On the morning of October 2, the Faculty of Geology, University of Science (Vietnam National University, Hanoi) organized a scientific conference "Lang Nu Disaster - Causes and Prevention Solutions".
Associate Professor Dr. Nguyen Chau Lan, Deputy Head of the Department of Geotechnical Engineering, Faculty of Construction, University of Transport, said that immediately after the disaster occurred in Lang Nu (Bao Yen, Lao Cai), Professor Tran Thanh Ha, Principal of the University of Mining and Geology and a group of scientists went to the scene to survey and collect data here and some key areas in Lao Cai.
“Initially, we determined that the cause of the Lang Nu disaster was a mudslide. Accordingly, up to 1.6 million cubic meters of mud, rocks and water from the top of Con Voi Mountain, 3.6km from Lang Nu, poured down on Lang Nu village,” Mr. Lan informed.
During the process of overflowing, the rock and soil were blocked in a narrow area (only about 100m wide) about 2km from the landslide site. This location accidentally created a natural dam, increasing the risk of flood failure.
Associate Professor Dr. Nguyen Chau Lan said that mudslides were the cause of the Lang Nu disaster. Photo: Binh Minh
At the time of the flood, the rainfall in the area was very heavy, with a total accumulated rainfall of up to 633mm, of which hourly rainfall reached 57mm, causing the mud and rock flood to move extremely quickly.
After entering data into the model, Mr. Lan received simulation results showing that the depth of accumulation of mud flow is 8 - 15m, the deepest point is about 18m, the flow velocity is very large up to 20 m/s. Therefore, the flow time from the mountain down (for the entire distance of 3.6km) is about 300 seconds (ie 5 minutes).
"Nu Village belongs to the Con Voi mountain strata, the rocks are strongly pressed and have a slope of 40 - 50 degrees. Nu Village is located on the Red River fault, causing the soil and rocks in this area to have a significant decrease in strength. This is an area with a high risk of major landslides," said Mr. Lan.
According to Mr. Lan, the estimated volume of landslide is up to 1.6 million m3. This landslide originated from the top of Con Voi mountain, about 3.6 km from Lang Nu and during the process of flowing down, it was blocked in a narrow area only about 100 m wide, about 2 km from the landslide origin point.
Mr. Lan said that this flash flood is not just a single phenomenon, but has happened in many places around the world. Among them is the disaster that happened in Seoul, South Korea in 2011.
"Currently, many geological cracks have appeared in mountainous provinces such as Ha Giang, Lao Cai, etc., enough time for authorities to respond. One of the immediate solutions is to cover the cracks with tarpaulin, combined with a horizontal drainage and drainage system, to prevent water from seeping deep into the ground, limiting the risk of landslides. This is a simple measure that localities can quickly deploy, then use other technical solutions to handle the cracks," said Associate Professor, Dr. Nguyen Chau Lan.
Lang Nu village, Phuc Khanh commune, Bao Yen district (Lao Cai) with 35 houses and 128 people were almost flattened after the terrible flash flood on the morning of September 10. Photo: Pham Hung
In order to prevent similar disasters, Associate Professor Dr. Do Minh Duc (University of Natural Sciences) recommended the need to build a database and establish a mapping system to delineate high-risk areas. This includes notes on different types of landslides and flash floods.
In addition, rainfall is a major trigger for landslides. Current rainfall monitoring systems need to be more dense; early detection of extreme rainfall; in-depth monitoring systems for slope stability; improved forecasting accuracy through the application of big data analytics and artificial intelligence;
Strengthen early warning information communication, ensuring that authorities at all levels, especially people in landslide-affected areas, receive timely and accurate information and clearly understand the actions to be taken when required.
Source: https://danviet.vn/lu-quet-mang-16-trieu-m3-nuoc-va-dat-da-vui-lap-thon-lang-nu-chi-trong-5-phut-20241002160431459.htm
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