Debris flow low-frequency evaluation method and system based on flow velocity calculation

Abstract

The invention relates to a debris flow low-frequency evaluation method and system based on flow velocity calculation, and the method comprises the following steps: collecting historical large low-frequency debris flow disaster cases, analyzing the valley terrain of the historical large low-frequency debris flow disaster, and determining the terrain features of the large low-frequency debris flow disaster; collecting to-be-recognized valley terrain data, and recognizing whether the to-be-recognized valley terrain is a large low-frequency debris flow disaster valley terrain or not according to the terrain features; according to the flow velocity, calculating and identifying the recurrence period of the large low-frequency debris flow disaster hidden danger gully; and according to the recurrence period of the large-scale low-frequency debris flow disaster hidden danger gully, combined with the weather forecast before the recurrence period, sending out a corresponding large-scale low-frequency debris flow disaster early warning.

Description

Technical Field

[0001] The present application relates to the field of disaster prediction, and more specifically, to a method and system for evaluating the low frequency of debris flows based on flow velocity calculation. Background Art

[0002] Low-frequency debris flow mainly refers to debris flow with low frequency, for example, once every 20 to 50 years. Compared with medium and high frequency debris flow, low-frequency debris flow may cause people to misjudge its risk due to its low frequency of occurrence, so when it occurs, it may cause greater disasters and losses. The occurrence of low-frequency debris flow usually requires two main conditions: one is heavy rainfall events, and the other is that the solid materials (such as mud, stones, etc.) stored in the ditch bed need to exceed a certain thickness. The formation of such debris flow is closely related to factors such as rainfall intensity, landslides on the upper and middle slopes of the basin, and the conditions of loose soil and rock accumulation in the ditch bed. Under the combined effect of these factors, debris flow may suddenly start to form under extreme rainfall conditions. For example, a large amount of loose materials accumulated at the foot of the slope become unstable and start to form a highly destructive debris flow under the action of short-term heavy rainfall. Due to the sporadic and uncertain nature of low-frequency debris flow, and the fact that they usually occur in basins with good vegetation coverage, they pose a potential high risk to people living in mountainous areas or nearby basins. Traditional debris flow assessment methods mainly rely on statistical analysis of historical disaster data to determine the frequency and degree of danger of debris flows. However, the accuracy of this method is limited in some areas where historical data is lacking. Due to the low frequency of debris flows, traditional methods have certain difficulties in predicting the possibility of future debris flows. Especially for those areas that have not experienced debris flows for a long time, it is difficult to determine whether there is still a risk of debris flows. Therefore, there is an urgent need for an effective analysis and prediction method for low-frequency debris flows.

[0003] Existing technologies such as the Chinese patent with patent number "CN104598737A" disclose a debris flow forecasting method and system. The method includes a hardware network monitoring system, a software network determination system and a forecasting system. First, drilling and sampling are carried out at the debris flow monitoring site. The hardware network monitoring system is set up at the monitoring site that meets the debris flow occurrence conditions. The rain intensity and rainfall on the slope are recorded in real time through the rain gauge. The infrasound generator and electromagnetic wave generator in the mesh send out a signal when the source is displaced. After the software network determination system receives the data transmitted from the debris flow monitoring site through remote communication means, it calculates the displacement, combines the future rainfall information in the meteorological forecast data, and compares it with the alarm threshold. When the forecast conditions are met, the forecast information is sent out through the forecast system.

[0004] The problem with the above-mentioned prior art is that the drilling and sampling methods can only reflect the local geological conditions of the sampling point. The formation of debris flow involves a large range of mountain geological structure. Drilling and sampling are only carried out at the monitoring site that meets the conditions for debris flow occurrence, which may miss some potential debris flow source areas. A large number of hardware equipment are used to monitor areas where debris flow disasters may occur, and the equipment layout and maintenance costs are high. If the layout is unreasonable, it may lead to inaccurate judgment results on the possibility of debris flow occurrence. Summary of the invention

[0005] In order to solve the above technical problems, the present invention proposes a method and system for evaluating the low frequency of debris flow based on flow velocity calculation.

[0006] The technical solution of the present invention is as follows:

[0007] The present invention proposes a method for evaluating the low frequency of debris flow based on flow velocity calculation, comprising the following steps:

[0008] Step S1, collecting historical large-scale low-frequency debris flow disaster cases, analyzing the valley terrain of historical large-scale low-frequency debris flow disasters, and confirming the terrain characteristics of large-scale low-frequency debris flow disasters;

[0009] Step S2, collecting the terrain data of the valley to be identified, and identifying whether the valley to be identified is a large-scale low-frequency debris flow disaster valley terrain according to the terrain characteristics;

[0010] Step S3, calculating the recurrence period of the valley identified as a potential large-scale low-frequency debris flow disaster based on the flow velocity;

[0011] Step S4, issuing a corresponding large-scale low-frequency debris flow disaster warning according to the recurrence period of the valley with potential large-scale low-frequency debris flow disaster in combination with the weather forecast before the recurrence period.

[0012] As a preferred embodiment, the terrain features of large-scale low-frequency debris flow disasters are confirmed, wherein the terrain features for identifying large-scale low-frequency debris flow disasters are that the difference in terrain slope between two adjacent valley divisions is greater than 10 degrees, or there are terrain conditions in which the slope is not greater than 6 degrees in the area of ​​0 to 2 / 3 of the channel length.

[0013] As a preferred implementation, the method of identifying whether the terrain is a large-scale low-frequency debris flow disaster valley terrain according to the terrain characteristics comprises the following steps:

[0014] Filter the terrain data of valleys and gullies with large-scale low-frequency debris flow hazards to remove abnormal terrain lines and reverse slope conditions;

[0015] Based on the historical large-scale low-frequency debris flow disaster cases, the horizontal spacing of the critical points with the maximum difference in the slope of the valley terrain greater than 10 degrees is used to segment the scattered points;

[0016] Then, a straight line is fitted according to the segmented scattered data, the k and b coefficients of the straight line are determined, and the slope and inclination are calculated;

[0017] The segmented slope is obtained based on the calculated slope and inclination to confirm whether it meets the terrain characteristics of large-scale low-frequency debris flow disasters.

[0018] As a preferred implementation, the calculation of the recurrence period of the valley identified as a potential large-scale low-frequency debris flow disaster according to the flow velocity comprises the following steps:

[0019] Using the rainfall intensity and catchment area of ​​different return periods under heavy rainfall, the flood flow under different return period rainfall intensity is obtained;

[0020] The flow velocity of the water in the channel is calculated using the Manning formula, and the area of ​​the cross-section of the channel flood is calculated using the slope, channel width and Scheher coefficient to obtain the water level depth and flow velocity of the channel;

[0021] The critical velocity is obtained by using the formula for calculating the velocity of large rocks in the valley that can be activated in the debris flow investigation specification;

[0022] The triggering flow velocity of large rocks was compared with the debris flow velocity in the channel under different rainfall conditions to obtain the rainfall frequency that can trigger large rocks in the channel, which was used as the formation frequency of large low-frequency debris flows in the valley.

[0023] As a preferred implementation, the flood flow under different return periods of rainfall intensity and catchment area is obtained by using the rainfall intensity and catchment area under different return periods of heavy rainfall. The specific calculation formula is as follows:

[0024] Q = qAc;

[0025] Where, Q is the flood flow; q is the design rainstorm intensity; A is the site catchment area; c is the interception coefficient;

[0026] Among them: The rainstorm intensity is calculated according to the regional rainstorm intensity calculation standard. The specific formula is as follows:

[0027]

[0028] Where q is the design rainstorm intensity; P is the design return period; t is the precipitation duration; D, C, e, and n are parameters determined based on local rainfall statistics.

[0029] As a preferred implementation, the Manning formula is used to calculate the flow rate of the water flow in the channel, the slope, channel width and Scheherazade coefficient are used to calculate the area of ​​the cross-section of the channel flood, and the water level depth and flow rate of the channel are obtained. The specific calculation formula is as follows:

[0030]

[0031] The channel is approximated as a rectangle, and the area of ​​the water-passing section is obtained by the hydraulic radius formula; the specific formula is as follows:

[0032]

[0033] Then we get:

[0034]

[0035] In the formula, k is the conversion constant, n is the roughness, R h is the hydraulic radius; S is the slope; a is the area of ​​the water-passing section; P is the wetted perimeter; b is the channel width; and h is the water depth.

[0036] As a preferred implementation, the formula for calculating the startable velocity of large rocks in the valley in the debris flow investigation specification is used to obtain the critical velocity of large rocks. The specific calculation formula is as follows:

[0037]

[0038] Where: V s is the critical velocity of large rocks moving in debris flow; M is the friction coefficient; d max It is the largest stone particle size in the debris flow deposit.

[0039] On the other hand, the present invention also provides a debris flow low frequency evaluation system based on flow velocity calculation, comprising:

[0040] The feature extraction module collects historical large-scale low-frequency debris flow disaster cases, analyzes the valley terrain of historical large-scale low-frequency debris flow disasters, and confirms the terrain characteristics of large-scale low-frequency debris flow disasters;

[0041] The identification module collects the terrain data of the valley to be identified, and identifies whether the valley to be identified is a large-scale low-frequency debris flow disaster valley terrain according to the terrain characteristics;

[0042] The recurrence period calculation module calculates the recurrence period of the valleys identified as potential large-scale low-frequency debris flow hazards based on the flow velocity;

[0043] The early warning module issues corresponding large-scale low-frequency debris flow disaster warnings based on the recurrence period of valleys with potential large-scale low-frequency debris flow disasters and the weather forecast before the recurrence period.

[0044] On the other hand, the present invention further provides an electronic device having a computer program stored thereon, wherein when the computer program is executed by a processor, the method for evaluating the low frequency of debris flow based on flow velocity calculation as described in any embodiment of the present invention is implemented.

[0045] On the other hand, the present invention also provides a computer-readable medium for storing one or more programs. When the one or more programs are executed by the one or more processors, the one or more processors implement a method for evaluating the low frequency of debris flows based on flow velocity calculation as described in any embodiment of the present invention.

[0046] The present invention has the following beneficial effects:

[0047] 1. This method confirms the valley terrain characteristics of historical large-scale low-frequency debris flow disasters by analyzing historical large-scale low-frequency debris flow disaster cases. Through terrain survey, it can quickly identify whether the valley is a potential hazard of large-scale low-frequency debris flow disasters.

[0048] 2. This method evaluates the low frequency of large-scale low-frequency debris flow disasters through velocity calculation, and obtains the recurrence period of large-scale low-frequency debris flow disasters. It only requires on-site site survey combined with the regional rainstorm intensity calculation standard. There is no need to deploy a large number of hardware monitoring equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0050] Figure 1 This is a schematic diagram of the method flow of Example 1;

[0051] Figure 2 It is the low-frequency debris flow compliance map (42 in total);

[0052] Figure 3 This is the proportion of low-frequency debris flow under various slope conditions;

[0053] Figure 4 Satellite image of the debris flow gully to be determined;

[0054] Figure 5 This is the provenance map of the debris flow gully 1 to be determined;

[0055] Figure 6 This is the flow area map of debris flow gully 1 to be determined;

[0056] Figure 7 This is the accumulation area map of debris flow gully 1 to be determined;

[0057] Figure 8 This is the relationship between the slope and horizontal distance of channel 1 (each section is about 6m);

[0058] Fig. 9 Slope and horizontal distance diagram of channel 1 (each section is about 25m);

[0059] Fig.10 Comparison of the calculated flow velocity in the channel at different return periods and the velocity at which large rocks can be moved. DETAILED DESCRIPTION

[0060] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0061] It should be understood that the step numbers used in this document are only for convenience of description and are not intended to limit the order in which the steps are executed.

[0062] It should be understood that the terms used in the present specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0063] The terms “include” and “comprising” indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0064] The term "and / or" means and includes any and all possible combinations of one or more of the associated listed items.

[0065] Embodiment 1:

[0066] In order to make the purpose, technical solutions and advantages of the present invention more clear, the following will be combined with the specific embodiments of the present application and refer to the attached Figure 1 , clearly and completely describe the technical solution of the present invention.

[0067] In order to solve the problems in the prior art, the present invention provides a method for evaluating the low frequency of debris flow based on flow velocity calculation, comprising the following steps:

[0068] Step S1, collecting historical large-scale low-frequency debris flow disaster cases, analyzing the valley terrain of historical large-scale low-frequency debris flow disasters, and confirming the terrain characteristics of large-scale low-frequency debris flow disasters;

[0069] like Figure 2As shown in the figure, the valley terrain of 42 debris flow gullies collected from historical large-scale low-frequency debris flow disaster cases is analyzed. It can be seen that there are valleys with different difference angles in the gully. The proportion of valleys with the largest difference in terrain slope greater than 10 degrees is 40%, and there is an obvious boundary and inflection point at 10 degrees. This shows that in low-frequency debris flow gullies, when the difference slope is about 10 degrees, it is an important sign of low-frequency debris flow. When it is gradually less than 10 degrees, the gully terrain tends to be smooth. Although it is a gully prone to debris flow, it will not form a low-frequency debris flow. When it is gradually greater than 10 degrees, the debris flow gully forms a large resistance when it is washed by upstream water, so it is more difficult to form a debris flow. The difference slope can be used to determine whether it is a low-frequency debris flow valley terrain.

[0070] According to the current standards and research results, the influence of debris flow on the ditch bed is the ditch bed slope when it is not eroded or silted. See Table 1 and Table 2 for details. It can be seen that for the start of debris flow materials, whether there is a critical slope is related to many factors, such as the composition of solid materials in the debris flow, the particle size of large stones, the width and roughness of the ditch, etc., so it is difficult to describe the critical slope with an accurate slope. However, according to relevant domestic and foreign literature and relevant domestic standards, it is generally believed that less than 6° (slope less than 10.5%) is a mildly prone to difficult level, because the debris flow solid materials in the ditch often slow down due to friction and gravitational potential energy under this slope, thereby accumulating. However, when this slope condition exists in the middle of the valley, a source of accumulation will also be generated. Therefore, the present invention uses this slope as an important condition for the source of low-frequency debris flow accumulation, that is, when this condition exists in the middle and upper part of the slope (0-2 / 3 ditch position, starting from the top of the ditch), it belongs to the judgment condition of a large low-frequency debris flow valley.

[0071] Table 1 Longitudinal slope of valleys with different proneness levels

[0072]

[0073]

[0074] Table 2 Summary of research results on non-erosion and non-siltation slope reduction at home and abroad

[0075]

[0076] In order to verify the rationality of the existence of gentle slope sections in low-frequency debris flow channels, this paper uses the collected 42 debris flow channels for analysis. With the increase of channel segment length, the difference in adjacent slopes continues to increase. When it is greater than 25m, the increase decreases. The critical point is in the segment length of 20m to 25m, that is, the critical condition that the difference in adjacent slopes is greater than 10° is met. In order to avoid statistical errors in channel terrain conditions in the future, the segment length of 25m is taken as the judgment condition after historical disaster statistics. Therefore, the scattered points are segmented at a horizontal spacing of 25m, and then the slope of each section is calculated separately. Statistics are performed to see whether each debris flow channel has a condition of less than 4 degrees to 13 degrees. The specific statistical table is shown in Table 3.

[0077] Table 3 Verification of the existence of different gentle slopes (4-13 degrees) and judgment thresholds for low-frequency debris flow channels

[0078]

[0079]

[0080] According to the above and below figures, when the terrain with a gradient of less than 6 degrees is set in the middle and upper part (with 25m as the segmentation condition, the maximum elevation as the starting point, and the terrain segment exists within 0 to 2 / 3 of the valley length) as the condition for judging the gentle section of the debris flow valley, 69% of the debris flow valleys meet this condition, and the overall satisfaction rate is high. For details, see Figure 3 .

[0081] In summary, the judgment conditions for large-scale low-frequency debris flow disasters are mainly based on the terrain conditions of the valley, that is, to judge whether there are "three-stage" valley conditions that are easy to accumulate. Specifically, it is to judge whether there are steep-gentle valley conditions, the difference in terrain slope between two adjacent valley sections is greater than 10 degrees, or there are terrain conditions with a slope of no more than 6 degrees in the area of ​​0 to 2 / 3 of the channel length (calculated from the top).

[0082] Step S2, collecting terrain data of valleys with hidden dangers of large-scale low-frequency debris flow disasters, and identifying whether it is a valley terrain with hidden dangers of large-scale low-frequency debris flow disasters according to the terrain characteristics;

[0083] The terrain data of the valley on the east side of a village was collected. The valley terrain belongs to the mountainous low-middle mountain geomorphic unit, with many gullies developed in a tree-like distribution. The terrain is high in the east and low in the west. The west side is the gully outlet. The village is located in the foothill accumulation landform area about 300m below the gully outlet. According to the on-site investigation, there are mainly 8 gullies (numbered gullies 1 to 8) developed in the mountainous area where the disaster is located. For details, see Figure 4 Whenever there is heavy rainfall, debris frequently washes into the gullies near the village, and there have been two large-scale mudslide disasters recorded by humans.

[0084] Regional landform: The landform of the area where the geological disaster site is located belongs to the tectonic erosion low-mountain landform unit. The surrounding terrain is undulating, with a relative height difference of more than 500m. Gullies are well developed in the area and the cutting is deep. The natural slope of the hillside is mostly 45-60°, and exceeds 70° in some places. The surface vegetation is relatively developed, mainly fir trees and ecological forests, and bedrock is exposed in some places.

[0085] Site topography: The disaster site is located in the mountains to the east of the village. The mountain gullies are well developed and are in the shape of tree branches. The catchment area is about 0.68km 2 The terrain is high in the east and low in the west. The west side is the gully exit. The top elevations on all sides are 520m to 1095m, and the bottom elevation in the middle is 480m to 540m. The overall height difference is about 40m to 555m. The village is located in the foothill accumulation landform area about 300m below the gully mouth. The terrain is relatively flat and open, with an overall slope of about 5°.

[0086] There are 8 gullies (numbered gullies 1 to 8) developed in the mountains. There are two gullies with large-scale debris flow disasters recorded by humans, namely gully 1 and gully 2. This embodiment mainly analyzes gully 1.

[0087] Gully 1: The gully extends for about 810m, with a longitudinal slope of about 12° to 40°, steep at the top and gentle at the bottom. There is surface runoff in the gully all year round, and the flow rate varies greatly with the seasons. It merges into the main gully at an elevation of about 540m. The slope of the upstream of the gully is 45°~65°, and more than 70° in the upper part. The slope cover is thin, most of the bedrock is exposed, the joints and fissures are relatively developed, the slope vegetation is relatively developed, the terrain is deeply cut, and the overall shape is "V". There are still large areas of colluvial deposits and slope deposits distributed at the foot of the slope and the bottom of the gully. The material composition is mainly broken, blocks, and boulders, with a maximum particle size of 3m; the terrain in the middle and lower reaches is generally cut, and the overall shape is an inverted trapezoid. The slopes on both sides have a slope of 30°~40°, and locally reach 45°. The vegetation on the slope is relatively developed, the cover layer is relatively thin, and there are broken stone slope deposits in some concave parts of the slope. The bedrock at the bottom of the gully is exposed, and there are a small amount of broken stones in some parts. The gully bottom is wide at an elevation of 540m~565m, and originally there were stepped paddy fields. In the upstream section of the main ditch (elevation 475m-540m), the bedrock is exposed, with a small amount of broken stones seen in some parts. In the midstream section at an elevation of 415m-475m, sand, broken stones and boulders are seen at the bottom of the ditch. In the midstream section at an elevation of 400m-415m, the bottom and banks of the ditch have been protected by mortar-laid blocks with a thickness of about 0.3m. Sand and broken stones are seen in the downstream section.

[0088] Main ditch: The main ditch has a bottom elevation of 440m to 540m. The terrain is deeply cut in the upper half and shallowly cut in the lower half. It extends for about 1,080m, with a longitudinal slope of about 3° to 12°, and flows into the river through the village. The slopes on both sides are 38° to 40°, the vegetation on the slope is well developed, and the cover layer is thin. The bedrock at the bottom of the ditch is exposed, and there is surface runoff. There are broken stones distributed in the ditch.

[0089] Source area: The length of this section of the gully is about 420m, the average width is about 2m, and the longitudinal slope is about 25°~40°. The longitudinal slope of the section from survey point DC21 to survey point DC24 is about 25°, and the longitudinal slope of the section above survey point DC24 is about 35~40°. The slopes on both sides of this section of the gully are steeper, all 45~65°, and the upper part is more than 70°. The slope cover is thin, most of the bedrock is exposed, the joints and fissures are well developed, the slope vegetation is well developed, and the terrain is deeply cut. According to the on-site investigation, there are still large areas of colluvial deposits and slope deposits distributed at the foot of the slope and the bottom of the gully. The material composition is mainly broken, blocks, and boulders. The maximum particle size can reach 3m, the distribution thickness is about 1~4m, the area is about 5000m2, and the volume is about 10000m3. It is mainly formed by the collapse and accumulation of bedrock exposed on both sides of the slope due to the development of joints and fissures, the crushing of rock mass, and the slope accumulation caused by rainwater erosion. For details, see Figure 5 .

[0090] Flow area: distributed in the area between 440 and 660 m above sea level at the bottom of the gully, the channel is about 915 m long and 2 to 6 m wide, with a trend of being narrow at the top and wide at the bottom, and a longitudinal slope of 10° to 22°, which is conducive to the flow of debris flow. Below the survey point DC19, there is a steep cliff with a slope greater than 75° and a height difference of about 10 m, which is conducive to the flow of debris flow and can generate greater kinetic energy. For details, see Figure 6 .

[0091] Accumulation area: The accumulation area is located in the foothills below the gully with an elevation of 396m to 440m. There are dry fields, villages, paddy fields, etc. The terrain is relatively open with an overall slope of about 5°. According to the drilling data, there are a lot of debris flow deposits in the accumulation area, with a maximum thickness of about 8.50m, fan-shaped distribution, and an estimated area of ​​about 80,000m 2 , with a volume of about 300,000m 3 The material composition is mainly broken stones and boulders. The current village is built on the debris flow accumulation body. For details, see Figure 7 .

[0092] In this embodiment, identifying whether the ditch 1 is a large-scale low-frequency debris flow disaster gully terrain includes the following steps:

[0093] Filter the terrain of channel 1 to remove abnormal terrain lines and reverse slope conditions;

[0094] Scatter points are segmented at a horizontal interval of 25m;

[0095] Then, a straight line is fitted according to the segmented scattered data, the k and b coefficients of the straight line are determined, and the slope and inclination are calculated; Figure 8 Fig. 9 .

[0096] from Figure 8 and Fig. 9It can be seen that there is a steep change between channel 1 and the upstream channel at a horizontal distance (730m-830m, from the top of the slope projection of 0), especially in the 0-600m section, the slope is greater than 30 degrees, and in the next channel (730-830m section), the slope drops sharply to 3-10 degrees. Therefore, it shows that there is a steep and rapid change section in the channel. On the other hand, there is a terrain with a slope of less than 13 degrees in the middle and lower part of the channel, which meets the qualitative identification characteristics of large-scale low-frequency debris flow disaster valleys.

[0097] Step S3, calculating and identifying the recurrence period of the valley with the potential risk of large-scale low-frequency debris flow disasters based on the flow velocity.

[0098] Gully 1 in the site: The material composition of the source area is mainly composed of crushed, lumpy and boulders, with a maximum particle size of 3m, a distribution thickness of about 1m to 4m, an average width of about 2m, and a longitudinal slope of about 25 to 40°; bedrock is visible at the bottom of the gully in the current circulation area, and a small amount of sand, crushed and lumpy stones can be seen in some parts. The particle size of the crushed and lumpy stones is mostly 5cm to 30cm, and some can reach 50cm. The overall volume is small, the width is about 2m to 6m, and it tends to be narrow at the top and wide at the bottom, with a longitudinal slope of 10 to 22°.

[0099] In this embodiment, the recurrence period of the valley identified as a potential large-scale low-frequency debris flow disaster is calculated based on the flow velocity, and the following steps are included:

[0100] Step S301, using the rainfall intensity and catchment area of ​​different return periods under the action of heavy rainfall to obtain the flood flow under different return period rainfall intensity;

[0101] The formula for calculating rainstorm intensity is based on the "Rainstorm Intensity Calculation Standard" DBJT 13-52-2021:

[0102]

[0103] Among them, q is the design rainstorm intensity; P is the design recurrence period; t is the rainfall duration, which is 20 minutes.

[0104] According to the intensity of rainstorm, the flood flow under different rainfall return periods can be obtained;

[0105] Flood flow Q = qAc = Va, where c is the interception coefficient, which is taken as 0.5, and A is the catchment area of ​​the site, which is taken as 0.68 km 2 .

[0106] Thus we can get:

[0107]

[0108] In the formula, V is the flood velocity; a is the area of ​​the flood section.

[0109] Step S302, using the Manning formula to calculate the flow velocity of the water flow in the channel, using the slope, channel width and Schertz coefficient to calculate the area of ​​the channel flood cross-section, and obtaining the water level depth and flow velocity of the channel;

[0110] It is known that the width of the debris flow is 2m. According to the formula of Xie Cai and Manning, the channel is approximated as a rectangle and calculated by the following formula:

[0111]

[0112] in:

[0113]

[0114] but:

[0115]

[0116] Wherein, Q is the flood flow; k is the conversion constant, which is 1 in the International System of Units; n is the roughness, which is 0.025 in this embodiment; R h is the hydraulic radius (m). If the channel is simplified into a rectangle, then the hydraulic radius is the quotient of the area and the perimeter. In this embodiment, the channel width b=2m; S is the slope, which can generally be replaced by the longitudinal slope of the channel bed. In this case, it is taken as 0.087; a is the area of ​​the water-passing section; P is the wetted perimeter; and h is the water depth.

[0117] Step S303, using the calculation formula for the startable flow velocity of large rocks in the valley in the debris flow investigation specification, the critical flow velocity can be obtained;

[0118] According to the flow rate that can be started by large rocks at 3m, the critical flow rate for the movement of large rocks in this valley is:

[0119]

[0120] Where: V s is the critical velocity of large rocks moving in debris flow; A is the friction coefficient; d max is the largest stone particle size in the debris flow deposit. The calculated critical speed of large stone movement is approximately taken as the flow velocity of the debris flow.

[0121] Step S304 compares the flow velocity of the large rocks with the debris flow velocity of the channel under different rainfall conditions to obtain the rainfall frequency that can activate the large rocks in the channel, and uses it as the formation frequency of large low-frequency debris flows in the valley.

[0122] Through steps S301-S303, the flow velocity of the channel under different rainfall return periods is calculated. By comparing the channel flow velocity with the theoretical startable flow velocity of large rocks in the channel, the return period of debris flow in the valley is obtained. The specific calculation results are shown in Table 6 and Fig.10As shown in the figure, it can be seen that when the rainfall recurrence period is 25 years, the flow velocity in the ditch is greater than the movable velocity of large rocks, thus determining that a debris flow disaster can be induced. Therefore, the recurrence period of this valley inducing a debris flow disaster again is 25 years.

[0123] Table 6 Calculation process data of the flow velocity of the channel under different return periods and the flow velocity at which large rocks can be moved

[0124]

[0125] Step S4, issuing a corresponding large-scale low-frequency debris flow disaster warning according to the recurrence period of the valley with potential large-scale low-frequency debris flow disaster in combination with the weather forecast before the recurrence period.

[0126] Embodiment 2:

[0127] This embodiment provides a debris flow low frequency evaluation system based on flow velocity calculation, including:

[0128] The feature extraction module collects historical large-scale low-frequency debris flow disaster cases, analyzes the valley terrain of historical large-scale low-frequency debris flow disasters, and confirms the terrain characteristics of large-scale low-frequency debris flow disasters;

[0129] The identification module collects the terrain data of the valley to be identified, and identifies whether the valley to be identified is a large-scale low-frequency debris flow disaster valley terrain according to the terrain characteristics;

[0130] The recurrence period calculation module calculates the recurrence period of the valleys identified as potential large-scale low-frequency debris flow hazards based on the flow velocity;

[0131] The early warning module issues corresponding large-scale low-frequency debris flow disaster warnings based on the recurrence period of valleys with potential large-scale low-frequency debris flow disasters and the weather forecast before the recurrence period.

[0132] Embodiment three:

[0133] This embodiment provides an electronic device having a computer program stored thereon. When the computer program is executed by a processor, a method for evaluating the low frequency of debris flow based on flow velocity calculation as described in any embodiment of the present invention is implemented.

[0134] Embodiment 4:

[0135] This embodiment provides a computer-readable medium for storing one or more programs. When the one or more programs are executed by the one or more processors, the one or more processors implement a method for evaluating the low frequency of debris flows based on flow velocity calculation as described in any embodiment of the present invention.

[0136] In the embodiments of the present application, "at least one" refers to one or more, and "more than one" refers to two or more. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent the existence of A alone, the existence of A and B at the same time, and the existence of B alone. Among them, A and B can be singular or plural. The character " / " generally indicates that the previous and next associated objects are in an "or" relationship. "At least one of the following" and similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one of a, b and c can be represented by: a, b, c, a and b, a and c, b and c, or a and b and c, where a, b, c can be single or multiple.

[0137] Those of ordinary skill in the art will appreciate that the various units and algorithm steps described in the embodiments disclosed herein can be implemented in a combination of electronic hardware, computer software, and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this application.

[0138] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0139] In several embodiments provided in the present application, if any function is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present application, or the part that contributes to the prior art or the part of the technical solution, can be embodied in the form of a software product, which is stored in a storage medium and includes several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present application. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (Read-Only Memory; hereinafter referred to as: ROM), random access memory (Random Access Memory; hereinafter referred to as: RAM), disk or optical disk, and other media that can store program codes.

[0140] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for evaluating the low frequency of debris flow based on velocity calculation, characterized in that: The following steps are involved: Step S1, collecting historical large-scale low-frequency debris flow disaster cases, analyzing the valley terrain of historical large-scale low-frequency debris flow disasters, and confirming the terrain characteristics of large-scale low-frequency debris flow disasters; Step S2, collecting the terrain data of the valley to be identified, and identifying whether the valley to be identified is a large-scale low-frequency debris flow disaster valley terrain according to the terrain characteristics; Step S3, calculating the recurrence period of the valley identified as a potential large-scale low-frequency debris flow disaster based on the flow velocity; Step S4, issuing a corresponding large-scale low-frequency debris flow disaster warning according to the recurrence period of the valley with potential large-scale low-frequency debris flow disaster in combination with the weather forecast before the recurrence period.

2. The method for evaluating low frequency of debris flow based on velocity calculation according to claim 1, characterized in that: The terrain characteristics of large-scale low-frequency debris flow disasters are confirmed, wherein the terrain characteristics for identifying large-scale low-frequency debris flow disasters are that the difference in terrain slope between two adjacent valley sections is greater than 10 degrees, or there is a terrain condition in which the slope is not greater than 6 degrees in the area of ​​0 to 2 / 3 of the channel length.

3. The method for evaluating low frequency of debris flow based on velocity calculation according to claim 1, characterized in that: The method of identifying whether the terrain is a large-scale low-frequency debris flow disaster valley terrain according to the terrain characteristics comprises the following steps: Filter the terrain data of valleys and gullies with large-scale low-frequency debris flow hazards to remove abnormal terrain lines and reverse slope conditions; Based on the historical large-scale low-frequency debris flow disaster cases, the horizontal spacing of the critical points with the maximum difference in the slope of the valley terrain greater than 10 degrees is used to segment the scattered points; Then, a straight line is fitted according to the segmented scattered data, the k and b coefficients of the straight line are determined, and the slope and inclination are calculated; The segmented slope is obtained based on the calculated slope and inclination to confirm whether it meets the terrain characteristics of large-scale low-frequency debris flow disasters.

4. The method for evaluating low frequency of debris flow based on velocity calculation according to claim 1, characterized in that: The method of calculating the recurrence period of the valley identified as a potential hazard of large-scale low-frequency debris flow disaster according to the flow velocity comprises the following steps: Using the rainfall intensity and catchment area of ​​different return periods under heavy rainfall, the flood flow under different return period rainfall intensity is obtained; The flow velocity of the water in the channel is calculated using the Manning formula, and the area of ​​the cross-section of the channel flood is calculated using the slope, channel width and Scheher coefficient to obtain the water level depth and flow velocity of the channel; The critical velocity is obtained by using the formula for calculating the velocity of large rocks in the valley that can be activated in the debris flow investigation specification; The triggering flow velocity of large rocks was compared with the debris flow velocity in the channel under different rainfall conditions to obtain the rainfall frequency that can trigger large rocks in the channel, which was used as the formation frequency of large low-frequency debris flows in the valley.

5. The method for evaluating low frequency of debris flow based on velocity calculation according to claim 4, characterized in that: The flood flow under different rainfall intensities and return periods under heavy rainfall is obtained by using the rainfall intensity and catchment area under different return periods. The specific calculation formula is as follows: Q = qAc; Where, Q is the flood flow; q is the design rainstorm intensity; A is the site catchment area; c is the interception coefficient; Among them: The rainstorm intensity is calculated according to the regional rainstorm intensity calculation standard. The specific formula is as follows: Where q is the design rainstorm intensity; P is the design return period; t is the precipitation duration; D, C, e, and n are parameters determined based on local rainfall statistics.

6. The method for evaluating low frequency of debris flow based on velocity calculation according to claim 4, characterized in that: The Manning formula is used to calculate the flow rate of the water flow in the channel, and the slope, channel width and Scheher coefficient are used to calculate the area of ​​the cross-section of the channel flood, and the water level depth and flow rate of the channel are obtained. The specific calculation formula is as follows: The channel is approximated as a rectangle, and the area of ​​the water-passing section is obtained by the hydraulic radius formula; the specific formula is as follows: Then we get: In the formula, k is the conversion constant, n is the roughness, R h is the hydraulic radius; S is the slope; a is the area of ​​the water-passing section; P is the wetted perimeter; b is the channel width; and h is the water depth.

7. The method for evaluating low frequency of debris flow based on velocity calculation according to claim 4, characterized in that: The formula for calculating the startable velocity of large rocks in the valley in the debris flow investigation specification is used to obtain the critical velocity of large rocks. The specific calculation formula is as follows: Where: V s is the critical velocity of large rocks moving in debris flow; M is the friction coefficient; d max It is the largest stone particle size in the debris flow deposit.

8. A debris flow low frequency evaluation system based on flow velocity calculation, characterized in that: include: The feature extraction module collects historical large-scale low-frequency debris flow disaster cases, analyzes the valley terrain of historical large-scale low-frequency debris flow disasters, and confirms the terrain characteristics of large-scale low-frequency debris flow disasters; The identification module collects the terrain data of the valley to be identified, and identifies whether the valley to be identified is a large-scale low-frequency debris flow disaster valley terrain according to the terrain characteristics; The recurrence period calculation module calculates the recurrence period of the valleys identified as potential large-scale low-frequency debris flow hazards based on the flow velocity; The early warning module issues corresponding large-scale low-frequency debris flow disaster warnings based on the recurrence period of the valleys with potential large-scale low-frequency debris flow disasters and the weather forecast before the recurrence period.

9. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the program, the method for evaluating the low frequency of debris flow based on flow velocity calculation as described in any one of claims 1 to 7 is implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the method for evaluating the low frequency of debris flow based on flow velocity calculation as described in any one of claims 1 to 7 is implemented.

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