A method for quantifying the flux of pollutant substances across a section of a tidal river

Abstract

The application discloses a kind of quantitative tidal river section pollutant flux analysis method, comprising the following steps: S1, the equation of concentration variation of pollutant is established;S2, the water flux equation of river section at the time period to be studied is established;S3, based on water flux equation and the equation of concentration variation of pollutant at the section, the pollutant flux equation of river section at the time period to be studied is established;According to the pollutant flux equation, the hourly flux of pollutant at the section at the time period to be studied is calculated.The application can calculate the hourly variation process of pollutant concentration which sufficiently reflects the concentration oscillation caused by reciprocating flow by inputting tidal level and limited concentration data into the equation of concentration variation of pollutant, and based on the hourly variation data of pollutant concentration, the pollutant flux at the section at a certain time period in the future can be calculated hourly according to the pollutant flux equation, and finally the total pollutant flux at the section per day can be counted, which provides scientific support for water safety decision-making of city managers.

Description

Technical Field

[0001] This invention relates to the field of pollutant flux. More specifically, this invention relates to a method for quantitative analysis of pollutant flux in tidal river sections. Background Technology

[0002] The main water sources for coastal cities in my country are estuarine-type water sources, meaning they directly draw freshwater resources from rivers distributed in estuary areas. However, due to the unique geographical location of estuarine-type water sources, the water movement in these rivers is simultaneously influenced by upstream runoff and ocean tides, creating tidal river sections with complex hydrodynamic environments and regular reciprocating flows. The existence of these reciprocating flows makes the water quality of these tidal river sections highly susceptible to the oscillating effects of pollutants and saltwater intrusion, thus impacting the water supply security of coastal cities.

[0003] The effective determination of cross-sectional fluxes of pollutants in tidal river sections, given the reciprocating flow and oscillation of water bodies and pollutants, has long been a hot topic in the field of water security. Currently, existing research techniques for quantifying pollutant fluxes in tidal river sections, both domestically and internationally, mainly include:

[0004] 1) Prototype observation: This method involves deploying water quality and flow monitoring stations at the proposed cross-section, characterized by long-term operation and high observation frequency, to continuously acquire key monitoring data. Further, it combines mathematical analysis and other methods to quantify the water and pollutant fluxes at the cross-section. However, this method has strict requirements on the observation timeframe, including the permanent operation of the monitoring stations and the hourly observation frequency. In practical applications, river cross-section flow monitoring mainly employs a combination of manual patrols, i.e., circling back and forth along the river cross-section to measure flow, making it difficult to continuously acquire hourly flow data. Furthermore, pollutant concentrations require chemical experimental analysis, which is time-consuming. For example, at the National Surface Water Monitoring Station, only four concentration values ​​can be measured within 24 hours, making it impossible to accurately calculate the pollutant flux at the cross-section.

[0005] 2) Model Inversion: This method uses mathematical or physical models as tools to establish an inversion model based on topographic, hydrological, and water quality data of tidal rivers. After calibration and verification, it quantifies water fluxes and pollutant fluxes at the research section. However, the basic input data for the model is obtained through prototype observations, and model inversion focuses on reviewing the history of pollutant transport in tidal rivers. When used for flux calculations in future scenarios, it is limited by the fixed nature of the model's topography and cannot accurately and quickly adapt to changes in the river channel environment. This problem can be addressed by updating the model's topography and recalibrating and verifying it, but this is time-consuming, lacks timeliness, and is not suitable for rapid analysis and quantification of pollutant fluxes. Summary of the Invention

[0006] Another objective of this invention is to provide a quantitative method for analyzing pollutant fluxes at tidal river sections, which can calculate pollutant fluxes at a cross-section at a future time period on an hourly basis, providing scientific support for urban managers' water security decisions.

[0007] To achieve these objectives and other advantages according to the present invention, a method for analyzing the flux of pollutants in a tidal river section is provided, comprising the following steps:

[0008] S1. Establish a pollutant concentration variation equation based on historical tidal data and historical pollutant concentration data of the upstream and downstream sections of the tidal river.

[0009] S2. Based on the constant non-uniform flow energy equation, establish the water flux equation at the river cross section during the study period;

[0010] S3. Based on the water flux equation and pollutant concentration change equation at the cross-section, establish the pollutant flux equation at the river cross-section during the proposed study period; calculate the hourly flux of pollutants at the cross-section during the proposed study period based on the pollutant flux equation; the proposed study period is a future period.

[0011] Preferably, step S1 specifically includes:

[0012] S11. Define the pollutant concentration range control factor and the tidal level factor as important influencing factors affecting pollutant concentration. Using pollutant concentration as the target factor, establish a mapping relationship between pollutant concentration at the tidal river section and the pollutant concentration range control factor and the tidal level factor.

[0013] S12. Obtain historical tidal data and pollutant concentration data of the upstream and downstream sections of the tidal river section, and establish a pollutant concentration change equation based on the mapping relationship.

[0014] Preferably, the mapping relationship is as follows:

[0015] C = f(θ,H);

[0016] In the formula: C is the pollutant concentration; H is the upstream or downstream tidal level factor; θ is the pollutant concentration variation control factor.

[0017] Preferably, in step S12, a pollutant concentration change equation is established by fitting multiple mathematical functions.

[0018] Preferably, step S2 specifically includes the following steps:

[0019] S21. Obtain the topographic elevation data of the upstream and downstream sections of the river cross-section during the study period. Based on the constant non-uniform flow energy equation, establish the flow equations at any time of the river cross-section under both high and low tide conditions. The cross-sectional flow equations are as follows:

[0020]

[0021]

[0022] In the formula: i = 1, 2, ..., 24; Q i <0 indicates high tide, Q i >0 indicates low tide; Z1 and Z2 are the tidal levels upstream and downstream of the cross-section, respectively, in meters; α1 and α2 are the velocity non-uniformity coefficients upstream and downstream of the cross-section, respectively; g is the acceleration due to gravity, in meters per second. 2 K1 and K2 are the upstream and downstream flow moduli at the cross-section, respectively; Δs is the length of the river segment between the upstream and downstream sections at the cross-section, in meters; ξ is the local head loss coefficient; A1 and A2 are the upstream and downstream flow areas at the cross-section, respectively, in meters. 2 .

[0023] S22. Based on the cross-sectional flow equation, establish the water flux equation at the cross-section during the study period:

[0024] V i =Q i Δt.

[0025] Preferably, in step S3, the pollutant flux equation is as follows:

[0026]

[0027] In the formula: C i Let be the pollutant concentration at time i.

[0028] This invention offers at least the following advantages: Building upon the limitations of continuous monitoring of cross-sectional flow, lengthy chemical analysis of pollutant concentrations, and the lack of timeliness in model-derived fluxes, this invention fully considers the correlation between pollutant concentration diffusion and the reciprocating flow of tidal river sections. By inputting tidal level and limited concentration data into the pollutant concentration change equation, it can calculate the hourly change process of pollutant concentration that fully reflects the concentration oscillations caused by the reciprocating flow. Based on the hourly pollutant concentration change data, and according to the pollutant flux equation, the pollutant flux at a cross-section for a future period can be calculated hourly. Ultimately, the total daily pollutant flux at the cross-section can be statistically analyzed, providing scientific support for urban managers' water security decisions.

[0029] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0030] Figure 1 This is a flowchart of the analysis process of the present invention;

[0031] Figure 2 COD of this invention cr Schematic diagram of the concentration-downstream tidal level fitting process;

[0032] Figure 3 This is a schematic diagram of the total nitrogen concentration-downstream tide level fitting process of the present invention. Detailed Implementation

[0033] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0034] It should be noted that in the description of this invention, the terms "lateral", "longitudinal", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0035] like Figure 1-3 As shown, this invention provides a method for analyzing the flux of pollutants in a tidal river section, comprising the following steps:

[0036] S1. Establish a pollutant concentration variation equation based on historical tidal level data and historical pollutant concentration data at the upstream and downstream sections of the tidal river; specifically including:

[0037] S11. Define the pollutant concentration variation control factor and tidal level factor as important influencing factors affecting pollutant concentration. Using pollutant concentration as the target factor, establish a mapping relationship between pollutant concentration at tidal river sections and the pollutant concentration variation control factor and tidal level factor:

[0038] C = f(θ,H);

[0039] In the formula: C is the pollutant concentration; H is the upstream or downstream tidal level factor; θ is the pollutant concentration variation control factor;

[0040] In addition to being affected by tides, the concentration of pollutants in tidal river sections is also affected by the amount of sewage discharged in the region. When the total amount of sewage discharged increases sharply, the concentration of pollutants will also increase sharply. Therefore, the introduction of a pollutant concentration variation control factor into the mapping relationship can comprehensively consider the impact of external factors on the pollutant concentration changes during the study period under future scenarios, and ensure the accuracy of the pollutant concentration change equation established subsequently.

[0041] S12. Through preliminary water quality testing at the tidal river section and tidal gauges at the upstream and downstream of the section, historical tidal data and historical pollutant concentration data at the upstream and downstream of the tidal river section are obtained. Based on the mapping relationship, a pollutant concentration change equation is constructed using various mathematical function fitting methods. The pollutant concentration change equation is the optimal equation for pollutant concentration and upstream or downstream tidal factor.

[0042] S2. Based on the energy equation of steady non-uniform flow, the water flux equation at the cross section during the study period is established. The specific process is as follows:

[0043] S21. Obtain the topographic elevation data of the upstream and downstream sections of the cross-section during the study period (a future period). Based on the constant non-uniform flow energy equation, establish the cross-sectional flow equation at any time under both high and low tide conditions:

[0044] The energy equation for a steady non-uniform flow is as follows:

[0045]

[0046] Δh w =Δh f +Δh j (2)

[0047]

[0048]

[0049]

[0050]

[0051]

[0052] In the formula: Z1 and Z2 are the tidal levels upstream and downstream of the cross-section, respectively, in meters (m); α1 and α2 are the velocity non-uniformity coefficients upstream and downstream of the cross-section, respectively; v1 and v2 are the velocity upstream and downstream of the cross-section, respectively, in meters per second (m / s); g is the acceleration due to gravity, in meters per second (m / s²). 2 ;Δh w Δh f and Δh j These represent the total head loss, friction head loss, and local head loss, respectively, in meters (m); Q is the water flow rate at the cross-section, in meters (m³). 3 / s; K1 and K2 are the upstream and downstream flow moduli at the cross-section, respectively; C h1 C h2R1 and R2 are the Chezy coefficients upstream and downstream of the cross-section, respectively; R1 and R2 are the hydraulic radii upstream and downstream of the cross-section, respectively, in meters; Δs is the length of the river segment between upstream and downstream of the cross-section, in meters; ξ is the local head loss coefficient; A1 and A2 are the flow areas upstream and downstream of the cross-section, respectively, in meters. 2 ;

[0053] Since there is a back-and-forth flow of water in the tidal section, it is assumed that the water flow rate Q is positive during ebb tide and negative during flood tide. According to formula (1), the river is divided into ebb and flow intervals as follows:

[0054] high tide:

[0055] ebb:

[0056] Furthermore, formulas 1-1 and 1-2 are combined and simplified to:

[0057]

[0058] For any time i = 1, 2, ..., 24, the cross-sectional flow rate Q at the corresponding time can be calculated. i :

[0059]

[0060]

[0061] S22. Based on the cross-sectional flow equation, establish the water flux equation at the cross-section during the study period:

[0062] V i =Q i Δt; (1-6)

[0063] S3. Assuming that the pollutants in the tidal river section are completely mixed with the water, based on the water flux equation and pollutant concentration change equation at the cross-section, the pollutant flux equation at the river cross-section during the study period is established as follows:

[0064]

[0065] In the formula: C i Let be the pollutant concentration at time i.

[0066] Based on the pollutant flux equation, the hourly flux of pollutants at the river cross-section during the study period was calculated. The calculation process is as follows:

[0067] Based on the obtained tidal data and daily average pollutant concentration data for the proposed study period, the hourly variation data of pollutant concentration can be calculated based on the pollutant concentration variation equation. Based on the upstream and downstream topographic elevation data and tidal data of the cross section for the proposed study period, the hourly water flux at the cross section can be calculated based on the water flux equation. Then, based on the pollutant flux equation, the hourly flux of pollutants at the cross section for the proposed study period can be calculated.

[0068] This invention addresses the practical limitations of continuous monitoring of flow at the study section, the long time required for chemical analysis of pollutant concentrations, and the lack of timeliness in model inversion flux. It fully considers the correlation between pollutant concentration diffusion and the reciprocating flow of water in tidal river sections. By inputting tidal level and limited concentration data into the pollutant concentration equation, it can calculate the hourly variation of pollutant concentration, fully reflecting the concentration oscillations caused by the reciprocating flow. Based on the hourly variation data of pollutant concentration, and according to the pollutant flux equation, the pollutant flux at the section can be calculated hourly. Finally, the total daily pollutant flux at the section during the study period can be statistically analyzed, providing scientific support for urban managers' water security decisions.

[0069] Example 1:

[0070] The important water quality control section of a tidal river is used as the application object of the pollutant flux analysis method of this invention. A permanent water quality monitoring station is set up at the water quality control section, which can provide pollutant concentration values ​​at four times within 24 hours during the study period. Permanent tide gauges are set up near the upstream and downstream of the water quality control section, which can provide the hourly tidal change process of the river section during the study period.

[0071] (1) Collect pollutants (COD) at the water quality control section of the tidal river. cr Historical data on total nitrogen concentration, and historical tidal data at locations 500m upstream and downstream. All data are for a duration of 25 hours, as shown in Table 1.

[0072] Table 1 Historical data on tide level and concentration

[0073]

[0074]

[0075] (2) Based on the COD of the water quality control sections in Table 1 cr Historical data on total nitrogen concentration and historical tidal data at 500m upstream and downstream of the water quality control section were used to establish a pollutant concentration change equation based on a mapping relationship. After fitting and optimization, COD... cr The concentration change equation is expressed using a power function, while the nitrogen concentration change equation is expressed using a cubic polynomial function. Furthermore, the downstream tidal level shows a better fit with the pollutant concentration, as shown in the fitting results. Figure 2, Figure 3 As shown, the concentration change process at this river cross-section is most significantly affected by the downstream tide level. Therefore, the equation for the pollutant concentration change at this river cross-section is an equation showing the change in pollutant concentration with the downstream tide level, as follows:

[0076]

[0077]

[0078] x = [arctan(H)] 3 -0.5;

[0079] In the above formula: H represents the downstream tidal level factor;

[0080] (3) COD data were collected at four different times within the 24-hour study period. cr The mean concentrations of pollutants and nitrogen pollutants (10.63 mg / L and 7.1 mg / L) are θ1 and θ2, respectively. Based on the pollutant concentration variation equation and the downstream tidal data of this river section during the study period, the COD for the study period was calculated. cr The hourly variation data of nitrogen pollutant concentrations are shown in Table 2.

[0081] Table 2 Hourly Calculation Results of CODcr and Nitrogen Pollutant Concentrations

[0082]

[0083]

[0084] (4) Obtain the topographic elevation data of the upstream and downstream sections during the study period at the cross-section, and calculate the water flux at the cross-section hourly according to formulas (1-4)-(1-6). The calculation results are shown in Table 3.

[0085] Table 3 Calculation results of water flux at cross-sections

[0086]

[0087] (5) Calculate the COD at the cross-section hourly according to formula (1-7). cr Pollutant flux and nitrogen pollutant flux can ultimately yield COD. cr The total flux of pollutants and nitrogen pollutants through the cross section in a day is shown in Table 4. City managers can make corresponding decisions on water security based on the total flux data.

[0088] Table 4 Calculation results of pollutant flux at control sections

[0089]

[0090]

[0091] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for analyzing the flux of pollutants in a tidal river section, characterized in that, Includes the following steps: S1. Based on historical tidal level data and historical pollutant concentration data at the upstream and downstream sections of the tidal river, establish a pollutant concentration variation equation, which specifically includes: S11. Define the pollutant concentration range control factor and the tidal level factor as important influencing factors affecting pollutant concentration. Using pollutant concentration as the target factor, establish a mapping relationship between pollutant concentration at the tidal river section and the pollutant concentration range control factor and the tidal level factor. S12. Obtain historical tidal data and pollutant concentration data of the upstream and downstream sections of the tidal river section, and establish a pollutant concentration change equation based on the mapping relationship. S2. Based on the constant non-uniform flow energy equation, the water flux equation at the river cross-section during the study period is established, which specifically includes: S21. Obtain the topographic elevation data of the upstream and downstream sections of the river cross-section during the study period. Based on the constant non-uniform flow energy equation, establish the flow equations at any time of the river cross-section under both high and low tide conditions. The cross-sectional flow equations are as follows: ； ； In the formula: i =1, 2, ..., 24; For high tide conditions, This refers to the low tide condition; Z 1. Z 2 represents the tidal levels upstream and downstream of the cross-section, in meters (m). , These are the velocity non-uniformity coefficients at the upstream and downstream of the cross-section, respectively. g The acceleration due to gravity is expressed in m / s². K 1. K 2 represents the upstream and downstream flow moduli at the cross-section, respectively; Δ s The length of the river section between the upstream and downstream sections at the cross-section is in meters (m). This is the local head loss coefficient; A 1. A 2. The upstream and downstream flow areas at the respective cross-sections, in m² 2 ; S22. Based on the cross-sectional flow equation, establish the water flux equation at the cross-section during the study period: ； S3. Based on the water flux equation and pollutant concentration change equation at the cross-section, the pollutant flux equation at the river cross-section during the study period is established as follows: ； In the formula: C i For the first i The pollutant concentration at each time point; Based on the pollutant flux equation, the hourly flux of pollutants at the cross section during the proposed study period is calculated; the proposed study period is a future time period.

2. The method for analyzing pollutant fluxes in tidal river sections as described in claim 1, characterized in that, The mapping relationship is as follows: ； In the formula: C The concentration of pollutants; H For upstream or downstream tidal level factors; θ This is a pollutant concentration variation control factor.

3. The method for analyzing pollutant fluxes in tidal river sections as described in claim 1, characterized in that, In step S12, a pollutant concentration change equation is established using various mathematical function fitting methods.

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