River channel grading and staging drought alarm water level determination method considering water taking water level requirement

Abstract

The invention provides a river channel graded and staged drought alarm water level determination method considering a water taking level requirement, which comprises the following steps of: 1, determining a river channel drought alarm water level control section, and determining a control section water level control range according to the river channel drought alarm water level control section; 2, determining the response relation between the water intake water level of the water intake and the water level of the control section in the dry season within the water level control range of the control section; 3, according to the response relation between the water intake water level of the water intake within the water level control range of the control section and the water level of the control section in the dry season, determining water intake safety early warning indexes of the control section in a grading and staging mode; and 4, determining the graded and staged drought alarm water level of the control section according to the graded and staged water taking safety early warning index of the control section. According to the method, the problem that the control section graded and staged drought alarm water level and the water taking guarantee condition of the water taking users in the control range are unknown is solved, accurate regulation and control of later drought resistance and supply guarantee are facilitated, and scientificity and timeliness of regional drought early warning are improved.

Description

Technical Field

[0001] The present invention relates to the technical fields of water resources management and water disaster prevention, and specifically to a method for determining the graded and phased drought warning water levels of a river channel considering the requirements of water intake levels. Background Technique

[0002] In recent years, affected by the dual influences of global climate change and human activities, drought events have occurred frequently in China, and the contradiction between water supply and demand has become increasingly prominent. Scientifically determining the drought warning water level has become one of the key measures to cope with water resource shortages and drought risks. Currently, most drought warning water level standards are for reservoirs or lakes. For example, although the "Method for Determining Drought Warning Water Levels (Flows)" proposes a unified framework for determining the drought warning water levels of river channels, due to the diversity of river systems, the hydrological characteristics of natural river channels are different. At the same time, the distribution of water intake users and water intake facilities on the river channel are diverse, making it difficult to directly apply existing methods. At the same time, traditional methods mostly design graded and phased drought warning water levels based on the frequency of incoming water, and cannot directly link the drought warning water level with the water intake guarantee level of water intake users, unable to achieve precise response to drought warnings, and not conducive to the later-stage deployment of drought resistance work. Therefore, there is an urgent need for a method for determining the drought warning water level that targets the characteristics of river channels, integrates water intake level constraints and graded and phased warnings, so as to improve the scientific nature of water resources scheduling and the timeliness of drought resistance response. Summary of the Invention

[0003] The purpose of the present invention is to solve the problem that the conventional method for determining drought warning water levels (flows) cannot reflect the water intake guarantee situation of water intake users within the cross-section control range. Based on the water level response relationship between the control cross-section and the water intake during the dry season at the water intake, a method for determining the graded and phased drought warning water levels of a river channel considering the requirements of water intake levels is determined. Through drought warning applications, precise response to water intake guarantee is achieved. At the same time, combined with the method for determining drought warning water levels, the benefits of the water intake improvement project for water intake users can be quantitatively evaluated, guiding the upgrading transformation and planning layout of water intakes for water intake users within the river channel.

[0004] The present invention provides a method for determining the graded and phased drought warning water levels of a river channel considering the requirements of water intake levels, including the following steps:

[0005] Step 1: Determine the drought warning water level control cross-section of the river channel, and determine the water level control range of the control cross-section according to the drought warning water level control cross-section of the river channel;

[0006] Step 2: Determine the response relationship between the water intake level of the water intake within the water level control range of the control cross-section and the water level during the dry season of the control cross-section;

[0007] Step 3: Determine the water intake safety warning indicators for grading and phasing of the control cross-section according to the response relationship between the water intake level of the water intake within the water level control range of the control cross-section and the water level during the dry season of the control cross-section;

[0008] Step 4: Determine the drought warning water levels for different levels and periods of the control section according to the water intake safety warning indicators for different levels and periods of the control section.

[0009] Furthermore, Step 1 specifically includes:

[0010] Step 1.1: Determine the control sections for the river drought warning water levels: Sort out the distribution of the main hydrological stations in the river and the water intake points outside the river, calculate the proportion of the total water supply scale of the water plants at each hydrological station and the proportion of the effective irrigation area, and select the main control hydrological stations in the river according to the principle that the proportion of the total water supply scale and the proportion of the effective irrigation area are greater than the average level. Combine the distances between the main control hydrological stations and the importance of the cities where they are located to comprehensively determine the control sections for the river drought warning water levels;

[0011] Step 1.2: Determine the water level control range of the control section: Calculate the correlation between the water levels of the control section and the surrounding hydrological stations during the dry season, select the uppermost hydrological station with a correlation coefficient greater than the threshold θ as the starting point of the water level control range of the control section, and the lowermost hydrological station with a correlation coefficient greater than the threshold θ as the end point of the water level control range of the control section.

[0012] Furthermore, the calculation formulas for the proportion of the total water supply scale of the water plants at each hydrological station and the proportion of the effective irrigation area in Step 1.1 are as follows:

[0013]

[0014] In the formula, G i+1 is the proportion of the water supply scale of the water plant at the (i + 1)-th hydrological station; W i is the total water supply scale of the water plants that draw water from the river section between the i-th hydrological station and the (i + 1)-th hydrological station; S i+1 is the proportion of the effective irrigation area at the (i + 1)-th hydrological station; A i is the effective irrigation area of the irrigation district that draws water from the river section between the i-th hydrological station and the (i + 1)-th hydrological station.

[0015] Furthermore, Step 2 specifically includes:

[0016] Step 2.1: Extract the water surface slope between hydrological stations at different flow levels of the control section: According to the historical dry season hydrological data of each hydrological station, combined with the one-dimensional hydrodynamic model, construct the water surface profile at different flow levels within the control range, and combine the distances between adjacent hydrological stations to derive the water surface slope between each hydrological station at different flow levels.

[0017] Step 2.2: Determine the water level response relationship between the water intake and the control section during the low-flow period: According to the locations of the off-river water intakes of the water plants and irrigation areas along the radiation range controlled by the control section, measure the distance from the water intake to the hydrological station closest to the control section in the direction of the control section. Based on the water surface slope between the upstream and downstream hydrological stations of the river reach where the water intake is located and the water surface slope between the hydrological stations between the water intake and the control section, and combined with the distance from the water intake to the hydrological station closest to the control section in the direction of the control section and the distance between the hydrological stations, establish the water intake water level and the low-flow period water level response relationship of the control section within the water level control range of the water intake.

[0018] Furthermore, the water intake water level and the low-flow period water level response relationship of the control section within the water level control range in Step 2.2 are established according to Equation (2):

[0019]

[0020] In the formula, Z q is the water surface level at the water intake under the flow rate q of the control section, in m; Z kq is the water level under the flow rate q of the control section, in m, which can be calculated through the cross-section water level-flow relationship; λ iq is the water surface slope between the i-th hydrological station and the (i + 1)-th hydrological station between the water intake and the control section under the flow rate q of the control section, in m / km; L i is the distance between the i-th hydrological station and the (i + 1)-th hydrological station between the water intake and the control section, in km; λ q is the water surface slope of the river reach between the two hydrological stations to which the water intake belongs under the flow rate q of the control section; when the water intake is downstream of the control section, L q is the distance from the water intake to the nearest upstream hydrological station, and when the water intake is upstream of the control section, L q is the distance from the water intake to the nearest downstream hydrological station.

[0021] Furthermore, Step 3 specifically includes:

[0022] Step 3.1: Sort out the characteristics of water use demand within the control range: Sort out the characteristics of the crops planted in the irrigation area, query the crop irrigation system, and calculate the total water supply scale of the water plants and the total monthly water demand of the irrigation area within the cross-section control range;

[0023] Step 3.2: Establish the mapping relationship among the urban water supply guarantee ratio, the proportion of the drought - affected area in the irrigation district, and the water level at the control section: According to the response relationship between the water intake level at the water intake and the water level at the control section, combined with the minimum water intake level requirements of water users and the water intake characteristics of water intake facilities, analyze the maximum daily water intake of each water user at different water levels of the control section. Then, combined with the characteristics of the water demand cycle and the characteristics of water demand classification, establish the mapping relationship among the urban water supply guarantee ratio, the proportion of the drought - affected area in the irrigation district at different time periods, and the water level at the control section. Among them, the urban water supply guarantee ratio is the ratio of the total daily water intake of the water plant to the total water supply scale, and the proportion of the drought - affected area in the irrigation district is the ratio of the total monthly water intake to the total monthly water demand.

[0024] Step 3.3: Determine the water intake safety warning indicators for classification and staging: Classify based on the degree of water intake satisfaction and stage based on the characteristics of the water intake cycle. The degree of water intake satisfaction is expressed by the urban water supply guarantee ratio and the proportion of the drought - affected area in the irrigation district. Combining the mapping relationship among the urban water supply guarantee ratio, the proportion of the drought - affected area in the irrigation district at different time periods, and the water level at the control section, as well as the classification criteria, determine the water intake safety warning indicators for the control section for classification and staging.

[0025] Furthermore, the classification criteria corresponding to the urban water supply guarantee ratio and the proportion of the drought - affected area in the irrigation district in Step 3.3 are determined according to the water intake requirements of the region, or the requirements in the "National Flood Control and Drought Relief Emergency Plan" (January 10, 2006, State Council) for urban water supply and the drought - affected area of regional crops in the event of mild drought, moderate drought, severe drought, and extreme drought: When the urban water supply guarantee ratio is between 90% and 95%, it corresponds to mild drought; when it is between 80% and 90%, it corresponds to moderate drought; when it is between 70% and 80%, it corresponds to severe drought; when it is below 70%, it corresponds to extreme drought. When the proportion of the drought - affected area in the irrigation district is below 30%, it corresponds to mild drought; when it is between 31% and 50%, it corresponds to moderate drought; when it is between 51% and 80%, it corresponds to severe drought; when it is above 80%, it corresponds to extreme drought.

[0026] Furthermore, Step 4 specifically includes:

[0027] Step 4.1: Determine the shipping and ecological water demand at the control section in the river: Combining the approved results, sort out the shipping and ecological water requirements at the control section, and determine the lowest navigable water level and ecological water level according to the relevant relationship between the water level and flow at the control section. If there are no approved results, calculate the lowest navigable water level and ecological water level according to the "Standard for Inland Waterway Navigation" (GB 50139 - 2014) and the "Calculation Specification for Ecological Water Requirements of Rivers and Lakes" (SL / Z 712 - 2014).

[0028] Step 4.2: Determine the drought warning water levels for classification and staging: Compare the water intake safety warning indicators for classification and staging of the control section, the lowest navigable water level, and the ecological water level, and take the envelope line to determine the drought warning water levels for the control section for classification and staging.

[0029] Furthermore, in step 4.2, the outer envelope line is taken to determine the graded and phased drought warning water levels of the control section, as shown in Equation (3):

[0030] Z i,j = max(Zy i , Zg i,j , Zh, Ze)+θ, i = 1..n, j = 1..m (3)

[0031] In the formula, Z i,j is the drought warning water level of the i-th level and j-th phase, with the unit of m; Zy i is the water intake safety water level for urban water supply of the i-th level, with the unit of m; Zg i,j is the water intake safety water level for irrigation water use of the i-th level and j-th phase, with the unit of m; Zh is the lowest navigable water level, with the unit of m; Ze is the ecological water level, with the unit of m; θ is the safety threshold, with the unit of m, which is comprehensively determined by combining the river channel characteristics and the response time of drought resistance emergency measures.

[0032] The present invention has the following advantages: (1) Considering the water intake level requirements can solve the problem that the water intake guarantee situation of water users within the control range of the section is unclear caused by the conventional method for determining drought warning water levels (flows), and can accurately feedback the water intake volumes of each water user at different water levels of the control section; (2) The established mapping relationship between the urban water supply guarantee ratio, the proportion of the drought-affected area in the irrigation area, and the water level of the control section can quickly calculate the disaster impacts at different water levels of the control section, facilitate the water administrative department to make accurate response measures in a timely manner, and at the same time is beneficial for water users with higher water intake level requirements to propose an upgrading and transformation plan for the water intake. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a distribution map of water intake points and hydrological control stations between Luoshan Station and Jiujiang Station on the main stream of the Yangtze River;

[0034] Figure 2 is the water surface line of the river section within the control range at different flow levels in Hankou;

[0035] Figure 3 is the total daily water intake of water plants within the control range and its proportion at different water levels in Hankou;

[0036] Figure 4 is the proportion of the drought-affected area in the irrigation area within the control range at different water levels in Hankou;

[0037] Figure 5 is the water intake safety warning index system for graded and phased sections in Hankou;

[0038] Figure 6 is the graded and phased drought warning water levels of the Hankou section.

[0039] Figure 7This is a flowchart of a method for determining the graded and phased drought warning water levels of a river channel considering the requirements of water intake levels in an embodiment of the present invention. Detailed implementation manners

[0040] The following will describe in detail the implementation of the present invention in conjunction with the accompanying drawings, and clearly and completely describe the technical solutions in the present invention. However, they do not constitute a limitation to the present invention, but are only for illustration purposes, and at the same time, the advantages of the present invention are made clearer and easier to understand through the description.

[0041] Taking the determination of the drought warning water level of the Wuhan section of the main stream of the Yangtze River as an example, the method determined by the present invention is used for detailed description, and it is also of guiding significance for the determination of the drought warning water levels of other river channels.

[0042] In recent years, affected by the dual impacts of global climate change and human activities, drought events have occurred frequently in the Yangtze River Basin, and the contradiction between water resource supply and demand has become increasingly prominent. As an important urban agglomeration area in the middle reaches of the Yangtze River, the contradiction between water resource supply and demand in the Wuhan section is particularly prominent. On the one hand, the economy of Wuhan and its surrounding areas has developed rapidly, the population is dense, and the demand for water resources continues to grow; on the other hand, climate change has led to uneven precipitation distribution in the Yangtze River Basin, frequent drought events, and the water resource supply is facing huge pressure. Against this background, scientifically setting the drought warning water level of the Wuhan section and establishing an efficient drought warning mechanism have become key measures to cope with water resource shortage and drought risks.

[0043] Please refer to Figure 7 , an embodiment of the present invention provides a method for determining the graded and phased drought warning water levels of a river channel considering the requirements of water intake levels, including the following steps:

[0044] Step 1: Determine the control sections of the drought warning water levels of the river channel, and determine the water level control ranges of the control sections according to the control sections of the drought warning water levels of the river channel

[0045] 1. Determine the control sections of the drought warning water levels of the river channel

[0046] Hydrological stations such as Zhijiang, Shashi, Jianli, Luoshan, Hankou, Jiujiang, Anqing, Datong, and Nanjing are arranged in sequence along the main stream of the Yangtze River in the middle and lower reaches. For the distribution of water intake points and hydrological control stations between Hankou Station in the Wuhan section and Luoshan Station in the upstream Changsha-Yueyang section and Jiujiang Station in the downstream Jiujiang section, please refer to Figure 1 .

[0047] There are 67 urban water plants and 13 irrigation areas that draw water from the main stream of the Yangtze River between Luoshan Station and Jiujiang Station. The basic situations of urban water plants and irrigation areas are shown in Table 1.

[0048] Table 1 Basic situations of water intake points between Luoshan Station and Jiujiang Station on the main stream of the Yangtze River

[0049]

[0050] Calculate the proportion of the total water supply scale of water plants at each hydrological station and the proportion of the effective irrigation area. See Table 2 for details.

[0051] Table 2 Proportion of the total water supply scale of water plants at each hydrological station and proportion of the effective irrigation area

[0052]

[0053] From the proportion of the total water supply scale of water plants at each hydrological station and the proportion of the effective irrigation area, it can be seen that Hankou and Huangshigang stations exceed the average value of the proportion of the total water supply scale, and Shijitou, Hankou, and Matouzhen stations exceed the average value of the proportion of the irrigation area. The proportion of the total water supply scale and the proportion of the effective irrigation area of Hankou Station both exceed the average value. Considering the social and economic importance of Wuhan City, Hankou Station is selected as the drought warning water level control section of the Wuhan section of the Yangtze River main stream.

[0054] 2. Determine the water level control range of the control section

[0055] Analyze the correlation between the low-water levels of hydrological stations such as Luoshan, Shijitou, Huangshigang, Matouzhen, and Jiujiang and Hankou Station. The low-water levels during the dry season are selected as the water levels from September 2022 to February 2023. See Table 3 for the correlation coefficients between stations.

[0056] Table 3 Correlation between the low-water levels of Hankou Station and surrounding hydrological stations during the dry season

[0057] Hydrological station name Correlation coefficient with water level at Hankou Station Luoshan 0.8661 Shijitou 0.9361 Duoluokou 0.9378 Longwangmiao 0.9956 Huangshigang 0.9498 Matouzhen 0.8895 Jiujiang 0.8048

[0058] Determine the threshold θ to be 0.9. Select the uppermost Shijitou hydrological station with a correlation coefficient greater than the threshold of 0.9 as the starting point of the control range of the cross-section water level of the Yangtze River main stream, and the lowermost Huangshigang hydrological station with a correlation coefficient greater than the threshold of 0.9 as the end point of the control range of the cross-section water level of the Yangtze River main stream. Considering that there is a water intake at the confluence of the Han River in Wuhan City, the correlation between the low-water levels of Duoluokou and Longwangmiao stations in the lower reaches of the Han River and Hankou Station during the dry season is also analyzed. The results show that the correlation coefficient of the low-water levels during the dry season between the two is greater than the threshold of 0.9. Therefore, the water level control radiation range of Hankou Station is the Yangtze River main stream section between Shijitou and Huangshigang and the Han River main stream section below Duoluokou.

[0059] Step 2: Determine the response relationship between the water intake water level and the low-water level of the control section within the water level control range of the control section

[0060] 1. Extract the water surface slope between hydrological stations at different flow levels of the control section

[0061] Taking Shijitou to Huangshigang and Duoluokou to Hankou as the calculation scope, a one-dimensional hydrodynamic model is established. The water level and flow data of each hydrological station during the dry seasons (December to February) from 2011 to 2020 and the water level and flow data of each hydrological station from September 2022 to February 2023 are used for model verification and calibration. Combining with the one-dimensional hydrodynamic model, the water surface profiles between the hydrological stations from Shijitou to Huangshigang and between Duoluokou and Hankou at different flow levels are sorted out. Among them, the flow at Duoluokou is set at the low dry season flow of 600 m 3 / s. During the calculation, the water level elevations of Shijitou, Hankou, Huangshigang, Duoluokou, and Longwangmiao stations are unified as the Huanghai elevation.

[0062] From the water surface profiles within the control range of the control section at different flow levels, the water surface slope between each hydrological station within its control range at different flow levels is deduced. See Table 4 for details.

[0063] Table 4 Water surface slopes of each hydrological station within the control range of Hankou Station at different flow levels

[0064] Discharge Shijitou - Hankou Hankou - Huangshigang Duoluokou - Longwangmiao Longwangmiao - Hankou 8500 0.027 0.022 2.413 0.296 9000 0.026 0.023 2.451 0.167 9500 0.026 0.022 2.490 0.204 10000 0.027 0.022 2.345 0.130 11000 0.025 0.021 2.267 0.130 12000 0.023 0.023 2.296 0.259 13000 0.024 0.024 2.248 0.278

[0065] 2. Determine the water level response relationship between the water intake and the control section during the dry season

[0066] According to the locations of the water intake points of water plants and irrigation areas along the water level control radiation range of Hankou Station, sort out the distances between the water intake points within the control radiation range and the nearest hydrological stations and between each hydrological station. If the water intake is upstream of the control section, measure the distance from the water intake to the nearest hydrological station downstream; if it is downstream of the control section, measure the distance from the water intake to the upstream hydrological station. Based on the water surface slope between the upstream and downstream hydrological stations of the water intake and the water surface slope relationship between hydrological stations (Equation 1), establish the water level response relationship between the water intake levels of water plants and irrigation areas within the control range and the control section.

[0067]

[0068] Among them, Z q is the water surface level at the water intake at the q flow of the control section, m; Z kq is the water level at the q flow of the control section, m, which can be calculated through the cross-section water level and flow relationship; λ iq is the water surface slope between the i-th hydrological station and the (i + 1)-th hydrological station from the water intake to the control section (including the control section) at the q flow of the control section, m / km, and the water surface slope is interpolated from Table 3; L i is the distance between the i-th hydrological station and the (i + 1)-th hydrological station from the water intake to the control section (including the control section), km; λ q is the water surface slope of the river section between the two hydrological stations to which the water intake belongs at the q flow of the control section; when the water intake is downstream of the control section, L qL is the distance from the water intake to the nearest upstream hydrological station. When the water intake is located upstream of the control section, L q is the distance from the water intake to the nearest downstream hydrological station, in m.

[0069] Step 3: Determine the water intake safety warning indicators for different levels and periods of the control section according to the response relationship between the water intake level of the water intake within the water level control range of the control section and the low water period level of the control section

[0070] 1. Sort out the characteristics of water use demand within the control range

[0071] Within the control range of the Hankou section, the urban water plants mainly supply water to the surrounding towns. The water supply process is relatively stable throughout the year. There are many water supply sources in the 6 irrigation areas within the control range, and the planting structures are different, mainly rice. The water intake methods are all pumping by pumping stations. According to the proportion of the water supply source in the main stream of the Yangtze River in the total water supply sources of the irrigation area, combined with the irrigation systems of early rice, middle rice, late rice, and vegetables, the irrigation areas with the main stream of the Yangtze River as the water supply source and the 75% irrigation water demand of each irrigation area are calculated. See Tables 5 and 6 for details.

[0072] Table 5 Irrigation areas in ten thousand mu with the main stream of the Yangtze River as the water supply source within the control range of the Hankou section

[0073] Irrigation area name Early rice Middle rice Late rice Vegetables Sanhu Lianjiang Irrigation Area 0.00006 5 0.75 0 Dengjiakou Irrigation Area 0 0 0 0 Shangdongchengwan Irrigation Area 0 0 0 0 Shamao Irrigation Area 0 0 0 0 Yelu Irrigation Area 0.036 0.044 0.056 0.304 Yuwang Irrigation Area 0.032 0.04 0.06 0.4356 Subtotal 0.06806 5.084 0.866 0.7396

[0074] Table 6 Irrigation water demand process in ten thousand m with the main stream of the Yangtze River as the water supply source within the control range of the Hankou section 3

[0075] Frequency 4 5 6 7 8 9 10 11 12 1 2 3 Total 50％ 21 582 299 1085 1272 121 27 13 5 0 0 9 3434 75％ 36 838 185 1141 1574 225 62 12 12 0 15 12 4101

[0076] The irrigation water demand process with the main stream of the Yangtze River as the water supply source within the control range of the Hankou section shows that the water demand is mainly concentrated from April to October during the rice planting period, accounting for 99% of the annual water demand. The water use is less from January to February and from November to December, and the water use object is vegetables.

[0077] 2. Establish the mapping relationship between the urban water supply guarantee ratio, the proportion of the drought-affected area in the irrigation area, and the water level of the control section

[0078] According to the response relationship between the water intake and the water level of the Hankou section, combined with the relationship between the water intake head and the water intake volume of the water intake pump station of the water user and the minimum water intake level requirement, analyze the daily maximum water intake volume of each water user at different water levels of the Hankou section. Combining the characteristics of the water demand cycle and the characteristics of water demand classification, establish the mapping relationship between the urban water supply guarantee ratio, the proportion of the drought-affected area in the irrigation area, and the water level (flow) of the control section at different time periods. See Figure 3 、 Figure 4 , where the proportion of the drought-affected area in the irrigation area is the ratio of the monthly water intake volume to the monthly water demand volume.

[0079] 3. Determine the water intake safety warning indicators for different levels and periods

[0080] Based on the proportion of urban water supply guarantee and the proportion of drought - affected area in irrigation districts, it is graded, and based on the characteristics of the water intake cycle, it is divided into periods to determine the water intake safety early - warning index system for the Hankou section by grading and staging. Among them, the grading standards for the proportion of urban water supply guarantee and the proportion of drought - affected area in irrigation districts are determined according to the requirements when the urban water supply is lower than the normal demand and the area of drought - affected crops in the region is in light drought, moderate drought, severe drought, and extreme drought in the "National Flood Control and Drought Relief Emergency Plan" (January 10, 2006, State Council), as shown in Table 7.

[0081] Table 7 Drought grading standards

[0082] Drought warning level Mild drought Moderate drought Severe drought Extreme drought Proportion of urban water supply guarantee 95％ 90％ 80％ 70％ Proportion of drought - affected area in irrigation area 20％ 30％ 50％ 80％

[0083] The water intake safety early - warning index system for the Hankou section by grading and staging is shown in Figure 5 .

[0084] Step 4: Determine the drought warning water levels for the control section by grading and staging according to the water intake safety early - warning index of the control section by grading and staging

[0085] 1. Determine the water demand for shipping and ecological use at the control section in the river

[0086] Combined with the existing achievement reports, the lowest navigable water level at Hankou Station is 12.86 m, and the ecological flow is 7170 m 3 / s. According to the water level - discharge relationship, the water level corresponding to the ecological flow is 12 m, which is lower than the lowest navigable water level. When taking the envelope line later, the ecological flow requirements can be ignored.

[0087] 2. Determine the drought warning water levels for grading and staging

[0088] On the basis of constructing the water intake safety early - warning index system, combined with the lowest navigable operating water level and ecological water level requirements of the Hankou section, considering a safety threshold of 0.1 m, the envelope line method is used to determine the drought warning water levels for the Hankou section by grading and staging to meet different water use requirements, as shown in Figure 6 .

[0089] To sum up, compared with the conventional method for determining drought warning water levels, the method for determining drought warning water levels by grading and staging determined in the present invention can reflect the water supply guarantee situations of urban water plants and irrigation districts under different drought grades, facilitate the water administrative department to make precise response measures in a timely manner, and at the same time is beneficial for water users with higher water intake level requirements to propose plans for upgrading and transforming water intake ports.

[0090] As described above, it is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A method for determining the drought warning water level in stages and phases for a river channel considering the requirements of water intake water levels, characterized in that The following steps: Step 1: Determine the control section of the low-flow warning water level of the river course, and determine the water level control range of the control section according to the control section of the low-flow warning water level of the river course; Step 2: Determine the response relationship between the water intake level of the water intake and the low-flow period water level of the control section within the water level control range of the control section; Step 3: Determine the water intake safety warning indicators for different levels and periods of the control section according to the response relationship between the water intake level of the water intake and the low-flow period water level of the control section within the water level control range of the control section; Step 4: Determine the low-flow warning water levels for different levels and periods of the control section according to the water intake safety warning indicators for different levels and periods of the control section.

2. The method for determining the dry warning water level for river channel grading and staging considering the requirements of water intake levels as described in claim 1, characterized in that: Step 1 specifically includes: Step 1.1: Determine the control section of the low-flow warning water level of the river course: Sort out the distribution of the main hydrological stations of the river course and the water intakes outside the river course, calculate the proportion of the total water supply scale of each hydrological station to the water plant and the proportion of the effective irrigation area, and select the main control hydrological stations of the river course according to the principle that the proportion of the total water supply scale and the proportion of the effective irrigation area are greater than the average level. Combine the distance between the main control hydrological stations and the importance of the cities where they are located to comprehensively determine the control section of the low-flow warning water level of the river course; Step 1.2: Determine the water level control range of the control section: Calculate the correlation relationship between the water levels of the control section and the surrounding hydrological stations during the low-flow period, select the most upstream hydrological station with a correlation coefficient greater than the threshold θ as the starting point of the water level control range of the control section, and the most downstream hydrological station with a correlation coefficient greater than the threshold θ as the end point of the water level control range of the control section.

3. The method for determining the dry warning water level of river classification and staging considering the requirements of water intake water level as described in claim 2, characterized in that: The calculation formulas for the proportion of the total water supply scale of each hydrological station to the water plant and the proportion of the effective irrigation area in Step 1.1 are as follows: where G i+1 is the proportion of the water supply scale of the waterworks at the (i + 1)-th hydrological station; W i is the total water supply scale of the waterworks that withdraw water from the river section between the i-th hydrological station and the (i + 1)-th hydrological station; S i+1 is the proportion of the effective irrigation area at the (i + 1)-th hydrological station; A i is the effective irrigation area of the irrigation district that withdraws water from the river section between the i-th hydrological station and the (i + 1)-th hydrological station.

4. The method for determining the dry warning water level in graded and phased river channels considering the requirements of water intake levels as described in claim 1, characterized in that: Step 2 specifically includes: Step 2.1: Extract the water surface slope between hydrological stations at different flow levels of the control section: According to the historical low-flow period hydrological data of each hydrological station, combined with the one-dimensional hydrodynamic model, construct the water surface profile at different flow levels within the control range, and combine the distance between adjacent hydrological stations to deduce the water surface slope between each hydrological station at different flow levels. Step 2.2: Determine the response relationship between the water intake level of the water intake and the low-flow period water level of the control section: According to the positions of the water intakes outside the river course of the water plants and irrigation areas along the control radiation range of the control section, measure the distance from the water intake to the hydrological station closest to the control section in the direction of the control section. According to the water surface slope between the upstream and downstream hydrological stations of the river section where the water intake is located and the water surface slope between each hydrological station between the water intake and the control section, and then combine the distance from the water intake to the hydrological station closest to the control section in the direction of the control section and the distance between hydrological stations to establish the response relationship between the water intake level of the water intake and the low-flow period water level of the control section within the water level control range of the control section.

5. The method for determining the drought warning water level for river classification and staging considering the requirements of water intake water levels as described in claim 4, wherein: The response relationship between the water intake level of the water intake and the low-flow period water level of the control section within the water level control range of the control section in Step 2.2 is established according to Equation (2): Where, Z q is the water surface level at the water intake under the flow rate q of the control section, m; Z kq is the water level under the flow rate q of the control section, m, which can be calculated through the water level - discharge relationship of the section; λ iq is the water surface slope between the i-th hydrological station and the (i + 1)-th hydrological station from the water intake to the control section under the flow rate q of the control section, m / km; L i is the distance between the i-th hydrological station and the (i + 1)-th hydrological station from the water intake to the control section, km; λ q is the water surface slope of the river reach between the two hydrological stations to which the water intake belongs under the flow rate q of the control section; when the water intake is downstream of the control section, L q is the distance from the water intake to the nearest upstream hydrological station, and when the water intake is upstream of the control section, L q is the distance from the water intake to the nearest downstream hydrological station.

6. The method for determining the drought warning water level in graded and phased river channels considering the water intake water level requirements as described in claim 1, characterized in that: Step 3 specifically includes: Step 3.1: Sort out the characteristics of water use demand within the control range: Sort out the characteristics of the crops planted in the irrigation area, query the crop irrigation system, and calculate the total water supply scale of the water plants and the total water demand of the irrigation area for each month of the year within the section control range; Step 3.2: Establish the mapping relationship among the urban water supply security ratio, the proportion of drought-affected area in the irrigation district, and the water level at the control section: According to the response relationship between the water intake level at the water intake and the water level at the control section, combined with the minimum water intake level requirements of water users and the water intake characteristics of water intake facilities, analyze the maximum daily water intake of each water user at different water levels of the control section. Combining the characteristics of the water demand cycle and the characteristics of water demand classification, establish the mapping relationship among the urban water supply security ratio, the proportion of drought-affected area in the irrigation district at different time periods, and the water level at the control section, where the urban water supply security ratio is the ratio of the total daily water intake of the water plant to the total water supply scale, and the proportion of drought-affected area in the irrigation district is the ratio of the total monthly water intake to the total monthly water demand. Step 3.3: Determine the water intake safety warning indicators for different levels and periods: Classify based on the water intake satisfaction level and divide into periods based on the characteristics of the water intake cycle. The water intake satisfaction level is expressed by the urban water supply security ratio and the proportion of drought-affected area in the irrigation district. Combining the mapping relationship among the urban water supply security ratio, the proportion of drought-affected area in the irrigation district at different time periods, and the water level at the control section and the classification criteria, determine the water intake safety warning indicators for different levels and periods of the control section.

7. A method for determining the drought warning water level in stages and phases for a river channel considering the requirements of water intake water levels, characterized in that: The classification criteria corresponding to the urban water supply security ratio and the proportion of drought-affected area in the irrigation district in Step 3.3 are determined according to the water intake requirements of the region, or adopt the requirements in the "National Flood Control and Drought Relief Emergency Plan" (January 10, 2006, State Council) for urban water supply and the drought-affected area of regional crops in case of mild drought, moderate drought, severe drought, and extreme drought: The urban water supply security ratio corresponding to mild drought is 90% - 95%, corresponding to moderate drought between 80% - 90%, corresponding to severe drought between 70% - 80%, and less than 70% corresponding to extreme drought; the proportion of drought-affected area in the irrigation district corresponding to mild drought is below 30%, corresponding to moderate drought between 31% - 50%, corresponding to severe drought between 51% - 80%, and more than 80% corresponding to extreme drought.

8. The method for determining the drought warning water level in stages and phases for a river course considering the water intake water level requirement as described in claim 1, wherein: Step Four specifically includes: Step 4.1: Determine the shipping and ecological water demand at the control section in the river: Combining the approved results, sort out the shipping and ecological water requirements at the control section, and determine the lowest navigable water level and ecological water level according to the relationship between the water level and flow at the control section; if there are no approved results, calculate the lowest navigable water level and ecological water level according to the "Standard for Inland Waterway Navigation" (GB 50139 - 2014) and the "Calculation Specification for Ecological Water Requirements of Rivers and Lakes" (SL / Z 712 - 2014). Step 4.2: Determine the drought warning water levels for different levels and periods: Compare the water intake safety warning indicators for different levels and periods of the control section, the lowest navigable water level, and the ecological water level, and take the envelope line to determine the drought warning water levels for different levels and periods of the control section.

9. The method for determining the drought warning water level for river channel classification and staging considering the requirements of water intake water level as claimed in claim 8, wherein: In Step 4.2, the envelope line is taken to determine the drought warning water levels for different levels and periods of the control section, as shown in Equation (3): Z i,j = max(Zy i , Zg i,j , Zh, Ze)+θ, i = 1..n, j = 1..m (3) where Z i,j is the drought warning water level of the j-th period of the i-th level, with the unit of m; Zy i is the water intake safety level for urban water supply of the i-th level, with the unit of m; Zg i,j is the water intake safety level for irrigation water use of the j-th period of the i-th level, with the unit of m; Zh is the lowest navigable water level, with the unit of m; Ze is the ecological water level, with the unit of m; θ is the safety threshold, with the unit of m, and is determined comprehensively considering the river characteristics and the response time of drought resistance emergency measures.

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