How to break the barrier lake formed by landslide
Recently, an early warning message of the formation of a dammed lake in the upper reaches of the Qingjiang River has attracted intense public attention.
The Flood Control and Drought Relief Headquarters of Enshi City, Hubei Province recently issued an early warning that due to the landslide of the sand dam in Mazhe Village, Tunpu Township, the upper reaches of the Qingjiang River, a barrier lake is formed in the upper reaches of the Qingjiang River, and the dam may break at any time and cause floods to leak.
How is the barrier lake formed? What is the progress of Qingjiang dammed lake disposal? What are the usual disposal measures for the dangerous situation of dammed lakes? A reporter from Science and Technology Daily conducted an interview on this.
Landslide forms a barrier lake
Recently, the Enshi Municipal People's Government held a press conference to introduce the geological disasters of the sand dam and the disposal of the Qingjiang dammed lake.
According to reports, the geological landslide site is located in the sand dam of Mazhe Village, Tunpu Township, Enshi City, which is one of the 167 geological disaster monitoring sites in the city. Due to its location in the Qingjiang River Valley and its special geology, geological landslides have occurred in this area to varying degrees since the 1970s.
After the plum blossoms began on June 8 this year, Enshi City experienced continuous heavy rainfall. The cumulative rainfall during the plum rain period reached 907 mm, which was 1.56 times more than the same period in history, and was the highest value in history since the meteorological observations were recorded in 1951. Due to continuous heavy rainfall, geological deformation of the sand dam in Mazhe Village was induced and landslides and debris flows appeared. At around 5:30 am on July 21, a large amount of mud slipped into the Qingjiang River, blocking the river course and forming a barrier lake.
When analyzing the formation process of a barrier lake, Sun Dongya, a professor-level senior engineer at the Flood Control, Drought Relief and Disaster Mitigation Center of the Ministry of Water Resources, introduced that generally speaking, after the mountains on both sides of the river collapse or slide under the action of external forces, the rocks on the mountain are broken, blocking the river and forming a dam. , The upstream of the barrier dam continues to store water, forming a barrier lake.
The natural causes of landslides mainly include earthquakes and heavy rainfall. Sun Dongya used heavy rainfall as an example to further explain that after rainwater penetrates into the cracks of the rock mass, under the action of seepage force and water pressure, coupled with the gravity of the rock mass itself, the rock mass may slide toward the open surface. In addition, the long-term scouring action of water will hollow out the foot of the slope of the mountain. If the support is lost, the upper mountain is prone to collapse under the action of gravity.
If the dam breaks instantaneously, the damage is great
"Barrier dams formed under natural conditions are often unstable in structure and prone to dam breaks. Once the dam breaks, the flood peak discharge is very large, which will threaten the production and life of residents on both sides of the downstream." Sun Dongya pointed out that the barrier dam is very easy Sudden failure due to flooding, etc., makes the instant dam failure more harmful.
In response to the danger of Qingjiang Barrier Lake, Enshi City quickly launched the "joint adjustment and joint control" dispatch mechanism. On the one hand, the local area increased the discharge flow of the Yunlong River Reservoir upstream of the dammed lake, washed the weir body, lowered the height of the dam body, and reduced the threat of the dammed lake. On the other hand, the downstream Dalongtan Reservoir was flooded and flooded to deal with possible moments of the dammed lake. Dam failure risk. At the same time, early warning was given to the upstream and downstream areas of the landslide, especially Enshi Prefecture, and an emergency plan for the evacuation and resettlement of the people in the affected area was formulated.
Through the joint implementation of various measures, certain progress has been made in the disposal of the danger situation. Incoming water from the upper reaches of the Qingjiang River and the discharge flow from the Yunlonghe Reservoir have already broken through the top of the barrier dam. The water flow reached 200 cubic meters per second. The upstream water level dropped and the risk of instantaneous dam failure of the barrier lake was reduced.
In the next step, the local area will continue to do a good job of monitoring and early warning, start a video surveillance system, monitor and early warning of the landslide area 24 hours a day, provide scientific data for emergency work, and actively prevent various secondary disasters formed by barrier lakes.
Controlling the drain flow is the key
Sun Dongya introduced that the disposal of dammed lakes is mainly divided into two categories. One is the simplest and traditional way, which is to let it collapse naturally, provided that the collapse of the dammed lake will not cause catastrophic effects on the downstream; the other is Manual intervention is to dig diversion grooves before floods overflow the barrier dam, guide the barrier dam to gradually break, and the lake water slowly drains to avoid sudden dam failure and excessive flood peak flow.
"To prevent the sudden collapse of a barrier dam and cause flood disasters, controlling the discharge flow is the key." Sun Dongya said, if the discharge channel needs to be excavated manually, the discharge channel should be excavated into an S shape to extend the flow path and avoid Excessive flow velocity in the chute caused sudden collapse.
At the same time, it is necessary to strengthen rainfall and water level monitoring, predict the failure mode of the dam, analyze the peak flow of the dam failure and the possible downstream inundation area, and do a good job in the transfer and resettlement of the affected persons and the protection of important infrastructure.
Our reporter Tang Ting