Road debris flow risk evaluation method based on FLO-2D

Abstract

The invention provides a highway debris flow risk evaluation method based on FLO-2D. The method comprises the following steps: obtaining Gaofen-7 satellite images to generate sub-meter resolution DEM data of a research area so as to fully describe topographic features of a V-shaped valley; establishing a rainfall-melt water double-source driving module, and coupling a short-duration rainfall model and a glacier ablation flow calculation model to output a mixed runoff process line; and inputting the sub-meter resolution DEM data, the coupling runoff process line and the debris flow characteristic parameters into FLO-2D debris flow numerical simulation software, calculating to obtain a spatial-temporal evolution diagram of the flow velocity, the flow depth and the accumulation range of the debris flow along the highway, and evaluating the threat degree of the debris flow to the highway by adopting an intensity-reproduction period risk evaluation model. The method has the beneficial effects that through effective combination of multi-source data, the movement process of the rainfall-melt debris flow in the alpine and canyon is truly simulated, the threat degree of the debris flow to the highway is evaluated, and technical support is provided for subsequent work such as prevention and treatment of the debris flow, highway maintenance and traffic safety guarantee.

Description

Technical Field

[0001] The present invention relates to the field of transportation engineering, and in particular to a highway debris flow hazard assessment method based on FLO-2D. Background Art

[0002] my country is one of the countries with the most extensive high-altitude highways in the world, and debris flows pose a particularly significant threat to transportation arteries. Disasters frequently occur along high-altitude highway sections, such as the China-Pakistan Economic Corridor. To ensure safe highway operations, it is necessary to accurately simulate the movement and hazard range of debris flows in complex environments to support engineering protection decisions. Current numerical simulation tools for debris flows include RAMMS, ANSYS CFX, Massflow, and FLO-2D. FLO-2D, with its ability to dynamically visualize debris flow velocity, depth, and evolution, accurately reproduces fluid motion patterns, and has become a mainstream tool for highway hazard assessment. However, existing research using FLO-2D to simulate precipitation-meltwater coupled debris flows on the China-Pakistan Highway faces significant limitations. First, terrain data accuracy is insufficient: debris flow gullies in this region are often narrow, V-shaped, deep, and steep. Traditional open-source DEM data (such as SRTM 30m and ALOS 12.5m) struggle to accurately depict gully morphology, resulting in offset flow paths and distorted accumulation ranges in simulations. Second, the driving mechanism is poorly characterized: existing methods often focus on single-precipitation debris flows, ignoring the synergistic effects of glacial meltwater and heavy rainfall, and failing to establish a dual-source confluence model. This results in significant deviations in predicted peak flow and fluid composition. The root cause lies in the quality of hydrological input data and topographic foundations, which directly constrains simulation reliability. Current simulations generally rely on low-resolution DEMs and simplified hydrological models, which are unable to adapt to the complex dynamics of coupled debris flows. Therefore, it is imperative to develop a FLO-2D hazard assessment method that integrates the sub-meter-level Gaofen-7 satellite DEM and dual-source driving mechanisms. This method can provide a scientific basis for highway disaster warning and protective engineering design. Summary of the Invention

[0003] In order to solve the above problems, the present invention provides a FLO-2D-based highway debris flow hazard assessment method, a debris flow numerical simulation method based on a precipitation-meltwater coupling model and a high-resolution 7 image to obtain a high-precision ground model, and an assessment model combining intensity-recurrence period hazard zoning, which can effectively evaluate the hazard of highway debris flows and solve the above problems.

[0004] A highway debris flow hazard assessment method based on FLO-2D mainly includes the following steps:

[0005] S1. Obtain the Gaofen-7 satellite image covering the study area and generate a high-precision DEM from the Gaofen-7 satellite image data using ENVI software;

[0006] S2. Input the obtained DEM of the study area into ArcGIS software, process it in ArcGIS software and output it in ASCII format;

[0007] S3. Collect meteorological data of the study area and obtain the clear water flow of debris flow through the precipitation-meltwater coupling model, and then obtain the peak flow of debris flow;

[0008] S4. Conduct on-site investigation and exploration of the study area, collect historical data and geographical characteristics data of the study area, and determine the characteristic values ​​of debris flows in the study area;

[0009] S5. Inputting the ASCII format ground elevation data, the debris flow peak flow line, and the debris flow characteristic values ​​into the FLO-2D software, performing numerical simulation calculations on the debris flow, and obtaining debris flow simulation results under different recurrence periods;

[0010] S6. Combine the intensity-recurrence period hazard zoning model to divide the debris flow-affected area into hazard zones, and obtain a highway hazard level division map based on the hazard zoning results.

[0011] Furthermore, the process of using ENVI software to process the high-resolution 7 image to obtain a high-precision DEM in step S1 includes: reading the foresight and backsight images, selecting whether to define control points and defining the number of control points, selecting the connecting points of the same name points in the stereo image pair, generating the epipolar image, extracting the DEM, and the like.

[0012] Furthermore, the process of processing the DEM obtained in S1 using ArcGIS in step S2 includes: inputting DEM and checking the coordinate system, performing depression filling preprocessing, calculating the flow direction of the study area, calculating the cumulative amount of confluence, extracting the river network, determining the basin outlet point, and generating the basin boundary.

[0013] Furthermore, the process of using the precipitation-meltwater coupling model to obtain the debris flow peak flow in step S3 includes: collecting historical meteorological data and hydrological parameters of the study area, determining the hydrological model, calibrating the hydrological and model parameters, calculating the clear water flow under different design scenarios, using the matching method to calculate the debris flow peak flow, and using the pentagon generalization method to draw the debris flow flow duration curve.

[0014] Furthermore, the process of determining the characteristic values ​​of debris flow in the study area in step S4 includes: determining the Manning coefficient, volume concentration, yield stress and viscosity coefficient, laminar flow resistance coefficient, and duration through field research combined with the FLO-2D software user manual.

[0015] Furthermore, in step S5, the process of using FLO-2D software to perform numerical simulation of debris flow includes: importing ASCII format ground elevation data and debris flow peak flow lines, inputting debris flow characteristic values ​​one by one, and using FLO-2D to run the calculation of debris flow numerical simulation. The obtained debris flow result values ​​include debris flow siltation range, flow velocity, flow depth, intensity, etc.

[0016] Furthermore, in step S6, the process of determining the highway hazard level by combining the intensity-recurrence period hazard zoning model includes: combining the design scenario (recurrence period) with the simulated intensity of the debris flow to divide the impact area of ​​the debris flow into three levels: high, medium, and low, and dividing the hazard levels of different locations on the highway based on the hazard zoning results.

[0017] The technical solution provided by this invention has the beneficial effect of fully utilizing existing technologies and data, effectively combining multi-source data, and realistically simulating the movement of precipitation-meltwater debris flows in high mountain canyons. It also assesses the threat posed by debris flows to highways, providing technical support for subsequent debris flow prevention and control, highway maintenance, and ensuring traffic safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a flow chart of a highway debris flow hazard assessment method based on FLO-2D provided by the present invention;

[0019] Figure 2 This is a schematic diagram of the risk grading model of bonding strength-recurrence cycle provided by the present invention;

[0020] Figure 3 This is a schematic diagram of the classification of highway debris flow hazard levels based on the hazard classification model provided by the present invention. DETAILED DESCRIPTION

[0021] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described in detail with reference to the accompanying drawings.

[0022] The present invention provides a FLO-2D-based highway debris flow hazard assessment method. The implementation of the present invention takes the Laqigou debris flow on the China-Pakistan Highway as an example. Figure 1 As shown in the figure, debris flow duration curves under different scenarios were obtained based on the precipitation-meltwater coupling model. High-resolution 7 imagery was used to obtain a high-precision ground model. ASCII-formatted ground elevation data for the study area, debris flow duration curves, and debris flow characteristic values ​​were then input into FLO-2D software for simulation calculations. Ultimately, the debris flow impact range, flow velocity, and intensity were determined. Finally, the intensity-recurrence period hazard zoning model was used to categorize the debris flow-affected area. Based on these hazard zoning results, the degree of debris flow threat at different locations on the highway was assessed.

[0023] Figure 1 This is a flowchart of a highway debris flow hazard assessment method based on FLO-2D provided by the present invention. Please refer to Figure 1 , specifically including the following steps:

[0024] Step 1: Use the Gaofen 7 image to obtain a high-precision DEM using ENVI software:

[0025] (1) Open ENVI, click File-Open, and select the GF-7 forward view (*_FWD.tif) and back view (*_BWD.tif) images.

[0026] (2) Right-click the image layer, select View Metadata, and confirm that the parameters on the RPC tab are complete.

[0027] (3) Click Toolbox-Photogrammetry-DEM Extraction-DEM Extraction Wizard to start the DEM extraction function.

[0028] (4) Click Input Left Image to select the GF-7 rear view image; click Input Right Image to select the GF-7 front view image.

[0029] (5) Set the epipolar geometry model: Click Matching Algorithm, select Epipolar Geometry, click Output Epipolar Resampling, check Yes, and click Run to generate the epipolar image.

[0030] (6) Configure the dense matching parameters: Disparity Method → ​​Semi-Global Matching (SGM); Correlation Window Size → enter 11 (default); Disparity Search Range → set -30 to 30 (adjust according to the terrain); and finally click Next.

[0031] (7) Generate the initial DEM: Click DEM Resolution (meters) and enter 2.0 (GF-7 recommended value); select Triangulation for Interpolation Method and click Finish. The processing is complete.

[0032] (8) DEM post-processing and optimization: Double-click the generated DEM layer to automatically open the DEM Editing Tool. Click Fill Holes and set Max Hole Size to 500 to fill the holes. Click Smooth and select a 3×3 window to smooth the noise. Manual editing: Use Erase to erase erroneous values ​​in water bodies and building areas.

[0033] (9) Export DEM results: right-click the DEM layer, select File-SaveAs, select GeoTIFF format, and set the output path.

[0034] Step 2: Use the Gaofen 7 image to obtain a high-precision DEM using ENVI software:

[0035] (1) Input the DEM and check the coordinate system: Open ArcMap, click Add Data, and load the DEM generated by GF-7. Right-click the DEM layer, select Properties, and then click the Source tab to check the Spatial Reference. If the coordinate system is missing, click ArcToolbox, Data Management Tools, Projections and Transformations, and DefineProjection to specify a coordinate system (e.g., WGS_1984_UTM_Zone_48N).

[0036] (2) Depression filling preprocessing: Open ArcToolbox and click SpatialAnalyst Tools > Hydrology > Fill. Set the depression filling parameters: Input surface raster, select DEM; Output surface raster: Fill_DEM.tif; Z limit (optional): Set the maximum fill depth (default is no fill). Click OK to generate a depression-free DEM.

[0037] (3) Calculate flow direction: Open ArcToolbox > Spatial Analyst Tools > Hydrology > FlowDirection. Set the following parameters: Input surface raster: Fill_DEM.tif; Output flow direction raster: FlowDir.tif; Force all edge cells to flow outward: Select NORMAL (default). Click OK to generate the flow direction raster (values ​​1-128 represent 8 directions).

[0038] (4) Calculate runoff accumulation: Open ArcToolbox > Spatial Analyst Tools > Hydrology > FlowAccumulation. Set the following parameters: Input flow direction raster: FlowDir.tif; Output accumulation raster: FlowAccum.tif; Output data type: Select FLOAT (for higher accuracy). Click OK to generate the runoff accumulation raster (high values ​​= potential river channels).

[0039] (5) Extracting the river network: ① Define the river network threshold. Open the Raster Calculator and enter the formula: Con("FlowAccum.tif">Threshold, 1); recommended thresholds: plain areas = 500, mountain areas = 1000 (adjusted based on the accumulation histogram); output: StreamNet.tif. ② Vectorize the river network. Open ArcToolbox-Spatial Analyst Tools-Hydrology-Stream to Feature: Input stream raster: StreamNet.tif; Input flowdirection raster: FlowDir.tif; Output polyline features: RiverNetwork.shp.

[0040] (6) Generate watershed boundaries: Open ArcToolbox-Spatial Analyst Tools-Hydrology-Watershed, and set the parameters: Input flow direction raster: FlowDir.tif; Input raster pourpoint: Snapped_Outlet.tif; Output raster: Watershed.tif. Vectorize boundaries: Open ArcToolbox-Conversion Tools-From Raster-Raster to Polygon, and set the parameters: Input raster: Watershed.tif; Output polygons: Watershed_Boundary.shp.

[0041] Step 3: Use the precipitation-meltwater coupling model to obtain the peak flow rate of the debris flow:

[0042] (1) Collect meteorological data of the study area, including temperature, precipitation, snow area and snow depth.

[0043] (2) Determine the hydrological model and calibrate the hydrological and model parameters to calculate the clear water flow under different design scenarios;

[0044] This paper uses the precipitation-meltwater coupling formula to calculate the clear water peak flow in the study area, which is as follows:

[0045]

[0046] Where Q is the peak flood discharge, m³ / s; H24 is the total basin rainfall, using the statistical value of 24-hour rainfall, mm; M1 is the 24-hour meltwater volume, mm; n is the rainstorm parameter, with a value of 0.62; and τ is the basin runoff time, hours. Where L is the main channel depth; S is the average main channel slope; and the calculated τ value is 6.76. μ is the average infiltration intensity, mm / h; and F is the total basin area, km².

[0047] The meltwater equivalent M1 of ice and snow in the entire basin within 24 hours is calculated based on the degree-day model established based on the relationship between ice and snow melt and temperature:

[0048]

[0049] Where: is the average temperature of the day, ℃; S1 is the area of ​​snowmelt water, km 2 ; DDF is the degree-day factor of glacier or snow, mm / (d·℃).

[0050] Since the melting of ice and snow is closely related to its contact area with the air, the contact area between the ice and snow area and the air is different under different slope projection areas. Considering the influence of slope, the degree-day factor (DDF) can be obtained by the following formula:

[0051] DDF=(0.009×ELE-0.934×LAT-8.1)×cosθ (3)

[0052] Where: ELE represents the altitude above sea level (m); LAT represents the latitude (°); and θ represents the average slope above the snowmelt zone (°). Based on the actual conditions in Laqigou, the DDF is calculated to be 4.5 mm / (d·°C).

[0053] (3) Use the matching method to calculate the peak flow of debris flow:

[0054] The peak flow of debris flow can be calculated by using the matching method based on the flood peak flow. The calculation formula is:

[0055]

[0056]

[0057] Where: Qc is the peak discharge of the debris flow, m³ / s; φc is the correction coefficient for the peak discharge of the debris flow; Du is the blockage coefficient, which is 2.65; γc is the bulk density of the debris flow, t / m³; γw is the specific gravity of clear water, t / m³; and γs is the specific gravity of solid matter in the debris flow, t / m³. Given γc = 18.32 t / m³ and γs = 25.41 t / m³, φc = 1.17.

[0058] (4) Use the pentagonal generalization method to draw the debris flow flow duration curve: Using the pentagonal generalization method, the debris flow flow is set to reach its maximum value at half of the total duration, that is, the debris flow peak flow appears in the middle of the duration. At one-third of the duration, the debris flow flow is set to one-third of the peak flow flow, and at two-thirds of the duration, the debris flow flow is set to one-quarter of the peak flow flow.

[0059] Step 4: Determine the characteristic values ​​of debris flow in the study area:

[0060] Through field research and combined with the FLO-2D software user manual, the range of characteristic values ​​of debris flows was preliminarily determined. Then, relevant literature and materials of the study area were consulted, and the characteristic values ​​of debris flows were finally determined by referring to the values ​​obtained by predecessors, including: Manning coefficient, volume concentration, yield stress and viscosity coefficient, laminar resistance coefficient, and duration.

[0061] Step 5: Use FLO-2D software to perform numerical simulation of debris flow:

[0062] FLO-2D is essentially a numerical simulation method based on the central finite difference method and non-Newtonian body model to solve the fluid kinematic characteristics. When calculating, two main control equations are considered:

[0063] ①Continuity equation:

[0064]

[0065] Where t is the duration of a debris flow, h is the depth of the debris flow, u and v are the average flow velocities of the debris flow in the X-axis and Y-axis directions, respectively, and I is the rainfall intensity of the debris flow.

[0066] ②Equation of motion:

[0067]

[0068]

[0069] Where g represents the acceleration due to gravity; Sfx and Sfy represent the friction slope; Sox and Soy represent the slope of the bed bottom; Formulas 7 and 8 are the momentum equations in the X and Y directions, respectively, which indicate that the forces in the two directions are always in equilibrium. The main body of the momentum equation is the dynamic wave model, which mainly considers the influence of acceleration on the movement of the debris flow.

[0070] (1) Open flo-2d-pre-processor-GDS. Then click file-new project-from existing ASC grid file to import the converted ASCII format ground elevation data.

[0071] (2) Generate a calculation grid. Click Grid-create grid (Figure 4). The size of the grid can be set according to the size of the ditch area and the requirements for calculation accuracy. The grid size in Figure 4 is 20*20m. The smaller the grid, the slower the calculation and the higher the accuracy.

[0072] (3) Grid-Set computation area-define modeling boundary with polygon.

[0073] (4) Assign Grid-Interpolate Elevation Points to the elevation of the calculation area.

[0074] (5) To set the Manning coefficient, select the table Grid in the watershed - Grid-select - Inner cell, and then assign a value.

[0075] (6) In the Tools menu, set other parameters of the debris flow: Tools-Mud and SedimentTransport (set volume concentration, yield stress and viscosity coefficient, laminar flow resistance coefficient, and duration).

[0076] (7) After the parameter settings are completed, click File——run flow-2d to enter the debris flow numerical simulation calculation.

[0077] (8) Click File——run flow-2d to enter the simulation calculation result viewing interface.

[0078] Step 6: Evaluate the highway hazard level using the intensity-recurrence cycle hazard zoning model:

[0079] (1) In the simulation, debris flow intensity is classified according to flow depth h (m) and flow velocity v (m / s). hv is obtained by multiplying the simulated depth (H) and the simulated velocity (V). Based on different combinations of H and hv, the intensity of the Laqigou debris flow is classified into different levels, as shown in Table 1. Based on the classification criteria in Table 1, the classification results of debris flow intensity with different return periods are obtained. Table 1 Classification of debris flow intensity

[0080] (2) The present invention divides the hazard level of the Laqigou debris flow into three levels: low, medium and high, based on the intensity and recurrence period of the debris flow. Figure 2 , and based on this, the threat level of debris flow to the highway was assessed. Figure 3 .

[0081] The beneficial effects brought about by the present invention are: making full use of existing technologies and materials, through the effective combination of multi-source data, more realistically simulating the movement process of precipitation-meltwater type debris flows in narrow mountain valleys, and evaluating the degree of threat posed by debris flows to roads, providing technical support for subsequent debris flow prevention and control, road maintenance and traffic safety assurance.

[0082] The above content is only a preferred embodiment of the present invention and does not limit its scope of protection. As long as the relevant modifications, replacements or improvements do not deviate from the core concept and basic principles of the present invention, they should be included in the scope of protection of the present invention.

Claims

1. A highway debris flow hazard assessment method based on FLO-2D, characterized in that: The following steps are involved: S1. Obtain the Gaofen-7 satellite image covering the study area and generate a high-precision DEM from the Gaofen-7 satellite image data using ENVI software; S2. Input the obtained DEM of the study area into ArcGIS software, process it in ArcGIS software and output it in ASCII format; S3. Collect meteorological data of the study area and obtain the clear water flow of debris flow through the precipitation-meltwater coupling model, and then obtain the peak flow of debris flow; S4. Conduct on-site investigation and exploration of the study area, collect historical data and geographical characteristics data of the study area, and determine the characteristic values ​​of debris flows in the study area; S5. Inputting the ASCII format ground elevation data, the debris flow peak flow line, and the debris flow characteristic values ​​into the FLO-2D software, performing numerical simulation calculations on the debris flow, and obtaining debris flow simulation results under different recurrence periods; S6. Combine the intensity-recurrence period hazard zoning model to divide the debris flow-affected area into hazard zones, and obtain a highway hazard level division map based on the hazard zoning results.

2. The FLO-2D highway debris flow hazard assessment method according to claim 1, characterized in that: The step S1, using ENVI software to process the high-resolution 7 image to obtain a high-precision DEM, includes the following steps: reading the foresight and backsight images, selecting whether to define control points and defining the number of control points, selecting the connecting points of the same name points in the stereo image pair, generating the epipolar image, extracting the DEM, and the like.

3. The FLO-2D highway debris flow hazard assessment method according to claim 1, characterized in that: In step S2, the process of processing the DEM obtained in S1 using ArcGIS includes: inputting DEM and checking the coordinate system, performing depression filling preprocessing, calculating the flow direction of the study area, calculating the cumulative amount of confluence, extracting the river network, determining the basin outlet point, and generating the basin boundary.

4. The FLO-2D highway debris flow hazard assessment method according to claim 1, characterized in that: In step S3, the process of obtaining the peak flow of debris flow using the precipitation-meltwater coupling model includes: collecting historical meteorological data and hydrological parameters of the study area, determining the hydrological model, calibrating the hydrological and model parameters, calculating the clear water flow under different design scenarios, using the matching method to calculate the peak flow of debris flow, and using the pentagon generalization method to draw the debris flow flow duration curve.

5. The FLO-2D highway debris flow hazard assessment method according to claim 1, characterized in that: In step S4, the process of determining the characteristic values ​​of debris flow in the study area includes: determining the Manning coefficient, volume concentration, yield stress and viscosity coefficient, laminar flow resistance coefficient, and duration through field research combined with the FLO-2D software user manual.

6. The FLO-2D highway debris flow hazard assessment method according to claim 1, characterized in that: In step S5, the process of using FLO-2D software to perform numerical simulation of debris flow includes: importing ASCII format ground elevation data and debris flow peak flow lines, inputting debris flow characteristic values ​​one by one, and running the calculation of debris flow numerical simulation using FLO-2D. The obtained debris flow result values ​​include debris flow siltation range, flow velocity, flow depth, intensity, etc.

7. The FLO-2D highway debris flow hazard assessment method according to claim 1, characterized in that: In step S6, the process of determining the highway hazard level by combining the intensity-recurrence period hazard zoning model includes: combining the design scenario (recurrence period) with the simulated intensity of the debris flow to divide the affected area of ​​the debris flow into three levels: high, medium, and low, and dividing the hazard levels of different locations on the highway based on the hazard zoning results.

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