A method for identifying different starting type debris flow basins at regional scale

Abstract

This invention discloses a method for identifying debris flow basins with different initiation types at a regional scale, comprising the following steps: S1, extracting watershed units; S2, based on the watershed units, determining potential debris flow basins within each watershed unit; S3, obtaining the average source activity value M of all grids contained in each potential debris flow basin, and classifying the potential debris flow basins into hydraulic debris flow basins and a first unidentified basin based on the value of M; S4, performing slope source movement capacity analysis on the first unidentified basin, determining it as either a soil-based debris flow basin or a second unidentified basin; S5, performing source activity analysis in the channel of the second unidentified basin, determining it as either a soil-based debris flow basin or a hydraulic debris flow basin. This invention identifies debris flow basins with different initiation types at a regional scale, providing a possibility for more accurately improving the assessment and early warning function of debris flow susceptibility at the regional scale.

Description

Technical Field

[0001] This invention relates to the field of debris flow basin identification, and more specifically to a method for identifying debris flow basins with different initiation types at a regional scale. Background Technology

[0002] Debris flows are one of the major geological hazards occurring in mountainous areas. Susceptibility assessment and early warning are key non-engineering measures for debris flow prevention and mitigation at the regional scale. From a formation mechanism perspective, debris flows are divided into two main types: soil-based and hydraulic. During a debris flow event, soil-based debris flows are primarily replenished by slope instability, while hydraulic debris flows are primarily replenished by water erosion of the gully bed. Because the formation conditions of these two types of debris flows differ significantly, dividing the watersheds for each type at the regional scale is helpful in selecting evaluation factors and early warning models for different types of debris flows during susceptibility assessment and early warning, thereby improving the accuracy of the assessment and warning results. Currently, there is a lack of methods for classifying these two types of debris flows at the regional scale. Summary of the Invention

[0003] To address the aforementioned issues, this invention provides a method for identifying debris flow basins with different initiation types at a regional scale by comprehensively considering material supply and motion characteristics. This method can provide more scientific and refined input data for regional debris flow susceptibility assessment and early warning.

[0004] This invention is achieved through the following technical solution: A method for identifying debris flow basins with different initiation types at a regional scale includes the following steps: S1, extracting basin units; S2, based on the basin units, determining the potential debris flow basins within each basin unit; S3, obtaining the average source activity M of all grids contained in each potential debris flow basin, and classifying the potential debris flow basins into hydraulic debris flow basins and a first basin to be identified based on the value of M; S4, performing slope source motion capacity analysis on the first basin to be identified, calculating the friction coefficient of the source grid motion, and statistically analyzing the source grid motion friction coefficient greater than... The number of source grids with a slope source friction coefficient threshold is determined as follows: If the proportion of such grids in all source grids within the first watershed to be identified is higher than 50%, the first watershed to be identified is classified as a soil-type debris flow watershed; if the proportion of such grids in all source grids within the first watershed to be identified is not higher than 50%, the first watershed to be identified is classified as the second watershed to be identified. S5. A source activity analysis is performed in the channel of the second watershed to be identified. If the shear force of the deposited material is greater than the critical shear force required for its activation, it can be activated under common flood conditions, i.e., it meets the criteria... If the second watershed to be identified is a soil-type debris flow watershed, then it is determined that the second watershed is a soil-type debris flow watershed. If the formula is not satisfied... If so, it is classified as a hydraulic debris flow basin; among which Water density (kg / m³) 3 ); Acceleration due to gravity (m / s²) 2 ); Shields' dimensionless critical parameter refers to the parameter used in natural rivers and debris flow channels when the particle size falls within the gravel-pebble gradation range. The value is typically between 0.03 and 0.06. Density of solid particles (kg / m³) 3 ); D The characteristic grain size (in meters) of the sediment can be found by referring to the geological rock group type at the location of the grid. The gradient of the channel at the sedimentation point, and the flow depth at the sedimentation point during frequent floods. , The calculation formula is as follows: ,in , The design flood flow rate (m³) at the accumulation location is the annual return period. 3 / s); c The rainfall-runoff coefficient was determined by consulting a hydrological handbook. I The rainfall intensity of the 1-hour design storm with a return period of once a year in the study area is expressed in mm / h and determined by consulting the hydrological manual. n The roughness coefficient of the trench bed was determined by consulting a hydraulics handbook. Let represent the channel width, in meters (m). By measuring some channel widths in the study area, a functional relationship between channel width and catchment area was fitted. The catchment area is the area of ​​water at the location where water accumulates. gradient with the channel All of these can be obtained through DEM data analysis. The friction coefficient of the source grid motion in S4 is the friction coefficient required for each source grid to move from the source to the watershed outlet. The threshold value for the friction coefficient of material source motion on the slope is a constant, and a value of 0.176 is recommended.

[0005] The specific method for determining potential debris flow basins in S2 is as follows: determine whether the extracted basin units meet the basic energy conditions for debris flow formation. In the formula: A The drainage area (km²) 2 ); H The relative height of the watershed (m) is the difference in elevation between the highest and lowest points within the watershed. and The coefficient is obtained using the following method: SS1, using the area of ​​the identified debris flow basin within the study area. A and relative height H Perform power function fitting, i.e. Thus, the coefficients are obtained. SS2, for each debris flow basin i Utilizing its area And relative height, calculate SS3, Statistics The minimum value is assigned to the coefficient. ,Right now .

[0006] Compared with the prior art, the present invention has the following advantages and beneficial effects: This invention identifies debris flow basins with different initiation types based on a regional scale. Through basin unit extraction, potential debris flow basin determination, slope source activity evaluation, slope source movement capacity analysis, and source activity analysis of sediment deposited in gullies under frequent floods, hydraulic and soil-based debris flow basins are gradually identified. This method provides more scientific and refined input data for regional-scale debris flow susceptibility assessment and early warning, and offers the possibility of more accurately improving regional-scale debris flow susceptibility assessment and early warning functions. Attached Figure Description

[0007] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings: Figure 1 Extracted image of watershed unit; Figure 2 Map showing the results of potential debris flow basin identification; Figure 3 Map showing the initial identification results of hydraulic debris flow basins; Figure 4 Map showing the initial identification results of soil-based debris flow basins; Figure 5 This is the final identification result for debris flow watershed types. Detailed Implementation

[0008] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0009] Example 1

[0010] The implementation of this invention mainly includes the following steps: watershed unit extraction, determination of potential debris flow watersheds, evaluation of slope sediment source activity, analysis of slope sediment source mobility, and analysis of sediment source activity in gullies under frequent floods. These steps are detailed below: 1. Watershed unit extraction

[0011] Debris flows are a type of geological hazard that occurs in small watersheds. Therefore, identifying watersheds with different initiation types of debris flows at a regional scale first requires dividing the study area into small watersheds; this step is called watershed unit extraction. Watershed unit extraction can be performed using the hydrological analysis module of ArcGIS software, or using the watershed division function of a hydrological model, or by combining analysis along the main rivers of the study area with a digital elevation model (DEM) and ArcGIS software. Currently, the technical methods involved in this step are mature, and the technical details will not be elaborated further.

[0012] 2. Determination of Potential Debris Flow Watersheds

[0013] Whether soil-related or hydraulic, debris flows require a certain amount of gravitational potential energy to form. Therefore, for the watershed units extracted in step 1, we determine which units meet the basic energy conditions for debris flow formation based on the watershed's energy conditions. These units are referred to as potential debris flow watersheds. This invention uses watershed area... A and relative height H Determine the basic energy conditions for the formation of debris flows:

[0014] In the formula: A The drainage area (km²) 2 ); H The relative height of the watershed (m) is the difference in elevation between the highest and lowest points within the watershed. and The coefficients are obtained using the following method: ①Utilize the area of ​​the identified debris flow basin within the study area A and relative height H Perform power function fitting, i.e. Thus, the coefficients are obtained. ; ② For each debris flow basin i Utilizing its area And relative height, calculate ; ③Statistics The minimum value is assigned to the coefficient. ,Right now .

[0015] Slope source activity assessment Debris sources can originate from slopes or channel bed deposits. Since channel bed deposits are slope sources that have remained in the channel for a longer period, the initial source of solid material in debris flows is the slope. The purpose of slope source activity assessment is to evaluate the relative capacity of different slopes within the study area to provide material sources. The main ways slopes provide material sources are collapses and landslides; therefore, slope source activity assessment reflects the susceptibility of collapses and landslides within the study area. This step can be conducted using various methods, such as the analytic hierarchy process (AHP), statistical methods like frequency ratios, and artificial intelligence methods like machine learning. The technical methods involved in this step are mature, and their details will not be elaborated further.

[0016] The basic unit for assessing slope source activity is the grid. After assessing the source activity of each grid, the average source activity value M of all grids within each potential debris flow basin is calculated. Based on M, potential debris flow basins are divided into five categories: extremely low activity (M<0.2), low activity (M=0.2~0.4), medium activity (M=0.4~0.6), high activity (M=0.6~0.8), and extremely high activity (M>0.8). Among these, basins with extremely low and low activity have a weak ability to directly supply source material from the slope; that is, the slope source material needs to accumulate in the gully over a long period to provide sufficient material for debris flow formation. Therefore, basins with extremely low and low activity are unlikely to develop soil-based debris flows and are directly classified as hydraulic debris flow basins. For basins with medium, high, and extremely high activity, further analysis of the slope source movement characteristics is needed to determine the debris flow initiation type; hence, these are named unidentified basins.

[0017] Analysis of slope material source movement capacity The ability of a material source on a slope to move under gravity is expressed by the coefficient of friction. This is expressed as the ratio of the elevation difference between the sediment deposition location and the initiation location to the horizontal distance of the sediment source movement. If, under the influence of gravity, most of the slope sediment sources within the watershed can move directly to the watershed outlet, it indicates that soil-based debris flows mainly occur within the watershed. To determine whether most sediment sources within the watershed can move to the watershed outlet, the following analysis steps are performed for each watershed to be identified: ① The grids with a slope source activity level higher than a certain threshold M0 within the watershed are identified as source grids, where M0 is the boundary value (0.4) between the low activity and medium activity watersheds in step 3. ② Calculate the elevation difference between each source grid and the watershed outlet within the watershed. ; ③ Calculate the flow length from each source raster to the watershed outlet using ArcGIS. ; ④ Calculate the friction coefficient required for the material source to move to the outlet of the watershed for each material source grid. : .

[0018] ⑤ Statistics (in the formula) The threshold for the friction coefficient is recommended to be 0.176. The proportion of the source grid in all source grids in the watershed should be considered. If the proportion is higher than 50%, the watershed should be classified as a soil-type debris flow watershed.

[0019] For debris flow basins with a proportion not exceeding 50%, the sediment source is mainly deposited in the gully and has not moved to the basin outlet. Further analysis is needed to determine whether the sediment source deposited in the gully can participate in debris flow under the action of frequent floods. These basins are referred to as unidentified basins.

[0020] Analysis of the provenance activity of sediments deposited in gullies under frequent floods If sediment deposited in a gully due to slope instability can be activated and migrated under the influence of a once-in-a-year flood, it indicates that the sediment source is sensitive to rainfall and can quickly participate in debris flow movement after slope instability. This suggests that the debris flow formation has a low dependence on hydrodynamics and is still a soil-driven debris flow. Determining whether sediment deposited in a gully can be activated under a once-in-a-year flood requires examining each grid cell where the sediment source cannot directly move to the gully mouth. j The following steps will be taken in the analysis: ① Search downstream along the direction of the maximum slope of the grid to find the nearest channel location to the grid, which will be the deposition location of the source material of the grid; ② Analyze the catchment area at the sedimentation location using DEM data. gradient with the channel ; ③ Calculate the flow depth at the location where the water settles during frequent floods. The calculation formula is as follows:

[0021] In the formula: The design flood flow rate (m³) at the accumulation location is the annual return period. 3 / s); c The rainfall-runoff coefficient was determined by consulting a hydrological handbook. I The design rainfall intensity (mm / h) for a 1-hour storm with a return period of once a year in the study area was determined by consulting the hydrological manual; n The roughness coefficient of the trench bed was determined by consulting a hydraulics handbook. Let the channel width be (m). By measuring some channel widths in the study area, a functional relationship between channel width and catchment area is fitted, and then... Calculated.

[0022] ④ If the following equation is satisfied, the shear force of the water flow on the sediment is greater than the critical shear force required for its activation, and it can be activated under normal flood conditions:

[0023] In the formula: Water density (kg / m³) 3 ); Acceleration due to gravity (m / s²) 2 ); Shields' dimensionless critical parameter refers to the parameter used in natural rivers and debris flow channels when the particle size falls within the gravel-pebble gradation range. The value is typically between 0.03 and 0.06. Density of solid particles (kg / m³) 3 ); D The characteristic grain size (m) of the sediment is obtained from the table below based on the geological rock group type at the location of the grid:

[0024] If the total number of source grids that meet the above conditions and the total number of source grids that can move to the outlet of the basin in step 4 is greater than 50% of the total number of source grids in the basin, then the basin is identified as a soil-type debris flow basin.

[0025] Classification of two types of debris flow watersheds In the potential debris flow basins obtained in step 2, the hydraulic debris flow basins identified in step 3 and the soil debris flow basins identified in steps 4 and 5 are removed. The remaining channel material sources cannot be activated under the action of frequent floods and require greater hydrodynamic conditions to participate in debris flow activities, so they are all identified as hydraulic debris flow basins.

[0026] This technical implementation description will be carried out using the upper reaches of the Minjiang River as an example. The upper reaches of the Minjiang River refer to the entire watershed area of ​​the river from its source to the Baopingkou area of ​​Dujiangyan and its tributaries. It is located in northern Sichuan Province and covers most areas of Songpan County, Heishui County, Maoxian County, Wenchuan County, and Lixian County, as well as a small part of Dujiangyan City, with a total area of ​​approximately 21,900 square kilometers.

[0027] Watershed unit extraction Using 30 m resolution DEM data of the upper reaches of the Minjiang River and ArcGIS software for joint analysis (for details, see the reference: Shao Shiqi, Zhang Shaojie, Wen Baoping, He Mingqiong, Yang Hongjuan. A refined extraction method for debris flow watershed units based on the hierarchical characteristics of the river network—taking the upper reaches of the Minjiang River as an example. Acta Mountainologica Sinica, 2025, 43(4): 621-634.), a total of 3309 watershed units were obtained. The results are as follows: Figure 1 As shown.

[0028] Determination of potential debris flow basins Using watershed area A and relative heightH Determine the basic energy conditions for the formation of debris flows:

[0029] In the formula: A The drainage area (km²) 2 ); H The relative height of the watershed (m) is the difference in elevation between the highest and lowest points within the watershed. and The coefficients are obtained using the following method: ①Utilizing the area of ​​the 359 debris flow basins already identified within the study area A and relative height H By performing power function fitting, we obtain Thus, the coefficients are obtained. ; ② For each debris flow basin i Utilizing its area and relative height ,calculate ; ③Statistics The minimum value is assigned to the coefficient. ,Right now .

[0030] For the aforementioned 3309 watershed units, the area of ​​each watershed unit was calculated. A and relative height H There are 3065 watershed units that satisfy Equation 1, which are potential debris flow watersheds. The other watershed units that do not satisfy Equation 1 are non-debris flow watersheds. The results are as follows: Figure 2 As shown.

[0031] Slope source activity assessment Using a 30 m × 30 m grid as the evaluation object, the analytic hierarchy process (AHP) was employed to assess slope source activity. After the grid source activity assessment was completed, the average source activity value (M) of all grids within each potential debris flow basin was calculated. Based on M, potential debris flow basins were classified into five categories: extremely low activity (M < 0.2), low activity (M = 0.2–0.4), moderate activity (M = 0.4–0.6, excluding 0.4), high activity (M = 0.6–0.8), and extremely high activity (M > 0.8). Basins with extremely low and low activity were directly classified as hydraulic basins, while basins with moderate, high, and extremely high activity were designated as unidentified basins. The results are as follows: Figure 3 As shown, the dividing point of the M value between hydraulic watersheds and watersheds to be identified is 0.4.

[0032] Analysis of slope material source movement capacity For each watershed to be identified, the following analysis steps are performed: ① Grids with a slope source activity degree higher than 0.4 within the watershed are identified as source grids; ② Calculate the elevation difference between each source grid and the watershed outlet within the watershed. ; ③ Calculate the flow length from each source raster to the watershed outlet using ArcGIS. ; ④ Calculate the friction coefficient required for the material source to move to the outlet of the watershed for each material source grid. : .

[0033] ⑤ Statistics ( If the proportion of the source raster in the watershed is higher than 50%, the watershed is classified as a soil-type debris flow watershed, and other watersheds to be identified remain unidentified. The results are as follows: Figure 4 As shown.

[0034] Analysis of the provenance activity of sediments deposited in gullies under frequent floods For each watershed to be identified, in order to determine whether the sediment deposited on the slope in the gully can be activated under a common flood, a source grid is set up for each source in the watershed that cannot directly move to the gully mouth. j The following steps will be taken in the analysis: ① Search downstream along the direction of the maximum slope of the grid to find the nearest channel location to the grid, which will be the deposition location of the source material of the grid; ② Analyze the catchment area at the sedimentation location using DEM data. gradient with the channel ; ③ Calculate the flow depth at the location where the water settles during frequent floods. The calculation formula is as follows:

[0035] In the formula: The design flood flow rate (m³) at the accumulation location is the annual return period. 3 / s); c The rainfall-runoff coefficient is 0.77 in the upper reaches of the Minjiang River. I The design rainfall intensity (mm / h) for a 1-hour rainstorm with a return period of once a year in the study area is taken as 10 mm / h in the upper reaches of the Minjiang River; n The roughness coefficient of the ditch bed is 0.04 in the upper reaches of the Minjiang River; Let the channel width be (m). By measuring the width of some channels in the upper reaches of the Minjiang River, a functional relationship between the channel width and the catchment area was fitted. Then through Calculated, i.e. .

[0036] ④ If the following equation is satisfied, the shear force of the water flow on the sediment is greater than the critical shear force required for its activation, and it can be activated under normal flood conditions:

[0037] In the formula: The density of water (1000 kg / m³) 3 ); The acceleration due to gravity (9.81 m / s²) 2 ); 0.045 is the dimensionless critical parameter for Shields. The density of solid particles (2700 kg / m³) 3 ); D The characteristic grain size (m) of the sediment is obtained from the table below based on the geological rock group type at the location of the grid:

[0038] If the total number of grids meeting the above conditions and the total number of grids that can move to the watershed outlet in step 4 exceeds 50% of the total number of grids in the watershed, then the watershed is classified as a soil-related debris flow watershed, i.e. Figure 5 Soil-related watersheds (3).

[0039] Of the potential debris flow basins obtained in Step 2, excluding the hydraulic debris flow basins identified in Step 3 and the soil-based debris flow basins identified in Steps 4 and 5, the remaining channel sediment sources cannot be activated under frequent floods and require significant hydrodynamic conditions to participate in debris flow activity. Therefore, they are all classified as hydraulic debris flow basins. Figure 5 The final identification results for the hydraulic watersheds (3) are as follows: Figure 5 As shown.

[0040] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for identifying debris flow watersheds with different initiation types at a regional scale, characterized in that, The process includes the following steps: S1, extracting watershed units; S2, based on watershed units, determining potential debris flow watersheds within the watershed units; S3, obtaining the average source activity M of all grids contained in each potential debris flow watershed, and classifying potential debris flow watersheds into hydraulic debris flow watersheds and the first watershed to be identified based on the value of M. S4. Analyze the slope source mobility capacity of the first watershed to be identified, calculate the friction coefficient of the source grid, and count the number of source grids whose friction coefficient is greater than the threshold of the slope source mobility friction coefficient. If the proportion of such grids in all source grids in the first watershed to be identified is higher than 50%, then the first watershed to be identified is classified as a soil-type debris flow watershed. If the proportion of such grids in all source grids in the first watershed to be identified is not higher than 50%, then the first watershed to be identified is classified as the second watershed to be identified. S5. Analyze the source activity in the channel of the second watershed to be identified. If the shear force of the deposited material is greater than the critical shear force required for its activation, it can be activated under normal flood conditions, i.e., it meets the requirements. If the second watershed to be identified is a soil-type debris flow watershed, then it is determined that the second watershed is a soil-type debris flow watershed. If the formula is not satisfied... If so, it is classified as a hydraulic debris flow basin; among which Density of water, in kg / m³ 3 ; This is the acceleration due to gravity, measured in m / s². 2 ; For Shields, the dimensionless critical parameter; Density of solid particles, in kg / m³ 3 ; D The characteristic grain size of the sediment is expressed in meters (m), which can be found by referring to the geological rock group type at the location of the grid. The gradient of the channel at the sedimentation point, and the flow depth at the sedimentation point during frequent floods. , The calculation formula is as follows: ,in , The design flood flow rate (m³) at the accumulation location is the annual return period. 3 / s); c The rainfall-runoff coefficient was determined by consulting a hydrological handbook. I The rainfall intensity of the 1-hour design storm with a return period of once a year in the study area is expressed in mm / h and determined by consulting the hydrological manual. n The roughness coefficient of the trench bed was determined by consulting a hydraulics handbook. Let represent the channel width, in meters (m). By measuring some channel widths in the study area, a functional relationship between channel width and catchment area was fitted. The catchment area is the area of ​​water at the location where water accumulates. gradient with the ditch All of these can be obtained through DEM data analysis.

2. The debris flow basin identification method according to claim 1, characterized in that, The specific method for determining potential debris flow basins in S2 is as follows: determine whether the extracted basin units meet the basic energy conditions for debris flow formation. In the formula: A The drainage area is expressed in km². 2 ; H The relative height of the watershed, in meters, is the difference in elevation between the highest and lowest points within the watershed. and The coefficient is obtained using the following method: SS1, using the area of ​​the identified debris flow basin within the study area. A and relative height H Perform power function fitting, i.e. Thus, the coefficients are obtained. SS2, for each debris flow basin i Utilizing its area and relative height ,calculate SS3, Statistics The minimum value is assigned to the coefficient. ,Right now .

3. The debris flow basin identification method according to claim 1, characterized in that, For S3, if the potential debris flow basin has M < 0.4, it is classified as a hydraulic debris flow basin.

4. The debris flow basin identification method according to claim 1, characterized in that, The specific method for calculating the motion friction coefficient of the source grid is as follows: grids with a slope source activity level higher than a certain threshold M0 within the watershed are identified as source grids, where M0 is the boundary value of 0.4 between the low activity and medium activity watersheds in step 3. Calculate the elevation difference between each source grid and the watershed outlet within the watershed. ; Calculate the flow length from each source raster to the watershed outlet using ArcGIS. ④ Calculate the friction coefficient required for the material source to move from each source grid to the watershed outlet. : .

Images