Since the beginning of this year, the tragedies caused by landslides and mudslides have often been reported. Why is flooding mudslides so fierce that it can bring so much harm? What areas of our country are prone to mountain torrents and mudslides? Facing fierce mountain torrents

Debris flow, how should we respond?

May 8, 2016, Fujian San Ming Taining occur with sudden landslides. In response to the landslide sensation, the Provincial Meteorological Bureau quickly organized the Provincial Meteorological Observatory and the Sanming Meteorological Observatory to carry out the deployment of disaster rescue and disaster relief meteorological service support.

Landslides and debris flows are easy to carry together

"Debris flow is laden with sand, stones and other materials or other special mountain torrent valley areas due to heavy rain, snow or other natural disasters caused by the formation of." NMC senior Xufeng Wen said, "to see the general, occur Debris flow disasters require three conditions, namely, energy conditions, material conditions, and excitation conditions.” In recent years, China is in the main flood season, with large precipitation, frequent short-term heavy rainfall, and good excitation conditions, so it is prone to geological disasters such as mudslides .

Precipitation is one of the important factors in inducing geological disasters. Therefore, debris flow disasters mainly occur in China's rainy season ( April to September ), with obvious seasonality.

When we talk about mudslides, we will always catch a mountain torrent. According to Xu Fengwen, the main difference between flash floods and mudslides is that debris and sediment in debris flow fluids are large in volume and have greater destructive forces; while flash floods are turbid, but the sediment content is small, and the sediment content is less than 15%. . In addition, landslides must have sufficient water, a lot of debris and loose material a certain valley slope terrain, three are indispensable; and as long as there is a lot of short-term precipitation, certain bus topography to the formation of mountain flood, so flash floods easier occur. Taken together, most of the mudslides have been accompanied by flash floods.

Disasters such as flash floods and landslides induced by floods often result in casualties, damage to houses, fields, roads and bridges, and may even result in dam failures. In addition, when the mudslides break out, they will also destroy towns, mines, and villages and block rivers . This will not only stop shipping but also cause floods.

Flooding and Debris Flow in Mountainous Areas in China

Which areas of our country are prone to flash floods? Xu Fengwen pointed out that in the analysis of geological disaster zoning, it is necessary to comprehensively consider factors such as the climatic characteristics of precipitation, the large geomorphological patterns, and the geological conditions within the area. West of Sichuan Basin is highly prone areas; Yunnan-Guizhou Plateau, Qinling, north of South Africa, southeastern Northeast China for high-prone areas.

According to statistics, China's disastrous mudslides, landslides, and collapsed areas are widely distributed in plateaus, mountainous regions, and hilly regions. They are mainly distributed in the Chuanyu Mountain, Qinling Mountains, Yunnan-Guizhou Plateau, Loess Plateau, Yanshan, Taihangshan, Changbaishan, Tianshan and Qinghai-Tibet Plateaus. The distribution of flash floods is more extensive.

Landslides and debris flows are often the result of a combination of natural and human factors. The disasters are characterized by aggressiveness, heavy damage, frequent activities, and repeated disasters.

Xu Fengwen emphasized that China is a mountainous country, with mountainous areas accounting for 69.4 percent of the total land area , and mountainous areas accounting for more than half of the country's total population. “The mountainous geological structure is complex and the ecological environment is fragile. With the accelerated construction of mountainous areas , the ecological environment has been destroyed, the geological environment is relatively fragile, and geological disasters have frequently occurred due to special geological conditions, weather and climate backgrounds, population distribution, and basic conditions for survival. the people's lives and property posed a serious threat. "positively because of this, in addition to Shanghai, other mountainous provinces (autonomous regions and municipalities) are likely to flood disasters occur.

Group survey prevention against disaster losses

Face flash floods mudslides, April 7, 2003, the Ministry of Land and the signing of the China Meteorological Administration, "on joint geological disaster weather forecasting and early warning agreement" to jointly promote the early warning of geological disasters, weather forecast, perfect linkage of early warning, information sharing, Business cooperation and joint scientific and technological research work mechanisms.

Liu Chuanzheng, deputy chief engineer of China Geological Environment Monitoring Institute, believes that group surveying and prevention is a means of effectively reducing geological disasters. "Self-identification, self-monitoring, self forecasts, self-protection, self-treatment and self-emergency" working body system, is currently the mountainous area of socio-economic development, urban and rural communities in response to geological disasters and an effective means of self-risk management.

Affected by El Niño, China's rain belts are mostly concentrated in the southern region this year. Strong and sustained heavy rains have made the risk of outbreaks of mountain floods and mudslides high. Attention should be given to them.

At present, it is precisely during the summer holidays that there are many people traveling abroad. Therefore, Xu Fengwen reminds that: to listen to the local weather forecast and warning information in time; when you go to the mountain to play outdoors, you must choose a flat highland as the camp, avoiding the bend of the river (ditch) as far as possible. The concave shore or local narrow height and low convex shore; avoid camping tents at the ditch or low level in the ditch. When there is prolonged rainfall or heavy rain, the occurrence of torrential debris flows should be guarded; when signs of torrential debris flow are found, the terrain should be observed immediately, running to the slopes or highlands on both sides of the gully, not to hide from the steepness of rolling stones and heavy accumulations. Below the hillside, do not stay in low-lying areas.

Landslide refers to the phenomenon that the slope or slope of the soil layer or rock layer slides down the slope under the influence of river erosion, rainfall, earthquake, artificial cut slope and other factors. Landslides are also called slippery, and there are popular names such as “walking mountains”, “mountain mountains” or “ mountains peeling”.

Debris flow refers to a special torrent of solid material such as muddy sand, rocks, etc. that is generated on the valleys or slopes under the action of surface water flowing from precipitation, dam breaks, or melting of ice and snow. Commonly known as "walking 蛟 、 “ “ 出 出 出 出 出 出 出 出 出 出 出 出 出 出 出 出 出 出 出 出 出 出 出 出 出 出 出 出 出 出 出 .

Landslide and mudslide characteristics

Landslides are characterized by "sliding" along slopes. Debris flow is characterized by "flowing" along the ditch. Whether it is “sliding” or “flowing”, it is a form of movement in which matter moves from high to low under the action of gravity. Therefore, the speeds of “sliding” and “flowing” are all constrained by the slope of the terrain. That is, when the slope of the terrain is relatively slow, the speed of the landslide and mud-rock flow is slow; when the terrain is steep, the landslide and mud-rock flow move faster. Landslide and debris flow identification

( I) Landslide identification basis

1. Terrain and geomorphology basis: When a slope-like chair-shaped horseshoe-shaped terrain or an irregular sill is developed on a slope, its shape is obviously inconsistent with the surrounding slopes; there is a depression in the upper part of the slope, and the lower slope foot extends more than the two sides. into the river bed; two valleys in the upper part of the slope and turned to the source of convergence; topography phenomenon explained above, these lots may have been landslides. There are obvious cracks on the slope, and the cracks have been extended and widened in the near future; the houses on the slope have cracked and tilted; the soil on the slope foot has been squeezed out and collapsed frequently; the above-mentioned landform phenomenon may be the basis for the formation of landslides.

2. Stratigraphic basis: In the section where landslides have occurred, the types and occurrences of rock layers or soils are often significantly different from the surrounding non-sliding slopes. Compared to non-sliding over the slope section than the slide had generally messy sequence than rock or soil, relatively loose structure.

3 , groundwater based on: landslides will destroy the integrity of the original slope aquifer, resulting in changes in groundwater flow paths, excretion sites. When the spring and found the local slope on the whole slope point, incompatible with the distribution of water seepage, where many existing springs or other spring suddenly appeared dry within a short period of time, it may be combined with other evidence to determine whether there is formed landslide.

4. Vegetation basis: The trees on the surface of the slope are rampant. Generally, the slope has undergone a sharp slide. The trunk of the slope surface is bent down the slope and the upper trunk maintains a vertical growth, which is generally the result of a long-term slow sliding of the slope .

(II) Identification of debris flow ditch

1. According to sources: The formation of debris flows must involve a certain amount of loose soil and stones. Therefore, there are many broken mountains and evacuated materials on both sides of the valley, and there are obvious landslides and collapses on both sides of the valley. Vegetation is not developed, and valleys with strong soil erosion and slope erosion are prone to mudslides.

2. Based on topography and geomorphology: Valleys that can collect large amounts of water and maintain high water flow speeds can accommodate and handle large amounts of soil and stone. The upper reaches of the valley are surrounded on three sides by mountains and steep slopes. The planform of the ditch is funnel-shaped, spoon-shaped, and leaf -shaped. The middle valley is narrow and the downstream valley is open. The elevation difference between the upper and lower reaches of the valley is more than 300 meters , and the slope on both sides of the valley is greater than 25. The terrain conditions are conducive to the formation of mudslides.

3. Water source: Water provides the dynamic conditions for the formation of debris flow. Of storm-prone area, there is the danger of dam reservoirs, embankments downstream, seasonal snow ablation zone, provided a large amount of water in a short time conditions, it is advantageous to debris flow. Among them, in areas with frequent local heavy rainstorms, the highest frequency of mudslides occurred.

If a ditch is conducive to the formation of debris flow in terms of source, terrain, and water source, this ditch must be a debris flow ditch. But the frequency, size, degree of viscous landslides, will change as these factors change occurs. There have been landslides and mudslides, and there is still danger of mudslides in the future.

Prevention of landslides and mudslides

In mountainous environments, landslides and debris flows are unavoidable. However, by taking active defense measures, the hazards of landslides and mudslides can be mitigated.

(i) Avoiding landslides focuses on identifying precursors. Landslides can often be stopped without human resources, but we can safely evacuation of dangerous areas as early as possible by clarifying the characteristics of the precursors exposed before the outbreak. A precursor to the collapse of the main features like the following aspects: the collapse of the leading edge off the block, fall, collapse of small small collapse continue to occur; the emergence of new collapse of the foot acting rupture, can smell a strange odor; from time to time to hear rock tear , friction, cracking sound; heat occurs, radon gas, the water quality, water and other abnormalities; abnormal phenomenon animals and plants. If such signs are found, people living near landslides or walking on landslides will have to shift their evacuation early. If you find that the leading edge of the hillside soil uplift, mountain sharply long, wide cracks and other anomalies, but also to take early measures to hedge metastasis.

(b) The mudslide will run towards the sides of the hill when it breaks out. Debris flows often occur in specific mudslide valleys. Therefore, mastering the techniques for judging mudslides and moving them away from them is necessary for self-help. The debris flow valley upstream like funnels, rice scoops, leaves, the middle reaches of the deep and narrow, the downstream is more open, the upper and lower valleys relative elevation is generally more than 300 meters . If there are Shantang reservoirs in the upper reaches of the gully, or there is abundant groundwater in the gullies, they will be more prone to mudslides when they encounter continuous heavy rainfall . It should be particularly vigilant that mudslides often erupt, and therefore the chances of escape are small. Therefore, when the roar heard inside ravine, or see the main river flood rise, sudden drying up of water normal, should immediately mudslides coming to consciousness, and to take immediate measures to escape. In the escape, it is necessary to pay attention to choosing the correct direction: Do not run upstream or downstream in the direction of the ditch. You should run toward the slope on both sides of the ditch, but be careful not to stay on the slope.

How did the torrential mudslides escape?

(1) When it is known that a landslide will occur within a certain period of time in an area, emergency evacuation and protection measures shall be taken in the area, and personnel shall be forcibly moved to safe areas.

(2) Do not run upstream or downstream from the debris flow ditch. Run on the slopes on both sides of the ditch and do not stop at the slopes.

(3) To establish a temporary shelter, avoiding the position of the shed to avoid the concave bank of the ditch, and under the small, low-lying convex bank and the steep hillside, should be placed on the low-gradation slope or the higher position close to the village. On the terrace.

How do you get out of danger quickly when you encounter a flash flood early in the morning ?

According to the early lessons learned from the early midnight crashes and heavy mudslides, there are the following tips.

All residents living in flood-prone areas or gullies, canyons, and creeks must maintain high vigilance whenever they experience heavy rainstorms, especially at night. If there are any abnormalities, they should immediately organize personnel to leave the site quickly and choose a safe place nearby. Settle down and try to contact the outside world and do a good job in the next step. You must not feel lucky or rescue your property and delay the timing of your evasion, causing undue casualties.