Water intake site selection method

Abstract

The invention relates to the field of site selection methods, and particularly provides a water intake site selection method, which comprises the following steps: S1, obtaining water quality pollution source data and soil environment analysis data of a hub river drainage basin, and obtaining a preliminary water quality distribution diagram of the hub river drainage basin; s2, simulating the influence of the saltwater upstream on the water quality of the reservoir area, and obtaining the saltwater upstream law of the reservoir area under different boundary conditions; s3, obtaining the influence of saline water upstream on the arrangement position of a drinking water intake and / or an agricultural water intake in a certain place, and obtaining an updated water quality distribution diagram; s4, comparing the updated water quality distribution diagram with a domestic agricultural water standard, and judging whether the position of the water intake is qualified or not; the positions of the unqualified water intakes are adjusted in the water quality distribution diagram and judged again until the unqualified water intakes are qualified, and the final water intake arrangement is obtained. The method is easy to operate and has high scientificity and rationality, and practice shows that the water intake site selection method is high in accuracy and convenient to apply and popularize.

Description

Technical Field

[0001] The invention relates to the field of site selection methods, and in particular to a water intake site selection method. Background Art

[0002] There are many water supply and irrigation water intakes in the river basin along a canal. The construction of the canal project mainly involves canal excavation, dredging, and straightening. The implementation of the project has brought many adverse effects on the existing water intakes. After the canal was opened, the water supply and irrigation water intake on the original river were adversely affected due to the impact of cargo transportation on the water quality in the canal and the upstream movement of salt water. A certain reservoir area is the source of domestic water in the urban area and the source of irrigation water for the East-West Canal. In recent years, domestic water and agricultural water use have shown a gradual increase. Therefore, during the implementation and operation of the project, the impact of salt water upstream on the water quality of the water source should be fully considered, and the water intakes should be reasonably arranged to ensure the requirements of water quantity, water quality, and water depth. Therefore, it is very necessary to study the impact of salt water upstream on the water environment of the hub river section, clarify the salinity distribution characteristics of drinking water intakes and agricultural intakes under different boundary conditions, and determine a scientific and reasonable method for selecting water intakes. This is of practical significance for ensuring the safety, stability, and reliability of urban water supply. Summary of the invention

[0003] The purpose of the present invention is to provide a water intake site selection method in view of the problems existing in the prior art.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is:

[0005] A method for selecting a water intake site comprises the following steps:

[0006] S1. Obtain water pollution source data and soil environment analysis data in the hub river basin, and obtain a preliminary water quality distribution map of the hub river basin;

[0007] S2. Simulate the impact of salt water upstream on the water quality of the reservoir area and obtain the law of salt water upstream in the reservoir area under different boundary conditions;

[0008] S3. Obtain the impact of saltwater upstream on the location of a drinking water intake and / or agricultural water intake in a certain place, and obtain an updated water quality distribution map;

[0009] S4. Use the updated water quality distribution map to compare with the domestic and agricultural water use standards to determine whether the water intake location is qualified; the unqualified water intake locations are adjusted in the water quality distribution map and re-judged until they are qualified, thereby obtaining the final water intake layout.

[0010] The present invention provides a method for selecting a water intake site, comprising the following steps: S1, obtaining water pollution source data and soil environment analysis data of a hub river basin, and obtaining a preliminary water quality distribution map of the hub river basin; S2, simulating the impact of salt water upstream on the water quality of the reservoir area, and obtaining the law of salt water upstream in the reservoir area under different boundary conditions; S3, obtaining the impact of salt water upstream on the layout of a drinking water intake and / or an agricultural water intake in a certain place, and obtaining an updated water quality distribution map; S4, using the updated water quality distribution map to compare with the living and agricultural water standards to determine whether the water intake location is qualified; the location of the unqualified water intake is adjusted and re-judged in the water quality distribution map until it is qualified, and the final water intake layout is obtained. The method is simple to operate, has high scientificity and rationality, and practice shows that the water intake site selection method has high accuracy and is easy to promote and apply.

[0011] Furthermore, in S1, the water pollution source data of the hub river basin include the current status data of the pollution sources in the river basin and the water environment data of the reservoir area;

[0012] Preferably, the pollution source status data includes point source pollution data and non-point source pollution data;

[0013] More preferably, the point source pollution data include wastewater discharge from industrial pollution sources in river basins, sewage and pollutant discharge from sewage treatment plants, and sewage discharge from urban domestic pollution sources;

[0014] Non-point source pollution data include pollutant emissions from agricultural pollution sources, sewage and pollutant emissions from rural biological pollution sources, and pollutant emissions from livestock and poultry breeding pollution sources;

[0015] Preferably; reservoir water environment data, including water environment status and water resource allocation.

[0016] Furthermore, in S1, the soil environmental analysis data includes an analysis of soil salinity in the main canal irrigation areas on both sides of the hub river; preferably, it includes testing soil samples for pH, electrical conductivity and salinity indicators.

[0017] Furthermore, S2, the specific operation method of simulating the impact of salt water upstream on the water quality of the reservoir area,

[0018] According to the current status of the hub basin and the salinity characteristics simulated during the operation period after completion, the test salinity is set within a certain range, and several salinity gradients are set within the salinity range. According to the changing characteristics of the main pollutants in the surface water under different salinity scenarios, the impact of salinity on water environment pollutants is evaluated.

[0019] Furthermore, in S2, the specific operation process of obtaining the salt water upstream law of the reservoir under different boundary conditions is as follows:

[0020] Construct a three-dimensional salt water upstream numerical model in the reservoir area;

[0021] The three-dimensional salt water upstream numerical model is used to simulate the salinity distribution in the reservoir area after salt water upstream.

[0022] A three-dimensional salt water upstream numerical model was used to simulate the salinity distribution in the reservoir area under different upstream pilot channel outlet control salinity conditions.

[0023] Furthermore, the three-dimensional salt water upstream numerical model of the reservoir area is simulated using the following method:

[0024] The three-dimensional hydrodynamic module FM in the MIKE software is used to analyze the hydrodynamic environment of the QN reservoir area based on the numerical solution of the incompressible Reynolds-averaged NS equations and the Boussinesq and hydrostatic pressure assumptions; the continuity equation and the horizontal momentum equation are applied.

[0025] Furthermore, a three-dimensional salt water upstream numerical model was used to simulate the salinity distribution pattern of the reservoir area after salt water upstream, including the salinity of the navigation channel downstream of the ship lock as the salinity boundary, the salinity of the lock chamber under the independent filling and discharge mode as the salinity boundary, and the salinity of the lock chamber under the mutual filling and discharge mode as the salinity boundary.

[0026] Furthermore, it also includes using a three-dimensional salt water upstream numerical model to simulate the salinity distribution law of the reservoir area under different upstream pilot channel outlet control salinity conditions, including selecting the periods of minimum and maximum simulated flow rates to conduct salinity structure analysis of salinity data along the central axis of the channel, and selecting the period of minimum simulated flow rate to conduct vertical salinity result analysis at a distance from the spillway as an example.

[0027] Furthermore, the specific operation process of obtaining the impact of salt water upstream on the location of drinking water intake and / or agricultural water intake in a certain place is as follows:

[0028] The law of salt water upstream in the reservoir under different boundary conditions is simulated and calculated, and the salt water upstream in the reservoir is simulated and calculated when no anti-salinity measures are taken after the canal project, and the salinity distribution of water bodies at the drinking water intake and / or agricultural water intake of a certain place is obtained.

[0029] Furthermore, it also includes studying the impact of the controlled salinity of the upstream navigation channel outlet on the salinity distribution of the reservoir water intake after the ship lock adopts anti-salinity measures, taking into account the adverse conditions under extreme conditions, using different salinity boundaries, and during the simulation period, the salinity of the upstream navigation channel outlet of the ship lock is kept unchanged at this salinity for numerical model calculations to obtain the salinity distribution of the water body at a certain drinking water intake and / or agricultural water intake under different salinity boundary conditions.

[0030] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0031] The present invention provides a method for selecting a water intake site, comprising the following steps: S1, obtaining water pollution source data and soil environment analysis data of a hub river basin, and obtaining a preliminary water quality distribution map of the hub river basin; S2, simulating the impact of salt water upstream on the water quality of the reservoir area, and obtaining the law of salt water upstream in the reservoir area under different boundary conditions; S3, obtaining the impact of salt water upstream on the layout of a drinking water intake and / or an agricultural water intake in a certain place, and obtaining an updated water quality distribution map; S4, using the updated water quality distribution map to compare with the living and agricultural water standards to determine whether the water intake location is qualified; the location of the unqualified water intake is adjusted and re-judged in the water quality distribution map until it is qualified, and the final water intake layout is obtained. The method is simple to operate, has high scientificity and rationality, and practice shows that the water intake site selection method has high accuracy and is easy to promote and apply. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is the vertical distribution diagram of water salinity.

[0033] Figure 2 This is the vertical distribution diagram of water salinity.

[0034] Figure 3 This is the vertical distribution diagram of water salinity.

[0035] Figure 4 This is the salinity boundary of 1‰ and the vertical distribution of water salinity (minimum upstream flow).

[0036] Figure 5 This is the salinity boundary of 1‰ and the vertical distribution of water salinity (maximum upstream flow).

[0037] Figure 6 This is the salinity boundary of 1‰ and the vertical distribution of water salinity (5km away from the spillway).

[0038] Figure 7 This is the salinity boundary of 3‰ and the vertical distribution of water salinity (minimum upstream flow).

[0039] Figure 8 This is the salinity boundary of 3‰ and the vertical distribution of water salinity (maximum upstream flow).

[0040] Fig. 9 This is the salinity boundary of 3‰ and the vertical distribution of water salinity (5km away from the spillway).

[0041] Fig.10 These are the salinity diagrams of the downstream navigation channel (K98+600) of the ship lock, the salinity of the lock chamber under the independent filling and discharge (non-water-saving) mode, and the salinity of the lock chamber under the mutual filling and discharge (water-saving) mode.

[0042] Fig.11This is the salinity distribution map of the water body at the drinking water intake in QZ City when the salinity boundary is the salinity of the navigation channel downstream of the ship lock (K98+600).

[0043] Fig.12 This is the average salinity distribution map of the drinking water intake in QZ City when the salinity boundary is the salinity of the navigation channel downstream of the ship lock (K98+600).

[0044] Fig.13 Distribution diagrams of salinity in the downstream navigation channel (K98+600) of the ship lock, salinity in the lock chamber under independent filling and discharge (non-water-saving) mode, and salinity in the lock chamber under mutual filling and discharge (water-saving) mode.

[0045] Fig.14 This is the water salinity distribution diagram of the East-West Canal Intake Scheme 1 when the salinity boundary is the salinity of the navigation channel downstream of the ship lock (K98+600).

[0046] Fig.15 This is the average salinity diagram of the water body in Plan 1 of the East-West Canal water intake when the salinity boundary is the salinity of the navigation channel downstream of the ship lock (K98+600).

[0047] Fig.16 This is the water body salinity distribution diagram of the East-West Canal water intake distribution scheme 1 when the salinity boundary is the lock chamber salinity under the independent filling and discharge (non-water saving) mode.

[0048] Fig.17 The average salinity distribution diagram of the water body in Plan 1 of the East-West Canal water intake when the salinity boundary is the salinity of the lock chamber under the independent filling and discharge (non-water-saving) mode.

[0049] Fig.18 This is the water body salinity distribution diagram of the East-West Canal water intake scheme 1 when the salinity boundary is the salinity of the lock chamber under the mutual injection and discharge (water saving) mode.

[0050] Fig.19 The average salinity distribution diagram of the water body in the East-West Canal water intake scheme 1 when the salinity boundary is the salinity of the lock chamber under the mutual injection and discharge (water saving) mode. DETAILED DESCRIPTION

[0051] The present invention will be described in detail below in conjunction with the accompanying drawings.

[0052] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0053] Example

[0054] The present invention provides a method for selecting a water intake site, comprising the following steps:

[0055] S1. Obtain water pollution source data and soil environment analysis data in the hub river basin, and obtain a preliminary water quality distribution map of the hub river basin;

[0056] S2. Simulate the impact of salt water upstream on the water quality of the reservoir area and obtain the law of salt water upstream in the reservoir area under different boundary conditions;

[0057] S3. Obtain the impact of saltwater upstream on the location of a drinking water intake and / or agricultural water intake in a certain place, and obtain an updated water quality distribution map;

[0058] S4. Use the updated water quality distribution map to compare with the domestic and agricultural water use standards to determine whether the water intake location is qualified; the unqualified water intake locations are adjusted in the water quality distribution map and re-judged until they are qualified, thereby obtaining the final water intake layout.

[0059] In some embodiments, the specific operation process of step S1 is as follows:

[0060] Current status of main pollution sources in QN reservoir area

[0061] Point source pollution

[0062] 1. Industrial pollution sources

[0063] The investigation of industrial pollution sources is mainly based on environmental statistical data in 2020. According to the investigation, the large industrial enterprises that discharge wastewater into the QN reservoir area are mainly Pingji Sugar Co., Ltd. of a certain group.

[0064] The investigation found that the company's total emissions of chemical oxygen demand, ammonia nitrogen, total nitrogen and total phosphorus in 2020 were 29.86t / a, 2.43t / a, 3.53t / a and 0.06t / a, respectively, and the emissions were mainly concentrated from December to February of the following year.

[0065] 2. Emissions from sewage treatment plants

[0066] According to the survey, two sewage treatment plants have been built along the QN reservoir area, namely the PJ Town Sewage Treatment Plant and the LW Lingang Industrial Park Sewage Treatment Plant.

[0067] The main survey indicators of sewage treatment plants along the PL Canal project are the wastewater discharge volume of sewage treatment plants, chemical oxygen demand, ammonia nitrogen, total nitrogen and total phosphorus emissions in the wastewater.

[0068] According to the investigation, the PJ Town Wastewater Treatment Plant and the LW Lingang Industrial Park Wastewater Treatment Plant both implement the Class A standard. Statistics show that the total wastewater discharge of sewage treatment plants along the reservoir area in 2020 was 1.182 million t / a, and the total discharge of chemical oxygen demand, ammonia nitrogen, total nitrogen, and total phosphorus were 56.22 t / a, 5.59 t / a, 17.89 t / a, and 8.29 t / a, respectively. The pollutant discharge of each sewage treatment plant meets the standards.

[0069] 3. Urban life pollution sources

[0070] The urban domestic pollution sources counted in this section refer to the urban domestic sewage that is not treated by urban sewage treatment plants. The survey scope includes 1 township in LS County, 2 townships in QB District and 1 township in QN District.

[0071] Most of the domestic sewage outlets along the reservoir area have been intercepted, and the sewage is collected and discharged through sewage treatment plants for unified treatment. The sewage outlets that have not been intercepted are also being intercepted and rectified.

[0072] Non-point source pollution

[0073] 1. Agricultural pollution sources

[0074] Agricultural pollution sources mainly refer to fertilizers applied in agricultural production that enter farmland and land. Nutrients cannot be completely absorbed by crops, and the remaining part enters the water body with surface runoff. The fertilizer loss coefficient of different land use methods was calculated, and the agricultural non-point source pollution entry coefficient was taken as 0.2. In 2019, the total agricultural pollutant emissions in the QN reservoir area were chemical oxygen demand 157.47t / a, ammonia nitrogen 12.02t / d, total nitrogen 79.89t / a, and total phosphorus 8.87t / a.

[0075] 2. Rural life pollution sources

[0076] Rural domestic pollution is mainly generated by sewage, garbage, and human and animal feces generated in daily life being discharged into surrounding farmland and ditches, and pollutants partially enter water bodies through surface runoff. Referring to the "Guidelines for the Determination of National Water Environment Capacity", the per capita sewage discharge in rural areas is determined to be 150L / person·d, and the per capita pollution coefficient is chemical oxygen demand: 32g / person·d; ammonia nitrogen: 3.8g / person·d; total nitrogen: 10.6g / person·d; total phosphorus: 0.41g / person·d. The rural domestic pollution storage coefficient is 0.15.

[0077] 3. Pollution sources from livestock and poultry breeding

[0078] The pollutant emissions from livestock and poultry breeding were estimated based on the parameters provided in the National Water Resources Comprehensive Planning and Surface Water Resources Protection Training Manual. The emissions from pig, cattle, sheep, and poultry manure were 3.5kg / day / head, 25kg / day / head, 2kg / day / head, and 0.1kg / day / head, respectively. The livestock and poultry pollution emission storage coefficient was 0.15.

[0079] The total amount of non-point source pollution entering the QN reservoir area is statistically summarized as chemical oxygen demand 2285.60 t / a, ammonia nitrogen 81.52 t / a, total nitrogen 582.90 t / a, and total phosphorus 506.05 t / a. See Table 1 for details.

[0080] Table 1

[0081]

[0082] Overall, non-point source pollutants mainly come from rural domestic pollution sources and livestock and poultry breeding pollution sources. From the perspective of pollution source categories, chemical oxygen demand mainly comes from rural domestic pollution sources and livestock and poultry breeding pollution sources; ammonia nitrogen mainly comes from rural domestic pollution sources; total nitrogen mainly comes from rural domestic pollution sources and livestock and poultry breeding pollution sources; total phosphorus mainly comes from livestock and poultry breeding pollution sources.

[0083] QN Reservoir Water Environment

[0084] Water environment status

[0085] According to the investigation, the main assessment section within the QN reservoir area is the QN sluice section. According to the water quality evaluation data provided by the QZ Municipal Environmental Protection Bureau, the water quality of the main sections was generally good from 2018 to 2020, and the overall comprehensive water quality category of each section was II to III.

[0086] According to the water quality monitoring data, the water quality of the QN reservoir area is generally good. In terms of the permanganate index, except for SY Bridge which is Class III water in accordance with GB3838, the other points all meet the Class II water standard; in terms of the ammonia nitrogen index, except for SY Bridge which is Class II, the other points all meet the Class I water standard; for the total phosphorus index, the four monitoring points can all meet the Class II water standard.

[0087] Water resources allocation

[0088] (1) Current status of domestic water use

[0089] There are 12 domestic water intakes along the QN reservoir area, including 2 in LS County, 5 in QB District, and 5 in QN District, with a total daily water intake of approximately 19,200 m 3 , covering a population of approximately 56,500 people.

[0090] (2) Current status of agricultural water use

[0091] There are 45 irrigation water intakes located in QN and QB areas. According to incomplete statistics, the designed irrigation area of ​​the covered irrigation area is 8,256.41 mu, the effective irrigation area is 2,767.41 mu, the actual irrigation area is 2,767.41 mu, and the water transfer channel is 19.733 km long.

[0092] Analysis of soil salt content in the irrigation area of ​​the East-West Canal

[0093] The catchment area above the QN sluice gate is 2141km 2It is a comprehensive utilization project mainly for urban water supply and irrigation, taking into account power generation and shipping. It is a medium-sized reservoir and large (2) type sluice gate. The designed irrigation area is 121,700 mu, and the actual irrigation area is 29,000 mu. The normal water level of the dam is 8.5m, and there are east-west irrigation diversion canals upstream of the gate. The designed water diversion flow of the East Canal is 2.53m 3 / s, with a total length of 19.95km; the designed water diversion flow of the West Main Canal is 11.6m 3 / s, total length 5km.

[0094] Saline-alkali soil is a general term that includes saline soil, alkaline soil, and various salinized and alkaline soils. Saline soil refers to soils with soluble salt content that is harmful to crop growth, and its salt content index varies with different salt compositions. Alkaline soil refers to soils that contain a large amount of exchangeable sodium that is harmful to plant growth and changes soil properties. Studies have shown that saline-alkali land is mainly distributed in inland arid, semi-arid areas, and coastal areas.

[0095] After the completion of the PL Canal, the salt content of the QN sluice river section will increase due to the upstream movement of salt water. In order to analyze the potential impact of river water irrigation on the soil environment, the soil salt content of the East and West Canal irrigation areas was investigated to examine the current salinization of the soil in the irrigation areas and provide data reference for irrigation water after the implementation of the project. There are 14 sampling points in the survey scope of the West Canal; there are a total of 20 sampling points in the survey scope of the East Canal, which will be sampled in November 2022 and January 2023. The detection indicators include pH value, conductivity and salt content. The pH value test method is based on "Soil Monitoring Part 2-Determination of Soil pH" (NY / T1121.2-2006), the conductivity test method is based on "Determination of Soil Conductivity-Electrode Method" (HJ 802-2006), and the salt content test method is based on "Soil Monitoring Part 16-Determination of Total Water-soluble Salt in Soil" (NY / T 1121.16-2006).

[0096] The survey shows that saline-alkali soils are widely distributed in the coastal areas of eastern my country, and the soil salt composition is mainly chlorides; due to the large rainfall in the Guangxi Zhuang Autonomous Region, the leaching effect on the soil is strong, and some soils form acidic saline-alkali soils under the influence of rainfall leaching and microorganisms, and the salt composition is mainly sulfate and chloride. According to the "Technical Regulations for Monitoring and Evaluation of Coastal Soil Salinization" (HY / T0320-2021). It can be seen that the soil salt content at the sampling point (wasteland) in XP Village has reached the saline soil standard, the soil salt content at the sampling point (wasteland) in GS Village has reached the severe salinization soil standard, and the soil salt content at the sampling points in JS Village and JY Village has reached the mild salinization soil standard.

[0097] QN Reservoir Water Intake Standard

[0098] Domestic water

[0099] Article 5.1 of the "Sanitary Standard for Drinking Water" (GB 5749-2022) stipulates that when surface water is used as a source of drinking water, the water quality of the source water shall comply with the requirements of GB 3838. The "Surface Water Environmental Quality Standard" (GB3838-2002) stipulates that the water quality of centralized surface water sources for drinking water shall meet the standards of Class III water and above. Article 5.1.2 of the "Outdoor Water Supply Design Standard" (GB 50013-2018) stipulates that the selection of water sources shall be comprehensively determined after technical and economic comparisons, and shall meet the following conditions:

[0100] Located in the water intake area specified in the water body functional zoning;

[0101] Not easily polluted, making it easy to establish water source protection areas;

[0102] The selection order should be local water first, then transit water, natural river channels first, then rivers that need to regulate runoff;

[0103] The amount of water available is sufficient and reliable;

[0104] The water quality complies with the relevant current national standards;

[0105] Integrated utilization with agriculture and water conservancy;

[0106] Water intake, water delivery and water purification facilities are safe, economical and easy to maintain;

[0107] It has traffic, transportation and construction conditions.

[0108] The "Standard for Quality of Drinking Water Sources" (CJ 3020-1993) divides the quality of drinking water sources into two levels. Level 1 source water: good water quality. Groundwater only needs to be disinfected, and surface water can be used for drinking after simple purification (such as filtration) and disinfection. Level 2 source water: water quality is slightly polluted. After conventional purification treatment (such as flocculation, sedimentation, filtration, disinfection, etc.), its water quality can meet the requirements of GB5749 and can be used for drinking. Source water with water quality concentration exceeding the limit of the level 2 standard is not suitable as a source of drinking water. If it is necessary to use it due to limited conditions, it should be treated with the corresponding purification process. The treated water quality should comply with the provisions of GB5749 and obtain approval from the provincial, municipal and autonomous region health departments (bureaus) and competent departments. Both GB3838 and CJ 3020 stipulate that the chloride content in drinking water source water should be ≤250mg / L, which is equivalent to a salinity of ≤0.45‰.

[0109] The survey shows that the current water quality of the QN reservoir area is Class II to Class III water, meeting the relevant requirements of GB 5749, GB 50013, GB 3838, and CJ3020.

[0110] 2.4.2 Agricultural water use

[0111] Combined with relevant evaluation standards and literature research, the soil within the scope of this survey is weakly acidic soil, which is generally non-salinized soil. Some soils in some villages in the West Main Canal irrigation area have a certain degree of salinization problem, and the soils in the East Main Canal irrigation area are all non-salinized soils. "Farmland Irrigation Water Quality Standard" GB 5084-2021 puts forward requirements for the quality of irrigation water. After the completion of the PL Canal, the salt content of the QN hub river section will increase due to the upstream movement of salt water, which is the main factor that may affect the quality of irrigation water for the East and West Main Canals. According to the requirements of GB 5084, the total salt content of irrigation water in non-saline-alkali soil areas is ≤1000mg / L, and the total salt content of irrigation water in saline-alkali soil areas is ≤2000mg / L. In order to ensure agricultural water use in the irrigation area, considering that the soil in the East and West Main Canal irrigation area is generally non-salinized soil, the total salt content of its irrigation water should be ≤1000mg / L.

[0112] Analysis on the impact of saltwater upstream on water quality in QN reservoir area

[0113] By simulating the upstream of saltwater, the influence of salinity on pollutants in the water environment was evaluated according to the changing characteristics of the main pollutants in the surface water under different salinity scenarios. According to the current situation of the QN hub section of the PL Canal and the salinity characteristics simulated during the operation period after completion, the experimental salinity was set in the range of 0-6‰, and a total of 8 salinity gradients (0, 0.45‰, 1‰, 2‰, 3‰, 4‰, 5‰, 6‰) were set within this range. Based on the results of the analysis of the current salinity composition of the QN hub section of the PL Canal, the main component of salinity in the water environment of the basin is chloride ions. Therefore, this experimental study used chloride ions (sodium chloride) to simulate the salinity in the water phase. All experimental groups were set up in three parallels, the experimental temperature was controlled at 25±1℃, and the experimental water was obtained by filtering the raw water in the actual water environment through a 10-micron filter membrane (removing large particles and irrelevant impurities). The pollutant analysis and testing adopts the standard method described in the "Water and Wastewater Monitoring and Analysis Methods (Fourth Edition)", and the water quality results are evaluated based on the requirements for pollutant quality limits in the national standards "Surface Water Environmental Quality Standards" (GB3838-2002) and "Agricultural Irrigation Water Quality Standards" (GB5084-2021).

[0114] The study found that the implementation of the PL Canal project will cause a certain degree of saltwater upstream, and the impact of increased salinity on the main pollutants in the water body. The results show that higher salinity will change the content of nitrogen, phosphorus and organic matter in the water body to a certain extent, but if the salinity is controlled within the range required for drinking water and farmland irrigation, it will not have a significant impact on the main pollutants in the water body, and it can generally meet the Class III standard for surface water, that is, it will not cause water quality deterioration, nor will it increase the nitrogen and phosphorus pollution load of the Qin River entering the sea. Combined with the relevant research data of this project, after the completion of the PL Canal, the water quality of the QN reservoir area can meet the water quality requirements of GB3838 for centralized drinking water surface water sources.

[0115] Numerical simulation method for three-dimensional saltwater upstream in reservoir area

[0116] Model Governing Equations

[0117] The three-dimensional numerical model of saltwater upwelling in the QN reservoir area uses the three-dimensional hydrodynamic module (FM) in the MIKE software developed by the Danish Water Resources and Water Environment Institute (DHI). The calculation process of this study is based on the numerical solution of the incompressible Reynolds-averaged NS equations and the Boussinesq and hydrostatic pressure assumptions. The continuity equation and the horizontal momentum equation are used to analyze the hydrodynamic environment of the QN reservoir area. In addition, the σ coordinate transformation is used in the vertical direction.

[0118]

[0119] Where: t is time; x, y, z are coordinates; η is the surface water level of the water body; h is the total water depth; u, v, w are the velocity components in the x, y, z directions respectively; f is the Coriolis force coefficient; g is the gravitational acceleration; ρ is the water body density; v t is the vertical eddy viscosity coefficient; P a is atmospheric pressure; ρ0 is the reference density of water; q s is the flow rate of the point source; u q , v q is the flow velocity of the point source entering the surrounding water body.

[0120] The effective shear stress term in the momentum equation is represented by the stress gradient and is calculated as follows:

[0121]

[0122] Where: A is the horizontal eddy viscosity coefficient. The total water depth h in the model can be obtained through the moving boundary of the water surface as follows:

[0123] h=η+d (4.6)

[0124] Where: d is the still water depth; η is the surface water level of the water body. By integrating vertically, the following relationship is obtained:

[0125]

[0126] Where: is the average velocity of water depth along the x direction; is the depth-averaged velocity along the y direction.

[0127] The water density in the model is a function of salinity, and the state equation is the UNESCO formula. This project only involves density changes caused by salinity. The salinity transport equation is as follows:

[0128]

[0129] Where: S is salinity; D v is the vertical diffusion coefficient; S′ is the source salinity; F S is the salinity horizontal diffusion term, which can be expressed as follows:

[0130]

[0131] Where: D h is the horizontal diffusion coefficient. h and the vertical diffusion coefficient D v It is related to the eddy viscosity coefficient and is expressed by the following formula:

[0132]

[0133] Where: S is the Prandtl number, which is a constant.

[0134] The standard k-ε model is used to solve the vertical eddy viscosity coefficient, and the Smagorinsky equation is used to solve the horizontal eddy viscosity coefficient. The effective year related to the characteristic length is used to express the transport of small grid scales, and the characteristic length is used to calculate the influence of sub-grid eddies. The eddy viscosity on the grid is determined by the following formula:

[0135]

[0136] In the formula, c s is a constant, l is the characteristic length, S ji is the deformation rate.

[0137]

[0138] The k-ε formula is used for the vertical stress term, and the eddy viscosity is derived using the turbulence parameters. The formula is as follows:

[0139]

[0140] where k is the turbulent kinetic energy per unit mass (TKE), ε is the dissipation of TEK, and c μ is an empirical constant.

[0141] Model solution conditions

[0142] The velocity boundary conditions of the water surface and the riverbed bottom can be expressed as:

[0143] At the water surface (z = η)

[0144]

[0145] Riverbed bottom (z = -d)

[0146]

[0147] In the formula, τ sx , τ sy is the surface wind shear force: τ bx , τ by is the riverbed shear stress, and the Xie Cai formula can be used to establish the following relationship with the average flow velocity at water depth:

[0148]

[0149] Where C is the Xie Cai coefficient.

[0150] The law of salt water upstream in QN reservoir area

[0151] Salt water invades the QN reservoir through the QN ship lock, and the longitudinal distribution of salinity shows a trend of decreasing upstream, and the magnitude of the decrease is affected by the water conditions. Turbulent diffusion within a small scale range and the continuous change of the large-scale advection velocity field cause the mixing phenomenon of fresh and salt water exchange. During the upstream movement of salt water, runoff drives the density circulation, also known as gravity circulation. When the gravity circulation occurs, it is accompanied by vertical salinity stratification. The gravity circulation is most intense at the maximum salinity gradient, and the gravity circulation is proportional to the longitudinal salinity gradient. As the salinity gradient continues to increase, its density-driven diffusion continues to increase. The salt water intrusion in the upstream approach channel of the QN ship lock is not affected by tidal dynamics. Due to the density difference, the salt water sinks to the bottom, forming a salt water wedge upstream, and the bottom layer salinity is greater than the middle layer salinity, which is greater than the surface layer salinity.

[0152] Salinity distribution law in the reservoir area after salt water upstream

[0153] The moment with the largest salinity boundary during the simulation period was taken as an example to analyze the salinity results of the salinity data along the central axis of the waterway. The results are as follows: when the salinity boundary is the salinity of the downstream pilot channel of the QN ship lock (K98+600), the maximum salinity boundary occurs on January 28, which is 2.43‰; when the salinity boundary is the salinity of the lock chamber under the independent injection and discharge (non-water-saving) mode, the maximum salinity boundary occurs on January 30, which is 1.58‰; when the salinity boundary is the salinity of the lock chamber under the mutual injection and discharge (water-saving) mode, the maximum salinity boundary occurs on January 28, which is 1.92%.

[0154] When the salinity boundary is the salinity of the downstream approach channel of QN ship lock (K98+600), the salinity distribution along the way is

[0155] When the salinity boundary is the salinity of the downstream approach channel of QN ship lock (K98+600), the maximum salinity boundary occurs on January 28, which is 2.43‰; at this time, the upstream freshwater flow is 23.8m 3 / s. The vertical distribution of salinity in the surface, middle and bottom layers of the QN reservoir area is as follows: Figure 1. As can be seen from the figure, there is a certain salinity gradient in the surface, middle and bottom water bodies. The salinity of the bottom water body will drop to 1‰ when tracing back to 4.85km from the spillway, to 0.45‰ when tracing back to 6.69km from the spillway, and to 0‰ when tracing back to 7.54km from the spillway; the salinity of the middle water body will drop to 1‰ when tracing back to 4.51km from the spillway, to 0.45‰ when tracing back to 5.96km from the spillway, and to 0‰ when 7.46km from the spillway; the salinity of the surface water body will drop to 1‰ when tracing back to 2.07km from the spillway, to 0.45‰ when tracing back to 4.09km from the spillway, and to 0‰ at 6.97km.

[0156] Salinity distribution along the way when the salinity boundary is the salinity of the lock chamber in the independent water injection and discharge (non-water saving) mode

[0157] When the salinity boundary is the salinity of the lock chamber under the independent flooding and discharge (non-water saving) mode, the maximum salinity boundary occurs on January 30, which is 1.58‰; at this time, the upstream freshwater flow is 23.6m 3 / s. The vertical distribution of salinity in the surface, middle and bottom layers of the QN reservoir area is as follows: Figure 2 The salinity of the bottom water body will drop to 1‰ at 2.92km upstream from the spillway, to 0.45‰ at 4.97km upstream from the spillway, and to 0‰ at 6.87km upstream from the spillway; the salinity of the middle water body will drop to 1‰ at 2.43km upstream from the spillway, to 0.45‰ at 4.11km upstream from the spillway, and to 0‰ at 6.76km from the spillway; the salinity of the surface water body is always below 1‰, and will drop to 0.45‰ at 2.02km upstream from the spillway, and to 0‰ at 6.04km.

[0158] Salinity distribution along the way when the salinity boundary is the salinity of the lock chamber in the mutual injection and discharge (water saving) mode

[0159] When the salinity boundary is the salinity of the lock chamber under the mutual injection and discharge (water saving) mode, the maximum salinity boundary occurs on January 28, which is 1.92‰; at this time, the upstream freshwater flow is 23.8m 3 / s. The vertical distribution of salinity in the surface, middle and bottom layers of the QN reservoir area is as follows: Figure 3The salinity of the bottom water body will drop to 1‰ at 3.85km upstream from the spillway, to 0.45‰ at 5.81km upstream from the spillway, and to 0‰ at 7.33km upstream from the spillway; the salinity of the middle water body will drop to 1‰ at 2.95km upstream from the spillway, to 0.45‰ at 5.10km upstream from the spillway, and to 0‰ at 7.18km from the spillway; the salinity of the surface water body will drop to 1‰ at 1.55km upstream from the spillway, to 0.45‰ at 2.81km upstream from the spillway, and to 0‰ at 6.68km from the spillway.

[0160] Salinity distribution in the reservoir area under different upstream pilot channel outlet controlled salinity conditions

[0161] The day with the smallest flow rate during the simulation period, December 20 (average flow rate of 21.8m 3 / s) and the highest traffic on February 28 (average traffic of 111.3m 3 / s) was taken as an example to analyze the salinity results of salinity data along the central axis of the waterway; and the section 5km away from the QN hub sluice gate on December 20, when the flow rate was the smallest during the simulation period, was selected as an example to analyze the vertical salinity results.

[0162] Salinity distribution along the route when the salinity boundary is 1‰

[0163] The lowest upstream flow rate during the simulation period was on December 20 (average flow rate was 21.8 m 3 / s), vertical distribution of salinity of surface, middle and bottom water bodies in the QN reservoir area, such as Figure 4 . Due to the small flow from upstream, the salt water has a long upstream distance, and there is a certain salinity gradient in the surface, middle and bottom water bodies. The salinity of the surface water body will drop to 0.45‰ when it is traced back to 1.72km from the spillway, and to 0‰ when it is traced back to 6.95km from the spillway; the salinity of the middle water body will drop to 0.45‰ when it is traced back to 4.69km from the spillway, and to 0‰ when it is 7.49km from the spillway; the salinity of the bottom water body will drop to 0.45‰ when it is traced back to 4.97km from the spillway, and to 0‰ at 7.50km.

[0164] During the simulation period, the upstream flow was the largest on February 28 (average flow was 111.3m 3 / s), the vertical distribution curves of salinity in the surface, middle and bottom water bodies are as follows: Figure 5As the upstream freshwater flow increases, the upstream distance of salt water decreases. As can be seen from the figure, the salinity of the bottom water body will drop to 0.45‰ when it is traced back to 1.94km from the spillway, and drop to 0‰ when it is traced back to 2.04km from the spillway; the salinity of the middle water body will drop to 0.45‰ when it is traced back to 1.5km from the spillway, and drop to 0‰ when it is 2.03km from the spillway; the salinity of the surface water body is always below 0.45‰, and will drop to 0‰ when it is traced back to 1.97km from the spillway.

[0165] When the salinity boundary is 1‰, on December 20, when the upstream flow is the smallest during the simulation period, the salinity distribution of the surface, middle and bottom water bodies at a section 5 km away from the QN hub sluice gate is as follows Figure 6 There is an obvious stratification phenomenon in the vertical water salinity. The salinity of the middle water is greater than that of the surface water, and the salinity gradient between the middle and surface waters is 0.31‰; the salinity of the bottom water is greater than that of the middle water, and the salinity gradient between the bottom water and the middle water is 0.05‰.

[0166] The specific operations for the salinity distribution along the route when the salinity boundary is 1.5‰ and 2‰ are the same as those when the salinity is 1‰, and will not be described here.

[0167] Salinity distribution along the route when the salinity boundary is 3‰

[0168] When the salinity boundary is 3‰, the vertical distribution of salinity in the surface, middle and bottom water bodies of the QN reservoir on December 20, when the upstream flow is the smallest during the simulation period, is as follows: Figure 7 The salinity of the bottom water body will drop to 1‰ at a distance of 6.65km upstream from the spillway; it will drop to 0.45‰ at a distance of 7.53km upstream from the spillway, and it will drop to 0‰ at a distance of 7.97km upstream from the spillway; the salinity of the middle water body will drop to 1‰ at a distance of 6.06km upstream from the spillway; it will drop to 0.45‰ at a distance of 7.22km upstream from the spillway, and it will drop to 0‰ at a distance of 7.91km from the spillway; the salinity of the surface water body will drop to 1‰ at a distance of 3.19km upstream from the spillway; it will drop to 0.45‰ at a distance of 5.19km upstream from the spillway, and it will drop to 0‰ at 7.54km.

[0169] On February 28, when the upstream flow was the largest, the vertical distribution curves of salinity in the surface, middle and bottom layers of water were as follows: Figure 8 The salinity of the bottom water will drop to 1‰ at 2.53km upstream from the spillway, to 0.45‰ at 2.55km, and to 0‰ at 2.61km; the salinity of the middle water will drop to 1‰ at 2.27km upstream from the spillway, to 0.45‰ at 2.42km, and to 0‰ at 2.59km; the salinity of the surface water will drop to 1‰ at 0.98km upstream from the spillway, to 0.45‰ at 1.72km, and to 0‰ at 2.56km.

[0170] When the salinity boundary is 3‰, on December 20, when the upstream flow is the smallest during the simulation period, the salinity distribution of the surface, middle and bottom water bodies at the section 5 km away from the QN hub sluice gate is as follows Fig. 9 There is an obvious stratification phenomenon in the vertical water salinity. The salinity of the middle water is greater than that of the surface water, and the salinity gradient between the middle and surface waters is 1.2‰; the salinity of the bottom water is greater than that of the middle water, and the salinity gradient between the bottom water and the middle water is 0.1‰.

[0171] After the PL Canal project, salt water intruded into the QN reservoir area in a wedge shape, and the salinity increased vertically. After a certain distance upstream, the salt water reached equilibrium with the fresh water. The gravity circulation formed by the density gradient force caused vertical stratification of salinity in the section. The salinity of the bottom water body was greater than that of the middle water body, and the salinity of the middle water body was greater than that of the surface water body. The salinity gradient between the middle water body and the surface water body was greater than the salinity gradient between the bottom water body and the middle water body, and as the salinity boundary increased, the salinity gradient between the surface, middle and bottom water bodies also increased.

[0172] By studying the upward movement of salt water in the QN reservoir under different salinity boundary conditions, the following conclusions were drawn:

[0173] (1) The upward movement of salt water in the QN reservoir area is not affected by tidal dynamics. The salt water moves upward in a wedge shape, and the bottom salt water moves upward the farthest. The upward movement distance of salt water increases with the increase of salinity boundary and decreases with the increase of upstream flow. The upstream freshwater flow can effectively inhibit the upward movement distance of salt water in the QN reservoir area and reduce the salinity of the water body in the reservoir area.

[0174] (2) As the salt water in the QN reservoir area moves upstream in a wedge shape, the salt water reaches equilibrium with the fresh water after moving upstream for a certain distance. The gravity circulation formed by the density gradient force causes vertical stratification of salinity in the cross section. The salinity of the bottom water is greater than that of the middle water, and the salinity of the surface water is greater than that of the surface water. It is recommended that each water intake draw surface water.

[0175] Impact of saltwater upwelling on the location of drinking water intakes

[0176] Salinity distribution of drinking water intake in QZ city after saltwater upstreaming

[0177] Calculation conditions and working conditions

[0178] According to the research results of "The impact of QN ship lock operation on salt water upstream in the downstream river section", the salinity of the navigation channel (K98+600) downstream of QN ship lock during the dry season (December 1 to March 31 of the following year) was obtained, and the salinity of the lock chamber under the independent filling and discharge (non-water saving) mode and the lock chamber salinity under the mutual filling and discharge (water saving) mode (such as Fig.10); This is the salinity boundary of the three-dimensional numerical model of salt water upstream in the QN reservoir area. The salt water upstream in the QN reservoir area after the PL Canal project is simulated and calculated when no anti-salinity measures are taken, and the salinity distribution of the water body at the drinking water intake of QZ City is obtained. The salinity of the navigation channel downstream of the QN ship lock is affected by the freshwater flow and the Maowei sea tide level. The maximum salinity of the navigation channel downstream of the QN ship lock (K98+600) appeared on January 28, which was 2.43‰; the maximum salinity of the lock chamber under the independent filling and discharge (non-water saving) mode appeared on January 30, which was 1.58‰; the maximum salinity of the lock chamber under the mutual filling and discharge (water saving) mode appeared on January 28, which was 1.92‰. In order to improve the calculation efficiency, the numerical simulation does not consider the situation where the salinity is less than 0.1‰. Therefore, the simulation time starts from December 12 and ends on March 31 of the following year. The simulation time is 110 days in total. The calculation conditions are shown in Table 2.

[0179] Table 2 Calculation conditions

[0180]

[0181] Salinity distribution of drinking water intakes in QZ City

[0182] According to the engineering plan, after the PL Canal project, the drinking water intake of QZ City will be moved to Dafeng River, 7.4km away from the QN hub sluice gate (6.1km away from the upstream navigation channel of the QN ship lock). Fig.11 When the salinity of the downstream navigation channel (K98+600) is used as the salinity boundary, the salinity of the surface, middle and bottom water bodies at the drinking water intake of QZ City changes over time. In the recent dry season under the 90% flow guarantee rate after the PL Canal Project, the maximum salinity of the surface water body appeared on January 29, which was 0.03‰; the maximum salinity of the middle water body appeared on January 23, which was 0.05‰; the maximum salinity of the bottom water body appeared on January 30, which was 0.09‰. It can be seen that when the salinity of the downstream navigation channel is used as the salinity boundary, the salinity of the water body at the drinking water intake of QZ City is less than 0.1‰, which meets the drinking water salinity requirements in the relevant specifications. Fig.12 When the salinity boundary adopts the salinity of the downstream navigation channel (K98+600), the average salinity at the drinking water intake of QZ City changes over time. As can be seen from the figure, the average salinity of the water body at the drinking water intake of QZ City is always lower than 0.05‰; the maximum value occurs on January 23, which is 0.047‰. When the salinity boundary adopts the salinity of the lock chamber under the independent filling and discharge mode (non-water saving) and the lock chamber salinity under the mutual filling and discharge mode (water saving), the salinity of the surface, middle and bottom water bodies at the drinking water intake of QZ City during the simulation period is 0, and the salt water cannot be traced back to the drinking water intake of QZ City.

[0183] Effects of different upstream pilot channel outlet control salinity on the salinity of drinking water intake in QZ City

[0184] Calculation conditions and working conditions

[0185] From the above research results, it can be seen that the salinity boundary is the main influencing factor of the upstream distance of salt water in the QN reservoir area and the salinity distribution of the water body at the drinking water intake of QZ City. When encountering extreme conditions, such as extreme weather and ship lock maintenance, the salinity at the outlet of the upstream navigation channel of the QN ship lock may exceed the salinity boundary adopted above. This summary studies the influence of the salinity control at the outlet of the upstream navigation channel on the salinity distribution of the water intake of the QN reservoir area after the QN ship lock adopts anti-salinity measures. Considering the unfavorable conditions under extreme conditions, the salinity boundaries are 1‰, 1.5‰, 2‰, and 3‰, and the salinity at the outlet of the upstream navigation channel of the QN ship lock is kept unchanged during the simulation period. The numerical model calculation is carried out to obtain the salinity distribution of the water body at the drinking water intake of QZ City under different salinity boundary conditions. The freshwater flow rate adopts the flow rate with a 90% guarantee rate in the near future after the project. The simulation time starts from October 1st and ends on March 31st of the following year, and the simulation time is 182 days in total.

[0186] Salinity distribution of drinking water intakes in QZ City

[0187] According to the engineering plan, the drinking water intake of QZ City is 7.4km away from the QN hub sluice gate (6.1km away from the upstream navigation channel of QN ship lock), which is the same location as the Dafengjiang water intake. When the salinity boundary is 1‰, during the simulation period, the maximum salinity of the surface and middle water bodies at the drinking water intake of QZ City both appeared on December 25, which were 0.001‰ and 0.013‰ respectively, and the maximum salinity of the bottom water body appeared on December 26, which was 0.056‰; when the salinity boundary is 1.5‰, the maximum salinity of the surface water body at the drinking water intake of QZ City appeared on December 26, which was 0.003‰, the maximum salinity of the middle water body appeared on December 24, which was 0.050‰, and the maximum salinity of the bottom water body appeared on December 26. on December 25, it was 0.173‰; when the salinity boundary was 2‰, the maximum salinity of the surface water at the drinking water intake in QZ City was 0.005‰ on December 25, the maximum salinity of the middle water was 0.114‰ on December 24, and the maximum salinity of the bottom water was 0.312‰ on December 25; when the salinity boundary was 3‰, the maximum salinity of the surface, middle and bottom water at the drinking water intake in QZ City all occurred on December 25, which were 0.024‰, 0.339‰ and 0.584‰ respectively. When the salinity of the upstream pilot channel outlet is controlled at 1‰, 1.5‰ and 2‰, the salinity of the surface, middle and bottom layers at the drinking water intake of QZ City are all lower than 0.45‰, meeting the drinking water salinity control standard; when the salinity of the upstream pilot channel outlet is controlled at 3‰, the salinity of the surface and middle water bodies at the drinking water intake of QZ City are all lower than 0.45‰, and the salinity of the bottom water body is lower than 0.45‰ in some periods of time.

[0188] When the salinity boundary is 1‰, 1.5‰, 2‰, and 3‰, the average salinity of the section of the drinking water intake in QZ City changes with time. When the salinity boundary is 1‰, the maximum average salinity of the section of the drinking water intake in QZ City occurs on December 25, which is 0.023‰; when the salinity boundary is 1.5‰, the maximum average salinity of the section occurs on December 25, which is 0.075‰; when the salinity boundary is 2‰, the maximum average salinity of the section occurs on December 25, which is 0.144‰; when the salinity boundary is 3‰, the maximum average salinity of the section occurs on December 25, which is 0.316‰. When the salinity of the upstream pilot channel outlet is controlled at 1‰, 1.5‰, 2‰, and 3‰, the average salinity of the section of the drinking water intake in QZ City during the simulation period is lower than 0.45‰, meeting the drinking water salinity control standard.

[0189] The study found that:

[0190] (1) In the dry season under the 90% flow guarantee rate in the near future after the PL Canal project, when the salinity boundary adopts the salinity of the downstream navigation channel, the salinity of the water body at the drinking water intake of QZ City is less than 0.1‰, which meets the drinking water salinity requirements in relevant specifications; when the salinity boundary adopts the salinity of the lock chamber under the independent filling and discharge mode (non-water saving) and the lock chamber salinity under the mutual filling and discharge mode (water saving), the salinity of the surface, middle and bottom water bodies at the drinking water intake of QZ City during the simulation period are all 0, and the salt water cannot be traced back to the drinking water intake of QZ City.

[0191] (2) After the QN ship lock adopted anti-salinity measures, when the salinity at the upstream pilot channel outlet was controlled at 1‰, 1.5‰, and 2‰, the average salinity of the surface, middle, bottom layers, and cross-section at the drinking water intake of QZ City was lower than 0.45‰; when the salinity at the upstream pilot channel outlet was controlled at 3‰, the salinity of the surface, middle, and bottom layers of the water body and the average salinity of the cross-section at the drinking water intake of QZ City was lower than 0.45‰, meeting the drinking water salinity control standard.

[0192] Impact of saltwater upstream on the location of agricultural water intakes in the East-West Canal

[0193] like Fig.13As shown in the figure, after the PL Canal project, the QN reservoir area will serve as the source of agricultural irrigation water for QZ City. According to national standards, there are strict standards for the salinity of agricultural irrigation water. This chapter uses the three-dimensional numerical model of salt water upstream in the QN reservoir area to simulate the salt water intrusion in the QN reservoir area, and obtains the salinity distribution of each site selection scheme of the East-West Canal under different salinity conditions at the outlet of the upstream navigation channel of the ship lock, providing a theoretical basis and technical support for the site selection of the water intake of the East-West Canal. According to the design data, three options are considered for the site selection of the water intake of the East-West Canal, namely, Option 1 is located at the current QZ Water Plant, 1.99km away from the QN hub sluice gate; Option 2 is the newly proposed water intake gate, 1.56km away from the QN hub sluice gate (about 400m downstream of the QZ Water Plant); Option 3 is 150m before the QN hub sluice gate. The model adopts the dry season flow rate under the 90% guarantee rate in the near future after the project. According to the design data, the water diversion volume of the East-West Canal changes with time, and the maximum flow is 1.6m 3 / s (October), the minimum flow is 0.1m 3 / s (December to February of the following year), point sources are set up at corresponding locations to draw water from Dafeng River, QZ main urban area and east-west trunk canals.

[0194] Salinity distribution at the water intake of the East-West Canal after salt water upstreaming

[0195] Calculation conditions and working conditions

[0196] Considering the same calculation conditions as those used in the study on salinity distribution of drinking water intakes in QZ City after upstreaming of salt water, the model salinity boundary adopts the salinity of the navigation channel (K98+600) downstream of the QN ship lock during the dry season (December 1 to March 31 of the following year), the salinity of the lock chamber under the independent filling and discharge (non-water-saving) mode, and the salinity of the lock chamber under the mutual filling and discharge (water-saving) mode; the maximum salinity of the navigation channel (K98+600) downstream of the QN ship lock occurred on January 28, which was 2.43‰; the maximum salinity of the lock chamber under the independent filling and discharge (non-water-saving) mode occurred on January 30, which was 1.58‰; the maximum salinity of the lock chamber under the mutual filling and discharge (water-saving) mode occurred on January 28, which was 1.92‰. In order to improve the calculation efficiency, the numerical simulation does not consider the situation where the salinity is lower than 0.1‰. Therefore, the simulation time starts from December 12 and ends on March 31 of the following year, with a total simulation time of 110 days. The calculation conditions are shown in Table 3.

[0197] Table 3 Calculation conditions

[0198]

[0199] Salinity distribution of water intake scheme 1 of the East-West Canal case

[0200] The water intake plan 1 of the East-West Canal after the PL Canal Project is located at the current QZ Water Plant, 1.99km away from the QN hub sluice gate. Fig.14When the salinity of the downstream navigation channel (K98+600) is used as the salinity boundary, the salinity of the surface, middle and bottom water bodies at the location of the East-West Canal water intake scheme 1 changes over time. The vertical water body salinity stratification is obvious, and the salinity of the surface water body is lower than that of the middle and bottom water bodies. In the recent dry season under the 90% flow guarantee rate after the PL Canal Project, the maximum salinity of the surface water body appeared on January 29, which was 1.07‰; the maximum salinity of the middle water body appeared on February 2, which was 2.21‰; the maximum salinity of the bottom water body appeared on February 2, which was 2.27‰. It can be seen that when the salinity boundary adopts the salinity of the downstream navigation channel, the salinity of the surface water at the East-West Canal water intake scheme 1 is less than 1‰ most of the time, and the maximum value is only 1.07‰, which basically meets the salinity control standard for agricultural irrigation water; the time period when the salinity of the middle layer water exceeds 1‰ is from December 25 to February 20 of the following year, a total of 58 days; the time period when the salinity of the bottom layer water exceeds 1‰ is from December 24 to February 20 of the following year, a total of 59 days. Fig.15 When the salinity of the downstream navigation channel (K98+600) is used as the salinity boundary, the average salinity of the East-West Canal water intake Scheme 1 changes over time. The maximum average salinity of the water body occurred on January 28, which was 1.84‰; the period when the average salinity of the water body exceeded 1‰ was from January 1 to February 19, a total of 40 days.

[0201] Fig.16 When the salinity boundary adopts the lock chamber salinity under the independent water filling and discharge mode (non-water saving) mode, the salinity of the surface, middle and bottom water bodies at the East-West Canal water intake scheme 1 position changes over time. The maximum salinity of the surface water body occurred on January 27, which was 0.49‰; the maximum salinity of the middle water body occurred on January 25, which was 1.21‰; the maximum salinity of the bottom water body occurred on January 25, which was 1.23‰. It can be seen that when the salinity boundary adopts the lock chamber salinity under the independent water filling and discharge mode, the salinity of the surface water body at the East-West Canal water intake scheme 1 position is less than 1‰, which meets the agricultural irrigation water salinity control standard; the time period when the salinity of the middle water body exceeds 1‰ is from January 14 to February 7, a total of 25 days; the time period when the salinity of the bottom water body exceeds 1‰ is from January 13 to February 7, a total of 26 days. Fig.17 This is a graph showing the change of average salinity over time at the East-West Canal water intake Scheme 1 location when the salinity boundary adopts the independent water injection and discharge (non-water saving) mode for the lock chamber salinity. It can be seen from the figure that when the salinity boundary adopts the independent water injection and discharge (non-water saving) mode for the lock chamber salinity, the average salinity of the water body at the East-West Canal water intake Scheme 1 location is always lower than 1‰; the maximum value occurs on January 25, which is 0.97‰.

[0202] Fig.18When the salinity boundary adopts the lock chamber salinity under the mutual injection and mutual discharge (water saving) mode, the salinity of the surface, middle and bottom water bodies at the East-West Canal water intake scheme 1 changes over time. Compared with the non-water saving mode of the QN ship lock, the salinity of the surface, middle and bottom water bodies at the water intake increased due to the reduction of fresh water discharged in the water saving mode. The maximum salinity of the surface water body appeared on January 28, which was 0.77‰; the maximum salinity of the middle water body appeared on January 28, which was 1.68‰; the maximum salinity of the bottom water body appeared on January 28, which was 1.72‰. It can be seen that the salinity of the surface water body at the East-West Canal water intake scheme 1 is less than 1‰, which meets the salinity control standard for agricultural irrigation water; the time period when the salinity of the middle water body exceeds 1‰ is from January 2 to February 18, a total of 48 days; the time period when the salinity of the bottom water body exceeds 1‰ is from January 2 to February 19, a total of 49 days. Fig.19 The average salinity of the East-West Canal water intake scheme 1 changes over time when the salinity boundary adopts the lock chamber salinity under the mutual injection and discharge (water saving) mode. The maximum average salinity of the water body occurred on January 28, which was 1.39‰; the period when the average salinity of the water body exceeded 1‰ was from January 4 to February 10, a total of 37 days.

[0203] Table 4 Summary of calculation results of salinity distribution of the East-West Canal water intake scheme 1 after upstream salt water

[0204]

[0205] The study found that when the salinity boundary adopts the salinity of the downstream navigation channel and the salinity of the lock chamber under the mutual injection and discharge (water-saving) mode, the salinity of the surface water body is less than 1‰; the average salinity of the middle layer, bottom layer and cross section is less than 1‰. When the salinity boundary adopts the salinity of the lock chamber under the independent injection and discharge (non-water-saving) mode, the salinity of the surface water body and the average salinity of the cross section are less than 1‰; the salinity of the middle layer and bottom layer is greater than 1‰. When the salinity of the upstream navigation channel outlet is controlled at 1‰, the salinity of the water body is less than 1‰. When the salinity of the upstream navigation channel outlet is controlled at 1.5‰ and 2‰, the salinity of the surface water body is less than 1‰. When the salinity of the upstream navigation channel outlet is controlled at 3‰, the salinity of the water body is greater than 1‰.

[0206] After comprehensive consideration, after the PL Canal project, the QN ship lock will be operated in an independent filling and discharge (non-water-saving) mode during the dry season, or anti-salinity measures will be taken at the QN ship lock and the upstream navigation channel outlet will be controlled at 1‰, and the water intake of the East-West Main Canal will be set 150m before the QN hub discharge gate to meet the demand, which can ensure that the salinity of the irrigation water quality of the East-West Main Canal meets the salinity requirements in the relevant standards.

[0207] in conclusion

[0208] (1) The water quality in the QN reservoir area is generally good. The main sources of pollutants include industry, sewage treatment plants, agriculture, etc., and their discharge is within the permitted range. The overall comprehensive water quality category of each section of the river is II-III, which can meet the relevant provisions of GB 3838 for drinking water sources. The soil in the East and West Canal irrigation area is weakly acidic. No soil salinization problem was found in the East Canal irrigation area. There are different degrees of soil salinization problems in XP Village, GS Village, JS Village, and JY Village in the West Canal irrigation area. The soil in the East and West Irrigation Area is generally non-salinized soil.

[0209] (2) Under different salinity gradients (0.45‰, 1‰, 2‰, 3‰, 4‰, 5‰, 6‰), salinity will slightly change the COD, TN, and TP content of the water body, but it does not show a significant upward trend, and therefore will not increase the nitrogen and phosphorus pollution load of the Qin River entering the sea in the QN reservoir area. The layout of the water intake in the QN reservoir area during the operation of the PL Canal mainly depends on the salinity distribution. Combined with the provisions of GB 3838, CJ 3020, and GB 5084, the salinity of drinking water source water should be ≤0.45‰, and the salinity of irrigation water source water should be controlled below 1‰.

[0210] (3) The salt water in the QN reservoir area moves upstream in a wedge shape, and the bottom salt water moves upstream the farthest. The salt water moves upstream in a distance that increases with the increase of the salinity boundary and decreases with the increase of the upstream flow. The salinity of the bottom water is greater than that of the middle water, and the salinity is greater than that of the surface water. It is recommended that each water intake draw water from the surface.

[0211] (4) When the salinity at the outlet of the upstream pilot channel was controlled at 1‰, 1.5‰, and 2‰, the average salinity of the surface, middle, bottom, and cross-section of the drinking water intake in QZ City was all lower than 0.45‰; after the QN ship lock adopted anti-salinity measures, it was feasible to set the drinking water intake at the Dafengjiang water intake, which was 7.4 km away from the QN hub sluice gate (6.1 km away from the upstream pilot channel of the QN ship lock).

[0212] (5) During the operation period of the PL Canal Project, after the QN ship lock adopts salt collection pits or air curtain anti-salinity measures, the salinity of the upstream navigation channel outlet will be controlled within 1‰. The water intake of the East-West Canal is set before the QN hub sluice gate, and the salinity of the water body at the water intake is less than 1‰, meeting the relevant requirements of GB 5084.

[0213] suggestion

[0214] (1) In order to ensure the safety and reliability of domestic and agricultural water, it is recommended to refer to the Technical Specifications for the Demarcation of Drinking Water Source Protection Areas HJ 338 and relevant laws and regulations to re-demarcate the first-level and second-level protection areas of drinking water sources as soon as possible; at the same time, strengthen the protection of water sources, expand the protection scope, and effectively control and treat pollution sources.

[0215] (2) In order to prevent the sudden deterioration of water quality in the QN reservoir area, which would cause difficulties in treatment and result in water quality failing to meet the standards for domestic or irrigation water, it is recommended to gradually build an online water source monitoring and early warning system, strengthen real-time monitoring of salinity, COD, ammonia nitrogen and microbiological indicators, increase the accumulation of water quality data, and improve the accuracy of water environment analysis, so as to initiate preventive measures to ensure water supply safety and provide a reference for water supply decision-making in QZ City.

[0216] (3) Current regulations require cities to set up reasonable backup water sources or emergency water sources. The current backup water sources for QZ City are the Daman Reservoir and Duikanlong Reservoir, which are difficult to meet the normal water supply requirements of QZ City during the construction period of the PL Canal. Therefore, it is recommended to strengthen the treatment capacity of the water plant and increase the ability to resist risks.

[0217] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for selecting a water intake site, characterized in that: The following steps are involved: S1. Obtain water pollution source data and soil environment analysis data in the hub river basin, and obtain a preliminary water quality distribution map of the hub river basin; S2. Simulate the impact of salt water upstream on the water quality of the reservoir area and obtain the law of salt water upstream in the reservoir area under different boundary conditions; S3. Obtain the impact of saltwater upstream on the location of a drinking water intake and / or agricultural water intake in a certain place, and obtain an updated water quality distribution map; S4. Use the updated water quality distribution map to compare with the domestic and agricultural water use standards to determine whether the water intake location is qualified; the unqualified water intake locations are adjusted in the water quality distribution map and re-judged until they are qualified, thereby obtaining the final water intake layout.

2. The water intake site selection method according to claim 1, characterized in that: In S1, the water quality pollution source data of the hub river basin include the current status data of the pollution sources in the river basin and the water environment data of the reservoir area; Preferably, the pollution source status data includes point source pollution data and non-point source pollution data; More preferably, the point source pollution data include wastewater discharge from industrial pollution sources in river basins, sewage and pollutant discharge from sewage treatment plants, and sewage discharge from urban domestic pollution sources; Non-point source pollution data include pollutant emissions from agricultural pollution sources, sewage and pollutant emissions from rural biological pollution sources, and pollutant emissions from livestock and poultry breeding pollution sources; Preferably; reservoir water environment data, including water environment status and water resource allocation.

3. The water intake site selection method according to claim 1, characterized in that: In S1, the soil environmental analysis data includes the analysis of soil salinity in the main canal irrigation areas on both sides of the hub river; preferably, it includes soil sampling for pH value, electrical conductivity and salt content index testing.

4. The water intake site selection method according to claim 1, characterized in that: S2, the specific operation method of simulating the impact of salt water upstream on the water quality of the reservoir area, According to the current status of the hub basin and the salinity characteristics simulated during the operation period after completion, the test salinity is set within a certain range, and several salinity gradients are set within the salinity range. According to the changing characteristics of the main pollutants in the surface water under different salinity scenarios, the impact of salinity on water environment pollutants is evaluated.

5. The water intake site selection method according to claim 1, characterized in that: In S2, the specific operation process of obtaining the upward movement law of salt water in the reservoir under different boundary conditions is as follows: Construct a three-dimensional salt water upstream numerical model in the reservoir area; The three-dimensional salt water upstream numerical model is used to simulate the salinity distribution in the reservoir area after salt water upstream. A three-dimensional salt water upstream numerical model was used to simulate the salinity distribution in the reservoir area under different upstream pilot channel outlet control salinity conditions.

6. The water intake site selection method according to claim 5, characterized in that: The three-dimensional salt water upstream numerical model of the reservoir area is simulated by the following method: The three-dimensional hydrodynamic module FM in MIKE software is used to analyze the hydrodynamic environment of the QN reservoir area based on the numerical solution of the incompressible Reynolds-averaged NS equations and the Boussinesq and hydrostatic pressure assumptions; the continuity equation and the horizontal momentum equation are applied.

7. The water intake site selection method according to claim 5, characterized in that: The three-dimensional salt water upstream numerical model is used to simulate the salinity distribution law of the reservoir area after salt water upstream, including the salinity of the navigation channel downstream of the ship lock as the salinity boundary, the salinity of the lock chamber under the independent filling and discharge mode as the salinity boundary, and the salinity of the lock chamber under the mutual filling and discharge mode as the salinity boundary.

8. The water intake site selection method according to claim 7, characterized in that: It also includes the use of a three-dimensional salt water upstream numerical model to simulate the salinity distribution law of the reservoir area under different upstream pilot channel outlet control salinity conditions, including selecting the periods of minimum and maximum simulated flow rates to conduct salinity structure analysis of salinity data along the central axis of the channel, and selecting the end face at a certain distance from the spillway during the period of minimum simulated flow rates as an example to conduct vertical salinity result analysis.

9. The water intake site selection method according to any one of claims 1 to 8, characterized in that: The specific operation process of obtaining the impact of salt water upstream on the location of drinking water intake and / or agricultural water intake in a certain place is as follows: The law of salt water upstream in the reservoir under different boundary conditions is simulated and calculated, and the salt water upstream in the reservoir is simulated and calculated when no anti-salinity measures are taken after the canal project, and the salinity distribution of water bodies at the drinking water intake and / or agricultural water intake of a certain place is obtained.

10. The water intake site selection method according to claim 9, characterized in that: It also includes studying the impact of controlled salinity at the upstream navigation channel outlet on the salinity distribution of the reservoir water intake after the ship lock adopts anti-salinity measures, taking into account adverse conditions under extreme conditions, using different salinity boundaries, and during the simulation period, the salinity of the upstream navigation channel outlet of the ship lock is kept constant at this salinity for numerical model calculations to obtain the salinity distribution of water bodies at a certain drinking water intake and / or agricultural water intake under different salinity boundary conditions.

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