pollutants flowing from the water intake section to the downstream assessment section According to the "Regulations for Calculating the Pollutant Carrying Capacity of Water Areas" (GB / T 25173-2010), a one-dimensional river model is selected for analysis. The pollutant concentration at the downstream assessment section in Mode 1 is a known quantity, the pollutant concentration C of the centralized wastewater discharge 退 is a known quantity, and the pipeline water conveyance utilization coefficient η1, water use discharge coefficient η2, and sewage treatment loss coefficient η3 are known quantities. The concentration reduction rate p is calculated.

[0149] Design stage:

[0150] Select the existing water quality information of projects of the same scale and calculate the reduction coefficient according to the water volume.

[0151] m 退 =Q 退 C 退

[0152] Among them:

[0153] Q 退 =Q 取 η1η2η3

[0154] In the formula: η1, η2, and η3 are respectively the pipeline water conveyance utilization coefficient, water use discharge coefficient, and sewage treatment loss coefficient of existing projects of the same scale;

[0155] C 退 is the pollutant concentration of the wastewater discharge of existing projects of the same scale.

[0156] The formula for calculating the total amount of wastewater discharge in the design stage under Water Intake Scheme 1 is as follows:

[0157]

[0158] The formula for calculating the total amount of wastewater discharge in the design stage under Water Intake Scheme 2 is as follows:

[0159]

[0160] Planning and demonstration stage:

[0161] m 退 = Q 退 C 退

[0162] Where:

[0163] Q 退 = Q 取 η1η2η3

[0164] In the formula: η1, η2, and η3 are the pipeline water conveyance utilization coefficient, water discharge coefficient, and sewage treatment loss coefficient, respectively;

[0165] C 退 is the initial water quality standard of the plan. The water quality standard is based on the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants" (GB18918 - 2002).

[0166] The calculation formula for the total amount of pollutants in the wastewater discharged during the planning and management stage under Intake Scheme 1 is as follows:

[0167]

[0168] The calculation formula for the total amount of pollutants in the wastewater discharged during the planning and management stage under Intake Scheme 2 is as follows:

[0169]

[0170] C, with both centralized wastewater discharge and in - line wastewater discharge

[0171] According to the law of conservation of mass, the following relationship exists between the total amount of pollutants at the intake section and the total amount of pollutants at the downstream assessment section:

[0172] Total amount of pollutants at the downstream section = Total amount of pollutants at the intake section - Reduction amount of pollutants in the interval + Inflow amount of pollutants in the interval

[0173] Q2C2 = Q′0C x + Q q1 C q1 + Q q2 C q2 + Q 退 C 退 + Q 进1 C 进1 + Q 进2 C 进2

[0174] Among them, Q′0C x 、Q q1 C q1 、Q q2C q2 and Q 退 C 退 is the impact term of water intake activities on pollutants; Q 进1 C 进1 and Q 进2 C 进2 is the impact term of non - water intake activities on pollutants.

[0175] The following relationships exist for different water intake schemes:

[0176]

[0177]

[0178] For the impact term of water intake activities on pollutants, both the total amount of pollutants discharged downstream and the reduction amount of pollutants in the interval change.

[0179] For the impact term of non - water intake activities on pollutants, considering that the intensity of human activities is very high, according to the existing methods and the requirements of relevant evaluation specifications, the workload of data collection, analysis and calculation, modeling, etc. for this part is large, difficult and inefficient. Since these changing factors are not caused by water intake from production and construction projects, they are strictly the same under the two water intake schemes. That is

[0180] Through formula transformation, it can be obtained that:

[0181]

[0182] Therefore, the impact of changing the water intake conditions on the pollutant concentration at the downstream assessment section can be expressed by the concentration reduction rate as:

[0183]

[0184] Among them, the discharge flow at the water intake section is a known quantity, the flow at the downstream assessment section is a known quantity, and the pollutant concentration of the pollutants flowing from the water intake section to the downstream assessment section. According to the "Regulations for Calculating the Pollutant Assimilation Capacity of Water Areas" (GB / T 25173 - 2010), the one - dimensional river model analysis is selected. The initial pollutant concentration C0 at the water intake section is a known quantity, and the pollutant concentration at the downstream assessment section in Mode 1 is a known quantity. The unit - width leakage return flow q0 of the irrigation area, the corresponding pollutant concentration C q , the seepage coefficient γ, the river reach length l, the drainage ditch length L, and the groundwater depth h are known quantities, and the measured large cross - section A is a known quantity. The concentration reduction rate p is calculated.

[0185] During the irrigation period, the concentrated river water withdrawal includes irrigation return flow and seepage drainage. During the non-irrigation period, the concentrated river water withdrawal is only seepage drainage.

[0186] Considering that the main factors affecting seepage drainage (drainage ditch spacing, depth, soil hydraulic properties) remain unchanged, the irrigation return flow is the difference between the irrigation period flow and the minimum flow during the non-irrigation period at the concentrated water withdrawal location.

[0187] Considering the transition of water in the irrigation area from unsaturated to saturated state during the paddy field flooding period, and the change processes of surface seepage and deep seepage after soil saturation, the free seepage unsteady flow formula of river channels is used to calculate the seepage flow process from the irrigation area to the drainage ditches:

[0188] q0 = εLμ(G0)′

[0189] Where:

[0190]

[0191]

[0192]

[0193] In the formula: q0 is the unit width flow of seepage drainage in the irrigation area, m 2 / s;

[0194] ε is the seepage loss in the irrigation area, mm; calculated using measured data

[0195] L is the spacing of the drainage ditches, m;

[0196] μ is the specific yield of the soil;

[0197] a is the hydraulic diffusivity;

[0198] T is the calculation time period, d;

[0199] is the relative time;

[0200] (G0)′ is the river channel flow function;

[0201] α is the reciprocal of the delay index.

[0202] The mass m of non-point source pollutants in the irrigation area seeping into the drainage ditches at time t t is the product of the seepage water flow (the product of the unit width flow and the length L of the last-level drainage ditch) and the seepage concentration C t :

[0203] m t = q0LC t

[0204] Although the transformation of non-point source pollution in soil includes various physical, chemical, and biological processes, since the vast majority of these transformation processes can be described by the first-order kinetic equation, a comprehensive first-order kinetic coefficient is used to describe the concentration decay of non-point source pollutants in soil under the combined action of various physical, chemical, and biological processes:

[0205] c t+1 =c t e -kt

[0206] In the formula: c t and c t+1 are the concentrations of the exuded pollutants at times t and t + 1, respectively, in mg / L; where the pollutant concentration at time t = 0 is C0.

[0207] k is the comprehensive first-order kinetic coefficient, in d -1 .

[0208] The calculation formula for the total amount of pollutants in the seepage drainage of the lower irrigation area under Water Intake Scheme 1 is as follows:

[0209]

[0210] The calculation formula for the total amount of pollutants in the seepage drainage of the lower irrigation area under Water Intake Scheme 2 is as follows:

[0211]

[0212] The along-channel water recession of the river includes the along-channel water recession from the water intake section to the centralized water recession section and from the centralized water recession section to the downstream assessment section.

[0213] For the along-channel water recession from the water intake section to the centralized water recession section, considering the elevation of the irrigation area water level caused by the increase in water intake and the unchanged pollutant concentration, the Darcy formula is used to calculate the along-channel water recession process of the river section in the irrigation area:

[0214]

[0215] In the formula: Q is the seepage flow rate, in m 3 / s;

[0216] γ is the seepage coefficient, reflecting the water permeability of the soil, in m / s;

[0217] A is the cross-sectional area of the river, in m 2 .

[0218] h2 and h1 are the groundwater depths upstream and downstream of the irrigation area, respectively, in m;

[0219] l is the length of the river section with seepage in the irrigation area, in m.

[0220] The calculation formula for the along-channel water recession of the river section in the lower irrigation area under Water Intake Scheme 1 is as follows:

[0221]

[0222] For the second water intake scheme, the formula for the river reach drawdown in the lower irrigation area is as follows:

[0223]

[0224] Since the pollutant concentration remains unchanged, the total amount of pollutants in the river reach drawdown in the lower irrigation area under the two water intake schemes is calculated as follows:

[0225]

[0226]

[0227] Finally, it should be noted that the above is only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred layout scheme, those of ordinary skill in the art should understand that the technical solution of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for evaluating the impact of changing the water intake method on the pollutant concentration in the downstream river channel, characterized in that: Including the following steps: 1) Classify according to the impact of water intake activities on pollutants: The first category is without return flow, that is, both the in - line return flow and the centralized return flow are 0; the second category is only considering the centralized return flow, that is, the in - line return flow is 0; the third category is both with centralized return flow and in - line return flow; 2) For those determined to be the first category in step 1), the method for evaluating the impact of changing the water intake method on the pollutant concentration in the downstream river channel is as follows: Calculate the change rate p of the pollutant concentration at the downstream assessment section after changing the water intake conditions through the following formula: In the formula: Q2 is the flow rate at the downstream assessment section; Q′0 is the discharge flow at the water intake section; The discharge flow at the water intake section = the flow rate at the water intake section - the water intake flow rate; C2 is the pollutant concentration at the downstream assessment section, mg / L; C x is the pollutant concentration of the polluted water flow at the water intake section flowing to the downstream assessment section, mg / L; In the symbols of formula (1), different superscripts represent different water intake methods. Superscript 1 represents water intake method 1, and superscript 2 represents water intake method 2; 3) For those determined to be the second category in step 1), the method for evaluating the impact of changing the water intake method on the pollutant concentration in the downstream river channel is as follows: Calculate the change rate p of the pollutant concentration at the downstream assessment section after changing the water intake conditions through the following formula: Where: Q 取 is the water intake flow rate; η1 is the pipeline water conveyance utilization coefficient, η2 is the water use discharge coefficient, and η3 is the sewage treatment loss coefficient; C 退 is the concentrated backwater pollutant concentration, mg / L; other symbols have the same meanings as those in formula (1); different superscripts in the symbols of formula (2) represent different water intake methods, where superscript 1 represents water intake method 1 and superscript 2 represents water intake method 2; 4) For those determined to be the third category in step 1), the method for evaluating the impact of changing the water intake method on the pollutant concentration in the downstream river channel is as follows: Calculate the change rate p of the pollutant concentration at the downstream assessment section after changing the water intake conditions through the following formula: In the formula: $q_0$ is the unit-width flow rate of seepage return flow in the irrigation area, m 2 / s; C q is the pollutant concentration corresponding to the unit-width flow rate $q_0$ of seepage return flow in the irrigation area, mg / L; L is the length of the drainage ditch, m; $\gamma$ is the seepage coefficient, m / s; A is the cross-sectional area of the river, m 2 ; $h_2$ and $h_1$ are the groundwater depths upstream and downstream of the irrigation area respectively, m; l is the length of the seepage channel in the irrigation area, m; other symbols have the same meanings as those in formula (1); different superscripts in the symbols of formula (3) represent different water intake methods, superscript 1 represents water intake method 1, and superscript 2 represents water intake method 2; 5) Impact assessment of the change in water intake method: Based on the pollutant concentration C at the downstream assessment section under the current situation 现状 and the pollutant concentration limit C of the water function area 考核 , analyze the impact of water intake on the river environment. When C 现状 *(1 - p) does not exceed C 考核 , the impact of the change in water intake method on the pollutant concentration in the downstream river channel is very small.

2. The method for evaluating the impact of changing the water intake method on the pollutant concentration in the downstream river channel according to claim 1, characterized in that: Calculate the pollutant concentration C of the pollutants flowing from the water intake section to the downstream assessment section x , and the specific formula is as follows: where: C is the pollutant concentration of the pollutants flowing from the water intake section to the downstream assessment section x , mg / L; x is the distance from the assessment section to the water intake section, m; v is the average flow velocity of the river channel cross - section under the design flow rate, m / s; C0 is the pollutant concentration before water intake at the water intake section, mg / L; K is the comprehensive attenuation coefficient of pollutants, s -1 .

3. The method for evaluating the impact of changing the water intake method on the pollutant concentration in the downstream river channel according to claim 1, characterized in that, The pollutants in the downstream river channel are representative pollutants. Select the main pollutants and the pollutants with the greatest risk of exceeding the standard as representative pollutants according to the monitoring at the downstream assessment section.

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