CN113420515B - Landslide debris flow formation evolution simulation method based on rainfall data - Google Patents
Landslide debris flow formation evolution simulation method based on rainfall data Download PDFInfo
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Abstract
The invention discloses a landslide debris flow formation evolution simulation method based on rainfall data, which comprises the following steps of: s1, acquiring rainfall data, runoff generating infiltration parameters, soil types, soil distribution conditions and topographic data of a debris flow source area by using fixed-point monitoring and field tests; s2, obtaining a dynamic model suitable for describing each stage of debris flow motion by analyzing the processes and mechanisms of slope instability caused by rainfall in the mountainous area, debris flow generation, confluence and development; and S3, considering rainfall infiltration, slope body and channel erosion, soil body damage and debris flow movement processes, realizing hydrological simulation and calculation of slope body instability damage caused by rainfall and debris flow convergence and propagation, and disclosing an evolution mechanism of rainfall-landslide-debris flow. The invention considers the processes of rainwater infiltration, surface runoff, channel erosion, soil body destruction and the like, realizes the whole process of debris flow generation and propagation, and realizes the simulation of convergence and propagation, thereby providing an important basis for the prevention and treatment of debris flow disasters.
Description
Technical Field
The invention relates to a mountainous area debris flow geological disaster prevention and control technology watershed, in particular to a landslide debris flow formation evolution simulation method based on rainfall data.
Background
Debris flow is a global geological disaster problem, and is particularly serious in southwest mountainous areas of China. They are often characterized by high flow velocity, large impact force, long movement distance and the like, and are easily induced by external factors such as strong earthquake, heavy rain and the like, thereby causing a great deal of casualties and serious economic loss. The formation and propagation of the debris flow are very complex processes, mainly including a watershed hydrological process, a rainfall infiltration process, a soil body destruction process, a slope and channel erosion process, a soil body supply process, a debris flow movement process and the like, so that the process and mechanism of inoculation and development of the debris flow are very difficult to study. The source area and the caused influence effect of the debris flow can be well determined through field investigation, but the development and propagation process mechanism of the debris flow cannot be well researched; the physical model test can well research the mechanism of the generation and development of the debris flow, but the physical model test is limited by the research scale, and the size effect causes the test result to have larger difference with the practical situation. With the continuous development of computer technology, the research on the numerical simulation of the debris flow shows stronger feasibility.
At present, simulation aiming at debris flow mainly focuses on simulating the processes of starting, moving, accumulating and the like of the debris flow under real terrain by using a Navier-Stokes equation speed averaging method. However, the solution process related to the high-order partial differential equation is complex, and although the method is widely applied to the dynamics simulation of the debris flow, the solution process is complex and time-consuming, the requirement on the performance of a computer is extremely high, and the solution of a large-scale problem is not facilitated. Moreover, the partial simulation method only aims at the movement condition of the fluid in the debris flow, ignores the channel erosion and soil body damage conditions in the development and propagation processes of the debris flow, and the material source supply processes of the debris flow by the processes, which is inconsistent with the actual situation. Therefore, an accurate and simple simulation method for simulating the debris flow from starting to transmission is established to reveal the formation and transmission mechanism and clarify the evolution law of the debris flow, and the method is extremely important for preventing and treating debris flow disasters.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a landslide debris flow formation evolution simulation method based on rainfall data, which considers the processes of rainwater infiltration, surface runoff, channel erosion, soil body damage and the like, realizes the whole process production convergence and propagation simulation of debris flow generation and propagation, and provides an important basis for prevention and control of debris flow disasters.
The purpose of the invention is realized by the following technical scheme: a landslide debris flow formation evolution simulation method based on rainfall data comprises the following steps:
s1, acquiring rainfall data, runoff yield infiltration parameters, soil types, soil distribution conditions and topographic data of a debris flow source area by using fixed-point monitoring and field tests;
s2, obtaining a dynamic model suitable for describing each stage of debris flow motion by analyzing the processes and mechanisms of slope instability caused by rainfall in the mountainous area, debris flow generation, confluence and development;
s3, considering rainfall infiltration, slope body and channel erosion, soil body damage and debris flow movement processes, hydrologic simulation and calculation of slope body instability damage caused by rainfall and debris flow convergence and propagation are achieved, and an evolution mechanism of rainfall-landslide-debris flow is disclosed.
Wherein the step S3 comprises:
s301, preparation of basic data in a forming stage:
the step S301 includes:
(1) Calculating a rainfall duration curve in the area:
for each computational grid, corresponding rainfall intensity at each moment is represented by coordinates (x, y, t, r); wherein x and y are respectively an x coordinate and a y coordinate of the calculation grid, t is a calculation moment, r is the rainfall intensity of the grid at the corresponding calculation moment t, and the rainfall intensity is collected through site fixed-point monitoring;
(2) Calculating terrain raster data of the area:
for each computational grid cell, a unique coordinate (x, y, z) is required to represent; wherein x and y are respectively an x coordinate and a y coordinate of the computational grid, z is an elevation of a central point of the computational grid, and grid terrain data is acquired by field three-dimensional laser scanning;
(3) Calculating parameter information required by simulation in the region, wherein the parameter information comprises soil thickness, distribution condition, particle grading distribution, permeability, natural soil moisture content, saturated moisture content, internal soil friction angle and soil cohesive force:
a unique coordinate (x, y, i-n) is required for each computational grid to represent; wherein x and y are respectively the x coordinate and the y coordinate of the computational grid, i-n are various parameters of each computational grid, n is the number of the parameters, and the information of each parameter is acquired through field test.
S302, simulating the debris flow forming and propagating process.
The step S302 includes:
after the rainfall duration curves within the calculation area are entered, the plant entrapment process is calculated in each calculation grid:
P eff ＝P-I
wherein P is rainfall, I is plant interception capacity, and the plant interception capacity accounts for 0-5% of the rainfall. Obtaining the effective rainfall P which is lowered to the ground surface after calculation eff And the effective rainfall is used for the next infiltration calculation.
the infiltration uses a shorter time step Δ t than other processes short Is calculated, that is to say Δ t can be calculated within the time of Δ t short The time step is run for a plurality of times. Δ t short ＝d cell /v max At each short time step Δ t short The inner effective rainfall will be added to the surface water of each computing unit. d cell Is the length of the calculation unit, v max Is the maximum radial flow velocity within the calculation region. The surface water depth is calculated as follows:
wherein R is 0 Is the surface water level, R prev Is the surface wetting front depth, P, after the previous time step eff.t Is the effective rainfall intensity over time at.
Infiltration capacity:
wherein: a is a 0 Is a priority flow factor; k is the hydraulic conductivity, R 0 The surface water level depth before infiltration, psi is the soil suction at the wetting front, d 0 The depth of the wetting front before infiltration.
The infiltration capacity in the calculation unit exceeds the maximum possible infiltration capacity, and the infiltration depth d of the whole soil body is expressed as:
d＝d 0 +Δt short f/Δθ
the infiltration capacity in the calculation unit is less than or equal to the maximum possible infiltration capacity, and the whole soil body infiltration depth d is
Where Δ θ is the difference between the saturated water content and the initial water content (Δ θ = θ) s -θ i ) S is the content of large stone blocks, and when the infiltration depth is greater than the thickness of soil body, the surface runoff depth R f ＝d-d soil And calculating the surface runoff of the next stage by the generated surface runoff.
wherein v is flow Is the surface runoff speed, q is the runoff flow of each unit, alpha is the slope inclination of the calculation unit, n man Is the Manning coefficient.
the erosion process of the slope and the channel is considered while the surface runoff is calculated, and the movement process of silt in each calculation grid is mainly considered:
q cr ＝ST 2 0.065(s-1) 1.67 g 0.5 D50 1.5 (sinα) -1.12
wherein q is b Volume flow rate per unit width of bed mass movement, q cr The critical starting flow rate of silt starting, s is the density ratio of particles to fluid, D30, D50 and D90 respectively account for 30 percent of the weight of soil mass smaller than the particle size, the particle sizes under the conditions of 50 percent and 90 percent are obtained, and g is the gravity acceleration; the amount of the eroded soil or the deposited soil is calculated according to the following formula:
d w ＝ST 3 (l 0 -q b /v flow )for l 0 ＜q b /v flow
d w ＝ST 4 (l 0 -q b /v flow )for l 0 ＞q b /v flow
wherein l 0 Is the initial depth of the mobile bed load at the beginning of the calculation, d w Negative values indicate separation erosion, and when positive values indicate deposition, only saturated soil can allow separation erosion; the bed load formed by erosion participates in the propagation process of runoff by superposition, wherein the bed load depth l = l 0 -d w ＝q b /v flow The concentration of silt C = l/(l + R); ST in the above respective formulae 1 、ST 2 、ST 3 、ST 4 Are all constants; from experience, ST 1 Generally set to 1.0,ST 2 The general value range is 0.005-0.01 3 The value is typically 0.1 times the length of the computational unit, ST 4 Generally, the value range is 0.005-0.01.
And 5, in the steps 1 to 4, mainly calculating the change condition of each physical quantity in each calculation unit independently, and linking the calculated physical quantities of each adjacent calculation unit after the calculation is finished to perform confluence calculation:
R＝R f +∑IF-OF
wherein, SIG IF is the flow rate OF the upstream adjacent unit flowing into the computing unit, OF is the flow rate OF the computing unit, and R is the water level OF the computing unit after considering confluence; n is the number of units that the upstream slope contributes to the calculated increase in unit interflow, d h,i Is the horizontal distance of cell i from the center point of the calculation cell, d h To calculate the horizontal distance of a cell from the center point of an adjacent cell in the downstream direction.
FOS＝T f /(T+F s )
safety coefficient and shear strength of FOS as slope body
Shear force->
G is the weight of soil mass per unit width, G = gamma. Delta. X. D, and the permeability F s ＝Δx·d·γ w sina; wherein, c s Is the soil mass cohesion force>
The internal friction angle of the soil body, gamma the volume weight of the soil body, deltax the horizontal length of the slope unit, and d i To the depth of the potentially damaging surface, gamma w Is the volume weight of water; and adding the damaged soil body into a water body of the runoff or the channel for subsequent calculation.
And 7, finally, calculating the movement of the debris flow:
wherein v is i Calculating the movement speed of the debris flow on the unit, wherein M/D is the mass damping ratio of the soil body; v. of i-1 The speed of the previous grid; delta alpha i The gradient difference between the grid and the previous grid; parameter ζ i And eta i Can be calculated as follows:
in the formula: g is gravity acceleration; alpha is alpha i Is the slope of the grid; mu is the kinetic friction coefficient of the soil body, mu =0.13A -0.25 Calculating the catchment area of the drainage basin; l is the length of the grid, related to the slope and the unit length.
And (3) circularly executing the steps 1-7 within delta t in each time step, updating the runoff depth, the depth of eroded soil, the depth parameter of damaged soil and the movement speed of the debris flow, and ending the whole debris flow simulation process until the set final calculation time is reached.
The invention has the beneficial effects that:
1. the method is based on the empirical model, the physical concept is clear, and the solving process is simpler and more effective than the traditional process, so that a lower computer can be occupied, and the calculation scale is greatly expanded;
2. the invention can consider the movement of channel silt and the soil body destruction process of the side slope, and realize the replenishment effect of the channel silt and the soil body destruction process on the evolution of the debris flow, which has important significance for researching the debris flow disaster-causing mechanism;
3. the invention can comprehensively simulate the whole movement process of debris flow starting and spreading and has positive significance for analyzing the dynamic behavior of debris flow disasters;
4. the method realizes the visualization of the debris flow disasters by utilizing numerical simulation, determines the evolution law on the basis, and has important practical significance for guiding the prevention and treatment work of the debris flow disasters in mountainous areas and guaranteeing the life safety of people.
Drawings
FIG. 1 is a flow chart of a method of the present invention;
FIG. 2 is a schematic diagram of a simulation principle of a debris flow formation and propagation process;
fig. 3 is a graph of the flow value simulation results for mudstone t =00, t =02 in the example;
FIG. 4 is a schematic diagram showing the comparison of runoff speed, runoff depth and bed load depth results of slope monitoring points under different simulated rainfall conditions.
Detailed Description
The technical solutions of the present invention are further described in detail below with reference to the accompanying drawings, but the scope of the present invention is not limited to the following.
As shown in fig. 1, a landslide debris flow evolution simulation method based on rainfall data includes the following steps:
s1, acquiring rainfall data, runoff yield infiltration parameters, soil types, soil distribution conditions and topographic data of a debris flow source area by using fixed-point monitoring and field tests;
s2, obtaining a dynamic model suitable for describing each stage of debris flow motion by analyzing the processes and mechanisms of slope instability caused by rainfall in the mountainous area, debris flow generation, confluence and development;
and S3, considering rainfall infiltration, slope body and channel erosion, soil body damage and debris flow movement processes, realizing hydrological simulation and calculation of slope body instability damage caused by rainfall and debris flow convergence and propagation, and disclosing an evolution mechanism of rainfall-landslide-debris flow.
Specifically, the preparation phase of the basic input data:
acquiring rainfall data through a field rainfall station, and finely interpolating and determining the rainfall data of the whole area through the rainfall data of different rainfall stations, namely, each calculation grid has corresponding rainfall intensity at each moment and coordinates are expressed as (x, y, t, r); wherein x and y are respectively the x coordinate and y coordinate of the calculation grid, t is the calculation time, and r is the rainfall intensity of the grid corresponding to the calculation time t
High-precision terrain raster data in a calculation area are acquired on site through a three-dimensional laser scanner and an unmanned aerial vehicle, namely, each calculation grid needs to be represented by unique coordinates (x, y, z); wherein x and y are respectively the x coordinate and the y coordinate of the computational grid, and z is the elevation of the central point of the computational grid;
by utilizing field investigation and indoor physical mechanical tests, parameters required by calculation such as the thickness, distribution condition, particle grading distribution, permeability, natural water content of soil, saturated water content, internal friction angle of soil, cohesive force of soil and the like in a calculation area are obtained. A unique coordinate (x, y, i-n) is required for each computational grid to represent; wherein x and y are respectively the x coordinate and the y coordinate of the computational grid, and i-n are various parameters of each computational grid;
as shown in fig. 2, after the preparation stage of the basic input data, the simulation process of the debris flow formation and propagation process is performed, and the simulation process mainly includes a hydrological calculation module (evaporation process, plant retention process, infiltration process, surface runoff calculation, and confluence calculation), a runoff erosion damage module (slope and channel erosion calculation), a slope stability module (slope damage process), and a debris flow module (debris flow movement propagation process), and specifically includes the following steps:
after the rainfall duration curves within the calculation area are entered, the plant entrapment process is calculated in each calculation grid:
P eff ＝P-I
wherein, P is rainfall, I is plant interception capacity, and the plant interception capacity accounts for 0-5% of the rainfall. Obtaining the effective rainfall P falling to the ground surface after calculation eff .. If the interception amount is larger than the rainfall intensity, the effective rainfall is 0, the subsequent calculation is suspended, and otherwise, the intercepted effective rainfall is subjected to the next calculation.
the infiltration uses a shorter time step Δ t than other processes short Is calculated, that is to say Δ t can be calculated within the time of Δ t short The time step is run for a plurality of times. Δ t short ＝d cell /v max At each short time step Δ t short The inner effective rainfall will be added to the surface water of each computing unit. d cell Is the length of the calculation unit, v max Is the maximum radial flow velocity within the calculation region. The surface water depth is calculated as follows:
wherein R is 0 Is the surface water level, R prev Is the surface wetting front depth, P, after the previous time step eff.t Is the effective rainfall intensity over the time at.
Infiltration capacity:
wherein: a is 0 Is a priority flow factor; k is the hydraulic conductivity, R 0 The surface water level depth before infiltration, psi is the soil suction at the wetting front, d 0 The depth of the wetting front before infiltration.
The infiltration capacity in the calculation unit exceeds the maximum possible infiltration capacity, and the infiltration depth d of the whole soil body is expressed as:
d＝d 0 +Δt short f/Δθ
the infiltration capacity in the calculation unit is less than or equal to the maximum possible infiltration capacity, and the whole soil body infiltration depth d is
Where Δ θ is the difference between the saturated water content and the initial water content (Δ θ = θ) s -θ i ) S is the content of large stone blocks, and when the infiltration depth is greater than the thickness of soil body, the surface runoff depth R f ＝d-d soil And calculating the surface runoff of the next stage by the generated surface runoff.
wherein v is flow Is the surface runoff speed, q is the runoff flow of each unit, alpha is the slope inclination of the calculation unit, n man Is the Manning coefficient.
the erosion process of the slope and the channel is considered while the surface runoff is calculated, and the movement process of silt in each calculation grid is mainly considered:
q cr ＝ST 2 0.065(s-1) 1.67 g 0.5 D50 1.5 (sinα) -1.12
wherein q is b Volume flow rate, q, of movement of the bed mass per unit width cr The critical starting flow rate for silt starting, s is the density ratio of particles to fluid, D30, D50 and D90 are respectively the weight of soil mass smaller than the particle size accounting for 30 percent, the particle sizes under the conditions of 50 percent and 90 percent, and g is gravity acceleration; the amount of eroded soil or deposited soil is calculated according to the following formula:
d w ＝ST 3 (l 0 -q b /v flow )for l 0 ＜q b /v flow
d w ＝ST 4 (l 0 -q b /v flow )for l 0 ＞q b /v flow
wherein l 0 Is the initial depth of the mobile bed load at the beginning of the calculation, d w Negative values indicate detached erosion and positive values indicate deposition, with saturated soil onlyThe body can allow for separation erosion; the bed load formed by erosion participates in the propagation process of runoff by superposition, wherein the bed load depth l = l 0 -d w ＝q b /v flow The concentration of silt C = l/(l + R); ST in the above formulae 1 、ST 2 、ST 3 、ST 4 Are all undetermined constants, according to experience, ST 1 Generally set to 1.0,ST 2 The general value range is 0.005-0.01 3 The value is typically 0.1 times the length of the computational unit, ST 4 Generally, the value range is 0.005-0.01. If the bed load depth is greater than the wetting front depth, then the runoff depth R = R is updated simultaneously f +(d-d w )θ s (1-s), if the bed mass depth is less than the wetting front, R = R f +(d+d w )θ s (1-s)。
And 5, in the steps 1 to 4, mainly calculating the change condition of each physical quantity in each calculation unit independently, and linking the calculated physical quantities of each adjacent calculation unit after the calculation is finished to perform confluence calculation:
R＝R f +∑IF-OF
wherein, SIG IF is the flow rate OF the upstream adjacent unit flowing into the computing unit, OF is the flow rate OF the computing unit, and R is the water level after the computing unit considers confluence; n is the number of units that the upstream slope contributes to the calculated increase in unit interflow, d h,i For the horizontal distance of cell i from the center point of the calculation cell, d h To calculate the horizontal distance of a cell from the center point of an adjacent cell in the downstream direction.
FOS＝T f /(T+F s )
safety coefficient and shear strength of FOS as slope body
Shear force->
G is the weight of soil mass per unit width, G = gamma. Delta. X. D, and the permeability F s ＝Δx·d·γ w sina; wherein, c s Is the soil mass cohesion force and is combined with the soil mass>
Is the internal friction angle of the soil body, gamma is the bulk density of the soil body, delta x is the horizontal length of the slope unit, d i Depth of surface of potential damage, γ w Is the volume weight of water.
And 7, finally, calculating the movement of the debris flow:
wherein v is i Calculating the movement speed of the debris flow on the unit, wherein M/D is the mass damping ratio of the soil body; v. of i-1 The speed of the previous grid; delta alpha i The gradient difference between the grid and the previous grid; parameter ζ i And eta i Can be calculated as follows:
in the formula: g is the acceleration of gravity; alpha is alpha i Is the slope of the grid; mu is the kinetic friction coefficient of the soil body, mu =0.13A -0.25 A is calculating the catchment area of the drainage basin; l is the length of the grid, related to the slope and the unit length.
And 8, circularly executing the steps 1-7 within delta t in each time step, updating the runoff depth, the depth of eroded soil, the depth parameter of damaged soil and the movement speed of the debris flow, and ending the whole debris flow simulation process until the set final calculation time is reached.
The present invention will be further described with reference to the following examples.
In the examples of the present application:
the Wenjin ditch is located in the clear and plain village in the northern mountain area of Mian bamboo city of Sichuan province, the left bank of Mian river, the ditch opening to 700 meters in the downstream clear and plain village towns (along Mian river), and the catchment area is about 7.18km 2 The length of the main channel in the middle is about 4.9km, main branch streams are concentrated at the upstream, and the average specific drop of the channel reaches 30%. Influenced by the earthquake in Wenchuan, a large amount of loose materials are accumulated in the trench, and debris flow is very easy to occur under the conditions of rainfall and the like, so that the safety of peripheral facilities and personnel is threatened. In the early morning of 8 and 13 months in 2010, catastrophic debris flow occurs in the Genjia ditch, and the total volume of the flushed debris flow reaches 310 multiplied by 10 4 m 3 The long river silts up to about 1.6km, so 5 people die, one person is missing, a large number of houses are buried, and huge economic loss is caused.
Fig. 3 is a graph of flow number simulation results of a chinese ditch mudstone t =00, t =02 (flow velocity, flow depth, erosion depth, respectively, from left to right), where (a), t =00, (b), t =02
Fig. 4 is a comparison graph of runoff speed, runoff depth and bed load depth results of slope monitoring points of a housekeeping ditch under different rainfall intensity conditions, wherein: (a) the runoff rate; (b), runoff depth, (c) bed load depth.
The invention is used for carrying out the comprehensive simulation of the whole process from the starting to the spreading of the debris flow on the Venturi channel, and the concrete steps are as follows:
inputting rainfall duration curves (and corresponding rainfall intensity for each computing unit at each moment) in the computing area, topographic data and physical and mechanical parameters (such as soil thickness, soil permeability, particle composition parameters, natural water content, saturated water content and the like) of soil bodies in the computing area. And in the data loading process, the system automatically matches the parameters of the same computing unit together and stores each data.
In the hydrological calculation process, executing the calculation steps 1-3, calculating rainfall, infiltration and surface runoff; next, executing steps 4 and 5 in a runoff erosion damage module, and performing erosion calculation and confluence calculation on the slope and the channel; and then, executing a step 6 in a block stability module to calculate potential slope damage, and finally executing a step 7 in a debris flow movement module to calculate movement of the debris flow. And (3) after the calculation in a single time step is finished, circularly performing the steps 1-7, simultaneously updating the runoff depth, the depth of eroded soil, the depth parameter of damaged soil and the movement speed of the debris flow until the specified calculation time is reached, and finally performing the overall evaluation of the debris flow starting and propagation process. The hydrological process is used as a main line to simulate the whole debris flow, and the channel erosion and slope body damage are main supply sources of the debris flow.
After the debris flow simulation calculation, the calculation results can be stored according to the change conditions of the physical quantities of each calculation unit and a specific format, and the debris flow forming and propagation process can be reproduced by loading the debris flow movement results, so that the scientificity and reliability of debris flow dynamic process research are improved, and the method has important significance for guiding debris flow disaster prevention and control work and researching a physical mechanical mechanism of debris flow forming and propagation.
The foregoing is a preferred embodiment of the present invention, it is to be understood that the invention is not limited to the form disclosed herein, but is not to be construed as excluding other embodiments, and is capable of other combinations, modifications, and environments and is capable of changes within the scope of the inventive concept as expressed herein, commensurate with the above teachings, or the skill or knowledge of the relevant art. And that modifications and variations may be effected by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (1)
1. A landslide debris flow formation evolution simulation method based on rainfall data is characterized by comprising the following steps: the method comprises the following steps:
s1, acquiring rainfall data, runoff yield infiltration parameters, soil types, soil distribution conditions and topographic data of a debris flow source area by using fixed-point monitoring and field tests;
s2, obtaining a dynamic model suitable for describing each stage of debris flow movement by analyzing the processes and mechanisms of slope instability caused by rainfall in the mountainous area, debris flow runoff generation, confluence and development;
s3, considering rainfall infiltration, slope body and channel erosion, soil body damage and debris flow movement processes, realizing hydrological simulation and calculation of slope body instability damage and debris flow convergence and propagation caused by rainfall, and revealing an evolution mechanism of rainfall-landslide-debris flow;
the step S3 includes:
s301, preparing basic data of a forming stage;
s302, simulating a debris flow forming and transmitting process;
the step S301 includes:
(1) Calculating a rainfall duration curve in the area:
for each computing grid, corresponding rainfall intensity at each moment is represented as (x, y, t, r) by coordinates; wherein x and y are respectively an x coordinate and a y coordinate of the calculation grid, t is a calculation moment, r is the rainfall intensity of the grid at the corresponding calculation moment t, and the rainfall intensity is collected through site fixed-point monitoring;
(2) Calculating terrain raster data of the area:
for each computational grid cell, a unique coordinate (x, y, z) is required to represent; wherein x and y are respectively an x coordinate and a y coordinate of the computational grid, z is an elevation of a central point of the computational grid, and grid terrain data is acquired by field three-dimensional laser scanning;
(3) Calculating parameter information required by simulation in the region, wherein the parameter information comprises soil thickness, distribution condition, particle grading distribution, permeability, natural soil moisture content, saturated moisture content, internal soil friction angle and soil cohesive force:
for each computational grid, a unique coordinate (x, y, i-n) is required to represent; wherein x and y are respectively the x coordinate and the y coordinate of the computational grid, i-n are various parameters of each computational grid, n is the number of the parameters, and the information of each parameter is acquired through field test;
the step S302 includes:
step 1, plant interception process:
after the rainfall duration curves within the calculation area are entered, the plant entrapment process is calculated in each calculation grid:
P eff ＝P-I
wherein P is rainfall, I is plant interception capacity, and the plant interception capacity accounts for 0-5% of the rainfall; obtaining the effective rainfall P falling to the ground surface after calculation eff The effective rainfall is taken into the next infiltration calculation;
step 2, infiltration process:
time step delta t for infiltration short To calculate, within a time of Δ t, Δ t short The time runs are multiple times:
Δt short ＝d cell /v max
at each short time step Δ t short The internal effective rainfall will be added to the surface water of each computing unit, where d cell Is the length of the calculation unit, v max Is the maximum radial flow velocity in the calculation region, and the surface water depth is calculated as follows:
wherein R is 0 Is the surface water level, R prev Is the surface wetting front depth, P, after the previous time step eff.t Is the effective rainfall intensity over time Δ t;
infiltration capacity:
wherein: a is 0 Is a priority flow factor; k is the hydraulic conductivity, R 0 The surface water level depth before infiltration, psi is the soil suction at the wetting front, d 0 Is moistened before infiltrationThe depth of the front;
the infiltration capacity in the calculation unit exceeds the maximum possible infiltration capacity, and the infiltration depth d of the whole soil body is expressed as:
d＝d 0 +Δt short f/Δθ
the infiltration capacity in the calculation unit is less than or equal to the maximum possible infiltration capacity, and the whole soil body infiltration depth d is
Where Δ θ is the difference between the saturated water content and the initial water content (Δ θ = θ) s -θ i ) S is the content of large stone blocks, and when the infiltration depth is greater than the thickness of soil body, the surface runoff depth R f ＝d-d soil Calculating the surface runoff of the next stage by the generated surface runoff;
step 3, calculating surface runoff:
wherein v is flow Is the surface runoff speed, q is the runoff flow of each unit, alpha is the slope inclination of the calculation unit, n man Is the Manning coefficient;
step 4, slope and channel erosion calculation:
the erosion process of a slope and a channel is considered while the surface runoff is calculated, and the movement process of silt in each calculation grid is considered:
q cr ＝ST 2 0.065(m-1) 1.67 g 0.5 D50 1.5 (sinα) -1.12
wherein q is b Volume flow rate, q, of movement of the bed mass per unit width cr The critical starting flow rate for silt starting, m is the density ratio of particles to fluid, D30, D50 and D90 are respectively the weight of soil mass smaller than the particle diameter accounting for 30 percent, the diameters of particles under the conditions of 50 percent and 90 percent, and g is gravity acceleration; the amount of the eroded soil or the deposited soil is calculated according to the following formula:
d w ＝ST 3 (l 0 -q b /v flow )for l 0 ＜q b /v flow
d w ＝ST 4 (l 0 -q b /v flow )for l 0 ＞q b /v flow
wherein l 0 Is the initial depth of the mobile bed load at the beginning of the calculation, d w Negative values indicate separation erosion, and when positive values indicate deposition, only saturated soil can allow separation erosion; the bed load formed by erosion participates in the propagation process of runoff by superposition, wherein the bed load depth l = l 0 -d w ＝q b /v flow The concentration of silt C = l/(l + R); wherein, ST 1 、ST 2 、ST 3 、ST 4 Are all constants;
step 5, the steps 1 to 4 are mainly to calculate the change situation of each physical quantity in each calculation unit independently, and after the calculation is finished, the calculation physical quantities of each adjacent calculation grid unit are related to perform confluence calculation:
R＝R f +∑IF-OF
where Σ IF is an upstream neighbor listThe flow rate OF the elements flowing into the computing unit, OF is the runoff outflow rate OF the computing unit, and R is the water level OF the computing unit after the confluence is considered; n is the number of units that the upstream slope contributes to the calculated increase in unit interflow, d h,i For the horizontal distance of cell i from the center point of the calculation cell, d h Calculating the horizontal distance between the cell and the center point of the adjacent cell in the downstream direction;
and 6, after the rainfall, infiltration, runoff, confluence and erosion processes are calculated, calculating the stability of the slope body:
FOS＝T f /(T+F s )
safety coefficient and shear strength of FOS as slope
Shear force->
G is the soil mass weight per unit width, G = gamma. Delta. X. D, and the permeability F s ＝Δx·d·γ w sina; wherein, c s Is the soil mass cohesion force>
Is the internal friction angle of the soil body, gamma is the bulk density of the soil body, delta x is the horizontal length of the slope unit, d i To the depth of the potentially damaging surface, gamma w Is the volume weight of water; adding the damaged soil body into a water body of a runoff or a channel for subsequent calculation;
and 7, calculating the movement of the debris flow:
wherein v is i Calculating the movement speed of the debris flow on the unit, wherein M/D is the mass damping ratio of the soil body; v. of i-1 The speed of the previous grid; delta alpha i The gradient difference between the grid and the previous grid; parameter ζ i And eta i Can be calculated according to the following formula：
In the formula: g is the acceleration of gravity; alpha (alpha) ("alpha") i Is the slope of the grid; mu is the kinetic friction coefficient of the soil body, mu =0.13A -0.25 A is calculating the catchment area of the drainage basin; l is the length of the grid, related to the slope and unit length;
and 8, circularly executing the steps 1-7 within delta t in each time step, updating the runoff depth, the depth of eroded soil, the depth parameter of damaged soil and the movement speed of the debris flow, and ending the whole debris flow simulation process until the set final calculation time is reached.
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