The object of the dam releases is to minimise the peak flood height by spreading the wave over a greater distance of river, like a long flat wave rather than a high sharp one. Which would be the case without the dam.
I think Wivenhoe can go to 200%, but it is more likely they will increase the outflow to keep the level below that. They will want to be in a position to be able to reduce the outflow if inflows increase sharply.
I see that Anna has admitted that the dam is saving Brisbane from worse fate;
"Without a doubt the Wivenhoe Dam has already saved Brisbane from a catastrophic flood in the next 48 hours," said Bligh. "The dam will see releases over the next two to three days, larger than it has ever seen in its history since it was fully operational in 1984."
