Method for judging the hazard of moraine lake outburst and its application

Abstract

The present invention discloses a method and application for determining the hazard of a moraine lake outburst. The method calculates a moraine lake outburst susceptibility factor and its conversion value, a moraine lake outburst debris flow probability assessment factor and its conversion value, a moraine lake outburst probability factor for debris flow blocking the main river and its conversion value, and a moraine lake outburst probability factor for the main river's peak flow. Based on the conversion values, a comprehensive moraine lake outburst hazard assessment value is calculated and the moraine lake outburst hazard level is determined. This method addresses the characteristics of moraine lake outburst hazard and comprehensively considers multiple factors that influence the risk of a moraine lake outburst, including outburst floods, debris flows, blocking the main river, and floods caused by re-outburst. This improves the accuracy of the moraine lake outburst hazard assessment results and prioritizes the peak flow factor, which has the greatest impact on the hazard, making the hazard assessment results more reasonable and reliable.

Description

Technical Field

[0001] The present 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 determining the hazard of a moraine lake outburst. The present invention also relates to the application of the method for determining the hazard of a moraine lake outburst. Background Art

[0002] Moraine lakes in alpine mountainous areas often experience glacial lake outbursts, generating large-volume floods. These floods, when there is sufficient downstream material and channel slope, often result in debris flows. Because these debris flows are characterized by high flow and large volume, they can also block the main downstream river channel. Further outbursts can cause even larger flash floods, severely damaging downstream riverside facilities, roads, and residents, creating a chain reaction of disasters and wreaking havoc in the mountainous areas downstream.

[0003] Moraine lakes have the potential to burst, so a key factor influencing their risk is their susceptibility to outburst. The higher the susceptibility, the greater the risk. Moraine lakes can cause floods and debris flows, but this doesn't always happen, and further research is needed to determine whether such a flow will occur. The higher the likelihood of a debris flow, the greater the risk. Even if a glacial lake burst creates a debris flow, it doesn't necessarily block the main downstream river channel. Whether this blockage is achieved remains to be determined. If the main river is completely blocked, it could burst again, resulting in a larger outburst flood, causing significant damage downstream and creating a chain reaction. Therefore, the greater the likelihood of a debris flow blocking the main river channel, the greater the risk of a glacial lake burst. The peak flow of floods or debris flows after a moraine lake bursts, or the peak flow of floods that block the main river and then bursts, will affect the safety of roads, railways, hydropower, residents and other facilities downstream of the moraine lake and downstream of the main river confluence, and is a key factor in judging the danger of a moraine lake burst.

[0004] While research and technology have made significant progress in understanding the susceptibility of moraine lake outbursts and the potential for rarefied debris flows to block rivers, methods and techniques for assessing the likelihood of debris flows forming after a moraine lake outburst are still lacking. Methods and techniques for calculating the peak discharge of a debris flow after a river blockage are also lacking, and a comprehensive approach to assessing the risk of moraine lake outbursts is even more lacking. Current research on the likelihood of debris flows, both domestically and internationally, focuses primarily on the potential for gully and slope debris flows. Both are triggered by rainfall, so factors such as the catchment area of ​​gully debris flows and the slope gradient of slope debris flows have significant influences on the formation of these two types of debris flows. However, rainfall is the most influential factor, as it is both a triggering factor and a source of water for debris flows. Other influencing factors include: 1) Ravine debris flows: Source conditions for debris flows include source particle size, source lithology, degree of weathering, structure, and fault zones; topographic conditions for debris flows include longitudinal gradient of the channel, drainage area, drainage shape coefficient, gully length, elevation difference, and drainage development. 2) Slope debris flows: Source conditions include parent rock lithology, soil permeability, clay mineral properties and content; and topographic conditions include slope, soil thickness, and width. However, the probability of these debris flows differs significantly from that of glacial lake outbursts. First, the triggering factors, namely the water source conditions, are completely different. Debris flows caused by glacial lake outbursts are concentrated and result in a massive peak discharge. Second, the channels downstream of glacial lakes are wide, U-shaped valleys with a relatively small longitudinal gradient due to glacial erosion and a large drainage area. Finally, the source material is often more abundant and dispersed throughout the wide channel downstream of glacial lakes. Therefore, the probability of gully debris flows based on the traditional method is completely inappropriate for assessing the probability of such glacial lake outbursts. Research on the peak discharge of floods caused by dam erosion and failure has a long history, but this has primarily been based on simulations using parameters such as dam height, length, structure, breach width, and time to failure. For a potential dam blocking 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 blocking the river.

[0005] Currently, there is no comprehensive technical solution for assessing the hazard of moraine lake outburst that considers factors such as the susceptibility of moraine lake outburst, the possibility of debris flow after outburst, the possibility of debris flow blocking the main river, and the peak flow of flood caused by dam outburst. Summary of the Invention

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

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

[0008] The first technical solution adopted by the present invention is: a method for determining the risk of moraine lake outburst, comprising the following steps:

[0009] Step 1: Calculate the susceptibility discriminant factor P1 of moraine lake outburst and its conversion value Z1;

[0010] Step 2: Calculate the probability evaluation factor P2 of glacial lake outburst debris flow and its conversion value Z2;

[0011] Step 3: Calculate the probability factor P3 of debris flow blocking the main river and its conversion value Z3;

[0012] Step 4: Calculate the conversion value Z4 of the moraine lake outburst in the main river flood peak flow;

[0013] Step 5: Calculate the comprehensive moraine lake outburst hazard judgment value P based on the transformed values ​​Z1, Z2, Z3, and Z4;

[0014] Step 6: Determine the hazard level of the moraine lake outburst according to the moraine lake outburst hazard discrimination value P.

[0015] The first technical solution of the present invention is also characterized in that:

[0016] Step 1 specifically includes the following steps:

[0017] Step 1.1: Calculate the susceptibility factor P1 for moraine lake outburst using formula (1):

[0018] P1=2.88X+0.72G+0.6R+0.5D+S+0.06T (1)

[0019] 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 moraine bank backwater slope, 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);

[0020] X = sin (θ / 2) (2)

[0021] 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 direction of the 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 direction of the south when projected on the plane;

[0022] (3)

[0023] In formula (3), is the volume of dangerous ice, calculated by formula (8); is the volume of the moraine lake, calculated by formula (9);

[0024] R=H / L (4)

[0025] In formula (4), H is the vertical height difference between the center of mass of the dangerous ice body and the glacial lake; L is the movement distance from the center of mass of the dangerous ice body to the glacial lake;

[0026] D = tanβ (5)

[0027] In formula (5), β is the slope of the backwater slope of the moraine bank;

[0028] S = tanα (6)

[0029] In formula (6), α is the slope of the dangerous ice body at the trailing edge of the glacial lake;

[0030] (7)

[0031] In formula (7), is the annual average temperature of the local weather 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 weather station;

[0032] (8)

[0033] In formula (8), is the area of ​​dangerous ice, calculated by formula (10); h is the thickness of dangerous ice, which is calculated by formula (11) for marine glaciers, by formula (12) for continental glaciers, and by formula (13) for hanging glaciers;

[0034] (9)

[0035] In formula (9), A is the area of ​​moraine lake;

[0036] (10)

[0037] In formula (10), W is the width of the transverse crack 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;

[0038] (11)

[0039] (12)

[0040] (13)

[0041] In formulas (11), (12), and (13), F is the area of ​​the parent glacier;

[0042] Step 1.2: Calculate the conversion value Z1 based on the susceptibility discrimination factor P1 of moraine lake outburst: when P1 ≥ 3.25, the susceptibility of moraine lake outburst is judged to be high, and the conversion value Z1 is set to 1; when 2 ≤ P1 < 3.25, the susceptibility of moraine lake outburst is judged to be medium, and the conversion value Z1 is set to 0.5; when P1 < 2, the susceptibility of moraine lake outburst is judged to be low, and the conversion value Z1 is set to 0.

[0043] Step 2 specifically includes the following steps:

[0044] Step 2.1: Calculate the probability assessment factor P2 of glacial lake outburst debris flow using formula (14):

[0045] (14)

[0046] In formula (14), 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 of gravity; 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);

[0047] (15)

[0048] S1=tanγ(16)

[0049] In formula (16), γ is the channel slope downstream of the moraine lake;

[0050] (17)

[0051] In formula (17), is the robustness coefficient, which is determined by the lithology in the downstream area of ​​the GLOF;

[0052] Step 2.2: Calculate the conversion value Z2 based on the glacial lake outburst debris flow probability evaluation factor P2: When P2 ≥ 3.8, the probability of a debris flow is high, and the conversion value Z2 is set to 1; when 2 ≤ P2 < 3.8, the probability of a debris flow is medium, and the conversion value Z2 is set to 0.5; when P2 < 2, the probability of a debris flow is low, and the conversion value Z2 is set to 0.

[0053] Step 3 specifically includes the following steps:

[0054] Step 3.1: Calculate the probability factor P3 of debris flow blocking the main river using formula (18):

[0055] (18)

[0056] In formula (18), is the debris flow volume, calculated by formula (19); The particle size of 50% of the dilute debris flow is replaced by the characteristic particle size d; is the peak discharge 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 tributary at the confluence; For the main river flow;

[0057] (19)

[0058] (20)

[0059] In formulas (19) and (20), is the volume concentration of sediment in debris flow, calculated by formula (21);

[0060] (twenty one)

[0061] (twenty two)

[0062] In formula (22), J is the longitudinal gradient of the main river channel at the confluence;

[0063] Step 3.2: Calculate the conversion value Z3 based on the probability discrimination factor P3 of debris flow blocking the main river: when P3 < 24.1, the possibility of blocking the river is judged to be small, and the conversion value Z3 is set to 0; when P3 ≥ 24.1, the possibility of blocking the river is judged to be high, and the conversion value Z3 is set to 1.

[0064] Step 4 specifically includes the following steps:

[0065] Step 4.1: Calculate the peak flood flow using formula (23) :

[0066] (twenty three)

[0067] 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);

[0068] (24)

[0069] In formula (24), is the debris flow accumulation range when the debris flow blocks the river, and is calculated by formula (25);

[0070] (25)

[0071] (26)

[0072] In formula (26), is the backwater inundation range of the barrier lake calculated according to the water depth below the water surface;

[0073] Step 4.2: Determine the value of the conversion value Z4 of the moraine lake breach at the peak discharge of the main river:

[0074] When Z1 = Z2 = 0, Z4 = 1;

[0075] When Z2 > 0 but Z3 = 0, ; when , Z4 = 1;

[0076] When Z3 > 0, or , take the larger value of Z4, but and when, Z4 = 1.

[0077] In Step 5, calculate the comprehensive moraine lake breach hazard discriminant value P by formula (27):

[0078] P = Z1 + Z2 + Z3 + Z4 (27).

[0079] Step 6 is specifically as follows:

[0080] Condition 1:

[0081] When P ≤ 2 and Z1 = 0.5, or when Z1 = 0, determine that the moraine lake breach hazard level is "low";

[0082] When P ≤ 2 and Z1 = 1, or when 2 < P ≤ 4 and Z1 = 0.5, determine that the moraine lake breach hazard level is "medium";

[0083] When 2 < P ≤ 4 and Z1 = 1, or when P > 4 and Z1 = 0.5, determine that the moraine lake breach hazard level is "high";

[0084] When P > 4 and Z1 = 1, determine that the moraine lake breach hazard level is "very high";

[0085] Condition 2:

[0086] 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 determined in condition 1. If the hazard level of moraine lake outburst is already determined to be “very high” in condition 1 or if Z1=0, the hazard level of moraine lake outburst is no longer increased by one level based on condition 1.

[0087] The second technical solution adopted by the present invention is: application of the method for judging the hazard of moraine lake outburst. The above-mentioned method for judging the hazard of moraine lake outburst is suitable for judging the hazard level of moraine lake outburst in high-altitude mountainous areas.

[0088] The beneficial effects of the present invention are as follows: the method and application of judging the hazard of moraine lake outburst of the present invention, based on the characteristics of the hazard of moraine lake outburst, analyzes and comprehensively considers multiple conditions that affect the hazard of moraine lake outburst, such as outburst floods, debris flows, blockage of main rivers, and floods caused by re-outburst, thereby improving the accuracy of the judgment results of the hazard of moraine lake outburst, and highlighting the consideration of the flood peak flow factor that has the greatest impact on the hazard, making the hazard assessment results more reasonable and reliable. DETAILED DESCRIPTION

[0089] The present invention is described in detail below with reference to specific embodiments.

[0090] Example 1

[0091] Moraine lake outbursts often trigger debris flows, but they don't always result in them. First, the floodwaters from a moraine lake outburst must be large enough to provide sufficient water for a debris flow to form. Second, sufficient material resources are required for a debris flow to form. Finally, certain topographical conditions are required to ensure that the debris flow continues downstream, rather than simply accumulating immediately after formation.

[0092] 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 mutually influential, and eventually form debris flow. Although the peak flow of the 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 a 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 material source comes from the collapse or landslide in the area, and the hard rock (solidity coefficient Large) often collapses, which makes the source of material in this area not only less, but also the particle size of the source material is large, making it relatively difficult to form debris flow; soft rock (firmness coefficient Landslides often occur in areas with small sediment sources, resulting in both abundant and small-sized sediment particles, making debris flows more likely to form. Another factor influencing debris flow formation is topography. Regarding the characteristic of debris flows caused by glacial lake outbursts, topographic factors include the longitudinal gradient and width of the channel downstream of the lake. If the longitudinal gradient is too shallow, even if a debris flow briefly forms, it will accumulate due to the low longitudinal gradient. If the longitudinal gradient is large, the resulting debris flow will continue downstream to the main river mouth. Furthermore, the width of the downstream channel also significantly affects the formation of debris flows: a wider channel disperses the debris flow, making accumulation more likely when the longitudinal gradient is low; conversely, accumulation is less likely when the channel is narrow. Because channels downstream of glacial lakes are generally wide (due to their large drainage area and the wide "U"-shaped valley formed by long-term glacial erosion), a large average slope is required for debris flows to occur.

[0093] The dam body is eroded and damaged by water flow, and the calculation of the peak flow rate of the 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 and then breaks out is simple and reliable. The calculation of the height of the landslide dam needs to consider the accumulation range of the debris flow, which is related to the intersection angle, and the calculation result is also more reasonable.

[0094] The process of a moraine lake outburst, resulting in floods, debris flows, river blockage, and subsequent flooding, is a highly complex one, involving multiple key issues, including the outburst of the moraine lake, peak discharge of the outburst flood, the formation of a debris flow and its peak discharge, debris flow blocking the main river, and peak discharge of a landslide dam breach. Without a comprehensive hazard assessment of any of these elements, it is difficult to accurately assess the risk of a moraine lake outburst. However, there is currently no moraine lake outburst hazard assessment method that comprehensively considers these factors and conditions. The moraine lake outburst hazard assessment method provided by the present invention comprehensively considers these conditions and their relationship to the moraine lake outburst hazard, particularly the crucial influence of the final peak discharge, resulting in a practical and reliable hazard assessment.

[0095] The main features of the method for determining the risk of moraine lake outburst provided by the present invention are as follows:

[0096] 1) Based on the characteristics of moraine lake outburst hazards, this method analyzes and makes comprehensive judgments based on multiple factors that affect the outburst hazard, including outburst floods, debris flows, blockage of the main river, and floods caused by re-outburst. This can effectively determine the outburst hazard of moraine lakes and greatly improve the accuracy of the judgment results.

[0097] 2) The peak discharge of a moraine lake outburst is the key to the formation of a debris flow and also the water source condition for the formation of a debris flow. First, calculating the peak discharge of a moraine lake outburst provides an important basis for correctly judging the possibility of a moraine lake outburst forming a debris flow, making the final judgment more reliable.

[0098] 3) Full consideration of the source conditions for debris flows is a key factor: a moraine lake outburst without a source is a flash flood, not a debris flow. The robustness coefficient of the regional lithology of the source is used to determine the source's abundance and particle size, further estimating the likelihood of debris flow formation and making the results more applicable.

[0099] 4) The important influence of topographic conditions on the formation of debris flows caused by moraine lake outbursts was fully considered. The average longitudinal gradient (average channel slope) and average channel width of the downstream channel of the moraine lake were used as topographic judgment parameters for the formation of debris flows, making the judgment of the possibility of debris flows more reasonable and reliable.

[0100] 5) Considering the uncertainty of the landslide dam body, 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.

[0101] 6) Taking into account the possibility of debris flow forming a landslide dam, the influence of the intersection angle is fully utilized to reasonably calculate the accumulation range of the debris flow, making the calculation of the landslide lake depth more reasonable.

[0102] 7) Comprehensively consider multiple influencing factors affecting 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.

[0103] Example 2

[0104] The present invention provides a method for determining the risk of a moraine lake outburst, comprising the following steps:

[0105] 1) Determine the basic parameters of the moraine lake using Google Earth, including the slope of the parent glacier θ, the slope of the moraine bank β, the slope of the dangerous ice body at the rear edge of the glacial lake α, the vertical height difference H between the center of mass of the dangerous ice body and 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 in 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 center of mass of the dangerous ice body and the local meteorological station .

[0106] 2) Calculate the susceptibility factor P1 of moraine lake outburst according to formula (1);

[0107] P1=2.88X+0.72G+0.6R+0.5D+S+0.06T (1)

[0108] Where: P1 is the susceptibility factor of moraine lakes, X is the slope factor of the parent glacier, which is calculated by formula (2);

[0109] X = sin (θ / 2) (2)

[0110] G is the volume factor of dangerous ice and moraine lake, which is calculated by formula (3);

[0111] (3)

[0112] R is the ice avalanche motion factor, which is calculated by formula (4). If R>2, then R=2;

[0113] R=H / L (4)

[0114] D is the slope factor of the moraine bank backwater slope, which is calculated by formula (5);

[0115] D = tanβ (5)

[0116] S is the dangerous ice slope factor, which is calculated by formula (6);

[0117] S = tanα (6)

[0118] T is the equivalent annual average temperature of the dangerous ice body, calculated by formula (7);

[0119] (7)

[0120] 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 direction of the 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 direction of the south when projected on the plane;

[0121] is the volume of dangerous ice ( ), calculated by formula (8);

[0122] is the volume of moraine lake ( ), calculated by formula (9);

[0123] H is the vertical height difference between the centroid of the dangerous ice body and the glacial lake (m);

[0124] L is the distance from the center of mass of the dangerous ice body to the glacial lake (m);

[0125] β is the slope of the moraine bank's backwater slope (degrees);

[0126] α is the slope of dangerous ice at the trailing edge of the glacial lake (degrees);

[0127] is the annual average temperature (degrees) at the local weather station, obtained by consulting local meteorological data;

[0128] c is the coefficient, c=0.006;

[0129] The altitude difference between the center of mass of the dangerous ice body and the local meteorological station (m);

[0130] (8)

[0131] (9)

[0132] Where: A is the area of ​​moraine lake ( );

[0133] is the area of ​​dangerous ice ( ), calculated by formula (10);

[0134] (10)

[0135] Where: W is the width of the transverse crack of the dangerous ice body (m);

[0136] 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);

[0137] h is the thickness of the dangerous ice body (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);

[0138] (11)

[0139] (12)

[0140] (13)

[0141] Where: F is the area of ​​the parent glacier ( );

[0142] 3) The susceptibility of moraine lake outburst is determined by the susceptibility discriminant factor P1. When P1 ≥ 3.25, the susceptibility of moraine lake outburst is high; when 2 ≤ P1 < 3.25, the susceptibility of moraine lake outburst is medium; and when P1 < 2, the susceptibility of moraine lake outburst is low.

[0143] 4) The basic parameters of the channel downstream of the moraine lake were determined using Google Earth, including the channel slope downstream of the moraine lake, the average width of the channel downstream of the GLOF, and the main lithology in the downstream area of ​​the GLOF.

[0144] 5) Calculate the probability evaluation factor P2 of glacial lake outburst debris flow, which is determined according to formula (14):

[0145] (14)

[0146] Where: P2 is the probability judgment value of debris flow;

[0147] is the peak discharge of the moraine lake outburst flood ( ), calculated by formula (15);

[0148] S1 is the average longitudinal gradient of the channel downstream of the moraine lake, calculated by formula (16);

[0149] g is the acceleration due to gravity;

[0150] is the average width of the downstream channel of the GLOF (m);

[0151] d is the characteristic value of particle size in the downstream basin of the GLOF (m), calculated by Equation (17);

[0152] (15)

[0153] S1=tanγ(16)

[0154] (17)

[0155] Where: γ is the channel slope downstream of the moraine lake;

[0156] is the strength coefficient, which is determined by the main lithology in the downstream area of ​​the GLOF, see Table 1:

[0157] Table 1 Robustness coefficient table

[0158]

[0159] 6) The probability of debris flow is determined by the probability discrimination factor P2 of moraine lake outburst debris flow. When P2 ≥ 3.8, the probability of debris flow is high; when 2 ≤ P2 < 3.8, the probability of debris flow is medium; and when P2 < 2, the probability of debris flow is low.

[0160] 7) Use Google Earth to determine the basic parameters of the channel and main river downstream of Moraine Lake, including the intersection angle between the debris flow tributary and the main river, the width of the main river at the confluence, the width of the debris flow tributary at the confluence, the longitudinal gradient of the main river at the confluence, and the discharge of the main river (consult local hydrological data).

[0161] 8) Calculate the probability factor P3 of debris flow blocking the main river, which is determined according to formula (18):

[0162] (18)

[0163] Where: P3 is the discrimination value of rare debris flow blocking the river;

[0164] is the volume of debris flow ( ), calculated by formula (19);

[0165] is the peak flow of debris flow ( ), calculated by formula (20);

[0166] The main river flow ( );

[0167] Φ is the intersection angle between the debris flow tributary and the main river (degrees);

[0168] is the main river water depth (m), calculated by formula (22);

[0169] B is the width of the main river at the confluence (m);

[0170] b is the width of the debris flow tributary at the intersection (m);

[0171] is the 50% particle size of the dilute debris flow (mm), and is replaced by the characteristic particle size d;

[0172] (19)

[0173] (20)

[0174] Where: is the volume concentration of sediment in debris flow, calculated by formula (21);

[0175] (twenty one)

[0176] (twenty two)

[0177] Where: J is the longitudinal gradient of the main river channel at the confluence.

[0178] 9) The probability of debris flow blocking the main river is determined by the probability factor P3: P3 < 24.1: the probability of river blocking is small; P3 ≥ 24.1: the probability of river blocking is high.

[0179] 10) When a debris flow blocks the main river, a barrier lake is formed upstream. The water erodes the outburst flood. The outburst flood peak flow is calculated according to the following formula:

[0180] (twenty three)

[0181] Where: The peak flow of the landslide dam burst ( );

[0182] is the water depth above the breach when the debris flow blocks the dam, calculated by formula (24);

[0183] is the reservoir volume above the breach when the debris flow blocks the dam, calculated by formula (26);

[0184] (twenty four)

[0185] Where: The debris flow accumulation range when the debris flow blocks the river ( ), calculated by formula (25);

[0186] (25)

[0187] (26)

[0188] Where: To follow the water surface Backwater inundation range of the landslide dam calculated by water depth ( ).

[0189] 11) Based on the susceptibility of moraine lake outbursts to occur, the discriminant factor P1 and its conversion value Z1, the discriminant factor P2 and its conversion value Z2 for the likelihood of glacial lake outburst debris flows to occur, the discriminant factor P3 and its conversion value Z3 for the likelihood of glacial lake outburst debris flows to block the river, and the conversion value Z4 for the peak flow of the main river caused by moraine lake outbursts, see Table 2:

[0190] Table 2 Judgment results and conversion values

[0191]

[0192] The combined value P of the comprehensive moraine lake outburst hazard is calculated by formula (27):

[0193] P=Z1+Z2+Z3+Z4(27).

[0194] Among Z1, Z2, and Z3, there is a progressive relationship: when the susceptibility of glacial lake outburst is low (Z1 = 0), the corresponding probability of debris flow occurrence is small (Z2 = 0), the probability of debris flow blocking the river is small (Z3 = 0), and the risk of glacial lake outburst is low. When the probability of debris flow occurrence is small (Z2 = 0), the corresponding probability of debris flow blocking the river is small (Z3 = 0).

[0195] Principle for the value of the 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 When, Z4 = 1; 3) When Z3 > 0, or , take the larger Z4 value; but , and When, Z4 = 1.

[0196] 12) According to the discriminant value P of the risk of glacial lake outburst, judge the risk of glacial lake outburst: The discriminant value P of the risk of glacial lake outburst can be used to judge the risk of glacial lake outburst: P ≤ 2 and Z1 = 0.5, or Z1 = 0: low risk; P ≤ 2 and Z1 = 1, or 2 < P ≤ 4 and Z1 = 0.5: medium risk; 2 < P ≤ 4 and Z1 = 1, or P > 4 and Z1 = 0.5: high risk; P > 4 and Z1 = 1: very high risk. When the flood discharge of glacial lake outburst , or the debris flow discharge , or the re - outburst discharge of the main river blocked by debris flow , any one greater than 1000 When, the risk level of glacial lake outburst is increased by one level (except for very high risk or Z1 = 0).

[0197] Example 3

[0198] Table 3 shows the events of moraine lake outburst and the results of the susceptibility of glacial lake outburst judged by the method for judging the risk of moraine lake outburst of the present invention.

[0199] Table 3 Moraine lake outburst events and current susceptibility

[0200]

[0201] Example 4

[0202] Table 4 shows the table of the probability of debris flow formation after the outburst of moraine lake judged by the method for judging the risk of moraine lake outburst of the present invention.

[0203] Table 4 Parameters of the probability of debris flow formation after moraine lake outburst

[0204]

[0205] Example 5

[0206] Table 5 is a table showing the possibility of debris flow blocking the river formed after the outburst of the moraine lake judged by the method for judging the outburst risk of the moraine lake of the present invention and the peak discharge of the subsequent outburst after the river is blocked.

[0207] Table 5 Possibility of debris flow blocking the river caused by the outburst of the moraine lake and outburst parameters

[0208]

[0209] Example 6

[0210] Table 6 is a table showing the outburst risk of the moraine lake comprehensively judged by the method for judging the outburst risk of the moraine lake of the present invention.

[0211] Table 6 Outburst risk of the moraine lake

[0212]

[0213] According to the outburst risk discrimination value P of the ice lake, judge the outburst risk of the ice lake: The outburst risk discrimination value P of the ice lake can judge the outburst risk of the ice lake: P≤2 and Z1 = Ͳ.5, or Z1 = 0: low risk; P≤2 and Z1 = 1, or 2 < P≤4, and Z1 = Ͳ.5: medium risk; 2 < P≤4, and Z1 = 1, or P>4, and Z1 = Ͳ.5: high risk; P>4, and Z1 = 1: very high risk. When the outburst flood discharge of the ice lake , or the debris flow discharge , or the discharge of the debris flow blocking the main river and then outbursting again , any one is greater than 1000 m³ / s, the outburst risk level of the ice lake is increased by one level (except for very high risk or Z1 = 0).

[0214] After the outburst of the moraine lake, there may be the following possibilities: outburst to the bottom, and the moraine lake is no longer dangerous; partial outburst, and there may be subsequent outbursts. Since the moraine lakes that have already outburst are often moraine lakes that are relatively easy to outburst in terms of the possibility of outburst, and there are few moraine lakes that outburst to the bottom. By the method for judging the outburst risk of the moraine lake of the present invention, among the 16 moraine lakes that have outburst before, there are 2 moraine lakes with low risk, accounting for 12.5%; 2 moraine lakes with medium risk, accounting for 12.5%; 5 moraine lakes with high risk, accounting for 31.25%; 7 moraine lakes with very high risk, 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 risk of a moraine lake outburst, characterized in that: It includes the following steps: Step 1: Calculate the susceptibility discriminant factor P1 of moraine lake outburst and its conversion value Z1; Step 2: Calculate the evaluation factor P2 of the occurrence possibility of debris flow caused by ice lake outburst and its conversion value Z2; Step 3: Calculate the discriminant factor P3 of the possibility of debris flow blocking the main river and its conversion value Z3; specifically including the following steps: Step 3.1: Calculate the discriminant factor P3 of the possibility of debris flow blocking the main river through Equation (18): （18） In formula (18), is the debris flow volume, calculated by formula (19); The particle size of 50% of the dilute debris flow is replaced by the characteristic particle size d; is the peak discharge 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 tributary at the confluence; For the main river flow; （19） （20） In formulas (19) and (20), It is the peak discharge of the moraine lake outburst flood; is the volume concentration of sediment in debris flow, calculated by formula (21); （21） In formula (21), is the robustness coefficient, which is determined by the lithology in the downstream area of ​​the GLOF; （22） In Equation (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; Step 4: Calculate the conversion value Z4 of the peak discharge of the main river caused by moraine lake outburst; specifically including the following steps: Step 4.1: Calculate the peak flood flow using formula (23) : （23） In formula (23), g is the acceleration due to gravity; 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 landslide dam calculated by water depth; Step 4.2: Determine the value of the conversion value Z4 of the peak discharge of the main river caused by moraine lake outburst: 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 When Z4=1; Step 5: Calculate the comprehensive discriminant value P of the risk of moraine lake outburst through Equation (27) according to the conversion values Z1, Z2, Z3 and Z4: P = Z1 + Z2 + Z3 + Z4 (27) Step 6: According to the discriminant value P of the risk of moraine lake outburst, judge the risk level of moraine lake outburst specifically as follows: Condition 1: When P ≤ 2 and Z1 = 0.5, or when Z1 = 0, it is judged that the risk level of moraine lake outburst is "low"; When P ≤ 2 and Z1 = 1, or when 2 < P ≤ 4 and Z1 = 0.5, it is judged that the risk level of moraine lake outburst 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 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 determined in condition 1. If the hazard level of moraine lake outburst is already determined to be "very high" in condition 1 or if Z1=0, the hazard level of moraine lake outburst is no longer increased by one level based on condition 1.

2. The method for determining the risk of a moraine lake outburst according to claim 1, wherein: The specific steps of Step 1 are as follows: Step 1.1: Calculate the susceptibility discriminant factor P1 of moraine lake outburst through Equation (1): P1 = 2.88X + 0.72G + 0.6R + 0.5D + S + 0.06T (1) In Equation (1), X is the mother glacier slope aspect factor, which is calculated by Equation (2); G is the volume factor of the dangerous ice body and the moraine lake, which is calculated by Equation (3); R is the ice avalanche movement factor, which is calculated by Equation (4). If R > 2, then take R = 2; D is the slope factor of the backwater slope of the moraine dam, which is calculated by Equation (5); S is the slope factor of the dangerous ice body, which is calculated by Equation (6); T is the equivalent annual average temperature of the dangerous ice body, which is calculated by Equation (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 direction of the 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 direction of the 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 Equation (4), H is the vertical height difference from the centroid of the dangerous ice body to the ice lake; L is the movement distance from the centroid of the dangerous ice body to the ice lake; D = tanβ (5) In Equation (5), β is the slope of the backwater slope of the moraine dam; S = tanα (6) In Equation (6), α is the slope of the dangerous ice body at the rear edge of the ice lake; （7） In formula (7), is the annual average temperature of the local weather 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 weather station; （8） In formula (8), is the area of ​​dangerous ice, calculated by formula (10); h is the thickness of dangerous ice, which is calculated by formula (11) for marine glaciers, by formula (12) for continental glaciers, and by formula (13) for hanging glaciers; （9） In Equation (9), A is the area of the moraine lake; （10） In formula (10), W is the width of the transverse crack 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 Equations (11), (12), (13), F is the area of the mother glacier; Step 1.2: Calculate the conversion value Z1 based on the susceptibility discrimination factor P1 of moraine lake outburst: when P1 ≥ 3.25, the susceptibility of moraine lake outburst is judged to be high, and the conversion value Z1 is set to 1; when 2 ≤ P1 < 3.25, the susceptibility of moraine lake outburst is judged to be medium, and the conversion value Z1 is set to 0.5; when P1 < 2, the susceptibility of moraine 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, wherein: 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), Calculated by formula (15); S1 is the average longitudinal gradient of the channel downstream of the moraine lake, calculated by formula (16); 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） Step 2.2: Calculate the conversion value Z2 based on the glacial lake outburst debris flow probability evaluation factor P2: When P2 ≥ 3.8, the probability of a debris flow is high, and the conversion value Z2 is set to 1; when 2 ≤ P2 < 3.8, the probability of a debris flow is medium, and the conversion value Z2 is set to 0.5; when P2 < 2, the probability of a 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 1, wherein: It is applicable to the judgment of the hazard level of moraine lake outburst in alpine mountainous areas.

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