A calculation method, risk assessment method, application and storage medium for sediment production in a silt dam basin

Abstract

The present invention discloses a calculation method, risk assessment method, application, and storage medium for sediment production in a silt dam basin, and belongs to the technical field of water conservancy engineering technology; the technical key points are that the method comprises the following steps: step a: obtaining the expected rainfall at the geographical location of the silt dam basin according to meteorological forecast information, and judging the type of rainfall time-course curve; step b: calculating the flood flow Q and the total flood volume W in the silt dam basin; step c: calculating the sediment production according to the type of rainfall time-course curve. The technical solution of the present application can be effectively used for the risk assessment of silt dams in areas with loess geological conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of water conservancy engineering technology, and more specifically, to a calculation method, risk assessment method, application, and storage medium for sediment production in a silt dam basin. Background Art

[0002] Research has found (Reference 1: Zhang FY, Yan BB, Feng XM, et al. A rapid loess mudflow triggered by the check dam failure in a bulldoze mountain area, [J] Lanzhou, China. Landslides, 2019, 16: 1981-1992): Silt dams are more prone to failure than earth-rock dams, and the consequences and severity of their failures are far more serious than those of conventional earth-rock dams. This is mainly because the construction of silt dams is mainly based on siltation dams. The siltation storage capacity continues to increase over time, resulting in a continuous decrease in flood storage capacity. In addition, the abnormal weather and heavy rains in recent years have caused the water level in the silt dam reservoir area to rise abnormally, resulting in a great risk of chain-type disasters caused by failures, threatening the safe operation of silt dams.

[0003] With the surge in heavy rains and the accumulation of silt, the effective storage capacity of the silt dam has continued to decrease, and collapse has become the primary problem threatening the safe operation of the silt dam.

[0004] To solve the above problems:

[0005] Reference 2: "Zhang Xingxing, Chen Zuyu. Analysis of flood outburst of silt dam system in small watershed [J] Chinese Journal of Geotechnical Engineering, 2019, 41(10): 1845-1853" Based on the analysis of runoff generation and convergence, a simulation calculation program for the continuous outburst of silt dam system in small watershed was established to provide a basis for evaluating the overall flood control capacity of the dam system. However, there is still the problem that the uneven distribution of rainfall in different time periods leads to inaccurate outburst prediction.

[0006] Reference 3: "Zu Qiang, Chen Zuyu, Yu Shu, et al. Risk analysis of cascading dam failure in small watersheds under extreme rainfall conditions [J]. Journal of Soil and Water Conservation, 2022, 36(01): 30-37" The flood process line is generalized into a triangle, and a cascading dam failure model considering complex inflow is established.

[0007] Reference 4: "Hang Penglei. Risk Assessment of Flood Breach of Silt Dam System in the Loess Plateau [D]. Master's Thesis, Xi'an: Xi'an University of Technology, 2020" analyzes the breach process of silt dams under floods with different return periods.

[0008] Reference 5: "Zhong Shaohua. Research on flood control risk assessment and risk elimination methods of silt dams in Wangmaogou Basin [D]. Master's thesis, Xi'an: Xi'an University of Technology, 2020" analyzed the precipitation data in the basin and obtained the number of dam breaks and flood characteristics under design rainstorms with different return periods.

[0009] The studies in References 2-5 mainly focus on the breach process under the action of floods, ignoring the impact mechanism of rainfall-induced sediment production on the chain-like disaster-causing process of silt dam breach.

[0010] The Loess Plateau is one of the regions with the highest erosion rates in the world, and sediment factors cannot be ignored. At present, water and sediment research on silt dams is mostly focused on sediment deposition analysis and sediment control efficiency research. For example:

[0011] Reference 5: "Bai L, Wang N, Jiao J, et al. Soil erosion and sediment interception by check dams in a watershed for an extreme rainstorm on the Loess Plateau, China [J]. International Journal of Sediment Research, 2020, 35: 408-416" uses the amount of sediment deposited in a watershed to infer the amount of soil erosion under extreme rainstorms in the basin.

[0012] Reference 6: "Li P, Xu G, Lu K, et al. Runoff change and sediment source during rainstorms in an ecologically constructed watershed on the Loess Plateau, China [J]. Science of the Total Environment, 2019, 664: 968-974" uses a multivariate mixed model to study the changes in rainstorm runoff and sediment sources in a small watershed silt dam.

[0013] Reference 7: "Sun P, Wu Y. Dynamic Modeling Framework of Sediment Trapped by Check-Dam Networks: A Case Study of a Typical Watershed on the Chinese Loess Plateau [J]. Engineering, 2022" A DCDam model was developed based on the SWAT model to quantitatively estimate the amount of sediment trapped by the silt dam.

[0014] The above studies mostly focus on the sediment interception efficiency of silt dams, and the chain disaster risk of silt dam failure under the action of water and sediment has not been considered. In summary, the existing chain disaster risk of silt dam failure simplifies the rainfall and flood process, ignoring the surge process of rainstorm and mountain torrent runoff and the impact of water and sediment coupling disaster.

[0015] Currently, there is no perfect risk analysis model for chain disasters caused by silt dam failure that can fully consider the water-sediment coupling mechanism. Summary of the invention

[0016] The purpose of this application is to provide a method for calculating the sediment production in a silt dam basin in response to the above-mentioned deficiencies in the prior art.

[0017] Another object of the present application is to provide a risk assessment method, which is a chain disaster risk assessment method for silt dams that takes into account rainfall-flood-sediment-burst, and is used to assess whether a dam burst will occur.

[0018] Another object of the present application is to provide a risk assessment method for application in risk assessment of silt dam breach in Loess Plateau region.

[0019] Another object of the present application is to provide a storage medium.

[0020] The technical solution of this application is as follows:

[0021] A method for calculating sediment yield in a silt dam basin comprises the following steps:

[0022] Step a: According to the meteorological forecast information, the expected rainfall at the geographical location of the silt dam basin is obtained, and the type of rainfall time course curve is determined;

[0023] Step b: Calculate the flood flow Q and total flood volume W in the silt dam basin;

[0024] Step c: Calculate the sediment yield based on the type of rainfall time-history curve.

[0025] Furthermore, in step a: the rainfall time-history curve is divided into five types: early type, bimodal type, uniform type, late type, and intermediate type;

[0026] Among them, the early type is characterized by 80% of the cumulative rainfall falling in the first half of the cumulative rainfall duration;

[0027] Among them, the bimodal type is characterized by the occurrence of larger rainfall twice at intervals, forming two rain peaks;

[0028] Among them, the uniform type is characterized by a linear function type in which the accumulated rainfall is proportional to time;

[0029] Among them, the late type is characterized by rainfall mainly concentrated in the second half of the rainfall period, with less rainfall in the early period;

[0030] Among them, the intermediate type is characterized by rainfall concentrated in the time period of 0.4-0.7 of the cumulative rainfall time.

[0031] Further, in step c:

[0032] When the rainfall time-history curve is bimodal, the sediment yield is calculated using the following formula:

[0033] Sed=18.12×(Q×W) 0.56 ;

[0034] Where: Sed is the sediment yield from rainfall (kg / m 3 ), Q is the flood flow (m 3 / s; W is the total flood volume (m 3 );

[0035] When the rainfall time curve type is early type, uniform type, late type, or intermediate type, the following formula is used to calculate the sediment yield:

[0036] Sed = m × Q;

[0037] Where: Sed is the sediment yield from rainfall (kg / m 3 );m is the influence coefficient of rainfall time-history curve type. The corresponding values ​​of rainfall time-history curve types are early type, uniform type, late type and intermediate type are: 55-57, 250-255, 47-49 and 240-250 respectively.

[0038] A risk assessment method is a chain disaster risk assessment method for a silt dam that takes rainfall, flood, sediment and breach into consideration, and comprises the following steps:

[0039] Step a: According to the meteorological forecast information, the expected rainfall at the geographical location of the silt dam basin is obtained, and the type of rainfall time course curve is determined;

[0040] Step b: Obtain the elevation data of the silt dam basin, determine the confluence direction, determine the basin outlet location, and generate the river confluence line;

[0041] Step c: Calculate the runoff of the dam control area to obtain the calculation results of the flood process line, peak flow and total flood volume;

[0042] Step d: Calculate the sediment yield according to the type of rainfall time-history curve;

[0043] Step e: Determine the breach of the dam based on the calculation results of sediment production: compare the total amount of water and sediment entering the reservoir with the remaining storage capacity of the dam. When the amount of water and sediment entering the reservoir exceeds the remaining storage capacity, it is determined that a breach has occurred.

[0044] Furthermore, in step a: the rainfall time-history curve is divided into five types: early type, bimodal type, uniform type, late type, and intermediate type;

[0045] Among them, the early type is characterized by 80% of the cumulative rainfall falling in the first half of the cumulative rainfall duration;

[0046] Among them, the bimodal type is characterized by the occurrence of larger rainfall twice at intervals, forming two rain peaks;

[0047] Among them, the uniform type is characterized by a linear function type in which the accumulated rainfall is proportional to time;

[0048] Among them, the late type is characterized by rainfall mainly concentrated in the second half of the rainfall period, with less rainfall in the early period;

[0049] Among them, the intermediate type is characterized by rainfall concentrated in the time period of 0.4-0.7 of the cumulative rainfall time.

[0050] Further, in step d:

[0051] When the rainfall time-history curve is bimodal, the sediment yield is calculated using the following formula:

[0052] Sed=18.12×(Q×W) 0.56 ;

[0053] Where: Sed is the sediment yield from rainfall (kg / m 3 ), Q is the flood flow (m 3 / s; W is the total flood volume (m 3 );

[0054] When the rainfall time curve type is early type, uniform type, late type, or intermediate type, the following formula is used to calculate the sediment yield:

[0055] Sed = m × Q;

[0056] Where: Sed is the sediment yield from rainfall (kg / m 3 );m is the influence coefficient of rainfall time-history curve type. The corresponding values ​​of rainfall time-history curve types are early type, uniform type, late type and intermediate type are: 55-57, 250-255, 47-49 and 240-250 respectively.

[0057] An application of the aforementioned risk assessment method to the risk assessment of silt dam breach in the Loess Plateau region.

[0058] A storage medium stores a computer program capable of executing the aforementioned computing method.

[0059] The beneficial effects of this application are:

[0060] First, this application proposes a basic concept for calculating sediment yield based on the type of rainfall time-history curve. Specifically, the rainfall time-history curve is divided into five types: early type, bimodal type, uniform type, late type, and intermediate type. The characteristic of the early type is that 80% of the cumulative rainfall falls in the first half of the cumulative rainfall duration; the characteristic of the bimodal type is that a larger rainfall occurs twice at intervals, forming two rain peaks; the characteristic of the uniform type is that the cumulative rainfall is proportional to time as a linear function; the characteristic of the late type is that the rainfall is mainly concentrated in the second half of the rainfall, and there is less rainfall in the early stage; the characteristic of the intermediate type is that the rainfall is concentrated in the 0.4-0.7 time period of the cumulative rainfall time.

[0061] The calculation formula for sediment yield of different rainfall time curve types is as follows:

[0062] When the rainfall time-history curve is bimodal, the sediment yield is calculated using the following formula:

[0063] Sed=18.12×(Q×W) 0.56 ;

[0064] Where: Sed is the sediment yield from rainfall (kg / m 3 ), Q is the flood flow (m 3 / s; W is the total flood volume (m 3 );

[0065] When the rainfall time curve type is early type, uniform type, late type, or intermediate type, the following formula is used to calculate the sediment yield:

[0066] Sed = m × Q;

[0067] Where: Sed is the sediment yield from rainfall (kg / m 3 );m is the influence coefficient of rainfall time-history curve type. The corresponding values ​​of rainfall time-history curve types are early type, uniform type, late type and intermediate type are: 55-57, 250-255, 47-49 and 240-250 respectively.

[0068] Second, the method of this application is mainly applicable to the risk assessment of silt dams in areas with loess geological conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] The present invention will be further described in detail below in conjunction with the embodiments in the accompanying drawings, but this does not constitute any limitation to the present invention.

[0070] Figure 1 It is the fitting result of the previous rainfall pattern.

[0071] Figure 2 It is the fitting result of bimodal rainfall.

[0072] Figure 3 It is the fitting result of uniform rainfall.

[0073] Figure 4 It is the fitting result of late rainfall.

[0074] Figure 5 It is the fitting result of intermediate rainfall.

[0075] Figure 6 It is a generalized diagram of Snyder's unit line method.

[0076] Figure 7 This is a schematic diagram of base flow retreat.

[0077] Figure 8 It is a technical diagram of the rainfall-flood-sediment-burst model.

[0078] Fig. 9 This is the distribution map of the dam system in the Wangmaogou Basin.

[0079] Fig.10 This is a schematic diagram of the rainfall-flood model of Huangbaigou No. 2 Dam.

[0080] Fig.11 This is a schematic diagram of the rainfall-flood model of Guandigou 4 Dam.

[0081] Fig.12 This is a diagram of the burst flow process.

[0082] Fig.13 This is the Guandigou No. 3 dam breach and flooding risk map.

[0083] Fig.14 This is the Beitagou Dam breach and flooding risk map. DETAILED DESCRIPTION

[0084] The present invention is described in detail below in conjunction with specific implementation modes.

[0085] <I. Overall process of the method>

[0086] A chain disaster risk assessment method for silt dams considering rainfall-flood-sediment-burst includes the following steps:

[0087] Step a: According to the meteorological forecast information, the expected rainfall at the geographical location of the silt dam basin is obtained;

[0088] The predicted rainfall is processed into five types: early type, bimodal type, uniform type, late type, and intermediate type, and different types of predicted rainfall duration processes are obtained;

[0089] Step b: Download the elevation DEM data of the basin’s geographical location from the “Geospatial Data Cloud” website, and cut out the basin’s DEM data according to the basin’s range;

[0090] Import the clipped watershed DEM data into the software, perform "filling" processing on the DEM data, determine the "confluence direction", determine the location of the watershed outlet, and generate the river confluence line;

[0091] Step c: Input the different types of predicted rainfall durations obtained from the processing into the model, and establish the rainfall data module required by the model (HEC-HMS software can complete step c);

[0092] Step d: Query the hydrological manual at the basin location to find the specific parameters of the initial loss and post-loss required for rainfall runoff, and input the parameters into the model; run the model to calculate the runoff results of the dam control area of ​​the silt dam, and obtain the flood process line, peak flow and total flood volume (HEC-HMS software can complete step d);

[0093] Step e: Different rainfall-sediment yield formulas are used according to different rainfall types. The rainfall-sediment yield formula is shown in Table 1; the rainfall-sediment yield is calculated according to the formula;

[0094] Table 1 Calculation formula for sediment yield under different rainfall types

[0095]

[0096] Step f: Based on the sediment production calculation results, the sediment-laden flood flow process is input into the model to determine whether the silt dam has failed.

[0097] <2. Theoretical Basis for Rainfall Type Classification>

[0098] The rainfall process is often complex and diverse. Using a single rainfall model ignores the diverse characteristics of rainfall distribution. The rainfall process is the basis of surface runoff and flood calculations. Using a single rainfall model will lead to a large deviation between the results and the actual situation.

[0099] The rainfall types are divided, and the rainstorm process is divided into different types according to the rules. The function is fitted for each rainfall type, and the cumulative rainfall time-course function of each rainfall type is constructed. This is used as the basis for the derivation of rainfall data in the silt dam area of ​​the Loess Plateau where there is a lack of rainfall duration data, which truly reflects the actual occurrence process of rainstorms and simulates the water-sediment coupling process of the silt dam in a more refined manner. At the same time, the possible duration of rainstorms can be deduced based on the predicted future rainfall, providing a basis for risk analysis and early warning of silt dams.

[0100] Statistical processing of rainstorm data is used to classify different rain types. The specific classification steps are as follows:

[0101] (1) The rainfall and rainfall duration are dimensionless, and the instantaneous rainfall and rainfall duration are divided by the total rainfall and total rainfall duration, respectively.

[0102] (2) Accumulate the dimensionless rainfall and duration so that the cumulative value reaches 1.

[0103] (3) Divide the dimensionless duration into three equal time periods and calculate the cumulative rainfall in each of the three time periods.

[0104] (4) Different rainfall types are classified according to the location of the maximum accumulated rainfall.

[0105] According to the data of 22 rainstorms counted in the basin (Wangmaogou Basin is taken as an example here), the rainfall process is divided into five types of rainstorms: early type (7 events), double peak type (6 events), uniform type (4 events), late type (3 events) and intermediate type (2 events).

[0106] a. Early stage

[0107] Early rainstorm (such as Figure 1 ) is characterized by about 80% of the cumulative rainfall falling in the first half of the cumulative rainfall period. Among the 22 rainstorms counted, 7 rainstorms were early-stage rainstorms, accounting for 32%. Early-stage rainstorms are frequent rainfall types in the basin. By fitting the early-stage rainstorm function formula, it is fitted into a quartic polynomial:

[0108] y=6.627x 4 -14.262x 3 +8.508x 2 +0.223x-0.078

[0109] b. Double peak type

[0110] Bimodal rainfall (such as Figure 2 ) is characterized by two large rainfall intervals, forming two rain peaks, which are second only to the previous rainfall. The double-peak rainfall is also the most frequent rainstorm in the basin, which occurs 6 times in total, accounting for 27%. The function of the double-peak rainfall is constructed and fitted to obtain the double-peak rainfall function:

[0111] y=75.138x 6 -245.84x 5 +300.98x 4 -167.4x 3 +39.526x 2 -1.3521x-0.0478

[0112] c. Uniform type

[0113] Uniform rainfall (such as Figure 3) The cumulative rainfall is proportional to time and is a linear function. The rainfall is a constant value with little difference with the rainfall duration. The uniform rainfall accumulation occurs 4 times in the basin, accounting for 18%. The uniform rainfall function is:

[0114] y=x

[0115] d. Late type

[0116] Late rainfall (such as Figure 4 ) is characterized by rainfall mainly concentrated in the second half of the rainfall, with less rainfall in the early stage. According to statistical data, the late rainfall in the basin occurred 3 times, accounting for 14%. The late rainfall function obtained by fitting is:

[0117] y=-3.9731x 4 +5.9461x 3 -1.0822x 2 +0.0868x+0.0285

[0118] e. Intermediate

[0119] Intermediate rainfall (such as Figure 5 ) is characterized by rainfall concentrated in the 0.4-0.7 time period of the cumulative rainfall time, and the maximum rainfall occurs in the middle of the rainfall time. According to statistical data, the intermediate type of the basin appears twice, accounting for 9%, with the lowest frequency. The function of the intermediate rainfall type obtained by fitting is:

[0120] 42.278x 6 -99.535x 5 +67.685x 4 -3.4555x 3 -8.6308x 2 +2.7764x-0.1044.

[0121] <3. Model Construction>

[0122] Construction of rainfall-flood model: obtain rainfall data of the area to be simulated; download DEM elevation data at the basin location (data can be obtained from the geospatial data cloud website), and cut out DEM data according to the range of the basin; transform the coordinate system of DEM data; use the model to fill the basin DEM data for the original discontinuity of DEM; determine the flow direction of water in the basin; extract the river network, mark the basin exit point through the extracted river network, and divide the required sub-basin range.

[0123] The runoff calculation adopts the initial loss and steady infiltration method. The principle of the initial loss and steady infiltration method is simple and requires few parameters. This method divides the overall rainfall loss into the initial loss part and the final loss part. When rainfall occurs, the loss of rainfall due to interception, filling, soil infiltration, etc. of the vegetation canopy will not form runoff. This part of the loss of rainfall is called the initial loss; the final loss is the rainfall loss caused by continuous soil infiltration after the rainfall gradually accumulates to form runoff. The formula for calculating net rain by this method is:

[0124]

[0125] Where: R i is the flow rate (mm); P i is the rainfall (mm); I a is the initial loss (mm); f c is the average loss rate (mm / h).

[0126] The direct runoff calculation uses the Snyder unit line method. Snyder derived a mathematical relationship equation for estimating unit line parameters proposed in the analysis of data-free areas in the United States, and selected the Snyder unit line method to calculate the basin runoff process. The relationship between the unit line peak value and lag time of the unit line precipitation per unit area in the basin is:

[0127]

[0128]

[0129]

[0130] Among them: U P is the peak value of unit line flood (m 3 / s; A is the basin area (km 2 );C1 is the conversion coefficient, the international unit value is 2.75; C P is the peak coefficient of the unit line; t P is the flood peak hysteresis time in the basin; L is the basin length (m); γ is the basin slope (‰); S is the maximum water storage capacity of the soil; the CN value is related to factors such as the previous soil moisture level, slope, soil type and land use status of the basin.

[0131] The exponential decay method is selected for base flow calculation. It is assumed that the base flow decays exponentially from the initial flow value. The base flow calculation formula is:

[0132] Q t =Q0k t (5)

[0133] Where: Q t Base flow (m 3 / s); Q0 is the initial base flow (m3 / s); k is the exponential decay constant.

[0134] The flood evolution module selects the lumped flood evolution model Muskingum method. Muskingum method requires few parameters and is widely used. The river flow calculation equation is:

[0135] O2=C0I2+C1I1+C2O1 (6)

[0136]

[0137] C0+C1+C2=1 (8)

[0138] Where: O1 and O2 are the outflows at the beginning and end of the calculation time period (m 3 / s); I1 and I2 are the inflow rates at the upper end at the beginning and end of the calculation period (m 3 / s); Δt is the calculation time period (h); K is the storage constant; x is the flow rate weight factor.

[0139] Establish a watershed meteorological model, input watershed rainfall data, determine the model running time, set watershed model parameters, and finally establish a rainfall-flood model.

[0140] <4. Construction of sand production model>

[0141] Construction of rainfall-flood-sediment model: Based on rainfall data, the hourly rainfall is input into the model, the model running time and parameters are set, and the model is run to obtain the basin flood peak flow Q, total flood volume W and flood process line under rainfall. The flood sediment yield is calculated based on Table 1.

[0142] Based on the above two models, the peak flow and total flood volume obtained from the rainfall-flood model are brought into the sediment model. The two models are coupled to obtain the sediment yield in the silt dam control area, thus realizing the coupling of rainfall-flood-sediment.

[0143] <V. Construction of rainfall-flood-sediment-burst model>

[0144] Based on the sediment-containing flood process line and DEM data, a silt dam breach model was established according to the relationship between dam height, reservoir capacity and water level.

[0145] Based on the sand-containing flood process line data input into the model, the silt dam breach is determined and the breach simulation analysis is realized.

[0146] By establishing a coupled model of rainfall-flood-sediment-burst, the entire process from rainfall to burst can be analyzed and studied, the safety status of the silt dam under rainfall conditions can be determined, the burst flow, flow velocity and other parameters can be obtained, and the dam burst flood inundation analysis can be realized.

[0147] It should be noted that the construction of models 3, 4 and 5 were all set up in the hydrological simulation software HEC-HMS.

[0148] <VI. Practical case application in Wangmaogou Basin>

[0149] The Wangmaogou Basin experienced heavy rainfall on July 15, 2012 and July 26, 2017, which caused the collapse of small and medium-sized dams in the Wangmaogou Basin to varying degrees. This is a typical dam collapse event, so it was selected as a research case. The layout of the dam system in the basin is as follows: Fig. 9 shown.

[0150] Step S1: Collect rainfall data

[0151] On July 15, 2012, the maximum rainfall in the Wangmaogou Basin reached 75.7 mm in one hour, and the rainfall lasted for 2 hours and 45 minutes, with a cumulative rainfall of 90.5 mm. The rainfall caused 24 silt dams in the Jiuyuangou Basin to be damaged to varying degrees. On July 26, 2017, the maximum rainfall in the Wangmaogou Basin was 51.2 mm in one hour, and the rainfall lasted for 8 hours and 10 minutes, with a cumulative rainfall of 148.8 mm.

[0152] Table 2 Rainfall duration data

[0153]

[0154] Step S2: Model building

[0155] Download the DEM elevation data of the basin location (30m accuracy data can be obtained from the Geospatial Data Cloud website), and cut out the DEM data according to the basin range; transform the DEM data into a coordinate system; use the model to fill the basin DEM data for the original discontinuity of the DEM; determine the flow direction of the basin water; extract the river network, mark the basin exit point through the extracted river network, and divide the required sub-basin range. Build the model structure Fig.10 and Fig.11 .

[0156] Step S3: Rainfall type classification and flood and sediment generation calculation

[0157] According to the rainfall type classification method, the rainfall types of 2012.7.15 and 2017.7.26 were classified, and it was finally determined that the rainfall type of 2012.7.15 was "pre-type" rainfall, and the rainfall type of 2017.7.26 was "double peak" rainfall. Different sediment yield coefficients N were taken according to the two rainfall types. The constructed rainfall-flood model was used to analyze the runoff generation and confluence process, and the total amount of flood inflow and peak flow of the selected 5 silt dams were obtained. The calculation results of flood and sediment generation are shown in Table 3.

[0158] The rainfall induced floods and carried sand into the reservoir area, where a large amount of sand was deposited, causing the reservoir water level to rise sharply. The sand yield of each silt dam during the two rainfalls was obtained, and the bulk density of the sand was taken as 1.35 g cm -3 The calculation results of water-sediment coupling analysis are shown in Table 3.

[0159] Table 3 Results of rainfall-flood-sediment coupling analysis

[0160]

[0161] Compared with the actual sediment yield, the relative error is between 5.6% and 16.5%, and the model can predict the rainfall sediment yield well. The proportion of sediment to the total volume of water and sand under the two rainfalls is between 4.9% and 19.6%. The proportion of sediment to the total volume of water and sand on July 15, 2012 is greater than that on July 26, 2017. Therefore, the greater the rainfall intensity, the greater the amount of sediment produced.

[0162] Step S4: Risk analysis of dam failure

[0163] The total amount of flood and sediment was coupled to obtain the flow process of sediment-carrying flood into the reservoir. The obtained water and sediment flow process into the reservoir was used as the upstream boundary condition for the disaster analysis of the rainfall-flood-sediment-burst model. Based on the relationship data of the storage capacity and water level of the silt dam, the chain disaster process of silt dam burst was analyzed. The results showed that under the rainfall on July 15, 2012 and July 26, 2017, the Beitagou Dam and Guandigou Dam 3 of the selected 5 silt dams burst, while Huangbogou Dam 2, Guandigou Dam 4 and Kanghegou Dam 3 did not burst.

[0164] like Fig.14 As shown in the figure, during the rainfall on July 15, 2012, the Beitagou Dam breached 3h 33min after the rainfall, and the Guandigou Dam 3 breached 1h 29min after the rainfall; during the rainfall on July 26, 2017, the Beitagou Dam breached 8h 19min after the rainfall, and the Guandigou Dam 3 breached 4h 8min after the rainfall. It took 1h 48min for the Guandigou Dam 3 breach flood to reach the Guandigou Dam 1, about 534m downstream; it took 21min for the Beitagou Dam breach flood to reach the Guandigou Dam 2, about 116m downstream. The breach flow rate of Guandigou Dam 3 reached its maximum value 9min after the breach, and the breach flow rate of Beitagou Dam reached its maximum value 4min after the breach; the maximum flooding depth appeared at the head of the breach flood. The Beitagou Dam breach flood flooded an area of ​​0.0034km 2 The flooded and breached area of ​​Guandigou 3 dam is 0.028km 2 There are no residential areas downstream of Beitagou Dam and Guandigou 3 Dam. The flooded area is the reservoir area of ​​Guandigou 1 Dam and Guandigou 2 Dam downstream. The water and sand in the reservoir area of ​​Beitagou Dam and Guandigou 3 Dam flow down to the downstream silt dam, which has a certain impact on the safe operation of the downstream dam.

[0165] The above embodiments are preferred implementation modes of the present invention and are only used to facilitate the description of the present invention. They are not intended to limit the present invention in any form. Any person with ordinary knowledge in the relevant technical field, if they do not depart from the scope of the technical features of the present invention, can make equivalent embodiments by partial changes or modifications to the technical contents disclosed in the present invention, and they still fall within the scope of the technical features of the present invention without departing from the technical features of the present invention.

Claims

1. A method for calculating sediment production in a silt dam basin, characterized in that: The following steps are involved: Step a: According to the meteorological forecast information, the expected rainfall at the geographical location of the silt dam basin is obtained, and the type of rainfall time course curve is determined; In step a: the rainfall time-history curve is divided into five types: early type, bimodal type, uniform type, late type, and intermediate type; Among them, the early type is characterized by 80% of the cumulative rainfall falling in the first half of the cumulative rainfall duration; Among them, the bimodal type is characterized by the occurrence of larger rainfall twice at intervals, forming two rain peaks; Among them, the uniform type is characterized by a linear function type in which the accumulated rainfall is proportional to time; Among them, the late type is characterized by rainfall mainly concentrated in the second half of the rainfall period, with less rainfall in the early period; Among them, the intermediate type is characterized by rainfall concentrated in the time period of 0.4-0.7 of the cumulative rainfall time; Step b: Calculate the flood flow Q and total flood volume W in the silt dam basin; Step c: Calculate the sediment yield based on the type of rainfall time-history curve.

2. The method for calculating sediment yield in a silt dam basin according to claim 1, characterized in that: In step c: When the rainfall time-history curve is bimodal, the sediment yield is calculated using the following formula: But=18.12×(Q×W) 0.56 ; Where: Sed is the sediment yield from rainfall (kg / m 3 ), Q is the flood flow (m 3 / s; W is the total flood volume (m 3 ); When the rainfall time-course curve is of the early type, uniform type, late type, or intermediate type, the following formula is used to calculate the sediment yield: Sed = m × Q; Where: Sed is the sediment yield from rainfall (kg / m 3 );m is the influence coefficient of rainfall time-history curve type. The corresponding values ​​of rainfall time-history curve types are early type, uniform type, late type and intermediate type are: 55-57, 250-255, 47-49 and 240-250 respectively.

3. A risk assessment method, which is a chain disaster risk assessment method for silt dams considering rainfall-flood-sediment-burst, characterized in that: The steps include: Step a: According to the meteorological forecast information, the expected rainfall at the geographical location of the silt dam basin is obtained, and the type of rainfall time course curve is determined; In step a: the rainfall time-history curve is divided into five types: early type, bimodal type, uniform type, late type, and intermediate type; Among them, the early type is characterized by 80% of the cumulative rainfall falling in the first half of the cumulative rainfall duration; Among them, the bimodal type is characterized by the occurrence of larger rainfall twice at intervals, forming two rain peaks; Among them, the uniform type is characterized by a linear function type in which the accumulated rainfall is proportional to time; Among them, the late type is characterized by rainfall mainly concentrated in the second half of the rainfall period, with less rainfall in the early period; Among them, the intermediate type is characterized by rainfall concentrated in the time period of 0.4-0.7 of the cumulative rainfall time; Step b: Obtain the elevation data of the silt dam basin, determine the confluence direction, determine the basin outlet location, and generate the river confluence line; Step c: Calculate the runoff of the dam control area to obtain the calculation results of the flood process line, peak flow and total flood volume; Step d: Calculate the sediment yield according to the type of rainfall time-history curve; Step e: Determine the breach of the dam based on the calculation results of sediment production: compare the total amount of water and sediment entering the reservoir with the remaining storage capacity of the dam. When the amount of water and sediment entering the reservoir exceeds the remaining storage capacity, it is determined that a breach has occurred.

4. The risk assessment method according to claim 3, characterized in that: In step d: When the rainfall time-history curve is bimodal, the sediment yield is calculated using the following formula: But=18.12×(Q×W) 0.56 ; Where: Sed is the sediment yield from rainfall (kg / m 3 ), Q is the flood flow (m 3 / s; W is the total flood volume (m 3 ); When the rainfall time-course curve is of the early type, uniform type, late type, or intermediate type, the following formula is used to calculate the sediment yield: Sed = m × Q; Where: Sed is the sediment yield from rainfall (kg / m 3 );m is the influence coefficient of rainfall time-history curve type. The corresponding values ​​of rainfall time-history curve types are early type, uniform type, late type and intermediate type are: 55-57, 250-255, 47-49 and 240-250 respectively.

5. A storage medium, characterized in that: The computer program capable of executing the calculation method according to claim 1 or 2 is stored therein.

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