6 June 2008
Tangjiashan – delayed again
Posted by Dave Petley
Xinhua is now reporting that the flow through the sluice has now been delayed through the use of a 60 cm high temporary dam (see below). This is an interesting development – I wonder why they have decided to do this at this late stage. Delaying the flow has a risk associated with it as the body of water will be larger, and thus the flood is potentially more damaging. Presumably they feel that the risks posed by this delay are more than compensated for by the larger channel, which reduces the chances of the dam eroding away quickly. I have noted before that in my view the channel is too small, but I am surprised that they have done this at this late stage.
The decision not to use dynamite, noted at the bottom of the text below, is undeniably sensible!
Original Xinhua text:
Water level of China’s main quake lake Tangjiashan topped the lowest point of 740meters by 0.20 meters on a sluice channel at 4:00 a.m. Saturday, but it was prevented from overflowing by a temporary dam added to protect workers on emergency construction downstream. More than 100 armed police were airlifted to Tangjiashan to broaden and deepen the sluice channel on Friday afternoon, said an expert at local commanding center on early Saturday morning. The temporary dam was 0.6 meters high, said the expert. Local headquarters said rainfall was heavy at the lake, with an average of two millimeters per hour. The swollen lake was formed by a massive landslide that blocked the flow of the Jianjiang River in Beichuan County, Mianyang City, following the May 12 earthquake in the country’s southwest. It held more than 220 million cubic meters of water and posed a threat to about 1.3 million people downstream. Some 600 armed police and soldiers worked for six days and nights to dig a 475-meter channel to divert water from the lake. More than 250,000 people in low-lying areas in Mianyang have been relocated under a plan based on the assumption that a third of the lake volume breached its banks. Two other plans require the relocation of 1.2 million people if half the lake volume is released or 1.3 million if the barrier fully opened. The swollen quake lake has put China’s longest oil pipeline at risk. The pipeline, winding from Lanzhou via Chengdu to Chongqing, was 60 kilometers downstream from the lake. With a capacity of transferring six million tons of oil each year, the pipeline provides 70 percent of product oil to Sichuan and neighboring Chongqing Municipality. If the line was cut, refined oil in storage could only supply Sichuan for three days, whereas repair work would take 30 days. Emergency plans have been drafted, according to colonel Liu Yongzhan. “Gate valve of the pipeline will be shut to prevent potential pollution, and a float bridge shall be later set up, so that a temporary line would ensure resumption of oil supply within48 days,” he said. Engineers have feared that the lake could burst and cause a flood, citing unforeseen factors such as fresh landslides, heavier than expected rain and the instability of the mud and rock dam. The plan of using dynamite to blast the lake had once been under discussion but was later announced as given up, according to Liu Ning, chief engineer of the Ministry of Water Resources. “We will not use dynamite if water in the lake could spill over naturally,” he said. “Blast might incur unexpected result.”
Dave Petley is the Vice-Chancellor of the University of Hull in the United Kingdom. His blog provides commentary and analysis of landslide events occurring worldwide, including the landslides themselves, latest research, and conferences and meetings.
Just watched CCTV-4, the drainage had started at 7:08 am Beijiang time.
Xinhua: MIANYANG, Sichuan Province, June 7 (Xinhua) — The long-awaited drainage of China’s Tangjiashan “quake lake” started at 7:08 a.m. Saturday, when its water flowed into a manmade sluice channel. A Xinhua reporter at the commanding center saw water passing the sluice channel via satellite monitor. The overflow has been estimated to occur Friday night when water level reached the lowest point of 740 meters on the sluice channel, but it was delayed by a 0.6-meter-high temporary dam erected on Friday afternoon to protect workers on emergency construction downstream.
China Daily story:http://www.chinadaily.com.cn/china/2008-06/07/content_6744346.htmPeople living along the east bank of the city’s Fujiang River, which will be flooded if the lake bursts its bank, had been evacuated. Those on the higher west bank stayed, but were told to remain alert.A bridge of the Baoji-Chengdu railway, which crosses the Fujiang River, has been reinforced. Each pier was surrounded by dozens of tires fastened by steel bars to prevent it from being hit by objects in the floodwater.The height, not the physical toughness, of the riverbank, is the real concern, said Ding Ji’an, general manager of the Mianyang Architectural Design Institute.Fucheng, the city’s central business district, lies on the west side of the Fujiang River, while Youxian, a mainly residential district, lies on the east.The riverbank is more than 10 m high on the Fucheng side. But only about 6 m high on the Youxian side, Ding said.
MIANYANG, Sichuan Province, June 7 (Xinhua) — The long-awaited drainage of China’s Tangjiashan “quake lake” started at 7:08 a.m. Saturday, when its water flowed into a manmade sluice channel. A Xinhua reporter at the commanding center saw water passing the sluice channel via satellite monitor. The flow was rapid, steady and gradually increasing in volume. The water level at the entry of the sluice channel was 740.37 meters above the sea level. The overflow has been estimated to occur Friday night when water level reached the lowest point of 740 meters on the sluice channel, but it was delayed by a 0.6-meter-high temporary dam erected on Friday afternoon to protect workers dredging the sluice channel.
Dear All:The Tangjiashan landslide lake was overflow at 7:08 Beijing time. The seepage was increased and connected from different seepage points last night.
Audio interview from CCTV with some video, uploaded within the last hour, it’s in Chinese so I don’t know what the details are.
again Xinhua: MIANYANG, Sichuan Province, June 7 (Xinhua) — The long-awaited drainage of China’s Tangjiashan “quake lake” started at 7:08 a.m. Saturday, when its water flowed into a manmade sluice channel. A Xinhua reporter at the commanding center saw water passing the sluice channel via satellite monitor. The flow was rapid, steady and gradually increasing in volume. The water level at the entry of the sluice channel was 740.37 meters above the sea level. The channel bifurcated, and some of the water diverged into the separate small channel at 9:30 a.m.. Soldiers of the armed police force are still working at the exit of the sluice channel to expand the channel and make it steepy so that the flow could be speeded up.