At 0:00 on July 22, Enshi City, Enshi Prefecture, Hubei Province held a press conference to introduce the relevant situation of the sand dam landslide.
Earlier, the Enshi City Flood Control and Drought Relief Headquarters issued an early warning that the sand dam landslide caused the formation of a dammed lake in the upper reaches of the Qingjiang River, and there was a danger of flooding due to dam failure at any time.
The Paper (www.thepaper.cn) learned from the press conference that after relevant measures were taken, the upstream water level dropped and the risk of dam failure in the barrier lake was eased.
According to experts, the landslide is an old landslide, and there have been many partial landslides. This time, the landslide body was saturated and slipped due to continuous heavy rainfall, and the surface water on the west side of the gully further slipped into the Qingjiang River. It is a typical landslide induced by natural factors.
Enshi's precipitation during the rainy season this year hit a record high
According to reports, the geological landslide site is located in the sand dam of Mazhe Village, Tunpu Township, Enshi City, and is one of the 167 geological disaster monitoring sites in Enshi 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. Since the plum rains began on June 8 this year, Enshi City has experienced continuous heavy rainfall, with a long period of time, heavy rainfall, and high intensity. The cumulative rainfall during the plum rain period reached 907 mm, which is 1.56 times more than the same period in history (only 354 mm in the same period in history). It is the highest value in history since there were meteorological observation records in 1951.
Due to continuous heavy rainfall, geological deformation of the sand dam in Mazhe Village was induced and landslides and debris flows appeared. Especially at around 5:30 am on July 21, about 1.5 million cubic meters of soil slipped into the Qingjiang River, blocking the Qingjiang River and forming a barrier lake.
1.5 million cubic meters of soil, if you start to dig from the surface of a standard football field, you need to dig down 210 meters when the entire football field is dug.
According to Fu Qiang, assistant to the leader and senior engineer of the Second Geological Team of the Geological Bureau of Hubei Province, the landslide has a "tongue" shape in plan, with a longitudinal length of 1200-1500 meters and a lateral width of 320-580 meters; the landslide is the Quaternary residual slope accumulation layer The loose layer is 10 to 43 meters thick, with an average thickness of 25 meters. The landslide volume is about 10 million cubic meters. It is a super-large soil landslide with a main sliding direction of about 195 degrees. The elevation of the front edge of the landslide is about 690 meters, the elevation of the trailing edge is about 950 meters, and the height difference between the front and the back is about 260 meters; the front edge of the landslide is located on the high and steep slope on the left bank of the Qingjiang River, the bank slope is about 150 meters high; the back edge of the landslide is located above the Tunyu Highway , The east and west sides are bounded by gullies, and the perimeter of the landslide is clear. The total area of the landslide deformation and impact area is about 1.76 square kilometers.
Pan Wei, a senior engineer at the Wuhan Geological Survey Center of China Geological Survey, analyzed that the landslide was an old landslide. There had been many local landslides. This time it was caused by continuous heavy rainfall which caused the landslide body to slip due to saturation and instability. The surface water of the side gullies further slides into the Qingjiang River. It is a typical landslide induced by natural factors.
More than 8,000 people were transferred, and the risk of dam failure was eased
Pan Wei said that this was a very successful early warning forecast of geological disasters. Since the monitoring reports were timely and the early handling was done properly, no casualties occurred when the masses were evacuated and moved quickly.
It is understood that as early as 16:00 on the 17th, the geological hazard monitors of Tunpu Township found surface cracks in the geological hazard point of the sand dam of Mazhe Village during their daily inspections of geological hazards, and reported the landslide danger in time. Since then, the responsible persons and experts of relevant departments at all levels in the provinces and cities have made many on-site site visits, research and judgment consultations, dispatch and command, and organize the transfer of local people to avoid danger.
As of 15:00 on the 21st, all people in the affected area have been transferred and properly resettled. A total of 8397 people from 1963 households have been transferred.
After the formation of the barrier lake, according to the opinions of the expert group, Enshi City quickly launched the "joint adjustment and joint control" dispatch mechanism. The measures of "flooding, drainage, and timely warning" were adopted to increase the discharge flow of Yunlonghe Reservoir upstream of the barrier lake, scour the weir body, reduce the height of the weir body, and reduce the threat of the barrier lake; discharge and escalate the downstream Dalongtan Reservoir Reservoir, to deal with the possible risk of dam failure of the barrier lake; provide early warning to the upstream and downstream areas of the landslide site, especially Enshi Prefecture, and formulate emergency plans for the evacuation and resettlement of the affected areas.
Up to now, the inflow from the upper reaches of the Qingjiang River and the discharge flow from the Yunlong River Reservoir have washed away the top of the dammed lake (water flow reaches 200 cubic meters per second), and the upstream water level is falling (compared with 12:00 on the 21st, the upstream water level Down 4.27 meters), the risk of dam failure of the barrier lake has been eased.
Pan Wei suggested that the next step is to strengthen professional monitoring and early warning, timely grasp and accurately delineate the scope of danger; continue to conduct landslide inspections and timely grasp the characteristics and models of landslide deformation dynamics; timely analyze and determine the development trend and risk range of landslides to provide rescue and relief services Technical basis. At the same time, do a good job of observing the siltation and water level and flow of the Qingjiang reach in the landslide area, and coordinate the upstream and downstream water regime observation and information notification. After the emergency phase, the landslide survey and treatment project demonstration will also be organized.
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