The Three Gorges Dam impounds 39.3 cubic kilometers of water. Although the top of the dam is 185m above sea level, according to wiki the dam itself is 181m tall! That means the bottom of the dam is only 13 feet above sea level! I know that sounds crazy, but look at this:
https://maps.google.com/maps?q=three+gorges+dam&hl=en&ll=34.885931,115.839844&spn=10.93081,19.753418&sll=37.160317,115.488281&sspn=42.053626,79.013672&t=p&hq=three+gorges+dam&z=6
Whatever its elevation is, it’s not a lot. In fact, it’s so low that the surge from the dam failing would dwarf it. I’m going to thumbnail it to 10m because that number is easy to use.
40 cubic km of water weighs 40 trillion kilograms, that’s 400 trillion Newtons, dropped from a height of 10m is….4 quadrillion Joules
(and it took me an hour to figure that out)
according to this handy scale
http://en.wikipedia.org/wiki/Gigajoule#Gigajoule
is 4 exajoules, which is a lot, according to this scale:
http://en.wikipedia.org/wiki/Richter_magnitude_scale#Examples
Same size as the 2004 tsunami.
But it won’t blow up the world. It would be a lot worse if you measured from the top of the dam, and I don’t remember enough calculus to work out with the constantly dropping level of the surge and the speed of the water carrying it across the delta…. the whole dam would probably drain before it reached the ocean. But, basically, the important thing is that China can only accidentally destroy their own country, they will not destroy the world.
Glad I finally did the math on that.
So, anyway, they want to do it again.
http://www.eco-business.com/news/china-approves-its-next-biggest-hydro-dam-despite-negative-impact/