24 September 2008

More trouble at Tangjiashan

Posted by Dave Petley

Tangjiashan was the most serious of the “quake lakes” (valley-blocking landslides) generated by the Wenchuan earthquake. Back in June I followed the remarkable exercise undertaken by the Chinese authorities to mitigate the problem by draining the lake. Once the lake was drained the concern was what would happen in the wet season.

Today, China.org.cn is reporting that new problems have developed:

Two people were dead and 30 were missing amid torrential rain in one of the counties that was hardest-hit by the May 12 earthquake, local authorities said on Wednesday. More than 300 people sustained injuries and about 6,000 were stranded or in dire need of help, according to the local committee in charge of post-quake restoration. Downpours began to pound Beichuan County in Sichuan Province, southwest China, on Monday night, collapsing more than 1,100 houses since then. Heavy rain, with maximum and average totals of 352.8 mm and 150 mm respectively, triggered mountain torrents, cave-ins and landslides. Local party chiefs were supervising relief work.

In a slightly older report, Xinhua gives slightly more detail:

Fourteen people have gone missing in the wake of landslides triggered by heavy rain in the quake-hit Beichuan County of Sichuan Province in southwest China, a local official said on Wednesday. Some villagers in Leigu town have also been injured, said Zuo Daifu, a county official in charge the reconstruction of Beichuan. The town received 104 mm of rain between 8 a.m. Tuesday and 7 a.m. Wednesday. Heavy rain totaling 194 mm during the period also hit the Tangjiashan area, blocking the sluice of the dangerous Tangjiashan quake lake and raising its water level by five meters.

It goes without saying that a landslide that has blocked the sluice, given its size, must be a fairly large slide. The image below shows water flowing over the channel during release of the water. Note the scale of the channel compared to the bulldozers parked on the dam. Of course the flow will be much lower now.

There can be little doubt that the authorities will be able to deal with this blockage once again, but the challenges ahead in terms of instability are clear.