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Recently, heavy rainfall in the southern part of China has become a disaster. Jiangnan, South China and Southwest China have suffered heavy rains and even heavy rains. In the next three days, heavy rainfall in southern China and other places in Yunnan will continue, and it is necessary to strengthen the prevention of geological disasters such as mountain torrents and mudslides.
According to news from the Central Meteorological Observatory, in the next three days, Yunnan and southern South China are still the main targets of heavy rainfall. Among them, from day to night, there are heavy rains in parts of central Sichuan Plateau, central and western Yunnan, southwestern Guangdong, southwestern Guangxi, Hainan, eastern Fujian, and northern Taiwan; southeastern Guangxi, southwestern Guangdong, Heavy rains occurred in the local areas of western Hainan and other places.
Due to the recent frequent rainfall in the above areas, geological disasters such as mountain torrents and mudslides are more likely to occur. Therefore, the meteorological department recommends that all relevant departments should be vigilant, pay attention to the weather in a timely manner, and pay attention to preventive work.
Geological disasters such as mudslides and their defenses
Mountain torrent is a rapid and powerful surface runoff phenomenon occurring in mountain streams. It refers to the estuary that flows in the mountainous area with small area or periodic flowing water. It is a surface runoff with short duration and skyrocketing. The torrential floods are sudden, the water flow concentration is large, the erosion and destructive power is strong, and the water flows in the mud and sand and even the stones, which often cause local floods, which are generally divided into storm floods, snowmelt flash floods, and glacier flash floods. Mountain torrents and their induced mudslides and landslides often cause casualties and damage to houses, fields, roads and bridges, and may even lead to dams and mountain ponds that cause serious damage to the national economy and people's lives and property.
What are the formation factors of torrents?
Geological and geomorphic factors: The terrain of mountain flood disaster-prone areas is often high in mountain height, steep in slope, deep in valley, large in cutting depth, and developed in eroded valleys. Most of its geology is soil with low osmotic strength, such as argillaceous rock and shale development. The soil with weaker corrosion resistance is easy to soften and easily disintegrate when it is in contact with water. It is very beneficial to the rapid accumulation of surface runoff after heavy rainfall. When a strong surface runoff is encountered, a mountain flood disaster is formed.
Meteorological and hydrological factors: The unstable climate system in the hills often results in sustained or concentrated high-intensity rainfall. According to statistics, the occurrence of mountain torrent disasters is mainly due to the fact that the previous rainfall in the affected areas continued to be excessive, which made the soil water saturated and the surface loose. After the short-term heavy rainfall in the local area, the rainfall quickly merged into surface runoff and caused the water level of the gully to rise, the debris flow, and collapse. Landslides. From the physical process of overall occurrence and development, it is known that mountain flood disasters are mainly caused by continuous rainfall and short-term heavy rainfall.
Factors of human activity: excessive development of land in hilly areas, or land reclamation on steep slopes, or damage to the mountain caused by engineering construction, changes in topography, landforms, destruction of natural vegetation, deforestation, loss of water conservation, are prone to flash floods.
Main characteristics of torrents
During the flood season from April to September, especially during the main flood season from June to August, it is a period of frequent flood disasters. In the same basin, even in the same year, there may be many mountain flood disasters, so it has the characteristics of strong seasonality and high frequency.
The small watershed in the hilly area has small channel area and channel storage capacity, large channel slope, short process and short flood duration, but the water level increases greatly and the flood peak flow rate is high. The rainfall production is rapid, generally only a few hours. The torrential rain that stimulates the flash floods is sudden, which leads to the suddenness of the mountain flood disasters. The flash floods lasted for a short time and the disasters were very rapid.
There are high empty surfaces on both sides of the stream source or valley, and collapse often occurs. Complex geological structures and a large amount of loose solid matter on the surface are important factors that aggravate the debris flow disaster. In the scope of the rainstorm center, the loose deposits formed by the collapse of the previous period formed a debris flow simultaneously in each branch trench under the action of heavy rain.
Due to the relatively backward economic development of mountainous areas, the early warning and forecasting facilities are not perfect, and effective measures cannot be taken in time to reduce flood damage. In addition, the regularity research on mountain flood disasters is not enough, there is no quantitative discriminant standard. The previous mountain flood disaster prevention plan is not very operational, and the mountain flood disasters have poor predictability and difficult defense.
Mountain torrent is a rapid and powerful surface runoff phenomenon occurring in mountain streams. It refers to the estuary that flows in the mountainous area with small area or periodic flowing water. It is a surface runoff with short duration and skyrocketing. Mountain torrents can be divided into general flash floods, high sandy torrents, thin mudslides and thick mudslides. The density of general flash floods is >1.1t/m3, the high sandy sedimentation is 1.1-1.3t/m3, the dilute debris flow is 1.3-1.8t/m3, and the thick debris flow is <1.8t/m3. If it is divided from rainfall to disaster formation, it can be divided into five types of disasters: high-speed landslide type, collapse flow type, siltation type, scouring bank type and loose deposit type.
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