Fine calculation method for total pollutant emission under complex river condition

Abstract

The invention discloses a fine calculation method for the total pollutant discharge amount under the complex river condition, and relates to the technical field of pollutant discharge control, and the method comprises the steps: building a physical experiment model, and setting the pollution load of each river reach of the physical experiment model; a complex river water environment mathematical model is established according to the set physical experiment model, and the pollutant concentration of the research river reach under the preset environment condition is calculated; and respectively calculating the pollutant water environment capacities of the research river reach in the dry season and the wet season, giving weights to the research river reach in the dry season and the wet season, and calculating to obtain the total allowable discharge amount of the drainage basin pollutants of the research river reach. According to the method, accurate calculation of the permissible emission amount of the specific pollutants under the complex river condition is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of pollutant emission control, and more specifically, to a refined calculation method for the total amount of pollutant emissions under complex river conditions. Background Art

[0002] In the field of river pollution control and management, accurately calculating the total allowable emissions of characteristic pollutants in the basin is crucial for protecting the water environment quality of rivers. Certain achievements have been made in the calculation methods for the total amount of river pollutants emissions, but in the face of complex river conditions, there are still many deficiencies in the existing technologies. On the one hand, the existing research has insufficient understanding of the discrete characteristics of complex rivers. Complex river channel morphology, large seasonal variations in water volume, high water and sediment content, and the coexistence of frozen and non-frozen sections make the transport and mixing mechanisms of pollutants in rivers extremely complex. However, it is difficult for existing technologies to comprehensively and accurately grasp the influence of these factors on the transport and mixing of pollutants, and it is impossible to accurately determine the transverse dispersion coefficient and longitudinal dispersion coefficient, resulting in large errors in calculating the diffusion range and concentration changes of pollutants.

[0003] On the other hand, in the construction of river water environment mathematical models, there are limitations in existing models. In traditional two-dimensional water environment mathematical models, the determination methods for the longitudinal dispersion coefficient, transverse dispersion coefficient, and pollutant decay coefficient are relatively simple, and the comprehensive influence of various factors under complex river conditions is not fully considered. For example, when calculating the longitudinal dispersion coefficient, key factors such as river flow characteristics, friction characteristics, and cross-sectional dimensions are not comprehensively covered; the calculation of the transverse dispersion coefficient often ignores the complex relationship with the longitudinal dispersion coefficient; for the pollutant decay coefficient, the influence of special conditions such as high sediment content and freezing on the water self-purification ability is not fully considered, resulting in a large deviation between the model calculation results and the actual situation and being unable to provide a reliable basis for river pollution control.

[0004] Therefore, how to calculate the total allowable emissions of characteristic pollutants under complex river conditions is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the present invention provides a refined calculation method for the total amount of pollutant emissions under complex river conditions to solve the problems existing in the above background art.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A refined calculation method for the total amount of pollutant emissions under complex river conditions includes:

[0008] Establishing a physical experiment model and setting the pollution load of each river section of the physical experiment model;

[0009] Establish a complex river water environment mathematical model based on the physical experiment model set up, and calculate the pollutant concentration in the research river section under the preset environmental conditions;

[0010] Calculate the water environment capacity of pollutants in the research river section during the dry season and the wet season respectively, assign weights to the dry season and the wet season of the research river section, and calculate and obtain the total allowable pollutant emissions in the basin of the research river section.

[0011] Preferably, the preset environmental conditions include:

[0012] The first preset environmental condition, complex river channel morphology;

[0013] The second preset environmental condition, complex river channel morphology, multi-sand condition;

[0014] The third preset environmental condition, complex river channel morphology, icing condition;

[0015] The fourth preset environmental condition, complex river channel morphology, multi-sand, icing condition;

[0016] Any one of the preset environmental conditions.

[0017] Preferably, calculating the pollutant concentration in the research river section under the first preset environmental condition specifically includes:

[0018]

[0019] F(k) = F(C, DO, Q, t, Δx, Δy);

[0020] Where, H is the water depth; W is the river width; a, b, γ, m, d, i are constants; u, v are the velocity components in the x and y directions respectively; u’ is the cross-section average flow velocity, u * is the bed bottom friction velocity; Q is the water body flow rate; D x is the longitudinal dispersion coefficient of the river; F(k) is the pollutant attenuation coefficient under the first preset environmental condition; C is the pollutant concentration; S is the external source; DO is the dissolved oxygen content of the water body; Q is the water body flow rate; t is the time; Δx, Δy are the longitudinal and transverse transport distances respectively.

[0021] Preferably, calculating the pollutant concentration in the research river section under the second preset environmental condition specifically includes:

[0022]

[0023] F(k) s = F(C, DO s , Q, t, Δx, Δy);

[0024] DO s = a - bT - cρ;

[0025] Wherein, H is the water depth; W is the river width; a, b, γ, m, d, i are constants; u and v are the velocity components in the x and y directions respectively; u’ is the cross-sectional average flow velocity, and u * is the frictional velocity at the river bed bottom; Q is the water body flow rate; D x is the longitudinal dispersion coefficient of the river; F(k) s is the pollutant decay coefficient under the second preset environmental condition; C is the pollutant concentration; S is the external source; DO s represents the influence of water and sediment content on dissolved oxygen; T represents the water temperature, ρ represents the sediment concentration, and a, b, c are coefficients; Q is the water body flow rate; t is the time; Δx and Δy are the longitudinal and transverse transport distances respectively.

[0026] Preferably, calculating the pollutant concentration of the research river section under the third preset environmental condition specifically includes:

[0027]

[0028] F(k) i = F(C, DO i , Q, t, Δx, Δy);

[0029] DO i = eh 2 + fh + g;

[0030] Wherein, H is the water depth; W is the river width; a, b, γ, m, d, i are constants; u and v are the velocity components in the x and y directions respectively; u’ is the cross-sectional average flow velocity, and u * is the frictional velocity at the river bed bottom; Q is the water body flow rate; D x is the longitudinal dispersion coefficient of the river; F(k) i is the pollutant decay coefficient under the third preset environmental condition; C is the pollutant concentration; S is the external source; DO i represents the influence of ice formation on the dissolved oxygen content of the water body; h represents the ice layer thickness, and e, f, g are coefficients; Q is the water body flow rate; t is the time; Δx and Δy are the longitudinal and transverse transport distances respectively.

[0031] Preferably, calculating the pollutant concentration of the research river section under the fourth preset environmental condition specifically includes:

[0032]

[0033] F(k) s,i = F(C, DO s , DO i , Q, t, Δx, Δy);

[0034] Wherein, F(k) s,iis the pollutant decay coefficient under the fourth preset environmental condition.

[0035] Preferably, calculate the water environment capacity of pollutants in the study river section during the dry season and the wet season respectively. The representative formula is:

[0036] w = Q 0 (C s - C 0 ) + KVC s ;

[0037] Among them, Q 0 is the inflow discharge of the inlet section, C s is the water quality standard of the water body, C 0 is the water quality concentration of the inlet section, K is the pollutant decay coefficient, and V is the volume of the water body.

[0038] As can be seen from the above technical solutions, compared with the prior art, the present invention discloses a method for accurately calculating the total amount of pollutant emissions under complex river conditions. Through physical experiments, measure and analyze the transport and mixing mechanisms of pollutants in the complex river channel morphology model, measure the influence of different cross-sectional morphologies, hydrodynamic conditions changes, water sediment content, icing, etc. on the changes of flow velocity and pollutant concentration in the river channel, so as to determine the influencing factors of the transverse dispersion coefficient and the longitudinal dispersion coefficient, analyze and reveal the transport and mixing mechanisms of pollutants under complex river conditions, establish calculation formulas for the transverse and longitudinal dispersion coefficients considering the diverse river channel morphologies, large seasonal variations in water volume, high water sediment content, and coexistence of icing and non-icing sections in the basin, and achieve accurate calculation of the permitted total emissions of characteristic pollutants under complex river conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to the provided drawings.

[0040] Figure 1 is the flowchart of the method steps provided by the present invention;

[0041] Figure 2 is the schematic plan view of the physical model provided by the present invention;

[0042] Figure 3 is the schematic cross-sectional view of the physical model provided by the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0043] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0044] An embodiment of the present invention discloses a refined calculation method for the total amount of pollutant emissions under complex river conditions, as Figure 1 shown, including:

[0045] Establish a physical experiment model and set the pollution load of each river section of the physical experiment model;

[0046] Establish a complex river water environment mathematical model according to the set physical experiment model, and calculate the pollutant concentration of the research river section under preset environmental conditions;

[0047] Calculate the water environment capacity of pollutants in the research river section during the dry season and the wet season respectively, assign weights to the dry season and the wet season of the research river section, and calculate and obtain the total permitted pollutant emissions of the basin of the research river section.

[0048] In a specific embodiment, the preset environmental conditions include:

[0049] The first preset environmental condition, a complex river channel morphology;

[0050] The second preset environmental condition, a complex river channel morphology and a multi-sand condition;

[0051] The third preset environmental condition, a complex river channel morphology and an icing condition;

[0052] The fourth preset environmental condition, a complex river channel morphology, a multi-sand and an icing condition;

[0053] Any one of the preset environmental conditions.

[0054] Among them, a complex river channel generally means that the cross-sectional shapes of each river section of the river are different, including bends, straight sections, constrictions, bifurcations, etc. Different river channel morphologies have different effects on pollutant transport, and it is difficult to accurately simulate with a simple straight river model. The multi-sand condition refers to a river with a large amount of sediment, generally referring to a river with a high content of suspended solids (suspended sediment) in the water body, a relatively large fineness of the suspended solids, a relatively shallow riverbed depth, and a relatively slow flow velocity. Among them, the content of suspended solids in the water body exceeds 10 mg / L, and the suspended solids with a particle size of more than 4 mm exceed 2 mg / L.

[0055] In a specific embodiment, calculating the pollutant concentration of the research river section under the first preset environmental condition specifically includes:

[0056]

[0057] F(k) = F(C, DO, Q, t, Δx, Δy);

[0058] Wherein, H is the water depth; W is the river width; a, b, γ, m, d, i are constants; u and v are the velocity components in the x and y directions respectively; u’ is the cross-sectional average flow velocity, and u * is the frictional velocity at the river bed bottom; Q is the water body flow rate; D x is the longitudinal dispersion coefficient of the river; F(k) is the pollutant attenuation coefficient under the first preset environmental condition; C is the pollutant concentration; S is the external source; DO is the dissolved oxygen content of the water body; Q is the water body flow rate; t is the time; Δx and Δy are the longitudinal and lateral transport distances respectively.

[0059] In a specific embodiment, calculating the pollutant concentration of the research river section under the second preset environmental condition specifically includes:

[0060]

[0061] F(k) s = F(C, DO s , Q, t, Δx, Δy);

[0062] DO s = a - bT - cρ;

[0063] Wherein, H is the water depth; W is the river width; a, b, γ, m, d, i are constants; u and v are the velocity components in the x and y directions respectively; u’ is the cross-sectional average flow velocity, and u * is the frictional velocity at the river bed bottom; Q is the water body flow rate; D x is the longitudinal dispersion coefficient of the river; F(k) s is the pollutant attenuation coefficient under the second preset environmental condition; C is the pollutant concentration; S is the external source; DO s represents the influence of sediment content on dissolved oxygen; T represents the water temperature, ρ represents the sediment concentration, and a, b, c are coefficients; Q is the water body flow rate; t is the time; Δx and Δy are the longitudinal and lateral transport distances respectively.

[0064] In a specific embodiment, calculating the pollutant concentration of the research river section under the third preset environmental condition specifically includes:

[0065]

[0066] F(k) i = F(C, DO i , Q, t, Δx, Δy);

[0067] DO i = eh 2 + fh + g;

[0068] Wherein, H is the water depth; W is the river width; a, b, γ, m, d, i are constants; u and v are the velocity components in the x and y directions respectively; u’ is the cross-sectional average flow velocity, and u * is the frictional velocity at the bottom of the riverbed; Q is the water body flow rate; D x is the longitudinal dispersion coefficient of the river; F(k) i is the pollutant decay coefficient under the third preset environmental condition; C is the pollutant concentration; S is the external source; DO i represents the impact of icing on the dissolved oxygen content in the water body; h represents the ice layer thickness, and e, f, g are coefficients; Q is the water body flow rate; t is the time; Δx and Δy are the longitudinal and lateral transport distances respectively.

[0069] In a specific embodiment, calculating the pollutant concentration of the research river section under the fourth preset environmental condition specifically includes:

[0070]

[0071] F(k) s,i = F(C, DO s , DO i , Q, t, Δx, Δy);

[0072] Wherein, F(k) s,i is the pollutant decay coefficient under the fourth preset environmental condition.

[0073] In a specific embodiment, the pollutant water environmental capacity of the research river section in the dry season and the wet season is calculated respectively, and the representative formula is:

[0074] w = Q 0 (C s - C 0 ) + KVC s ;

[0075] Wherein, Q 0 is the inflow rate of the inlet section, C s is the water quality standard of the water body, C 0 is the water quality concentration of the inlet section, K is the pollutant decay coefficient, and V is the volume of the water body.

[0076] In a specific embodiment, aiming at the complex river channel morphology in the upper and middle reaches of the Yellow River, a straight-bending-straight river physical experiment model is made. The physical experiment model is 12 m in total length, 1 m at the widest part of the water surface, about 10 m in the length of the main experimental section, and the bottom slope can be adjusted. An inlet system and an outlet system are respectively arranged at the upstream and downstream of the physical experiment model. By adjusting the water depth in the model, the cross-section of the model shows cross-section shapes such as wide and shallow type and narrow and deep type respectively. The lengths of the two straight sections before the inlet section and after the outlet section of the bend are both 2 m, asFigure 2 as shown in Figure 3 shown

[0077] The physical experiment is carried out as follows:

[0078] i. Select monitoring cross-sections at intervals of 45° along the continuous bending section of the physical experiment model, measure the three-dimensional flow velocity distribution in the model with an ADCP measuring instrument, and release tracers. Use a concentration measuring instrument to measure the along-channel changes of pollutants at different positions in the cross-section, and analyze the transport and mixing mechanisms of pollutants in the complex river channel morphology model;

[0079] ii. By adjusting the water depth in the flume and changing the cross-sectional shape of the flume, measure the influence of different cross-sectional shapes on the change of pollutant concentration;

[0080] iii. By changing the magnitude of the inlet flow rate, measure the influence of the change of hydrodynamic conditions on the change of flow velocity and concentration distribution in the river channel;

[0081] iv. Release different amounts of sediment and repeat step i to analyze the influence of the sediment content in the water body on the change of flow velocity and pollutant concentration;

[0082] v. According to relevant research, select appropriate plywood to float on the water surface and fix it on the side wall of the model, and repeat steps i and iv to simulate the influence of icing on the change of water body flow velocity and pollutant concentration;

[0083] Deeply analyze and sort out the above physical experiment data, determine the influencing factors of the transverse dispersion coefficient and the longitudinal dispersion coefficient, analyze and reveal the transport and mixing mechanism of pollutants under complex river conditions, and establish calculation formulas for the transverse and longitudinal dispersion coefficients considering the diverse river channel morphology, large seasonal changes in water volume, high water and sediment content, and the coexistence of icing and non-icing sections in the upper and middle reaches of the Yellow River.

[0084] The spatio-temporal variation process of water body pollutant concentration mainly includes the convective diffusion process of pollutants with water body flow and their own biochemical degradation and attenuation process. The water quality process control mass balance equation in the two-dimensional plane model is usually expressed by the following pollutant convective diffusion attenuation equation:

[0085]

[0086] where H represents the water depth, C is the pollutant concentration, u and v are the velocity components in the x and y directions respectively, D x , D y are the horizontal dispersion coefficients in the x and y directions respectively, that is, the longitudinal dispersion coefficient and the transverse dispersion coefficient of the river, S c is the attenuation term related to the concentration of the transported substance, and S is the external source or sink term.

[0087] S c = k × C (2)

[0088] k represents the attenuation rate such as the biochemical degradation of pollutants in water bodies.

[0089] Based on the two-dimensional water environment mathematical model to calculate the river water environment capacity, the most important task is to clarify the values of D x 、D y and k.

[0090] In this project, the longitudinal dispersion coefficient D of the river x is calculated according to the empirical formula proposed based on the river flow characteristics, friction characteristics, cross-sectional dimensions, etc.:

[0091]

[0092] where, W is the river width, H is the water depth, u’ is the cross-sectional average flow velocity, and u * is the friction velocity at the bottom of the riverbed. The constants m, d, and i are calculated according to physical experiments.

[0093] For the lateral dispersion coefficient D y , since generally the lateral flow velocity of the river channel is much smaller than the longitudinal flow velocity, the lateral dispersion effect is relatively small. In the present invention, the lateral dispersion coefficient is solved through the longitudinal dispersion coefficient according to the empirical formula,

[0094]

[0095] The pollutant attenuation coefficient k is determined by multiple factors. Aiming at the complex conditions in the upper and middle reaches of the Yellow River, the present invention mainly considers the influence of the coexistence of sediment-laden, ice-covered sections and ice-free sections on the dissolved oxygen content in the water body, that is, on the self-purification ability of the water body, and then calibrates the pollutant attenuation coefficient solving equation through a method combining numerical simulation and physical model.

[0096] F(k) = F(C, DO, Q, t, Δx, Δy) (5)

[0097] where, C is the pollutant concentration, DO is the dissolved oxygen content in the water body, Q is the water body flow rate, t is the time, and Δx, Δy are the longitudinal and lateral transport distances respectively. It can be seen that the dissolved oxygen DO content is an important variable for calculating the pollutant attenuation coefficient.

[0098] In the present invention, the dissolved oxygen content in the water body is mainly affected by the water and sediment content and the icing situation. Among them, the influence of icing on the self-purification ability of the water body only occurs in the dry season. The relationship between dissolved oxygen and sediment concentration can be expressed as:

[0099] DO s = a - bT - cρ (6)

[0100] where, DO sRepresents the influence of water and sediment content on dissolved oxygen, T represents water temperature, ρ represents sediment concentration, and the coefficients a, b, and c can be calculated based on physical experiments.

[0101] Therefore, only considering the influence of water and sediment, the pollutant decay coefficient is

[0102] F(k) s = F(C, DO s , Q, t, Δx, Δy) (7)

[0103] Regarding the influence of ice formation on the dissolved oxygen content in water bodies, the dissolved oxygen content shows a "U-shaped" change curve during the ice-covered period, and the proposed equation is:

[0104] DO i = eh 2 + fh + g (e > 0) (8)

[0105] Among them, DO i represents the influence of ice formation on the dissolved oxygen content in water bodies, h represents the ice layer thickness, and the coefficients e, f, and g can be calculated based on actual measurements of physical experiments.

[0106] Therefore, only considering the influence of ice formation, the pollutant decay coefficient is

[0107] F(k) i = F(C, DO i , Q, t, Δx, Δy) (9)

[0108] Considering both the influence of water and sediment and ice formation, the pollutant decay coefficient is

[0109] F(k) s,i = F(C, DO s , DO i , Q, t, Δx, Δy) (10)

[0110] In summary, under complex river channel morphology, the mass balance equation for water quality process control in the two-dimensional model is improved as follows

[0111]

[0112] Under complex river channel morphology and multi-sediment conditions, the mass balance equation for water quality process control in the two-dimensional model is improved to

[0113]

[0114] Under complex river channel morphology and ice formation conditions, the mass balance equation for water quality process control in the two-dimensional model is improved to

[0115]

[0116] Under complex river channel morphology, high sediment content, and icing conditions, the quality balance equation for water quality process control in the two-dimensional model is improved to

[0117]

[0118] The pollution loads in the study basin include two categories: point sources and non-point sources. Among them, non-point source pollution is mainly concentrated in the wet season. Therefore, from the perspective of total quantity control, the permitted pollutant emissions are calculated separately for the point source and non-point source pollution loads corresponding to different water conditions, and the combination of the two is the total permitted pollutant emissions in the basin.

[0119] The specific calculation steps are as follows:

[0120] i Generalize the point source pollution load to each river reach according to the actual location of the river discharge outlets, and at the same time divide the non-point source pollution into the river reaches surrounding the land area.

[0121] ii Calculate the pollutant concentration in each river reach through the established two-dimensional water environment mathematical model of the complex river.

[0122] iii Calculate the water environment capacity of the pollutants in the study river reaches during the dry season and the wet season respectively. The calculation formula is as follows:

[0123] w = Q 0 (C s - C 0 ) + KVC s (15)

[0124] Where: Q 0 is the inflow discharge at the inlet section, Cs is the water quality standard of the water body, C 0 is the water quality concentration at the inlet section, K is the pollutant decay coefficient, and V is the water body volume.

[0125] iv Assign weights to the water environment capacity during the dry season and the wet season according to the actual situation, comprehensively calculate the water environment capacity of the basin, and then obtain the total permitted pollutant emissions in the basin.

[0126] In this specification, each embodiment is described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. For the same or similar parts among the embodiments, reference can be made to each other. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and reference can be made to the description in the method part for related parts.

[0127] The foregoing description of the disclosed embodiments enables those skilled in the art to practice or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A refined calculation method for the total amount of pollutant emissions under complex river conditions, characterized in that: include: Establishing a physical experimental model, and setting the pollution load of each river section of the physical experimental model; Establish a mathematical model of complex river water environment based on the completed physical experimental model, and calculate the pollutant concentration of the study river section under the preset environmental conditions; The pollutant water environmental capacity of the study river section in the dry season and the wet season is calculated respectively, and the dry season and the wet season weights are assigned to the study river section to calculate and obtain the total permitted discharge amount of pollutants in the basin of the study river section.

2. According to the method for calculating the total amount of pollutant emissions under complex river conditions in detail in claim 1, it is characterized by: The preset environmental conditions include: The first preset environmental conditions are complex river morphology; The second preset environmental conditions are complex river morphology and sandy conditions; The third preset environmental conditions include complex river morphology and icing conditions; Fourth, preset environmental conditions, complex river morphology, sandy conditions, and icy conditions; Any one of the preset environmental conditions.

3. The method for calculating the total amount of pollutant emissions under complex river conditions according to claim 2 is characterized in that: Calculating the pollutant concentration of the study river section under the first preset environmental conditions specifically includes: F(k)=F(C,DO,Q,t,Δx,Δy); Where H is the water depth; W is the river width; a, b, γ, m, d, i are constants; u and v are the velocity components in the x and y directions respectively; u' is the average flow velocity in the cross section, u * is the friction velocity at the bottom of the riverbed; Q is the water flow; D x is the longitudinal dispersion coefficient of the river; F(k) is the pollutant attenuation coefficient under the first preset environmental conditions; C is the pollutant concentration; S is the external source; DO is the dissolved oxygen content of the water body; Q is the water flow; t is the time; Δx and Δy are the longitudinal and lateral transport distances, respectively.

4. The method for calculating the total amount of pollutant emissions under complex river conditions according to claim 3 is characterized in that: Calculating the pollutant concentration of the study river section under the second preset environmental conditions specifically includes: F(k) s =F(C,DO s ,Q,t,Δx,Δy); DO s =a-bT-cρ; Where H is the water depth; W is the river width; a, b, γ, m, d, i are constants; u and v are the velocity components in the x and y directions respectively; u' is the average flow velocity in the cross section, u * is the friction velocity at the bottom of the riverbed; Q is the water flow; D x is the longitudinal dispersion coefficient of the river; F(k) s is the pollutant attenuation coefficient under the second preset environmental conditions; C is the pollutant concentration; S is the external source; DO s represents the influence of water and sediment content on dissolved oxygen; T represents water temperature, ρ represents sediment content, a, b, c are coefficients; Q is water flow; t is time; Δx, Δy are longitudinal and lateral transport distances, respectively.

5. The method for calculating the total amount of pollutant discharge under complex river conditions according to claim 4 is characterized in that: Calculating the pollutant concentration of the study river section under the third preset environmental conditions specifically includes: F(k) i =F(C,DO i ,Q,t,Δx,Δy); DO i =eh 2 +fh+g; Where H is the water depth; W is the river width; a, b, γ, m, d, i are constants; u and v are the velocity components in the x and y directions respectively; u' is the average flow velocity in the cross section, u * is the friction velocity at the bottom of the riverbed; Q is the water flow; D x is the longitudinal dispersion coefficient of the river; F(k) i is the pollutant attenuation coefficient under the third preset environmental condition; C is the pollutant concentration; S is the external source; DO i represents the effect of freezing on the dissolved oxygen content of water; h represents the thickness of the ice layer, e, f, g are coefficients; Q is the water flow rate; t is time; Δx, Δy are the longitudinal and lateral transport distances, respectively.

6. The method for calculating the total amount of pollutant discharge under complex river conditions according to claim 5 is characterized in that: Calculation of pollutant concentrations in the study river section under the fourth preset environmental condition specifically includes: F(k) s,i =F(C,DO s ,DO i ,Q,t,Δx,Δy); Among them, F(k) s,i is the pollutant attenuation coefficient under the fourth preset environmental conditions.

7. The method for calculating the total amount of pollutant discharge under complex river conditions according to claim 1 is characterized in that: The water environmental capacity of pollutants in the studied river section during the dry season and the wet season is calculated respectively. The representative formula is: w=Q0(C s -C0)+KVC s ; Among them, Q0 is the inflow flow rate of the water inlet section, C s is the water quality standard of the water body, C0 is the water quality concentration at the water inlet section, K is the pollutant attenuation coefficient, and V is the volume of the water body.

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