Precursors and Causes of Debris Flow: Why did the Debris Flow happen before it happened?

Characteristics of Debris Flow and Its Precursors

1. Debris flow activities are sudden at high speed, which not only aggravates the disaster situation, but also is difficult to accurately predict and effectively prevent.

2. Debris flow activity has periodic revival.

3. Chain and quality. Often caused by landslides, collapses, mudslides, landslides, collapses, etc.

4. The precursor is that there is a roar in the upstream valley, the water level in the main stream rises, and the normal running water suddenly stops.

Ways to avoid and escape debris flow

Methods to reduce debris flow disasters can be divided into non-emergency measures and emergency measures.

Non-emergency measures:

1) Avoidance measures: In the debris flow development and distribution area, the site selection and tourism development of industrial and mining, villages and towns, railways, highways, bridges and reservoirs must be carried out under the condition of finding out the debris flow ditch and its harm, and try to avoid the areas and lots that may cause direct harm, such as the middle and upper reaches of the debris flow ditch and the ditch, the low water level section at the intersection of main tributaries and ditches, and the low water level terrace or slope near the riverbed. When it is really unavoidable, we should consider building protective works or taking other measures;

2) Biological measures: It is a long-term control measure, which helps to slow down the formation of debris flow and achieve certain prevention and control purposes. The main methods are closing hillsides to facilitate afforestation, returning farmland to forests, strengthening topsoil, conserving water and soil, and reducing the probability and scale of debris flow;

3) Engineering facilities: protection, drainage, soil retaining, crossing and other engineering facilities. , mainly used to protect dangerous objects from damage, such as slope protection, retaining wall, groin and other projects. Drainage ditches, diversion dikes, rapids, aqueducts and other projects built to improve the direction and velocity of debris flow. In order to control the interception of discharged materials and weaken the impact energy of debris flow, sand dams, silt yards and river closure projects were built;

4) Comprehensive prevention and control measures: combining biological measures with several engineering measures suitable for a certain debris flow danger area, comprehensively and uniformly rectifying the small debris flow watershed to effectively prevent and reduce the occurrence of disasters;

5) Debris flow forecast: In space, according to the geological, geomorphological, rainfall and other conditions, according to the development degree and scale of debris flow, the dangerous areas are divided into high risk areas, medium risk areas and general risk areas. In terms of time, it can be divided into long-term and short-term forecasts.

(2) Emergency measures: July to August every year is a period prone to mudslides, and emergency measures should be taken to avoid and prevent them. First of all, we should avoid the dangerous area of debris flow and try to take preventive measures before the arrival of debris flow. Necessary relocation and temporary protective measures should be taken in areas where mudslides are developed, and emergency arrangements should be made in advance for industrial, mining and villages and towns seriously threatened by mudslides.

Emergency measures mainly include:

1) popularize the knowledge of debris flow: organize drills in flood season and evacuate in an orderly manner. For example, in the debris flow prone area of Beishan, Beijing, the local government has summed up a set of emergency prevention and control methods for debris flow: "Three Guarantees and Four Implementations". Among them, the "three guarantees" are Baocun, Baodui, Hu Bao and everyone, that is, from the township leaders one by one, it is everyone's responsibility to ensure the safety of the flood season and ensure the safety of the elderly, the sick and the disabled.

2) Prevention first: Debris flow usually occurs during the summer rainstorm, and this season is the best time for people to choose to visit the narrow valleys in mountainous areas. Therefore, when people travel, they must listen to the local weather forecast in advance, and don't travel in the valley in rainy weather or after several days of rain.

3) Choose a nearby safe zone to build temporary shelters: temporary shelters should be built on high bedrock platforms and low and gentle ridges. It shall not be built on the bank of ditch bed, lower terrace, platform and toe of slope, the downstream edge of concave bank or convex bank of river bend;

4) After a long period of rain or rainstorm gradually subsides or just stops, you should not return to the danger zone immediately: debris flow often lags behind the occurrence of rainstorm. For example, in June 199 1, 10, it rained all day in Miyun county, Beijing, and the rain stopped at 8 pm. Some villagers in Koumen village went home to avoid mountain torrents, and as a result, they were hit by mudslides, killing five people. In addition, the intermittent flow of viscous debris flow is sometimes mistaken for the end of debris flow. In short, only when it is confirmed that the debris flow will not occur or the debris flow has completely ended can the alarm be lifted;

5) Don't be lucky: When there is a lot of rain during the day, you must pay close attention to the rain at night or at night, and it is best to act in advance. There should be no luck in sleeping indoors;

6) Pay close attention to the occurrence and development of debris flow to reduce and avoid the occurrence of secondary disasters: When debris flow blocks rivers and dams, measures should be taken as soon as possible to destroy the dams, so that the upstream water body can flow down as soon as possible to avoid secondary flood disasters, and at the same time, notify the upstream and downstream affected areas to do disaster prevention and avoidance work. When roads, railways and bridges are washed away, timely actions should be taken to stop the passage of vehicles to avoid vehicle subversion and casualties;

7) Take the correct escape method: Debris flow is different from landslides, landslides and earthquakes, and has great mobility, impact force and handling capacity. Therefore, in the debris flow area, do not run down or up the ditch, but run to the slopes on both sides, leaving the ditch and valley, but be careful not to stay on the soft and unstable slope, so as to avoid the slope instability and decline, and should be in the place where the basement is stable and gentle.

In addition, don't climb trees to escape, because debris flow is different from ordinary floods, and all obstacles along the way can be removed, so climbing trees to escape is not advisable.

The curved concave banks or narrow convex banks with low height of rivers (ditches) should be avoided, because the debris flow has strong scouring ability and is straight, which is very dangerous.

When traveling in mountainous and semi-mountainous areas, if you hear abnormal noise and see stones and mud falling frequently and rushing in a certain direction, it means that there may be mudslides nearby; If the noise is getting louder and louder and the debris is clearly visible, it means that the debris flow is about to flow, so we should abandon the heavy objects immediately and escape as soon as possible.

The scope of debris flow is generally not very wide. When you escape, you can escape to the height that did not happen according to the terrain on the spot.

When camping in mountainous areas, don't choose rivers with low flood discharge such as valleys, winding rivers and assembly places. During the construction of chengdu-kunming railway in China, hundreds of construction teams were swept away by mudslides at night.

Self-rescue and epidemic prevention after debris flow: When industrial and mining areas, villages and towns, and tourists are attacked by debris flow, people should be immediately organized to rescue the wounded and repair water, electricity and traffic lines to ensure the smooth progress of disaster relief. After the river (ditch) valley was looted by mudslides, it was unrecognizable and full of holes. Not only the original river (ditch) bed is illegible due to scouring and silting, but also the roads crossing or along the river (ditch) valley are often buried and destroyed without a trace, and gravel and sediment fill the ditches along the way, which is easy to cause falls and bumps when walking. Therefore, attention should be paid to avoid all kinds of injuries when carrying out emergency rescue and disaster relief.

Debris flows often sweep houses, livestock and soil along the way. After the debris flow is over, the relevant road sections should be cleaned and disinfected to avoid and prevent the occurrence and spread of epidemic diseases and do a good job in health and epidemic prevention. (Excerpted from Survival at the Disaster Site-Self-help and Treatment)