Calculation method of groove trough type debris flow rain fall threshold

Abstract

To provide a calculation method of a groove trough type debris flow rain fall threshold.SOLUTION: There is provided a calculation method of a groove trough type debris flow rain fall threshold configured to: calculate an outflow hydrograph in a rain fall condition in a different reproduction period, and water power intensity in a different calculation unit, and then calculate critical water power intensity required for starting a groove trough type debris flow; compare the water power intensities calculated by different calculation units in the debris flow formation region with critical water power intensity for starting the groove trough type debris flow, for determining stability of the calculation unit; calculate a ratio of an area where an unstable unit exists; and determine whether the corresponding rain fall event causes a debris flow. The advantageous point of the invention is that it is possible to whether the groove trough type debris flow occurs, and in addition, it is also possible to determine a generation scale of the debris flow, and therefore, the invention can achieve better application ability.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to the technical field of debris flow prevention works, and in particular to a method for calculating a rainfall threshold for a ditch valley type debris flow. [Background technology]

[0002] A ditch valley debris flow is a type of debris flow that is usually caused by slope erosion and often occurs in the watersheds of the southwest mountainous region. The rainfall threshold model based on empirical statistics is the most widely used rainfall threshold model at present, because it is easy to apply and requires few parameters. The determination of the rainfall threshold for ditch valley debris flow based on empirical statistics generally involves statistical analysis of historical rainfall events that induce ditch valley debris flows, plotting their rainfall intensity and time-dependent conditions in double logarithmic coordinates, and fitting the lower percentile horizontal lines of these data points using relevant statistical analysis software, and this power-exponential curve or linear line is the corresponding rainfall threshold. The most commonly used among them is the ID model, where I represents the average rainfall intensity and D represents the rainfall time-dependent time. The ID threshold model, which is a rainfall threshold based on empirical statistics, is easy to apply, but the triggering of debris flow is not determined only by the amount of rainfall, so the differences in topography and material source conditions all affect the prediction results of the threshold model. Rainfall thresholds based on empirical statistics do not take into account the interaction mechanisms between rock masses and the external environment, leading to many misjudgments.

[0003] For the triggering of valley-type debris flow, the super-strong hydraulic conditions in the ditch are the fundamental control factor, so currently, some studies combine the hydrological process with the rainfall threshold of valley-type debris flow, calculate the valley peak discharge under different rainfall conditions or different rainfall events in a hydrological model, and compare the calculated valley peak discharge with the critical discharge that triggers valley-type debris flow. That is, if the calculated valley peak discharge is equal to or greater than the peak discharge that triggers valley-type debris flow, it is considered that this rainfall event will trigger valley-type debris flow, and if the calculated valley peak discharge is less than the peak discharge that triggers valley-type debris flow, it is considered that this rainfall event will not trigger valley-type debris flow, and thus determine the rainfall threshold at which valley-type debris flow occurs. However, the current calculation method of valley-type debris flow rainfall threshold based on valley peak discharge can only determine whether valley-type debris flow has occurred, but cannot determine the scale of occurrence and location of valley-type debris flow, which is limited. Summary of the Invention [Problem to be solved by the invention]

[0004] The objective of the present invention is to overcome the shortcomings of the prior art and provide a method for calculating the ditch valley type debris flow rainfall threshold. [Means for solving the problem]

[0005] The object of the present invention is realized by the following technical solution, which is a method for calculating a ditch-valley type debris flow rainfall threshold, comprising the following steps: S1, obtain the extreme rainfall characteristics of the ditch valley type debris flow basin, calculate the rainfall intensity of the ditch valley type debris flow in different rainfall return periods, The rainfall intensity in different rainfall return periods in steps S2 and S1 is used as input to calculate runoff hydrographs under rainfall conditions in different return periods in a groove valley type debris flow basin. S3, using the runoff hydrograph obtained in step S2 as input, calculate the hydraulic strength of different calculation units of the ditch valley type debris flow basin by calculating the hydraulic conditions of different calculation units of the ditch valley type debris flow basin; S4. Obtain basic information on the basin of a groove-valley type debris flow, and calculate the critical hydraulic power strength required to trigger a groove-valley type debris flow. S5: Compare the hydraulic strength of different calculation units of the groove valley-type debris flow basin obtained in step S3 with the critical hydraulic strength for the initiation of the groove valley-type debris flow obtained in step S4. If the calculated hydraulic strength is equal to or greater than the critical hydraulic strength, the calculation unit is an unstable unit. If the calculated hydraulic strength is less than the critical hydraulic strength, the calculation unit is a stable unit. By calculating the total area of ​​the unstable units and their proportion to the entire debris flow basin, the occurrence scale of the groove valley-type debris flow under rainfall conditions of different return periods is determined.

[0006] Specifically, the extreme rainfall characteristics in step S1 include once in 5 years, once in 10 years, once in 20 years, and once in 100 years extreme rainfall in the ditch valley type debris flow basin.

[0007] Specifically, the rainfall intensity of the different rainfall reproduction periods of the groove valley type debris flow in step S1 can be calculated by the following formula: JPEG2025009582000002.jpg6170JPEG2025009582000003.jpg5170 is the average rainfall in the ditch valley type debris flow basin, in mm.

[0008] Specifically, in step S2, the runoff hydrographs under different rainfall conditions in different return periods for the ditch valley type debris flow basin are calculated using the following formula: In the formula, Q is the surface runoff depth of the debris flow basin, mm; C is the rainfall, mm; A is the water content of the debris flow basin, mm; A max is the maximum water content in the debris-flow basin in mm, D is the overland runoff coefficient in the debris-flow basin, and B is the overland runoff threshold in the debris-flow basin.

[0009] Specifically, the hydraulic conditions of different calculation units of the ditch valley type debris flow basin in step S3 can be calculated by the following equation: In the formula, t represents time, a is a vector containing flow variables, b and c are flow vectors in the x and y directions, and E 1 and E2 are the floor slope and friction effect source term vectors, respectively, Here, a is calculated using the following formula: JPEG2025009582000006.jpg19170b is calculated using the following formula: JPEG2025009582000007.jpg24170c is calculated using the following formula: JPEG2025009582000008.jpg29170E 1 is calculated using the following formula: JPEG2025009582000009.jpg35170E 2 is calculated using the following formula: JPEG2025009582000010.jpg38170In equations (4), (5), (6), (7) and (8), h is the water depth, m; u is the outflow velocity in the x direction, m / s; v is the outflow velocity in the y direction, m / s; and ρ is the water density, kg / m 3 where g is the acceleration due to gravity, θ is the slope of the groove bed in °, and μ x is the x-component of friction stress between the water flow and the ground, Pa, and μ y is the y-component of frictional stress between the water flow and the ground, Pa.

[0010] Specifically, μ in step S3 x is calculated using the following formula: JPEG2025009582000011.jpg7170μ y is calculated using the following formula: JPEG2025009582000012.jpg7170In equations (9) and (10), δ is the roughness coefficient, which is calculated using the following equation: JPEG2025009582000013.jpg6170In the formula, η represents the Manning coefficient.

[0011] Specifically, the hydraulic strength F of different calculation units of the ditch valley type debris flow basin in step S3 * is calculated using the following formula: In the JPEG2025009582000014.jpg12170 formula, d 50represents the grain size when the cumulative content of the source soil mass of the groove valley type debris flow reaches 50%, and ρ s represents the density of the source soil, g / cm 3 It is.

[0012] Specifically, in step S4, the critical hydraulic power strength Fc required to trigger a groove-valley type debris flow is calculated using the following formula: JPEG2025009582000015.jpg5170Here, X = 0.407ln(142tanθ), and θ represents the slope of the channel bed of the debris flow basin.

[0013] Specifically, in step S5, if the proportion of the total area of ​​the unstable units is 10% or more, that is, if the rainfall event is considered to lead to the occurrence of a debris flow, and if the proportion of the total area of ​​the unstable units is less than 10%, it is considered that the rainfall event will not lead to the occurrence of a debris flow. By distinguishing between rainfall events that induce groove-valley-type debris flows and rainfall events that cannot induce debris flows, the rainfall threshold for groove-valley-type debris flows is determined. Effect of the Invention

[0014] The present invention has the following advantages:

[0015] 1. The present invention combines the extreme rainfall distribution characteristics of the valley-type debris flow area, the rainfall-runoff relationship of the valley-type debris flow catchment area, and the hydraulic conditions of the valley-type debris flow formation area. Compared with the conventional method for calculating the rainfall threshold of debris flow, the present invention considers the influence of the differences in the topography, underlying layer and material source conditions of the valley-type debris flow formation area, improves the accuracy of the rainfall threshold calculation, reduces the occurrence of misjudgment, and provides a more reasonable and accurate basis for the risk assessment of valley-type debris flow disasters, and has good ubiquity.

[0016] 2. The calculation method for the rainfall threshold of ditch valley-type debris flow established in this invention can not only determine whether ditch valley-type debris flow has occurred, but also the scale of the debris flow occurrence, so it has better applicability.

[0017] 3. The present invention requires few parameters for calculation, and the parameters are easy to obtain, the calculation accuracy is high, and it can be applied to the rapid establishment of the ditch valley type debris flow rainfall threshold when the previous period of mass investigation work is lacking. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a schematic diagram illustrating the principle of the method for calculating the ditch valley type debris flow rainfall threshold of the present invention. [Diagram 2] 1 shows runoff hydrographs under different rainfall reproduction period conditions with rainfall time of 1 hour in an embodiment of the present invention. [Diagram 3] 1 shows runoff hydrographs under different rainfall reproduction period conditions with a rainfall time course of 3 hours in an embodiment of the present invention. [Figure 4] 1 shows runoff hydrographs under different rainfall reproduction period conditions with a rainfall time course of 6 hours in an embodiment of the present invention. [Diagram 5] 1 shows runoff hydrographs under different rainfall reproduction period conditions over a 24-hour rainfall time course in an embodiment of the present invention. [Figure 6] FIG. 1 is a schematic diagram showing the distribution of hydraulic strength F* of a debris flow basin under different rainfall recurrence conditions with a rainfall time of 1 hour in an embodiment of the present invention. [Figure 7] FIG. 1 is a schematic diagram showing the distribution of hydraulic strength F* of a debris flow basin under different rainfall recurrence conditions with a rainfall time of 3 hours in an embodiment of the present invention. [Figure 8] FIG. 1 is a schematic diagram showing the distribution of hydraulic strength F* of a debris flow basin under different rainfall recurrence conditions with a rainfall time of 6 hours in an embodiment of the present invention. [Figure 9] FIG. 1 is a schematic diagram showing the distribution of hydraulic strength F* of a debris flow basin under different rainfall recurrence conditions with a rainfall time of 24 hours in an embodiment of the present invention. [Figure 10] FIG. 1 is a schematic diagram of the magnitude of rainfall threshold for a ditch valley type debris flow in an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] As shown in FIG. 1, a method for calculating a ditch valley type debris flow rainfall threshold includes the following steps: S1. Obtain the extreme rainfall characteristics of the ditch valley type debris flow basin. The extreme rainfall characteristics include the extreme rainfall of once in 5 years, once in 10 years, once in 20 years and once in 100 years in the ditch valley type debris flow basin. Calculate the rainfall intensity of different rainfall return periods of the ditch valley type debris flow by the following formula: JPEG2025009582000016.jpg6170JPEG2025009582000017.jpg17170The rainfall intensity in different rainfall return periods in steps S2 and S1 was input, and the runoff hydrographs under rainfall conditions in different return periods for the ditch valley type debris flow basin were calculated using the following formula: In the formula, Q is the surface runoff depth of the debris flow basin, mm; C is the rainfall, mm; A is the water content of the debris flow basin, mm; A max is the maximum water content of the debris-flow basin in mm, D is the surface runoff coefficient of the debris-flow basin, B is the surface runoff threshold of the debris-flow basin, S3 and S2 are input with the runoff hydrographs obtained in the ditch valley type debris flow basin under different rainfall conditions in different return periods, and the hydraulic conditions of different calculation units of the ditch valley type debris flow basin are calculated by the following formula. The hydraulic conditions include runoff depth and runoff flow velocity: In the formula, t represents time, a is a vector containing flow variables, b and c are flow vectors in the x and y directions, respectively, and E 1 and E 2 are the floor slope and friction effect source term vectors, respectively, Here, a is calculated using the following formula: JPEG2025009582000020.jpg19170b is calculated using the following formula: JPEG2025009582000021.jpg24170c is calculated using the following formula: JPEG2025009582000022.jpg29170E 1 is calculated using the following formula: JPEG2025009582000023.jpg35170E2 is calculated using the following formula: JPEG2025009582000024.jpg38170In equations (4), (5), (6), (7) and (8), h is the water depth, m, which may be collected by on-site monitoring or determined from fundamental data, u is the discharge velocity in the x direction, m / s, which may be collected by on-site monitoring or determined from fundamental data, v is the discharge velocity in the y direction, m / s, which may be collected by on-site monitoring or determined from fundamental data, and ρ is the water density, kg / m 3 where g is the acceleration due to gravity, θ is the slope of the groove bed in ° and is determined from basic data, and μ x is the x-component of friction stress between the water flow and the ground, Pa, and μ y is the y-component of friction stress between the water flow and the ground, Pa, μ x is calculated using the following formula: JPEG2025009582000025.jpg7170μ y is calculated using the following formula: JPEG2025009582000026.jpg7170In equations (9) and (10), δ is the roughness coefficient, which is calculated by the following equation: JPEG2025009582000027.jpg6170In the formula, η is the Manning coefficient, which can be determined by basic data, g is the gravitational acceleration, h is the water depth, m, which can be collected by on-site monitoring or determined by basic data, Then, the hydraulic strength F of different calculation units of the ditch valley type debris flow basin is calculated by the following formula: * Calculate In the JPEG2025009582000028.jpg12170 formula, d 50 represents the grain size when the cumulative content of the material source soil mass of the groove valley type debris flow reaches 50%, and is determined by basic data, ρ s represents the density of the source soil, g / cm 3 and is determined by basic data. S4, obtain basic information on the ditch valley type debris flow basin, including the bed slope of the debris flow basin, the grain size distribution and volume weight of the debris flow basin material source, and calculate the critical hydraulic power strength Fc required to trigger the ditch valley type debris flow using the following formula: JPEG2025009582000029.jpg5170, where X = 0.407ln(142tanθ), θ represents the slope of the debris flow basin channel bed in °, determined by the basic data; S5, compare the hydraulic power strength F* of different calculation units of the debris flow basin under rainfall conditions of different return periods obtained in step S3 with the critical hydraulic power strength Fc required for the initiation of a debris flow to determine whether a debris flow will occur. If the F* corresponding to a calculation unit is greater than or equal to Fc, the calculation unit is determined to be an unstable unit, i.e., a debris flow will occur in the calculation unit; if the F* value corresponding to a calculation unit is less than Fc, the calculation unit is determined to be a stable unit, i.e., a debris flow will not occur in the calculation unit, and the total area or By calculating the ratio of the total area of ​​unstable units to the total area of ​​the debris flow basin, it is possible to determine whether or not a groove-valley-type debris flow will occur and its scale; if the ratio of the total area of ​​unstable units is 10% or more, it is determined that this rainfall event will lead to the occurrence of a debris flow, and if the ratio of the total area of ​​unstable units is less than 10%, it is determined that this rainfall event will not lead to the occurrence of a debris flow; by distinguishing between rainfall events that induce groove-valley-type debris flows and rainfall events that cannot induce debris flows, the rainfall threshold for a groove-valley-type debris flow is determined. The data obtained from the field survey is collectively referred to as the basic data for this technical proposal.

[0020] Taking a small watershed prone to ditch valley type debris flow on the RR Provincial Highway in FD City, XX Province, China as an example, the material source grain size distribution and topographical conditions of the ditch valley type debris flow basin are shown in Tables 1 and 2.

[0021] JPEG2025009582000030.jpg15170

[0022] JPEG2025009582000031.jpg15170

[0023] Combining the grain size distribution of the material source in the debris flow formation area and the characteristics of the groove valley topography, the following equation is used: JPEG2025009582000032.jpg5170

[0024] The critical hydraulic strength F of this debris flow basin c can be calculated to be 0.14, Based on the theory of rainfall return period, the rainfall distribution under different rainfall return period conditions is shown in Table 3.

[0025] JPEG2025009582000033.jpg34170

[0026] Using equation (2), runoff hydrographs can be obtained under different rainfall return conditions, as shown in Figures 2-5. The obtained runoff hydrograph is used as input, and the hydraulic strength F of each calculation unit is calculated by (4)-(12). * The calculated hydraulic strength F * is the critical hydraulic strength F for the initiation of a debris flow. c If so, the unit is unstable and the calculated F * is the critical hydraulic strength F for the initiation of a debris flow. c If the rainfall occurrence period is less than 100 km, the unit is stable. Figures 6-9 show the hydraulic strength F of the debris flow formation area under different rainfall occurrence period conditions. * This shows the distribution of If the ratio of the total area of ​​unstable units to the debris-flow basin area is 10% or more, it is determined that this rainfall event will lead to the occurrence of a furrow-valley-type debris flow, and if the ratio of the total area of ​​unstable units to the debris-flow basin area is less than 10%, it is determined that this rainfall event will not lead to the occurrence of a furrow-valley-type debris flow. By distinguishing between rainfall events that can induce furrow-valley-type debris flows and rainfall events that cannot induce debris flows, the rainfall threshold for furrow-valley-type debris flows is determined to be large, as shown in Figure 10 .

Claims

1. A method for calculating a valley debris flow rainfall threshold, comprising the steps of: S1, obtain the extreme rainfall characteristics of the ditch valley type debris flow basin, and calculate the rainfall intensity of the ditch valley type debris flow in different rainfall return periods; The rainfall intensities in different rainfall return periods in steps S2 and S1 are input, and runoff hydrographs are calculated under rainfall conditions in different return periods in the ditch valley type debris flow basin; S3, using the runoff hydrograph obtained in step S2 as input, calculate the hydraulic conditions of different calculation units of the ditch valley type debris flow basin, thereby calculating the hydraulic strength of different calculation units of the ditch valley type debris flow basin; S4. Obtain basic information on the basin of a groove-valley type debris flow and calculate the critical hydraulic power intensity required to trigger a groove-valley type debris flow; S5. A method for calculating a rainfall threshold for a groove-valley-type debris flow, characterized in that the hydraulic strengths of different calculation units of the groove-valley-type debris flow basin obtained in steps S3 are compared with the critical hydraulic strength for the initiation of a groove-valley-type debris flow obtained in step S4, and if the calculated hydraulic strength is equal to or greater than the critical hydraulic strength, the calculation unit is an unstable unit, and if the calculated hydraulic strength is less than the critical hydraulic strength, the calculation unit is a stable unit; and by calculating the total area of ​​the unstable units and their proportion to the entire debris flow basin, it is determined whether a groove-valley-type debris flow will occur under rainfall conditions of different return periods.

2. The method for calculating the ditch valley type debris flow rainfall threshold as claimed in claim 1, characterized in that the extreme rainfall characteristics in step S1 include once in 5 years, once in 10 years, once in 20 years and once in 100 years extreme rainfall data of the ditch valley type debris flow basin.

3. The rainfall intensity of the groove valley type debris flow in different rainfall reproduction periods in step S1 is calculated using the following formula: The method for calculating a ditch valley type debris flow rainfall threshold according to claim 2, characterized in that: is the average rainfall in the ditch valley type debris flow basin, in mm.

4. In step S2, the runoff hydrographs for different rainfall conditions in different return periods for the ditch valley type debris flow basin are calculated using the following formula: In the formula, Q is the surface runoff depth of the debris flow basin, mm; C is the rainfall, mm; A is the water content of the debris flow basin, mm; A ｍａｘ The method for calculating the ditch valley type debris flow rainfall threshold according to claim 1, characterized in that: D is the maximum water content mm of the debris flow basin, D is the surface runoff coefficient of the debris flow basin, and B is the surface runoff threshold of the debris flow basin.

5. The hydraulic conditions of different calculation units of the groove valley type debris flow basin in step S3 are calculated by the following formula: In the formula, t represents time, a is a vector containing flow variables, b and c are flow vectors in the x and y directions, respectively, and E １ and E. ２ are the floor slope and friction effect source term vectors, respectively, Here, a is calculated using the following formula: b is calculated using the following formula: c is calculated using the following formula: E １ is calculated using the following formula: E ２ is calculated using the following formula: In equations (4), (5), (6), (7) and (8), h is the water depth in m, u is the discharge velocity in the x direction in m / s, v is the discharge velocity in the y direction in m / s and ρ is the water density in kg / m ３ where g is the acceleration due to gravity, θ is the slope of the groove bed in °, and μ ｘ is the x-direction component of friction stress between the water flow and the ground, Pa, and μ ｙ The method for calculating a ditch valley type debris flow rainfall threshold according to claim 1, characterized in that: is the y-direction component of the friction stress between the water flow and the ground, in Pa.

6. μ in step S3 ｘ is calculated using the following formula: μ ｙ is calculated using the following formula: In equations (9) and (10), δ is a roughness coefficient, which is calculated by the following equation: The method for calculating the ditch valley type debris flow rainfall threshold according to claim 5, characterized in that in the formula, η represents the Manning coefficient.

7. The hydraulic strength F of different calculation units of the groove valley type debris flow basin in step S3 ＊ is calculated using the following formula: In the formula, d ５０ represents the grain size when the cumulative content of the source soil mass of the groove valley type debris flow reaches 50%, and ρ ｓ represents the density of the source soil, g / cm ３ The method for calculating a ditch valley type debris flow rainfall threshold according to claim 6, characterized in that:

8. In step S4, the critical hydraulic power strength Fc required to trigger a groove-valley type debris flow is calculated using the following formula: The method for calculating the ditch valley type debris flow rainfall threshold value according to claim 1, characterized in that: X = 0.407ln(142tanθ), θ represents the ditch bed slope of the debris flow basin, in degrees.

9. The method for calculating the rainfall threshold for a ditch valley-type debris flow as described in claim 1, characterized in that in step S5, if the proportion of the total area of ​​the unstable units is 10% or more, it is determined that this rainfall event will lead to the occurrence of a debris flow, and if the proportion of the total area of ​​the unstable units is less than 10%, it is determined that this rainfall event will not lead to the occurrence of a debris flow, and the rainfall threshold for a ditch valley-type debris flow is determined by distinguishing between rainfall events that induce a ditch valley-type debris flow and rainfall events that cannot induce a debris flow.

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