A method for quickly determining land surface source into river "observation value"

Abstract

The application discloses a method for quickly determining land surface source river "observation value" based on a river water quality model, coupling comprehensive weight coefficient alpha and through reverse iteration calculation. Compared with the prior art, the method makes up for the deficiency of the scarcity of land surface source river quantity data, can quickly and effectively calculate the land surface source river "observation value" based on a small amount of water quality monitoring section data, breaks through the bottleneck of land surface source pollution monitoring, and solves the problem of insufficient measured data in large-scale, large-space surface source pollution model parameter calibration. The application is not limited by the geographical position of the river and sampling time, can quickly calculate the land surface source river "observation value", improve the simulation accuracy of the surface source pollution model, and improve the efficiency of water environment pollution control.

Description

Technical Field

[0001] This invention relates to a method for rapidly determining the "observation value" of land surface sources entering a river. Background Technology

[0002] With socio-economic development, non-point source pollution has become one of the most challenging pollution control problems globally. Utilizing non-point source pollution models to describe the migration and transformation of non-point source pollutants and analyze the temporal and spatial distribution characteristics of non-point source pollution is of great significance for effectively controlling water pollution. The "observed values" of land-based non-point source pollution entering rivers are the foundation for parameter calibration and result verification of non-point source pollution models; their quantity and observation accuracy determine the simulation accuracy of the models. Due to the randomness and dispersion of non-point source pollution, the amount entering rivers is difficult to monitor, resulting in scarce "observed values" of non-point source pollution entering rivers, severely impacting the efficiency of water pollution control. Previous studies have primarily relied on tracking heavy rainfall events and sampling in safe and representative catchment areas to obtain "observed values" of land-based non-point source pollution entering rivers. The high time and economic costs of sampling often lead to a scarcity of data on non-point source pollution entering rivers. Therefore, there is an urgent need to find a method to quickly determine the "observed values" of land-based non-point source pollution entering rivers to improve the simulation accuracy of non-point source pollution models, enhance the efficiency of water pollution control, and serve the national strategy of ecological civilization construction.

[0003] Rivers are the primary carriers of pollutants, and the migration and transformation of pollutants in water can be simulated using water quality models. Therefore, this invention, combined with river water quality models, proposes a method for rapidly determining the "observed values" of land-based non-point source pollution entering rivers. This method compensates for the scarcity of data on land-based non-point source pollution entering rivers, allowing for rapid calculation of these "observed values" based on limited water quality monitoring data. This overcomes the bottleneck of difficult monitoring of land-based non-point source pollution entering rivers and solves the problem of insufficient measured data for timely parameter scaling in non-point source pollution models. Summary of the Invention

[0004] The purpose of this invention is to solve the problem that the randomness and dispersion of non-point source pollution entering rivers make it difficult to obtain measured data, and to provide a method for quickly determining the "observed value" of land-based non-point source pollution entering rivers.

[0005] The present invention achieves the above objectives through the following technical solutions.

[0006] This invention includes the following steps:

[0007] Step 1: Select the river section for monitoring and calibration, and calibrate the degradation coefficient.

[0008] A section of the river within the study area with no tributaries flowing into it, no point sources flowing into it, and with smooth and straight water flow was selected as the monitoring and calibration section. During the non-rainfall period, on-site monitoring was conducted at the upstream and downstream sections of the river section. Based on the monitored water quality data, the degradation coefficient ε of the target non-point source pollution index in the water quality model was calibrated. The target non-point source pollution index is any one of total nitrogen, total phosphorus, ammonia nitrogen, or COD.

[0009] Step 2: Calculate the contribution of all non-point source inflows to the concentration at downstream water quality monitoring sections.

[0010] As shown in Figure 1, the main sources of pollutants at the downstream water quality monitoring section are upstream inflow, point source pollution entering the river, and non-point source pollution entering the river. Therefore, we calculate the concentration V of pollution indicators from the upstream water quality monitoring section and point source inflows at the downstream water quality monitoring section using Formula 1. b Then, the contribution value W of all non-point source inflows to the concentration of downstream water quality monitoring sections is obtained using Formula 2. S .

[0011] In Figure 1, V af V represents the concentration of pollution indicators observed at the upstream water quality monitoring section, in mg / L. ad V represents the concentration of pollution indicators observed at downstream water quality monitoring sections, in mg / L. S, k S represents the concentration of non-point source pollution entering rivers from land, in mg / L; k is the number of the non-point source inlet, ranging from 1 to M, where M is the total number of non-point source inlets; k For land-based surface water sources flowing into rivers; d S , k V is the distance (m) from the k-th land surface source inflow point to the downstream water quality monitoring section; P, l The concentration of pollutants entering the river from point source inlets is expressed in mg / L, where l is the inlet number from 1 to N, and N is the total number of point source inlets. l Numbering the point source estuary; d P, l Let be the distance from the river mouth of the l-th point source to the downstream water quality monitoring section, in meters.

[0012] Formula 1:

[0013]

[0014] Formula 2:

[0015]

[0016] In the formula, V P, l The concentration of point source pollution indicators entering the river is expressed in mg / L, where l is the point source inlet number from 1 to N, and N is the total number of point source inlets. P, l f is the distance from the l-th point source inlet to the downstream water quality monitoring section, in meters.P, l Q represents the average river velocity from the l-th point source inlet to the downstream water quality monitoring section, in m / s; P, l Let L be the inflow volume into the river during the calculation period for the l-th point source estuary; V be the inflow volume. af Q represents the concentration of non-point source pollution indicators observed at the upstream water quality monitoring section, in mg / L. af The inflow volume at the upstream water quality monitoring section during the calculation period is L; α is an adjustment coefficient; A k Let m be the area of ​​the catchment area controlled by the k-th non-point source river inlet. 2 L k V is the distance (m) from the farthest point within the control area of ​​the k-th surface source inlet to the inlet. ad The concentration of pollutants observed at downstream water quality monitoring sections is measured in mg / L; V b The concentration (mg / L) of pollutants from upstream water quality monitoring sections and point source inflows to downstream water quality monitoring sections; W S The contribution of all non-point source inflows to the downstream water quality monitoring section concentration is expressed in mg / L. The water volume of each point source and non-point source inflow in the formula is calculated using a stormwater model.

[0017] Step 3: Iteratively calculate the "observed values" of land surface water sources flowing into rivers.

[0018] (1) Based on each surface source inlet S k Distance d to the downstream water quality monitoring section S, k S k Control the farthest point within the catchment area to S k Distance L k and S k Control area A k S was determined comprehensively. k Weight β of the contribution to the concentration at downstream water quality monitoring sections k Based on this, the contribution values ​​W of all non-point source inflows to the downstream water quality monitoring section concentration calculated in step two are used. S Distribute to S according to weight k V0 serves as the initial value for the concentration of pollution indicators at various land-based non-point source river estuaries. S,k ;

[0019] (2) Based on water quality models, degradation coefficients of pollution indicators ε, and d S, k The simulated pollution index concentration V at the downstream water quality control section is calculated according to Formula 5. sd ;

[0020] Formula 3:

[0021]

[0022] Formula 4:

[0023]

[0024] Formula 5:

[0025]

[0026] In the formula, V sd Simulated pollution index concentration at downstream water quality monitoring section, mg / L; V S, k ε represents the concentration of non-point source pollution entering the river, in mg / L; k is the number of the non-point source inlet, from 1 to M, where M is the total number of non-point source inlets, in mg / L; ε is the river degradation coefficient; d S, k f is the distance from the k-th non-point source inflow point to the downstream water quality monitoring section, in meters. S, k Let Q be the average river velocity from the k-th non-point source inflow point to the downstream water quality monitoring section, in m / s; S, k Calculate the inflow volume (L) and V of the k-th surface source inflow point within the specified time period. P, l The concentration of point source pollution entering the river is expressed in mg / L, where l is the point source inlet number from 1 to N, and N is the total number of point source inlets. P, l f is the distance from the l-th point source inlet to the downstream water quality monitoring section, in meters. P, l Q represents the average river velocity from the point source inflow to the downstream water quality monitoring section, in m / s; P, l Let L be the inflow volume into the river during the calculation period for the l-th point source estuary; V be the inflow volume. af Q represents the concentration of non-point source pollution indicators observed at the upstream water quality monitoring section, in mg / L. af The inflow rate at the upstream water quality monitoring section during the calculation period is L; α is an adjustment coefficient; β k W represents the weight of the contribution of the k-th non-point source inflow to the concentration at the downstream water quality monitoring section; S A represents the contribution of all non-point source inflows to the concentration at downstream water quality monitoring sections, in mg / L; k Let m be the area of ​​the catchment area controlled by the k-th non-point source river inlet. 2 L k is the distance from the farthest point within the control range of the k-th surface source inlet to the inlet.

[0027] (3) If V sd With V ad If the results do not match, adjust α in (1) and repeat step (2) until the calculated V is obtained. sd With V ad The results match, and at this point, the concentration of non-point source pollution indicators entering the river at a single non-point source inlet has been determined, i.e., V at this time. S, k By multiplying this concentration by the water volume calculated based on the stormwater model, the "observed value" of the inflow load from each land surface source into the river can be obtained.

[0028] In summary, based on the above steps, we can quickly determine the "observed values" of land-based non-point source pollution entering rivers, which are difficult to monitor using conventional methods and exhibit strong randomness and dispersion, using a small amount of water quality monitoring data. This method comprehensively considers potential factors affecting the spatiotemporal variability of non-point source pollution, such as catchment area, confluence path, and river migration and degradation, and can accurately reflect the true value of land-based non-point source pollution entering rivers, thus replacing the observed values.

[0029] The beneficial effects of this invention are as follows:

[0030] This invention is a method for rapidly determining the "observed value" of land-based non-point source pollution entering rivers through reverse iterative calculation based on river water quality models and coupled comprehensive weight coefficients. Compared with existing technologies, this method overcomes the scarcity of land-based non-point source pollution data, and can quickly extrapolate the "observed value" of land-based non-point source pollution entering rivers based on a small amount of water quality monitoring section data. It breaks through the bottleneck of difficult monitoring of land-based non-point source pollution entering rivers and solves the problem of insufficient measured data for large-scale, large-space non-point source pollution model parameter rates. Detailed Implementation

[0031] The present invention will be further described below:

[0032] This invention takes the Nansha River basin in Beijing as an example to calculate the "observed values" at various land-based non-point source pollution inflow points between the upstream Houshajian water quality monitoring section and the downstream Yuhe rubber dam water quality monitoring section. The specific implementation steps are explained below using the non-point source pollution from the rainstorm on July 24, 2018, as an example:

[0033] Step 1: Select the river section for monitoring and calibration, and calibrate the degradation coefficient.

[0034] A typical river section within the Nansha River basin in Beijing, characterized by no tributaries, no point source inflows, smooth water flow, and a straight channel—the straight section between the Houshajian water quality monitoring section and the Yuhe Rubber Dam water quality monitoring section—was selected as the calibration section. During the non-rainfall period, non-point source pollution indicators at the upstream and downstream sections of this river section were monitored in the field. The degradation coefficients of total nitrogen, total phosphorus, ammonia nitrogen, and COD in the water quality model were calibrated, yielding degradation coefficients of 0.11, 0.14, 0.28, and 0.15, respectively. These degradation coefficients were then applied to the river section between the Houshajian and Yuhe Rubber Dam water quality monitoring sections in the Nansha River basin. (See Appendix 2.)

[0035] Step 2: Calculate the contribution of all non-point source inflows to the concentration at downstream water quality monitoring sections.

[0036] As shown in Figures 1 and 2, rainfall on July 24, 2018, resulted in 11 non-point source pollution inflows into the river. Therefore, the pollutants at the downstream water quality monitoring section originated from the upstream Houshajian inflow, 9 point source pollution inflows, and 11 non-point source pollution inflows. Specifically, at the upstream Houshajian water quality monitoring section at 11:10 on July 24, 2018, the observed concentrations of total nitrogen, total phosphorus, ammonia nitrogen, and COD were 1.58, 0.02, 0.30, and 7.10 mg / L, respectively.

[0037] In Figure 1, V af V represents the concentration of pollution indicators observed at the upstream water quality monitoring section, in mg / L. ad V represents the concentration of pollution indicators observed at downstream water quality monitoring sections, in mg / L. S, k The concentration of non-point source pollution entering rivers from land (k is the number of the non-point source inlet, k from 1 to M, where M is the total number of non-point source inlets), mg / L; S k Numbering for land surface source river estuaries; d S, k V is the distance (m) from the k-th land surface source inflow point to the downstream water quality monitoring section; P, l The concentration of pollutants entering the river from point source inlets is expressed in mg / L, where l is the inlet number from 1 to N, and N is the total number of point source inlets. l The point source flows into the river estuary; d P, l Let be the distance from the river mouth of the l-th point source to the downstream water quality monitoring section, in meters.

[0038] Therefore, we use Formula 1 to calculate the concentration V of the pollution index at the upstream water quality monitoring section and the point source inlet to the downstream Yuhe rubber dam water quality monitoring section. b Then, using Formula 2, we obtain the contribution values ​​W of all non-point source inflows to the concentrations of four pollution indicators—total nitrogen, total phosphorus, ammonia nitrogen, and COD—at downstream water quality monitoring sections. S The concentrations were 4.60, 0.27, 2.24, and 11.22 mg / L, respectively.

[0039] Formula 1:

[0040]

[0041] Formula 2:

[0042]

[0043] In the formula, V P, l The concentration of point source pollution indicators entering the river is expressed in mg / L, where l is the point source inlet number from 1 to N, and N is the total number of point source inlets. P, l f is the distance from the l-th point source inlet to the downstream water quality monitoring section, in meters. P, lQ represents the average river velocity from the l-th point source inlet to the downstream water quality monitoring section, in m / s; P, l Let L be the inflow volume into the river during the calculation period for the l-th point source estuary; V be the inflow volume. af Q represents the concentration of non-point source pollution indicators observed at the upstream water quality monitoring section, in mg / L. af The inflow volume at the upstream water quality monitoring section during the calculation period is L; α is an adjustment coefficient; A k Let m be the area of ​​the catchment area controlled by the k-th non-point source river inlet. 2 L k V is the distance (m) from the farthest point within the control area of ​​the k-th surface source inlet to the inlet. ad The concentration of pollutants observed at downstream water quality monitoring sections is measured in mg / L; V b W represents the concentration of pollutants from upstream water quality monitoring sections and point source pollutants at downstream water quality monitoring sections, expressed in mg / L. S The contribution of all non-point source inflows to the downstream water quality monitoring section concentration is expressed in mg / L. The water volume of each point source and non-point source inflow in the formula is calculated using a stormwater model.

[0044] Step 3: Iteratively calculate the "observed values" of land surface water sources flowing into rivers.

[0045] (1) Based on each surface source inlet S k Distance d to the downstream water quality monitoring section S, k S k Control the farthest point within the catchment area to S k Distance L k and S k Control area to determine S k Weight β of the contribution to the concentration at downstream water quality monitoring sections k Based on this, the contribution values ​​W of all non-point source inflows to the downstream water quality monitoring section concentration calculated in step two are used. S Distribute to S according to weight k V0 serves as the initial value for the concentration of pollution indicators at various land-based non-point source river estuaries. S,k ;

[0046] (2) Based on water quality models, degradation coefficients of pollution indicators ε, and d S, k The simulated pollution index concentration V at the downstream water quality control section is calculated according to Formula 5. sd ;

[0047] Formula 3:

[0048]

[0049] Formula 4:

[0050]

[0051] Formula 5:

[0052]

[0053] In the formula, V sd Simulated pollution index concentration at downstream water quality monitoring section, mg / L; V S, k ε represents the concentration of non-point source pollution entering the river, in mg / L; k is the number of the non-point source inlet, from 1 to M, where M is the total number of non-point source inlets; ε is the river degradation coefficient; d S, k f is the distance from the k-th non-point source inflow point to the downstream water quality monitoring section, in meters. S, k Let Q be the average river velocity from the k-th non-point source inflow point to the downstream water quality monitoring section, in m / s; S, k Calculate the inflow volume (L) and V of the k-th surface source inflow point within the specified time period. P, l The concentration of point source pollution entering the river is expressed in mg / L, where l is the point source inlet number from 1 to N, and N is the total number of point source inlets. P, l f is the distance from the l-th point source inlet to the downstream water quality monitoring section, in meters. P, l Q represents the average river velocity from the point source inflow to the downstream water quality monitoring section, in m / s; P, l Let L be the inflow volume into the river during the calculation period for the l-th point source estuary; V be the inflow volume. af Q represents the concentration of non-point source pollution indicators observed at the upstream water quality monitoring section, in mg / L. af The inflow rate at the upstream water quality monitoring section during the calculation period is L; α is an adjustment coefficient; β k W represents the weight of the contribution of the k-th non-point source inflow to the concentration at the downstream water quality monitoring section; S A represents the contribution of all non-point source inflows to the concentration at downstream water quality monitoring sections, in mg / L; k Let m be the area of ​​the catchment area controlled by the k-th non-point source river inlet. 2 L k is the distance from the farthest point within the control range of the k-th surface source inlet to the inlet.

[0054] (3) If V sd With V ad If the results do not match, adjust the adjustment coefficient α in (1) and repeat step (2). Repeat this iterative process until the calculated V is obtained. sd With V ad The results were consistent, with observed concentrations of total nitrogen, total phosphorus, ammonia nitrogen, and COD of 5.82, 0.84, 5.30, and 36.90 mg / L, respectively. At this point, the concentrations of non-point source pollution indicators entering the river at a single non-point source inlet have been determined. Multiplying these concentrations by the water volume calculated based on the stormwater model allows for the estimation of the "observed values" of the inflow load from each land-based non-point source into the river (as shown in the table below).

[0055] Observed values ​​of land-based non-source heat load into rivers (unit: kg)

[0056]

[0057] In summary, based on the above steps, the "observed values" of land-based non-point source pollution loads in the Nansha River basin of Beijing can be quickly determined using water quality monitoring data from the Houshajian station in the upper reaches and the Yuhe Rubber Dam station in the lower reaches. This method comprehensively considers potential factors affecting the spatiotemporal variation of non-point source pollution, such as catchment area, confluence path, and river migration and degradation, and can accurately reflect the true value of land-based non-point source pollution inflows, thus replacing the observed values. Attached Figure Description

[0058] Figure 1 is a schematic diagram of the equation.

[0059] Figure 2 is a schematic diagram of the river section.

[0060] Figure 1 shows the equation. In the diagram, V af V represents the concentration of pollution indicators observed at the upstream water quality monitoring section, in mg / L. ad V represents the concentration of pollution indicators observed at downstream water quality monitoring sections, in mg / L. S, k S represents the concentration of non-point source pollution entering rivers from land, in mg / L; k is the number of the non-point source inlet, ranging from 1 to M, where M is the total number of non-point source inlets; k For land-based surface water sources flowing into rivers; d S , k V is the distance (m) from the k-th land surface source inflow point to the downstream water quality monitoring section; P, l The concentration of pollutants entering the river from point source inlets is expressed in mg / L, where l is the inlet number from 1 to N, and N is the total number of point source inlets. l Numbering the point source estuary; d P, l Let be the distance from the river mouth of the l-th point source to the downstream water quality monitoring section, in meters.

[0061] Figure 2 shows a schematic diagram of the river section. The typical river section in the Nansha River Basin of Beijing, which has no tributaries or point sources flowing into it, and has a smooth and straight channel, is selected as the monitoring calibration section. The section is the straight section between the Houshajian water quality monitoring section and the Yuhe Rubber Dam water quality monitoring section. There are 11 non-point source inflows, 9 point source discharge outlets, 2 monitoring calibration sections and 1 water quality monitoring section.

[0062] This invention makes full use of limited monitoring section observation data, and based on a small amount of water quality monitoring section data, it can quickly and effectively calculate the "observed values" of land non-point source pollution entering rivers between various monitoring sections. This overcomes the bottleneck of difficult monitoring of land non-point source pollution entering rivers and solves the problem of insufficient measured data for large-scale, large-space non-point source pollution model parameter rate calculations. The application scope of this invention is not limited by the river's geographical location or sampling time, and it can quickly calculate the "observed values" of land non-point source pollution entering rivers.

[0063] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for rapidly determining the "observed value" of land surface source inflow into rivers, characterized in that... This method compensates for the scarcity of data on land-based non-point source pollution entering rivers. Based on a limited amount of water quality monitoring data, it rapidly extrapolates the "observed values" of land-based non-point source pollution entering rivers between various monitoring sections. The specific steps include: Step 1: Select the river section for monitoring and calibration, and calibrate the degradation coefficient. The river section within the study area with no tributaries flowing into it, no point sources flowing into it, and smooth and straight water flow was selected as the monitoring and calibration section. During the non-rainfall period, the upstream and downstream sections of the river section were monitored in the field. The degradation coefficient ε of the target non-point source pollution index in the water quality model was calibrated based on the monitored water quality data. The target non-point source pollution index is any one of total nitrogen, total phosphorus, ammonia nitrogen or COD. Step 2: Calculate the contribution of all non-point source inflows to the concentration at downstream water quality monitoring sections. The main sources of pollutants at the downstream water quality monitoring section are upstream water inflow, point source pollution entering the river, and non-point source pollution entering the river. Therefore, we use Formula 1 to calculate the concentration V of pollution indicators from the upstream water quality monitoring section and point source inflows at the downstream water quality monitoring section when they converge. b Then, the contribution value W of all non-point source inflows to the concentration of downstream water quality monitoring sections is obtained using Formula 2. S ; Formula 1: Formula 2: In the formula, V P, l The concentration of point source pollution indicators entering the river is given by d, where l is the point source inlet number from 1 to N, and N is the total number of point source inlets. P, l f is the distance from the l-th point source inlet to the downstream water quality monitoring section, in meters. P, l Q represents the average river velocity from the l-th point source inlet to the downstream water quality monitoring section, in m / s; P, l Let L be the inflow volume into the river during the calculation period for the l-th point source estuary; V be the inflow volume. af Q represents the concentration of non-point source pollution indicators observed at the upstream water quality monitoring section, in mg / L. af The inflow volume at the upstream water quality monitoring section during the calculation period is L; α is an adjustment coefficient; A k Let m be the area of ​​the catchment area controlled by the k-th non-point source river inlet. 2 L k V is the distance (m) from the farthest point within the control area of ​​the k-th surface source inlet to the inlet. ad The concentration of pollutants observed at downstream water quality monitoring sections is measured in mg / L; V b The concentration (mg / L) of pollutants from upstream water quality monitoring sections and point source inflows to downstream water quality monitoring sections; W S The contribution of all non-point source inlets to the concentration at downstream water quality monitoring sections is expressed in mg / L; the water volume of each point source and non-point source inlet in the formula is calculated using a stormwater model. Step 3: Iteratively calculate the "observed values" of land surface water sources flowing into the river. (1) Based on each surface source inlet S k Distance d to the downstream water quality monitoring section S, k S k Control the farthest point within the catchment area to S k Distance L k and S k Control area A k S was determined comprehensively. k Weight β of the contribution to the concentration at downstream water quality monitoring sections k Based on this, the contribution values ​​W of all non-point source inflows to the downstream water quality monitoring section concentration calculated in step two are used. S Distribute to S according to weight k V0 serves as the initial value for the concentration of pollution indicators at various land-based non-point source river estuaries. S,k ; (2) Based on water quality models, degradation coefficients of pollution indicators ε, and d S, k The simulated pollution index concentration V at the downstream water quality control section is calculated according to Formula 5. sd ; Formula 3: Formula 4: Formula 5: In the formula, V sd Simulated pollution index concentration at downstream water quality monitoring section, mg / L; V S, k The concentration of non-point source pollution entering rivers is denoted as mg / L, where k is the number of the non-point source inlet, ranging from 1 to M, and M is the total number of non-point source inlets. ε is the river degradation coefficient. S, k f is the distance from the k-th non-point source inflow point to the downstream water quality monitoring section, in meters. S, k Let Q be the average river velocity from the k-th non-point source inflow point to the downstream water quality monitoring section, in m / s; S, k Calculate the inflow volume (L) and V of the k-th surface source inflow point within the specified time period. P, l The concentration of point source pollution entering the river is expressed in mg / L, where l is the point source inlet number from 1 to N, and N is the total number of point source inlets. P, l f is the distance from the l-th point source inlet to the downstream water quality monitoring section, in meters. P, l Q represents the average river velocity from the point source inflow to the downstream water quality monitoring section, in m / s; P, l Let L be the inflow volume into the river during the calculation period for the l-th point source estuary; V be the inflow volume. af Q represents the concentration of non-point source pollution indicators observed at the upstream water quality monitoring section, in mg / L. af The inflow rate at the upstream water quality monitoring section during the calculation period is L; α is an adjustment coefficient; β k W represents the weight of the contribution of the k-th non-point source inflow to the concentration at the downstream water quality monitoring section; S A represents the contribution of all non-point source inflows to the concentration at downstream water quality monitoring sections, in mg / L; k Let m be the area of ​​the catchment area controlled by the k-th non-point source river inlet. 2 L k Let be the distance from the farthest point within the control range of the k-th surface source inlet to the inlet; (3) If V sd With V ad If the results do not match, adjust α in (1) and repeat step (2) until the calculated V is obtained. sd With V ad The results match, and at this point, the concentration of non-point source pollution indicators entering the river at a single non-point source inlet has been determined, i.e., V at this time. S, k By multiplying this concentration by the water volume calculated based on the stormwater model, the "observed value" of the inflow load of each land surface source into the river can be obtained. In summary, based on the above steps, we can quickly determine the "observed values" of land-based non-point source pollution entering rivers, which are difficult to monitor using conventional methods and are highly random and dispersed, using a small amount of water quality monitoring section data. This method comprehensively considers three potential factors affecting the spatiotemporal variation of non-point source pollution: catchment area, confluence path, and river migration and degradation. It can accurately reflect the true value of land-based non-point source pollution entering rivers and can be used to replace the observed values.

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