Cross-basin water regulation, supply and distribution integrated decision-making method for guaranteeing ecological flow

Abstract

The invention belongs to the technical field of reservoir dispatching, and particularly provides a cross-basin water dispatching, supply and distribution integrated decision-making method for guaranteeing ecological flow, which comprises the following steps: constructing a two-stage optimization dispatching model of a cross-basin water supply reservoir system based on a dynamic optimality principle; quantitatively describing ecological water demand processes of a water source area and a water receiving area in the cross-basin system engineering under different ecological water demand levels by utilizing a Tennant method; performing optimization calculation on the optimization scheduling model under different ecological water demand levels by utilizing dynamic planning to obtain a regional water regulation and supply process; constructing a regional water resource optimal configuration model according to the water regulation and supply results; factors such as ecological water demand guarantee degree and decision manager preference are comprehensively considered, and a practical regional water distribution scheme is formulated. According to the method, the water transfer amount and the water supply amount of the cross-basin reservoir system can be effectively determined, meanwhile, the water competition problem of'life, living and living 'of a region is solved, and technical support is provided for reasonability and scientificity of decision making of the cross-basin reservoir system.

Description

Technical Field

[0001] The present invention belongs to the technical field of reservoir regulation, and in particular, relates to an integrated decision-making method for cross-basin water supply and distribution to ensure ecological flow. Background Art

[0002] Affected by climate change and strong human activities, the temporal and spatial distribution of water resources has become increasingly unbalanced, and the frequency and intensity of regional waterlogging, drought, floods and other disasters have become more frequent and severe. As one of the main measures for the "spatial balance" of water resources, inter-basin water transfer projects achieve the goal of regional water resource balance by diverting and transferring surplus water resources from the water source area to the receiving area with relatively scarce water resources, using the hydrological compensation and reservoir capacity compensation of different basins. Therefore, the construction of an inter-basin water resources optimization and allocation model has important scientific significance and application value for scientifically determining the diversion, transmission, distribution, storage and supply of the project and ensuring regional water supply security. At the same time, inter-basin water transfer projects integrate water resources diversion, transmission, distribution, supply and storage, involving many variables. The diversion, transmission, distribution and supply and storage decisions are interconnected and mutually restricted, resulting in the problem of inter-basin reservoir optimization scheduling with high decision-making quantity dimensions and complex decision-making structure. It is a difficult problem for reservoir optimization scheduling and sustainable utilization of water resources. In particular, the inter-basin reservoir system often faces the problem of competition for water use in production, life, and ecology during the secondary distribution of regional water resources. Unreasonable regional water distribution plans will affect the stable development of the social economy and cause damage to the health of river water ecology, thus affecting the rationality and scientific nature of decision-making in the inter-basin reservoir system.

[0003] However, the existing cross-basin water resources optimization and supply allocation technology lacks sufficient attention in the integrated modeling decision-making technology. It usually adopts a rigid nested boundary constraint method to determine the water supply and regional allocation of water, resulting in weak linkage in the decision-making process and poor systematization of the optimization scheduling structure. In addition, the existing allocation schemes often focus on meeting the water needs of production and life, and rarely consider the ecological flow process of rivers with different health levels. Especially for cross-basin water transfer projects, it is necessary to comprehensively coordinate the ecological and environmental water requirements of different regions to achieve sustainable development of the ecological environment and social economy. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide an integrated decision-making method for cross-basin water supply and distribution to ensure ecological flow, so as to ensure that the water resources in the region can meet the water needs of various industries and at the same time ensure the healthy development of the ecosystem.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a cross-basin water supply and distribution integrated decision-making method to ensure ecological flow, comprising the following steps:

[0006] Step 1: Construct a two-stage optimal operation model for the cross-basin water supply reservoir system based on the principle of dynamic optimality;

[0007] Step 2: Quantitatively describe the ecological water demand processes in the water source area and the water receiving area of the cross-basin water supply reservoir system project through the Tennant method;

[0008] Step 3: Use the dynamic programming solution technique to optimize and solve the two-stage optimal operation model for the cross-basin water supply reservoir system based on the principle of dynamic optimality in Step 1. Select different combinations of wet, normal, and dry scenarios to obtain the water transfer and supply processes in the region under different ecological water demand levels;

[0009] Step 4: According to the basic principles of optimal water volume allocation and the water transfer and supply results of the cross-basin project obtained in Step 3, with the total regional water supply as a rigid constraint and the lowest comprehensive water shortage degree of different water use departments as the allocation goal, construct a regional water resources optimal allocation model;

[0010] Step 5: Develop a regional optimal water distribution plan that meets the actual management requirements.

[0011] In the preferred solution, in Step 1, when constructing the two-stage optimal operation model for the cross-basin water supply reservoir system based on the principle of dynamic optimality, it specifically includes the following steps:

[0012] S101: First, construct the objective function, define the objective function as the optimization of the comprehensive benefit of the cross-basin water supply project system, and the expression is:

[0013]

[0014] In the formula, represents the water supply benefit function of the water source reservoir; represents the water supply benefit function of the water receiving reservoir; represents the water transfer cost function; t 总 represents the total decision time range; m represents the number of water receiving reservoirs, represents the water supply volume of the water source reservoir at time t; R t j represents the water supply volume of the water receiving reservoir j at time t; T t j represents the water transferred into the water receiving reservoir j at time t;

[0015] S102: Construct the constraint conditions: The two-stage optimal operation model of the cross-basin water supply reservoir system needs to satisfy the water volume balance equations, storage volume constraints, water supply constraints, and water transfer volume constraints of the water source reservoir and each water receiving reservoir;

[0016] S103. According to the Bellman optimality principle, the long-term optimal scheduling problem is transformed into a two-stage optimization problem associated with a state transition equation. The water storage S is defined as the state variable, and the water supply R and the water transfer volume T are defined as decision variables. The expression of the Bellman equation is:

[0017]

[0018] In the formula, is the value function of the inter-basin water supply system for the reservoir group water storage state combination at the t-th time period, representing the maximum benefit value represented by this water storage state combination during the period from the t-th time period to the end of the scheduling period. represents the water storage of the water source reservoir at the beginning of the t-th time period. represents the water storage of the water receiving reservoir at the beginning of the t-th time period.

[0019] The change of the water storage state of the inter-basin reservoir system over time is described by the reservoir water balance equation, and the expression is:

[0020]

[0021] In the formula, represents the water storage of the water source reservoir at the end of the t-th time period, that is, at the (t + 1)-th moment. represents the total water supply of the water source reservoir in the t-th time period. represents the total water transfer volume of all water receiving reservoirs in the t-th time period. represents the available water volume of the water source reservoir in the t-th time period, which is defined as the water storage of the water source reservoir at the beginning of the t-th time period plus the incoming water volume, and then minus the water volume lost due to evaporation and seepage. represents the water storage of the water receiving reservoir j at the beginning of the (t + 1)-th time period; T t j represents the water transfer volume of the water receiving reservoir j in the t-th time period. represents the available water volume of the water receiving reservoir j in the t-th time period, which is defined as the water storage of the water receiving reservoir at the beginning of this time period plus the incoming water volume, and then minus the water volume lost due to evaporation and seepage.

[0022] The above Bellman equation is simplified, and the expression is:

[0023]

[0024] In the preferred solution, in step 2, quantitatively describing the ecological water demand processes in the water source area and the water receiving area of the inter-basin water supply reservoir system by the Tennant method includes the following steps:

[0025] S201. Collect and sort out the long-term hydrological data of the study area, and calculate the corresponding average runoff of the study area as the reference point for calculating the basin ecological water demand.

[0026] S202. Based on the Tennant method recommendation standard, set the runoff percentage threshold standard under different ecological conditions, and combine with the multi-year average runoff data of the research area to calculate the ecological water demand process under different ecological water demand levels.

[0027] In the preferred solution, in step 3, the process of obtaining the water transfer and supply process in the region under different ecological water demand levels includes the following steps:

[0028] S301. Based on the historical runoff and water demand data of relevant reservoirs in the inter-basin water supply reservoir system, randomly generate simulation data through the Monte Carlo method;

[0029] S302. Sort the simulated runoff of each reservoir in ascending order of annual runoff. Take the scenario where the sorting is less than 37.5% as the dry year scenario, 37.5% - 62.5% as the normal year scenario, and greater than 62.5% as the wet year scenario;

[0030] S303. According to the ecological water demand under different ecological water demand levels in step 2, substitute it into the two-stage optimal operation model of the inter-basin water supply reservoir system, and use the dynamic programming algorithm to solve and calculate;

[0031] S304. Set the dry-wet-normal combination standard, select different dry-wet-normal combination scenarios to obtain the water transfer and supply process in the region under different ecological water demand levels.

[0032] In the preferred solution, in step S304, when selecting different dry-wet-normal combination scenarios, select two types of extreme scenarios: synchronous and asynchronous dry-wet-normal.

[0033] In the preferred solution, in step 4, constructing the regional water resources optimal allocation model includes constructing the objective function and constraint conditions, and then using linear programming to solve the optimal allocation model of the total regional water supply.

[0034] In the preferred solution, the objective function includes:

[0035] 1) Ecological water supply objective:

[0036]

[0037] In the formula, f1 represents the objective function of ecological water supply users; represents the ecological water demand of the receiving reservoir j at time t; represents the ecological available water supply of the receiving reservoir j at time t;

[0038] 2) Agricultural water supply objective:

[0039]

[0040] In the formula, f2 represents the objective function of agricultural water supply users; represents the agricultural water demand of receiving reservoir j at time period t; represents the available agricultural water supply of receiving reservoir j at time period t;

[0041] (3) Objectives of domestic and industrial water supply:

[0042]

[0043] In the formula, f3 represents the objective function of domestic and industrial water supply users; represents the domestic and industrial water demand of receiving reservoir j at time period t; represents the available domestic and industrial water supply of receiving reservoir j at time period t;

[0044] (4) The overall objective function is as follows:

[0045]

[0046] In the formula, F represents the overall objective function; ω1 represents the importance decision weight coefficient of the first sub-objective function; ω2 represents the importance decision weight coefficient of the second sub-objective function; ω3 represents the importance decision weight coefficient of the third sub-objective function.

[0047] In the optimal solution, the constraint conditions include:

[0048] 1) Total water supply constraint:

[0049]

[0050] In the formula, represents the ecological water supply of receiving area j at time period t; represents the agricultural water supply of receiving area j at time period t; represents the domestic and industrial water supply of receiving area j at time period t; represents the total water supply of receiving area j at time period t, corresponding to the total water supply of each area obtained from the optimal operation of the inter-basin water transfer reservoir system;

[0051] 2) Water supply constraint for water use departments

[0052] ① Supply-demand constraint for ecological water supply users:

[0053]

[0054] In the formula, represents the available ecological water supply of receiving reservoir j at time period t; Denotes the ecological water demand of the receiving reservoir j during period t, which is respectively set to the index values of different ecological water demand levels in the Tennant method; η represents the ecological guarantee coefficient; Is the minimum ecological flow;

[0055] ② Agricultural water supply user supply-demand constraint:

[0056]

[0057] In the formula, Denotes the water supply volume of the receiving reservoir j to agricultural water supply users during period t; Denotes the agricultural water demand of the receiving reservoir j during period t;

[0058] ③ Domestic and industrial water supply user supply-demand constraint:

[0059]

[0060] In the formula, Denotes the domestic and industrial water supply volume of the receiving reservoir j during period t; Denotes the domestic and industrial water demand of the receiving reservoir j during period t.

[0061] In the preferred solution, in step 5, when determining the optimal regional water resources allocation plan, the following three types of situations are set for specific analysis:

[0062] 1) Domestic and industrial water supply users > agricultural water supply users > ecological water supply users;

[0063] 2) Domestic and industrial water supply users > agricultural water supply users = ecological water supply users;

[0064] 3) Domestic and industrial water supply users > ecological water supply users > agricultural water supply users.

[0065] In the preferred solution, in step 5, the following steps are used to obtain the determined regional water resources allocation plan:

[0066] S501. Based on the above three situations, set the weight combination scenarios of the importance decision weight coefficients of the sub-objective functions for constructing the regional water resources optimal allocation model;

[0067] S502. Set the ecological water demand level, and substitute the long-term sequence total water supply results of each reservoir area obtained from the set ecological water demand level into the regional water resources optimal allocation model, and use the method of linear programming to solve the regional water resources optimal allocation model of each area to obtain the optimal weight combination;

[0068] S503. Based on the obtained optimal weight combination, set the ecological water demand level, set the ecological security coefficient, and use the method of linear programming to solve the regional water resources optimization allocation model for each region, obtain the water shortage rates of each water supply user, and determine the optimal ecological security coefficient and the regional water resources allocation plan.

[0069] The integrated decision-making method for cross-basin water transfer, supply and distribution to ensure ecological flow provided by the present invention has the following beneficial effects:

[0070] 1. Regarding the problem of ensuring ecological flow, by using dynamic programming and linear programming solution techniques, the water transfer and water distribution processes are precisely controlled, further improving the utilization efficiency of water resources and the guarantee effect of ecological flow.

[0071] 2. The present invention can not only dynamically adapt to the changes in different river basins, but also take into account the social and economic water demand while achieving the ecological flow target, achieving double optimization of economic benefits and ecological benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] The present invention will be further described below in conjunction with the drawings and embodiments:

[0073] Figure 1 is the overall flow chart of the present invention;

[0074] Figure 2 is the schematic diagram of the cross-basin water supply reservoir system in the embodiment of the present invention;

[0075] Figure 3 is the water transfer result of the FJK reservoir in the three ecological water demand levels and the synchronous wet, normal and dry scenarios in the embodiment of the present invention;

[0076] Figure 4 is the water transfer result of the FJK reservoir in the three ecological water demand levels and the asynchronous wet, normal and dry scenarios in the embodiment of the present invention;

[0077] Figure 5 is the water supply result of the FJK reservoir in the three ecological water demand levels and the synchronous wet, normal and dry scenarios in the embodiment of the present invention;

[0078] Figure 6 is the water supply result of the FJK reservoir in the three ecological water demand levels and the asynchronous wet, normal and dry scenarios in the embodiment of the present invention;

[0079] Figure 7 is the water shortage rate of THK, FJK, LHK and XJM when the weight of each water supply user in each reservoir in the embodiment of the present invention is that the ecological weight < agricultural weight;

[0080] Figure 8 is the water shortage rate of THK and XJM when the weight of each water supply user in each reservoir in the embodiment of the present invention is that the ecological weight < agricultural weight;

[0081] Figure 9 It is the water shortage rate of THK under the weight combination scenarios 3 and 8 considering three ecological water requirement levels in the embodiments of the present invention.

[0082] Figure 10 It is the water shortage rate of THK considering different ecological guarantee coefficients under the weight combination scenario 3 in the embodiments of the present invention. Detailed implementation manners

[0083] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0084] An integrated decision-making method for cross-basin water transfer, supply and distribution to ensure ecological flow, as Figure 1 shown, includes the following steps:

[0085] Step 1: Based on the two-stage dynamic decision-making modeling theory of dynamic programming, generalize the reservoir operation process of a single water source and multiple water receiving areas in the present invention, and construct a two-stage optimal scheduling model of a cross-basin water supply reservoir system based on the characteristics of sequential decision-making of reservoir scheduling using the principle of dynamic optimality.

[0086] Specifically, it includes the following steps:

[0087] S101: The objective function of the model can be defined as the maximization of the difference between the water supply benefits of the water source area and the water receiving areas and the water transfer cost:

[0088]

[0089] In the formula, represents the water supply benefit function of the water source reservoir (usually a concave function); represents the water supply benefit function of the water receiving reservoir (usually a concave function); represents the water transfer cost function (usually a convex function); t 总 represents the total decision time range; m represents the number of water receiving reservoirs.

[0090] The decision variables of the model mainly include the water supply and transfer volumes of the cross-basin water supply system in each time period, which are the variables in step S101 and where represents the available water volume of the water source reservoir at time t; represents the available water volume of the water receiving reservoir j at time t; T t j represents the adjustable water volume that can be transferred into the water receiving reservoir j at time t.

[0091] S102. Construct constraint conditions: The two-stage optimal operation model of the cross-basin water supply reservoir system needs to satisfy the water balance equations, storage volume constraints, water supply constraints, and water transfer volume constraints of the source reservoir and each receiving reservoir.

[0092] To optimize the benefits of the cross-basin water supply reservoir system, the scheduling operation of the system needs to satisfy the physical and engineering constraint conditions such as the water balance equations, storage volume, water supply volume, and water transfer volume of the source reservoir and each receiving reservoir. For the present invention, WA t represents the available water volume, which is defined as the storage volume of the source reservoir at the beginning of the time period plus the incoming water volume minus the evaporation and seepage water volume:

[0093] WA t = S t + I t - E t ;

[0094] In the formula, WA t represents the available water volume of the reservoir in the t-th time period; S t represents the storage volume of the reservoir at the moment t (at the beginning of the t-th time period); I t represents the incoming water volume of the reservoir in the t-th time period; E t represents the evaporation and seepage water volume of the reservoir in the t-th time period.

[0095] (1) Water balance equation

[0096] ① Water balance equation of the source reservoir

[0097] The water balance of the source reservoir should satisfy that the sum of the storage volume of the source reservoir at the moment t + 1 (i.e., at the end of the t-th time period) and the total water supply volume of the source reservoir in the t-th time period is equal to the difference between the available water volume of the source reservoir in the t-th time period and the total water transfer volume:

[0098]

[0099] In the formula, represents the storage volume of the source reservoir at the moment t + 1 (i.e., at the end of the t-th time period); represents the total water supply volume of the source reservoir in the t-th time period; represents the storage volume of the source reservoir at the moment t (at the beginning of the t-th time period); represents the incoming water volume of the source reservoir in the t-th time period; represents the evaporation and seepage water volume of the source reservoir in the t-th time period; represents the total water transfer volume of the source reservoir in the t-th time period, that is, the total water inflow volume of all receiving reservoirs; represents the available water volume of the source reservoir in the t-th time period, which is defined as the storage volume of the receiving reservoir at the beginning of the t-th time period plus the incoming water volume, and then minus the water volume lost due to evaporation and seepage.

[0100] ②Water balance equation of the water-receiving reservoir

[0101] Similarly, it can be obtained that the water balance of the water-receiving reservoir should satisfy that the sum of the water storage volume of the water-receiving reservoir at time t + 1 (i.e., the end of time period t) and the total water supply volume during time period t is equal to the sum of the available water volume and the transferred water volume of the water-receiving reservoir during time period t:

[0102]

[0103] In the formula, represents the water storage volume of water-receiving reservoir j at time t + 1 (i.e., the end of time period t); represents the total water supply volume of water-receiving reservoir j during time period t; represents the water storage volume of water-receiving reservoir j at time t (the beginning of time period t); represents the incoming water volume of water-receiving reservoir j during time period t; represents the evaporation and seepage water volume of water-receiving reservoir j during time period t; represents the transferred water volume of water-receiving reservoir j during time period t; represents the available water volume of water-receiving reservoir j during time period t, which is defined as the sum of the water storage volume at the beginning of the time period, the incoming water volume, and subtracting the evaporation and leakage water volume.

[0104] (2) Water storage volume constraint of the system

[0105] At time t + 1 (i.e., the end of time period t), the water storage volume of the water source reservoir should be less than or equal to the maximum storage capacity of the water source reservoir, and the water storage volume of water-receiving reservoir j should be less than or equal to the maximum storage capacity of water-receiving reservoir j, and both must not be lower than the dead storage capacity of each reservoir:

[0106]

[0107] In the formula, represents the water storage volume of the water source reservoir at time t + 1 (i.e., the end of time period t); represents the water storage volume of water-receiving reservoir j at time t + 1 (i.e., the end of time period t); represents the dead storage capacity of the water source reservoir; represents the dead storage capacity of water-receiving reservoir j; represents the maximum storage capacity of the water source reservoir; represents the maximum storage capacity of water-receiving reservoir j.

[0108] (3) Total water supply volume constraint of the system

[0109] During time period t, the total water supply volume of each reservoir should be less than or equal to its total water demand, and the water supply volume should not take a negative value:

[0110]

[0111] In the formula, Denote the total water supply of the water source reservoir in period t; Denote the total water supply of the receiving reservoir j in period t; Denote the total water demand of the water source reservoir in period t, including the ecological water demand, agricultural water demand, industrial and domestic water demand of the water source reservoir; Denote the total water demand of the receiving reservoir j in period t, including the ecological water demand, agricultural water demand, industrial and domestic water demand of the water source reservoir.

[0112] (4) Water transfer volume constraint of the system

[0113] The total water transfer volume of the water source reservoir in period t should be less than or equal to the maximum water diversion capacity of the water source reservoir, and the adjustable water transfer volume of the receiving reservoir j should also not be higher than the maximum water diversion capacity of the receiving reservoir j, and both must meet the non - negative constraint, that is:

[0114]

[0115] In the formula, Denote the total water transfer volume of the water source reservoir in period t; Denote the maximum water transfer volume of the water source reservoir; Denote the water transfer volume of the receiving reservoir j in period t; Is the maximum water transfer volume of the receiving reservoir j.

[0116] S103. According to the Bellman optimality principle, transform the long - time - series optimal scheduling model into a series of two - stage optimization problems associated by state - transfer equations. Based on the long - time - series optimal scheduling model of the inter - basin water supply reservoir system in step 1, define the water storage S as the state variable, and the water supply R and water transfer volume T as the decision variables:

[0117]

[0118] In the formula, Is the value function of the inter - basin water supply system regarding the water storage state combination of the reservoir group in the t - th period Which represents the maximum benefit value of the water storage state combination during the period from the t - th period to the end of the scheduling period.

[0119] The change of the water storage state of the inter - basin reservoir system with time is usually described by the reservoir water balance equation. That is, the state - transfer equation in the Bellman equation is defined as the reservoir water balance equation here:

[0120]

[0121] If only considering the water balance equation of the reservoirs in the inter - basin water supply reservoir system, that is, when the inequality constraint conditions in the system do not play a restrictive role, the Lagrange equation can be used to simplify the above - mentioned Bellman equation:

[0122]

[0123] Step 2: Quantitatively describe the ecological water demand processes in the water source area and the water receiving area of the inter-basin water supply reservoir system by the Tennant method, and obtain the ecological water demand processes under different ecological water demand levels. Specifically, it includes the following steps:

[0124] S201: Data collection and mean value calculation. The specific method is as follows:

[0125] Collect and sort out the long-term hydrological data of the study area, calculate the corresponding average runoff of the study area respectively, and use it as the reference point for calculating the basin ecological water demand.

[0126] Step 202: Divide the ecological status levels. The specific method is as follows:

[0127] According to the recommended standards of the Tennant method in Table 1, set the percentage threshold standards of runoff under different ecological statuses, combine with the multi-year average runoff data of the study area, calculate the corresponding ecological water demand process, and make appropriate adjustments according to the seasonal ecological demand to ensure that the obtained ecological water demand can meet the requirements of the ecosystem.

[0128] Table 1 Percentage of multi-year average natural runoff corresponding to different ecological statuses of the Tennant method

[0129]

[0130] Step 3: Import the ecological water demands under different ecological water demand levels in Step 2, set the dry-wet-year combination standard, and use the dynamic programming solution technology to optimize and solve the two-stage optimal operation model of the inter-basin water supply reservoir system based on the dynamic optimality principle in Step 1. Select two types of extreme scenarios, synchronous and asynchronous dry-wet-year scenarios, to obtain the water supply and operation results of the region under the two scenarios for different ecological water demand levels. Specifically, it includes the following steps:

[0131] S301: Based on the historical runoff and water demand data of relevant reservoirs in the inter-basin water supply reservoir system, randomly generate simulation data by the Monte Carlo method.

[0132] S302: Sort the annual runoff of each reservoir in ascending order of the data. Based on the dry-wet-year encounter analysis, take the scenario with a sorting less than 37.5% as the dry year scenario, the scenario with 37.5% - 62.5% as the normal year scenario, and the scenario with more than 62.5% as the wet year scenario.

[0133] S303. Calculate the values of each reservoir at the good, very good, and excellent levels of ecological water demand according to the Tennant method, and determine the ecological water demand process at different levels. Substitute the ecological water demands at the good and very good levels into the two-stage optimal operation model of the inter-basin water supply reservoir system, and use the dynamic programming algorithm for solution calculation.

[0134] S304. According to the setting standards of the wet, normal, and dry scenarios, select different combinations of wet, normal, and dry scenarios, mainly divided into two extreme scenarios of synchronous and asynchronous wet, normal, and dry conditions, to provide a source of hydrological and ecological input data for the quantitative analysis of water regulation and supply decisions in subsequent different combinations of scenarios.

[0135] Step 4. According to the basic principles of optimal water volume allocation and the water regulation and supply results of the inter-basin project obtained in Step 3, with the total regional water supply as a rigid constraint and the lowest comprehensive water shortage degree of different water use sectors as the allocation goal, taking into account the restrictions of projects and water demand, etc., construct a regional water resources optimal allocation model.

[0136] In the regional water volume optimal allocation plan of the inter-basin water supply reservoir system, in order to solve the contradiction between regional water resources supply and demand and promote the balanced development of social economy and ecological environment, the following basic principles of optimal water volume allocation are usually followed:

[0137] (1) The principle of overall consideration and ecological protection. The formulation of the water volume allocation plan needs to ensure the basic water volume required for the ecological environment, and prevent and reduce the possible damage to the ecological environment system caused by water shortage. Generally speaking, the guarantee rate of domestic water use should reach 95%, the guarantee rate of industrial water use should be above 90%, and the guarantee rate of farmland irrigation and ecological environment water use should be above 75%.

[0138] (2) The principle of sustainable utilization of water resources. The water volume allocation plan needs to fully consider the principle of sustainable development of the regional social economy and environmental ecology, avoid overusing water resources, maintain biodiversity and the stability of the ecosystem, and promote the sustainable and coordinated development of the economic society and ecological environment.

[0139] (3) The principle of fairness in water volume allocation. The formulation of the water volume allocation plan needs to be based on a full and comprehensive consideration of the water use needs of each water supply user, and according to the regional economic and social development level, water resources conditions and regional ecological environment characteristics, allocate water resources fairly and reasonably, and promote the coordinated development of industries as much as possible.

[0140] Specifically, it includes the following steps:

[0141] S401. Optimize the objective function of the water distribution model, and the specific method is as follows:

[0142] (1) Ecological water supply target

[0143] Aquatic ecosystems rely on certain water flow conditions to maintain their structure and functions. Sufficient ecological water helps maintain the sustainable development of aquatic ecosystems. It is necessary to keep the ecological water shortage rate as low as possible to ensure that the ecosystem has enough water to maintain its basic functions and diversity:

[0144]

[0145] In the formula, f1 represents the objective function of the ecological water supply user; represents the ecological water demand of the receiving reservoir j in period t; It represents the ecological water supply of the receiving reservoir j in period t.

[0146] (2) Agricultural water supply targets

[0147] Agriculture is the foundation of the national economy, and the growth of crops cannot be separated from sufficient irrigation water. Therefore, it is necessary to ensure that the water shortage rate of agricultural water users is as low as possible, which will help ensure food production and maintain national and regional food security:

[0148]

[0149] Where f2 represents the objective function of agricultural water supply users; represents the agricultural water demand of the receiving reservoir j during period t; It represents the agricultural water supply of the receiving reservoir j during period t.

[0150] (3) Domestic and industrial water supply targets

[0151] Domestic water is directly related to the life, health and safety of residents, while industrial water affects the normal operation of the social economy. Because the domestic and industrial water demand in this study area is quite different from the agricultural water demand, this paper considers domestic and industrial water demand as a water use department. Here, it is necessary to give priority to minimizing the water shortage rate of domestic and industrial water supply users as much as possible to maintain social stability and economic development:

[0152]

[0153] Where f3 represents the objective function of domestic and industrial water supply users; represents the domestic and industrial water demand of the receiving reservoir j during period t; It represents the amount of water available for domestic and industrial use of the receiving reservoir j during period t.

[0154] The overall objective function is as follows:

[0155]

[0156] In the formula, F represents the overall objective function; ω1 represents the importance decision weight coefficient of the first sub-objective function; ω2 represents the importance decision weight coefficient of the second sub-objective function; ω3 represents the importance decision weight coefficient of the third sub-objective function.

[0157] S402. The regional optimal water distribution model usually needs to satisfy the total water supply constraint, the water demand constraints of each water use department, and the minimum water supply and other limiting conditions. The constraint conditions of the optimal water distribution model are as follows:

[0158] (1) Total water supply constraint

[0159] The actual water supply allocated to each water supply user of the receiving reservoir j at time t should be equal to the total water supply determined by the improved dynamic programming algorithm in step 4:

[0160]

[0161] In the formula, represents the ecological water supply of the receiving area j at time t; represents the agricultural water supply of the receiving area j at time t; represents the domestic and industrial water supply of the receiving area j at time t; represents the total water supply of the receiving area j at time t, corresponding to the total water supply of each area obtained from the optimal operation of the inter-basin water supply reservoir system.

[0162] (2) Water supply constraint of water use departments

[0163] ① Supply-demand constraint of ecological water supply users

[0164] The actual water supply to ecological water supply users should be less than or equal to the rated demand of ecological water supply users and must meet their minimum water supply requirements:

[0165]

[0166] In the formula, represents the ecological available water volume of the receiving reservoir j at time t; represents the ecological water demand of the receiving reservoir j at time t, which can be set to the index values of the ecological water demand being good, very good, and excellent in the Tennant method according to the water supply and regulation decision situation; η represents the ecological guarantee coefficient; is the minimum ecological flow, and here the index value of the ecological water demand being poor in the Tennant method is taken.

[0167] ② Supply-demand constraint of agricultural water supply users

[0168] The actual water supply to agricultural water supply users should be less than or equal to the rated demand of agricultural water supply users and must meet their minimum water supply requirements:

[0169]

[0170] In the formula, represents the water supply volume of the receiving reservoir j to agricultural water users during the t period; represents the agricultural water demand of the receiving reservoir j during the t period.

[0171] ③ Supply-demand constraints for domestic and industrial water users

[0172] The actual water supply volume to domestic and industrial water users should be less than or equal to the rated water demand for domestic and industrial use and must meet the requirements of its minimum water supply constraints:

[0173]

[0174] In the formula, represents the domestic and industrial water supply volume of the receiving reservoir j during the t period; represents the domestic and industrial water demand of the receiving reservoir j during the t period.

[0175] Step 5. On the basis of constructing the optimization configuration model in Step 4, comprehensively consider the competing water relationships and their evolution laws among different water use sectors under the combined influence of ecological water demand, its guarantee degree, and the preferences of decision-makers and managers, and formulate a regional optimized water distribution plan that meets the actual management requirements to effectively solve the problem of competing water for "production, life, and ecology" in the region.

[0176] When determining the optimal regional water resources allocation plan, the following three scenarios are set for specific analysis:

[0177] 1) Domestic and industrial water users > Agricultural water users > Ecological water users.

[0178] The scenario where the target weight of ecological water users is less than the target weight of agricultural water users is consistent with the traditional order of considering the priority levels of water resources allocation. In this part, mainly explore the impact of the increase in the weight ratio of ecological water users on agricultural water users and domestic and industrial water users without changing the traditional priority order of water supply users.

[0179] 2) Domestic and industrial water users > Agricultural water users = Ecological water users.

[0180] In the part of the scenario where the weights of ecological water users are equal to those of agricultural water users, mainly analyze the impact of gradually reducing the weight coefficients of domestic and industrial water users when the weights of ecological water users and agricultural water users are the same.

[0181] 3) Domestic and industrial water users > Ecological water users > Agricultural water users.

[0182] For the scenario where the weight of ecological water supply users is greater than that of agricultural water supply users, it is necessary to analyze the degree of reduction in the available water resources for agricultural water supply users due to the increase in the weight of ecological water supply users, as well as the water resource supply stability of domestic and industrial water supply users under the condition of maintaining the highest priority.

[0183] The following steps are adopted to obtain the regional water resource allocation scheme:

[0184] S501. Based on the above three scenarios, set the weight combination scenarios of the importance decision weight coefficients for constructing the sub-objective function of the regional water resource optimization allocation model.

[0185] S502. Set the ecological water demand level, and substitute the total water supply results of each reservoir area in the long time series obtained by setting the ecological water demand level into the regional water resource optimization allocation model. Use the method of linear programming to solve the regional water resource optimization allocation model for each region to obtain the optimal weight combination.

[0186] Substitute the total water supply results of each reservoir area in the long time series obtained by setting the ecological water demand level to good, very good, and excellent into the regional optimized water distribution model. Use the method of linear programming to solve and calculate the optimized water distribution model for each region (only considering the case of not setting the minimum ecological guarantee coefficient here), and the optimal weight combination can be obtained by comprehensively comparing and analyzing the changes in the ecological water demand for each water supply user under the three specific weight combinations.

[0187] S503. According to the obtained optimal weight combination, set the ecological water demand level, set the ecological guarantee coefficient, and use the method of linear programming to solve the regional water resource optimization allocation model for each region to obtain the water shortage rate of each water supply user, and determine the optimal ecological guarantee coefficient and the regional water resource allocation scheme.

[0188] Based on the three types of optimal weight combination selection schemes of the present invention, continue to analyze the impact of the change in the water demand of ecological water supply users on other water supply users under specific weight scenarios, so as to further explore the game relationship between water resources and water ecology.

[0189] The minimum ecological flow refers to the minimum amount of water required to maintain the balance of the water ecosystem and ensure the basic ecological functions and biodiversity of the water ecosystem. Determining the minimum ecological flow helps to clearly define the basic water demand conditions for the healthy operation of the river ecosystem, helps decision-makers balance the relationship between ecological protection and economic and social development, and avoids problems of ecological system damage caused by overuse of water resources.

[0190] Specific implementation cases

[0191] In this embodiment, for a cross-basin water supply reservoir system composed of five reservoir areas (denoted as DJK, THK, FJK, LHK, and XJM, where DJK is the water source reservoir, and THK, FJK, LHK, and XJM are all water receiving reservoirs) in the backbone project of the water network in a certain province, an integrated decision-making technology for cross-basin water transfer and distribution to ensure ecological flow is set up. Specifically as follows:

[0192] Step 1: According to the actual situation of the project, study the two-stage optimal operation model of the cross-basin water supply reservoir system based on the principle of dynamic optimality for the optimal water supply and transfer decision-making under different ecological grades in each region, where:

[0193] (1) Objective function of the optimal operation model of the project's water supply and transfer system:

[0194]

[0195] In the formula, represents the water supply benefit function of DJK; represents the water supply benefit functions of FJK, LHK, and XJM for water supply to the corresponding areas; represents the water transfer cost function for water transfer to FJK, LHK, and XJM; t 总 represents the total decision time range.

[0196] In this embodiment, the formula of the project's water supply benefit function:

[0197]

[0198] In the formula, represents the water supply benefit function of any reservoir in the project for water supply to the corresponding area; R t # represents the water supply volume of any reservoir in the project for water supply to the corresponding area; Here represents the total water demand of the corresponding area of any reservoir in the project, including ecological water demand, agricultural water demand, domestic and industrial water demand; when β < 1, the water supply benefit function is a concave function, indicating that the marginal benefit of water supply decreases with the increase of water supply volume. According to the actual situation of the project, β can be taken as 0.6.

[0199] Formula of the project's water transfer cost function:

[0200]

[0201] In the formula, represents the water transfer cost function for water transfer to any water receiving reservoir in the project; T t j represents the adjustable water volume for water transfer to any water receiving reservoir in the project; It represents the maximum adjustable water inflow of any water-receiving reservoir in the project; when α > 1, the benefit function of water transfer is a convex function, indicating that as the water transfer volume increases, the marginal cost of water transfer increases. According to the actual situation of the project, α can be taken as 20.

[0202] (4) Decision variables of the optimal operation model for the project's water supply and transfer system

[0203] The decision variables of the project's optimal operation model mainly include the water supply and transfer volumes of the project's water supply system in each time period. Specifically, It represents the available water supply volume of DJK for water supply to the corresponding area in time period t; They respectively represent the total available water supply volumes of FJK, LHK, and XJM in time period t; T t 2 、T t 3 They respectively represent the water inflow volumes of FJK, LHK, and XJM in time period t.

[0204] (5) Constraint conditions of the optimal operation model for the project's water supply and transfer system

[0205] ① Water balance equation of the project's water supply reservoir system:

[0206]

[0207] ② Water storage constraint equation of the project's water supply reservoir system:

[0208]

[0209] ③ Total water supply constraint of the optimal operation model for the project's water supply and transfer system:

[0210]

[0211] ④ Water transfer volume constraint of the optimal operation model for the project's water supply and transfer system:

[0212]

[0213] In the formula, when j = 1, 2, 3, they respectively represent FJK, LHK, and XJM; It represents the water storage volume of DJK at the moment of t + 1 (i.e., the end of time period t); It represents the total water supply volume of DJK in time period t; It represents the water storage volume of DJK at the moment of t (the beginning of time period t); It represents the water inflow volume of DJK in time period t; It represents the evaporation and seepage water volume of DJK in time period t; It represents the total water transfer out volume of DJK in time period t; Denote the available water volume of DJK in period t, which is defined as the water storage volume of DJK at the beginning of the period plus the incoming water volume minus the evaporation and seepage water volume; Denote the water storage volume of receiving reservoir j at the moment of t + 1 (i.e., the end of period t); Denote the total water supply volume of receiving reservoir j in period t; Denote the water storage volume of receiving reservoir j at moment t (the beginning of period t); Denote the incoming water volume of receiving reservoir j in period t; Denote the evaporation and seepage water volume of receiving reservoir j in period t; Denote the transferred-in water volume of receiving reservoir j in period t; Denote the available water volume of receiving reservoir j in period t, which is defined as the water storage volume of receiving reservoir j at the beginning of period t plus the incoming water volume minus the evaporation and seepage water volume; Denote the dead storage capacity of DJK; Denote the maximum storage capacity of DJK; Denote the dead storage capacity of receiving reservoir j; Denote the maximum storage capacity of receiving reservoir j; Denote the total water demand volume of DJK in period t, including the ecological water demand volume, agricultural water demand volume, domestic and industrial water demand volume of DJK; Denote the total water demand volume of receiving reservoir j in period t, including the ecological water demand volume, agricultural water demand volume, domestic and industrial water demand volume of DJK; Denote the maximum transferred-out water volume of DJK; Is the maximum transferred-in water volume of receiving reservoir j.

[0214] According to the above formula and combined with the situation of the embodiment, the reservoir storage capacity limit, water transfer volume limit, domestic and industrial water demand volume and agricultural water demand volume of the project are obtained.

[0215] Step 2: Adopt the Tennant method in hydrological methods to quantitatively describe the ecological water demand process of each receiving reservoir area of the project. According to the long-term sequential hydrological data of THK, FJK, LHK and XJM, calculate the average monthly runoff volume corresponding to the four regions respectively, and use it as the benchmark point for calculating the environmental ecological water demand. According to the recommended standards of the Tennant method in Table 1, apply the runoff percentage threshold standards under 5 ecological conditions (respectively excellent, very good, good, general and poor) to the average monthly runoff volume of the four receiving areas, and adjust the percentage threshold indicators of the corresponding months according to the different ecological water demand situations in the flood season (May - October) and the non-flood season (November - April of the next year), and calculate the ecological water demand process of the corresponding months.

[0216] Step 3: Using the dynamic programming solution technique, optimize and solve the two-stage optimal operation model of the inter-basin water supply reservoir system in Step 1 under different ecological water requirement levels to obtain the water transfer and supply processes of each region. The specific process is as follows:

[0217] Step 3.1: Substitute the ecological water requirement processes under the excellent, very good, and good levels into the two-stage optimal operation model of the inter-basin water supply reservoir system, and use the dynamic programming solution technique to solve it to obtain the specific results of water supply and transfer.

[0218] Step 3.2: In this embodiment, the DJK reservoir is regarded as the water source area, and the FJK and THK reservoir areas that are relatively close geographically are regarded as aggregation area A. Similarly, the LHK reservoir area and the XJM reservoir area can be regarded as aggregation area B. However, since the terrain of the THK reservoir area is relatively high, it only serves as a compensation regulation reservoir. The pattern of the inter-basin water supply reservoir system is as Figure 2 . In the analysis of the joint water transfer of the project in this embodiment, the water transfer situations of FJK, LHK, and XJM are mainly analyzed and discussed for three ecological water requirement levels (excellent, very good, good) and two types of wet-dry combinations (synchronous and asynchronous).

[0219] (1) For the setting of the synchronous wet-dry combination scenario, it is mainly divided into the water transfer situations under the scenarios where the water source area, aggregation area A, and aggregation area B are all in wet years, all in normal years, and all in dry years. Here, the average value of the water transfer volume in a specific scenario is taken for analysis. Taking the FJK reservoir as an example, its water transfer results in the synchronous wet-dry scenario under three ecological water requirement levels are shown in Figure 3 .

[0220] Analyze the three scenarios of same wet, same normal, and same dry. The water transfer volume in normal years and dry years will increase correspondingly to relieve the water use pressure in each region. As the ecological water requirement levels of each reservoir area increase together, the corresponding water transfer volume of FJK shows an obvious increasing trend, and the increase is the most obvious in the case of all wet years, that is, the ecological water requirement can be guaranteed to the greatest extent in wet years. Comprehensive analysis shows that this operation strategy can respond to the changes in ecological water requirement in the synchronous wet-dry situation and has a certain scientific rationality.

[0221] (2) In the asynchronous wet-dry scenario, the situation where the water supply risk and ecological water requirement shortage are most likely to occur is mainly when the water source area is in a dry scenario. In this embodiment, the probabilities of aggregation area A being in a dry scenario and aggregation area B being in a wet scenario, and aggregation area A being in a wet scenario and aggregation area B being in a dry scenario are extremely low, and since there is no water shortage situation in both scenarios, they are not specifically analyzed here. Only the wet-dry combination scenarios of other regions when the water source area is in a dry year scenario are discussed. Taking the FJK reservoir as an example, its water transfer results in the asynchronous wet-dry scenario under three ecological water requirement levels are shown in Figure 4 .

[0222] As the level of the ecological water demand setting for each region increases, the law of the increasing water transfer volume of FJK is not significant enough, indicating that the competition for water resources is relatively fierce in dry years, and the impact of ecological water demand on the water supply and transfer decision-making is relatively not obvious.

[0223] Step 3.3: In this embodiment, the water supply results are analyzed under different scenarios of abundant, normal, and dry water encounters to evaluate the response degree of the inter-basin water supply reservoir system model in the wet, normal, and dry seasons. The following will analyze the water supply results of each region under two types of extreme scenarios, namely synchronous and asynchronous abundant, normal, and dry water, and discuss the changes in the water supply volume under different ecological water demand levels.

[0224] (1) The synchronous abundant, normal, and dry water scenario can more obviously reflect the response of the water supply and transfer decision-making of the inter-basin water supply reservoir joint system to different scenarios, and is relatively representative. Here, the water supply results of the project in the source area, aggregation area A, and aggregation area B under the synchronous abundant, normal, and dry water conditions will be analyzed first, that is, the total regional water supply under the scenarios of wet year, normal year, and dry year for the three of them will be analyzed. Taking the FJK reservoir as an example, its water supply results under the synchronous abundant, normal, and dry water scenario at three ecological water demand levels are shown in Figure 5 .

[0225] Comparative analysis of different ecological water demand level settings under the same abundant, normal, and dry water encounter scenarios shows that as the ecological water demand level increases, the available water supply volume of each region also increases accordingly, indicating that the system can timely adjust the available water supply volume for different water demand scenarios and has strong robustness.

[0226] (2) Analyze the water supply results of the source area, aggregation area A, and aggregation area B under the asynchronous abundant, normal, and dry water conditions. Taking the FJK reservoir as an example, its water supply results under the asynchronous abundant, normal, and dry water scenario at three ecological water demand levels are shown in Figure 6 .

[0227] Even in the scenario where the source area is in a dry year, the inter-basin water supply reservoir system model can also comprehensively regulate the total regional water supply of each reservoir. The overall system has strong rationality and robustness. In addition, under specific abundant, normal, and dry water encounter scenarios, 94.7% of the total monthly regional water supply increases as the ecological water demand setting level increases, indicating that the system model can respond to the changes in the ecological water demand level settings of each region and realize the optimal regulation of the comprehensive water supply situation of the system.

[0228] Step 4: Obtain the regional water resources optimal allocation models of THK, FJK, LHK, and XJM in the project according to Step 4 in the specification respectively;

[0229] Step 5. Analyze the changes in the weight coefficients of each water supply user in each reservoir and the impacts of the changes in the minimum guarantee coefficient of ecological water demand on agricultural water supply users, domestic and industrial water supply users, and use the linear programming method to solve the water shortage rates of each water supply user.

[0230] Step 5.1. The setting of the weight coefficients of each water supply user in each reservoir is shown in Tables 2A - C:

[0231] Table 2A Weight Coefficient and Scenario Setting When the Ecological Weight is Less Than the Agricultural Weight

[0232]

[0233] Table 2B Weight Coefficient and Scenario Setting When the Ecological Weight is Equal to the Agricultural Weight

[0234]

[0235] Table 2C Weight Coefficient and Scenario Setting When the Ecological Weight is Greater Than the Agricultural Weight

[0236]

[0237] Step 5.2. (1) When the ecological water demand level is good, when the ecological weight < agricultural weight, through comprehensive analysis, the water shortage rates of multiple water supply users under the weight combination scenario 3 are relatively low and can be used as the optimal target weight combination under this classification. The specific results are shown in Figure 7 . The water shortage rates of each water supply user in FJK and LHK are basically 0, and they are less sensitive to the target weight combination, while the water shortage situations in THK and XJM are more obvious and they are more sensitive to the target weight combination. Therefore, in the subsequent exploration of weight combination scenarios, only THK and XJM are analyzed.

[0238] (2) When the ecological water demand level is good, when the ecological weight = agricultural weight, through comprehensive analysis, the weight combination scenario 8 is used as the optimal weight combination under this classification. The specific results are shown in Figure 8 . The water shortage situations of ecological water supply users and agricultural water supply users in THK and XJM are slightly alleviated, and the impacts on domestic and industrial water supply users are not obvious, indicating that appropriately increasing the weight ratio coefficients of agriculture and ecology is conducive to comprehensive development.

[0239] (3) When the ecological weight > agricultural weight, through comprehensive analysis, the water shortage situation of agricultural water supply users intensifies at this time and is close to the minimum value of the agricultural water supply constraint condition, which is not conducive to comprehensive social development. Therefore, this weight combination scenario is not selected. Step 5.3. Consider the impacts of different ecological water demand levels on weight combination scenarios 3 and 8. Taking the THK Reservoir as an example, the specific results are shown in Figure 9Through comprehensive analysis, it is found that the comprehensive water shortage situation of THK under the weight combination scenario 3 is relatively mild, which can be used as the optimal weight scenario combination of the embodiment.

[0240] Step 5.4: Select the weight combination scenario 3. Under the three ecological water demand level standards, set the ecological security coefficients to 0.6, 0.7, and 0.8 respectively to solve the water shortage rates of the THK and XJM areas. Taking THK as an example, under the good ecological water demand level standard, confirm the influence of different ecological security coefficients on the water shortage rate of THK. The results are shown in Figure 10 。

[0241] Through comprehensive analysis, it can be seen that when the lowest ecological security coefficient is set to 0.6, it can not only ensure the ecological flow but also ease the competition relationship among multiple water supply users, achieving the goal of comprehensive social development.

[0242] It is easy for those skilled in the art to understand that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An integrated decision-making method for cross-basin water transfer, supply, and distribution to ensure ecological flow, characterized in that, It includes the following steps: Step 1: Construct a two-stage optimal operation model for the cross-basin water supply reservoir system based on the principle of dynamic optimality; Step 2: Quantitatively describe the ecological water demand processes in the water source area and the water receiving area of the cross-basin water supply reservoir system project through the Tennant method; Step 3: Use the dynamic programming solution technique to optimize and solve the two-stage optimal operation model for the cross-basin water supply reservoir system based on the principle of dynamic optimality in Step 1, select different wet, normal, and dry combination scenarios, and obtain the water transfer and supply processes in the region under different ecological water demand levels; Step 4: According to the basic principles of optimal water volume allocation and the water transfer and supply results of the cross-basin project obtained in Step 3, with the total regional water supply as a rigid constraint and the lowest comprehensive water shortage degree of different water use departments as the allocation goal, construct a regional water resources optimal allocation model; Step 5: Develop a regional optimal water distribution plan that meets the actual management requirements.

2. The integrated decision-making method for cross-basin water transfer, supply and distribution to ensure ecological flow according to claim 1, characterized in that In Step 1, constructing a two-stage optimal operation model for the cross-basin water supply reservoir system based on the principle of dynamic optimality specifically includes the following steps: S101: First, construct an objective function, define the objective function as the optimization of the comprehensive benefits of the cross-basin water supply project system, and the expression is: In the formula, represents the water supply benefit function of the water source reservoir; represents the water supply benefit function of the receiving reservoir; represents the water transfer cost function; t 总 represents the total decision time range; m represents the number of receiving reservoirs, represents the water supply volume of the water source reservoir at time t; represents the water supply volume of receiving reservoir j at time t; represents the water transfer volume of receiving reservoir j at time t; S102: Construct constraint conditions: The two-stage optimal operation model of the cross-basin water supply reservoir system needs to satisfy the water volume balance equations, water storage capacity constraints, water supply capacity constraints, and water transfer volume constraints of the water source reservoir and each water receiving reservoir; S103: According to the Bellman optimality principle, transform the long-term optimal operation problem into a two-stage optimal problem associated by a state transition equation. Define the water storage volume S as the state variable, the water supply volume R and the water transfer volume T as the decision variables, and the Bellman equation expression is: In the formula, is the value function of the reservoir group storage state combination of the cross-basin water supply system in the t-th period , representing the maximum benefit value represented by this storage state combination during the period from the t-th period to the end of the scheduling period. represents the initial storage volume of the water source reservoir at the beginning of the t-th period, and represents the initial storage volume of the water receiving reservoir at the beginning of the t-th period. The change of the water storage state of the cross-basin reservoir system over time is described by the reservoir water volume balance equation, and the expression is: In the formula, represents the water storage volume of the water source reservoir at the end of the t period, i.e., at the moment of t + 1; represents the total water supply volume of the water source reservoir during the t period; represents the total water transfer volume of all receiving reservoirs during the t period; represents the available water volume of the water source reservoir during the t period, which is defined as the water storage volume of the water source reservoir at the beginning of the t period plus the incoming water volume, and then minus the water volume lost due to evaporation and seepage; represents the water storage volume of receiving reservoir j at the beginning of the (t + 1) period; represents the water transfer volume of receiving reservoir j during the t period; represents the available water volume of receiving reservoir j during the t period, which is defined as the water storage volume of receiving reservoir at the beginning of this period plus the incoming water volume, and then minus the water volume lost due to evaporation and seepage. Simplify the above Bellman equation, and the expression is:

3. An integrated decision-making method for cross-basin water transfer, supply and distribution to ensure ecological flow according to claim 1, characterized in that, In Step 2, quantitatively describing the ecological water demand processes in the water source area and the water receiving area of the cross-basin water supply reservoir system project through the Tennant method includes the following steps: S201: Collect and organize the long-term hydrological data of the study area, calculate the corresponding average runoff of the study area, and use it as the benchmark point for calculating the basin ecological water demand; S202: Based on the recommended standards of the Tennant method, set the runoff percentage threshold standards under different ecological conditions, and combine with the multi-year average runoff data of the study area to calculate the ecological water demand processes under different ecological water demand levels.

4. The integrated decision-making method for cross-basin water transfer, supply and distribution to ensure ecological flow according to claim 1, characterized in that In Step 3, the process of obtaining the water transfer and supply processes in the region under different ecological water demand levels includes the following steps: S301: Based on the historical runoff and water demand data of the relevant reservoirs in the cross-basin water supply reservoir system, randomly generate simulation data through the Monte Carlo method; S302: Sort the simulated runoff of each reservoir in ascending order of annual runoff. Take the scenarios with a sorting less than 37.5% as dry year scenarios, 37.5% - 62.5% as normal year scenarios, and greater than 62.5% as wet year scenarios; S303. Substitute the ecological water requirements at different ecological water requirement levels in step 2 into the two-stage optimal operation model of the inter-basin water supply reservoir system, and use the dynamic programming algorithm to solve and calculate; S304. Set the combination standards of wet, normal, and dry years, select different scenarios of wet, normal, and dry year combinations, and obtain the water transfer and supply processes in the region at different ecological water requirement levels.

5. The integrated decision-making method for cross-basin water transfer, supply and distribution to ensure ecological flow according to claim 4, wherein In step S304, when selecting different scenarios of wet, normal, and dry year combinations, two types of extreme scenarios, i.e., synchronous and asynchronous wet, normal, and dry years, are selected.

6. The integrated decision-making method for cross-basin water transfer, supply and distribution to ensure ecological flow according to claim 1, characterized in that In step 4, constructing the regional water resources optimal allocation model includes constructing the objective function and constraint conditions, and then using linear programming to solve the optimal allocation model of the total regional water supply.

7. An integrated decision-making method for cross-basin water transfer, supply and distribution to ensure ecological flow according to claim 6, characterized in that, The objective function includes: 1) Ecological water supply objective: In the formula, f1 represents the objective function of ecological water supply users; represents the ecological water demand of receiving reservoir j at time t; represents the ecological available water volume of receiving reservoir j at time t; 2) Agricultural water supply objective: In the formula, f2 represents the objective function of agricultural water supply users; represents the agricultural water demand of receiving reservoir j at time period t; represents the agricultural water supply available to receiving reservoir j at time period t; (3) Domestic and industrial water supply objective: In the formula, f3 represents the objective function of domestic and industrial water supply users; represents the domestic and industrial water demand of receiving reservoir j during period t; represents the available domestic and industrial water supply of receiving reservoir j during period t; 4) The overall objective function is as follows: In the formula, F represents the overall objective function; ω1 represents the importance decision weight coefficient of the first sub-objective function; ω2 represents the importance decision weight coefficient of the second sub-objective function; ω3 represents the importance decision weight coefficient of the third sub-objective function.

8. An integrated decision-making method for cross-basin water transfer, supply and distribution to ensure ecological flow according to claim 6, characterized in that, The constraint conditions include: 1) Total water supply constraint: In the formula, represents the ecological water supply volume of water-receiving area j during period t; represents the agricultural water supply volume of water-receiving area j during period t; represents the domestic and industrial water supply volume of water-receiving area j during period t; represents the total water supply volume of water-receiving area j during period t, corresponding to the total water supply volume of each area obtained from the optimal operation of the inter-basin water supply reservoir system; 2) Water supply constraints for water use sectors ① Supply-demand constraints for ecological water supply users: In the formula, represents the ecological available water volume of the receiving reservoir j during the t period; represents the ecological water demand of the receiving reservoir j during the t period, which are respectively set as the index values of different ecological water demand levels in the Tennant method; η represents the ecological guarantee coefficient; is the minimum ecological flow rate; ② Supply-demand constraints for agricultural water supply users: In the formula, represents the water supply volume of the receiving reservoir j to agricultural water users during the t period; represents the agricultural water demand of the receiving reservoir j during the t period; ③ Supply-demand constraints for domestic and industrial water supply users: In the formula, represents the domestic and industrial water supply volume of the water-receiving reservoir j during the t period; represents the domestic and industrial water demand volume of the water-receiving reservoir j during the t period.

9. The integrated decision-making method for cross-basin water transfer, supply and distribution to ensure ecological flow according to claim 1, wherein In step 5, when determining the optimal regional water resources allocation plan, the following three types of situations are set for specific analysis: 1) Domestic and industrial water supply users > agricultural water supply users > ecological water supply users; 2) Domestic and industrial water supply users > agricultural water supply users = ecological water supply users; 3) Domestic and industrial water supply users > ecological water supply users > agricultural water supply users.

10. The integrated decision-making method for cross-basin water transfer, supply and distribution to ensure ecological flow according to claim 9, characterized in that, In step 5, the following steps are adopted to obtain the regional water resources allocation plan: S501. Based on the above three situations, set the weight combination scenarios of the importance decision weight coefficients of the sub-objective functions for constructing the regional water resources optimal allocation model; S502. Set the ecological water requirement level, and substitute the total regional water supply results of each reservoir in the long time series obtained at the set ecological water requirement level into the regional water resources optimal allocation model. Use the method of linear programming to solve the regional water resources optimal allocation models of each region to obtain the optimal weight combination; S503. According to the obtained optimal weight combination, set the ecological water requirement level, set the ecological guarantee coefficient, use the method of linear programming to solve the regional water resources optimal allocation models of each region, obtain the water shortage rates of each water supply user, and determine the optimal ecological guarantee coefficient and the regional water resources allocation plan.

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