A decision-making method for reservoir ecological desilting scheme based on multi-objective constraints

Abstract

The invention relates to a decision-making method for a reservoir ecological desilting scheme based on multi-objective constraints. The method comprises the following steps: according to the desilting scale and in combination with geological exploration of sediment components, the economic benefits, social benefits and ecological benefits that may be generated by the desilting project are calculated; according to the desilting scale, the cost of the desilting project is calculated, and a cost-effectiveness function is established; the changes in water flow conditions and water environment factors in the reservoir area after the implementation of each scheme are simulated, the influence of each desilting scheme on river stability, river flood discharge, waterway safety and ecological environment is evaluated, the adverse influence degree of each scheme is quantitatively compared, and an influence degree objective function is established; the sediment transport effect of the desilting project is evaluated, the siltation rate in the desilting area is calculated, the reservoir capacity sustainable development index is defined and solved, thereby constructing an optimization system model with multi-objective constraints, determining the weight coefficients of each objective function, and solving the optimal solution of the multi-objective model, thereby determining the optimal desilting scheme with the minimum adverse influence, the best sustainable reservoir capacity effect and the minimum cost-effectiveness ratio.

Description

Technical Field

[0001] The invention relates to the field of reservoir dredging, and in particular to a reservoir ecological dredging plan decision-making method based on multi-objective constraints. Background Art

[0002] Reservoir ecological desilting can effectively increase reservoir capacity, improve water environment conditions in the reservoir area, and restore reservoir regulation and storage functions. It is also conducive to the performance of water supply, irrigation, power generation and other functions. Desilted silt can be used for embankment filling, construction and industrial materials, soil remediation, etc., which can alleviate the current shortage of mineral resources such as sand and gravel.

[0003] At present, the decision-making method for reservoir desilting is still insufficient. In the past, desilting activities were mostly based on channel dredging projects and river sand mining projects, that is, clearing the sections of rivers that hinder navigation, or clearing the sections of rivers rich in sand and gravel resources. However, the fundamental purpose of reservoir desilting is different from that of channel dredging and river sand mining. The primary purpose of reservoir desilting is to restore the reservoir capacity, ensure the sustainable function of the reservoir function, and promote the long-term use of the reservoir. At the same time, the constraints of reservoir desilting are also different from those of the above two. Most reservoirs are old and have a large amount of pollutants in the sediment due to their rich sediment. Therefore, reservoir desilting must use ecological desilting equipment and ensure that the diffusion range of pollutants complies with relevant regulations. Therefore, the decision-making of reservoir desilting is relatively complex. In addition to considering general economic factors such as cost-effectiveness, it is also necessary to consider comprehensive impacts such as the environment and factors such as the restoration of reservoir functions. The decision-making process is very difficult. Therefore, its improvement and innovation are imperative. Summary of the invention

[0004] In view of the above situation, in order to overcome the defects of the prior art, the purpose of the present invention is to provide a reservoir ecological dredging plan decision-making method based on multi-objective constraints, which can effectively solve the problem of finding the optimal dredging plan for the reservoir and guide the decision-making, design and evaluation of the reservoir dredging plan.

[0005] The technical solution provided by the present invention is:

[0006] A decision-making method for reservoir ecological desilting scheme based on multi-objective constraints is proposed. Through the characteristics of reservoir sedimentation and combined with reservoir functions, geological survey is carried out to determine the reservoir desilting alternative schemes. A multi-objective constraint system is constructed from the desilting effect, adverse impact and cost-effectiveness of each scheme:

[0007] First, according to the scale of dredging and combined with geological exploration of sediment composition, the possible economic, social and ecological benefits of the dredging project are calculated. The cost of the dredging project is calculated according to the scale of dredging, and a cost-effectiveness function is established. Secondly, the changes in water flow conditions and water environmental factors in the reservoir area after the implementation of each plan are simulated, the impact of each dredging plan on river stability, river flood discharge, waterway safety and ecological environment is evaluated, the degree of adverse impact of each plan is quantitatively compared, and an impact degree objective function is established. Thirdly, the changes in sediment transport and riverbed topography in the reservoir area after the implementation of the dredging project are simulated and calculated, the sediment transport effect of the dredging project is evaluated, the siltation rate in the dredged area is calculated, and the reservoir capacity sustainable development index is defined and solved, thereby constructing an optimization system model with multi-objective constraints, normalizing the function values ​​such as cost-effectiveness, adverse effects and sustainable effects of reservoir capacity, determining the weight coefficients of each objective function, and solving the optimal solution of the multi-objective model, thereby determining the optimal dredging plan with the least adverse effects, the best sustainable effects of reservoir capacity and the smallest cost-effectiveness.

[0008] Preferably, when determining the alternative dredging plans for the reservoir, firstly, the siltation distribution is carried out based on the current topography and initial topography of the reservoir, as well as the reservoir siltation trend in the next 10 years, to obtain the current total reservoir storage capacity siltation loss rate, beneficial storage capacity siltation loss rate, siltation location, and beneficial storage capacity siltation loss rate and siltation location in the next 10 years; according to the four dredging ranges of only clearing the current local siltation body at the water intake, clearing the current siltation body within the beneficial storage capacity, clearing the siltation body within the beneficial storage capacity in the next 10 years, and clearing all siltation since the reservoir was formed, while avoiding ecological red lines and ecologically sensitive areas, and avoiding the safety distance required by the operation regulations of water-related projects and facilities in the reservoir area, the dredging ranges of the four alternative dredging plans, namely, micro, small, medium, and large, are determined.

[0009] The specific method for analyzing the reservoir siltation trend in the next 10 years is to establish a one-dimensional mathematical model of scour and siltation of the entire reservoir riverbed based on the HEC model. According to the general river simulation plan, a 10-year water and sediment sequence including typical water and sediment years of abundant water and abundant sediment, low water and little sediment, and medium water and medium sediment is selected. The existing measured topography is used as the initial condition to predict and calculate the siltation in the reservoir area, and the siltation locations of the reservoir area's beneficial storage capacity in the next 10 years are counted.

[0010] The specific steps include:

[0011] A. Screening the sedimentation area in the reservoir area; collecting topographic survey data of empty reservoirs or reservoir areas in the initial stage of reservoir construction, carrying out topographic survey of the existing reservoir area below the verification flood level at a scale of 1:2000, overlaying the empty reservoir topography and the existing topography to obtain the distribution of sedimentation in the reservoir area, including the overall sedimentation distribution, the sedimentation distribution within the beneficial reservoir capacity, and the sedimentation distribution of the local water intake in front of the dam;

[0012] B. Based on the HEC model, a one-dimensional mathematical model of erosion and deposition of the riverbed in the reservoir area is established. A 10-year water-sediment sequence including typical water-sediment years with abundant sediment in flood season, little sediment in drought season, and medium sediment in water season is selected. The existing measured topography is used as the initial condition to predict and calculate the sediment deposition in the reservoir area, and the sediment deposition locations of the reservoir area's beneficial storage capacity in the next 10 years are counted.

[0013] C. Investigate the ecological red lines and environmentally sensitive areas in the reservoir area, including nature reserves, drinking water sources, aquatic germplasm resource protection areas, wetland parks and other ecological red line areas; determine the dredging scopes of the four dredging alternative plans, namely, micro, small, medium and large, according to the four dredging scopes of only clearing the existing local siltation at the water intake, clearing the existing siltation within the reservoir capacity, clearing the siltation within the reservoir capacity for future benefits, and clearing all siltation since the reservoir was built. At the same time, avoid the ecological red lines and ecologically sensitive areas, and avoid the safety distance required by the operation regulations of water-related projects and facilities in the reservoir area.

[0014] Conduct geological survey on the determined desilting area to obtain the vertical distribution characteristics of the sediment and determine the plane area A (m 2 ), dredging depth h(m), excavation slope s, calculate the total dredging volume Q(m 3 ):

[0015]

[0016] In the formula, n is the number of desilting areas, and i is the desilting area number;

[0017] The plane area A of the dredging area is determined by the above dredging scope steps; the excavation slope s is determined by relevant specifications; the dredging depth h for the four dredging alternatives of micro, small, medium and large is: micro: dredging to the water level corresponding to the beneficial reservoir capacity; small: dredging to the water level corresponding to the beneficial reservoir capacity; medium: considering the increased siltation thickness in the next 10 years, on the basis of dredging to the water level corresponding to the beneficial reservoir capacity, excavate the same siltation thickness downward; large: dredging uniformly to the initial reservoir bottom;

[0018] The specific method of geological survey is as follows: geological survey is carried out on the desilting range determined in the above steps, an exploration profile is arranged every 1km in each area, 2 boreholes are arranged in each profile, and a group of original samples are taken at least every 3m in each borehole to test the physical properties of the sediment, including the particle size, density, moisture content, and specific gravity of the sediment, so as to obtain the vertical distribution of the sediment suitable for mining in each area, thereby determining the plane area A (m 2 ), dredging depth h(m), excavation slope s, calculate the total dredging volume Q(m 3 ) and preliminarily formulate alternative plans for reservoir desilting.

[0019] Finally, four alternative desilting plans for micro, small, medium and large reservoirs corresponding to the desilting scopes were determined;

[0020] The variables related to the reservoir desilting alternative plan are expressed as x=[Q, n, A, h, s];

[0021] Preferably, the specific method for establishing the cost-effectiveness function comprises the following steps:

[0022] 1. Formulate a plan for resource utilization of silt with full gradation

[0023] According to the results of geological survey, the dredged material particle size is divided into different levels according to the particle size: [d0, d1], [d1, d2]…[d m-1 ,d m ], the total amount of matter in different particle size intervals is expressed as q1, q2, …q m , propose resource utilization plans for different particle sizes of sediment in the dredged materials: the dredged materials with a particle size of less than 0.15mm are used for soil remediation, the particles with a size of 0.15mm to 5mm are used for building materials, and the particles with a size greater than 5mm are used for road subgrade and embankment filling;

[0024] 2. Calculate the economic benefits of the project, including resource benefits, water supply benefits, and power generation benefits, and establish a benefit objective function

[0025] The benefits generated by the resource utilization of dredging materials are expressed as:

[0026] B1=∑q j p j

[0027] Where: q j Indicates the total amount of each particle size (m 3 );

[0028] p j Indicates the net income per unit area of ​​each particle size (yuan / m 3 );

[0029] Water supply benefit refers to the economic benefit generated by the increased water supply after the reservoir capacity is restored. Water supply methods include agricultural water, industrial water, and domestic water. The water supply benefit B2 is calculated using the following formula:

[0030] B2=∑w l r l

[0031] Where: w l Indicates the amount of water for various purposes (m 3 );

[0032] r l Indicates the water price for each purpose (yuan / m 3 );

[0033] The power generation benefit refers to the income generated by restoring part of the reservoir capacity for power generation, and its calculation formula is as follows:

[0034] B3=ewQ

[0035] Where: w represents the power generation per cubic meter of water (kwh / m 3 );

[0036] e represents the on-grid electricity price (yuan / kwh);

[0037] Overall benefit B:

[0038] B=B1+B2+B3

[0039] 3. Carry out cost estimation of dredging project and establish cost objective function.

[0040] The cost C is related to all variables of the dredging scheme. The cost includes the cost of preliminary work and the cost of the construction stage. The cost function is expressed as:

[0041] C=g1(X)+g2(X)

[0042] g1(X) is the cost of preliminary work, which is calculated in accordance with the "Interim Provisions on Fees for Consulting on Preliminary Work of Construction Projects" (State Planning Commission, 1999

[1283] Document); g2(X) is the cost of the construction phase, which is calculated in accordance with the "Quota of Machinery Hours for Water Conservancy Project Construction" and "Quota of Budget for Water Conservancy Construction Projects" (Water General Administration, 2002

[116] Document);

[0043] 4. Finding the cost-effectiveness ratio

[0044] The cost-effectiveness function is:

[0045] Preferably, the specific method for establishing the impact degree objective function is:

[0046] The quantitative indicators reflecting the degree of impact refer to the changes in river flow and riverbed caused by the implementation of the dredging project, including the change in flow velocity (Δv) and flow direction (Δa) before and after the project, and the impact range of pollutants caused by sediment disturbance (Δl);

[0047] Based on EFDC software, a two-dimensional water flow and water quality mathematical model or physical model is established to simulate the changes in river flow conditions and water quality caused by the implementation of dredging projects for different reservoir dredging alternatives, and the flow velocity changes (Δv), flow direction changes (Δa), and the pollutant impact range (Δl) caused by sediment disturbance after the implementation of each reservoir dredging alternative plan are statistically analyzed; among them, Δv is not greater than 0.4m / s, Δa is not greater than 5 degrees (according to the "Technical Specifications for Dredging and Filling Engineering" and "Inland Navigation Standards"), and Δl is not greater than 50m (according to the "Technical Guidelines for Environmental Impact Assessment"); since the dimensions and order of magnitude of each change are different, each change is first normalized, and then the normalized values ​​are directly added to obtain the overall quantitative indicators of the impact of each scheme project:

[0048] F=Δv'+Δa'+Δl'

[0049] That is, an impact degree objective function is established to compare the F values ​​of each scheme. The smaller the F value, the smaller the impact;

[0050] Preferably, the method for solving the reservoir capacity sustainable development index is:

[0051] Based on HEC software, a one-dimensional water-sediment mathematical model of the reservoir area was established to simulate and calculate the changes in sediment transport and riverbed topography in the reservoir area after the implementation of the dredging project for different reservoir dredging alternatives. The sediment discharge ratio (η) and the time required for silting back to the original topography (t) after the implementation of the project were statistically analyzed, which respectively represent the quantitative indicators of the sediment discharge and transport effect of the dredging project on the reservoir and the sustainability of the dredging plan. The various changes were normalized to obtain the reservoir capacity sustainable development index:

[0052] W=η'+t'

[0053] Preferably, when constructing a multi-objective constraint optimization system model, the multi-objective constraint conditions include minimum adverse impact, optimal storage capacity sustainable effect, and minimum cost-effectiveness ratio. The model is expressed as follows:

[0054]

[0055] In engineering applications, in order to simplify calculations, multiple objectives are synthesized into a single objective. Since the dimensions of each function are not uniform, they are first normalized to establish a weighted and evaluated function. The optimization system model of multi-objective constraints is transformed into:

[0056]

[0057] The primary goal of the reservoir desilting project is to restore the reservoir function. The desilting project should be sustainable, but the premise is that the implementation of the project should not have adverse effects on the river flow, flood discharge, ecological environment, etc. of the reservoir. Finally, the project should have certain economic benefits. Therefore, according to the above-mentioned minimum adverse impact, the best sustainable effect of reservoir capacity, and the minimum cost-effectiveness ratio, each target variable is linearly assigned, and ω1=0.17, ω2=0.50, ω3=0.33 are obtained;

[0058] Substitute the independent variables of the alternative desilting plans for each reservoir into the equations of the constraint function and solve the U(x) value. The plan with the smallest value is the optimal plan under the multi-objective constraint framework, that is, the desilting plan with the least adverse impact, the most favorable sustainable reservoir capacity, and the lowest cost-effectiveness.

[0059] Compared with the prior art, the present invention provides a decision-making method for reservoir ecological desilting scheme based on multi-objective constraints, quantifies the benefits, impacts and reservoir sustainability of the project, constructs a multi-objective optimization system model for reservoir desilting projects, establishes a linear evaluation objective function, and clarifies the principle for determining the optimal solution. This method can quickly determine the desilting scheme with the minimum adverse impact, the best reservoir sustainability effect, and the minimum cost-effectiveness ratio, and guides the decision-making, design and implementation of reservoir desilting projects. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 A schematic diagram of the design process of the optimal dredging solution in the present invention;

[0061] Figure 2 The overall idea of ​​the ecological dredging design scheme of Tongjiezi Reservoir in the embodiment of the present invention;

[0062] Figure 3 This is a distribution map of the desilting area in the Tongjiezi Reservoir according to an embodiment of the present invention;

[0063] Figure 4 A two-dimensional modeling diagram of the desilting area of ​​Tongjiezi Reservoir according to an embodiment of the present invention;

[0064] Figure 5 This is a cross-sectional design diagram of the optimal ecological dredging solution according to an embodiment of the present invention. DETAILED DESCRIPTION

[0065] The specific implementation modes of the present invention are further described in detail below in conjunction with the embodiments.

[0066] 1) Analyze the current status and trend of reservoir siltation, count the ecologically sensitive areas in the reservoir area, and determine the scope of dredging.

[0067] Tongjiezi Hydropower Station is located in Sichuan Province, China, in the lower reaches of Dadu River, 80km from Leshan City. It is a solid gravity overflow dam with a maximum dam height of 82m and a total storage capacity of 200 million m 3The project started in 1985, the first unit started generating electricity in December 1992, and was completed in December 1994. According to the analysis of the measured underwater terrain, the Tongjiezi Reservoir has been storing water for more than 20 years, and the sedimentation has developed rapidly. In 2019, it has basically reached a balance between erosion and siltation, and the estimated amount is more than 40 million m 3 The loss of storage capacity below the normal water level exceeds 50%, and the loss of storage capacity for economic use is about 7%. The most obvious siltation is within 8.5 km in front of the dam, and the maximum siltation thickness at the deep elevation is about 40m. The most serious siltation areas are mainly within 1.5km to 4.5km in front of the dam, and within 6km to 8.5km in front of the dam.

[0068] According to the simulation results of the one-dimensional full-sand riverbed scouring and silting mathematical model in the reservoir area, the reservoir area of ​​Tongjiezi Hydropower Station will show a small silting trend in the next 10 years, and the silting increase will not be large, mainly due to the silting of the beneficial reservoir capacity. The siltation is mainly distributed in the 13km range in front of the dam, of which the siltation in the 4.5km in front of the dam is about 4 million m 3 .

[0069] According to the investigation, the environmentally sensitive areas of Tongjiezi Reservoir include the Tongci Township centralized groundwater drinking water source protection area and Sichuan Shawan Dadu River National Wetland Park.

[0070] Therefore, the appropriate desilting range is determined to be 1.5km to 4.5km in front of the dam, and 6km to 8.5km in front of the dam. Figure 3 .

[0071] 2) Conduct geological surveys, analyze the vertical distribution characteristics of sediments, and preliminarily determine the ecological dredging plan.

[0072] A geological survey section is set up every 1 km within the recommended desilting range (location see Figure 3 ), 2-3 boreholes were arranged in each section for engineering geological exploration. According to the drilling, the stratum structure within the exploration depth range (9.6-33.8m) is as follows: the upper part is medium-fine sand, 4.9-29.0m thick, with an average thickness of 20m, and the overall trend is gradually thickening from upstream to the front of the dam, with a loose to slightly dense structure, and the lower part is sand and gravel, with a medium-dense to dense structure. Most of the drilling holes have not been exposed, and the maximum exposed thickness is 4.8m.

[0073] Therefore, according to different degrees of reservoir recovery, four ecological desilting plans are formulated. Plan 1 is to completely clear the silt in the reservoir area, and Plan 2 is to clear the silt in the beneficial reservoir after considering the continuous siltation in the next 10 years; Plan 3 is to clear the silt in the existing beneficial reservoir, and Plan 4 is to clear the silt near the water intake 1.5 km in front of the dam. The characteristic variables of each plan are shown in the following table:

[0074] Table 1 Characteristic values ​​of various dredging schemes

[0075]

[0076]

[0077] 3) Calculate the economic benefits of the dredging project.

[0078] First, a resource utilization plan for the full gradation of silt was formulated. According to the analysis of the physical and chemical characteristics of the silt, the average density of the silt was 2.74 g / cm 3 The content of the coarser part with a particle size composition of >0.15mm accounts for 93%, and this part of the sediment can be used as construction sand. The content of the finer part with a particle size composition of ≤0.15mm accounts for 7%, and the indicators of heavy metal and organic pollutant detection items do not exceed the risk screening value of agricultural land soil pollution.

[0079] Through market demand research, it was found that the Hulu flood control project in Shawan District and the urban construction construction currently under construction have a large demand for sand and gravel resources, so coarse sand can be directly used for engineering construction. Fine-grained sediment ≤ 0.15mm can be used for agricultural land reclamation and regional land reclamation backfill for resettlement of immigrants for the Angu Hydropower Station project downstream of the reservoir.

[0080] According to B = ∑q j p j +∑w l r l +ewQ, determine the value of each parameter, see the table below.

[0081] Table 2 Parameter values ​​in the benefit objective function of this case

[0082]

[0083] 4) Calculate the cost of the project.

[0084] This case is located in Sichuan Province. Therefore, with reference to relevant regulations such as "Regulations on the Preparation of Design Estimates for Water Conservancy and Hydropower Engineering in Sichuan Province", "Budget Quotas for Water Conservancy and Hydropower Construction Projects in Sichuan Province", "Water Conservancy Project Construction Machinery Unit Hourly Rate Quotas", "Water Conservancy and Hydropower Equipment Installation Project Budget Quotas", and "Engineering Survey and Design Fee Standards", the costs and cost-effectiveness of each plan were calculated, as shown in the table below.

[0085] Table 3 Statistics of costs and benefits of each plan

[0086] project Solution 1 Solution 1 Option 3 Option 4 Cost (ten thousand yuan) 263794 85978 26147 6171 Economic benefits (ten thousand yuan) 294195 91865 27062 5344 Cost-effectiveness 0.90 0.94 0.97 1.15

[0087] 5) Conduct an impact analysis of the dredging plan, including its impact on river stability, flood control safety, and the impact on the ecological environment.

[0088] Based on EFDC software, a two-dimensional mathematical model of water flow and sediment is used to calculate the water flow numerical model of the river section in the Tongjiezi Reservoir area ( Figure 4 ), statistically analyze the flow velocity change (Δv), mainstream line change (Δa), and pollutant impact range (Δl), and add the normalized maximum values ​​of each quantity to get the impact index. The statistical values ​​of each change are shown in the table below.

[0089] Table 4 Statistics of the impact of each scheme project

[0090] Change value Solution 1 Solution 1 Option 3 Option 4 <![CDATA[Maximum variation range of flow velocity (m 3 / s)]]> -2.2～+0.7 -0.8～+0.25 -0.3～+0.11 -0.53～0.15 Mainstream angle change (°) 6 3 2 1 Pollutant impact range (m) 13 8 4 3 Impact Index 1.0 0.45 0.08 0.03

[0091] 6) Based on HEC software, a one-dimensional water-sediment mathematical model of the reservoir area was established to simulate and calculate the changes in sediment transport and riverbed topography in the reservoir area after the implementation of the dredging project. The sediment discharge ratio (η) and the time required for siltation to reach equilibrium (t) after the implementation of the project were statistically analyzed, and the reservoir capacity sustainability index was calculated.

[0092] Table 5 Calculation of storage capacity sustainability index for each scheme

[0093] project Solution 1 Solution 1 Option 3 Option 4 Sand discharge ratio after the project (%) 86.74 85.46 84.85 82 Time from siltation to equilibrium (years) 10 5 1 0.5 Storage Capacity Sustainability Index 3.45 2.22 1.24 1.09

[0094] 7) Solve the evaluation objective function value and determine the optimal solution.

[0095] After normalizing the cost-effectiveness ratio, comprehensive impact index and reservoir capacity sustainability index respectively, they are substituted into the objective function U(x) to calculate the function value.

[0096] min U(x)=0.17R'+0.50F'-0.33W'

[0097] In this case, the evaluation objective function values ​​of the four schemes are 0.17, 0.09, 0.05, and 0.17 respectively. Therefore, Scheme 3 is the optimal ecological dredging scheme.

[0098] This plan has been successfully implemented after approval by the Sichuan Provincial Water Resources Department, effectively restoring the reservoir's regulating capacity and improving the water ecological environment.

Claims

1. A decision-making method for reservoir ecological desilting scheme based on multi-objective constraints, characterized in that: Based on the characteristics of reservoir sedimentation and combined with the reservoir function, geological surveys were carried out to determine the reservoir desilting alternatives, and a multi-objective constraint system was constructed based on the desilting effects, adverse effects and cost-effectiveness of each plan: First, according to the scale of dredging and combined with geological exploration of sediment composition, the possible economic, social and ecological benefits of the dredging project are calculated. The cost of the dredging project is calculated according to the scale of dredging, and a cost-effectiveness function is established. Secondly, the changes in water flow conditions and water environmental factors in the reservoir area after the implementation of each plan are simulated, the impact of each dredging plan on river stability, river flood discharge, waterway safety and ecological environment is evaluated, the degree of adverse impact of each plan is quantitatively compared, and an impact degree objective function is established. Thirdly, the changes in sediment transport and riverbed topography in the reservoir area after the implementation of the dredging project are simulated and calculated, the sediment transport effect of the dredging project is evaluated, the siltation rate in the dredged area is calculated, and the reservoir capacity sustainable development index is defined and solved, thereby constructing a multi-objective constraint optimization system model, normalizing the function values ​​of cost-effectiveness, adverse effects and reservoir capacity sustainable effects, determining the weight coefficients of each objective function, and solving the optimal solution of the multi-objective model, thereby determining the optimal dredging plan with the least adverse effects, the best reservoir capacity sustainable effects and the smallest cost-effectiveness.

2. The reservoir ecological desilting plan decision-making method based on multi-objective constraints according to claim 1 is characterized in that: When determining the alternative desilting plan for the reservoir, firstly, the siltation distribution is carried out based on the current topography and initial topography of the reservoir, as well as the reservoir siltation trend analysis in the next 10 years, to obtain the current total reservoir storage capacity siltation loss rate, beneficial storage capacity siltation loss rate, siltation location, and beneficial storage capacity siltation loss rate and siltation location in the next 10 years; according to the four desilting ranges of only clearing the current local siltation body at the water intake, clearing the current siltation body within the beneficial storage capacity, clearing the siltation body within the beneficial storage capacity in the next 10 years, and clearing all siltation since the reservoir was built, while avoiding the ecological red line and ecological sensitive areas, and avoiding the safety distance required by the operation regulations of water-related projects and facilities in the reservoir area, the desilting ranges of the four alternative desilting plans of micro, small, medium and large are determined; Conduct geological survey on the determined desilting area to obtain the vertical distribution characteristics of the sediment and determine the plane area A (m 2 ), dredging depth h(m), excavation slope s, calculate the total dredging volume Q(m 3 ): In the formula, n is the number of desilting areas, and i is the desilting area number; Finally, four alternative desilting plans for micro, small, medium and large reservoirs corresponding to the desilting scopes were determined; The variables related to the reservoir desilting alternative plan are expressed as x=[Q, n, A, h, s].

3. The reservoir ecological desilting plan decision-making method based on multi-objective constraints according to claim 2 is characterized in that: The specific method of establishing the cost-effectiveness function includes the following steps:

1. Formulate a plan for resource utilization of silt with full gradation According to the results of geological survey, the dredged material particle size is divided into different levels according to the particle size: [d0, d1], [d1, d2]…[d m-1 ,d m ], the total amount of matter in different particle size intervals is expressed as q1, q2, …q m , propose resource utilization plans for different particle sizes of sediment in the dredged materials: the dredged materials with a particle size of less than 0.15mm are used for soil remediation, the particles with a size of 0.15mm to 5mm are used for building materials, and the particles with a size greater than 5mm are used for road subgrade and embankment filling; 2. Calculate the economic benefits of the project, including resource benefits, water supply benefits, and power generation benefits, and establish a benefit objective function The benefits generated by the resource utilization of dredging materials are expressed as: B1=∑q j p j Where: q j Indicates the total amount of each particle size (m 3 ); p j Indicates the net income per unit area of ​​each particle size (yuan / m 3 ); Water supply benefit refers to the economic benefit generated by the increased water supply after the reservoir capacity is restored. Water supply methods include agricultural water, industrial water, and domestic water. The water supply benefit B2 is calculated using the following formula: B2=∑w l r l Where: w l Indicates the amount of water for various purposes (m 3 ); r l Indicates the water price for each purpose (yuan / m 3 ); The power generation benefit refers to the income generated by restoring part of the reservoir capacity for power generation, and its calculation formula is as follows: B3=ewQ Where: w represents the power generation per cubic meter of water (kwh / m 3 ); e represents the on-grid electricity price (yuan / kwh); Overall benefit B: B=B1+B2+B3 3. Cost calculation of dredging project and establishment of cost objective function The cost C includes the pre-work costs and the construction phase costs, so the cost function is expressed as: C=g1(X)+g2(X) g1(X) is the cost of preliminary work; g2(X) is the cost of the construction phase; 4. Finding the cost-effectiveness ratio The cost-effectiveness function is: .

4. The reservoir ecological desilting plan decision-making method based on multi-objective constraints according to claim 3 is characterized in that: The specific method to establish the impact degree objective function is: A two-dimensional mathematical model or physical model of water flow and water quality is established to simulate the changes in river flow conditions and water quality caused by the implementation of dredging projects for different reservoir dredging alternatives, and the flow velocity change Δv, flow direction change Δa, and pollutant impact range Δl caused by sediment disturbance after the implementation of each reservoir dredging alternative are statistically analyzed; since the dimensions and magnitudes of each change are different, each change is first normalized, and then the normalized values ​​are directly added to obtain the overall quantitative index of the impact of each scheme project: F = Δv' + Δa' + Δl'.

5. The reservoir ecological desilting plan decision-making method based on multi-objective constraints according to claim 4 is characterized in that: The method for solving the sustainable development index of reservoir capacity is: A one-dimensional water-sediment mathematical model of the reservoir area was established to simulate and calculate the changes in sediment transport and riverbed topography in the reservoir area after the implementation of the dredging project for different reservoir dredging alternatives. The sediment discharge ratio η of the reservoir and the time t required for silting back to the original topography after the implementation of the project were statistically analyzed, which respectively represent the quantitative indicators of the sediment discharge and transport effect of the dredging project on the reservoir and the sustainability of the dredging plan. The various changes were normalized to obtain the reservoir capacity sustainable development index: W = η' + t'.

6. The reservoir ecological desilting plan decision-making method based on multi-objective constraints according to claim 5 is characterized in that: When constructing a multi-objective constraint optimization system model, the multi-objective constraint conditions include minimum adverse impact, optimal sustainable storage capacity effect, and minimum cost-effectiveness ratio. The model is expressed as follows: The multiple objectives are synthesized into a single objective. Since the dimensions of each function are not uniform, they are first normalized to establish a weighted and evaluated function. The optimization system model of multi-objective constraints is transformed into: According to the above-mentioned minimum adverse impact, optimal sustainable storage capacity effect, and minimum cost-effectiveness ratio, each target variable is linearly assigned, and ω1=0.17, ω2=0.50, and ω3=0.33 are obtained; Substitute the independent variables of the alternative desilting plans for each reservoir into the equations of the constraint function and solve the U(x) value. The plan with the smallest value is the optimal plan under the multi-objective constraint framework, that is, the desilting plan with the least adverse impact, the most favorable sustainable reservoir capacity, and the lowest cost-effectiveness.

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