7 June 2008
Updated: Tangjiashan – flow rate information
Posted by Dave Petley
Xinhua is now reporting that the discharge in the sluice has now reached 40 cubic metres per second. This means that it is less than half that required to balance inflow at the current rate (c. 100 cubic metres per second). So far at least the channel is apparently stable. The same report indicates that the lake volume is now 229.5 million cubic metres.
This is good news. The lake should continue to fill slowly until the water depth is greater enough to drive enough water through the channel to balance the inflow. The potential for erosion will increase, but so far so good. No heavy rainfall is expected for at least a week, which provides time enlarge the channel further to deal with the summer floods.
Updated: an anonymous poster (thanks!) has drawn my attention to this AP image, which is captioned: Water from the Tangjiashan “quake lake” flows down a landside site in the quake-devastated Mianyang City, southwest China’s Sichuan Province.
I suspect that this was taken soon after flow started as this is clearly not 40 cubic metres per second. I guess that the channel on the right us the one that is referred to in the Xinhua posts as having ongoing works to widen it. Note that the main flow, before it starts to split, does appear to be eroding the channel bed at least to a certain degree.
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.
Water level increased to 740.85m at 15:00 (Beijing time) from 740.67m (at 12:00). The seepage flow is also increasing. I think the rate of flow from excavated channel is very small compare to inflow. Link of photo of excavated channel and out flowing water: http://66.163.168.225/babelfish/translate_url_content?.intl=us&lp;=zh_en&trurl;=http%3a%2f%2fnews.sohu.com%2f20080607%2fn257349510.shtml
Update (http://news.xinhuanet.com/english/2008-06/07/content_8325421.htm):MIANYANG, Sichuan Province, June 7 (Xinhua) — The water flow at the sluice channel of the Tangjiashan quake lake has speeded up as engineering soldiers blasted off a boulder in the man-made sluice channel on Saturday afternoon. Experts calculated that the water flows at seven to eight cubicmeters per second, far more than the previous two cubic meters per second.
from latest Xinhua: The lake started to drain on Saturday morning and water flowed at a speed of nearly 10 cubic meters per second at 7 p.m., far more than the previous two cubic meters per second. Rao Xiping, head of the Beichuan hydrometeorological station, said the water level of the lake was still rising due to the slowness of the water flow. The water level in the lake stood at 741.02 meters above the sea level at 6 p.m., 0.65 meter higher than that triggering the quake lake’s overflowing.