How can we avoid risks in the face of heavy rain or even floods?

Affected by the northward movement of the remnant circulation of this year's fifth typhoon "Dusurui", many places in the north have experienced large-scale heavy rainfall in the past two days.

At 18:00 on July 29, the Central Meteorological Observatory issued the highest level of red warning for heavy rain. It is reported that this is the second red warning for heavy rain in history issued by the Central Meteorological Observatory since the early warning release mechanism was officially launched in 2010. Starting from the 29th, rainfall gradually spread in North China and the Huanghuai area, and some areas in Beijing, Tianjin, Hebei, Shandong, Henan and Shanxi experienced heavy rain or torrential rain, and some areas experienced extremely heavy rain. The Central Meteorological Observatory continued to issue a red warning for heavy rain at 10:00 on July 31.

National heavy rainfall forecast map

Heavy rains can not only cause mountain torrents and geological disasters, but also bring many inconveniences to our lives and threaten the safety of life and property in the affected areas.

In the face of heavy rain or even floods, what knowledge do we need to master and what preparations do we need to make?

Part 1

The “flood beast” is not just a name

The causes and types of floods are numerous and complex. Heavy rains, typhoons, earthquakes, volcanic eruptions, tsunamis, etc. can all cause floods, and even human factors can cause floods. Here we mainly introduce two common floods - heavy rain floods and dam breach floods .

As the name suggests, rainstorm floods are floods caused by heavy rain or rainstorms . Due to excessive rainfall, the drainage system is overloaded, causing rainwater to gather into rivers, which in turn causes flood disasters. During the spring and summer rainstorms, the possibility of sudden rainstorm floods increases greatly, and they can occur in both urban and rural areas. Once a flood occurs, it can affect traffic at the least, and in severe cases it can cause power outages in the region, and even cause casualties.

Heavy rain and floods not only occur in the south where the average annual rainfall is higher, but can also occur in the north where the average annual rainfall is lower due to excessive rainfall in a short period of time .

I believe that residents in the Beijing-Tianjin-Hebei region will still be haunted by the torrential rain in Beijing on July 21, 2012. The heavy rain in July of that year was the heaviest rainstorm and flood disaster Beijing and its surrounding areas had experienced in 61 years, which directly led to the collapse of more than 10,000 houses in Beijing alone, 79 deaths, and serious impacts on the city's infrastructure and residents' daily lives. In the worst hours of the rainstorm, rivers backflowed, houses were flooded, and traffic was paralyzed. Afterwards, it was calculated that the property losses amounted to 11.2 billion yuan.

Dam breach floods mainly occur in riverside and coastal areas. They are caused by high water levels that overflow dams or rapid water flows that cause dam breaches when the flood peak arrives.

The Xiangjiang River is approaching its highest water level in history (Photo source: Zhuzhou Evening News)

Although dam failure is relatively rare, once it occurs, it is very likely to cause serious damage and casualties to the downstream areas where the dam is located . There are three main reasons for dam failure: first, unreasonable dam design, second, dam disrepair, and third, sudden earthquakes or heavy rains . The first two situations are very rare in modern times, and most of them can be predicted. The government can evacuate people in advance to reduce casualties. Sudden earthquakes and heavy rains require vigilance, especially small dams have limited carrying capacity, which can easily reach the critical point and fail during the rainy season, so more attention needs to be paid.

Floods have always been a huge enemy of our production and life. When describing terrible things, we often use "flood beasts" to describe them, and its destructive power can be seen. However, in the face of floods, we are by no means powerless. We can still use some methods to minimize the impact of floods .

Part 2

How do water conservancy projects prevent floods?

The most effective protection against floods is undoubtedly water conservancy projects . Water conservancy facilities such as dams, reservoirs, and flood discharge areas can effectively protect our lives and property during floods. At this point, some friends may have questions. Water conservancy projects have been built in the 70 years since the founding of New China, including super-large projects such as the Three Gorges Dam. Why are there still floods? Does it mean that water conservancy projects are not very meaningful in flood control, and "heaven's will prevails over man"? The answer is no. Let's start with several common water conservancy projects and talk about how water conservancy projects protect cities.

Floods are essentially a sudden increase in river flow. The sudden increase in river flow in a short period of time is the flood peak, which is also the direct way for floods to cause harm. Therefore, our means of preventing floods are simple, that is, not to let the flood peak exceed the carrying capacity of the river and reservoir . There are two ways to achieve this goal: expand the capacity of the river and weaken the flood peak . The former is mainly achieved by dredging the river and raising the dam to strengthen the discharge capacity and the carrying capacity of the river; the latter is achieved by storing water in the reservoir and discharging flood water.

The first water conservancy project built after the founding of New China was the Jingjiang Flood Diversion Area to prevent floods. Jingjiang is a section of the Yangtze River. There is a widely circulated saying in the local area: "The most dangerous part of the Yangtze River is Jingjiang". Because of the low terrain, the silt brought by the Yangtze River has been deposited in large quantities here, raising the river channel. In addition, the river channel of the Jingjiang section is particularly tortuous, and it is known as the Nine Bends and Turns. This has led to frequent floods in the Jingjiang River, and the Jingjiang Flood Diversion Area is to weaken the flood peak by diverting floodwaters.

Jingjiang flood diversion area (Photo source: Baidu Encyclopedia)

However, flood diversion is the last way to prevent floods, because once the flood diversion gates are opened, the houses and fields of the people in the flood diversion area will inevitably be flooded . At present, the Jingjiang flood diversion area has only been used once in 1954, and it is hoped that this project can always be in a state of "prepared but not used".

Unlike flood diversion areas, the flood control function of reservoirs is not to divert water, but to "flatten flood peaks." When heavy rainfall occurs upstream and a flood peak is likely to occur, the reservoir will open the gates to release floodwater to empty the storage, so that as much water as possible can be stored when the flood peak comes, reducing the flow downstream and achieving the purpose of reducing the flood peak.

Part 3

How should we avoid risks when encountering floods?

Although we now have very complete water conservancy facilities, urban waterlogging and rainstorm floods are still difficult to completely avoid. When we encounter floods, what methods should we use to maximize the safety of our lives and property?

During the flood season, the most important thing is to pay attention to early warning information in a timely manner . During the flood season, people in areas prone to flood disasters should develop the good habit of paying attention to weather forecasts and relevant early warning information. Reduce travel during periods of heavy rain and avoid dangerous areas where floods may occur. If you live near flood-prone areas, prepare to evacuate in time to prevent disasters before they happen.

If a flood comes and we don't have time to evacuate, we must quickly move to nearby hillsides, highlands, buildings, flood shelters, etc., or immediately climb to roofs, high floors of buildings, big trees, high walls and other high places for temporary shelter . At the same time, we must contact the local government flood control department as soon as possible, report our location and danger, and actively seek rescue.

If the flood continues to rise, the temporary shelter will be submerged. At this time, we must not panic and try to swim to a safe place. It is best to quickly find some floating materials such as door panels, tables and chairs, wooden beds, large pieces of foam plastic, etc. to make a raft, and at least tie plastic bottles, foam boards and other objects to yourself.

If we accidentally fall into the water, we must not panic or give up trying to survive . We should first try to stand up in the water. Try to keep your head above the water and adjust your breathing. If possible, take off your shoes in time to prevent slipping and make it easier to kick the water. If you encounter fixed objects in the water, you must hold on to them firmly, stabilize your body and actively wait for rescue.

If you encounter a flood indoors, you should not take it lightly. A large number of victims died from electric shock in flood disasters. When we find that water has flooded into our home, we must cut off the power supply in time and move to a higher floor or roof with food, drinking water and communication equipment .

When traveling on flooded roads, if you cannot see the road conditions, be sure to prepare a long pole or something similar . Keep monitoring the depth of the water ahead and never go into deep water. Falling into sewers or pits accounts for a large proportion of casualties caused by urban flooding.

Finally, do not go under trees or on top of mountains during heavy rain to avoid being struck by lightning .

In addition, the disasters caused by floods are not declared over when the floods recede . Because floods will contaminate drinking water in the disaster area and destroy local health resources, which makes it easy for intestinal soft infections and epidemic hemorrhagic fever to spread after the flood. Post-disaster disease prevention and ensuring "no major epidemics in major disasters" are also important parts of disaster prevention and relief work. Paying attention to food and drinking water hygiene is the key to preventing infectious diseases. Secondly, we should try to avoid contact with the remaining water bodies after the disaster and avoid mosquito bites. And most importantly: do not let feces and urine enter the water. In short, mastering the knowledge of flood risk avoidance can help us get through the difficulties during the flood season to a certain extent.

Produced by: Science Popularization China

Author: Zhiyao

Producer: China Science Expo

This article only represents the author's views and does not represent the position of China Science Expo

This article was first published in China Science Expo (kepubolan)

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