30 May 2010
Flow through the spillway continues to increase slowly. So far there are no signs of the development of a breach, but the amount of water passing through the spillway remains much less than the inflow. This image, taken yesterday morning, shows water passing through the channel:
The difference between the flow in the channel and the amount of water coming through the dam as seepage (the large channel bottom right) at this time is very clear. The channel flow at this time was in the order of 20 cubic feet per second; the seepage is over 100 cubic feet per second. Since then channel flow has increased (I’ll blog on this shortly).
It is important to stress that the threat has not reduced. There was always a good chance that flow would develop slowly and that erosion would take time to initiate. Flow needs to reach >2,500 cubic feet per second to equilibriate the lake level even at the current rate of inflow. The river discharge will more than double over the next month, putting further stress on the spillway. The best image illustrating the latent threat at this site is this one, also taken yesterday:
At the moment this is very reminiscent of the early stages of flow at Tangjiashan: