River bank vegetation buffer zone optimal configuration design method

Abstract

The invention discloses an optimal configuration design method for a river bank vegetation buffer zone in the technical field of hydraulic engineering. The method comprises the following steps: (1) constructing a bank slope and near-shore land vegetation buffer zone configuration scheme; (2) constructing a river bank vegetation buffer zone width optimization model; taking the minimum construction investment of the vegetation buffer zone as an objective function, considering bank slope shallow soil layer stability constraints, pollutant reduction and water and soil conservation constraints and sediment interception constraints, constructing a mathematical model, and optimizing the width of the vegetation buffer zone; (3) model solving: solving by adopting a nonlinear programming solving method to obtain an optimal width; and (4) the optimal configuration scheme of the riverbank vegetation buffer zone is given by comparing and selecting the optimization results of the three schemes in the step (1), the optimal configuration of the riverbank vegetation buffer zone can be realized, the design level of water conservancy projects is improved, the project investment is reduced, the water and soil loss is reduced, the ecological environment of a river channel is improved, and the method has important significance in enabling the project to continuously play benefits.

Description

Technical Field

[0001] The invention relates to the technical field of water conservancy engineering, and in particular to a method for optimizing the configuration of a riverbank vegetation buffer zone. Background Art

[0002] The riverbank vegetation buffer zone is an important buffer zone for the transition from aquatic ecosystem to terrestrial ecosystem. It has multiple functions such as protecting biodiversity, stabilizing riverbanks, reducing soil erosion, intercepting and degrading surface runoff pollution. Relevant studies have shown that the larger the width of the buffer zone, the smaller the amount of soil erosion, and the higher the purification effect on the water body, interception of pollution and sediment efficiency. However, too high a buffer zone width will unreasonably occupy the available land resource space of the river bank, resulting in conflicts between the buffer zone and production and construction, or greatly increasing the construction cost. Therefore, the reasonable configuration of the riverbank vegetation buffer zone and the determination of its width are key technical issues that need to be solved in the design of river bank slopes. It is necessary to adopt a reasonable design method to determine the structure and width of the riverbank vegetation buffer zone, that is, to select a suitable configuration scheme and the optimal width while considering the actual local conditions, so that it can meet the requirements of bank slope stability, soil and water conservation, and ecological environmental protection, and meet the requirements of the lowest construction cost. Summary of the invention

[0003] With regard to the design of vegetation buffer zones in river bank slope design, the requirements of slope stability, soil and water conservation, river water quality protection, and minimum construction cost are considered. The present invention provides a riverbank vegetation buffer zone optimization configuration design method, which can achieve the optimal configuration of riverbank vegetation buffer zones, and is of great significance to improving the design level of such water conservancy projects, reducing project investment, reducing soil and water loss, improving the river ecological environment, and enabling the project to continue to produce benefits.

[0004] The object of the present invention is achieved by: a method for designing an optimal configuration of a riverbank vegetation buffer zone, comprising the following steps:

[0005] (1) Construct a configuration plan for the vegetation buffer zone on the bank slope and nearshore land according to local actual conditions;

[0006] (2) Constructing a model to optimize the width of the riverbank vegetation buffer zone. Specifically, taking the minimum investment in the construction of the vegetation buffer zone as the objective function, considering the constraints of shallow soil stability on the bank slope, pollutant reduction and soil and water conservation, and sediment interception, a mathematical model was constructed to optimize the width of the vegetation buffer zone.

[0007] (3) solving the model by using a nonlinear programming method to obtain the optimal width of the riverbank vegetation buffer zone for the three schemes described in step (1);

[0008] (4) By comparing the optimization results of the three schemes described in step (1), the optimal configuration scheme of the riparian vegetation buffer zone is given.

[0009] Furthermore, step (1) specifically includes three solutions:

[0010] Plan 1 adopts a three-stage structure, that is, the nearshore land is a herbaceous area, the bank slope is a mixed area of ​​trees and shrubs and a tree area;

[0011] Plan 2 adopts a two-stage structure, that is, the nearshore land is a herbaceous area, and the bank slope is a tree area;

[0012] Plan 3 adopts a two-stage structure, that is, the nearshore land is a herbaceous area, and the slope is a mixed area of ​​trees and shrubs.

[0013] Furthermore, the investment in vegetation buffer zone construction in step (2) includes earth excavation and landfill costs and vegetation planting costs, and the objective function is to minimize the total investment cost of vegetation buffer zone construction, as shown in the following formula:

[0014] ;

[0015] Where: Z is the investment cost per unit length of vegetation buffer zone, RMB / m; x1 is the width of the tree area of ​​the vegetation buffer zone, m; x2 is the width of the tree-shrub mixed area of ​​the vegetation buffer zone, m; x3 is the width of the herb area, m; c1, c2, c3 are the unit earthwork excavation costs of the tree area, tree-shrub mixed area, and herb area of ​​the vegetation buffer zone, RMB / m 3 ; h1, h2, h3 are the excavation depths of the tree area, tree-shrub mixed area, and herb area of ​​the vegetation buffer zone, m; K1, K2, K3 are the vegetation planting costs of the tree area, tree-shrub mixed area, and herb area of ​​the vegetation buffer zone, yuan / m 2 .

[0016] Furthermore, in step (2), the shallow soil layer stability constraint of the bank slope requires that the shallow soil layer stability coefficient of the bank slope should be greater than the standard value of the specification. The specific calculation formula is:

[0017] ;

[0018] ;

[0019] ;

[0020] Where: is the sliding force, kN; is the soil deadweight, kN; is the bank slope angle, °; is the soil weight, kN / m 3 ; is the width of the tree area in the vegetation buffer zone, m; L is the length of the vegetation buffer zone, m; h is the average length of the tree root system, m; is the anti-sliding force, kN; is the shear resistance of the soil bottom, kPa; is the shear resistance of the side soil, kPa; is the shear resistance of the root system, kPa; F is the stability coefficient of the shallow soil layer of the slope; is the internal friction angle of soil, °; It is the standard value.

[0021] Furthermore, the constraints for pollutant reduction and soil and water conservation in step (2) are:

[0022] ;

[0023] ;

[0024] ;

[0025] ;

[0026] in, The pollution removal efficiency of the vegetation buffer zone is When planning the width of the vegetation buffer zone, m; The pollution removal efficiency of the vegetation buffer zone is The width of the planned vegetation buffer zone, m; The pollution removal efficiency ratio of the vegetation buffer zone; To plan vegetation buffer zones and refer to the slope roughness of vegetation buffer zones; For planning vegetation buffer zones and reference vegetation buffer zones, saturated hydraulic conductivity, cmh -1 ; The slope of the river bank for planning vegetation buffer zone and reference vegetation buffer zone, %; Soil water holding capacity for planned vegetation buffer zones and reference vegetation buffer zones, cm; is the width of the buffer zone, m; T is the time it takes for runoff to flow through the buffer zone, s; s is the slope of the river bank, %.

[0027] Furthermore, the sediment interception constraint in step (2) is:

[0028]

[0029] Where: is the sediment interception rate, %, is the required sediment interception rate, %.

[0030] Furthermore, the solution process of step (3) specifically includes:

[0031] (3-1) Given an initial point that satisfies all inequality constraints , initial penalty factor , reduction factor <1, allowable error >0, set k=1;

[0032] (3-2) As the initial point, apply the unconstrained optimization method to find the penalty function The extreme point ;

[0033] (3-3) Check the penalty function The extreme point Has it converged to the optimal solution of the problem? If the convergence criterion is met, the optimal solution of the constraint problem is obtained. , stop iteration. Otherwise go to step 4;

[0034] (3-4) Reduce the penalty factor ,Right now ( is the penalty factor reduction coefficient). As the starting point for the next iteration, set Go to step 2 to perform unconstrained optimization calculation.

[0035] Furthermore, step (4) specifically includes:

[0036] (4-1) Using the riverbank vegetation buffer zone width optimization model, the three schemes constructed in step (1) are optimized and solved to obtain the optimal width of the vegetation buffer zone for each scheme;

[0037] (4-2) Compare the results of the three options and select the option with a smaller vegetation buffer zone width, less investment, and the most suitable for local conditions as the optimal configuration option for decision makers to choose as a reference.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] In water conservancy project planning, the configuration and design of riverbank vegetation buffer zones are generally determined by designers based on experience or by mathematical calculations, which are not optimal results. The present invention takes the minimum investment in the construction of vegetation buffer zones as the objective function, considers the stability constraints of the shallow soil layer of the bank slope, the constraints of pollutant reduction and soil and water conservation, and the constraints of sediment interception, and constructs a mathematical model to obtain the optimal configuration scheme and optimal design width of the vegetation buffer zone. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0041] Figure 1 Schematic diagram of the riparian vegetation buffer zone structure.

[0042] Figure 2 Schematic diagram of the force analysis of tree root system on slope stabilization.

[0043] Figure 3 This is the flow chart of the optimization solution using the interior point penalty function method. DETAILED DESCRIPTION

[0044] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] A method for optimizing the configuration of a river vegetation buffer zone comprises the following steps:

[0046] (1) According to the local actual situation, construct a configuration plan for the vegetation buffer zone of the bank slope and nearshore land. Plan 1 adopts a three-stage structure, that is, the nearshore land is a herbaceous area, the bank slope is a mixed area of ​​trees and shrubs and a tree area, such as Figure 1 As shown in the figure; Scheme 2 adopts a two-stage structure, that is, the nearshore land is a herbaceous area, and the bank slope is Figure 1 The mixed tree and shrub area and the tree area are merged into the tree area; Plan 3 adopts a two-stage structure, that is, the nearshore land is the herbaceous area, and the slope merges the mixed tree and shrub area and the tree area into the mixed tree and shrub area.

[0047] (2) Construct a model to optimize the width of the riverbank vegetation buffer zone. Taking the minimum investment in the construction of the vegetation buffer zone as the objective function, and taking into account constraints such as the stability of the shallow soil layer on the bank slope, pollutant reduction, soil and water conservation, and sediment interception, a mathematical model was constructed to optimize the width of the vegetation buffer zone.

[0048] (3) Solve the model to obtain the optimal width of the riverbank vegetation buffer zone for the three schemes described in step (1). Since the mathematical model is a nonlinear programming model with inequality constraints, it can be solved by nonlinear programming methods such as the interior point penalty function method.

[0049] (4) By comparing the optimization results of the three schemes described in step (1), the optimal configuration scheme of the riparian vegetation buffer zone is given.

[0050] Preferably, the mathematical model constructed in step (2) is as follows:

[0051] Objective function:

[0052] The investment in vegetation buffer zone construction mainly includes earth excavation and landfill costs and vegetation planting costs. The objective function is to minimize the total investment cost of vegetation buffer zone construction, as shown in the following formula.

[0053] ;

[0054] Where: Z is the investment cost per unit length of vegetation buffer zone, RMB / m; x1 is the width of the tree area of ​​the vegetation buffer zone, m; x2 is the width of the tree-shrub mixed area of ​​the vegetation buffer zone, m; x3 is the width of the herb area, m; c1, c2, c3 are the unit earthwork excavation costs of the tree area, tree-shrub mixed area, and herb area of ​​the vegetation buffer zone, RMB / m 3 ; h1, h2, h3 are the excavation depths of the tree area, tree-shrub mixed area, and herb area of ​​the vegetation buffer zone, m; K1, K2, K3 are the vegetation planting costs of the tree area, tree-shrub mixed area, and herb area of ​​the vegetation buffer zone, yuan / m 2 .

[0055] Constraints:

[0056] 1) Stability constraints of shallow soil layer on the slope

[0057] Planting vegetation buffer zones on river banks results in the presence of loose and weak shallow soil layers on the surface of the slopes. In this area, there are a large number of plant roots, which can curb the sliding of the soil, anchor the soil, and reduce soil erosion. This paper considers the case where the stability of the shallow soil layer is not affected by the groundwater level, and conducts a force analysis of the shallow soil layer of the slope per unit length (in meters) to stabilize the slope by tree roots. The force analysis results are shown in Figure 2 .

[0058] The root system strengthens the soil mainly through cohesion and friction. The soil generates sliding force due to its own gravity. At the same time, the shear resistance of the side soil, the shear resistance of the root system, and the shear resistance of the bottom of the soil constitute the anti-sliding force of the slope. The ratio of the two is the safety factor of the shallow soil layer of the slope. The soil shear strength formula is: Substituting in, we get the stability coefficient of the shallow soil layer of the slope. Finally, the stability safety factor of the shallow soil layer of the slope should be greater than the standard value of the relevant specifications, as shown below.

[0059] ;

[0060] ;

[0061] ;

[0062] Where: is the sliding force, kN; is the soil deadweight, kN; is the bank slope angle, °; is the soil weight, kN / m 3 ; is the width of the tree area in the vegetation buffer zone, m; L is the length of the vegetation buffer zone, m; h is the average length of the tree root system, m; is the anti-sliding force, kN; is the shear resistance of the soil bottom, kPa; is the shear resistance of the side soil, kPa; is the shear resistance of the root system, kPa; F is the stability coefficient of the shallow soil layer of the slope; is the internal friction angle of soil, °; It is the standard value.

[0063] 2) Based on the maximum and minimum constraints of pollutant reduction (Phillips model) and soil and water conservation (Nieswand model)

[0064] Phillips Model

[0065] The Phillips model aims to reduce pollution and protect river water quality. It is a mathematical model for calculating the width of riverbank buffer zones based on pollutants in suspended and dissolved states in vegetation buffer zones. The three models are the Phillips hydrological model and the Phillips time model.

[0066] The Phillips hydrological model is a mathematical model for removing suspended pollutants within vegetated buffer zones, as shown below:

[0067] ;

[0068] Where: are the energy loss of the vegetation buffer zone slope flow through the planned vegetation buffer zone and the reference vegetation buffer zone respectively; To plan vegetation buffer zones and refer to the pollution removal efficiency of vegetation buffer zones; To plan vegetation buffer zones and refer to the slope roughness of vegetation buffer zones; The width of the planned vegetation buffer zone and the reference vegetation buffer zone (m); For planning vegetation buffer zones and reference vegetation buffer zones, the saturated hydraulic conductivity (cmh -1 ); It is the river bank slope (%) for the planned vegetation buffer zone and the reference vegetation buffer zone.

[0069] make is the pollution removal efficiency ratio of vegetation buffer zone, then:

[0070] ;

[0071] Substituting the above formula into the Phillips hydrological model, we get:

[0072] ;

[0073] Where: The pollution removal efficiency of the vegetation buffer zone is When planning the width of the vegetation buffer zone, m; is the ratio of the pollution removal efficiency of the vegetation buffer zone, is the width of the reference vegetation buffer zone, m, and the other symbols are the same as before.

[0074] The Phillips time model is a mathematical model for removing dissolved pollutants in riverbank vegetation buffer zones. The formula is as follows:

[0075] ;

[0076] Where: The residence time of pollutants in overland flow and underground overland flow in the planned vegetation buffer zone and the reference vegetation buffer zone; It is the soil water holding capacity (cm) of the planned vegetation buffer zone and the reference vegetation buffer zone. The other symbols are the same as before.

[0077] Will Substituting into the Phillips time model, we have:

[0078] ;

[0079] Where: The pollution removal efficiency of the vegetation buffer zone is The width of the planned vegetation buffer zone, m; other symbols are the same as before.

[0080] Nieswand Model

[0081] The Nieswand model is a mathematical model that aims to maintain water and soil in vegetation buffer zones and protect river banks from erosion. The width of the buffer zone is obtained by the time T of different river runoffs passing through the buffer zone, that is:

[0082] ;

[0083] Where: is the width of the buffer zone, m; T is the time it takes for runoff to flow through the buffer zone, s; s is the slope of the river bank, %.

[0084] The riparian buffer zone that meets the calculation results of both the Phillips model and the Nieswand model has the best effect of reducing pollution and conserving water and soil, and its width is the largest. This width is taken as the maximum width of the riparian zone; the riparian zone width that only meets the calculation results of one of the models has the basic function of reducing pollution and conserving water and soil, and its width is the smallest. This width is taken as the minimum width of the riverbank, as shown in the following formula.

[0085] ;

[0086] 3) Sediment interception constraints

[0087] The VFSMOD model is a model for calculating the effect of vegetation buffer strips on the purification of sediment in slope runoff. The present invention uses this model to simulate and analyze the interception efficiency of sediment with different vegetation buffer strip widths, thereby fitting the functional relationship between different vegetation buffer strip widths and sediment interception rates. The sediment interception rate should be greater than the required value, as shown in the following formula.

[0088] ;

[0089] Where: is the sediment interception rate, %, is the required sediment interception rate, %; other symbols are the same as before.

[0090] Preferably, the specific steps of step (3) are as follows:

[0091] Since the mathematical model is a nonlinear programming model with inequality constraints, the present invention uses the interior point penalty function method to solve it. The interior point penalty function adds a penalty term to the objective function to penalize solutions that violate the constraints, thereby converting the constrained problem into an unconstrained problem, and promoting the algorithm to be more inclined to solutions that satisfy the constraints during the search process.

[0092] 1) Given an initial point that satisfies all inequality constraints , initial penalty factor , reduction factor <1, allowable error >0, set k=1.

[0093] 2) As the initial point, apply the unconstrained optimization method to find the penalty function The extreme point

[0094] 3) Check the penalty function The extreme point Has it converged to the optimal solution of the problem? If the convergence criterion is met, the optimal solution of the constraint problem is obtained. , stop the iteration. Otherwise, go to step 4.

[0095] 4) Reduce the penalty factor ,Right now ( is the penalty factor reduction coefficient). As the starting point for the next iteration, set Go to step 2 to perform unconstrained optimization calculation.

[0096] Preferably, the specific steps of step (4) are as follows:

[0097] 1) The riparian vegetation buffer zone width optimization model constructed by the present invention is used to optimize and solve the three schemes constructed in step (1), and the optimal width of the vegetation buffer zone of each scheme can be obtained.

[0098] 2) Compare the results of the three options and select the option with a smaller vegetation buffer zone width, less investment, and the most suitable for local conditions as the optimal configuration option for decision makers to refer to.

[0099] The present invention is further described below in conjunction with the design of a river vegetation buffer zone in a high sandy area along the river. The river is located in a high sandy area along the river in Jiangsu Province, and the cross-sectional parameters are: bottom width 15m, mouth width 40m, and side slope 1:2.5.

[0100] (1) In accordance with Figure 1 Construct a three-section structure of the riverbank vegetation buffer zone.

[0101] (2) Construct a mathematical model. The specific implementation steps are as follows:

[0102] 1) Objective function: Based on the local construction cost data, Take 15 yuan / m 3 , Take 13 yuan / m 3 , Take 10 yuan / m 3 ; Take 0.9m, Take 0.45m, Take 0.3m; Take 25 yuan / m 2 , Take 20 yuan / m 2 , Take 15 yuan / m 2 ; Take the unit length as 1m. Substitute the above parameters into the objective function and get:

[0103] ;

[0104] 2) Constraints:

[0105] Shallow soil layer stability constraints on bank slope

[0106] Sandy soil cohesion c=0; soil weight γ=19.5kN / m 3 ; Slope angle α=5°; Friction angle φ=38°; Shear strength increment of the lateral root system on the soil According to the Technical Specifications for Building Slope Engineering, the stability coefficient In the sandy soil area, it should be greater than 1.25. Substituting the above parameters into the stability constraints of the shallow soil layer of the slope, we can get:

[0107]

[0108] Maximum and minimum constraints

[0109] Taking into account the regional characteristics and current situation, the pollution removal efficiency ratio of vegetation buffer zone is set. The value is 1, that is, the pollution removal efficiency of the planned vegetation buffer zone is equal to that of the reference vegetation buffer zone. The parameters required by the model and the calculation results are shown in Table 1.

[0110] Table 1 Reference buffer zone and planning and buffer characteristic parameters

[0111]

[0112] In summary, the maximum and minimum constraints on the width of the river vegetation buffer zone are:

[0113]

[0114] Sediment interception restraint

[0115] The characteristic parameters of high sandy soil areas that need to be input using the VFSMOD model are shown in Table 2.

[0116] Table 2 VFSMOD model input characteristic parameter table

[0117]

[0118] Calculate the width of the tree plant belt according to the model characteristic parameters in Table 2 , Width of mixed tree and shrub plant belt , Width of herbaceous plant belt Sediment interception rate , the specific calculation results are shown in Table 3.

[0119] Table 3 Calculation results of sediment interception rate under different buffer zone widths%

[0120]

[0121] According to the calculation results in Table 3, the width of the tree plant belt is fitted. , Width of mixed tree and shrub plant belt , Width of herbaceous plant belt Sediment interception rate The functional relationship between them is expressed as the correlation coefficient R 2 Reflects the fitting accuracy (R 2 =0.99), the fitting relationship is:

[0122]

[0123] According to the Sediment Design Manual, the sediment interception rate should be greater than 72%, and the present invention takes it as 75%.

[0124] Therefore, the sediment interception constraints can be summarized as:

[0125]

[0126] In summary, the optimization model for the width of the riverbank vegetation buffer zone is:

[0127]

[0128] (3) Solve the model and obtain the optimization result. The interior point penalty function method is used to solve the above nonlinear programming model, and the optimal solution is: the width of the tree vegetation belt =6.4m; Width of mixed vegetation belt with trees and shrubs =10.6m; width of herbaceous plant belt =34.3m;MinZ=976.3 yuan.

[0129] (4) Compare and select options to obtain the optimal configuration plan for the riverbank vegetation buffer zone.

[0130] The same method as above is used to optimize and solve Scheme 2 and Scheme 3 constructed in step (1). The optimization results are shown in Table 4.

[0131] Table 4 Comparison of optimization schemes for relevant parameters of riparian vegetation buffer zone construction

[0132]

[0133] As can be seen from Table 4, Scheme 1 not only has the smallest construction investment, but also has the shortest total width of the vegetation buffer zone, which can reduce a large amount of human resources in subsequent management and maintenance work. From the perspective of long-term benefits, it is more economical and reasonable. Therefore, the optimal configuration scheme of the river vegetation buffer zone is: adopt a three-stage structure, with a total width of 51.3m for the vegetation buffer zone, including 34.3m for the herbaceous area, 10.6m for the mixed tree and shrub area, and 6.4m for the tree area.

[0134] This invention aims at the problem of optimizing the configuration of riverbank vegetation buffer zones. It takes the minimum investment cost for the construction of vegetation buffer zones as the objective function, comprehensively considers constraints such as the stability of the shallow soil layer on the slope, pollutant reduction, soil and water conservation, and sediment interception, and constructs a nonlinear mathematical model for optimizing the width of vegetation buffer zones. It uses the interior point penalty function method to solve the model, and obtains the optimal configuration scheme of the riverbank buffer zone and the optimal width of the riverbank buffer zone through scheme comparison, which provides a technical basis for the planning of such water conservancy projects and is of great significance to the sustainable development of the river ecological environment.

[0135] The above embodiments are only used to help understand the method and core idea of ​​the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A method for optimizing the configuration of a riverbank vegetation buffer zone, characterized in that: The following steps are involved: (1) Construct a configuration plan for the vegetation buffer zone on the bank slope and nearshore land according to local actual conditions; (2) Constructing a model to optimize the width of the riverbank vegetation buffer zone. Specifically, taking the minimum investment in the construction of the vegetation buffer zone as the objective function, considering the constraints of shallow soil stability on the bank slope, pollutant reduction and soil and water conservation, and sediment interception, a mathematical model was constructed to optimize the width of the vegetation buffer zone. (3) solving the model by using a nonlinear programming method to obtain the optimal width of the riverbank vegetation buffer zone for the three schemes described in step (1); (4) By comparing the optimization results of the three schemes described in step (1), the optimal configuration scheme of the riparian vegetation buffer zone is given.

2. The method for optimizing the configuration of a riparian vegetation buffer zone according to claim 1, characterized in that: Step (1) specifically includes three options: Plan 1 adopts a three-stage structure, that is, the nearshore land is a herbaceous area, the bank slope is a mixed area of ​​trees and shrubs and a tree area; Plan 2 adopts a two-stage structure, that is, the nearshore land is a herbaceous area, and the bank slope is a tree area; Plan 3 adopts a two-stage structure, that is, the nearshore land is a herbaceous area, and the slope is a mixed area of ​​trees and shrubs.

3. The method for optimizing the configuration of a riparian vegetation buffer zone according to claim 2, characterized in that: In step (2), the investment in vegetation buffer zone construction includes earth excavation and landfill costs and vegetation planting costs. The objective function is to minimize the total investment cost of vegetation buffer zone construction, as shown in the following formula: ； Where: Z is the investment cost per unit length of vegetation buffer zone, RMB / m; x1 is the width of the tree area of ​​the vegetation buffer zone, m; x2 is the width of the tree-shrub mixed area of ​​the vegetation buffer zone, m; x3 is the width of the herb area, m; c1, c2, c3 are the unit earthwork excavation costs of the tree area, tree-shrub mixed area, and herb area of ​​the vegetation buffer zone, RMB / m 3 ; h1, h2, h3 are the excavation depths of the tree area, tree-shrub mixed area, and herb area of ​​the vegetation buffer zone, m; K1, K2, K3 are the vegetation planting costs of the tree area, tree-shrub mixed area, and herb area of ​​the vegetation buffer zone, yuan / m 2 .

4. The method for optimizing the configuration of a riparian vegetation buffer zone according to claim 3, characterized in that: In step (2), the shallow soil layer stability constraint of the bank slope requires that the shallow soil layer stability coefficient of the bank slope should be greater than the standard value of the specification. The specific calculation formula is: ； ； ； Where: is the sliding force, kN; is the soil deadweight, kN; is the bank slope angle, °; is the soil weight, kN / m 3 ; is the width of the tree area in the vegetation buffer zone, m; L is the length of the vegetation buffer zone, m; h is the average length of the tree root system, m; is the anti-sliding force, kN; is the shear resistance of the soil bottom, kPa; is the shear resistance of the side soil, kPa; is the shear resistance of the root system, kPa; F is the stability coefficient of the shallow soil layer of the slope; is the internal friction angle of soil, °; It is the standard value.

5. The method for optimizing the configuration of a riparian vegetation buffer zone according to claim 4, characterized in that: The constraints for pollutant reduction and soil and water conservation in step (2) are: ； ； ； ； in, The pollution removal efficiency of the vegetation buffer zone is When planning the width of the vegetation buffer zone, m; The pollution removal efficiency of the vegetation buffer zone is The width of the planned vegetation buffer zone, m; The pollution removal efficiency ratio of the vegetation buffer zone; To plan vegetation buffer zones and refer to the slope roughness of vegetation buffer zones; For planning vegetation buffer zones and reference vegetation buffer zones, saturated hydraulic conductivity, cmh -1 ; The slope of the river bank for planning vegetation buffer zone and reference vegetation buffer zone, %; Soil water holding capacity for planned vegetation buffer zones and reference vegetation buffer zones, cm; is the width of the buffer zone, m; T is the time it takes for runoff to flow through the buffer zone, s; s is the slope of the river bank, %.

6. The method for optimizing the configuration of a riparian vegetation buffer zone according to claim 5, characterized in that: The sediment interception constraint in step (2) is: ； Where: is the sediment interception rate, %, is the required sediment interception rate, %.

7. The method for optimizing the configuration of a riparian vegetation buffer zone according to claim 6, characterized in that: The solution process of step (3) specifically includes: (3-1) Given an initial point that satisfies all inequality constraints , initial penalty factor , reduction factor <1, allowable error >0, set k=1; (3-2) As the initial point, apply the unconstrained optimization method to find the penalty function The extreme point ; (3-3) Check the penalty function The extreme point Has it converged to the optimal solution of the problem? If the convergence criterion is met, the optimal solution of the constraint problem is obtained. , stop the iteration. Otherwise, go to step 4; (3-4) Reduce the penalty factor ,Right now ( is the penalty factor reduction coefficient). As the starting point for the next iteration, set Go to step 2 to perform unconstrained optimization calculation.

8. The method for optimizing the configuration of a riparian vegetation buffer zone according to claim 7, characterized in that: Step (4) specifically includes: (4-1) Using the riverbank vegetation buffer zone width optimization model, the three schemes constructed in step (1) are optimized and solved to obtain the optimal width of the vegetation buffer zone for each scheme; (4-2) Compare the results of the three options and select the option with a smaller vegetation buffer zone width, less investment, and the most suitable for local conditions as the optimal configuration option for decision makers to choose as a reference.

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