Flash floods are a natural phenomenon that occurs during the rainy season and are found only in mountainous regions. Many people mistakenly believe that flash floods are the same as debris flows.
Formation Process of Flash Floods
Essentially, flash floods are similar to other types of floods, meaning that water suddenly pours down from high ground, causing significant destruction to the downstream area. However, unlike debris flows, flash floods occur during the rainy season and are specific to mountainous areas.
Flash floods have caused many houses and structures in Muong Loi commune, Dien Bien district to be eroded and deeply submerged.
Due to the uneven surface of the Earth, mountainous areas have many interlacing hills and ridges; between them are valleys connected to streams and small rivers. At the points where streams and small rivers flow through the sides of the valley hills, the water drainage paths narrow and constrict at a single point, which is often where flash floods originate. When heavy rains occur upstream, water flows down rapidly; the constricted point fails to drain the water promptly, causing the water to rise quickly upstream and create a powerful current at the narrowed point, resulting in a flash flood.
This terrain causes the water flowing from above to become trapped, posing dangers to both the upstream and downstream areas. While the upstream area is devastated by the rising and stagnant water, the downstream area suffers from torrents of powerful water rushing down, sweeping away everything in its path.
When Do Flash Floods Occur?
Flash floods can also occur in areas with limestone mountains, where there are often caves and underground reservoirs connected to the outside by small, narrow cave entrances and gorges. During heavy rainfall, water quickly accumulates in lakes and underground caves, causing water levels to rise and exert high pressure, leading to flash floods at the exits.
