Method for calculating water intake guarantee rate of downstream nuclear power user of multi-gate dam river

Abstract

This invention discloses a method for calculating the water intake guarantee rate for downstream nuclear power users in multi-dam rivers. The method includes the following steps: Step 1, determining the water conveyance section, dam distribution, and initial storage capacity of the multi-dam river; Step 2, constructing a distributed water cycle model to obtain the dynamic flow process of the sub-basin; Step 3, considering upstream inflow and external water conveyance processes, calculating the outflow from the water conveyance point; Step 4, calculating the storage capacity and outflow of each dam unit in stages from upstream to downstream of the water conveyance section; Step 5, clarifying the water intake guarantee rate requirements for downstream nuclear power users, calculating the water demand and available water volume; Step 6: Based on long-series calculation results, providing the water intake guarantee rate for nuclear power users. This invention achieves the organic integration of the distributed water cycle model with water conservancy project scheduling and human water intake and drainage processes, quantifying the water intake guarantee rate, and providing technical support for the ecological protection and water resource development and utilization management of multi-dam rivers.

Description

Technical Field

[0001] This invention belongs to the field of hydrology and water resource utilization technology, and in particular relates to a method for calculating the water intake guarantee rate for nuclear power users downstream of multi-dam rivers. Background Technology

[0002] Constructing dams and gates (such as flat gates, hydraulic lifting gates, and rubber dams) on rivers is an important way for humans to develop and utilize water resources. For a long time, people have used dam and gate systems to regulate river flow, achieving comprehensive services such as flood control, water supply, irrigation, power generation, and navigation. Utilizing the natural channels of rivers to deliver water to downstream users does not occupy land resources, requires no additional large-scale infrastructure (such as water supply pipelines), significantly reduces construction investment and operating costs, and improves conditions for hydropower generation, navigation, and agricultural irrigation at dam and gate hydroelectric power stations. It also helps maintain the river ecosystem along the river, resulting in significant socio-economic benefits.

[0003] Due to the obstruction caused by dam projects, water supply to downstream users in rivers with multiple dams is significantly influenced by a variety of complex factors, including river flow patterns, water supply scale, dam scheduling, evaporation and leakage, and human activities such as water intake and drainage. If a downstream water user is a nuclear power plant, its production process involves generating heat through nuclear fission. This heat must be continuously removed through cooling water to maintain the normal operation and safety of the reactor. If cooling is interrupted, the reactor may run out of control due to the inability to dissipate heat, leading to a serious safety accident. Therefore, downstream nuclear power users are characterized by large demand for production water (cooling water) and the inability to interrupt water supply. Scientifically calculating the water intake guarantee rate for downstream nuclear power users in rivers with multiple dams is of great significance for water resource management. Currently, when using rivers with multiple dams for water supply, the water intake guarantee rate for downstream water users is mostly based on hydrological analysis, which does not fully reflect the dam scheduling process and human activity decisions. Therefore, how to scientifically and efficiently calculate the water intake guarantee rate for downstream nuclear power users in rivers with multiple dams is a pressing technical problem that needs to be solved in this field. Summary of the Invention

[0004] The purpose of this invention is to provide a method for calculating the water intake guarantee rate for nuclear power users downstream of multi-dam rivers, so as to solve the above-mentioned technical problems.

[0005] To achieve the above objectives, the present invention provides the following technical solution: The present invention discloses a method for calculating the water intake guarantee rate for nuclear power users downstream of multi-dam rivers, the method comprising the following steps:

[0006] Step 1: Determine the water conveyance section, dam distribution, and initial storage capacity of the river with multiple dams: Based on the planning or design scheme of the water conveyance project in the basin or region where the river with multiple dams is located, identify the location of the upstream water conveyance point and the location of the downstream water users, and determine the scope of the water conveyance section of the river with multiple dams; then, based on the relevant basin planning and water conservancy project data, determine the number, spatial distribution, and characteristic parameters of the dams in the water conveyance section; and determine the initial storage capacity of each dam.

[0007] Step 2: Construct a distributed water cycle model to obtain the dynamic flow process of sub-basins: Construct a distributed water cycle model for the basin where the river with multiple dams is located, and then use the constructed distributed water cycle model to calculate the daily dynamic flow process of all sub-basins in the basin where the river with multiple dams is located.

[0008] Step 3: Considering the upstream inflow and external water transfer processes, calculate the outflow at the water transfer point: Perform spatial overlay analysis of the water transfer section and sub-basins to identify the sub-basins corresponding to the upstream of the water transfer point in the water transfer section; Based on the simulation results of the distributed water cycle model, read the flow processes of each sub-basin upstream of the water transfer point and summarize them as the upstream inflow; Combined with the basic needs of downstream water users of the multi-dam river, and based on the planning and related design schemes of the external water source project, determine the external water transfer volume corresponding to the water transfer point; Ignoring water mixing losses, take the sum of the upstream inflow and the external water transfer volume as the outflow at the water transfer point of the multi-dam river section, calculated using the following formula:

[0009] (1)

[0010] In the formula, Let m be the outflow rate at the water conveyance point of the water conveyance section at time t. 3 ; The upstream inflow of water to the water transfer point at time t in the i-th sub-basin is obtained by reading the calculation results from the distributed water cycle model, m. 3 ; The number of upstream sub-basins corresponding to the water transfer point; Let m be the external water transfer volume corresponding to the water transfer point at time t. 3 ;

[0011] Step 4: From upstream to downstream of the water conveyance section, calculate the storage and outflow of each dam unit in stages: First, determine the number and scope of dam units in the water conveyance section; then, perform spatial overlay analysis on each dam unit and all sub-basins of the watershed to identify the sub-basins corresponding to each dam unit in the water conveyance section, read the calculation results of the distributed water cycle model, and summarize the calculation as the interval inflow of the dam unit; based on the calculated outflow of the upstream water conveyance point, combined with the interval inflow, considering the water loss due to evaporation, seepage, and human activities, and combined with the dam scheduling water level restrictions and downstream ecological flow indicators, calculate the storage and outflow at different times. The specific calculation formula is as follows:

[0012] (2)

[0013] (3)

[0014] (4)

[0015] (5)

[0016] In the formula, Let m be the inflow of the j-th dam unit at time t. If j=1, it is the outflow from the water conveyance point; if j>1, it is the outflow from the upstream dam unit. 3 j=1,2,3…J+1, where J is the number of dam units in the water conveyance section; Let m be the interval inflow of the j-th dam unit at time t, derived from the calculation results of the distributed water cycle model. 3 ; and The net evaporation and seepage of the j-th dam unit at time t are respectively, m 3 ; Let m be the water consumption during human activities in the j-th dam unit at time t. 3 ; For the ecological flow index requirement of the j-th dam unit at time t, m 3 ; Let m be the water storage capacity of the j-th dam unit at time t. 3 ; and The actual water storage capacity of the j-th dam unit at time t and time t-1 are respectively, m 3 When t=1, This refers to the initial water storage volume in step 1; Let be the restricted water storage capacity of the j-th dam unit at time t. The limiting water level of the j-th dam unit at time t; The function is the water level-reservoir capacity curve for the j-th dam unit; Let m be the outflow of the j-th dam unit at time t. 3 ;

[0017] Step 5: Clarify the water availability guarantee rate requirements for downstream nuclear power users and calculate the water demand and available water volume: First, clarify the water availability guarantee rate requirements for downstream nuclear power users. The water availability guarantee rate represents the probability that the water demand can be met in terms of available time. Then, based on the characteristics of the downstream nuclear power users' living and production activities, calculate the water demand using the following formula:

[0018] (twenty three)

[0019] In the formula, Let m be the water demand of the nuclear power user at time t. 3 ; , , , These represent the water demand at time t, including the water supply to the cooling tower, the water supply to the plant's water system, the water supply for desalination, the water supply for industrial and domestic use, and the water demand due to unforeseen circumstances and leakage, m. 3 ;

[0020] Then, based on the location characteristics of the downstream nuclear power user's water intake project and the outflow of the dam unit where the water intake is located, the available water volume is determined and divided into two types:

[0021] a) When a nuclear power user draws water from the last dam unit of the water conveyance section, the amount of water that can be drawn is less than the water intake capacity limit and the outflow of that dam unit; the specific calculation formula is as follows:

[0022] (twenty four)

[0023] In the formula, Let m be the amount of water available to downstream nuclear power users at time t. 3 ; For the water intake capacity limitation of downstream nuclear power users at time t, m 3 If there are no restrictions =∞; Let m be the outflow rate of the dam unit where the upstream water intake of the nuclear power user is located at time t. 3 ;

[0024] b) When a nuclear power user takes water downstream of the last dam in the water conveyance section, the amount of water the nuclear power user can take is less than the water intake capacity limit and the outflow of the dam unit minus the downstream discharge requirement. The specific calculation formula is as follows:

[0025] (25)

[0026] In the formula, Let m be the downstream water intake flow requirement of the nuclear power user at time t. 3 ;

[0027] According to the relevant technical specifications and industry standards for hydrology of nuclear power plant projects, the data for calculating the water intake guarantee rate of downstream nuclear power users is a long series of data, with a data length of more than 30 years; based on the above steps 2 to 5, the daily water intake of nuclear power users in the long series is calculated until the requirement of the number of years for the long series calculation is met;

[0028] Step 6: Based on the long-term calculation results, give the water availability guarantee rate for nuclear power users: Based on the calculation results of the daily available water volume for nuclear power users obtained in the above steps, and taking into account the continuity and reliability requirements of water use for nuclear power users, when the available water volume in a certain year cannot meet the water demand for any one day, it is determined that the water demand for that year is not met. The water availability guarantee rate is calculated according to this criterion. The specific calculation formula is as follows:

[0029] (26)

[0030] In the formula, The water intake guarantee rate for downstream nuclear power users is %; Y is the number of years calculated from long-series data; ty represents the year number, ty=1,2,3……Y; The starting date of year ty; This is the end date of year ty.

[0031] Furthermore, the determination of the scope of the multi-dam river water conveyance section in step 1 is as follows: if both the water conveyance point and the water intake point are located on the main stream of the river, then the water conveyance section is located on the main stream of the river; if the water conveyance point is located on a tributary and the water intake point is located on the main stream of the river, then the water conveyance section is located on both the main stream and the tributary.

[0032] The characteristic parameters of the sluice gates and dams in the water conveyance section specifically include the water level-area curve, which is the functional relationship between the reservoir water level and its corresponding water storage area; the water level-storage capacity curve, which is the functional relationship between the reservoir water level and its corresponding water storage volume; the sluice gate and dam scheduling restriction water level and ecological flow release index requirements for different periods, including flood season and non-flood season.

[0033] The specific process for determining the initial water storage of each dam is as follows: if there is observation data for a long series of dams, the actual water storage of the reservoir in the starting year of the long series calculation is directly taken as the initial value; if there is a lack of observation data for a long series of dams, the water storage corresponding to the dead storage level is used as the initial value; the long series refers to data data of more than 30 years.

[0034] Furthermore, the construction of the distributed water cycle model described in step 2 specifically includes the following steps:

[0035] 1) Conduct multi-source data collection and processing: This includes collecting and processing data on river systems, meteorology and hydrology, land use, topography, soil geology, vegetation cover, water conservancy and soil conservation projects, and human activities involving drainage.

[0036] 2) Spatial Discretization and Unit Division: Based on high-resolution DEM data, spatial discretization is performed using spatial analysis methods to divide the data into regular grids, hydrological response units, or sub-basins. Sub-basins are preferred, and in actual simulations, they are further subdivided according to contour zones to reflect the influence of topography on precipitation, evapotranspiration, and runoff. The sub-basin division process includes steps such as depression filling, water flow direction determination, runoff accumulation calculation, threshold determination and river network vector generation, and sub-basin catchment area extraction.

[0037] 3) Conduct modular calculations of the water cycle: including precipitation interception and evapotranspiration, infiltration and soil movement, runoff generation, runoff confluence and human activities such as water intake and drainage, as well as special processes;

[0038] 4) Conduct parameter calibration and model validation: Based on historical measured data from hydrological stations along the water conveyance section, identify soil hydrological parameters, runoff parameters, and confluence parameters in the model; calculate the Nash coefficient by comparing the simulated and measured values ​​of the model, requiring a calibration period of not less than 0.6 and a validation period of not less than 0.5 to validate the reliability of the distributed water cycle model.

[0039] Furthermore, the calculation process for the net evaporation and seepage of each dam unit in step 4 is as follows:

[0040] 1) Dam Collapse Period: During this period, each dam unit is a river section and possesses the basic characteristics of a river. Therefore, evaporation and seepage calculations are performed according to the principles of river management.

[0041] (6)

[0042] (7)

[0043] In the formula, Let m be the water surface area of ​​the j-th dam unit at time t. 2 ; , where is the water surface evaporation pan observation value at the meteorological station near the j-th dam unit at time t, in mm; Ke is the evaporation conversion factor, with a value of 0.7~0.8; Let be the rainfall intensity (in mm) of the j-th dam unit at time t; The river length of the j-th dam unit, in meters; Let be the width of the river surface in the j-th dam unit, in meters. Under specific inflow conditions, the width of the river surface is affected by various factors such as river cross-sectional parameters, topography, and slope. Based on the remote sensing monitoring results, the average width of the river is used for simplified calculation.

[0044] River seepage is the amount of water lost from the riverbed to the soil during river flow. It is calculated using an empirical formula:

[0045] (8)

[0046] In the formula, Let be the seepage coefficient of the river section of the j-th dam unit. It is dimensionless and determined based on the actual survey data of the river. For cohesive soil riverbeds, it is 0.01~0.05, and for sandy soil, it is 0.1~0.3. Using flow conversion units, the inflow of the j-th gate / dam unit at time t is converted into m. 3 / s, with a time step of day and hour, then this coefficient is equal to 1 / 86400;

[0047] 2) Dam Operation Period: During this period, in addition to the dam-reservoir section in the river channel, each dam unit also has a river section of a specific length. Quantitatively identifying the lengths of the reservoir section and the river section is fundamental. The specific calculation formula is as follows:

[0048] (9)

[0049] (10)

[0050] (11)

[0051] (12)

[0052] (13)

[0053] (14)

[0054] (15)

[0055] In the formula, and , respectively, represent the lengths of the river section and the reservoir section of the j-th dam unit, in meters; and The net evaporation of the river section and reservoir section of the j-th dam unit at time t, respectively, is m. 3 ; and These represent the water surface areas (m) of the river segment and reservoir segment of the j-th dam unit at time t. 2 ; The function () is the water storage-area curve of the reservoir section of the j-th dam unit, which is determined based on the engineering design data; and Let be the average width of the water surface of the river section and the reservoir section of the j-th dam unit, respectively, in meters. Based on the remote sensing monitoring results, the average width of the river section and the dam end is used for simplified calculation.

[0056] The seepage volume in this river section during this period refers to the water loss caused by the riverbed seeping into the soil during the flow of river water. It is calculated using an empirical formula, as follows:

[0057] (16)

[0058] (17)

[0059] (18)

[0060] In the formula, Let be the seepage coefficient of the river section in the j-th dam unit. It is dimensionless and determined based on the actual survey data of the river section. For cohesive soil riverbed, it is 0.01~0.05, and for sandy soil, it is 0.1~0.3. and Let m represent the seepage amounts in the river section and reservoir section of the j-th dam unit, respectively. 3 ; Let be the seepage coefficient of the j-th dam unit reservoir section. It is dimensionless and is determined based on the geological, soil, and seepage prevention characteristics of the dam area, ranging from 1% to 5%.

[0061] Furthermore, the water consumption during human activities in each dam unit in step 4 includes water consumption for agricultural irrigation, domestic use, industry, and ecological users. The calculation formula is as follows:

[0062] (19)

[0063] In the formula, , , and These represent the water withdrawals for agricultural irrigation, domestic, industrial, and ecological users in the j-th dam unit, respectively, in m. 3 ; , , and These are the proportionality coefficients of drainage or return water from agricultural irrigation, domestic, industrial, and ecological water users in the j-th dam unit, respectively, and are dimensionless.

[0064] If a water user draws water from the j-th dam unit and then returns the water to the (j+1)-th and (j+2)-th dam units, then the water in the j-th dam unit will be... , , and Set to zero, and then return the water to the (j+1)th or (j+2)th dam unit's water balance; if a water user takes water from the jth dam unit and returns the water to the (j+1)th dam unit after use, the calculation formula is as follows:

[0065] (20)

[0066] (twenty one)

[0067] In the formula, Let m be the water consumption during human activities in the (j+1)th dam unit at time t. 3 .

[0068] Furthermore, in step 4, the ecological flow index requirements for each dam unit are quantified based on relevant technical standards, specifications, or guidelines, combined with the life process requirements of downstream ecological protection targets, using hydrological methods, hydrodynamic methods, habitat simulation methods, and holistic analysis methods. If the local water management department has determined the minimum ecological flow for the dam, the larger of the two values ​​is taken as the ecological flow index requirement for that dam unit, as detailed below:

[0069] (twenty two)

[0070] In the formula, The minimum downstream ecological flow rate determined by the water management department for the j-th dam unit at time t; The outflow ecological flow is calculated for the j-th gate / dam unit at time t.

[0071] Furthermore, the specific requirements for the water supply guarantee rate of downstream nuclear power users mentioned in step 5 are as follows: based on the continuity requirements of water use in the nuclear power production process, the minimum time step for the water supply guarantee rate is calculated in days, and the water supply guarantee rate of downstream nuclear power users is required to reach 97%.

[0072] The beneficial effects of this invention are as follows: The method described in this invention, from the perspective of the watershed, incorporates a distributed water cycle model, which can effectively characterize the inflow process, evaporation, seepage, dam regulation, human access and drainage processes in multi-dam rivers, as well as the water demand and availability of downstream nuclear power users. It dynamically extrapolates and calculates the inflow, water transport, regulation, and water intake processes of the watershed. This invention achieves the organic integration of the distributed water cycle model with water conservancy project scheduling and human access and drainage processes. It considers both the natural watershed water cycle processes such as runoff generation, confluence, evaporation, and seepage, and the social impact of water conservancy project scheduling and human water use activities on the river's water volume process. Furthermore, it quantitatively calculates the water intake guarantee rate by combining the water intake capacity and demand requirements of downstream nuclear power users, providing technical support for the ecological protection and water resource development and utilization management of multi-dam rivers.

[0073] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0074] Figure 1 This is a flowchart of the method described in this invention;

[0075] Figure 2 This is a map showing the water conveyance section of the river with multiple dams and the distribution of its dams in Example 1;

[0076] Figure 3 This is a diagram showing the correspondence between the water conveyance river section and the sub-basin in Example 1;

[0077] Figure 4 This is a water storage-area curve of the reservoir section of the dam A in Example 1;

[0078] Figure 5 This is a schematic diagram of the monthly water demand calculation results for downstream nuclear power users in Example 1;

[0079] Figure 6 This is a schematic diagram showing a long-term daily comparison of the available water and water demand of downstream nuclear power users in Example 1. Detailed Implementation

[0080] This invention discloses a method for calculating the water intake guarantee rate for nuclear power users downstream of multi-dam rivers, such as... Figure 1 As shown, the method includes the following steps:

[0081] Step 1: Determine the water conveyance section, dam distribution, and initial water storage capacity of the multi-dam river.

[0082] 1) Determine the water conveyance section. Based on the planning or design scheme of the water conveyance project in the basin or region where the multi-dam river is located, identify the location of the upstream water conveyance point and the location of the downstream water users, and determine the main scope of the multi-dam river water conveyance section; if both the water conveyance point and the water intake point are located on the main stream of the river, then the water conveyance section is located on the main stream of the river; if the water conveyance point is located on a tributary and the water intake point is located on the main stream, then the water conveyance section is located on both the main stream and the tributary.

[0083] 2) Determine the spatial distribution and characteristic parameters of each dam. Based on the determined water conveyance section, and according to relevant basin planning, water conservancy project feasibility studies, design, or construction data, determine the number and spatial distribution of the main dams in the water conveyance section. Based on the engineering design data of the dams in the water conveyance section, determine the basic characteristics of each dam, specifically including the water level-area curve (the functional relationship between reservoir water level and its corresponding water storage area), the water level-storage capacity curve (the functional relationship between reservoir water level and its corresponding water storage volume), the dam scheduling restriction water level at different times (including flood season and non-flood season), and the ecological flow release index requirements, etc.

[0084] 3) Determine the initial water storage capacity of each sluice gate and dam. If there is observation data for a long series of sluice gates and dams (e.g., measured data over 30 years), the actual water storage capacity of the reservoir in the starting year of the long series calculation (e.g., the initial water storage capacity) can be directly used as the initial value. If observation data for a long series of sluice gates and dams is lacking, the water storage capacity corresponding to the dead storage level can be used as the initial value to verify the reliability of water intake under drought conditions.

[0085] Step 2: Construct a distributed water cycle model to obtain the dynamic flow process of the sub-basin.

[0086] A distributed water cycle model is constructed for a river basin with multiple dams, integrating the comprehensive impacts of river systems, meteorology and hydrology, land use, topography, soil geology, vegetation cover, water conservancy and soil conservation projects, and human activities such as water intake and drainage on the water cycle. The model meticulously simulates natural and social water cycle processes, including evaporation, infiltration, surface runoff, interflow, and human activities, to reflect the spatial heterogeneity and physical driving mechanisms of the water cycle. Representative distributed water cycle models include WEP-L, VIC, SWAT, and TOPMODEL.

[0087] The main steps in constructing a distributed water cycle model are as follows:

[0088] 1) Conduct multi-source data collection and processing: This includes collecting and processing basic data related to river systems, meteorology and hydrology, land use, topography, soil geology, vegetation cover, water conservancy and soil conservation projects, and human activities such as water intake and drainage.

[0089] 2) Spatial Discretization and Unit Division: Based on high-resolution DEM data (such as 10m, 30m, etc.), spatial discretization is performed using spatial analysis techniques. This can result in regular grids, hydrological response units (HRUs), or sub-basins. Sub-basins are preferred. In actual simulations, sub-basins can be further subdivided by contour zones to reflect the influence of topography on precipitation, evapotranspiration, and runoff. The sub-basin division process typically includes steps such as depression filling, flow direction determination, runoff accumulation calculation, threshold determination and river network vector generation, and sub-basin catchment area extraction.

[0090] 3) Conduct water cycle module calculations: This typically includes precipitation interception and evapotranspiration, infiltration and soil movement, runoff generation, runoff confluence and human activities such as water intake and drainage, as well as special processes (such as snowmelt, reservoir scheduling, etc.).

[0091] 4) Conduct parameter calibration and model validation: Based on historical measured data from hydrological stations along the water conveyance section, identify key parameters in the model, such as soil hydrological parameters (e.g., saturated hydraulic conductivity, porosity), runoff parameters (e.g., CN value, water storage capacity), and confluence parameters (e.g., Manning roughness, river slope). By comparing the simulated and measured values ​​of the model, calculate the Nash coefficient (not less than 0.6 during calibration and not less than 0.5 during validation) to validate the reliability of the distributed water cycle model.

[0092] Then, the completed distributed water cycle model is used to calculate the daily dynamic flow process of all sub-basins in the basin where the multi-dam river is located.

[0093] Step 3: Consider the upstream inflow and external water transfer processes, and calculate the outflow at the water transfer point.

[0094] Using the spatial analysis capabilities of GIS, the water conveyance section and its sub-basins are spatially overlaid to identify the sub-basins upstream of the water conveyance point. Based on the simulation results of the distributed water cycle model, the flow processes of each sub-basin upstream of the water conveyance point are read and summarized as the upstream inflow. Considering the basic needs of downstream water users in the multi-dam river, and based on the planning and design schemes of external water source projects, the external water conveyance volume corresponding to the water conveyance point is determined. Without considering water mixing losses, the sum of the upstream inflow and the external water conveyance volume is taken as the outflow from the water conveyance point of the multi-dam river section. The main calculation formula is as follows:

[0095] (1)

[0096] In the formula, Let m be the outflow rate at the water conveyance point of the water conveyance section at time t. 3 ; The upstream inflow of water to the water transfer point at time t in the i-th sub-basin is obtained by reading the calculation results from the distributed water cycle model, m. 3 ; The number of upstream sub-basins corresponding to the water transfer point; Let m be the external water transfer volume corresponding to the water transfer point at time t. 3 .

[0097] Step 4: Calculate the water storage and outflow of each dam unit in stages, from upstream to downstream of the water conveyance section.

[0098] 1) Determine the number and scope of gate and dam units in the water conveyance section: Taking into account factors such as the water conveyance location, gate and dam distribution, and downstream user water intake location, determine the number of each gate and dam unit (i.e., the number of gates and dams) along the water conveyance section from the water conveyance point to the downstream water intake user, and determine the scope of each gate and dam unit in the river section.

[0099] 2) Dynamic calculation of water storage and outflow at each dam: Utilizing the spatial analysis function of GIS, each dam unit is spatially overlaid with all sub-basins of the watershed to identify the sub-basins corresponding to each dam unit in the water conveyance section. The calculation results of the distributed water cycle model are read and summarized as the interval inflow for that dam unit. Based on the calculated outflow from the upstream water conveyance point, combined with the interval inflow, and considering water losses due to evaporation, seepage, and human activities, and considering the dam's water level control requirements and downstream ecological flow indicators, the water storage and outflow at different times are calculated. The specific calculation formula is as follows:

[0100] (2)

[0101] (3)

[0102] (4)

[0103] (5)

[0104] In the formula, Let m be the inflow of the j-th dam unit at time t. If j=1, it is the outflow from the water conveyance point; if j>1, it is the outflow from the upstream dam unit. 3 j=1,2,3…J+1, where J is the number of dam units in the water conveyance section; Let m be the interval inflow of the j-th dam unit at time t, derived from the calculation results of the distributed water cycle model. 3 ; and The net evaporation and seepage of the j-th dam unit at time t are respectively, m 3 ; Let m be the water consumption during human activities in the j-th dam unit at time t. 3 ; For the ecological flow index requirement of the j-th dam unit at time t, m 3 ; Let m be the water storage capacity of the j-th dam unit at time t. 3 ; and The actual water storage capacity of the j-th dam unit at time t and time t-1 are respectively, m 3 When t=1, This refers to the initial water storage volume in step 1; Let be the restricted water storage capacity of the j-th dam unit at time t. The limiting water level of the j-th dam unit at time t; The function is the water level-reservoir capacity curve for the j-th dam unit; Let m be the outflow of the j-th dam unit at time t. 3 .

[0105] The calculation of net evaporation and seepage for each dam unit is influenced by a combination of factors, including river characteristics, dam construction parameters, and dam scheduling. The calculation methods differ at different times, as detailed below:

[0106] 1) Dam Collapse Period: During this period, each dam unit is a river section and possesses the basic characteristics of a river. Therefore, evaporation and seepage calculations are performed according to the principles of river management.

[0107] (6)

[0108] (7)

[0109] In the formula, The water surface area of ​​the j-th dam unit at time t, m 2 ; , where is the water surface evaporation pan observation value (e.g., E601 type evaporation pan) of the meteorological station near the j-th dam unit at time t, in mm; Ke is the evaporation conversion factor, usually taken as 0.7~0.8; Let be the rainfall intensity (in mm) of the j-th dam unit at time t; The river length of the j-th dam unit, in meters; Let be the width of the river surface in the j-th dam unit, in meters. Under specific inflow conditions, the width of the river surface is mainly affected by various factors such as river cross-sectional parameters, topography, and slope. Based on the remote sensing monitoring results, the average width of the river is used for simplified calculation.

[0110] River seepage is the amount of water lost from the riverbed to the soil during the flow of river water. It can be calculated using an empirical formula, as follows:

[0111] (8)

[0112] In the formula, Let be the seepage coefficient of the river section of the j-th dam unit. It is dimensionless and determined based on the actual survey data of the river. For example, it is 0.01~0.05 for cohesive soil riverbed and 0.1~0.3 for sandy soil. Using flow conversion units, the inflow of the j-th gate / dam unit at time t is converted into m. 3 / s, with a time step of day and hour, then this coefficient equals 1 / 86400.

[0113] 2) Dam Operation Period: During this period, in addition to the dam-reservoir section in the river channel, each dam unit may also have a river section of a specific length. Quantitatively identifying the lengths of the reservoir section and the river section is fundamental. The specific calculation formula is as follows:

[0114] (9)

[0115] (10)

[0116] (11)

[0117] (12)

[0118] (13)

[0119] (14)

[0120] (15)

[0121] In the formula, and , respectively, represent the lengths of the river section and the reservoir section of the j-th dam unit, in meters; and The net evaporation of the river section and reservoir section of the j-th dam unit at time t, respectively, is m. 3 ; and These represent the water surface areas (m) of the river segment and reservoir segment of the j-th dam unit at time t. 2 ; The function () is the water storage-area curve of the reservoir section of the j-th dam unit. This curve is mainly determined based on the engineering design data. and Let be the average width of the river section and the reservoir section of the j-th dam unit, respectively, in meters. Based on remote sensing monitoring results, the average width of the river section and the dam end is used for simplified calculation.

[0122] Similarly, the seepage volume of the river section during this period refers to the water loss caused by the riverbed seeping into the soil during the flow of the river. It can be calculated using an empirical formula, as follows:

[0123] (16)

[0124] (17)

[0125] (18)

[0126] In the formula, Let be the seepage coefficient of the river section in the j-th dam unit. It is dimensionless and determined based on the actual survey data of the river section. For example, it is 0.01~0.05 for cohesive soil riverbed and 0.1~0.3 for sandy soil. and Let m represent the seepage amounts in the river section and reservoir section of the j-th dam unit, respectively. 3 ; Let be the seepage coefficient of the j-th dam unit reservoir section. It is dimensionless and is determined based on the geology, soil, and seepage prevention characteristics of the dam area. It is usually between 1% and 5%.

[0127] The water consumption during human activities in each dam unit mainly includes water consumption for agricultural irrigation, domestic use, industry, and ecological users. The calculation formula is as follows:

[0128] (19)

[0129] In the formula, , , and These represent the water withdrawals for agricultural irrigation, domestic, industrial, and ecological users in the j-th dam unit, respectively, in m. 3 ; , , and These are the proportionality coefficients of drainage (or return water) from agricultural irrigation, domestic, industrial, and ecological water users in the j-th dam unit, respectively, and are dimensionless.

[0130] It should be noted that if a water user draws water from the j-th dam unit and then returns the water to the (j+1)-th and (j+2)-th dam units, the amount of water from the j-th dam unit should be... , , and Set to zero, and then return the water to the (j+1)th or (j+2)th dam unit's water balance. If a water user takes water from the jth dam unit and the returned water is then returned to the (j+1)th dam unit, the calculation formula is as follows:

[0131] (20)

[0132] (twenty one)

[0133] In the formula, Let m be the water consumption during human activities in the (j+1)th dam unit at time t. 3 .

[0134] The ecological discharge index requirements for each dam unit are quantified based on relevant technical standards, specifications, or guidelines, combined with the life process requirements of downstream ecological protection targets, using hydrological methods, hydrodynamic methods, habitat simulation methods, and holistic analysis methods. If the local water management department has determined the minimum ecological discharge flow for the dam, the larger of the two values ​​is taken as the ecological discharge index requirement for that dam unit, as detailed below:

[0135] (twenty two)

[0136] In the formula, The minimum downstream ecological flow rate determined by the water management department for the j-th dam unit at time t; The outflow ecological flow is calculated for the j-th gate / dam unit at time t.

[0137] Step 5: Determine the water intake guarantee rate requirements of downstream nuclear power users, and calculate the water demand and available water intake.

[0138] This step mainly involves clarifying the water availability guarantee rate requirements, water demand, and maximum water intake capacity of downstream nuclear power users, and calculating the available water intake, as detailed below:

[0139] 1) Clarify the water supply guarantee rate requirements for downstream nuclear power users. The water supply guarantee rate for downstream nuclear power users represents the probability that their water supply needs can be fully met in terms of time (duration), and is an important indicator for ensuring the safety of water supply for downstream nuclear power users. Based on the continuity requirements of water use in nuclear power production, the minimum time step for calculating the water supply guarantee rate should be calculated in days. Nuclear power users have extremely high requirements for water supply reliability, typically requiring a guarantee rate of 97%.

[0140] 2) Calculate the water demand of nuclear power users. Based on the characteristics of the downstream nuclear power users' living and production needs, calculate the water demand. Typically, the water demand of nuclear power users includes cooling tower makeup water, plant water system makeup water, desalination, industrial and domestic makeup water, unforeseen losses, and leakage. Because the circulating makeup water volume varies significantly under different operating conditions of a nuclear power plant, factors such as its secondary cooling cycle, warm wastewater discharge method, and temperature changes should be comprehensively considered to correct and adjust the water demand. The formula for calculating the water storage capacity of nuclear power users is:

[0141] (twenty three)

[0142] In the formula, Let m be the water demand of the nuclear power user at time t. 3 ; , , , These represent the water demand at time t, including the water supply to the cooling tower, the water supply to the plant's water system, the water supply for desalination, industrial and domestic use, and the water demand due to unforeseen circumstances and leakage. (m)3 .

[0143] 3) Calculate the available water volume for nuclear power users. Based on the location characteristics of the nuclear power user's water intake project and the outflow rate of the dam unit where the intake is located, determine the available water volume. This is divided into two main types:

[0144] a) When a nuclear power user draws water from the last dam unit of the water conveyance section, the amount of water they can draw should be less than the water intake capacity limit and the outflow of that dam unit. As calculated in the preceding steps, this outflow has already deducted the essential industrial and agricultural water use and the river's ecological water use. Furthermore, if the user has water intake capacity limitations, the impact of these limitations on their available water volume should be considered. The specific calculation formula is as follows:

[0145] (twenty four)

[0146] In the formula, Let m be the amount of water available to downstream nuclear power users at time t. 3 ; For the water intake capacity limitation of downstream nuclear power users at time t, m 3 If there are no restrictions =∞; Let m be the outflow rate of the dam unit where the upstream water intake of the nuclear power user is located at time t. 3 .

[0147] b) Nuclear power users take water downstream of the last dam in the water conveyance section. The water intake capacity of nuclear power users should be less than the water intake capacity limit and the outflow of the dam unit minus the required downstream flow at the intake section. The required downstream flow at the intake section usually needs to consider the ecological water demand of downstream river ecological protection targets and the basic water demand for downstream production and daily life, thereby maintaining the health of the river ecosystem and ensuring the basic water demand for the survival, health, and economic activities of human society in the downstream area. Similar to the calculation of the ecological flow of the dam unit, the ecological water demand of downstream river ecological protection targets should be quantitatively calculated based on relevant technical standards, specifications, or guidelines, combined with the life process needs of downstream ecological protection targets, using hydrological methods, hydrodynamic methods, habitat simulation methods, and overall analysis methods. The basic water demand for downstream production and daily life is usually determined based on relevant basic water use surveys for production and daily life or relevant comprehensive water resource planning. The specific calculation formula is as follows:

[0148] (25)

[0149] In the formula, Let m be the downstream water intake flow requirement of the nuclear power user at time t. 3To meet nuclear power safety requirements, according to relevant technical specifications and industry standards for hydrology in nuclear power plant engineering, the data for calculating the water availability guarantee rate for nuclear power users must be long-term data, with a data length of at least 30 years. Provided the basic data is complete, an even longer series (e.g., 50 years) is recommended. Based on steps 2 to 5 above, daily calculations of the available water for nuclear power users are performed for this long-term series until the required number of years for the calculation is met.

[0150] Step 6: Based on the long series of calculation results, give the water intake guarantee rate for nuclear power users.

[0151] Based on the calculation results of the daily water availability for nuclear power users obtained in the above steps, and taking into account the continuity and reliability requirements of water use for nuclear power users, if the available water availability in a given year cannot meet the water demand for any single day, it is determined that the water demand for that year is not met. The water availability guarantee rate is calculated according to this criterion. The specific formula for calculating the water availability guarantee rate is as follows:

[0152] (26)

[0153] In the formula, The water intake guarantee rate for downstream nuclear power users is %; Y is the number of years calculated from long-series data; ty represents the year number, ty=1,2,3……Y; The starting date of year ty; This is the end date of year ty.

[0154] Example 1

[0155] This embodiment is a specific application example of the above method.

[0156] In this embodiment, the multi-dam river is a river flowing into the sea in Shandong Province, my country. The upstream water conveyance point is located at point M on the main stream of the river, and the downstream water intake point is located at point N. The water conveyance section (MN) is approximately 35 km long, with an average channel width of 260 m. Three main dams (dam A, dam B, and dam C) are constructed along the water conveyance section. The downstream nuclear power user's water intake point is located at dam C, and the water intake guarantee rate is required to be 97%. Figure 2 As shown.

[0157] From the perspective of the watershed of rivers with multiple dams, basic data were collected on river systems, meteorology and hydrology, land use, topography, soil geology, vegetation cover, water conservancy and soil conservation projects, and human activities such as water intake and drainage. Based on data processing, a distributed water cycle model (WEP-L model) was constructed for the watershed of the rivers with multiple dams, dividing it into 39 sub-watershed control units, such as... Figure 3As shown, the model can simulate the daily water cycle process over a long period (65 years, from 1957 to 2021). A typical hydrological station (located between dam A and dam B) was selected to calibrate the parameters and validate the distributed water cycle model.

[0158] Spatial overlay analysis identified two sub-basin units corresponding to water transfer point M: sub-basin units 13 and 8. Based on the calculation results of the distributed water cycle model, the daily inflow process for these two sub-basin units was obtained. According to the relevant water source engineering planning and design scheme, the external water transfer volume is 3.47 m³. 3 / s, with an annual water transfer volume of approximately 109 million m³. 3 .

[0159] Since there are three sluice gates / dams in the water conveyance section, and considering the locations of the upstream water conveyance point and the downstream user's water intake point, three sluice gate / dam units are determined: sluice gate / dam unit 1 (from water conveyance point M to dam A), sluice gate / dam unit 2 (from dam A to dam B), and sluice gate / dam unit 3 (from dam B to dam C). The scheduling rules for each sluice gate / dam in the water conveyance section are shown in Table 1. The water level-storage capacity curve and the water storage-area curve for the reservoir section are derived based on the preliminary design scheme for the reinforcement and upgrading of each sluice gate / dam. For example, the water storage-area curve for dam A is shown below. Figure 4 As shown.

[0160] Table 1. Scheduling rules for each sluice gate and dam in the water conveyance section

[0161]

[0162] Due to the lack of measured evaporation data in this watershed, daily measured evaporation data from hydrological stations in neighboring watersheds with similar underlying surface conditions were used for calculation based on the principle of proximity. Human water use around each dam unit is mainly for agricultural irrigation. Based on the survey results of agricultural irrigation area, irrigation quota (gross), and irrigation system in surrounding townships (see Tables 2 and 3), the daily water consumption during human activities in the dam unit was calculated.

[0163] Table 2 Irrigation area, quota, and irrigation water consumption for each sluice gate / dam

[0164]

[0165] Table 3 Irrigation System for Each Sluice Gate and Dam

[0166]

[0167] Since there are no sensitive species downstream of this water conveyance section, the ecological flow control indicators for each dam and gate determined by the water management department using hydrological methods are shown in Table 4.

[0168] Table 4. Ecological Flow Requirements for Each Dam and Sluice Gate

[0169]

[0170] The design guarantee rate for water intake for downstream nuclear power users is required to be 97%. Water consumption by nuclear power users is significantly affected by temperature, with a marked increase in water demand during the summer months (June-August) due to higher temperatures. Taking into account factors such as cooling tower makeup water, plant water system makeup water, desalination, industrial and domestic makeup water, unforeseen losses, and leakage, the monthly water demand for this user is calculated as follows: Figure 5 As shown, the monthly water demand is evenly distributed across the days. The summarized results indicate that this user's annual water demand is approximately 0.52 billion m³. 3 According to the design scheme for nuclear power plant water supply and drainage engineering, its water intake capacity is limited to 2m³. 3 / s.

[0171] Using the method described in this invention, a comparison was obtained of the daily available water intake (water intake point located at dam C) and water demand of downstream users for a long series (23,741 days in total from 1957 to 2021). Figure 6 As shown in the figure. Statistical results indicate that downstream nuclear power users had sufficient water availability to meet their needs for 23,714 days, with 27 days where the available water availability did not meet the requirements. Summarizing by year, in the 65 years of the long-term series, there were only 44 years where the daily available water availability consistently met the demand, resulting in a water availability guarantee rate of 67.7%, which does not meet the required 97% water availability guarantee rate.

[0172] Overall, while utilizing multi-dam river water transfer reduces pipeline laying costs, significant water loss occurs due to factors such as agricultural irrigation water consumption, river evaporation, dam evaporation, and leakage from both the river and dams. This makes it difficult to guarantee the water security of downstream nuclear power users. Further analysis revealed that the period when the available water supply to nuclear power users could not meet their needs was mainly concentrated on September 1st and 2nd (as shown in Table 5). During this period, the dams along the water transfer channel switched from collapsed to normal operation, trapping water in the dam reservoir area and making it difficult to effectively transfer it to downstream users. Consequently, the available water supply could not meet their water requirements. The water supply guarantee rate can be improved by further increasing the water transfer volume in the basin and adding water regulation measures.

[0173] Table 5. Annual Water Demand Meeting Status of Users in the C-Series of River Barriers

[0174]

[0175]

[0176] Finally, it should be noted that the above description is only used to illustrate the technical solution of the present invention and not to limit it. Although the present invention has been described in detail with reference to the preferred arrangement, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for calculating the water intake guarantee rate for nuclear power users downstream of multi-dam rivers, characterized in that, The method includes the following steps: Step 1: Determine the water conveyance section, dam distribution, and initial storage capacity of the river with multiple dams: Based on the planning or design scheme of the water conveyance project in the basin or region where the river with multiple dams is located, identify the location of the upstream water conveyance point and the location of the downstream water users, and determine the scope of the water conveyance section of the river with multiple dams; then, based on the relevant basin planning and water conservancy project data, determine the number, spatial distribution, and characteristic parameters of the dams in the water conveyance section; and determine the initial storage capacity of each dam. Step 2: Construct a distributed water cycle model to obtain the dynamic flow process of sub-basins: Construct a distributed water cycle model for the basin where the river with multiple dams is located, and then use the constructed distributed water cycle model to calculate the daily dynamic flow process of all sub-basins in the basin where the river with multiple dams is located. Step 3: Considering the upstream inflow and external water transfer processes, calculate the outflow at the water transfer point: Perform spatial overlay analysis of the water transfer section and sub-basins to identify the sub-basins corresponding to the upstream of the water transfer point in the water transfer section; Based on the simulation results of the distributed water cycle model, read the flow processes of each sub-basin upstream of the water transfer point and summarize them as the upstream inflow; Combined with the basic needs of downstream water users of the multi-dam river, and based on the planning and related design schemes of the external water source project, determine the external water transfer volume corresponding to the water transfer point; Ignoring water mixing losses, take the sum of the upstream inflow and the external water transfer volume as the outflow at the water transfer point of the multi-dam river section, calculated using the following formula: （1） In the formula, Let m be the outflow rate at the water conveyance point of the water conveyance section at time t. 3 ; The upstream inflow of water to the water transfer point at time t in the i-th sub-basin is obtained by reading the calculation results from the distributed water cycle model, m. 3 ; The number of upstream sub-basins corresponding to the water transfer point; Let m be the external water transfer volume corresponding to the water transfer point at time t. 3 ; Step 4: From upstream to downstream of the water conveyance section, calculate the storage and outflow of each dam unit in stages: First, determine the number and scope of dam units in the water conveyance section; then, perform spatial overlay analysis on each dam unit and all sub-basins of the watershed to identify the sub-basins corresponding to each dam unit in the water conveyance section, read the calculation results of the distributed water cycle model, and summarize the calculation as the interval inflow of the dam unit; based on the calculated outflow of the upstream water conveyance point, combined with the interval inflow, considering the water loss due to evaporation, seepage, and human activities, and combined with the dam scheduling water level restrictions and downstream ecological flow indicators, calculate the storage and outflow at different times. The specific calculation formula is as follows: （2） （3） （4） （5） In the formula, Let m be the inflow of the j-th dam unit at time t. If j=1, it is the outflow from the water conveyance point; if j>1, it is the outflow from the upstream dam unit. 3 j=1,2,3…J+1, where J is the number of dam units in the water conveyance section; Let m be the interval inflow of the j-th dam unit at time t, derived from the calculation results of the distributed water cycle model. 3 ; and The net evaporation and seepage of the j-th dam unit at time t are respectively, m 3 ; Let m be the water consumption during human activities in the j-th dam unit at time t. 3 ; For the ecological flow index requirement of the j-th dam unit at time t, m 3 ; Let m be the water storage capacity of the j-th dam unit at time t. 3 ; and The actual water storage capacity of the j-th dam unit at time t and time t-1 are respectively, m 3 When t=1, This refers to the initial water storage volume in step 1; Let be the restricted water storage capacity of the j-th dam unit at time t. The limiting water level of the j-th dam unit at time t; The function is the water level-reservoir capacity curve for the j-th dam unit; Let m be the outflow of the j-th dam unit at time t. 3 ; Step 5: Clarify the water availability guarantee rate requirements for downstream nuclear power users and calculate the water demand and available water volume: First, clarify the water availability guarantee rate requirements for downstream nuclear power users. The water availability guarantee rate represents the probability that the water demand can be met in terms of available time. Then, based on the characteristics of the downstream nuclear power users' living and production activities, calculate the water demand using the following formula: （23） In the formula, Let m be the water demand of the nuclear power user at time t. 3 ; , , , These represent the water demand at time t, including the water supply to the cooling tower, the water supply to the plant's water system, the water supply for desalination, the water supply for industrial and domestic use, and the water demand due to unforeseen circumstances and leakage, m. 3 ; Then, based on the location characteristics of the downstream nuclear power user's water intake project and the outflow of the dam unit where the water intake is located, the available water volume is determined and divided into two types: a) When a nuclear power user draws water from the last dam unit of the water conveyance section, the amount of water that can be drawn is less than the water intake capacity limit and the outflow of that dam unit; the specific calculation formula is as follows: （24） In the formula, Let m be the amount of water available to downstream nuclear power users at time t. 3 ; For the water intake capacity limitation of downstream nuclear power users at time t, m 3 If there are no restrictions =∞; Let m be the outflow rate of the dam unit where the upstream water intake of the nuclear power user is located at time t. 3 ; b) When a nuclear power user takes water downstream of the last dam in the water conveyance section, the amount of water the nuclear power user can take is less than the water intake capacity limit and the outflow of the dam unit minus the downstream discharge requirement. The specific calculation formula is as follows: （25） In the formula, Let m be the downstream water intake flow requirement of the nuclear power user at time t. 3 ; According to the relevant technical specifications and industry standards for hydrology of nuclear power plant projects, the data for calculating the water intake guarantee rate of downstream nuclear power users is a long series of data, with a data length of more than 30 years; based on the above steps 2 to 5, the daily water intake of nuclear power users in the long series is calculated until the requirement of the number of years for the long series calculation is met; Step 6: Based on the long-term calculation results, give the water availability guarantee rate for nuclear power users: Based on the calculation results of the daily water availability of nuclear power users obtained in the above steps, and taking into account the continuity and reliability requirements of water use for nuclear power users, when the available water in a certain year cannot meet the water demand of any day, it is determined that the water demand for that year is not met. The water availability guarantee rate is calculated according to this criterion. The specific calculation formula is as follows: （26） In the formula, The water intake guarantee rate for downstream nuclear power users is %; Y is the number of years calculated from long-series data; ty represents the year number, ty=1,2,3……Y; The starting date of year ty; This is the end date of year ty.

2. The method for calculating the water intake guarantee rate for downstream nuclear power users in a multi-dam river according to claim 1, characterized in that, The specific definition of determining the scope of the water conveyance section of a multi-dam river in step 1 is as follows: if both the water conveyance point and the water intake point are located on the main stream of the river, then the water conveyance section is located on the main stream of the river; if the water conveyance point is located on a tributary and the water intake point is located on the main stream of the river, then the water conveyance section is located on both the main stream and the tributary. The characteristic parameters of the sluice gates and dams in the water conveyance section specifically include the water level-area curve, which is the functional relationship between the reservoir water level and its corresponding water storage area; the water level-storage capacity curve, which is the functional relationship between the reservoir water level and its corresponding water storage volume; the sluice gate and dam scheduling restriction water level and ecological flow release index requirements for different periods, including flood season and non-flood season. The specific process for determining the initial water storage of each dam is as follows: if there is observation data for a long series of dams, the actual water storage of the reservoir in the starting year of the long series calculation is directly taken as the initial value; if there is a lack of observation data for a long series of dams, the water storage corresponding to the dead storage level is used as the initial value; the long series refers to data data of more than 30 years.

3. The method for calculating the water intake guarantee rate for downstream nuclear power users in a multi-dam river according to claim 1, characterized in that, Step 2, which describes the construction of a distributed water cycle model, specifically includes the following steps: 1) Conduct multi-source data collection and processing: This includes collecting and processing data on river systems, meteorology and hydrology, land use, topography, soil geology, vegetation cover, water conservancy and soil conservation projects, and human activities involving drainage. 2) Spatial Discretization and Unit Division: Based on high-resolution DEM data, spatial discretization is performed using spatial analysis methods to divide the data into regular grids, hydrological response units, or sub-basins. Sub-basins are preferred, and in actual simulations, they are further subdivided according to contour zones to reflect the influence of topography on precipitation, evapotranspiration, and runoff. The sub-basin division process includes steps such as depression filling, water flow direction determination, runoff accumulation calculation, threshold determination and river network vector generation, and sub-basin catchment area extraction. 3) Conduct water cycle module calculations: including precipitation interception and evapotranspiration, infiltration and soil movement, runoff generation, runoff confluence and human activity water intake and drainage, as well as special processes, including snowmelt and reservoir scheduling; 4) Conduct parameter calibration and model validation: Based on historical measured data from hydrological stations along the water conveyance section, identify soil hydrological parameters, runoff parameters, and confluence parameters in the model; calculate the Nash coefficient by comparing the simulated and measured values ​​of the model, requiring a calibration period of not less than 0.6 and a validation period of not less than 0.5 to validate the reliability of the distributed water cycle model.

4. The method for calculating the water intake guarantee rate for downstream nuclear power users in a multi-dam river according to claim 1, characterized in that, The calculation process for the net evaporation and seepage of each dam unit in step 4 is as follows: 1) Dam Collapse Period: During this period, each dam unit is a river section and possesses the basic characteristics of a river. Therefore, evaporation and seepage calculations are performed according to the principles of river management. （6） （7） In the formula, Let m be the water surface area of ​​the j-th dam unit at time t. 2 ; , where is the water surface evaporation pan observation value at the meteorological station near the j-th dam unit at time t, in mm; Ke is the evaporation conversion factor, with a value of 0.7~0.8; Let be the rainfall intensity (in mm) of the j-th dam unit at time t; Let be the river length of the j-th dam unit, in meters. Let be the width of the river surface in the j-th dam unit, in meters. Under specific inflow conditions, the width of the river surface is affected by various factors such as river cross-sectional parameters, topography, and slope. Based on the remote sensing monitoring results, the average width of the river section is used for simplified calculation. River seepage is the amount of water lost from the riverbed to the soil during river flow. It is calculated using an empirical formula, specifically: （8） In the formula, Let be the seepage coefficient of the j-th dam unit river section, dimensionless, determined based on actual survey data of the river section, and 0.01~0.05 for cohesive soil riverbed and 0.1~0.3 for sandy soil; Using flow conversion units, the inflow of the j-th gate / dam unit at time t is converted into m. 3 / s, with a time step of day and hour, then this coefficient is equal to 1 / 86400; 2) Dam Operation Period: During this period, in addition to the dam-reservoir section in the river channel, each dam unit also has a river section of a specific length. Quantitatively identifying the lengths of the reservoir section and the river section is fundamental. The specific calculation formula is as follows: （9） （10） （11） （12） （13） （14） （15） In the formula, and , respectively, represent the lengths of the river section and the reservoir section of the j-th dam unit, in meters; and The net evaporation of the river section and the reservoir section of the j-th dam unit at time t, respectively, is m. 3 ; and These represent the water surface areas (m) of the river segment and reservoir segment of the j-th dam unit at time t. 2 ; The function () is the water storage-area curve of the reservoir section of the j-th dam unit, which is determined based on the engineering design data; and Let be the average width of the water surface of the river section and the reservoir section of the j-th dam unit, respectively, in meters. Based on the remote sensing monitoring results, the average width of the river section and the dam end is used for simplified calculation. The seepage volume in this river section during this period refers to the water loss caused by the riverbed seeping into the soil during the flow of river water. It is calculated using an empirical formula, as follows: （16） （17） （18） In the formula, and Let m represent the seepage amounts in the river section and reservoir section of the j-th dam unit, respectively. 3 ; Let be the seepage coefficient of the j-th dam unit reservoir section. It is dimensionless and is determined based on the geological, soil, and seepage prevention characteristics of the dam area, ranging from 1% to 5%.

5. The method for calculating the water intake guarantee rate for downstream nuclear power users in a multi-dam river according to claim 1, characterized in that, In step 4, the water consumption during human activities in each dam unit includes water consumption for agricultural irrigation, domestic use, industry, and ecological users. The calculation formula is as follows: （19） In the formula, , , and These represent the water withdrawals for agricultural irrigation, domestic, industrial, and ecological users in the j-th dam unit, respectively, in m. 3 ; , , and These are the proportionality coefficients of drainage or return water from agricultural irrigation, domestic, industrial, and ecological water users in the j-th dam unit, respectively, and are dimensionless. If a water user draws water from the j-th dam unit and then returns the water to the (j+1)-th and (j+2)-th dam units, then the water in the j-th dam unit will be... , , and Set to zero, and then return the water to the (j+1)th or (j+2)th dam unit's water balance; if a water user takes water from the jth dam unit and returns the water to the (j+1)th dam unit after use, the calculation formula is as follows: （20） （21） In the formula, Let m be the water consumption during human activities in the (j+1)th dam unit at time t. 3 .

6. The method for calculating the water intake guarantee rate for downstream nuclear power users in a multi-dam river according to claim 1, characterized in that, In step 4, the ecological discharge index requirements for each dam unit are quantified based on relevant technical standards, specifications, or guidelines, combined with the life process requirements of downstream ecological protection targets, using hydrological methods, hydrodynamic methods, habitat simulation methods, and holistic analysis methods. If the local water management department has determined the minimum ecological discharge flow for the dam, the larger of the two values ​​is taken as the ecological discharge index requirement for that dam unit, as detailed below: （22） In the formula, The minimum downstream ecological flow rate determined by the water management department for the j-th dam unit at time t; The outflow ecological flow is calculated for the j-th gate / dam unit at time t.

7. The method for calculating the water intake guarantee rate for downstream nuclear power users in a multi-dam river according to claim 1, characterized in that, The specific requirements for the water supply guarantee rate for downstream nuclear power users mentioned in step 5 are as follows: based on the continuity requirements of water use in the nuclear power production process, the minimum time step for the water supply guarantee rate is calculated in days, and the water supply guarantee rate for downstream nuclear power users is required to reach 97%.

Images