The chief engineer of China's Ministry of Water Resources, Liu Ning, believes that the Tangjiashan landslide dam may crumble at any moment. The dam holds back Tangjiashan Lake, a “quake lake” created on the Jian River.
The Sichuan earthquake released massive amounts of dirt and rock which dammed the Jian river and created the lake.
“According to historical records, the probability of landslide dams, which form after an earthquake, causing large scale flooding is as high as 93 per cent,” said Liu, who is also leader of the rescue team.
The dam is between 82 and 124 meters high, and the water level between 60 and 80 meters. This creates a huge risk for flooding downstream. The flooded area upstream of the landslide dam covers approximately 3550 square kilometres. According to experts, every 2mm of rain in this area will raise the water level by one meter. Average rainfalls in June, July and August are 140 mm, 260 mm and 330 mm respectively. This creates the potential for immediate failure of the Tangjiashan landslide dam. A collapse could trigger catastrophic landslides downstream.
“According to many field studies, a huge sliding mass is located underneath Xuanping County which is currently submerged under the water due to the Tangjiashan landslide dam,” said Liu. “As soon as there is a slide, it will trigger a huge surge and the dam will collapse in seconds.”
Since May 31, over 250,000 people have been evacuated from Mianyang City, just downstream of Tangjiashan Lake. At least 252 resettlement centers have been set up to ensure basic living conditions and needs are provided for the evacuees. Tangjiashan Lake was so named because of its proximity to Tanjiashan mountain.