The Tiangjiashan quake lake is draining, and officials have declared a “decisive victory”. Like Wellington said after the Battle of Waterloo, it was a damned close run thing.
Without demeaning the 10-day effort put into cutting drainage channels in extremely trying conditions, it was in the end the crude tactic of blasting holes in the rock and mud holding back the waters that released the torrent of water needed to get the quake lake’s levels subsiding.
The flow of water through the spillway peaked, as far as one can tell, at 80 cu. meters a second, while the inflow was at least 115 cu meters a second. After two massive blasts on Monday evening which broke through what Xinhua called the “bottleneck” in the spillway, the water outflow surged to 6,420 cubic meters per second before slowing to o a steady 3,888 cubic meters per second by early Tuesday afternoon, dropping the lake’s level by 20 meters and emptying half the water that was in it at its peak. The outflow, though, was still much faster than originally planned, and as TV shots of the river well down stream showed, a river bed that was nearly dry an hour and a half away form Tangjiashan, was in full flow.
This is an important propaganda victory for the authorities and the army, too. Attempts to drain the lake have been front and center of state media reports, displacing concerns about the shoddy construction of schools. For a while it looked as if the story might have a catastrophically bad ending in all regards. And the story isn’t fully over. There is still a lot of lake water being held back by no more than an unstable landslide, and rainy season ahead.
Sluicing of the Tangjiashan quake lake has started. Water levels reached the lip of the spillway cut earlier in the week on Saturday. Xinhua reports that work crews are trying to improve the flow so water can drain faster. The sluicing will stop the level of the lake rising further and hold the waters at a volume that engineers calculate won’t burst the dam created by landslides triggered by the May 12 earthquake.
Two key pieces of infrastructure lie downstream from the lake: the Fujiang river bridge on the Baoji-Chengdu Railway, an important part of the rail network in western China; and PetroChina’s Lanzhou-Chongqing pipeline which supplies 70% of Sichuan and Chongqing’s oil. If the pipe was ruptured, Sichuan has only three days of oil in store.
Its all gone relatively quiet over the draining of Tangjiashan, the quake-created lake that is top of the list of those at risk of catastrophic bursting.
Sluicing was meant to have started last week following a well-publicized effort to cut a drainage channel. The latest aftershock, a 5.3 that occurred on Thursday and sent waves across the lake, reminds us that the draining has still to start.
The waters, swollen by heavy rains, are reported to have risen to within 2 meters of flooding over the banks. As of 2 pm Wednesday, Xinhua reported, the lake contained 211.6 million cubic feet of water. Prime Minister Wen Jiabao visited the area on Thursday, saying “Now it’s a critical moment for the Tangjiashan quake lake, and the most important thing is to ensure there is no casualty of the people.”
This Bystander’s sense is that the situation in on a knife-edge. More evacuations are underway of the million people at risk should he worst happen.