A research method for the flow and sewage diversion ratios of bifurcated rivers and their evolution laws

Abstract

The present invention discloses a method for studying the flow diversion ratio and the sewage diversion ratio of a bifurcated river and their evolution law, including the following steps: investigation of hydrological information of the basin where the bifurcated river is located; calculation of the river flow in the basin under different guarantee rates; construction of a mathematical model of water environment; analysis of the law of the flow diversion ratio of the bifurcated river; analysis of the law of the sewage diversion ratio of the bifurcated river; analysis of the evolution law of the flow diversion ratio and the sewage diversion ratio of the bifurcated river. In view of the current situation that there is insufficient research on the sewage diversion ratio, flow diversion ratio and sewage diversion ratio evolution law of the bifurcated river, the present invention proposes a method for analyzing the flow diversion ratio and the sewage diversion ratio of the bifurcated river and their evolution law, which provides a scientific basis for the formulation of environmental management policies such as flood control and drainage, ecological water replenishment, total pollutant control, water environment protection, and water ecological restoration.

Description

Technical Field

[0001] The invention relates to the fields of flood control and drainage, total pollutant control, water environment protection, water ecological restoration, and in particular to a research method for studying the diversion ratio and pollution diversion ratio of a branched river channel and the evolution relationship between the two. Background Art

[0002] A bifurcated river is a type of plain river landform. The riverbed is bifurcated due to the mid-shoal and sandbar, just like the main trunk and branches of a tree. The main trunk is the mainstream, and the two branches are bifurcated flows. The diversion ratio refers to the percentage of the flow of a branch river to the flow of the main river. The pollution diversion ratio refers to the percentage of a certain pollutant flux in the branch river to the pollutant flux in the main stream.

[0003] The study of diversion ratio and pollution diversion ratio of bifurcated rivers and their evolution laws is an important component and basis for studying the migration and transformation of pollutants in plain river networks and the changes in microbial communities and functions in bifurcated rivers.

[0004] Previous researchers have studied the diversion ratio of bifurcated rivers, but there are fewer studies on the sewage diversion ratio of bifurcated rivers, and there is no research on the evolution law of the diversion ratio and sewage diversion ratio.

[0005] The entire river basin is a whole. We cannot just study the branched river channel in the basin. Instead, we need to build a model of the entire river basin to study the diversion ratio and pollution separation ratio of the branched river channel and its evolution law.

[0006] Studying the diversion ratio and pollution separation ratio of branched rivers in a river basin and their evolution laws can provide a scientific basis for controlling the total amount of water pollutants. Since different water bodies have different functional requirements, excessive pollutants received by water bodies will cause a series of consequences such as loss of water body functions and damage to water ecology. Therefore, we must rationally plan the emission location and emission amount of point source and non-point source pollutants in the river basin to achieve the goal of harmonious unity of society, economy and ecology. Summary of the invention

[0007] In view of the insufficient research on the sewage diversion ratio and the evolution law of the diversion ratio in bifurcated estuaries, the present invention provides a method for analyzing the diversion ratio and sewage diversion ratio of bifurcated rivers in a basin, and analyzing the evolution law of the diversion ratio and sewage diversion ratio, so as to provide theoretical and technical support for the total amount of pollutants in the basin, water resources protection, and water ecological restoration.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0009] A method for studying the flow diversion ratio and the sewage diversion ratio of a bifurcated river channel and their evolution law includes the following steps.

[0010] Step 1: Survey of hydrological information of the river basin where the bifurcated river is located, including the following two aspects of information: 1. River network distribution, river section conditions and pollution sources; 2. Actual water level information of water level stations, actual flow information of flow stations and actual daily rainfall information of rainfall stations.

[0011] Step 2, calculation of basin river flow under different guarantee rates, includes the following two steps.

[0012] Step 21: Based on the rainfall data of all rainfall stations collected in step 1 for more than 30 years, analyze each rainfall station and calculate the multi-year average value, C V value, maximum annual rainfall, year of maximum annual rainfall, minimum annual rainfall, year of minimum annual rainfall and ratio of extreme values ​​of wet and dry seasons.

[0013] Step 22, calculate the average annual precipitation in the basin for each year, draw the P-III frequency distribution curve of the average annual precipitation in the basin, and obtain the average annual precipitation and typical years under different guarantee rates based on the curve. Then, based on the monthly precipitation, basin area and runoff coefficient, calculate the total monthly runoff of the basin and the monthly runoff of each tributary in each typical year. The calculation formula is: runoff = basin area × precipitation × runoff coefficient.

[0014] Step 3, construction of the mathematical model of the water environment, includes the following two steps.

[0015] Step 31, simulation of the water environment mathematical model, using the river network and section information collected in step 1 to add to the water environment mathematical model, using the tributary monthly runoff calculated in step 22 as the upstream boundary condition, and using the monthly water levels of the downstream of the two branched river channels investigated in step 1 as the downstream boundary condition.

[0016] Step 32, calibration and verification of the mathematical model of water environment, input the model river network, section and boundary data of a certain year collected in step 1 into the model for calculation, and compare the calculation results with the annual water level information of the water level station and the annual flow information of the flow station at all water level stations (non-boundary) and flow stations in the branched river. If the absolute error between the hydrodynamic calculation results and the measured results is within 5%, the model hydrodynamic calibration is successful, and this model is used to predict water quality. If the error between the water quality calculation results and the measured results is within 5%, the model can be accurately used for simulation and prediction, and the next step can be continued; if the absolute error between the model calculation results and the measured results is greater than or equal to 5%, it is necessary to return to step 32 to recalibrate the model until the absolute error between the model calculation results and the measured results is within 5%.

[0017] Step 4, analysis of the diversion ratio law of the branched river channel, includes the following two steps.

[0018] Step 41, analyzing the relationship between the diversion ratio and the month and rainfall guarantee rate, the flow direction and flow of the two downstream branched rivers can be calculated through the water environment mathematical model, and then the flow change diagram and diversion ratio change diagram of the two downstream branched rivers in each typical year can be obtained, and the change pattern of the diversion ratio of the branched river with the month and rainfall guarantee rate can be analyzed.

[0019] Step 42, analysis of the relationship between the diversion ratio and the water level difference at the ends of the two downstream branched channels. The water level difference at the ends of the two downstream branched channels is calculated through the information of the water level stations at the ends of the two downstream branched channels in step 1, and then a relationship diagram between the flow of the two downstream branched channels, the diversion ratio and the water level difference at the ends of the two downstream branched channels is obtained, and the changing pattern between the diversion ratio and the water level difference is analyzed.

[0020] Step 5, analysis of the law of sewage distribution ratio in bifurcated rivers, includes the following two steps.

[0021] Step 51, analysis of the pollutant concentration and the pollution separation ratio, generalize a point source pollution in the upstream of the bifurcated river, calculate the water quality of the two downstream bifurcated rivers under different upstream flow rates through the model, make a relationship diagram between the pollutant concentration of the two downstream bifurcated rivers and the upstream flow rate, and analyze the evolution law between the pollutant concentration of the bifurcated river and the upstream flow rate; make a relationship diagram between the pollutant concentration of the two downstream bifurcated rivers under different upstream flow rates, and analyze the evolution law of the pollutant concentration and pollution separation ratio of the bifurcated river.

[0022] Step 52, analysis of the pollutant flux separation ratio, according to the formula: pollutant flux = pollutant concentration * flow rate, calculate the pollutant flux through the two downstream branched rivers, make a relationship diagram of the pollutant flux of the two downstream branched rivers under different upstream flow rates, and analyze the evolution law of the pollutant flux separation ratio of the branched rivers.

[0023] Step 6: Analyze the evolution law of the diversion ratio and sewage diversion ratio of the bifurcated river channel. Make relationship curves between the diversion ratio and sewage diversion ratio of the two downstream bifurcated rivers under different upstream flow rates, and analyze the relationship between the diversion ratio and sewage diversion ratio of the bifurcated river channel; conduct probability statistics on the diversion ratio and sewage diversion ratio in different months of different horizontal years, and analyze the probability distribution characteristics of the diversion ratio and sewage diversion ratio of the bifurcated river channel.

[0024] The spatial distance of the downstream confluence point of the branched river channel is between 0.5 times the shortest river channel of the branched river section and 3 times the longest branched river channel.

[0025] The number of the downstream branched river channels is greater than or equal to 2.

[0026] The confluent water body at the end of the branched river channel is different from the branched river channels in terms of water level, flow rate and ecological system.

[0027] The water level in the water body at the end of the branched river channel is higher than the water level of any branched river channel, which is called backflow.

[0028] The water body at the end of the branched river channel has a supporting phenomenon for the inflow of the branched river channel, that is, the water body at the end is affected by the upstream for a short time, and there is a phenomenon that the branched river channel cannot be merged. After the influence of the water body at the end is lifted, the branched river channel can continue to merge.

[0029] There is a diversion area in the bifurcated river channel, and its impact range is 1-6 times the width of the bifurcated river channel downstream of the bifurcated mouth. There is no pollution source in the diversion area.

[0030] The present invention has the following beneficial effects: In view of the current insufficient research on the sewage separation ratio, diversion ratio and evolution law of the sewage separation ratio of bifurcated rivers, the present invention proposes a research method for analyzing the diversion ratio and sewage separation ratio of bifurcated rivers and their evolution laws, providing a scientific basis for the formulation of environmental management policies such as flood control and drainage, ecological water replenishment, total pollutant control, water environment protection, and water ecological restoration. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is the water network of the Qinhuai River Basin. Point D is the bifurcation point. Sections DA and DB are the two downstream channels of the bifurcated river. DA represents the Qinhuai New River, and DB represents the Outer Qinhuai River. The triangle mark represents the location of the water level station, the hollow circle represents the location of the flow station, and the solid circle represents the location of the rainfall station.

[0032] Figure 2 It is the P-Ⅲ frequency distribution curve of the average annual rainfall in the basin. The horizontal axis is the rainfall guarantee rate, the vertical axis is the annual rainfall, and the points in the figure represent the annual rainfall and rainfall guarantee rate in a certain year.

[0033] Figure 3 This is a calibration verification diagram of the model calculation results and actual values. The curve in the figure represents the calculation results of the model, and the points in the figure represent the actual values ​​monitored by the water level station and flow station.

[0034] Figure 4-1 The figure shows the flow change chart of Qinhuai New River and Outer Qinhuai River from January to December in each typical year. A negative flow indicates backflow.

[0035] Figure 4-2 This is a graph showing the relationship between the flow rate of Qinhuai New River and Wai Qinhuai River, the diversion ratio, and the water level difference between the Qinhuai New River and Wai Qinhuai River at the end of the estuary. The points in the graph are the calculation results of the model, and the line in the graph is the trend line.

[0036] Figure 5-1 It is a relationship diagram between upstream flow and three pollutants in DA and DB sections. The horizontal axis is the upstream flow, the vertical axis is the pollutant concentration, the points in the figure are the calculation results of the model, and the line in the figure is the trend line.

[0037] Figure 5-2 It is a comparison chart of pollutant concentrations in the DA segment and the DB segment. The horizontal axis is the pollutant concentration in the DA segment, and the vertical axis is the pollutant concentration in the DB segment. The points in the figure are the model calculation results, and the line in the figure is the trend line.

[0038] Figure 6 The upper part is the relationship diagram between the diversion ratio and the sewage diversion ratio. The points in the figure are the calculation results of the model, and the line in the figure is the trend line. Figure 6 The lower part is the probability distribution diagram of the diversion ratio of the DA segment and the DB segment, with the horizontal axis being the percentage and the vertical axis being the number of occurrences. DETAILED DESCRIPTION

[0039] Next, the present invention is further described in detail based on the application example of the method in the Qinhuai River Basin in Nanjing City, Jiangsu Province, that is, the study of the diversion ratio and sewage separation ratio of the Outer Qinhuai River and the Qinhuai New River and their evolution laws, including the following steps.

[0040] Step 1: Survey of hydrological information in the Qinhuai River Basin, including the following two aspects of information: 1. The river network and river section conditions in the Qinhuai River Basin; 2. The locations of water level stations, flow stations and rainfall stations in the branched river areas, see Figure 1 , the DA and DB sections in the figure are the two downstream channels of the bifurcated river. 3. The water level data of the water level station in the bifurcated river area, the flow data of the flow station and the annual and daily rainfall data of the rainfall station.

[0041] Step 2, calculation of the river flow in the Qinhuai River Basin under different guarantee rates, includes the following two steps:

[0042] Step 21, based on the rainfall data of 20 rain gauges in the Qinhuai River Basin during the 45 years from 1962 to 2006 collected in step 1, each rain gauge is analyzed to calculate the multi-year average, CV value, maximum annual rainfall, year of maximum rainfall, minimum rainfall, year of minimum rainfall, and ratio of extreme values ​​of wet and dry seasons of each rain gauge.

[0043] Step 22, calculate the annual average value of all rainfall station data in the Qinhuai River Basin in each year, and draw the P-Ⅲ frequency distribution curve of the annual average rainfall in the basin, see Figure 2 , taking the years with guaranteed rainfall rates of 10%, 25%, 50%, 75%, 80%, 90% and 95% as typical years, and then calculating the total monthly runoff of the basin and the monthly runoff of each tributary in each typical year based on the monthly rainfall and basin area. The calculation formula is: runoff = basin area * rainfall.

[0044] Step 3, construction of the mathematical model of the water environment, includes the following two steps.

[0045] Step 31, simulation of the water environment mathematical model, using the river network and cross-section information collected in step 1 to add to the water environment mathematical model, using the tributary monthly runoff calculated in step 22 as the upstream boundary condition, and using the monthly water levels of the two branched river channels investigated in step 1 as the downstream boundary condition, generalizing a 1m 3 / s pollutant outlet, COD, NH3-N and TP concentrations are 300mg / L, 30mg / L and 3mg / L.

[0046] Step 32, calibration and verification of the water environment mathematical model. After calibration, the model river network, cross-section and boundary data of a certain year collected in step 1 are input into the model for calculation. The calculation results are compared with the annual water level information of the water level station and the annual flow information of the flow station at all water level stations (non-boundary) and flow stations in the bifurcated river. If the model calculation results are consistent with the measured results, the model verification is successful. Figure 3 , you can proceed to the next step; if the model calculation results are significantly different from the measured results, you need to recalibrate the model until the model calculation results are consistent with the measured results.

[0047] Step 4, analysis of the diversion ratio law of the branched river channel, includes the following two steps.

[0048] Step 41, the relationship between the diversion ratio and the month and the rainfall guarantee rate is analyzed. The flow direction and flow of the two downstream bifurcated rivers can be calculated through the water environment mathematical model, and then the flow change diagram and diversion ratio change diagram of the two downstream bifurcated rivers in each typical year can be obtained. Figure 4-1 , the analysis shows that, in general, the backflow of Qinhuai New River occurs in the flood season, and the runoff first increases and then decreases with the increase of the month. The annual maximum values ​​of the upstream total surface runoff and the flow of the A and B branch rivers are advanced with the increase of the rainfall guarantee rate, among which the upstream total surface runoff is the most obvious, with the maximum value advanced from August to April.

[0049] Step 42, analyzing the relationship between the diversion ratio and the water level difference at the ends of the two downstream branched channels. By using the information of the water level stations at the ends of the two downstream branched channels in step 1, the water level difference at the ends of the two downstream channels is calculated, and then a relationship diagram between the flow of the two downstream branched channels, the diversion ratio and the water level difference at the ends of the two downstream branched channels is obtained, see Figure 4-2, the analysis shows that the diversion of the outer Qinhuai River increases with the increase of the water level difference, and its growth rate also gradually increases. The diversion of the Qinhuai New River decreases with the increase of the water level difference, and its growth rate also gradually increases; when the water level difference is greater than 0.17m and the Qinhuai New River flows backward, the diversion increases with the increase of the water level difference, and its growth rate also gradually decreases. The diversion ratio of the outer Qinhuai River increases with the increase of the water level difference, and its growth rate gradually decreases. The diversion ratio of the Qinhuai New River decreases with the increase of the water level difference, and its reduction rate also gradually decreases.

[0050] Step 5, analysis of the law of sewage distribution ratio in bifurcated rivers, includes the following two steps.

[0051] Step 51, pollutant concentration ratio analysis, generalize a point source pollution in the upstream of the bifurcated river, calculate the water quality of the two downstream bifurcated rivers under different upstream flow rates through the model, and make a relationship diagram between the pollutant concentration and upstream flow rate of the two downstream bifurcated rivers, see Figure 5-1 , the analysis shows that the pollutant concentration in the downstream branched river decreases exponentially with the increase of upstream flow; the relationship between the pollutant concentrations of the two downstream branched rivers under different upstream flow rates is shown in Figure 5-2 , the analysis shows that the concentration of pollutants in the upstream does not change with the bifurcation of the river.

[0052] Step 52, analysis of the pollutant flux separation ratio, according to the formula: pollutant flux = pollutant concentration * flow rate, calculate the pollutant flux through the two downstream branched rivers, make a relationship diagram of the pollutant flux of the two downstream branched rivers under different upstream flow rates, and analyze the evolution law of the pollutant flux separation ratio of the branched rivers.

[0053] Step 6: Analyze the evolution of the diversion ratio and the sewage diversion ratio of the bifurcated river channel, and make a relationship curve diagram of the diversion ratio and the sewage diversion ratio of the two downstream bifurcated river channels under different upstream flow rates, see Figure 6 , the analysis shows that the diversion ratio of the bifurcated river channel is positively correlated with the sewage diversion ratio, and the ratio of the diversion ratio to the sewage diversion ratio is approximately 1, that is, the diversion ratio and the sewage diversion ratio are equal; the probability statistics of the diversion ratio and the sewage diversion ratio in different months of different horizontal years are carried out, and the analysis shows that the probability of the diversion ratio of the bifurcated river channel in the DB section is 86.3% between 0.3-0.8, and the probability of the diversion ratio of the bifurcated river channel in the DA section is 86.3% between 0.2-0.7.

Claims

1. A method for studying the flow diversion ratio and the sewage diversion ratio of a bifurcated river and their evolution law, characterized by comprising the following steps: Step 1: Survey of hydrological information of the river basin where the bifurcated river is located, including the following two aspects of information:

1. The distribution of river networks, river sections and pollution sources; 2. The actual water level information of water level stations, the actual flow information of flow stations and the actual annual and daily rainfall information of rainfall stations; Step 2, calculation of river flow in the basin under different guarantee rates, includes the following two steps: Step 21: Based on the rainfall data of all rainfall stations collected in step 1 for more than 30 years, analyze each rainfall station and calculate the multi-year average value, C V value, maximum annual rainfall, year of maximum annual rainfall, minimum annual rainfall, year of minimum annual rainfall and ratio of extreme values ​​of wet and dry seasons; Step 22, calculate the average annual rainfall in the basin in each year, draw the P-III frequency distribution curve of the average annual rainfall in the basin, obtain the average annual rainfall and typical years under different guarantee rates according to the curve, and then calculate the total monthly runoff of the basin and the monthly runoff of each tributary in each typical year according to the monthly rainfall, basin area and runoff coefficient. The calculation formula is: runoff = basin area × rainfall × runoff coefficient; Step 3, construction of the water environment mathematical model, includes the following two steps: Step 31, simulation of the water environment mathematical model, using the river network and cross-section information collected in step 1 to add to the water environment mathematical model, using the tributary monthly runoff calculated in step 22 as the upstream boundary condition, and using the monthly water levels of the two branched river channels investigated in step 1 as the downstream boundary condition; Step 32, calibration and verification of the mathematical model of water environment, input the model river network, section and boundary data of a certain year collected in step 1 into the model for calculation, compare the calculation results with the annual water level information of the water level station and the annual flow information of the flow station at all water level stations and flow stations in the branched river, if the absolute error between the hydrodynamic calculation result and the measured result is within 5%, the model hydrodynamic calibration is successful, and the model is used to predict water quality, if the error between the water quality calculation result and the measured result is within 5%, the model can be accurately used for simulation and prediction, and the next step can be continued; if the absolute error between the model calculation result and the measured result is greater than or equal to 5%, it is necessary to return to step 32 to recalibrate the model until the absolute error between the model calculation result and the measured result is within 5%; Step 4, analysis of the diversion ratio of the bifurcated river channel, includes the following two steps: Step 41, analyzing the relationship between the diversion ratio and the month and the rainfall guarantee rate, the flow direction and flow of the two downstream bifurcated rivers can be calculated by the water environment mathematical model, and then the flow change diagram and diversion ratio change diagram of the two downstream bifurcated rivers in each typical year are obtained, and the change law of the diversion ratio of the bifurcated river channel with the month and the rainfall guarantee rate is analyzed; Step 42, analyzing the relationship between the diversion ratio and the water level difference at the ends of the two downstream branched channels, by calculating the water level difference at the ends of the two downstream branched channels through the information of the water level stations at the ends of the two downstream branched channels in step 1, and then obtaining a relationship diagram between the flow of the two downstream branched channels, the diversion ratio and the water level difference at the ends of the two downstream branched channels, and analyzing the changing pattern between the diversion ratio and the water level difference; Step 5, analysis of the law of sewage separation ratio in bifurcated rivers, includes the following two steps: Step 51, analysis of the pollutant concentration separation ratio, generalizing a point source pollution at the upstream of the bifurcated river channel, calculating the water quality of the two downstream bifurcated river channels under different upstream flow rates through the model, making a relationship diagram between the pollutant concentration of the two downstream bifurcated river channels and the upstream flow rate, and analyzing the evolution law between the pollutant concentration of the bifurcated river channel and the upstream flow rate; making a relationship diagram between the pollutant concentration of the two downstream bifurcated river channels under different upstream flow rates, and analyzing the evolution law of the pollutant concentration separation ratio of the bifurcated river channel; Step 52, analyzing the separation ratio of pollutant flux, according to the formula: pollutant flux = pollutant concentration * flow rate, calculate the pollutant flux through the two downstream bifurcated rivers, make a relationship diagram of the pollutant flux of the two downstream bifurcated rivers under different upstream flow rates, and analyze the evolution law of the pollutant flux separation ratio of the bifurcated rivers; Step 6: Analyze the evolution law of the diversion ratio and the sewage diversion ratio of the bifurcated river channel, respectively draw the relationship curves of the diversion ratio and the sewage diversion ratio of the two downstream bifurcated river channels under different upstream flow rates, and analyze the relationship law between the diversion ratio and the sewage diversion ratio of the bifurcated river channel; The probability statistics of the diversion ratio and sewage diversion ratio in different months of different horizontal years are carried out to analyze the probability distribution characteristics of the diversion ratio and sewage diversion ratio of the bifurcated river.

2. The method for studying the flow diversion ratio and the sewage diversion ratio of a bifurcated river channel and their evolution law according to claim 1, characterized in that: The distance of the spatial position of the downstream confluence point of the bifurcated river channel is between 0.5 times the shortest bifurcated river channel and 3 times the longest bifurcated river channel.

3. The method for studying the flow diversion ratio and the sewage diversion ratio of a bifurcated river channel and their evolution law according to claim 1, characterized in that: The number of the downstream branched river channels is greater than or equal to 2.

4. The method for studying the flow diversion ratio and the sewage diversion ratio of a bifurcated river channel and their evolution law according to claim 1, characterized in that: The confluent water body at the end of the branched river channel is different from the branched river channels in terms of water level, flow and ecosystem.

5. The method for studying the flow diversion ratio and the sewage diversion ratio of a bifurcated river channel and their evolution law according to claim 1, characterized in that: The water level in the water body at the end of the branched river channel is higher than the water level of any branched river channel, which is called backflow.

6. The method for studying the flow diversion ratio and the sewage diversion ratio of a branched river and their evolution law according to claim 1, characterized in that: The water body at the end of the branched river channel has a supporting phenomenon for the inflow of the branched river channel, that is, the water body at the end is affected by the upstream for a short time, and there is a phenomenon that the branched river channel cannot merge into it. After the influence of the water body at the end is lifted, the branched river channel continues to merge into it.

7. The method for studying the flow separation ratio and the sewage separation ratio of a branched river and their evolution law according to claim 1 is characterized by: There is a diversion area in the bifurcated river channel, and its impact range is 1-6 times the width of the bifurcated river channel downstream of the bifurcated mouth. There is no pollution source in the diversion area.

Images