Update 6 (Final Update): A Great Success in "Quake Lake" Draining! Congratulations to Chinese Engineers! (唐家山堰塞湖排水获巨大成功! 热烈祝贺中国工程师们!)

A deep channel has cut through the landslide dam by the "natural" current. See photo to the left for the initially cut through channel around 9:00 a.m., June 10, Beijing time, with lake water surface elevation of about 742 m and discharge rate of about 1,200 cubic meters per second. Channel inlet bottom elevation was cut down from 740 m to about 720 m (about 20 meters lower) and channel was cut wider from about 10 m to about 150 m. The lake water level was brought down from its highest at 742.96 m (8:00 p.m., June 9, Beijing time) to the present reading of 719.48 m (8:00 p.m., June 10, Beijing time). As a result, over 100 million cubic meters of the lake water was drained out of the lake. The population at risk of future downstream flooding has been reduced from 1.3 million (upon catastrophic collapse of the landslide dam) to 50,000.

Although the peak discharge rate was very high at 6,420 cubic meters per second during the course of channel cutting and lake water draining (and was rapidly increased to this peak value from 500 cub. m/s within three and half hours, from 7.56 a.m. to 11:30 a.m. on June 10), the downstream area flooded by this release of water was far less than the planned 1/3 dam collapse inundation zone. Note over 200,000 people were already evacuated about 10 days ago, in preparation for the possible 1/3 dam collapse scenario. Therefore, I would define this initial draining of the "quake lake" water as a great success! The engineers' original drainage scheme including the sluice channel design worked.

Congratulations to the Chinese engineers for their great success!

P.S.: I am also glad that my projection of the unnecessary second, deeper drainage channel to "force" an additional outflow was correct (see my Update 5 posted on June 8). Construction of the second channel was stopped at 6:00 p.m., June 9 as the lake outflow through the first already-constructed channel increased to 81 cubic meters per second (cms) and was approaching the lake inflow rate of 115 cms.

Photo credit and info source: Xinhuanet