Method for judging moraine lake outburst risk and application

Abstract

According to the moraine lake outburst risk judgment method and the application, a moraine lake outburst susceptibility judgment factor and a conversion value thereof, a glacial lake outburst debris flow occurrence possibility evaluation factor and a conversion value thereof, a main river blockage possibility judgment factor and a conversion value thereof of debris flow, and a conversion value of moraine lake outburst in a main river flood peak flow are calculated; and calculating a comprehensive moraine lake outburst risk discriminant value according to the conversion value and judging a moraine lake outburst risk grade. Aiming at the characteristics of moraine lake outburst danger, according to multiple conditions such as outburst flood, debris flow, main river blockage and flood formed by re-outburst which influence the moraine lake outburst danger, one-by-one analysis and comprehensive consideration are performed, so that the accuracy of a moraine lake outburst danger judgment result is improved, and the accuracy of the moraine lake outburst danger judgment result is improved. And the flood peak flow factor which affects the dangerousness to the greatest extent is considered prominently, so that the dangerousness evaluation result is more reasonable and more reliable.

Description

Technical Field

[0001] The invention belongs to the technical field of flood and debris flow prevention and control engineering and water conservancy engineering, and specifically relates to a method for judging the danger of moraine lake outburst. The invention also relates to the application of the method for judging the danger of moraine lake outburst. Background Art

[0002] Glacial lakes in high-cold mountainous areas often experience glacial lake outbursts, forming large-volume outburst floods. When there are sufficient material sources and channel slopes downstream, debris flows often form. Because the debris flows formed by such glacial lake outbursts have the characteristics of large flow and huge total volume, they may also block the main river channel downstream and burst again to form larger mountain torrents, causing great harm to riverside facilities, roads, residents, etc. along the downstream river channel, forming a disaster chain effect, and causing serious damage to the downstream mountainous areas.

[0003] Moraine lakes may burst, so an important factor affecting the risk of Moraine Lake burst is the susceptibility of Moraine Lake burst. The higher the susceptibility, the greater the risk of Moraine Lake burst. Moraine Lake bursts and forms a burst flood, which may form a debris flow, but it does not necessarily form a debris flow. Research is still needed to determine whether a debris flow will occur. The higher the possibility of a debris flow after Moraine Lake bursts, the greater the risk of Moraine Lake burst. Even if a debris flow is formed after Moraine Lake bursts, the debris flow in the downstream main river channel will not necessarily cause the main river to be completely blocked. It is also necessary to determine whether the main river will be blocked. If the main river is completely blocked, it may burst again, forming a burst flood with a larger flow, causing huge damage to the downstream, and forming a disaster chain effect. Therefore, the greater the possibility of the main river being blocked by a debris flow, the greater the risk of Moraine Lake burst. The peak flow of floods or debris flows after the outburst of a moraine lake, or the peak flow of floods that block the main river and then burst, will affect the safety of roads, railways, hydropower, residents and other places and facilities downstream of the moraine lake and downstream of the confluence of the main river, and is a key factor in judging the danger of a moraine lake outburst.

[0004] Although current research and technology have made important progress in the susceptibility of moraine lake outbursts, the possibility of rare debris flows blocking rivers, and other important aspects related to the danger of moraine lake outbursts, there is still a lack of methods and technologies for judging the possibility of debris flows after moraine lake outbursts, as well as methods and technologies for calculating the peak flow rate of outbursts after debris flows block rivers, and even more so, a comprehensive method for judging the danger of moraine lake outbursts. At present, the research on the possibility of debris flows at home and abroad is mainly focused on the possibility of valley debris flows and slope debris flows. The inducing factors are rainfall, so the catchment area of ​​valley debris flows and the slope gradient of slope debris flows have an important influence on the formation of these two types of debris flows. However, the biggest influence is rainfall, because rainfall is both an inducing factor and a water source condition for the formation of debris flows. Other influencing factors include: 1) Valley debris flow: source conditions of debris flow: source particle size, source lithology, weathering degree, structure, fault zone, etc.; terrain conditions of debris flow: longitudinal gradient of channel, basin area, basin shape coefficient, gully length, height difference, basin development degree, etc. 2) Slope debris flow: source conditions: parent rock lithology, soil permeability, clay mineral characteristics and content, etc.; terrain conditions: slope, soil thickness, width, etc. However, the probability of occurrence of these debris flows is far different from the probability of occurrence of debris flows caused by the outburst of moraine lakes: first, the inducing factors, that is, the water source conditions are completely different. The debris flows caused by the outburst of moraine lakes are concentrated with huge peak flows of moraine lake outbursts; second, the channels downstream of moraine lakes are very wide "U"-shaped valleys due to glacial erosion and a large basin area, and the longitudinal gradient of the channels is relatively small; finally, the material source conditions are often relatively rich and scattered in the wide channels downstream of moraine lakes. Therefore, the original probability of occurrence of valley debris flows is completely inappropriate for the probability of occurrence of debris flows caused by the outburst of this type of moraine lake. The study of the peak flow of the outburst flood formed by the dam body being eroded and destroyed by water flow has a history of many years, but it is mainly simulated and calculated through parameters such as dam body height, dam body length, dam body structure, breach width, and dam body breach time. For a potential dam that blocks the main river (its height, length, structure, breach width, etc. are uncertain), it is unrealistic to use these detailed data to predict the dam burst flow. A simple and practical method is required to determine the calculation method of the peak flood flow after the glacial lake bursts and forms a debris flow that blocks the river and then bursts.

[0005] Currently, there is no comprehensive technical solution for assessing the hazard of moraine lake outburst that takes into account factors such as the susceptibility of moraine lake outburst, the possibility of mudslides after outburst, the possibility of mudslides blocking the main river, and the peak flow of floods caused by dam outburst. However, the major strategic needs for the development and construction of roads, railways, hydropower, residents, and mountainous areas in the western high-altitude mountainous areas have made the assessment of the hazard of moraine lake outburst increasingly important, and this problem needs to be solved urgently. Summary of the invention

[0006] The purpose of the present invention is to provide a method for judging the danger of moraine lake outburst, which solves the problem of low reliability of the existing method for judging the danger of moraine lake outburst.

[0007] Another object of the present invention is to provide an application of a method for determining the hazard of a moraine lake outburst.

[0008] The first technical solution adopted by the present invention is: a method for judging the danger of moraine lake outburst, comprising the following steps: Step 1, calculate the susceptibility discriminant factor P1 of moraine lake outburst and its conversion value Z1; Step 2, calculate the possibility assessment factor P2 of glacial lake outburst debris flow and its conversion value Z2; Step 3, calculate the possibility judgment factor P3 of debris flow blocking the main river and its conversion value Z3; Step 4, calculate the conversion value Z4 of the moraine lake outburst in the main river flood peak flow; Step 5, calculating the comprehensive moraine lake outburst hazard judgment value P according to the conversion values ​​Z1, Z2, Z3 and Z4; Step 6: Determine the hazard level of the moraine lake outburst according to the moraine lake outburst hazard discrimination value P.

[0009] The first technical solution of the present invention is also characterized in that: Step 1 specifically includes the following steps: Step 1.1: Calculate the susceptibility factor P1 of moraine lake outburst using formula (1): P1=2.88X+0.72G+0.6R+0.5D+S+0.06T (1) In formula (1), X is the slope factor of the parent glacier, which is calculated by formula (2); G is the volume factor of the dangerous ice body and moraine lake, which is calculated by formula (3); R is the ice avalanche movement factor, which is calculated by formula (4). If R>2, then R=2; D is the slope factor of the back slope of the moraine embankment, which is calculated by formula (5); S is the slope factor of the dangerous ice body, which is calculated by formula (6); T is the equivalent annual average temperature of the dangerous ice body, which is calculated by formula (7); X = sin(θ / 2)(2) In formula (2), θ is the slope of the parent glacier, , in the northern hemisphere, it refers to the angle between the plane normal of the parent glacier and the due north when projected on the plane; in the southern hemisphere, it refers to the angle between the plane normal of the parent glacier and the due south when projected on the plane; (3) In formula (3), is the volume of dangerous ice, calculated by formula (8); is the volume of the moraine lake, calculated by formula (9); R=H / L (4) In formula (4), H is the vertical height difference between the center of mass of the dangerous ice body and the ice lake; L is the movement distance from the center of mass of the dangerous ice body to the ice lake; D = tanβ (5) In formula (5), β is the slope of the backwater slope of the moraine embankment; S = tanα (6) In formula (6), α is the slope of dangerous ice at the rear edge of the glacial lake; (7) In formula (7), is the annual average temperature of the local meteorological station; c is the coefficient, c=0.006; is the altitude difference between the center of mass of the dangerous ice body and the local meteorological station; (8) In formula (8), is the area of ​​dangerous ice, calculated by formula (10); h is the thickness of dangerous ice, calculated by formula (11) for marine glaciers, by formula (12) for continental glaciers, and by formula (13) for hanging glaciers; (9) In formula (9), A is the area of ​​moraine lake; (10) In formula (10), W is the lateral crack width of the dangerous ice body; It is the distance between the transverse crack at the rear end of the dangerous ice body and the front end of the dangerous ice body; (11) (12) (13) In formulas (11), (12), and (13), F is the area of ​​the parent glacier; Step 1.2, calculate the conversion value Z1 based on the susceptibility discrimination factor P1 of glacial lake outburst: when P1≥3.25, the susceptibility of glacial lake outburst is judged to be high, and the conversion value Z1 is set to 1; when 2≤P1<3.25, the susceptibility of glacial lake outburst is judged to be medium, and the conversion value Z1 is set to 0.5; when P1<2, the susceptibility of glacial lake outburst is judged to be low, and the conversion value Z1 is set to 0.

[0010] Step 2 specifically includes the following steps: Step 2.1: Calculate the probability assessment factor P2 of glacial lake outburst debris flow using formula (14): (14) In formula (14), is the peak flow of the moraine lake outburst flood, calculated by formula (15); S1 is the average longitudinal gradient of the channel downstream of the moraine lake, calculated by formula (16); g is the gravitational acceleration; is the average width of the channel downstream of the GLOF; d is the characteristic value of the particle size in the downstream basin of the GLOF, calculated by formula (17); (15) S1 = tanγ (16) In formula (16), γ is the channel slope downstream of the moraine lake; (17) In formula (17), is the solidity coefficient, which is determined by the lithology in the downstream area of ​​the GLOF; Step 2.2, calculate the conversion value Z2 based on the evaluation factor P2 of the possibility of glacial lake outburst debris flow: when P2≥3.8, it is judged that the possibility of debris flow is high, and the conversion value Z2 is set to 1; when 2≤P2<3.8, it is judged that the possibility of debris flow is medium, and the conversion value Z2 is set to 0.5; when P2<2, it is judged that the possibility of debris flow is low, and the conversion value Z2 is set to 0.

[0011] Step 3 specifically includes the following steps: Step 3.1: Calculate the probability factor P3 of debris flow blocking the main river through formula (18): (18) In formula (18), is the debris flow volume, calculated by formula (19); The particle size of 50% of the particles in a rare debris flow is replaced by the characteristic particle size d; is the peak flow of debris flow, calculated by formula (20); Φ is the intersection angle between the debris flow tributary and the main river; is the water depth of the main river, calculated by formula (22); B is the width of the main river at the confluence; b is the width of the debris flow branch ditch at the confluence; For main river flow; (19) (20) In formula (19) and (20), is the volume concentration of sediment in debris flow, calculated by formula (21); (twenty one) (twenty two) In formula (22), J is the longitudinal gradient of the main river channel at the confluence; Step 3.2: Calculate its conversion value Z3 based on the discriminant factor P3 of the possibility of debris flow blocking the main river: When P3 < 24.1, it is judged that the possibility of river blocking is small, and the conversion value Z3 is set to 0; when P3 ≥ 24.1, it is judged that the possibility of river blocking is large, and the conversion value Z3 is set to 1.

[0012] Step 4 specifically includes the following steps: Step 4.1: Calculate the peak discharge of the outburst flood through Equation (23) : (23) In Equation (23), is the water depth above the breach when the debris flow barrier bursts, which is calculated by Equation (24); is the reservoir volume above the breach when the debris flow barrier bursts, which is calculated by Equation (26); (24) In Equation (24), is the debris flow accumulation range when the debris flow blocks the river, which is calculated by Equation (25); (25) (26) In Equation (26), is the backwater inundation range of the barrier lake calculated according to the water depth below the water surface ; Step 4.2: Determine the conversion value Z4 of the peak discharge of the main river during the outburst of the moraine lake: When Z1 = Z2 = 0, Z4 = 1; When Z2 > 0 but Z3 = 0, ; when Z4 = 1; When Z3 > 0, or , take the larger Z4 value, but and when, Z4 = 1.

[0013] In Step 5, calculate the comprehensive discriminant value P of the outburst risk of the moraine lake through Equation (27): P = Z1 + Z2 + Z3 + Z4 (27).

[0014] Step 6 is specifically: Condition 1: When P ≤ 2 and Z1 = 0.5, or when Z1 = 0, it is judged that the outburst risk level of the moraine lake is "low"; When P ≤ 2 and Z1 = 1, or when 2 < P ≤ 4 and Z1 = 0.5, it is judged that the outburst risk level of the moraine lake is "medium"; When 2 < P ≤ 4 and Z1 = 1, or when P > 4 and Z1 = 0.5, it is judged that the risk level of moraine lake outburst is "high"; When P > 4 and Z1 = 1, it is judged that the risk level of moraine lake outburst is "very high"; Condition two: When 、 or any one of them is greater than 1000 When, on the basis of the risk level of moraine lake outburst judged by Condition 1, it is upgraded by one level, where the risk level of moraine lake outburst judged by Condition 1 is "very high" or when Z1 = 0, it will no longer be upgraded on the basis of Condition 1.

[0015] The second technical solution adopted by the present invention is: the application of the method for judging the risk of moraine lake outburst. Using the above method for judging the risk of moraine lake outburst, it is applicable to judging the risk level of moraine lake outburst in alpine mountainous areas.

[0016] The beneficial effects of the present invention are: the method for judging the risk of moraine lake outburst and its application of the present invention, aiming at the characteristics of the risk of moraine lake outburst, according to multiple conditions affecting the risk of moraine lake outburst, such as outburst flood, debris flow, blocking the main river, and forming flood again due to re-outburst, etc., are analyzed one by one and comprehensively considered, improving the accuracy of the judgment result of the risk of moraine lake outburst, and highlighting the consideration of the peak discharge factor with the greatest impact on the risk, making the risk assessment result more reasonable and reliable. Specific implementation manners

[0017] The present invention will be described in detail below in conjunction with specific implementation manners.

[0018] Example 1 The outburst of moraine lakes often further induces debris flows, but not necessarily all will form debris flows. First, the flood discharge of the outburst of moraine lakes is very large, providing sufficient water sources for the formation of debris flows; second, sufficient material sources are needed to form debris flows; finally, certain topographic conditions are also required to enable the formed debris flows to continuously move downstream, rather than just silt up immediately after the formation of debris flows.

[0019] Water source, material source, topography and other conditions are the three major conditions for the formation of debris flow, but these conditions do not affect the formation of debris flow in isolation, but are interrelated and influence each other, and eventually form debris flow. Although the peak flow of moraine lake burst is very large, it will be weakened in the wide downstream channel, resulting in a smaller single-width flow and flow rate, which makes it difficult to start the channel material source to form debris flow; similarly, if the channel material source particles are large, the single-width flow or flow rate after the moraine lake burst is not enough to start these material sources, and debris flow will not form. The particle size of the debris flow source comes from the collapse or landslide in the area, and the hard rock (solidity coefficient Large) often collapses, which makes the source of the area not only less, but also the particle size of the source is large, making it relatively difficult to form debris flow; soft rock (firmness coefficient Landslides often occur in areas with large sources of material, which makes the source material particles in this area small, and it is relatively easy to form debris flows. Another factor that affects the formation of debris flows is topography. For the characteristic of debris flows formed by the outburst of moraine lakes, the topographic factors are the longitudinal gradient and width of the channel downstream of the moraine lake: if the longitudinal gradient is too small, even if a debris flow is formed briefly, it will be silted up due to the small longitudinal gradient; when the longitudinal gradient is large, the debris flow will move all the way downstream to the main river mouth. At the same time, because the downstream channel is wide, it will also have a huge impact on the formation of debris flows: the wider the channel, the debris flow is dispersed, and it is easier to silt up when the longitudinal gradient of the channel is small; on the contrary, it is less likely to silt up when the channel is narrow. Because the channels downstream of moraine lakes are generally wide channels (because the basin area is large and the long-term glacial erosion forms a wide "U"-shaped valley), the downstream channel needs a larger average slope for debris flows to occur.

[0020] The body of a landslide dam is damaged by erosion from the water flow, and the calculation of the peak flow rate of an outburst flood often requires many parameters, but they are difficult to obtain in practice. The method of using the water depth above the breach and reservoir capacity when the debris flow blocks the river to calculate the peak flow rate of the outburst flood after the debris flow blocks the river is simple and reliable. The calculation of the height of a landslide dam requires consideration of the debris flow accumulation range, which is related to the intersection angle, and the calculation result is more reasonable.

[0021] The process of moraine lake bursting to form floods, debris flows, blockage of the main river, and then bursting to form floods is a very complex process, involving multiple key issues such as moraine lake bursting, burst flood peak flow, formation of debris flows and their peak flow, debris flows blocking the main river, and burst flood peak flow of landslide dams. Without the risk assessment of any of these links, it is difficult to correctly assess the risk of moraine lake bursting. However, there is currently no moraine lake burst risk assessment method that comprehensively considers these factors and conditions. The moraine lake burst risk judgment method provided by the present invention comprehensively considers these conditions and their relationship with the moraine lake burst risk, especially the important influence of the final peak flow, so that the risk assessment result is practical and reliable.

[0022] The main features of the method for determining the danger of moraine lake outburst provided by the present invention are as follows: 1) According to the characteristics of the outburst hazard of moraine lakes, the outburst floods, debris flows, blockage of the main river, floods caused by re-outburst and other conditions that affect the outburst hazard of moraine lakes are analyzed one by one and a comprehensive judgment is made. This can effectively determine the outburst hazard of moraine lakes and greatly improve the accuracy of the judgment results of the outburst hazard of moraine lakes.

[0023] 2) The peak flow of moraine lake outburst is the key to the formation of debris flow and also the water source condition for the formation of debris flow. Firstly, the peak flow of moraine lake outburst is calculated, which provides an important basis for correctly judging the possibility of moraine lake outburst forming debris flow, making the final judgment more reliable.

[0024] 3) Fully considering the source conditions of debris flow is a key factor: the outburst of moraine lake without source is a flash flood rather than a debris flow. The solidity coefficient of the regional lithology of the source is used to judge the amount of source and the particle size of the source, and further judge the possibility of debris flow formation, making the judgment result more applicable.

[0025] 4) The important influence of terrain conditions on the formation of debris flows caused by the outburst of moraine lakes was fully considered, and the average longitudinal gradient (average slope) and average width of the channel downstream of the moraine lake were used as terrain judgment parameters for the formation of debris flows, making the judgment of the possibility of debris flows more reasonable and reliable.

[0026] 5) Considering the uncertainty of the barrier dam, the method of using the water depth above the breach and reservoir capacity when the debris flow blocks the river and then breaks the peak flow is simple, reliable and more applicable.

[0027] 6) Taking into account the possibility of debris flow forming a barrier dam, the influence of the intersection angle is fully utilized and the accumulation range of the debris flow is reasonably calculated, making the calculation of the water depth of the barrier lake more reasonable.

[0028] 7) Comprehensively consider multiple influencing factors that affect the risk of moraine lake outburst, highlight the flood peak flow factor that has the greatest impact on the risk, and give it the greatest influence in calculating the risk judgment factor, so that the risk assessment results are more reliable and reasonable.

[0029] Example 2 The present invention provides a method for determining the danger of moraine lake outburst, comprising the following steps: 1) Determine the basic parameters of the moraine lake through Google Earth, including the slope of the mother glacier θ, the slope of the moraine embankment β, the slope of the dangerous ice body at the rear edge of the glacial lake α, the vertical height difference H from the center of mass of the dangerous ice body to the glacial lake, the movement distance L from the center of mass of the dangerous ice body to the glacial lake, the width W of the lateral cracks of the dangerous ice body, and the distance between the lateral cracks at the rear end of the dangerous ice body and the front end of the dangerous ice body , the area of ​​the mother glacier F, the area of ​​the moraine lake A, and the altitude difference between the centroid of the dangerous ice body and the local meteorological station .

[0030] 2) Calculate the susceptibility factor P1 of moraine lake outburst according to formula (1); P1=2.88X+0.72G+0.6R+0.5D+S+0.06T (1) Where: P1 is the susceptibility factor of moraine lakes, X is the slope factor of the parent glacier, calculated by formula (2); X = sin(θ / 2)(2) G is the volume factor of dangerous ice and moraine lake, calculated by formula (3); (3) R is the ice avalanche motion factor, which is calculated by formula (4). If R>2, then R=2; R=H / L (4) D is the slope factor of the back slope of the moraine embankment, which is calculated by formula (5); D = tanβ (5) S is the dangerous ice body slope factor, calculated by formula (6); S = tanα (6) T is the equivalent annual average temperature of the dangerous ice body, calculated by formula (7); (7) Where: θ is the slope of the parent glacier, , in the northern hemisphere, it refers to the angle between the plane normal of the parent glacier and the due north when projected on the plane; in the southern hemisphere, it refers to the angle between the plane normal of the parent glacier and the due south when projected on the plane; is the volume of dangerous ice ( ), calculated by formula (8); is the volume of the moraine lake ( ), calculated by formula (9); H is the vertical height difference from the center of mass of the dangerous ice body to the glacial lake (m); L is the distance from the center of mass of the dangerous ice body to the ice lake (m); β is the slope of the backwater slope of the moraine bank (degrees); α is the slope of dangerous ice at the rear edge of the glacial lake (degrees); is the annual average temperature of the local weather station (degrees), obtained by consulting local meteorological data; c is the coefficient, c=0.006; The altitude difference between the center of mass of the dangerous ice body and the local meteorological station (m); (8) (9) Where: A is the area of ​​moraine lake ( ); is the dangerous ice area ( ), calculated by formula (10); (10) Where: W is the width of the lateral crack of the dangerous ice body (m); is the distance between the transverse crack at the rear end of the dangerous ice body and the front end of the dangerous ice body (m); h is the thickness of dangerous ice (m). When it is a marine glacier, it is calculated by formula (11); when it is a continental glacier, it is calculated by formula (12); when it is a hanging glacier, it is calculated by formula (13); (11) (12) (13) Where: F is the area of ​​the parent glacier ( ); 3) The susceptibility of glacial lake outburst is judged by the susceptibility discrimination factor P1. When P1≥3.25, the susceptibility of glacial lake outburst is high; when 2≤P1<3.25, the susceptibility of glacial lake outburst is medium; when P1<2, the susceptibility of glacial lake outburst is low.

[0031] 4) The basic parameters of the channel downstream of the moraine lake were determined through Google Earth, including the slope of the channel downstream of the moraine lake, the average width of the channel downstream of the glacial lake outburst, and the main lithology in the downstream area of ​​the glacial lake outburst.

[0032] 5) Calculate the probability assessment factor P2 of glacial lake outburst debris flow, which is determined according to formula (14): (14) Where: P2 is the probability judgment value of debris flow; is the peak discharge of the moraine lake outburst flood ( ), calculated by formula (15); S1 is the average longitudinal gradient of the channel downstream of the moraine lake, calculated by formula (16); g is the acceleration due to gravity; is the average width of the downstream channel of the GLOF (m); d is the characteristic value of particle size in the downstream watershed of the GLOF (m), calculated by formula (17); (15) S1 = tanγ (16) (17) Where: γ is the channel slope downstream of the moraine lake; is the strength coefficient, which is determined by the main lithology in the downstream area of ​​the GLOF, see Table 1: Table 1 Table of strength coefficients

[0033] 6) The possibility of debris flow is judged by the possibility discrimination factor P2 of moraine lake outburst debris flow. When P2≥3.8, the possibility of debris flow is high; 2≤P2<3.8, the possibility of debris flow is medium; P2<2, the possibility of debris flow is small.

[0034] 7) Use Google Earth to determine the basic parameters of the channel and main river downstream of the moraine lake, including the intersection angle between the debris flow tributary and the main river, the width of the main river at the intersection, the width of the debris flow tributary at the intersection, the longitudinal gradient of the main river at the intersection, and the flow of the main river (refer to local hydrological data).

[0035] 8) Calculate the probability factor P3 of debris flow blocking the main river, which is determined according to formula (18): (18) Where: P3 is the discrimination value of rare debris flow blocking the river; is the volume of debris flow ( ), calculated by formula (19); is the peak flow of debris flow ( ), calculated by formula (20); The main river flow ( ); Φ is the intersection angle between the debris flow tributary and the main river (degrees); is the main river water depth (m), calculated by formula (22); B is the width of the main river at the confluence (m); b is the width of the debris flow branch channel at the intersection (m); is the 50% particle size of the rare debris flow (mm), which is replaced by the characteristic particle size d; (19) (20) Where: is the volume concentration of sediment in debris flow, calculated by formula (21); (twenty one) (twenty two) Where: J is the longitudinal gradient of the main river channel at the confluence.

[0036] 9) The possibility of debris flow blocking the main river is determined by the probability factor P3: P3<24.1: the possibility of blocking the river is small; P3≥24.1: the possibility of blocking the river is high.

[0037] 10) After the debris flow blocks the main river, a barrier lake is formed upstream, and the water flow erodes the outburst flood. The outburst flood peak flow is calculated according to the following formula: (twenty three) Where: is the peak flow of the dam burst flood ( ); is the water depth above the breach when the debris flow blocks the dam, calculated by formula (24); is the reservoir volume above the breach when the debris flow blocks the dam, calculated by formula (26); (twenty four) Where: The debris flow accumulation range when the debris flow blocked the river ( ), calculated by formula (25); (25) (26) Where: To follow the water surface Backwater inundation range of the weir dam calculated by water depth ( ).

[0038] 11) Through the susceptibility of moraine lake outburst to occur, the discriminating factor P1 and its conversion value Z1, the possibility of glacial lake outburst debris flow to occur, the discriminating factor P2 and its conversion value Z2, the possibility of glacial lake outburst debris flow to block the river, the discriminating factor P3 and its conversion value Z3, and the conversion value Z4 of moraine lake outburst in the main river flood peak flow, see Table 2: Table 2 Judgment Results and Conversion Values

[0039] Combine to form the comprehensive judgment value P for the danger of moraine lake outburst, which is calculated by Equation (27): P = Z1 + Z2 + Z3 + Z4 (27).

[0040] Among them, Z1, Z2, and Z3 have a progressive relationship: when the susceptibility of moraine lake outburst is low (Z1 = 0), the corresponding possibility of debris flow occurrence is small (Z2 = 0), the possibility of debris flow blocking the river is small (Z3 = 0), and the danger of moraine lake outburst is low. When the possibility of debris flow occurrence is small (Z2 = 0), the corresponding possibility of debris flow blocking the river is small (Z3 = 0).

[0041] The principle for determining the value of conversion value Z4: 1) The minimum value of Z4 is 1, such as when Z1 = Z2 = 0; 2) When Z2 > 0, but Z3 = 0, ; when , Z4 = 1; 3) When Z3 > 0, or , take the larger value of Z4; but , and , Z4 = 1.

[0042] 12) According to the discrimination value P for the danger of moraine lake outburst, judge the danger of moraine lake outburst: The discrimination value P for the danger of moraine lake outburst can be used to judge the danger of moraine lake outburst: P ≤ 2 and Z1 = 0.5, or Z1 = 0: low danger; P ≤ 2 and Z1 = 1, or 2 < P ≤ 4, and Z1 = 0.5: medium danger; 2 < P ≤ 4, and Z1 = 1, or P > 4, and Z1 = 0.5: high danger; P > 4, and Z1 = 1: very high danger. When the flood discharge of moraine lake outburst , or the debris flow discharge , or the discharge of debris flow blocking the main river and then outbursting , any one greater than 1000 , the danger level of moraine lake outburst is increased by one level (except for very high danger, or Z1 = 0).

[0043] Example 3 Since the 20th century, a total of 69 moraine lake outburst events have occurred in the Himalayas, including 47 in China and 22 abroad. Among them, 38 moraine lake outburst events were caused by ice avalanches, accounting for 55.9% of the moraine lake outburst events, including 28 in China and 10 abroad. There are 16 well-documented moraine lake outburst events caused by ice avalanches, including 12 in China and 4 abroad. Table 3 shows these moraine lake outburst events and the results of the susceptibility of moraine lake outburst judged by the method for judging the danger of moraine lake outburst of the present invention.

[0044] Table 3 Moraine lake outburst events and their current susceptibility

[0045] Example 4 Since the 20th century, there have been 69 glacial lake outburst events in the Himalayas, including 47 in China and 22 abroad. There have been 38 moraine lake outburst events caused by ice avalanches, accounting for 55.9% of all glacial lake outburst events, including 28 in China and 10 abroad. There have been 16 moraine lake outburst events caused by ice avalanches with detailed literature records, including 12 in China and 4 abroad. Table 4 is a table showing the possibility of mudslides formed after the above moraine lake outburst using the moraine lake outburst hazard judgment method of the present invention.

[0046] Table 4 Parameters of the possibility of debris flow caused by moraine lake outburst

[0047] Example 5 Since the 20th century, there have been 69 glacial lake outburst events in the Himalayas, including 47 in China and 22 abroad. There have been 38 moraine lake outburst events caused by ice avalanches, accounting for 55.9% of all glacial lake outburst events, including 28 in China and 10 abroad. There have been 16 moraine lake outburst events with detailed literature records, including 12 in China and 4 abroad. Table 5 shows the possibility of mudslides blocking the river after the moraine lake outburst formed by the moraine lake outburst hazard judgment method of the present invention, as well as the peak flow table of the flood after the river is blocked.

[0048] Table 5 The possibility of moraine lake outburst debris flow blocking the river and outburst parameters

[0049] Example 6 Since the 20th century, there have been 69 glacial lake outburst events in the Himalayas, including 47 in China and 22 abroad. There were 38 moraine lake outburst events caused by ice avalanches, accounting for 55.9% of all glacial lake outburst events, including 28 in China and 10 abroad. There were 16 moraine lake outburst events caused by ice avalanches with detailed literature records, including 12 in China and 4 abroad. Table 6 is a table of moraine lake outburst hazards comprehensively judged by the moraine lake outburst hazard judgment method of the present invention.

[0050] Table 6 Moraine lake outburst hazard

[0051] According to the discriminant value P of the glacial lake outburst danger, judge the glacial lake outburst danger: The discriminant value P of the glacial lake outburst danger can be used to judge the glacial lake outburst danger: P ≤ 2 and Z1 = 0.5, or Z1 = 0: low danger; P ≤ 2 and Z1 = 1, or 2 < P ≤ 4, and Z1 = 0.5: medium danger; 2 < P ≤ 4, and Z1 = 1, or P > 4, and Z1 = 0.5: high danger; P > 4, and Z1 = 1: very high danger. When the glacial lake outburst flood discharge , or the debris flow discharge , or the discharge of the main river blocked by debris flow and then outburst , any one greater than 1000 , the danger level of the glacial lake outburst increases by one level (except for very high danger, or Z1 = 0).

[0052] After the moraine lake bursts, there may be the following possibilities: burst to the bottom, and the moraine lake is no longer dangerous; partial burst, and there may be subsequent bursts. Since the moraine lakes that have burst are often moraine lakes that are relatively easy to burst in terms of the possibility of bursting, and rarely are moraine lakes that burst to the bottom. By the method for judging the danger of moraine lake outburst of the present invention, among 16 moraine lakes that have burst in the past, there are 2 moraine lakes with low danger, accounting for 12.5%; 2 moraine lakes with medium danger, accounting for 12.5%; 5 moraine lakes with high danger, accounting for 31.25%; 7 moraine lakes with very high danger, accounting for 43.75%. Generally, it is more dangerous than ordinary moraine lakes, and it can be seen that the judgment result of the present invention is relatively reasonable.

Claims

1. A method for determining the danger of moraine lake outburst, characterized in that: The following steps are involved: Step 1, calculate the susceptibility discriminant factor P1 of moraine lake outburst and its conversion value Z1; Step 2, calculate the possibility assessment factor P2 of glacial lake outburst debris flow and its conversion value Z2; Step 3, calculate the possibility judgment factor P3 of debris flow blocking the main river and its conversion value Z3; Step 4, calculate the conversion value Z4 of the moraine lake outburst in the main river flood peak flow; Step 5, calculating the comprehensive moraine lake outburst hazard judgment value P according to the conversion values ​​Z1, Z2, Z3 and Z4; Step 6: Determine the hazard level of the moraine lake outburst according to the moraine lake outburst hazard discrimination value P.

2. The method for determining the risk of glacial lake outburst according to claim 1, characterized in that: The step 1 specifically comprises the following steps: Step 1.1: Calculate the susceptibility factor P1 of moraine lake outburst using formula (1): P1=2.88X+0.72G+0.6R+0.5D+S+0.06T (1) In formula (1), X is the slope factor of the parent glacier, which is calculated by formula (2); G is the volume factor of the dangerous ice body and moraine lake, which is calculated by formula (3); R is the ice avalanche movement factor, which is calculated by formula (4). If R>2, then R=2; D is the slope factor of the back slope of the moraine embankment, which is calculated by formula (5); S is the slope factor of the dangerous ice body, which is calculated by formula (6); T is the equivalent annual average temperature of the dangerous ice body, which is calculated by formula (7); X = sin(θ / 2)(2) In formula (2), θ is the slope of the parent glacier, , in the northern hemisphere, it refers to the angle between the plane normal of the parent glacier and the due north when projected on the plane; in the southern hemisphere, it refers to the angle between the plane normal of the parent glacier and the due south when projected on the plane; （3） In formula (3), is the volume of dangerous ice, calculated by formula (8); is the volume of the moraine lake, calculated by formula (9); R=H / L(4) In formula (4), H is the vertical height difference between the center of mass of the dangerous ice body and the ice lake; L is the movement distance from the center of mass of the dangerous ice body to the ice lake; D = tanβ (5) In formula (5), β is the slope of the backwater slope of the moraine embankment; S = tanα (6) In formula (6), α is the slope of dangerous ice at the rear edge of the glacial lake; （7） In formula (7), is the annual average temperature of the local meteorological station; c is the coefficient, c=0.006; is the altitude difference between the center of mass of the dangerous ice body and the local meteorological station; （8） In formula (8), is the area of ​​dangerous ice, calculated by formula (10); h is the thickness of dangerous ice, calculated by formula (11) for marine glaciers, by formula (12) for continental glaciers, and by formula (13) for hanging glaciers; （9） In formula (9), A is the area of ​​moraine lake; （10） In formula (10), W is the lateral crack width of the dangerous ice body; It is the distance between the transverse crack at the rear end of the dangerous ice body and the front end of the dangerous ice body; （11） （12） （13） In formulas (11), (12), and (13), F is the area of ​​the parent glacier; Step 1.2, calculate the conversion value Z1 based on the susceptibility discrimination factor P1 of glacial lake outburst: when P1≥3.25, the susceptibility of glacial lake outburst is judged to be high, and the conversion value Z1 is set to 1; when 2≤P1<3.25, the susceptibility of glacial lake outburst is judged to be medium, and the conversion value Z1 is set to 0.5; when P1<2, the susceptibility of glacial lake outburst is judged to be low, and the conversion value Z1 is set to 0.

3. The method for determining the risk of glacial lake outburst according to claim 2, characterized in that: The step 2 specifically includes the following steps: Step 2.1: Calculate the probability assessment factor P2 of glacial lake outburst debris flow using formula (14): （14） In formula (14), is the peak flow of the moraine lake outburst flood, calculated by formula (15); S1 is the average longitudinal gradient of the channel downstream of the moraine lake, calculated by formula (16); g is the gravitational acceleration; is the average width of the channel downstream of the GLOF; d is the characteristic value of the particle size in the downstream basin of the GLOF, calculated by formula (17); （15） S1 = tanγ (16) In formula (16), γ is the channel slope downstream of the moraine lake; （17） In formula (17), is the solidity coefficient, which is determined by the lithology in the downstream area of ​​the GLOF; Step 2.2, calculate the conversion value Z2 based on the evaluation factor P2 of the possibility of glacial lake outburst debris flow: when P2≥3.8, it is judged that the possibility of debris flow is high, and the conversion value Z2 is set to 1; when 2≤P2<3.8, it is judged that the possibility of debris flow is medium, and the conversion value Z2 is set to 0.5; when P2<2, it is judged that the possibility of debris flow is low, and the conversion value Z2 is set to 0.

4. The method for determining the risk of glacial lake outburst according to claim 3, characterized in that: The step 3 specifically comprises the following steps: Step 3.1: Calculate the probability factor P3 of debris flow blocking the main river through formula (18): （18） In formula (18), is the debris flow volume, calculated by formula (19); The particle size of 50% of the particles in a rare debris flow is replaced by the characteristic particle size d; is the peak flow of debris flow, calculated by formula (20); Φ is the intersection angle between the debris flow tributary and the main river; is the water depth of the main river, calculated by formula (22); B is the width of the main river at the confluence; b is the width of the debris flow branch ditch at the confluence; For main river flow; （19） （20） In formula (19) and (20), is the volume concentration of sediment in debris flow, calculated by formula (21); （21） （22） In formula (22), J is the longitudinal gradient of the main river channel at the confluence; Step 3.2: Calculate its conversion value Z3 based on the discriminant factor P3 of the possibility of debris flow blocking the main river: When P3 < 24.1, it is judged that the possibility of river blocking is small, and the conversion value Z3 is set to 0; when P3 ≥ 24.1, it is judged that the possibility of river blocking is large, and the conversion value Z3 is set to 1.

5. The method for determining the risk of glacial lake outburst according to claim 4, characterized in that: The specific steps of step 4 are as follows: Step 4.1: Calculate the peak outburst flow using formula (23): : （23） In formula (23), is the water depth above the breach when the debris flow blocks the dam, calculated by formula (24); is the reservoir volume above the breach when the debris flow blocks the dam, calculated by formula (26); （24） In formula (24), is the debris flow accumulation range when the debris flow blocks the river, calculated by formula (25); （25） （26） In formula (26), To follow the water surface Backwater inundation range of the weir dam calculated by water depth; Step 4.2: Obtain the conversion value Z4 of the outburst of the moraine lake at the peak discharge of the main river: When Z1 = Z2 = 0, Z4 = 1; When Z2>0 but Z3=0, ;when When Z4=1; When Z3>0, or , take the larger Z4 value, but and , Z4=1.

6. The method for determining the risk of glacial lake outburst according to claim 5, characterized in that: In step 5, the comprehensive discriminant value P of the outburst risk of the moraine lake is calculated by formula (27): P = Z1 + Z2 + Z3 + Z4 (27).

7. The method for determining the risk of glacial lake outburst according to claim 6, wherein: The specific content of step 6 is as follows: Condition 1: When P ≤ 2 and Z1 = 0.5, or when Z1 = 0, it is judged that the outburst risk level of the moraine lake is "low"; When P ≤ 2 and Z1 = 1, or when 2 < P ≤ 4 and Z1 = 0.5, it is judged that the outburst risk level of the moraine lake is "medium"; When 2 < P ≤ 4 and Z1 = 1, or when P > 4 and Z1 = 0.5, it is judged that the outburst risk level of the moraine lake is "high"; When P > 4 and Z1 = 1, it is judged that the outburst risk level of the moraine lake is "very high"; Condition 2: when , or Any one of them is greater than 1000 When Z1=0, the hazard level of moraine lake outburst is increased by one level based on the hazard level of moraine lake outburst judged in condition 1, where condition 1 has already judged the hazard level of moraine lake outburst to be "very high" or when Z1=0, it is no longer increased by one level based on condition 1.

8. The application of the method for determining the danger of moraine lake outburst is characterized by: The outburst risk judgment method of the moraine lake as described in claim 1 is adopted, which is applicable to the outburst risk level judgment of the moraine lake in alpine mountainous areas.

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