From a trickle to a torrent, you only have tens of seconds to escape!

Recently, two hikers in Taizhou, Zhejiang were unfortunately washed away by a fast-flowing current while exploring a scenic spot. Sadly, although the two were found by search and rescue personnel, they had no vital signs.

Figure 1: Hikers were washed away while crossing a stream (Source: Video screenshot)

The incident happened in a deserted scenic spot . On weekdays, there was only a trickle of water in the canyon. Who would have thought that it would turn into a torrent that swallowed up lives? What risks are hidden behind this? In order to avoid similar tragedies, what scientific knowledge and safety common sense do we need to know?

01 Sudden "Flood"

In nature, streams meander through the mountains and fields in a gentle and peaceful manner. However, when heavy rains come, these originally gentle streams may turn into violent torrents in an instant, rushing like wild horses, swallowing up all obstacles that block their way. In the face of natural disasters, life seems so fragile. The water level in the valley can rise sharply in just a few tens of seconds, which means that we only have a few fleeting seconds to escape!

Figure 2: Stream landscape at Yamugou Scenic Area in Zhaibao Village, Taiping Town, Jiangkou County, Tongren City, Guizhou Province (Source: Xinhuanet)

According to people's experience and lessons, the reasons why those seemingly calm streams in the valley suddenly turn into torrents in summer are mainly as follows:

One is the sudden heavy rainfall in the upper reaches . Summer rain usually comes and goes quickly, especially rainstorms or thunderstorms. It may rain in the upper reaches of the valley but not be felt downstream. When a large amount of rainwater flows into the stream quickly in a short period of time, it will cause the water level of the stream to rise sharply, thus forming a torrent.

The second is flood discharge from upstream reservoirs or lakes . Sometimes, in order to regulate the water level, upstream reservoirs or lakes may discharge flood water and issue advance notice.

The third factor is the influence of topographic factors . Valley terrain easily forms a narrow channel effect, that is, in a narrow valley, the water flow is restricted by the mountains on both sides, the flow rate is accelerated, and the water level rises.

Fourth, geological disasters . When geological conditions are unstable, the mountains on both sides of the valley may be induced to slide or cause mudslides due to heavy rain. When a large amount of soil and rocks flow into the stream with rainwater, the stream will be blocked in a short time. Once it collapses, it will instantly turn into a turbulent torrent.

02 What are the signs that a stream will turn into a flood?

Was there no sign of the sudden flooding of the valley?

(1) Abnormal sounds . If you hear rustling or roaring sounds in the valley but cannot find the source of the sound, and sometimes you can feel a slight vibration, this may be the sound of loose sand and rocks or flowing floods, which is usually a signal that a flash flood or mudslide is forming.

(2) Changes in water flow . If you find that the water level is rising rapidly, the flow rate is increasing significantly, or there are a lot of floating objects such as firewood, trees, etc. in the water flow, you must evacuate quickly.

The most important point is to pay attention to the weather forecast when going out in summer, and try not to camp in the river. If we carefully analyze the news reports about floods, we will find that before many disasters occur, the local meteorological department usually issues rainfall forecasts or warnings, but this very useful information is ignored by everyone.

However, some dangers appear suddenly and often catch people off guard. Due to the complexity and diversity of the mountain environment, affected by many factors such as altitude, topography, vegetation cover, etc., a rapidly changing mountain microclimate is often formed . Its prominent features are:

♦The temperature in the mountains changes quickly and the temperature difference is relatively large;

♦High humidity, prone to cloud formation;

♦Air pressure changes affect air flow and weather changes;

♦The wind speed and direction change frequently, and the wind speed at the canyon wind outlet is often higher.

Therefore, weather forecasts here are almost completely ineffective. It may be sunny one moment and stormy the next. It is this unpredictable weather feature that adds many subtle dangers to the valley.

03 Valley exploration, you can’t just go anywhere

Valley exploration is a very fashionable sport and has been a popular activity in many primary and secondary school research activities in recent years. However, since it is an extreme adventure sport after all, most people only focus on the mystery, excitement and fun of valley exploration, and often ignore the many hidden dangers, including getting lost, abnormal temperature and humidity, communication signal interruption, valley water level rise, and even the possibility of being attacked by wild creatures .

In recent years, immersive outdoor experiences such as camping in the wild and picnics in streams have become increasingly popular. In order to attract traffic and attention, some Internet celebrities on self-media platforms have launched many "Internet celebrity check-in places". However, some are wild scenic spots that have never been developed , and some are abandoned scenic spots with safety hazards . Experts have long reminded that these "Internet celebrity check-in places" are neither safe nor beautiful , but this still cannot stop the "Internet celebrity check-in" behavior, so that disasters occur from time to time. For example, on the morning of August 9, 2023, more than a dozen tourists were taking photos and checking in at Yuling Dam in Yucheng District, Ya'an, Sichuan, when they suddenly encountered rising water. Many people were washed away by the water, resulting in 7 deaths. The local authorities pointed out that the Yuling Dam where the accident occurred was not a tourist attraction, but a water conservancy project. There are warning signs on both sides of the Yuling Dam, which clearly prohibit people from entering the water.

As the old saying goes, "under a turbulent stream, there must be a deep pool; under a high hill, there must be a dredged valley." The reason is that turbulent water has strong kinetic energy and erosion power. During the long-term flow process, the water will continuously scour the riverbed and carry away loose sediments, thus forming deep pools in places where the riverbed is soft or where rock joints are developed. Therefore, those seemingly peaceful streams in the mountains may hide deadly dangers, especially near waterfalls, so you need to be more vigilant.

According to media reports, on July 23, 2023, an Indian man slipped and stepped into the water while trying to appreciate the beautiful scenery up close, and was swept away and died. On the afternoon of January 31, 2024, five tourists were suddenly hit by a flash flood at the famous Indonesian tourist attraction, the Thousand Layer Waterfall. After more than an hour, they were finally rescued with the help of a local rescue team.

Figure 3: There are often dangers under waterfalls (copyright image of the gallery, reprinting may cause copyright disputes)

04 Special reminder after the college entrance examination

It is important to note that the summer vacation, especially after the college entrance exam, is usually a high-risk period. In order to relieve the long-term accumulated study pressure, some students go on adventures in the mountains in groups of three or five to give themselves a meaningful graduation trip, but it is not uncommon for them to encounter dangerous situations.

For example, on June 10, 2011, 34 high school seniors who had just finished the college entrance examination went to Qiushan, Tailing Township, Yongxin County, Ji'an City, Jiangxi Province, and got lost on the way down the mountain and encountered rainy weather. After more than seven hours of search and rescue by firefighters, all the trapped students were finally rescued safely.

On the afternoon of July 25, 2023, a flash flood broke out in Xiaogou Village, Shengkang Town, Gucheng County, Xiangyang City, Hubei Province, and two people were washed into the cave. The situation was very critical. After the fire rescue personnel arrived at the scene, they found that the five-meter-wide river channel was turbid and unclear under the raging flood, and the once dry river channel had risen by nearly four meters. The fire rescue personnel finally rescued the trapped people by wading and building a rope bridge. It was later learned that the two trapped people were students who had just finished the college entrance examination. They drove to the valley with their families to play, but they were trapped when the valley suddenly rose.

05 How to avoid danger and escape?

If you accidentally encounter a flash flood, how can you escape? Fire rescue personnel have summarized some key knowledge for us:

1. When a flash flood occurs, do not delay or hesitate. Run to the shore as fast as possible to seize the "golden time" for escape.

2. When fleeing from the disaster site, choose the nearest safe route and run horizontally along the hillside. Never run down the hillside or downstream along the valley exit.

3. Mountain torrents flow rapidly and rise quickly. Do not swim to avoid being swept away by the torrents. Call the rescue number as soon as possible and wait for rescue on the spot.

Regarding the death of two hikers in Taizhou, Zhejiang, netizens have heatedly discussed the "death V" during rescue. Many people believe that the cause of the accident may be related to the lack of first aid experience in rapid waters and improper use of ropes. When the two people fell into the water, the ropes set up formed a very obvious V shape under the impact of the water flow, which is what we often call the "death V". Therefore, if outdoor adventures lack professional training and rescue experience, it is easy to get into trouble.

Figure 4 When water flows through a narrow valley, a narrow channel effect occurs, that is, the flow rate suddenly increases (copyright image of the library, reprinting and use may cause copyright disputes)

Valley exploration is not a simple game. You can’t just go there. It requires not only certain geographical and geological knowledge, but also rich wilderness survival experience and good physical fitness. Even professional explorers may encounter unexpected events, not to mention ordinary hikers. Therefore, if you have a strong curiosity about valley exploration, you must follow a professional team, participate in tourism projects that are already open to the public, and take those relatively mature tour routes.

Please keep three points in mind: don't be aggressive, don't take risks, and don't act alone .

Author: Ma Zhifei, a popular science writer and member of the Beijing Science Writers Association, has written more than 10 popular science books, including "A Dream of Red Mansions" and "Glass Earth". He has won the Ministry of Natural Resources' Excellent Popular Science Book Award, the Wu Dayou Popular Science Book Award, and the China Natural Resources Writers Association's "China Gem Literature Award" Popular Science Works Award.

Reviewer: Researcher Zhang Ying, Director of the China Science Writers Association, Secretary-General of the Emergency Science Popularization Committee

Produced by: Science Popularization China

Produced by: China Science and Technology Press Co., Ltd., China Science and Technology Publishing House (Beijing) Digital Media Co., Ltd.