The channel inlet would be made two meters deeper, and the channel outlet one meter deeper. Over almost the same channel length, the bottom slope would be much milder at about half of what originally planned. The changed channel dimensions are: Length = 320 m, top width = 50 m, bottom width = 8 m. Depth at upstream end = 10 m, that is, the dam was excavated from the original top surface elevation of 750 m down to 740 m. Depth at downstream end = 13 m, that is, the dam was excavated from the original top surface elevation of 752 m down to 739 m. The channel is expected to be completed by noon (New York time) or midnight (Beijing time) today.
At 14:10 Beijing time, the lake water level was 734 m, still 6 m below the channel bottom. The water level rising speed was 1.5 m per day. The lake level is expected to rise up to the channel bottom in three or four days and the water would start to discharge downstream through the channel.
Change to the deeper channel was attributed to a desire for an earlier water release (because of the decreased channel bottom elevation). They were able to make this change because the construction was several days ahead of schedule. The original plan to blow open an entrance to the drainage channel using explosives was also scraped since it was no longer necessary. The change to a milder bottom slope was not explained.
Due to complex and likely unknown soil properties of the massive landslide dam, there would still be a possibility of catotrophic collapse even with a proper design and construction of the drainage channel.
All the 190,000 people expected to be affected by the 1/3 dam collapse scenario have been evacuated.
I would define success as the downstream water level rises to or below that projected for the 1/3 dam collapse scenario. I am of course hoping for a smaller water level rise downstream (thus less damages) if the water release and dam removal would indeed occur slowly.
Yesterday, I sent my best wishes and my thoughts (or reminder) on proper design and construction of the drainage channel to the China Ministry of Water Resources. This is possibly the best thing that I could do for my motherland within the distance and time constraints.
“修好(改变)后的导流明渠全长320多米，顶宽50米，底宽8米。上游深度为10米。就是从原来的750高程降低到现在的740高程。下游深度为13米，也就是从原来的752高程降低到现在的739高程。导流明渠修好后将不再实施爆破导流，而是自然溢流。"
"目前，唐家山堰塞湖的水位是734米，距离最低过流面740还有6米，目前水位增长速度是每天1.5米左右。以这种速度计算的话，三、四天后唐家山堰塞湖将开始导流。"
"按唐家山堰塞湖三分之一溃坝方案需撤离的绵阳十九万民众今天上午八点已全部转移到安全地带。”
我认为如果排水除坝过程中下游水位不超过三分之一溃坝方案线, 就是成功。当然， 我希望湖水会真的慢慢下降，下游水位会上升更底而损失更小。
我已于昨天把我最良好的祝愿和对导流明渠最优设计与建造的想法(或提醒)发送给了中国水利部。由于距离及时间的限制，这也许是我能为我的祖国做的最好的事。
Info source: CCTV.com
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