when you see the capability of the high volume pumps they use - and you can see a few of them in the news pictures, they are about half-iso sized boxes - then 2m is quite understandable.
Nomore helos - the weight of the water on one side needs to be balanced by the weight of the dam on the other, they have simply put more weight on the dam wall where it had previously lost integrity.
Crab, I started looking at the mathematics of this and gave up! That aside, some good pictures and videos on the Daily Mail