Method for evaluating influence of reservoir-water diversion project joint regulation on downstream ecological flow

Abstract

The application discloses a kind of reservoir-water transfer project joint regulation and control influence evaluation method to downstream ecological flow, the method includes the following steps: step 1, research area data collection;Step 2, construct water transfer project water source area natural water cycle model WEP-NHA;Step 3, construct natural-social dual water cycle coupling model WEP-HA;Step 4, simulate runoff using WEP-HA model in water source area;Step 5, system analysis water source area key control section water quantity and ecological flow guarantee rate change degree under the superposition of reservoir and water transfer project.This method can realize the system simulation of the disturbance response of the complex system in the water source area, effectively reveal the comprehensive influence of the complex water conservancy system on water resources and ecological environment, have strong adaptability and predictability, effectively solve the simulation problem of the regulation and storage effect of the reservoir without data or little data, provide decision support for scientifically formulating water transfer scale and guaranteeing ecological flow.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of ecological protection and water resources management, and particularly relates to a method for evaluating the influence of reservoir-water diversion project joint regulation on downstream ecological flow. BACKGROUND

[0002] Related research shows that water diversion projects may cause significant disturbance to the complex natural-social system of the water source area, thereby affecting regional water resources, water ecology and economic society and other subsystems, and exacerbating the uncertainty and complexity in the system evolution process. In this case, it is urgent to build a quantitative analysis method that can represent the collaborative evolution process of multiple elements, for in-depth exploration of the water resources and water ecology change trend in the water source area after water diversion.

[0003] Under the non-stationary climate background of frequent extreme precipitation events and continuous climate warming, the spatio-temporal distribution pattern of water resources presents a new evolution trend, and the influence of water diversion projects on the runoff process and water distribution pattern in the water source area has become increasingly important. At present, researchers mainly use two methods to evaluate the influence of reservoir regulation and water diversion process on the hydrological process in the basin, namely the adjustment method based on long series of observed data and the simulation method based on hydrological model. However, both methods have certain limitations in practical application:

[0004] (1) Adjustment method based on long series of observed data: This method uses long series of historical observation data to analyze the runoff change of the control section of the downstream river channel after the implementation of the water diversion project by using water balance calculation and other means. However, this method has high requirements for data, usually requires more than 30 years of continuous observation data, and the missing data region needs to be extended by interpolation, which may introduce errors. In addition, the observed data is usually based on monthly or annual scale, which may lead to "smoothing" and "distortion" of the time series information in the adjustment process. More importantly, this method is based on historical hydrological regime and is difficult to reflect the potential changes of future water resources pattern under climate change; in addition, the adjustment calculation based on historical sequence is difficult to reflect the influence of climate change on regional water resources.

[0005] (2) Hydrological model-based simulation method: This method builds a water cycle coupling model to simulate the runoff evolution process under different scenarios to quantitatively evaluate the influence of water diversion projects on the hydrological process of the basin. This method has high temporal and spatial resolution and simulation accuracy, and is a commonly used technical path in the current environmental impact assessment of major water diversion projects, but there are still some limitations in practical application. On the one hand, for the simulation of reservoir regulation process, it usually depends on the existing regulation rules or regulation charts, but some built reservoirs lack regulation data, and the planning stage reservoir has not yet developed a complete regulation chapter, thereby limiting the applicability of the model in future water diversion scenario analysis. On the other hand, for the water diversion project in the demonstration stage, if the planning scheme clearly proposes that the water source project has regulation capacity and sets the recommended water diversion scale, the process of the reservoir achieving the water diversion guarantee rate through "storing in the wet season and supplementing in the dry season" needs to be simulated. However, such regulation rules are often not yet determined or are in the preparation stage, making it difficult to accurately depict the reservoir operation behavior, thereby increasing the technical difficulty and uncertainty of the analysis of the influence of the water diversion project on the water resources situation of the water source area.

[0006] Therefore, it is urgent to build a comprehensive evaluation method that integrates hydrological simulation and engineering operation logic, which can accurately simulate the runoff process and water distribution pattern of the water source area under the condition of joint regulation and control, and quantitatively evaluate the trend of the guarantee degree of the ecological flow of the key control section based on considering factors such as reservoir regulation, water diversion of the water diversion project, and regional water demand characteristics. SUMMARY

[0007] The purpose of the present application is to provide a method for evaluating the influence of reservoir-water diversion project joint regulation on downstream ecological flow to solve the above technical problems.

[0008] To achieve the above purpose, the present application provides the following technical scheme:

[0009] The present application discloses a method for evaluating the influence of reservoir-water diversion project joint regulation on downstream ecological flow, which comprises the following steps:

[0010] Step 1, collecting data of the research area: collecting basic data of the research area, including hydro-meteorological data, underlying surface data, terrain and soil data, river system data, vegetation data, water use data, water diversion project data; setting a river network extraction threshold according to the collected terrain and soil data and river system data, and dividing the sub-basins of the research area; and embedding the contour belt information to divide the basic calculation units on this basis; finally, uniformly distributing the basic data to each calculation unit;

[0011] Step 2, Constructing the natural water cycle model WEP-NHA of the water source area of the water diversion project: Using the distributed hydrological model WEP to simulate the daily runoff process, and carrying out zoned calibration and verification of the model parameters. The Nash efficiency coefficient NSE and the relative error RE are used to evaluate the simulation results, and finally the natural water cycle model WEP-NHA of the water source area of the water diversion project is constructed;

[0012] Step 3, Constructing the natural-society dual water cycle coupling model WEP-HA: Based on the constructed natural water cycle model WEP-NHA of the water source area of the water diversion project, embed the social and economic water use module, reservoir regulation module and water diversion module to form a coupling calculation framework of the interaction between natural water cycle and social water cycle, and construct the natural-society dual water cycle coupling model WEP-HA. The model is composed of a natural water cycle subsystem and a social water cycle subsystem: the natural water cycle subsystem takes WEP-NHA as the core to simulate the processes of precipitation, evapotranspiration, runoff generation and confluence; the social water cycle subsystem includes the social and economic water use module, the reservoir regulation module and the water diversion module, which respectively realize the simulation of water demand, the dynamic regulation of reservoir capacity and the allocation of cross-regional water;

[0013] Step 4, Simulating the runoff of the water source area using the WEP-HA model: Set different working conditions, simulate the daily runoff of the water source area using the WEP-HA model, and obtain the spatio-temporal distribution characteristics of the water source area under multiple scenarios;

[0014] Step 5, Systematically analyzing the changes in water quantity and ecological flow guarantee rate of typical sections in the water source area under the superposition of reservoirs and water diversion projects: Specifically including the following steps:

[0015] Step 51, Selecting typical sections: According to the characteristics of the river channel in the water source area and the operation characteristics of water conservancy projects, select river sections that meet at least one of the following conditions as typical sections, including: 1) located at the hydrological control point of the outlet of the basin or the inlet of the main tributary; 2) located in the river section directly affected by reservoir or water diversion hub regulation, with long-term continuous and reliable hydrological observation or stable calculation of flow data; 3) located in the ecologically sensitive river section, as the key position for ecological flow guarantee analysis;

[0016] Step 52, Analyzing the spatio-temporal distribution characteristics of water quantity: Based on the output results of the WEP-HA model, extract the daily runoff data of the river channel and typical sections in the water source area under each scenario, and analyze the spatio-temporal distribution rules and trends of water quantity under the superposition of reservoirs and water diversion projects;

[0017] Step 53, Calculating the ecological flow guarantee rate: Combined with the ecological water demand requirements of the typical sections, calculate the compliance of the ecological flow under multiple scenarios;

[0018] Step 54, comparison of the influence difference of different scenarios: comparative analysis of the typical section ecological flow guarantee rate and the river water distribution characteristics under each regulation scenario, and identification of the influence of different reservoir regulation and water transfer combination schemes on the downstream ecological flow.

[0019] Further, the hydro-meteorological data in step 1 includes precipitation, wind speed, relative humidity, sunshine hours and site measured runoff; the underlying surface data includes land use and irrigation area distribution; the terrain and soil data includes DEM and soil type; the river system data includes river system distribution, river section information, reservoir basic parameters and regulation information; the vegetation data includes leaf area index and normalized vegetation index; the water use data includes agricultural, industrial and domestic water use, and water intake information; and the water transfer engineering data includes location, water transfer scale, water source reservoir scale and designed water intake of water transfer tunnel.

[0020] Further, the calculation formulas of the Nash efficiency coefficient NSE and the relative error RE in step 2 are as follows:

[0021]

[0022]

[0023] In the formula, Q sim,i and Q obs,i are the runoff simulation value and the measured value, respectively, m 3 / s; N is the simulation series length; is the multi-year average value of the runoff measured value, m 3 / s.

[0024] Further, the specific process of embedding the social and economic water use module, the reservoir regulation module and the water transfer module in step 3 is as follows:

[0025] For the social and economic water use module: using the collected water use data of the study area, the data is distributed to each calculation unit according to the underlying surface data and irrigation system to input the WEP-NHA model;

[0026] For the reservoir regulation module: first, determine the reservoirs that need to be included in the reservoir regulation in the study area according to the regulation capacity; second, set the scheduling rules according to the collected reservoir operation data, which are as follows: 1) for reservoirs with complete operation data, use the existing scheduling rules and scheduling charts for regular scheduling simulation; 2) for reservoirs with no or little data, use the conceptual regulation rules based on the characteristic water level of the reservoir for regulation;

[0027] The characteristic water level-based reservoir conceptual storage and discharge rule is achieved by defining the dead water level, flood control limit water level, normal storage water level and flood control high water level parameters, realizing scientific generalization of the cascade reservoir dispatching process, and the reservoir outflow is determined by the inflow, storage capacity and control target. The reservoir storage capacity at time t is expressed as:

[0028] V t = V t-1 + Δt × (Q in - Q out ) - Q e (3)

[0029] In the formula, V t and V t-1 represent the final storage capacity and initial storage capacity at time t, Q in and Q out represent the inflow and outflow of the reservoir at time t, and Q e represents the loss term of the reservoir.

[0030] The outflow Q out is determined by the following formula:

[0031]

[0032] In the formula, V d , V c and V f represent the reservoir capacity corresponding to the dead water level, normal storage water level / flood control limit water level and flood control high water level respectively, Δt represents the time step, Q s represents the maximum acceptable outflow under flood control purposes, Q min and Q' min represent the minimum outflow before and after correction, Q n represents the normal outflow, k (k≤1) is an index representing the severity of the inflow flood, and r is a correction coefficient for measuring the relative deviation of the current storage capacity from the target storage capacity. The specific calculation formulas of k and r are as follows:

[0033]

[0034] Wherein:

[0035]

[0036] In the formula, I t represents the inflow at time t, V tar,m represents the target reservoir capacity of the mth month, c is a parameter, and Q s takes the runoff simulation value corresponding to the 99% cumulative probability at the dam site.

[0037] Q nThe calculation formula is:

[0038] Q n = V cw × 0.7 / (180×86400) + Q mean × 0.25 (8)

[0039] In the formula, V cw represents the reservoir capacity corresponding to the flood control limit water level; Q mean represents the multi-year average runoff at the dam site;

[0040] Q min In the regulation and storage process, the value is the ecological base flow of the dam site section of each reservoir, and the specific determination process is as follows: 1) for the built projects, the ecological flow approved by the relevant departments shall apply; 2) for the planned reservoirs, the ecological base flow target values in dry season and non-dry season are calculated respectively by comprehensively using Q90, Q95, 90% of the driest day flow, 7Q10 method and duration curve method; and when the reservoir water level drops to the dead water level and the inflow is less than the ecological flow discharge target, the reservoir discharges the ecological flow according to the inflow, and at this time the discharge capacity is Q' min ;

[0041] For the water transfer module: the water intake process of the water transfer project is described by the reservoir regulation and storage module, and the reservoir regulation and storage module first calculates the available water quantity for water transfer according to the regulation rules; the water transfer module determines the actual water transfer process in combination with the water source reservoir project scale and the tunnel design water diversion quantity; the water transfer term is introduced in the water balance equation to reflect the dynamic coupling relationship between the reservoir regulation and the water transfer project:

[0042] V t = V t-1 + Δt×(Q in - Q out )- Q e - Q tran_act (9)

[0043] In the formula, Q tran_act represents the actual water transfer quantity of the reservoir project at time t; Q tran_actThe determination of the actual water regulating capacity and the water releasing process of the water conservancy project in each period is made by combining the reservoir capacity / water level initial conditions and the water inflow changes of various water regulating conditions. First, according to whether it is in the flood season, the dispatch path is divided into two types of flood season and non-flood season, and the specific dispatch strategy is determined by combining the current water level and the relative relationship of the key control water level including the flood control high water level, the normal storage water level, the flood limit water level and the dead water level. In the non-flood season, when the water level is greater than or equal to the flood control high water level, the maximum discharge and water regulating are performed; when the normal storage water level is less than the water level and the water level is less than the flood control high water level, according to the inflow and water demand, the target discharge and water regulating or the ecological discharge and water regulating are selected; when the dead water level is less than the water level and the water level is less than the normal storage water level, according to the conditions, the target discharge and water regulating, the ecological discharge and water regulating or only the ecological discharge are selected; when the water level is less than or equal to the dead water level, the ecological discharge cannot be satisfied; in the flood season, when the water level is greater than or equal to the flood control high water level, the maximum discharge and water regulating are performed; when the flood limit water level is less than the water level and the water level is less than the flood control high water level, according to the inflow and water demand, the target discharge and water regulating or the ecological discharge and water regulating are selected; when the dead water level is less than the water level and the water level is less than the flood limit water level, according to the conditions, the target discharge and water regulating, the ecological discharge and water regulating or only the ecological discharge are selected; when the water level is less than or equal to the dead water level, the ecological discharge cannot be satisfied; and the flood control safety is placed as the primary constraint condition, the actual water regulating capacity in each period is dynamically determined through the scene-based and multi-branch water level zoning response mechanism.

[0044] Further, the setting of different working conditions in step 4 follows the following principles:

[0045] 1) Consistency of boundary conditions: consistent basic data is used for different working conditions to ensure the comparability of simulation results;

[0046] 2) Comprehensive combination of regulation and control: fully considering the social and economic water demand process, reservoir storage capacity and the operation characteristics of water regulating projects, the joint regulation and control scenes covering different reservoir storage rules, water regulating scales and operation modes are reasonably set.

[0047] Further, the spatio-temporal distribution characteristics in step 4 include the runoff process changes of different time scales, the flow differences of dry and wet seasons, the interannual fluctuation trends and the water distribution patterns between different spatial units; the different time scales include day by day, month by month and year by year; the different spatial units include sub-basins, contour zones and control sections.

[0048] Further, the calculation of the compliance of ecological flow in multiple scenes in step 53 is specifically: for the ecological base flow, the annual guarantee rate in the research period is required to be not less than 90%, that is, the number of years of compliance is not less than 90% of the total number of years; for the annual ecological water volume, the guarantee rate is required to be not less than 75%; wherein, the condition for judging the annual compliance of ecological base flow is that the proportion of each year of compliance is greater than or equal to 95%, and the base flow target period is continuous flow and the continuous non-compliance days are less than or equal to 7 days, which is expressed as:

[0049]

[0050] In the formula, n sat is the number of days per year when the daily flow exceeds the ecological base flow target; M is the total number of days in a year; Q j is the flow on the jth day of the year, m 3 / s; n gap represents the number of consecutive days in a year that do not meet the standard.

[0051] The method of the present application can realize system simulation of the response of the complex system in the water source area by constructing a natural-social dual water cycle coupling model and embedding the joint regulation mechanism of water diversion and water storage projects, can effectively reveal the comprehensive influence of complex water conservancy projects on water resources and ecological environment, has strong adaptability and predictability, can support simulation and comparison under different project layouts and operation scenarios, effectively solves the simulation problem of the regulation and storage effect of reservoirs with no or little data, and provides decision support for scientifically formulating the water diversion scale and guaranteeing the ecological flow.

[0052] The present application will be further described in detail below in combination with the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0053] Figure 1 is a flowchart of the method of the present application;

[0054] Figure 2 is a flowchart of the process of determining the actual adjustable water quantity and the discharged water quantity under different water diversion conditions;

[0055] Figure 3 is a flowchart of the process of determining the actual water diversion quantity of the project;

[0056] Figure 4 is a flowchart of the reservoir inflow and outflow flow simulation results in Example 1;

[0057] Figure 5 is a flowchart of the reservoir group water diversion process in Example 1. DETAILED DESCRIPTION

[0058] The present application discloses an evaluation method for the influence of reservoir-water diversion project joint regulation on downstream ecological flow, as shown in Figure 1 The method comprises the following steps:

[0059] Step 1: Data Collection in the Study Area: Collect basic data for the study area, specifically including hydrological and meteorological data (including precipitation, wind speed, relative humidity, sunshine duration, and measured runoff at stations), underlying surface data (including land use and irrigation area distribution), topographic and soil data (including DEM and soil type), river system data (including river system distribution, river cross-section information, basic reservoir parameters and regulation information), vegetation data (including leaf area index and normalized difference vegetation index), water intake data (including agricultural, industrial, and domestic water intake and water intake information), and water diversion project data (including location, water diversion scale, source reservoir scale, and designed water diversion volume of water conveyance tunnels), etc. Based on this, reasonable river network extraction thresholds were set according to the collected DEM and river system data, and the sub-basins of the study area were divided. Then, based on the spatial distribution information of plains and hilly areas extracted from the DEM, each sub-basin was further subdivided into multiple contour zones, forming a basic calculation unit of "sub-basin-contour zone" combination. Finally, the basic data was uniformly displayed in each calculation unit to provide data support for subsequent calculations.

[0060] Step 2: Construct the natural water cycle model WEP-NHA for the water source area of ​​the water transfer project: Use basic data to drive the distributed hydrological model WEP (Water and Energy Transfer Process) to simulate the daily runoff process, and combine the measured runoff data of the stations to calibrate and verify the main parameters of the model by region. The simulation results are evaluated using the Nash efficiency coefficient (NSE) and relative error (RE), and finally the natural water cycle model WEP-NHA for the water source area of ​​the water transfer project is constructed.

[0061] The formulas for calculating the Nash efficiency coefficient (NSE) and relative error (RE) are as follows:

[0062]

[0063] In the formula, Q sim,i and Q obs,i These are the simulated and measured values ​​of runoff (m). 3 / s); N is the length of the analog series; The average value of measured runoff over many years (m) 3 / s).

[0064] Step 3: Constructing the Natural-Social Dual Water Cycle Coupled Model WEP-HA: Based on the natural water cycle model WEP-NHA in the water source area of ​​the water transfer project, three functional modules—socio-economic water use, reservoir regulation, and water transfer—are embedded to form a coupled computational framework for the interaction between the natural and social water cycles, thus constructing the natural-social dual water cycle coupled model WEP-HA. This model consists of a natural water cycle subsystem and a social water cycle subsystem: the natural water cycle subsystem, with WEP-NHA as its core, simulates processes such as precipitation, evapotranspiration, runoff generation, and runoff confluence; the social water cycle subsystem includes modules for socio-economic water use, reservoir regulation, and water transfer, respectively realizing water demand simulation, dynamic reservoir capacity adjustment, and inter-regional water allocation. The natural and social water cycle subsystems are dynamically coupled along the time step through water balance equations, realizing the sequential calculation and feedback of runoff—water use—regulation—water transfer, thereby obtaining comprehensive water cycle simulation results that simultaneously reflect the impact of natural processes and human activities.

[0065] Specifically, for the socio-economic water use module: using collected water use data from agriculture, industry, and domestic use in the study area, the data is distributed to various computing units based on land use data, irrigation district distribution, and irrigation system to input into the WEP-NHA model.

[0066] For the reservoir regulation module: First, the reservoirs within the study area that need to be included in the regulation module are determined based on their regulation capacity. For example, in daily scheduling simulations, the regulation function of daily and weekly regulating reservoirs can be disregarded due to their small capacity and limited regulation capacity. Second, scheduling rules are set based on the completeness of the collected reservoir operation data, namely: 1) For reservoirs with complete and detailed operation data, conventional scheduling simulations are conducted using existing scheduling procedures and scheduling diagrams; 2) For reservoirs with little or no data, conceptual storage and release rules based on characteristic water levels are used for regulation.

[0067] The basic principle of the conceptual storage and release rule for reservoirs based on characteristic water levels is to scientifically generalize the scheduling process of cascade reservoirs by defining key parameters such as dead water level, flood control limit water level, normal storage water level, and flood control high water level. The reservoir outflow is jointly determined by the inflow, storage capacity, and control objectives. The reservoir storage capacity at time t can be expressed as:

[0068] V t =V t-1 +Δt×(Q in -Q out )-Q e (3)

[0069] In the formula, V t With V t-1 Q represents the water storage at the end of time t and the initial water storage, respectively; in and Qout represents the inflow and outflow of the reservoir at time t; Q e represents the loss term of the reservoir (including evaporation, seepage, etc.).

[0070] outflow Q out is determined by the following formula:

[0071]

[0072] In the formula, V d , V c , and V f respectively represent the dead water level, normal storage level (flood control limit water level in flood season), and flood control high water level corresponding to the reservoir capacity; Δt represents the time step; Q s represents the maximum acceptable outflow under the purpose of flood control, which can be the runoff simulation value corresponding to the cumulative probability of 99% at the dam site; Q min and Q' min respectively represent the minimum outflow before and after correction; Q n represents the normal outflow, reflecting the downstream human water demand situation; k (k≤1) is an index indicating the severity of the inflow flood; r represents the correction coefficient, which is used to measure the relative deviation of the current storage capacity from the target storage capacity. The specific calculation formulas of k and r are as follows:

[0073]

[0074] wherein:

[0075]

[0076] In the formula, I t represents the inflow at time t; V tar,m represents the target reservoir capacity in the mth month; c is a parameter to avoid excessive changes in the outflow of the multi-year regulation reservoir; Q s is the runoff simulation value corresponding to the cumulative probability of 99% at the dam site;

[0077] Q n has a greater impact on the regulation of the reservoir, and current research has found that the actual process can be more effectively reflected by determining it through the following formula:

[0078] Q n = V cw ×0.7 / (180×86400) + Q mean ×0.25 (8)

[0079] In the formula, V cw represents the reservoir capacity corresponding to the flood control limit water level; Q mean represents the multi-year average runoff at the dam site.

[0080] Q min The ecological base flow of the dam site section of each reservoir during the regulation and storage process can be taken as the value, and the specific determination process is as follows: 1) for the built project, the ecological flow approved by the relevant department is used as the reference; 2) for the planned reservoir, hydrological methods such as Q90, Q95, 90% of the driest day flow, 7Q10 method and duration curve method are comprehensively used to calculate the ecological base flow target value in the dry period and the non-dry period. In addition, the “Reservoir Ecological Flow Discharge Regulation” (SL / T819-2023) clearly points out that when the water level of the reservoir drops to the dead water level and the inflow is less than the ecological flow discharge target, the reservoir can discharge the ecological flow according to the inflow, and at this time the discharge capacity is Q min .

[0081] For the water transfer module: in the present application, the water transfer project belongs to the water source project with regulation capacity, that is, this type of project plans to build new reservoir projects in the water source area or utilize the built reservoir projects for water transfer, so as to meet the water transfer guarantee rate requirement through the storage and drought alleviation capacity of the reservoir. In the model, the water taking process of this type of project is accurately described by the reservoir regulation and storage module. The reservoir regulation and storage module first calculates the available water quantity for water transfer according to the regulation rules; the water transfer module determines the actual water transfer process in combination with the water source reservoir project scale, tunnel design water diversion quantity, etc. on this basis. The water transfer term is introduced into the water balance equation, which can uniformly reflect the dynamic coupling relationship between the reservoir regulation and the water transfer project.

[0082] V t =V t-1 +Δt×(Q in -Q out )-Q e -Q tran_act (9)

[0083] In the formula, Q tran_act represents the actual water transfer quantity of the reservoir project at time t.

[0084] Among them, the basis premise for determining Q tran_act is to preferentially guarantee the ecological flow and local domestic and productive water through the reservoir regulation and storage module, therefore, the actual water transfer quantity and discharge quantity process of the water conservancy project at each period need to be comprehensively determined in combination with the initial conditions of reservoir capacity / water level and inflow variation, etc., such as Figure 2The process is first divided into two types of flood season and non-flood season according to whether it is in flood season, and the specific scheduling strategy is determined by combining the relative relationship between the current water level and the key control water level (flood control high water level, normal storage level, flood limit water level, dead water level) in each path. In the non-flood season, when the water level ≥ the flood control high water level, execute the maximum discharge and water regulation; when the normal storage level ≤ the water level < the flood control high water level, according to the inflow and water demand, the target discharge and water regulation or ecological discharge and water regulation can be selected; when the dead water level < the water level < the normal storage level, according to the conditions, the target discharge and water regulation, ecological discharge and water regulation, or only ecological discharge can be selected; when the water level ≤ the dead water level, the ecological discharge cannot be satisfied. The judgment logic of the flood season stage is similar to the above, but the normal storage level is adjusted to the flood limit water level, that is, when the water level ≥ the flood control high water level, execute the maximum discharge and water regulation; when the flood limit water level ≤ the water level < the flood control high water level, according to the inflow and water demand, the target discharge and water regulation or ecological discharge and water regulation can be selected; when the dead water level < the water level < the flood limit water level, according to the conditions, the target discharge and water regulation, ecological discharge and water regulation, or only ecological discharge can be selected; when the water level ≤ the dead water level, the ecological discharge cannot be satisfied. And the flood control safety is placed as the primary constraint condition, so as to dynamically determine the actual adjustable water quantity Q tran_act of each period through the scene-based, multi-branch water level partition response mechanism, and realize the fine and safe control of the water regulation process.

[0085] Taking the initial (daily scale) reservoir water level in the non-flood season period as an example, the analysis of the outflow and the actual adjustable water quantity is shown in Figure 3 . First, according to the above-mentioned conceptual storage and discharge rule of the reservoir based on the characteristic water level, the real-time outflow of the reservoir is determined, and it is judged whether the outflow exceeds the ecological base flow. If not, the water regulation is not considered; if yes, the adjustable water quantity (the water quantity between the reservoir capacity at the end of the period and the dead storage) is checked whether it meets the design water diversion quantity. If yes, the water diversion is carried out according to the design water diversion quantity, and the outflow is not modified; if not, the outflow is modified to the ecological base flow, and the adjustable water quantity is checked again whether it exceeds the design water diversion quantity. If not, the actual water regulation quantity is the adjustable water quantity; if yes, the actual water regulation quantity is the design water diversion quantity, and the outflow is modified again.

[0086] Step 4, simulate the runoff of the water source area by using the WEP-HA model: set different working condition scenarios, and simulate the runoff of the water source area by using the WEP-HA model on a daily scale; the setting of the working condition scenarios should follow the following principles:

[0087] 1) Consistency of boundary conditions: consistent hydro-meteorological and basic data such as land use, water system and geological conditions should be used in different working condition scenarios to ensure the comparability of the simulation results.

[0088] 2) Regulation combination comprehensiveness: The socio-economic water demand process, reservoir regulation capacity, and water diversion project operation characteristics should be fully considered, and the joint regulation scenarios covering different reservoir regulation rules, water diversion scales, and operation modes should be reasonably set.

[0089] Through the above scenario simulation, the spatiotemporal distribution characteristics of the river water in the water source area under multiple scenarios can be obtained, including the runoff process changes at different time scales (daily, monthly, and yearly), the flow differences between dry and wet seasons, the interannual fluctuation trends, and the water distribution patterns among different spatial units (sub-basins, contour zones, and control sections), providing a data basis for subsequent analysis of the ecological flow guarantee degree.

[0090] Step 5, System analysis of the variation degree of water quantity and ecological flow guarantee rate at typical sections in the water source area under the superposition of reservoirs and water diversion projects: Specifically including the following steps:

[0091] Step 51, Selection of typical sections: According to the characteristics of the river in the water source area and the operation characteristics of the main water conservancy projects, the river sections meeting at least one of the following objective conditions are selected as typical sections, including: 1) Located at hydrological control points such as the outlet of the basin or the inlet of the main tributary; 2) Located in the river section directly affected by reservoir or water diversion hub regulation, with long-term continuous and reliable hydrological observation or stable calculation of flow data; 3) Located in the ecologically sensitive river section, as the key position for ecological flow guarantee analysis.

[0092] Step 52, Analysis of the spatiotemporal distribution characteristics of water quantity: Based on the output results of WEP-HA model, the daily runoff data of the river in the water source area and the typical sections under each scenario are extracted, and the spatiotemporal distribution rules and trends of water quantity under the superposition of reservoirs and water diversion projects are analyzed.

[0093] Step 53, Calculation of ecological flow guarantee rate: Combined with the ecological water demand requirements of typical sections, the compliance of ecological flow under multiple scenarios is calculated, specifically: For ecological base flow, the annual guarantee rate should not be less than 90% (i.e., the number of years meeting the standard should not be less than 90% of the total number of years); for annual ecological water quantity, the guarantee rate should not be less than 75%. The conditions for judging the annual compliance of ecological base flow are: the proportion of days meeting the standard each year is ≥95%, and the continuous non-compliance days are ≤7 days when there is a base flow target period, expressed as:

[0094]

[0095] In the formula, n sat is the number of days each year when the daily flow exceeds the ecological base flow target; M is the total number of days in a year; Q j is the flow on the jth day of the year, m 3 / s; n gap represents the number of consecutive non-compliance days in a year.

[0096] Step 54, comparison of the difference in the influence of different scenarios: comparative analysis of the ecological flow guarantee rate and the river water distribution characteristics of the typical section under different regulation scenarios, to identify the influence of different reservoir regulation and water transfer combination schemes on the downstream ecological flow, and to provide decision basis for water transfer scale optimization and ecological protection.

[0097] Embodiment one

[0098] This embodiment is an application example of the above method.

[0099] This embodiment takes the water source area of a large water transfer project in southwest China as the research area, and discloses an evaluation method for the influence of reservoir-water transfer project joint regulation on downstream ecological flow, which specifically includes the following steps:

[0100] Step 1, research area data collection: collect the basic data of the research area during the research period of 1956-2020, including hydro-meteorological data, underlying surface data, terrain and soil data, river system data, vegetation data, water use data, water transfer project data, etc. By adjusting the virtual river network extraction threshold, the research area is divided into 1089 sub-basins, and on this basis, the information of contour belts is embedded to further divide it into 7312 basic calculation units; combined with the distribution of basic data and the characteristics of calculation units, the data is uniformly distributed to each calculation unit.

[0101] Step 2, build water transfer project water source area natural water cycle model WEP-NHA: use the distributed hydrological model WEP to carry out daily runoff process simulation; based on the measured monthly restored runoff data of multiple stations, the main parameters of the model are calibrated and verified in different regions, the results show that the RE of monthly natural runoff simulation is basically controlled within 3%, the average NSE reaches 0.87, and the finally built water source area natural water cycle model WEP-NHA can effectively and accurately depict the river water process.

[0102] Step 3, build natural-society dual water cycle coupling model WEP-HA: embed the social and economic water use, reservoir regulation and water transfer module based on the WEP-NHA model, and build the natural-society dual water cycle coupling model WEP-HA.

[0103] Regarding the social and economic water use module: use the collected agricultural, industrial and domestic water use data in the research period of the research area, according to the land use data, irrigation district distribution and irrigation system, etc. The data is distributed to the calculation unit to input the WEP-NHA model, and the data set is used to verify the model; in the scenario analysis process, if the future scenario is considered, the future water demand prediction needs to be made according to the urbanization, population, GDP, agricultural development, etc.

[0104] As for the reservoir regulation module: considering the construction of the built and planned reservoirs in the study area, the model is operated at a daily scale. The daily regulation and weekly regulation reservoirs are not included in the daily operation simulation range due to their small storage capacity and limited regulation capacity. Combined with the collected operation data of the reservoirs in the study area, the conceptual reservoir regulation rule based on the characteristic water level is finally determined for regulation. To verify the applicability of the regulation rule in the study area, the monthly inflow and outflow of multiple built reservoirs are combined for evaluation. The relative error of the inflow and outflow runoff simulation of the verification reservoirs is basically controlled within 5% during the verification period, and the average Nash efficiency coefficients of the inflow and outflow are 0.88 and 0.73, respectively. Figure 4 The monthly simulation results of a certain reservoir from 2015 to 2018 are shown in the figure. The simulation results show that the constructed conceptual reservoir regulation rule has good applicability in the water source area and can be used for subsequent analysis.

[0105] As for the water transfer module: in this embodiment, the water source project of the water transfer project in the study area is a reservoir group, which is planned to be implemented in 2035. According to the planning, six water source reservoirs will be built on each tributary in the water source area basin A, and the water quantity will be transferred to the receiving area B through a unified water transfer line, as shown in Figure 5 When embedding the water transfer project module into the WEP-HA model, the water source reservoirs should be allocated to the corresponding sub-basins according to their latitude and longitude positions, and the planned water transfer scale and design water transfer flow of each reservoir should be determined to support the simulation and analysis of the water transfer process.

[0106] Step 4: Simulate the runoff in the water source area using the WEP-HA model: set different working conditions, and simulate the runoff in the water source area at a daily scale using the WEP-HA model. The scene setting should comply with the principles of "boundary condition consistency" and "regulation combination comprehensiveness". In this embodiment, the meteorological input data is selected by referring to the obtained basic data, the social and economic water demand data is predicted and set according to the regional development planning, and the engineering operation parameters are configured according to different reservoir regulation and water transfer combination schemes to form multiple scenarios, as shown in Table 1:

[0107] Table 1 Different scene settings

[0108]

[0109]

[0110] Step 5, system analysis of the variation degree of water quantity and ecological flow guarantee rate of typical section in water source area under the superposition of reservoir and water transfer project: comparative analysis of the ecological flow guarantee rate and the temporal and spatial distribution characteristics of river water quantity of key control section under three working conditions, and identification of the potential influence of different reservoir regulation and water transfer combination schemes on downstream ecological flow. In this embodiment, combined with the engineering layout characteristics, four typical sections are selected for analysis of annual ecological water quantity compliance degree and ecological base flow compliance degree, and the results are shown in Tables 2 and 3, respectively.

[0111] Table 2 Typical section annual ecological water quantity compliance degree

[0112]

[0113] Table 3 Typical section ecological base flow compliance degree

[0114]

[0115] Finally, it should be noted that the above description is only to illustrate the technical solutions of the present application and not to limit. Although the present application has been described in detail with reference to the preferred arrangement, it should be understood by those skilled in the art that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A method for evaluating the influence of joint regulation of reservoirs and water diversion projects on downstream ecological flow, characterized in that, The method comprises the following steps: Step 1, research area data collection: collecting basic data of the research area, including hydro-meteorological data, underlying surface data, terrain soil data, river system data, vegetation data, water use data, water transfer project data; setting a river network extraction threshold according to the collected terrain soil data and river system data, dividing the sub-basins of the research area; and embedding the contour band information to divide the basic calculation units on this basis; finally, the basic data is uniformly distributed to each calculation unit; Step 2, constructing a water source area natural water cycle model WEP-NHA of the water transfer project: using the basic data to drive the distributed hydrological model WEP to carry out daily runoff process simulation, and carrying out zoned calibration and verification of the model parameters, and using the Nash efficiency coefficient NSE and the relative error RE to evaluate the simulation results, and finally constructing the water source area natural water cycle model WEP-NHA of the water transfer project; Step 3, constructing a natural-society dual water cycle coupling model WEP-HA: on the basis of the constructed water source area natural water cycle model WEP-NHA of the water transfer project, embedding a social and economic water use module, a reservoir regulation module and a water transfer module to form a coupling calculation framework of the interaction between natural water cycle and social water cycle, and constructing a natural-society dual water cycle coupling model WEP-HA; the model is composed of a natural water cycle subsystem and a social water cycle subsystem: the natural water cycle subsystem takes WEP-NHA as the core to simulate the processes of precipitation, evapotranspiration, runoff generation and confluence; the social water cycle subsystem includes a social and economic water use module, a reservoir regulation module and a water transfer module, which respectively realize water demand simulation, reservoir capacity dynamic regulation and cross-region water allocation; Step 4, simulating the runoff of the water source area by using the WEP-HA model: setting different working conditions, simulating the runoff of the water source area at the daily scale by using the WEP-HA model, and obtaining the temporal and spatial distribution characteristics of the water source area river water under multiple scenarios; Step 5, systematically analyzing the change degree of the water quantity and the ecological flow guarantee rate of the typical section of the water source area under the superposition of the reservoir and the water transfer project: specifically comprising the following steps: Step 51, selecting a typical section: according to the characteristics of the river channel of the water source area and the operation characteristics of the water conservancy project, selecting a river section meeting at least one of the following conditions as a typical section, including: 1) located at the hydrological control point of the outlet of the basin or the inlet of the main tributary; 2) located in the river section directly affected by the regulation of the reservoir or the water transfer hub, and having long-term continuous and reliable hydrological observation or stable calculation of the flow data; 3) located in the ecologically sensitive river section, which is a key position for ecological flow guarantee analysis; Step 52, analyzing the temporal and spatial distribution characteristics of water quantity: based on the output results of the WEP-HA model, extracting the daily runoff data of the river channel and the typical section of the water source area under each scenario, and analyzing the temporal and spatial distribution law and change trend of the water quantity under the superposition of the reservoir and the water transfer project; Step 53, calculating the ecological flow guarantee rate: combining the ecological water demand requirement of the typical section, calculating the compliance of the ecological flow under multiple scenarios; Step 54, comparison of the influence difference of different scenarios: comparative analysis of the typical section ecological flow guarantee rate and river water distribution characteristics under each regulation scenario, and identification of the influence of different reservoir regulation and water diversion combination schemes on the downstream ecological flow.

2. The method according to claim 1, wherein the method is characterized in that, The hydro-meteorological data in step 1 include precipitation, wind speed, relative humidity, sunshine duration and site measured runoff; the underlying surface data include land use and irrigation area distribution; the terrain and soil data include DEM and soil type; the river system data include river system distribution, river section information, reservoir basic parameters and regulation information; the vegetation data include leaf area index and normalized vegetation index; the water use data include agricultural, industrial and domestic water use, and water intake information; and the water diversion engineering data include location, water diversion scale, water source reservoir scale and designed water intake of the water diversion tunnel.

3. The method according to claim 1, wherein the method is characterized by, The calculation formulas of the Nash efficiency coefficient NSE and the relative error RE in step 2 are as follows: where Q sim,i and Q obs,i are the simulated and measured values of runoff, respectively, m 3 / s; N is the length of the simulation series; is the multi-year average of the measured values of runoff, m 3 / s.

4. The method according to claim 1, wherein, The specific process of embedding the social and economic water use module, the reservoir regulation module and the water diversion module in step 3 is as follows: For the social and economic water use module: the collected water use data of the study area are distributed to each calculation unit according to the underlying surface data and irrigation system to input the WEP-NHA model; For the reservoir regulation module: first, the reservoirs that need to be included in the regulation of the study area are determined according to the regulation capacity; second, the regulation rules are set according to the collected reservoir operation data, which are as follows: 1) for reservoirs with complete operation data, the existing regulation rules and regulation charts are used for conventional regulation simulation; 2) for reservoirs without or with little data, the conceptual regulation rules based on characteristic water level are used for regulation. The conceptual regulation rules based on characteristic water level are used to scientifically generalize the regulation process of cascade reservoirs by defining the parameters of dead water level, flood control limit water level, normal water level and flood control high water level. The reservoir outflow is determined by the inflow, storage capacity and control target. The reservoir storage capacity at time t is represented as follows: V t = V t-1 + Δt x (Q in - Q out ) - Q e (3) In the formula, V t and V t-1 respectively represent the water storage at the end of time t and the initial water storage; Q in and Q out represent the inflow and outflow of the reservoir at time t; and Q e represents the loss term of the reservoir. Outflow Q out is determined by the following equation: In the formula, V d , V c , and V f respectively represent the dead water level, the normal storage water level / flood control limit water level, and the reservoir capacity corresponding to the flood control high water level; Δt represents the time step; Q s represents the maximum acceptable discharge under the flood control purpose; Q min and Q' min respectively represent the minimum discharge before and after the correction; Q n represents the normal discharge; k (k≤1) is an index indicating the severity of the inflow flood; and r represents a correction coefficient for measuring the relative deviation of the current storage amount from the target storage amount; wherein the specific calculation formulas of k and r are as follows: For the water diversion module: the water intake process of the water diversion project is described by the reservoir regulation module. The reservoir regulation module first calculates the available water for water diversion according to the regulation rules. Based on this, the water diversion module determines the actual water diversion process in combination with the water source reservoir project scale and the designed water intake of the tunnel. The water diversion term is introduced into the water balance equation to reflect the dynamic coupling relationship between reservoir regulation and water diversion projects. In the formula, I t represents the storage flow at time t; V tar,m represents the target storage capacity of the mth month; c is a parameter; Q s The value is the runoff simulation value corresponding to the 99% cumulative probability at the dam site; Q n The calculation formula is: Q n = V cw x 0.7 / (180 x 86400) + Q mean x 0.25 (8) In the formula, V cw represents the reservoir capacity corresponding to the flood control limit water level; Q mean represents the multi-year average runoff at the dam site; Q min The ecological base flow of each reservoir dam site section during the regulation and storage process is taken as the value, and the specific determination process is as follows: 1) for the built project, the ecological flow approved by the relevant department is used as the reference; 2) for the planned reservoir, the Q90, Q95, 90% of the driest day flow, 7Q10 method and duration curve method are comprehensively used to calculate the ecological base flow target value in the dry period and the non-dry period respectively; and when the reservoir water level drops to the dead water level and the inflow is less than the ecological flow discharge target, the reservoir discharges the ecological flow according to the inflow, and at this time, the discharge capacity is Q min ; The following principles are followed in step 4 to set different working condition scenarios: V t = V t-1 + Δt x (Q in - Q out ) - Q e - Q tran_act (9) In the formula, Q tran_act represents the actual adjustable water volume of the reservoir project at time t; Q tran_act The determination of the actual adjustable water volume of the reservoir project at time t is made by combining the initial conditions of reservoir capacity / water level and the water inflow variation of various water regulation conditions, and comprehensively determining the actual adjustable water volume and the water discharge process of the water conservancy project at each period. First, according to whether it is in the flood season, the regulation path is divided into two types of flood season and non-flood season, and the specific regulation strategy is determined in each path by combining the current water level and the relative relationship of the key control water level including the flood control high water level, the normal storage water level, the flood limit water level and the dead water level. In the non-flood season, when the water level is greater than or equal to the flood control high water level, the maximum discharge and water regulation are performed; when the normal storage water level is less than the water level and the flood control high water level, according to the inflow and water demand, the target discharge and water regulation or the ecological discharge and water regulation are selected; when the dead water level is less than the water level and the normal storage water level, according to the conditions, the target discharge and water regulation, the ecological discharge and water regulation, or only the ecological discharge are selected; when the water level is less than or equal to the dead water level, the ecological discharge cannot be satisfied; in the flood season, when the water level is greater than or equal to the flood control high water level, the maximum discharge and water regulation are performed; when the flood limit water level is less than the water level and the flood control high water level, according to the inflow and water demand, the target discharge and water regulation or the ecological discharge and water regulation are selected; when the dead water level is less than the water level and the flood limit water level, according to the conditions, the target discharge and water regulation, the ecological discharge and water regulation, or only the ecological discharge are selected; when the water level is less than or equal to the dead water level, the ecological discharge cannot be satisfied; and the flood control safety is placed as the primary constraint condition, the actual adjustable water volume at each period is dynamically determined through the scene-based and multi-branch water level zoning response mechanism.

5. The method according to claim 1, wherein, 1) consistency of boundary conditions: consistent basic data are used in different working condition scenarios to ensure the comparability of the simulation results; 2) comprehensiveness of regulation combination: the social and economic water demand process, reservoir regulation capacity and water diversion engineering operation characteristics are fully considered to reasonably set joint regulation scenarios covering different reservoir regulation rules, water diversion scales and operation modes. The time and space distribution characteristics in step 4 include runoff process changes at different time scales, flow differences between dry and wet seasons, interannual fluctuation trends and water distribution patterns between different spatial units. The different time scales include daily, monthly and annual. The different spatial units include sub-basins, contour zones and control sections.

6. The method according to claim 1, wherein, ​ 7. The method according to claim 1, wherein the method is characterized by, The calculation of the compliance of the ecological flow in multiple scenarios in step 53 is as follows: for the ecological base flow, the annual guarantee rate in the research period is required to be not less than 90%, that is, the number of years of compliance is not less than 90% of the total number of years; for the annual ecological water quantity, the guarantee rate is required to be not less than 75%; wherein, the condition for judging the annual compliance of the ecological base flow is that the proportion of days of compliance per year is greater than or equal to 95%, and the continuous non-compliance days are less than or equal to 7 days when there is a base flow target period, and the expression is: wherein n sat is the number of days per year that the daily flow exceeds the ecological baseflow target; M is the total number of days in a year; Q j is the flow on the jth day of the year, m 3 / s; n gap represents the number of consecutive non-compliance days within a year.

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