A method for selecting the location of a silt dam with the goal of flood control and economy

Abstract

The present invention provides a method for selecting the location of a silt dam with the goal of flood control and economy, comprising: constructing a functional relationship A(S) between the silt dam location S and the runoff area A; constructing a functional relationship L(S,H) between the silt dam location S, the silt dam height H and the silt dam span L; constructing a functional relationship V(S,H) between S, H and the silt dam flood detention capacity Vz Z (S,H); According to A(S) and V Z (S, H), the flood peak reduction degree R of the silt dam is obtained; according to the height H, L (S, H) of the silt dam and the unit price u of the material, the construction cost C of the silt dam is obtained; with the maximum R and the minimum C as the optimization target, S and H as the decision variables, a multi-objective optimization model is constructed, the Pareto front is solved and drawn, and the silt dam is laid out according to the Pareto front. The present invention can quickly obtain the trade-off relationship between R and C, and finally obtain the layout location and scale of the silt dam that meets both the requirements of flash flood disaster reduction and the investment cost.

Description

Technical Field

[0001] The present invention relates to the technical field of silt dam layout, and in particular to a method for selecting a silt dam layout position with the goals of flood control and economy. Background Art

[0002] The Loess Plateau in China is one of the most important ecologically fragile areas in the world. The terrain in this area is mostly hilly and mountainous, and the soil is mainly composed of clay and loose loess. When there is heavy rainfall, due to the poor permeability of the soil, rainwater is difficult to penetrate quickly, which is a typical over-infiltration runoff, causing water to gather quickly and form rainstorm runoff. In addition, the steep slope terrain and soil erosion problems in the region have further increased the risk of flash floods. These flash floods not only cause direct damage to surrounding farmland and villages, but also bring a large amount of silt scouring, causing siltation and blockage of downstream rivers, further endangering local water resources and ecological environment, exacerbating the fragility of the ecosystem, making it difficult to restore vegetation, and destroying the ecological balance.

[0003] In response to this problem, researchers have been exploring effective ecological governance and disaster prevention measures to reduce the impact of flash floods on the Loess Plateau. Among them, the silt dam, as an ecological engineering measure, has received widespread attention and application. Through the layout of the silt dam, the flow rate of water can be effectively slowed down, the erosion effect of water flow can be reduced, and the risks brought by flash floods can be reduced or avoided. In the past, the construction of silt dams was disorderly and spontaneous. Nowadays, with the increasing demand for ecological protection and high-quality development in the Yellow River Basin, the promotion of high-standard silt dam construction requires the layout of silt dams to form an organized, large-scale, scientific and reasonable planning layout.

[0004] At present, for the study of silt dams, some researchers are committed to using methods such as watershed monitoring and numerical simulation to compare the changes before and after the construction of silt dams in the target watershed to study the regulatory effect of silt dam construction on the basin topography, flood control capacity, hydrological sedimentation process, and the impact on the erosion dynamics and sediment transport of the basin. Other scholars have studied the timing of the construction of silt dam systems and the impact of continuous dam breaches on silt dam systems. In terms of the optimization of silt dam layout, some researchers have established a variety of silt dam layout evaluation models to evaluate and score multiple silt dam construction plans in the target watershed, and selected the silt dam design plan with the highest score as the most suitable for the target watershed. Most of the above studies are based on the research of built silt dams or silt dams with existing design plans. In the early planning stage of silt dam construction, there are few studies on the optimization of the layout location and layout scale of silt dams. In the actual design process of silt dams, the layout and design of silt dams must comprehensively consider the impacts of economy, technology, ecological environment, society, management and other aspects. This is obviously a multi-objective optimization problem. However, the location and scale of silt dams and the various benefits they generate are difficult to quantify, making it difficult to construct relevant mathematical models and optimization models. Summary of the invention

[0005] In order to fill the gap in the research of mathematical models for optimizing the layout of silt dams, the present invention provides a multi-objective optimization layout location selection method for silt dams with flood control and economy as the goals, which can quickly obtain the trade-off between the degree of flood peak reduction of the silt dam and the construction cost, and ultimately obtain the layout location and scale of the silt dam that meets the requirements of flash flood disaster reduction and meets the investment cost.

[0006] The present invention is achieved through the following technical solutions:

[0007] A multi-objective optimization layout location selection method for a silt dam with flood control and economic efficiency as the objectives includes:

[0008] The proposed silt dam is laid out on the main river channel of the target basin. The distance S from the basin outlet represents the location of the silt dam. The functional relationship A(S) between the silt dam location S and the runoff area A is constructed. The functional relationship L(S,H) between the silt dam location S, the silt dam height H and the silt dam span L is constructed. The functional relationship Vz between the silt dam location S, the silt dam height H and the silt dam flood detention capacity Vz is constructed. Z (S,H);

[0009] According to A(S) and V Z (S,H), calculate the flood peak reduction degree R of the silt dam; according to the height H, L(S,H) of the silt dam and the unit price u of the material, calculate the construction cost C of the silt dam;

[0010] Taking the maximum flood peak reduction degree R of the check dam and the minimum construction cost C of the check dam as the optimization objectives, and the check dam location S and the check dam height H as the decision variables, a multi-objective optimization model for the layout of single check dams in the main river channel of the target basin is constructed, the Pareto frontier is solved and drawn, and the check dams are laid out according to the Pareto frontier.

[0011] Preferably, based on the DEM of the target watershed, the main river channel of the target watershed is extracted through GIS software.

[0012] Preferably, a functional relationship A(S) between the silt dam layout position S and the runoff area A is constructed, specifically:

[0013] Warping dams were laid at different locations in the main river channel of the target basin. The location S of the warding dam and the corresponding runoff area A were calculated and extracted through GIS software. A curve of the relationship between A and S was drawn, and a cubic polynomial was used for curve fitting to obtain A(S).

[0014] Preferably, a functional relationship L(S,H) among the silt dam layout position S, the silt dam height H and the silt dam span L is constructed, specifically: silt dams of different heights H are laid out at different positions S of the main river channel of the target basin, and each height corresponds to a silt dam span L. A surface graph of the relationship L~(S,H) is drawn, and polynomial surface fitting is used to obtain L(S,H).

[0015] Preferably, a functional relationship V between the silt dam layout position S, the silt dam height H and the silt dam flood storage capacity Vz is constructed. Z (S,H), specifically: silt dams with different heights H are arranged at different positions S in the main river channel of the target basin, and the flood detention capacity Vz of the silt dam corresponding to S and H is calculated, and the surface diagram of the relationship between Vz and (S,H) is drawn, and the quadratic polynomial surface fitting is used to obtain Vz Z (S,H).

[0016] Preferably, according to A(S) and V Z (S,H), the flood peak reduction degree R of the silt dam is calculated, which is:

[0017]

[0018] Among them, K N , J N , m and n represent empirical parameters with a return period of N; Q0 represents the peak flow at the outlet of the basin when no silt dam is built, m 3 / s.

[0019] Furthermore, Q0 is calculated by the following formula:

[0020]

[0021] Among them, A0 represents the total area of ​​the target basin.

[0022] Preferably, the construction cost C of the silt dam is calculated according to the height H, L(S,H) of the silt dam and the unit price u of the material, which is specifically:

[0023] The silt dam is generalized as a tetrahedron, and its volume calculation formula is:

[0024] C=u(0.025H 3 +2.1H 2 +3H)*L(S,H) (Formula 9).

[0025] Preferably, the constraints of the multi-objective optimization model for the layout of a single dam in the main river channel of the target basin are:

[0026] a. Distance S from the basin outlet, 0≤S≤S max , S max is the length of the main river channel in the target basin;

[0027] b. The proposed silt dam height H is constrained, H min ≤H≤H max ;H max Refer to the maximum height of the silt dam in the "SL / T 804-2020 Technical Specifications for Silt Dams", H min Reference experience value;

[0028] c. Constraint on runoff generation and confluence area A, 0≤A≤A max After determining the target watershed, A max is a certain value;

[0029] d. Flood peak reduction degree R constraint, 0≤R≤100.

[0030] Preferably, a multi-objective genetic algorithm NSGA-II is used to solve a multi-objective optimization model for the layout of a single dam in the main river channel of the target basin.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The present invention determines a quantitative method for the layout position and layout scale of a silt dam in a watershed, represents the layout position by the distance S from the watershed outlet, generalizes the design scale of the silt dam, represents the construction scale of the silt dam by the height H of the silt dam, and calculates the volume V of the designed silt dam to calculate the construction cost of the silt dam as an optimization target; proposes an evaluation index of the effect of the silt dam on reducing mountain torrent disasters, the flood peak reduction degree R, which is used as one of the optimization targets in the method; and proposes three watershed characteristic databases and mathematical models thereof, including: runoff production and confluence area A=f(S), dam span L=f(S,H), flood detention reservoir capacity V Z=f(S,H), and the optimization target flood peak reduction degree of the silt dam is constructed. Then, the layout location and construction scale of the silt dam are taken as decision factors, and the flood peak reduction degree of the silt dam and the construction cost of the silt dam are taken as optimization targets. A mathematical model is constructed and multi-objective optimization is performed to quickly obtain the trade-off relationship between the flood peak reduction degree of the silt dam and the construction cost. Finally, the layout location and layout scale of the silt dam that meet the requirements of flash flood disaster reduction and investment cost can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic diagram of the runoff area of ​​the target basin and node positions. The runoff area of ​​the basin outlet is the total area of ​​the entire basin. If a silt dam is laid at a distance of S1 from the basin outlet, its runoff area will be A1 as shown in the figure, and it can be seen that each position S will correspond to a runoff area A.

[0034] Figure 2 It is a relationship diagram between the runoff area A of the target basin and the distance S from the basin outlet. After polynomial fitting, the functional relationship between S and A can be determined.

[0035] Figure 3 It is a cross-sectional diagram at the position S1 away from the basin outlet. The layout of the check dam should be perpendicular to the direction of the river, so each position S will correspond to a cross-section. In this section, each dam height H has a corresponding cross-sectional width L, which is the span of the check dam.

[0036] Figure 4 It is a surface diagram of the relationship between the silt dam layout position S, the silt dam height H and the silt dam span L. By appropriately selecting multiple sets of S and H parameters and extracting their corresponding L, a series of data sets can be obtained to draw the surface.

[0037] Figure 5 It is the height H of the check dam at the basin outlet S and the flood storage capacity V of the check dam. Z Schematic diagram of longitudinal section. Each position S and dam height H has a corresponding flood storage capacity V Z .

[0038] Figure 6 It is a surface diagram of the relationship between the silt dam layout position S, the silt dam height H and the silt dam span L. By appropriately selecting multiple groups of S and H parameters, the corresponding V Z , a series of data sets can be obtained to draw the surface.

[0039] Figure 7 It is a schematic diagram of a silt dam generalized into a quadrangular pyramid shape.

[0040] Figure 8 It is the Pareto frontier diagram of the multi-objective optimization model for the location of a single dam in the main river channel of the target basin. DETAILED DESCRIPTION

[0041] In order to further understand the present invention, the present invention is described below in conjunction with embodiments. These descriptions are only to further explain the features and advantages of the present invention and are not intended to limit the claims of the present invention.

[0042] The method for selecting the location of a silt dam with the goal of flood control and economy of the present invention comprises the following steps:

[0043] S1, extract the main river channel of the target basin: Based on the DEM (Digital Elevation Model) of the target basin, GIS software is used to fill depressions, calculate flow direction, calculate cumulative flow, and then extract the main river network by setting flow thresholds. Finally, the tributaries are removed and only the main river channel of the target basin is retained. See Figure 1 .

[0044] The distance S from the outlet of the target basin represents the location of the silt dam in the main river channel; the height H of the silt dam to be built represents the scale of the silt dam to be built.

[0045] S2, construct the functional relationship between the location S of the silt dam and the runoff area A. In the basin, each point S on the main river channel corresponds to a runoff area A, see Figure 1 . It can be calculated and extracted through GIS software, and nodes can be evenly set along the main river channel to draw the A-S relationship curve. Figure 2 , a cubic polynomial is used for curve fitting to obtain the functional relationship A=f(S), as shown in Formula 1.

[0046] A(S)=a A *S 3 +b A *S 2 +c A *S+d A (Formula 1)

[0047] Where: A(S) is the runoff area, km 2 ; a A 、b A 、c A d A All are fitting coefficients.

[0048] The functional relationship between the silt dam layout position S, silt dam height H and silt dam span L is constructed. In the basin, the dam axis of the silt dam is generally arranged perpendicular to the main river channel, so each layout position S corresponds to a cross section, see Figure 3 Based on this cross section, it is planned to build a silt dam with different heights H. Each height has a corresponding section width, which is expressed as the span L of the silt dam to be built. Figure 3 , and draw the L~(S,H) relationship surface diagram, see Figure 4 , polynomial surface fitting is used to obtain the functional relationship L = f(S, H), as shown in Formula 2, and L(S, H) is used to represent it in subsequent formulas.

[0049] L(S,H)=a L *S 2 +b L *H 2 +c L *S*H+d L *S+e L *H+f L (Formula 2)

[0050] Where: L(S,H) is the span of the silt dam, m; a L 、b L 、c L d L 、e L 、f L All are fitting coefficients.

[0051] The relationship between the location S of the silt dam, the height H of the silt dam and the flood detention capacity Vz of the silt dam is constructed. When the location S and the height H of the silt dam to be built are determined, the flood detention capacity Vz of the silt dam under this condition can be calculated. Figure 5 , and draw the Vz~(S,H) relationship surface diagram, see Figure 6 , using quadratic polynomial surface fitting, we get the functional relationship Vz = f(S,H), as shown in Formula 3. V is used in subsequent formulas. Z (S,H) is used to represent.

[0052] V Z (S,H)=a v *S 2 +b v *H 2 +c v *S*H+d v *S+e v *H+f v (Formula 3)

[0053] Where: V Z (S,H), flood storage capacity of silt dam, 10,000 m 3 ; a v 、b v 、c v d v 、e v 、f v All are fitting coefficients.

[0054] S3, the investment cost of the silt dam is represented by C, which is generalized as the product of the dam volume V and the unit price u of the material, as shown in Formula 4.

[0055] C=V*u (Formula 4)

[0056] In the formula, the dam volume V can be calculated from the distance S and the height H of the silt dam as follows:

[0057] In this method, the silt dam is generalized as a quadrangular platform. Figure 7 The volume calculation formula is shown in Formula 5.

[0058] V=(B+H*m)HL (Formula 5)

[0059] Where: V, dam volume, m 3 ; B, dam crest width, m; m, dam slope gradient.

[0060] According to Table 6.3.3 and Table 6.3.5 in the "SL / T 804-2020 Technical Specifications for Silt Dams", there is a functional relationship between the dam crest width B, the dam slope m, and the height of the silt dam. Taking the water drop dam as an example, see Formula 6 and Formula 7:

[0061] m=0.025H+2 (Formula 6)

[0062] B=0.1H+3 (Formula 7)

[0063] Substituting equation 2, equation 6, and equation 7 into equation 5, we get:

[0064] V=(0.025H 3 +2.1H 2 +3H)*L(S,H) (Formula 8)

[0065] Substituting the above results into formula 4, we can get the calculation formula for the construction cost of the silt dam:

[0066] C=u(0.025H 3 +2.1H 2 +3H)*L(S,H) (Formula 9)

[0067] S4, R is used to represent the degree of flood peak reduction after the construction of the check dam, which represents the benefit of the check dam in reducing mountain torrent disasters.

[0068]

[0069] Where: R represents the degree of flood peak reduction after the construction of the silt dam;

[0070] Q S Indicates the peak flow before the construction of the silt dam at a location S km from the basin outlet, m 3 / s;

[0071] q S It represents the peak flow after the construction of the silt dam at a distance of S km from the basin outlet, m 3 / s;

[0072] Q0 represents the peak flow at the outlet of the basin when no check dam is built, m 3 / s.

[0073] The calculation methods for each item in the above formula are as follows:

[0074] The peak flow calculation method refers to Section 5.2 of the "SL / T 804-2020 Technical Specifications for Silt Dams" - Design Peak Flow Calculation. Since most of the areas where silt dams are located do not have reliable historical flood monitoring and survey data, the empirical formula method applicable to areas without data is used, that is, the peak area correlation method, see formula 11.

[0075] Q P =K N *A n (Formula 11)

[0076] At the same time, the corresponding flood flow can be calculated:

[0077] W P =J N *A m (Formula 12)

[0078] Where: Q P represents the design peak with design frequency P; W P represents the total design flood volume with design frequency P; A represents the runoff area at the node location; K N , J N , m, n represent the empirical parameters of the return period N, which can be found in the local hydrological manual.

[0079] The design flood peak Q0 at the outlet of the target basin and the flood peak flow Q at a distance of Skm from the basin outlet can be calculated by formula 11. S .

[0080] Q0 is only related to the total area of ​​the target basin. Once the target basin is determined, the total area A0 will not change, so Q0 will not change either and can be regarded as a constant.

[0081]

[0082] Q S It will change with the location of the planned silt dam, and the calculation result is shown in Formula 14, where A(S) can be obtained from Formula 1.

[0083] Q S =K N *A(S)n (Formula 14)

[0084] q s The peak load calculation refers to Section 5.6 - Flood Control Calculation in the "SL / T 804-2020 Technical Specification for Silt Dams". This method only considers the single dam layout in the mainstream of the target basin, and the single dam flood control calculation method is used.

[0085]

[0086] Substituting equations 3, 11, and 12 into equation 15, we can get the peak flow after the silt dam is installed at a distance of S km from the basin outlet. Substituting it into equation 10, we can get the degree of flood peak reduction after the silt dam is built:

[0087]

[0088] S5, taking the flood peak reduction degree R of the silt dam and the construction cost C of the silt dam as the objective function of multi-objective optimization of the layout location of the single dam of the silt dam in the main river channel of the target basin;

[0089] The model is established as follows:

[0090]

[0091] Where: f1(X) is determined by Formula 16, and f2(X) is determined by Formula 9.

[0092] Determine the model decision variable X, X = [S (distance from the basin outlet), H (height of the proposed silt dam)];

[0093] Identify model constraints:

[0094] a. Distance S from the basin outlet, 0≤S≤S max Different target basins have different lengths of main river channels. Once the target basin is determined, its S max will also be a fixed value;

[0095] b. The proposed silt dam height H is constrained, H min ≤H≤H max , refer to the maximum height of the silt dam in the "SL / T 804-2020 Technical Specifications for Silt Dams", and the minimum height of the silt dam refers to the empirical value, which is generally 2m;

[0096] c. Constraint on runoff generation and confluence area A, 0≤A≤A max After determining the target watershed, A max is a certain value, that is, there is a nonlinear constraint, 0≤a A *S 3 +b A *S 2 +cA *S+d A ≤A max , a A 、b A 、c A d A All are fitting coefficients;

[0097] d. Flood peak reduction degree R constraint, 0≤R≤100.

[0098] After the above mathematical model parameters are determined, the multi-objective genetic algorithm NSGA-II (gamultiobj) is used to set appropriate solution parameters, including the optimal individual coefficient paretoFraction, population size populationsize, maximum evolution generations generations, stop generation stallGenLimit, and fitness function deviation TolFun. Finally, the Pareto frontier of the multi-objective optimization model for the layout of the single dam of the main river channel of the target basin is solved and drawn, see Figure 8 .

[0099] Through the optimization algorithm, a series of silt dam design schemes can be obtained, and the Pareto frontier diagram reflects the different trade-offs between the flood peak reduction degree and the construction cost of these schemes. Finally, a design scheme that is most suitable for practical application can be selected from these Pareto optimal solutions, providing strong support for designers in the design and decision-making of silt dam projects.

[0100] Examples

[0101] The target basin for the construction of the silt dam in this example is located in northern Shaanxi. The basin area is 16.4km 2 .

[0102] Step 1: Using the DEM of the target basin as the basic data, GIS software is used for processing. By filling depressions, calculating flow direction, and calculating cumulative flow, the main river network is extracted by setting flow thresholds. Finally, the tributaries are removed, and only the main river channel of the basin is retained. Finally, the main river channel of the target basin is extracted, such as Figure 1 As shown, the total length of the river is about 8km.

[0103] Step 2:

[0104] (1) Construct a functional relationship between the silt dam location S and the runoff area A. Set nodes at appropriate intervals along the main river channel and extract the runoff area of ​​the watershed controlled by the node location. The example watershed extraction results are shown in Table 1. The A-S relationship curve is drawn based on this, as shown in Figure 2 As shown, a polynomial fitting is performed. The higher the fitting order, the better the fitting effect. In this example, the fitting order is 3, and the A-S function relationship is obtained:

[0105] A=0.09619*S 3 -1.36362*S 2 +3.23847*S+14.40398

[0106] The R of the fitting function 2 It is 0.99113, indicating that the fitting result is good and can be used for subsequent optimization models.

[0107] Table 1 Extraction results of silt dam layout location S and runoff area A

[0108]

[0109] (2) Construct the functional relationship between the silt dam layout position S, silt dam height H and silt dam span L. The silt dam is generally laid perpendicular to the river direction, and the cross-sectional morphology is extracted at appropriate intervals in the main river, such as Figure 3 As shown in the figure, the cross-sectional width L corresponding to different H is extracted, which is used as the span of the proposed silt dam. The results of the example watershed extraction are shown in Table 2, and the L~(S,H) relationship surface diagram is drawn based on this. Figure 4 , using polynomial surface fitting, we get the functional relationship L = f(S, H). The higher the fitting order, the better the fitting effect. In this example, the fitting order of the two variables is 2, and the final functional relationship of L ~ (S, H) is:

[0110] L=2.2249*S 2 -0.0756*H 2 -0.1646*S*H-17.5718*S+6.3001*H+23.2940

[0111] The R of the fitted surface function 2 It is 0.93407, which indicates that the fitting result is good and can be used for subsequent optimization models.

[0112] (3) Construct the location S of the silt dam, the height H of the silt dam and the flood storage capacity V of the silt dam Z When the location S and height H of the silt dam are determined, the corresponding flood storage capacity V Z It will also be determined if Figure 5 The example watershed extraction results are shown in Table 2, which is used to draw V Z ~(S,H) relationship surface diagram, see Figure 6 , using polynomial surface fitting, we get V Z =f(S,H) function relationship. The higher the fitting order, the better the fitting effect. In this example, the fitting order of the two variables is 2, and the final V Z ~(S,H) function relationship:

[0113] VZ =6.2804*S 2 +1.3639*H 2 -2.1751*S*H-49.6403*S-3.7933*H+75.2700

[0114] The R of the fitted surface function 2 It is 0.92633, indicating that the fitting result is good and can be used for subsequent optimization models.

[0115] Table 2 Location S, height H, span L, and flood storage capacity V of the silt dam Z Extract results

[0116]

[0117] Step 3: Calculate the volume of the dam and simplify the calculation of the construction cost of the dam.

[0118] This method simplifies the calculation method of the investment of the silt dam project, and the total investment is expressed by the product of the total earthwork volume and the unit price of the earthwork. Through the analysis and summary of multiple silt dam design reports in northern Shaanxi, the final analysis shows that the unit price of the total earthwork volume ranges from 50,000 to 200,000 yuan / m 3 In this method, 100,000 / 10,000 m 3 As unit price u, through equations 4 to 9, the calculation formula for the construction cost of the silt dam is obtained:

[0119] C=0.001*(0.025H 3 +2.1H 2 +3H)*(2.2249*S 2 -0.0756*H 2 -0.1646*S*H-17.5718*S+6.3001*H+23.2940)

[0120] Step 4: Calculate the degree of flood peak reduction. In this example, the design flood peak of once in a hundred years is taken as an example. The parameter K in equations 11 and 12 is obtained through the "Shaanxi Province Small and Medium Basin Design Rainstorm Flood Atlas". N , J N , m, and n are 18.3, 0.85, 1.05, and 0.68, respectively. Substituting into formula 13, it can be seen that the design flood peak Q0 at the outlet of the target basin is:

[0121] Q0=18.3*16.4 0.68 =122.62m 3 / s

[0122] Substituting the above formula into formula 16, we can obtain the formula for the flood peak reduction degree R after the construction of the silt dam:

[0123] R=0.1756*(0.09619*S 3 -1.36362*S 2 +3.23847*S+14.40398) -0.37 *(6.2804*S 2 +1.3639*H 2 -2.1751*S*H-49.6403*S-3.7933*H+75.2700)*100%

[0124] Step 5: The flood peak reduction degree R of the silt dam and the construction cost C of the silt dam are used as the objective function of the multi-objective optimization of the single dam layout location of the silt dam in the main river channel of the target basin. The model is as follows:

[0125]

[0126] Model constraints:

[0127] a. Distance S from the basin outlet, 0≤S≤8;

[0128] b. The proposed silt dam height H is constrained, 5≤H≤30;

[0129] c. Constraint of runoff generation and confluence area A, 0≤0.09619*S 3 -1.36362*S 2 +3.23847*S+14.40398≤16.4;

[0130] d. Flood peak reduction degree R constraint, 0≤R≤100.

[0131] After the above mathematical model parameters are determined, the multi-objective genetic algorithm NSGA-II (gamultiobj) is used to set appropriate solution parameters, including the optimal individual coefficient paretoFraction, population size populationsize, maximum evolution generations generations, stop generation stallGenLimit, and fitness function deviation TolFun. Finally, the Pareto frontier of the multi-objective optimization model for the layout of the single dam of the main river channel of the target basin is solved and drawn, as shown in Table 3. Figure 8 .

[0132] Table 3 Pareto frontier of the multi-objective optimization model for the location of single dam in the main river channel of the target basin

[0133]

[0134]

[0135] After obtaining the Pareto frontier results, designers can use this result as a reference for design. Scenario 1: After calculation, the peak flow of the target basin once in 20 years is 79.53m 3 / s, if we want to reduce the once-in-a-century flood peak of 122.62m 3 / s is reduced to once in 20 years, that is, the flood peak reduction degree R is 64.86%, through Figure 8 The corresponding construction cost C is about 2.2 million yuan, and the dam location and dam height recommended by the model under this condition can be obtained. Scenario 2: If the existing relevant investment is 2.6 million yuan, through Figure 8 It can be seen that the optimal flood peak reduction effect under this condition is about 79.5%, that is, the maximum flood peak after reduction is 25.14m 3 / s and the two-year flood peak is 26.65m 3 / s equivalent.

[0136] Through the above embodiments, it can be clearly seen that the method can quickly obtain the trade-off between the degree of flood peak reduction of the silt dam and the construction cost, and can quickly provide decision makers with a relatively accurate and intuitive construction cost and benefit relationship diagram of the silt dam, which can provide a reference basis for silt dam construction projects in the project proposal stage and feasibility study stage.

Claims

1. A method for selecting the location of a silt dam with the goal of flood control and economy, characterized in that: include: The proposed silt dam is laid out on the main river channel of the target basin. The distance S from the basin outlet represents the location of the silt dam. The functional relationship A(S) between the silt dam location S and the runoff area A is constructed. The functional relationship L(S,H) between the silt dam location S, the silt dam height H and the silt dam span L is constructed. The functional relationship Vz between the silt dam location S, the silt dam height H and the silt dam flood detention capacity Vz is constructed. Z (S,H); According to A(S) and V Z (S,H), calculate the flood peak reduction degree R of the silt dam; according to the height H, L(S,H) of the silt dam and the unit price u of the material, calculate the construction cost C of the silt dam; Taking the maximum flood peak reduction degree R of the check dam and the minimum construction cost C of the check dam as the optimization objectives, and the check dam location S and the check dam height H as the decision variables, a multi-objective optimization model for the layout of single check dams in the main river channel of the target basin is constructed, the Pareto frontier is solved and drawn, and the check dams are laid out according to the Pareto frontier.

2. The method for selecting the location of a silt dam with the goal of flood control and economy according to claim 1, characterized in that: Based on the DEM of the target watershed, the main river channel of the target watershed is extracted using GIS software.

3. The method for selecting the location of a silt dam with the goal of flood control and economy according to claim 1, characterized in that: The functional relationship A(S) between the silt dam layout location S and the runoff area A is constructed as follows: Warping dams were laid at different locations in the main river channel of the target basin. The dam layout location S and the corresponding runoff area A were calculated and extracted using GIS software. A ~ S relationship curve was drawn, and a cubic polynomial was used for curve fitting to obtain A(S).

4. The method for selecting the location of a silt dam with the goal of flood control and economy according to claim 1, characterized in that: The functional relationship L(S,H) among the location S of the silt dam, the height H of the silt dam and the span L of the silt dam is constructed. Specifically, silt dams with different heights H are arranged at different locations S of the main river channel of the target basin. Each height corresponds to a span L of the silt dam. A surface diagram of the relationship L~(S,H) is drawn, and polynomial surface fitting is used to obtain L(S,H).

5. The method for selecting the location of a silt dam with the goal of flood control and economy according to claim 1, characterized in that: Construct the functional relationship between the silt dam layout position S, silt dam height H and silt dam flood storage capacity Vz Z (S,H), specifically: silt dams with different heights H are arranged at different positions S in the main river channel of the target basin, and the flood detention capacity Vz of the silt dam corresponding to S and H is calculated. Based on this, a surface diagram of the relationship between Vz and (S,H) is drawn, and a quadratic polynomial surface fitting is used to obtain Vz. Z (S,H).

6. The method for selecting the location of a silt dam with the goal of flood control and economy according to claim 1, characterized in that: According to A(S) and V Z (S,H), the flood peak reduction degree R of the silt dam is calculated, which is: (Formula 16) Q P =K N *A n (Formula 11) W P =J N *A m (Formula 12) Among them, Q P represents the design peak with design frequency P; W P represents the total design flood volume with design frequency P; K N , J N , m and n represent the empirical parameters with a return period of N in the empirical formula for calculating flood peak and flood volume; Q0 represents the flood peak flow at the outlet of the basin when no silt dam is deployed, m 3 / s.

7. The method for selecting the location of a silt dam with the goal of flood control and economy according to claim 6, characterized in that: Q0 is calculated by the following formula: (Formula 13) Among them, A0 represents the total area of ​​the target basin.

8. The method for selecting the location of a silt dam with the goal of flood control and economy as claimed in claim 1, characterized in that: According to the height H, L (S, H) of the silt dam and the unit price u of the material, the construction cost C of the silt dam is calculated as follows: The silt dam is generalized as a tetrahedron, and its volume calculation formula is: C = u(0.025H 3 +2.1H 2 +3H)*L(S,H) (Formula 9) 9. The method for selecting the location of a silt dam with the goal of flood control and economy according to claim 1, characterized in that: The constraints of the multi-objective optimization model for single dam layout of silt dams in the main river channel of the target basin are: a. Distance S from the basin outlet, 0≤S≤S max , S max is the length of the main river channel in the target basin; b. The proposed silt dam height H is constrained, H min ≤H≤H max ;H max Refer to the maximum height of the silt dam in the "SL∕T 804-2020 Technical Specifications for Silt Dams", H min Reference experience value; c. Constraint on runoff generation and confluence area A, 0≤A≤A max After determining the target watershed, A max is a certain value; d. Flood peak reduction degree R constraint, 0≤R≤100.

10. The method for selecting the location of a silt dam with the goal of flood control and economy according to claim 1, characterized in that: The multi-objective genetic algorithm NSGA-II is used to solve the multi-objective optimization model for the layout of single dams in the main river channel of the target basin.

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