Evaluation method of cascade sand trap dam group and its application

Abstract

This invention discloses a method for evaluating the sediment retention function of a cascade dam group and its application. Based on the actual performance of the sediment retention function of the cascade dam group, the method decomposes the retention function into three dimensions: interception and blocking function, drainage and sorting function, and storage capacity function. Three evaluation indicators—sediment interception rate, particle size coarsening rate, and reservoir siltation rate—and their mathematical calculation models are developed to characterize these functions respectively. From a systems engineering perspective, the method overcomes the limitation of not considering the changes in debris flow properties along the course of the flow, constructing an evaluation framework that reflects the mutual influence between upstream and downstream single-stage dams, thus reflecting the system's horizontal variation characteristics in the evaluation model. The invention provides a scheme for identifying the health status of the sediment retention function. It also provides an application scheme for the planning and evaluation of cascade dam groups, used for verifying and adjusting the sediment retention function of dam groups during the design phase, and for diagnosing typical problems and planning operation and maintenance modifications during the service phase. The solution of this invention has the advantages of being clear and concise, reducing the computational load while ensuring scientific calculation and comprehensive conclusions.

Description

Technical Field

[0001] This invention relates to a method for evaluating the storage capacity of a cascade silt-trapping dam group and its application, particularly a method for evaluating the storage capacity of a cascade silt-trapping dam group using a hierarchical index system, and an application scheme of this evaluation method in the planning of cascade silt-trapping dam groups. It belongs to the fields of water conservancy engineering, digital data processing, information processing technology specifically applicable to environmental management, supervision, or forecasting purposes, and mountain disaster environmental governance technology. Background Technology

[0002] Debris retaining dams are the most commonly used engineering facilities for preventing debris flow disasters in small watersheds in mountainous areas. In some small watersheds with high-risk disaster conditions due to certain topographical and geological conditions, debris flows induced by extreme precipitation are characterized by large scale, severe erosion along the flow path, and large siltation areas. Therefore, the design of debris retaining dam projects often needs to be upgraded from single-stage dams to a series of cascade dams along the watershed direction to achieve graded interception and control of debris flows along the flow path. The cascade dam group not only plays the disaster prevention function of single-stage debris retaining dams, but also forms a cascade reference surface, which helps to enhance the mutual protection of each level of debris retaining dams under the backfilling effect, and coordinates the reduction of scouring and downcutting damage of debris flows behind the dams within the dam group system.

[0003] In the prevention and control of debris flow disasters in small watersheds in mountainous areas, although cascade check dam groups have received widespread attention and application due to their systematic interception and full-process control functions, research on their interception function using existing technologies is still in its preliminary stage. Existing technology, "Energy Dissipation Effect Analysis of Cascade Check Dams for Debris Flow in the Duwen Expressway's Thorough Closure Gully" (Zhang Weixu, Chengdu University of Technology, 2016), discloses a method that uses the spatial distribution characteristics of the deposits behind the cascade check dam group as an indicator, and analyzes the solid material accumulation effect of the cascade check dam group on debris flow sources by utilizing data on the change rate of different types of debris flow deposits in different areas of the main gully before and after dam construction. Existing technology, "Benefit Analysis of Debris Flow Prevention and Control Project in the Hunshui Gully of the Daying River in Yunnan" (Yang Zaizhi, Yunnan University, 2021), discloses a method that uses the loose solid material reserve in the gully and the loose solid material interception volume of the cascade check dam group as indicators, and evaluates the interception benefits of the cascade check dam group based on their survey data and proportion relationship. The existing technology "Investigation and Analysis of Upstream and Downstream Scouring and Deposition Characteristics of Small Watershed Sand Barrier Dams" (Wang Jinshui et al., Journal of Yangtze River Scientific Research Institute, May 2024) is based on the analysis results of the dam type survey data of sand barrier dams in operation within a small watershed. It discloses a dam type combination mode (OS mode) that adopts an upstream permeable dam and a downstream solid dam. The upstream permeable dam intercepts large-diameter boulders, while the downstream solid dam intercepts small particles, forming a tiered sand barrier dam group with a graded interception and filtration function.

[0004] The existing technologies mentioned above are still at the stage of field survey data and qualitative analysis or quantitative description of single indicators for the storage function of cascade silt-trapping dam groups. They have not yet involved technical thinking on the systematic quantitative evaluation of the storage function of cascade silt-trapping dam groups, let alone a more systematic technical solution to the problem of evaluating the storage function of cascade silt-trapping dam groups. In particular, there is no technical solution that uses a combination of indicators to evaluate its storage function in a hierarchical manner. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for evaluating the storage capacity of a cascade silt-trapping dam group. This method utilizes the parameters of the cascade silt-trapping dam group to systematically and hierarchically evaluate the storage capacity of the cascade silt-trapping dam group from the perspective of the realization of the silt-trapping dam function.

[0006] To achieve the above objectives, the present invention provides a method for evaluating the interception and storage function of a cascade silt-trapping dam group, the technical solution of which is as follows.

[0007] A method for evaluating the sediment retention function of a cascade silt-trapping dam group. Conduct on-site investigations to obtain basic data. The on-site investigation area includes the construction planning area of ​​the cascade silt-trapping dam group project and the debris flow gully where it is located. The sediment interception rate was used to evaluate the interception effectiveness of a cascade sediment-trapping dam group. i Sediment interception rate of Class I silt-trapping dam oh i According to the model expression 1, i ≤ n , n It is the total number of stages of the cascade silt-trapping dam group; Formula 1 In the formula, C v - Debris flow sediment volume concentration, % E i -No. i The relative spacing between level 1 silt-trapping dams, a dimensionless quantity. J i -No. i The relative reservoir capacity of a grade-1 silt-trapping dam, dimensionless quantity. K i -No. i The relative opening width of a grade-separated silt-trapping dam, a dimensionless quantity. S - Debris flow gully gradient, dimensionless quantity. L i -No. i The spacing between level 1 silt-trapping dams, in meters. H i -No. i The height of a Class I silt-trapping dam is expressed in meters (m). V se - Debris flow sediment volume, unit m 3 , V i -No. i The reservoir capacity of a grade 1 silt-trapping dam, in meters (m). 3 , b i -No. i The width of the dam opening of a Class I silt-trapping dam, in meters. d max - Maximum particle size of debris flow sediment, in meters.

[0008] The aforementioned method for evaluating the sediment retention function of a cascade silt-trapping dam group uses the sediment interception rate to assess the interception effectiveness of the cascade silt-trapping dam group, characterizing the interception and blocking sub-item of the sediment retention function. Sediment interception rate oh i The derivation of the expression model (Equation 1) is based on the theoretical construction of previous research and the multiple regression analysis based on water tank experimental data. In the theoretical analysis, the first step is to... i Sediment interception rate of Class I silt-trapping dam oh i Defined as the ratio of the mass of sediment intercepted by the dam to the initial total mass of sediment in the debris flow; based on this, and through field observation and analysis, it was found that the relative dam spacing should be selected at both the cascade dam group system level and the single-stage dam unit level. E i Relative storage capacity J i Relative opening width K i Combined with the volume concentration of mudslide sediment C v These four dimensionless quantities form the independent variables of the measurement model. The four dimensionless quantities respectively represent the spatial location factors of the tiers (…). E i Storage capacity factor J i ), through structural functional factors ( K i ), material composition factors ( C v The model is introduced to fully express the sediment interception rate control factors at the observation and planning design level in the dam group system project, providing a basis for the practical application of the evaluation method of the sediment interception function of the cascade dam group.

[0009] This invention also provides the following optimization scheme for the above-mentioned method for evaluating the sediment retention function of a cascade dam group. The optimization technology improves the technical solution from multiple technical perspectives and can be implemented independently while maintaining technical independence, or simultaneously without causing logical conflicts between the preceding and following technologies.

[0010] Optimization 1: The particle size coarsening rate is used to evaluate the particle size separation efficiency of the cascade sand-trapping dam group. i Grain size coarsening rate of primary sediment trap dam D i According to the Equation 2 model expression.

[0011] Formula 2 In the formula, d 50-i -No. i Median particle size of sediment in the reservoir of a Class I silt-trapping dam, in meters; d 50 - Median particle size of debris flow sediment, in meters.

[0012] "Coarse particle interception and fine particle discharge" is the ideal technical function of a sediment-trapping dam, and the proportion of coarse particles in the intercepted material is a key indicator of interception efficiency. Preliminary field observations and investigations revealed that, in practical engineering, the interception efficiency of sediment with different particle sizes varies significantly due to their physical properties, making this crucial for evaluating the "coarse particle interception and fine particle discharge" function. However, existing technologies typically only use the median particle size d of the sediment when evaluating the sediment-trapping function of sediment-trapping dams. 50 The change in particle size can be used to characterize the degree of coarsening (e.g., comparing the initial inflow with the median particle size d of the sediment in the reservoir). 50 The ratio ignores the actual interception efficiency of each particle size group. Data from the water tank experiment proves that during the particle size coarsening process, oh i In practice, it acts as a "modulation factor." The higher the interception efficiency, the more significant the decrease in the proportion of coarse particles in the sediment behind the dam, and the more nonlinear amplification effect its contribution to the overall coarsening degree becomes.

[0013] The model in Equation 2 introduces as oh i The index extends the existing approach of relying solely on particle size ratio, reflecting the aforementioned "modulation" function. Model boundary conditions indicate that when... oh i =0 (i.e., no interception), D i =1 indicates that the particle size group does not change after the dam, which is consistent with physical reality; when oh i =1 (i.e., complete interception), D i = d50-i / d 50 At this point, the equation is transformed into a special case of the traditional method, which only uses the median particle size ratio. Equation 2 succinctly quantifies the physical process by which the interception efficiency determines the sorting effect, enabling a quantitative evaluation of the interception and sorting sub-items of the cascade silt-trapping dam group's interception and storage function.

[0014] Optimization 2: The long-term storage efficiency of the cascade silt-trapping dam group is assessed using the reservoir siltation rate. i Siltation rate of the first-class silt-trapping dam l i According to the Equation 3 model expression.

[0015] Formula 3 In the formula, V i -No. i The reservoir capacity of a grade 1 silt-trapping dam, in meters (m). 3 .

[0016] The siltation rate is a sub-item of the storage capacity of a silt-trapping dam, reflecting the effectiveness of the siltation function over a longer time period. Existing technologies generally consider long-term siltation effectiveness to be related to the upstream reservoir capacity: the larger the reservoir capacity, the better the long-term siltation effectiveness. However, this invention, based on preliminary field observations and analysis, found that reservoir capacity is not a sufficient condition for long-term siltation effectiveness. Besides reservoir capacity, the sediment volume characteristics of debris flows and the interception and sorting performance of the silt-trapping dam can jointly constrain long-term siltation effectiveness by influencing the siltation process and degree within the reservoir. A comprehensive index coupling the upstream sediment inflow, the proportion of upstream sediment intercepted, and the proportion of sediment particle size characteristics within the reservoir needs to be constructed to evaluate the reservoir capacity operation status of the silt-trapping dam. The model constructed using flume experimental data (Equation 3) shows the "transmission effect" among the three factors through boundary conditions: when any variable is 0, the siltation amount is 0, and the reservoir siltation state is also 0; as any variable increases, the siltation amount increases proportionally, consistent with physical process phenomena. Simultaneously, when… l i A value less than 1 indicates that the silt-trapping dam's reservoir capacity is not completely filled; conversely, a value greater than 1 indicates that the silt-trapping dam's reservoir capacity is completely filled. l i =1 is the theoretical upper limit of the storage capacity of the silt trap dam.

[0017] Optimization 3: The overall sediment interception efficiency of the cascade silt-trapping dam group is evaluated using the total sediment interception rate. The total sediment interception rate Ω is the sediment interception rate of each silt-trapping dam. oh i sum.

[0018] Formula 4 Fourthly, based on the empirical values ​​from investigations and experimental studies on the storage function of cascade silt-trapping dam groups, and grounded in the technical approach to assess storage function in this invention, a combination of storage health conditions is designed to evaluate whether the cascade silt-trapping dam group is in a healthy storage function state at the system level. This combination of storage health conditions includes three conditions corresponding to the sub-items of storage function. When all three conditions are simultaneously met, the storage function of the cascade silt-trapping dam group is deemed healthy. Each of the three conditions can also be used individually to assess the health status of its corresponding sub-item.

[0019] The three conditions for the combination of sediment retention and storage health conditions include: interception health condition: total sediment interception rate Ω of the dam group ≥ 0.5; coarsening health condition: sediment retention dams of all levels... D i The value decreases along the direction of the gully; reservoir capacity health conditions: various levels of silt-trapping dams. l i <0.8.

[0020] Because the control variables selected in the construction of the key calculation model of the cascade silt-trapping dam group assessment method of this invention fully consider the actual situation of the cascade silt-trapping dam group construction project, it provides a basis for the specific application of the assessment method in project practice. This invention also provides an application scheme for the cascade silt-trapping dam group assessment method, as follows.

[0021] The above-mentioned method for evaluating the interception and storage function of cascade silt-trapping dam groups is applied to the planning of cascade silt-trapping dam groups.

[0022] The application of the aforementioned assessment method for the sediment retention function of a cascade silt-trapping dam group can include planning in two scenarios: Scenario 1, during the design phase before the construction of the cascade silt-trapping dam group, the cascade silt-trapping dam group planning is a design adjustment plan for the cascade silt-trapping dam group during the design phase. Scenario 2, during the operation phase after the construction of the cascade silt-trapping dam group, the cascade silt-trapping dam group planning is a maintenance and renovation plan for the cascade silt-trapping dam group during the operation phase.

[0023] In Scenario 1, basic data for evaluating the interception function of the cascade silt-trapping dam group is obtained based on the design and planning project. Various interception function evaluation indicators of the cascade silt-trapping dam group are calculated using a model, and it is determined whether the combination of healthy interception conditions is met. If the combination of healthy interception conditions is met, the corresponding parameters of the cascade silt-trapping dam group are retained; otherwise, the design interception function is adjusted by adjusting the parameters of the cascade silt-trapping dam group until the combination of healthy interception conditions is met. Based on engineering design practice, the parameters of the cascade silt-trapping dam group can be adjusted in the following order until the interception function meets the combination of healthy interception conditions.

[0024] If the interception health conditions are not met, increase the number of silt traps n or upgrade the dam. V i Generally speaking, improvement V i Including the addition of downstream silt trapsH i and / or reduce the size of upstream silt traps. b i ; If the coarsening health conditions are not met, the dam type combination mode of the silt-trapping dam should be adjusted to an upstream permeable dam + a downstream solid dam, specifically targeting... D i Significantly large or small silt-trapping dams, reduce or increase their b i ; If the reservoir does not meet the requirements for healthy storage capacity, then add a sand-trapping dam. H i And prioritize targeting l i Significantly large increase in sediment trapping dams H i .

[0025] When adjusting the parameters of the cascade silt-trapping dam group, the parameters should be adjusted in the order of satisfying the interception health condition, the coarsening health condition, and the reservoir capacity health condition.

[0026] In Scenario Two, basic data for assessing the cascade silt-trapping dam group's interception function is obtained based on the cascade silt-trapping dam group operation and maintenance renovation project. Various interception function assessment indicators of the cascade silt-trapping dam group are calculated using a model, and it is determined whether the combination of healthy interception function conditions is met. If the combination of healthy interception function conditions is met, the cascade silt-trapping dam group continues to operate and undergoes routine monitoring and maintenance; otherwise, an operation and maintenance plan is determined based on the actual conditions of the silt-trapping dam group. When determining the operation and maintenance plan based on the actual conditions of the silt-trapping dam group, a typical problem diagnosis is first implemented to identify whether three typical problems exist. If no typical problems are diagnosed, it indicates that although the dam group's interception function has not yet reached an ideal state, there are no obvious shortcomings, and an operation plan that continues to operate under enhanced monitoring and maintenance conditions can be adopted. If typical problems exist, it indicates that the dam group's interception function has a clear shortcoming that needs to be addressed. A renovation plan that adjusts the dam group parameters should be determined as much as possible, based on the corresponding matching adjustment plan and the actual conditions of the cascade silt-trapping dam group, to compensate for the current shortcomings in the interception function.

[0027] Typical problem diagnosis and solution matching include: Typical problem diagnosis 1: If the interception health conditions are not met, the cascade silt-trapping dam group is diagnosed as being in a weak interception operation state; the matching adjustment plan is: to add a solid silt-trapping dam in a place where the terrain and geological conditions downstream of the cascade silt-trapping dam group allow, and to reduce the opening width of the permeable silt-trapping dam in the cascade silt-trapping dam group. Typical Problem Diagnosis 2: If the coarsening health conditions are not met, the cascade silt-trapping dam group is diagnosed as being in a state of sorting imbalance operation; the matching and adjustment scheme is: analyze the silt-trapping dams at each level. D i Value arrangement, by minimizing the adjustment of each level of the silt-trapping damb i This approach aims to ensure that the cascade silt-trapping dam group meets the coarsening and health requirements as much as possible. Typical problem diagnosis 3: If Ω ≥ 0.5 and there is at least one retaining dam l i ≥0.8 indicates that the cascade silt-trapping dam group is operating at high interception and high reservoir capacity; the matching adjustment plan is as follows: l i ≥0.8 silt-retaining dam dredging and expansion, for l i For silt traps with a strength ≥0.8 and permissible topographical and geological conditions, the dam body height should be increased. H i .

[0028] Because the modification of the cascade silt-trapping dam group during operation is subject to numerous constraints and limitations, the specific adjustment plan for the parameters of the cascade silt-trapping dam group cannot be positioned as ultimately achieving a healthy state of silt-trapping function, but rather as improving the silt-trapping function. Improving the silt-trapping function, in addition to achieving a healthy state of silt-trapping function, generally includes, for example, meeting the silt-trapping function health requirements as much as possible, meeting individual health conditions, getting closer to the silt-trapping function health status than before the modification, eliminating one or all typical problems, and achieving better sub-evaluation indicators for the silt-trapping function, etc.

[0029] The field investigation referred to in this technology includes various geological surveys, reconnaissance, mapping, and measurement work at the site of the project in the mountainous small watershed, as well as existing simulation experiments, testing experiments, observation experiments, and analysis experiments in the field, acquisition of historical disaster records, relevant technical specifications, and acquisition of experience methods and data that can be used for reference. The data obtained from the field investigation are collectively referred to as the basic data of this technical solution.

[0030] Compared with the prior art, the beneficial effects of the present invention are: (1) The most basic and intuitive manifestation of the interception function of cascade silt-trapping dams is the step-by-step interception of sediment. Based on this, the cascade silt-trapping dam group interception function evaluation method of the present invention first develops the sediment interception rate index and its calculation model as the basic evaluation scheme to evaluate the basic items of the interception function. (2) Based on the basic scheme, through multiple optimizations, the cascade silt-trapping dam group interception function evaluation technical scheme of the present invention has outstanding comprehensiveness and systematicness. The comprehensiveness is mainly reflected in: based on the actual performance of the interception function of the cascade silt-trapping dam group in disaster prevention and control, the interception function of the cascade silt-trapping dam group is interpreted in multiple dimensions, decomposed into interception and blocking sub-items, interception and drainage sub-items, and storage capacity sub-items, and corresponding evaluation indicators and their mathematical calculation models are developed. The three sub-items not only conform to the basic theory of silt-trapping dams, but also have practical observation significance, and together constitute an evaluation system containing three dimensions, which can comprehensively evaluate the interception function of the cascade dam system. The systematic nature is mainly reflected in the following aspects: From the perspective of systems engineering, it breaks through the limitation of the single-dam model failing to consider the changes in debris flow properties along the course, and constructs an index calculation model that can reflect the mutual influence between upstream and downstream single-stage dams. It also enables the system's horizontal change characteristics to be reflected in the technical solution through the calculation model. (3) On the basis of quantitative evaluation of indicators, this invention further develops the combination of conditions for identifying the health status of the interception function, so that the output results of the evaluation scheme can be extended from quantitative indicators to scientific qualitative analysis. (4) The three sub-functional indicators constructed by this invention are technically interconnected and coupled, and are progressively advanced in the calculation model, so that the whole set of interception function evaluation scheme has the advantages of being clear and concise, and reducing the amount of calculation while ensuring scientific calculation and comprehensive conclusions. (5) The control variables introduced by the various indicator calculation models come from the combination of field investigation, experimental simulation and engineering practice, which ensures that the evaluation scheme fits the actual situation of the cascade dam group construction project, can be effectively implemented in design and operation and maintenance projects, and can be applied to the planning, design and renovation of the cascade dam group. The application scheme of the method for evaluating the water retention function of a cascade silt-trapping dam group provided by this invention includes a design phase scheme and an operation phase scheme. The former, through the qualification calculation of the water retention function of the cascade silt-trapping dam group during design, can guide the design adjustment of corresponding parameters of the cascade silt-trapping dam group, and solve the technical problems of the health of the water retention function of the cascade silt-trapping dam group during design. The latter, through the qualification calculation of the water retention function of the cascade silt-trapping dam group during operation, can solve the technical problems of identifying the health status of the water retention function of the cascade silt-trapping dam group in service, as well as the technical problems of diagnosing three typical problems of water retention function, and determining the technical problems of dam group modification goals. This allows the modification of the cascade silt-trapping dam group in service to focus on improving its water retention function and to be scientifically and quantitatively guided. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the technical route for evaluating the storage and retention function of a cascade silt-trapping dam group.

[0032] Figure 2This is a schematic diagram of the application route (operation phase) of the evaluation method for the interception and storage function of a cascade silt-trapping dam group.

[0033] Figure 3 It is the width of the opening of the permeable silt-trapping dam. b i Meaning diagram.

[0034] Figure 4 This is a schematic diagram of the application route (design stage) for evaluating the interception and storage function of a cascade silt-trapping dam group. Detailed Implementation

[0035] The technical solution of the present invention will be further described below with reference to the accompanying drawings and taking the preferred embodiment as an example.

[0036] Example 1

[0037] The method of this invention is used to evaluate the impoundment function of a group of operational debris flow cascade dams and to provide a modification plan.

[0038] A small watershed in a mountainous area has a high risk of debris flow disasters, becoming a typical debris flow gully. Three check dams have been constructed along the gully direction, forming a three-tiered debris flow prevention and control system (number of check dams n=3) with a cascaded check dam group as the main body. Along the gully direction, the first-tier check dam (dam #1, ...) i =1) is a permeable silt-trapping dam (specifically a grid dam), a second-stage silt-trapping dam (dam #2, i =2) is a solid dam (specifically a solid gravity dam), a third-level silt-trapping dam (dam #3, i =3) Same as Dam #2. To measure the disaster reduction capacity of the interception and prevention system for debris flow in this gully, the interception and storage function assessment method of the cascade silt-trapping dam group of this invention is applied to evaluate the interception and storage function of the cascade silt-trapping dam group in operation, and to plan operation and maintenance transformation if necessary.

[0039] Figure 1 This is a schematic diagram of the technical route for evaluating the storage and retention function of a cascade silt-trapping dam group.

[0040] Figure 2 This is a schematic diagram of the application route (operation phase) of the evaluation method for the interception and storage function of a cascade silt-trapping dam group.

[0041] 1. Obtain basic data Conduct on-site surveys of the ditches to obtain basic data. The main basic data is shown in Table 1-1. The classification of data in the table is not a strict categorization, but rather intended to make the meaning of the listed data clear and easy to read. This section has the same meaning in Tables 2-1 and 3-1.

[0042] Table 1-1 Main Basic Data of Example 1

[0043] In the main basic data table, the debris flow characteristic data collection sections are set in the natural gully section upstream of the cascade check dam group that has not been affected by engineering projects. Total sediment volume V se Estimation methods using field monitoring data or on-site investigation: V se = C v * V sc ,in V sc This refers to the volumetric scale of the debris flow. (Dam spacing) L i This refers to the distance between a silt-trapping dam and its adjacent upstream silt-trapping dam. The width of the dam opening. b i The meaning is: for physical dams, b i It is the maximum width of a single spillway opening on the dam body; for a permeable silt trap dam, b i It is the maximum width of a single functional opening on the dam body.

[0044] Figure 3 It is the width of the opening of the permeable silt-trapping dam. b i Schematic diagram. In the diagram, (a) slot dam, (b) window dam, (c) pile forest dam, (d) grid dam, and (e) comb dam, with double-headed arrows indicating the width of a single functional opening.

[0045] 2. Evaluation of the sediment retention function of the cascade silt retention dam group 2.1 Evaluation of the interception effectiveness of the cascade silt-trapping dam group For each level of silt-trapping dam, the dimensionless quantity relative to the dam spacing is calculated according to the model in Equation 1. E i Relative storage capacity J i Relative opening width K i and sediment interception rate oh i .

[0046] The main calculation data are shown in Tables 1-2 and 1-3.

[0047] Table 1-2 Main Calculation Data for Example 1

[0048] The total sediment interception rate Ω of the cascade silt-trapping dam group is the sediment interception rate of the three-stage silt-trapping dams. oh i The sum, Ω= oh 1+ oh 2+ oh 3 = 0.299 + 0.245 + 0.230 = 0.780.

[0049] The interception efficiency index calculation results show that the total sediment interception rate of this cascade silt-trapping dam group Ω=0.780≥0.5. This cascade silt-trapping dam group meets the interception health conditions.

[0050] 2.2 Evaluation of particle size separation efficiency of cascade silt-trapping dam group The particle size coarsening rate index was used to further evaluate the particle size separation efficiency of the cascade silt-trapping dam group for permeating sediment.

[0051] For each level of sediment trap, the particle size coarsening rate is calculated according to the model in Equation 2. D i The main calculation data are shown in Table 1-3.

[0052] Table 1-3 Main Calculation Data for Example 1

[0053] The particle size separation efficiency index calculation results show that the particle size coarsening rate of each level of sand-trapping dam is... D i The coefficient of performance decreases along the gully direction from 1.152 to 1.115 to 1.050. This cascade silt-trapping dam group meets the coarsening health conditions.

[0054] 2.3 Long-term sediment retention efficiency assessment of the cascade sediment retention dam group Using reservoir siltation rate l The indicators are used to evaluate the long-term sediment retention efficiency of the cascade silt-trapping dam group during operation.

[0055] For each level of silt-trapping dam, the reservoir siltation rate is calculated according to model 3. l i This characterizes the degree of depletion of the silt-trapping dam's capacity under assessment conditions. The main calculation data are shown in Tables 1-4.

[0056] Table 1-4 Main Calculation Data for Example 1

[0057] Long-term sediment retention efficiency index calculation results show that for sediment retention dams of all levels, the sediment interception rate is... oh i With particle size coarsening rate D i Reservoir siltation rate calculated using parameters such as... l i The values ​​are all greater than 1, meaning that the degree of consumption of the reservoir capacity by the various levels of silt-trapping dams has reached and exceeded the state of full siltation. l i=1.000). This cascade silt-trapping dam group does not meet the reservoir capacity health requirements.

[0058] The cascade silt-trapping dam group does not meet the requirements for a healthy storage function.

[0059] 3. Planning for the operation and maintenance of water storage functions 3.1 Diagnosis of Typical Problems

[0060] After ruling out typical problems one and two, the diagnosis falls into typical problem three, namely, Ω ≥ 0.5 but with at least one (in this case, all) silt-trapping dam. l i ≥0.8 indicates that the reservoir is in a high-interception, high-capacity operation state, meaning that the overall interception effect is good, but all levels of the silt-trapping dams are full and the reservoir capacity is about to be exhausted, and the interception and storage function of the cascade silt-trapping dam group is about to fail.

[0061] 3.2 Determine the renovation plan right l i All silt-trapping dams with a diameter ≥0.8 should be dredged and their capacity expanded as much as possible; for silt-trapping dams where topographical and geological conditions permit, the dam body should be heightened by increasing the silt content. H i Increase storage capacity V i .

[0062] Example 2

[0063] The method of this invention is used to evaluate the impoundment function of a group of debris flow cascade dams in operation and to provide a modification plan.

[0064] A small watershed in a mountainous area has a high risk of debris flow disasters and is a typical debris flow gully. Three check dams have been constructed along the gully direction, forming a three-tiered debris flow prevention and control system (n=3) with a cascade check dam group as the main body. Along the gully direction, the first check dam (dam #1) is a permeable check dam (specifically a grid dam), while the second and third check dams (dam #2 and dam #3) are solid dams (specifically solid gravity dams). To assess the debris flow mitigation capacity of the prevention and control system for this gully, the cascade check dam group interception function evaluation method of this invention is applied to evaluate the interception function of the cascade check dam group in operation, and to plan operation and maintenance modifications if necessary. Similarities to Example 1 will not be repeated; the following focuses on describing the differences.

[0065] 1. Obtain basic data The main basic data is shown in Table 2-1.

[0066] Table 2-1 Main Basic Data of Example 2

[0067] 2. Evaluation of the sediment retention function of the cascade silt retention dam group Sediment interception rate oh Total sediment interception rate (Ω), particle size coarsening rate D , reservoir siltation rate l The sediment retention function of the cascade dam group was evaluated using various indicators. Relevant data are shown in Table 2-2.

[0068] Table 2-2 Main Calculation Data for Example 2

[0069] The cascade silt-trapping dam group does not meet the requirements for a healthy state, and only the interception sub-item meets the interception health conditions.

[0070] 3. Planning for the operation and maintenance of water storage functions 3.1 Diagnosis of Typical Problems Diagnosing and ruling out typical problems.

[0071] Diagnosis of Typical Problem 2: Silt-trapping Dams at All Levels D i The values ​​are 1.193, 1.214, and 1.069 respectively, showing no decrease along the channel direction, and therefore do not meet the coarsening health conditions. This belongs to typical problem two: the cascade silt-trapping dam group is in a state of disordered operation. D i It exhibits an abnormal distribution of "low-high-low" and a completely anomalous phenomenon of "thin interception upstream and coarse interception downstream".

[0072] Typical Problem 3 Diagnosis: Ω = 0.69 ≥ 0.5 and at least one retaining dam l i ≥0.8 indicates a typical problem, where the cascade silt-trapping dam group is operating under high interception and high reservoir capacity conditions.

[0073] 3.2 Determine the renovation plan For the second typical problem, the matching solution is to analyze the various levels of silt-trapping dams. D i Value arrangement, by minimizing the adjustment of each level of the silt-trapping dam b i The method aims to ensure that the cascade silt-trapping dam group meets the coarsening and health conditions as much as possible; for typical problem three, the matching solution is to... l i ≥0.8 silt-retaining dam dredging and expansion, and for l i For silt traps with a strength ≥0.8 and permissible topographical and geological conditions, the dam body height should be increased. H i .

[0074] Based on the above two matching schemes and the actual situation of the cascade silt-trapping dam group, the operation and maintenance renovation plan is determined as follows: (1) Renovate Dam No. 1 and Dam No. 2 to increase their opening width respectively. b i ,make D i Adjust to decrease along the course. (2) Dredge all levels of silt-trapping dams and expand their capacity as much as possible; raise the dam body of silt-trapping dams where the terrain and geological conditions permit, by increasing the dam height. H i Increase storage capacity V i .

[0075] Example 3

[0076] The method of this invention is used to evaluate the debris flow interception function of a series of cascade dams in a certain design and to provide design planning.

[0077] A small watershed in a mountainous area has a high risk of debris flow disasters and is a typical debris flow gully. It is planned to construct three check dams along the gully direction, forming a three-tiered debris flow prevention and control system (n=3) with a cascade check dam group as the main body. Along the gully direction, the first and second tier check dams (dam #1 and dam #2) are permeable check dams (specifically, grid dams), while the third tier check dam (dam #3) is a solid dam (specifically, a solid gravity dam). To assess the disaster reduction capacity of the prevention and control system for debris flows in this gully, the interception and storage function evaluation method of the cascade check dam group of this invention is used to evaluate the interception and storage function of the cascade check dam group currently in the design stage, and design adjustments are made as necessary. Similarities to Example 1 will not be repeated; the key differences will be described.

[0078] Figure 4 This is a schematic diagram of the application route (design stage) for evaluating the interception and storage function of a cascade silt-trapping dam group.

[0079] 1. Obtain basic data The main basic data is shown in Table 3-1.

[0080] Table 3-1 Main Basic Data of Example 3

[0081] 2. Evaluation of the sediment retention function of the cascade silt retention dam group Sediment interception rate oh Total sediment interception rate (Ω), particle size coarsening rate D , reservoir siltation rate l The sediment retention function of the cascade dam group was evaluated using various indicators. Relevant data are shown in Table 3-2.

[0082] Table 3-2 Main Calculation Data for Example 3

[0083] 3. Planning for adjustment of water storage and retention functions The total sediment interception rate Ω = 0.530, which meets the healthy interception conditions.

[0084] silt retention dams at all levels D i The values ​​are 1.109, 1.064, and 1.025 respectively, showing a decrease along the channel direction, which meets the conditions for coarsening health.

[0085] silt retention dams at all levels l i The values ​​are 0.854, 0.760, and 1.000 for dam #1 and dam #3, respectively. l i >0.8, does not meet the conditions for healthy storage capacity.

[0086] The parameters of the cascade silt-trapping dam group are adjusted in a smooth manner, in order to meet the interception health conditions, coarsening health conditions, and reservoir capacity health conditions.

[0087] Since the conditions for interception health are not met, the number of silt-trapping dam stages (n) should be increased or the dam level should be raised. V i Among them, improvement V i You can choose to add a downstream silt trap. H i Or reduce the size of the upstream check dam. b i In this example, the height of the three silt-trapping dams was increased. H i Increasing the dam opening width from 5.0 m to 6.0 m corresponds to an increase in reservoir capacity to approximately 700 m³. b i Make fine adjustments to the original design. b 1 =2.0 m、 b 2 =1.8m b 3 =0.49 m adjusted to b 1 =1.05 m、 b 2 =1.01 m、 b 3 =0.75 m. The new parameters were re-substituted into each model to calculate the various indicators of the water storage and retention function. The results are shown in Table 3-3.

[0088] Table 3-3 Main Calculation Data for Example 3

[0089] After adjusting the parameters and combining the healthy conditions for sediment retention, the sediment retention function of the cascade sediment retention dams has reached a healthy state.

Claims

1. A method for evaluating the sediment retention function of a cascade silt-trapping dam group, characterized by: Conduct on-site investigations to obtain basic data. The on-site investigation area includes the construction planning area of ​​the cascade silt-trapping dam group project and the debris flow gully where it is located. The sediment interception rate was used to evaluate the interception effectiveness of a cascade sediment-trapping dam group. i Sediment interception rate of Class I silt-trapping dam ω i According to the model expression 1, i ≤ n , n It is the total number of stages of the cascade silt-trapping dam group; Formula 1 wherein C v - debris flow sediment volume concentration, % E i -No. i The relative spacing between level 1 silt-trapping dams, a dimensionless quantity. J i -No. i The relative reservoir capacity of a grade-1 silt-trapping dam, dimensionless quantity. K i -No. i The relative opening width of a grade-separated silt-trapping dam, a dimensionless quantity. S - Debris flow gully gradient, dimensionless quantity. L i -No. i The spacing between level 1 silt-trapping dams, in meters. H i -No. i The height of a Class I silt-trapping dam is expressed in meters (m). V se - Debris flow sediment volume, unit m 3 , V i -No. i The reservoir capacity of a grade 1 silt-trapping dam, in meters (m). 3 , b i -No. i The width of the dam opening of a Class I silt-trapping dam, in meters. d max - Maximum particle size of debris flow sediment, in meters.

2. The method for evaluating the sediment retention function of a cascade silt-trapping dam group according to claim 1, characterized in that: The overall sediment interception efficiency of the cascade silt-trapping dam group is evaluated using the total sediment interception rate Ω, where Ω represents the sediment interception rate of each silt-trapping dam. ω i sum.

3. The method for evaluating the sediment retention function of a cascade silt-trapping dam group according to claim 2, characterized in that: The particle size coarsening rate was used to evaluate the particle size separation efficiency of the cascade sand-trapping dam group. i Grain size coarsening rate of primary sediment trap dam D i According to the Equation 2 model expression, Formula 2 In the formula, d 50-i -No. i Median particle size of sediment in the reservoir of a Class I silt-trapping dam, in meters. d 50 - Median particle size of debris flow sediment, in meters.

4. The method for evaluating the sediment retention function of a cascade silt-trapping dam group according to claim 3, characterized in that: The long-term storage efficiency of the cascade silt retention dam group was evaluated using the reservoir siltation rate. i Siltation rate of the first-class silt-trapping dam λ i According to the Equation 3 model, Formula 3 In the formula, V i -No. i The reservoir capacity of a grade 1 silt-trapping dam, in meters (m). 3 .

5. The method for evaluating the sediment retention function of a cascade sediment-trapping dam group according to claim 4, characterized in that: If the cascade silt-trapping dam group meets the combination of healthy silt-trapping conditions, its silt-trapping function is deemed healthy. The combination of healthy silt-trapping conditions includes: Healthy interception conditions: Total sediment interception rate Ω ≥ 0.5; Coarsening health conditions: silt-trapping dams at all levels D i The value decreases along the direction of the channel; Reservoir health conditions: various levels of silt traps λ i <0.

8.

6. The application of the evaluation method for the sediment retention function of a cascade silt-trapping dam group according to claim 5, characterized in that: It is applied to the planning of cascade silt-trapping dam groups.

7. The application of the evaluation method for the sediment retention function of a cascade silt-trapping dam group according to claim 6, characterized in that: This refers to the design adjustment plan for the cascade silt-trapping dam group during the design phase, including: Obtain basic data for evaluating the sand retention function of the cascade sand retention dam group based on the design and planning project of the cascade sand retention dam group; The evaluation indicators of the various interception functions of the cascade silt-trapping dam group were calculated based on the model, and it was determined whether the combination of healthy interception conditions was met. If the combination of conditions for sediment retention and storage is not met, adjust the parameters of the cascade sediment retention dam group until the combination of conditions for sediment retention and storage is met.

8. The application of the evaluation method for the sediment retention function of a cascade silt-trapping dam group according to claim 7, characterized in that: The parameters of the cascade silt-trapping dam group were adjusted in the following order until the combination of healthy silt-trapping conditions was met; If the aforementioned interception health conditions are not met, then increase the number of sand-trapping dam stages n or upgrade the dam. V i ; If the aforementioned coarsening health conditions are not met, the dam type combination mode of the silt-trapping dam should be adjusted to an upstream permeable dam + a downstream solid dam, specifically for... D i Significantly large or small silt-trapping dams, reduce or increase their b i ; If the reservoir's health conditions are not met, a sand-trapping dam should be added. H i .

9. The application of the evaluation method for the sediment retention function of a cascade silt-trapping dam group according to claim 6, characterized in that: This refers to the operation and maintenance plan for the cascade silt-trapping dam group during the operational phase, including: Based on the operation and maintenance renovation project of the cascade silt-trapping dam group, obtain basic data for evaluating the silt-trapping function of the cascade silt-trapping dam group; The model was used to calculate various retention and storage function evaluation indicators of the cascade silt retention dam group, and to determine whether the retention and storage functions are healthy. If the combination of conditions for sediment retention and storage is met, the cascade sediment retention dam group will continue to operate and undergo routine monitoring and maintenance. Conversely, the operation and maintenance plan should be determined based on the actual conditions of the cascade silt-trapping dam group.

10. The application of the evaluation method for the sediment retention function of a cascade silt-trapping dam group according to claim 9, characterized in that: When determining the operation and maintenance plan based on the actual conditions of the cascade silt-trapping dam group, typical problem diagnosis is carried out. If there are no typical problems, the cascade silt-trapping dam group will continue to operate under the condition of enhanced monitoring and maintenance. Otherwise, according to the typical problems, the adjustment plan is matched, and then the modification plan for adjusting the parameters of the cascade silt-trapping dam group is determined by combining the matching adjustment plans with the actual conditions of the cascade silt-trapping dam group, so as to improve the silt-trapping function. Typical problem diagnosis 1: If the interception health conditions are not met, the cascade silt-trapping dam group is diagnosed as being in a weak interception operation state; the matching adjustment plan is: to add a solid silt-trapping dam in a place where the terrain and geological conditions downstream of the cascade silt-trapping dam group allow, and to reduce the opening width of the permeable silt-trapping dam in the cascade silt-trapping dam group. Typical Problem Diagnosis 2: If the coarsening health conditions are not met, the cascade silt-trapping dam group is diagnosed as being in a state of sorting imbalance operation; the matching and adjustment scheme is: analyze the silt-trapping dams at each level. D i Value arrangement, by minimizing the adjustment of each level of the silt-trapping dam b i This approach aims to ensure that the cascade silt-trapping dam group meets the coarsening and health requirements as much as possible. Typical problem diagnosis 3: If Ω ≥ 0.5 and there is at least one retaining dam λ i ≥0.8 indicates that the cascade silt-trapping dam group is operating under high interception and high reservoir capacity conditions; The matching adjustment scheme is as follows: λ i ≥0.8 silt-retaining dam dredging and expansion, for λ i For silt traps with a strength ≥0.8 and permissible topographical and geological conditions, the dam body height should be increased. H i .

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