This link has some very quoteable quotes from Prof Neal Ashkanasy, a water resources engineer and psychologist who now works at the University of Queensland and a former national president of the Hydrology and Water Resources Institution of Engineers.:
“Wivenhoe accounts for only 40 per cent of Brisbane’s run-off water, with a major effect on flooding in the city being Lockyer Creek and the Bremer River, which empty into the Brisbane River below the dam”
“In my estimation, the Wivenhoe Dam kept 1.5m off the top of the 2011 flood, so its contribution to mitigation was significant”
“Bear in mind that the really big floods in 1893 and 1941 were over 8m on the gauge, and this one was only 4.5m. When John Oxley discovered Brisbane 180 years ago, the local Aboriginal people were very agitated about flooding, and they showed him high-water marks that would have been 12m.”
“The rules about the release of water are… mandated and cannot be played with, so it is my view the operators last week had little alternative other than to do what they did.”
“1974 the then premier, Joh Bjelke-Petersen, argued strongly for politicians to have the say on when water should be released, but the then water commissioner, Peter Bevan “put his job on the line” by refusing to allow it.”
“I have read where it is suggested Wivenhoe should have been kept at 75 per cent capacity. Imagine if that had been the case in the recent drought, when it went from 100 per cent to 17 per cent. What if the starting point then had been 75 per cent and not 100 per cent?”
One thing is for sure. Brisbane will have to face worse droughts and worse floods than we have experienced recently at some time in the future. We need to be ready to deal with both.
Some background items from this Larvatus Prodeo post by Brian:
"Anyone seriously interested should read and learn by heart this SEQ Water Strategy document (large pdf) which you can (download from here). One of the more interesting figures is this one:
The idea is that we have a 1% probability of being reduced to the T1 trigger (40% capacity) in the next 10 years. Knocking off 25% of storage from the top would compromise this safety margin and make water much more expensive.
At T2 (30% capacity), you should be building climate-independent extra capacity and have another 30 months to complete it.
Under this planning regime, which takes into account population projections, we should have medium level restrictions no more than once in 25 years, those restrictions should not last more than six months and should amount to no more than a reduction of 15% of normal entitlement.
Sounds rational to me.
While we are at it here are the SEQ dam capacities. There are no more sites available, other than building the Wolfdene at huge cost of resumptions.
This map shows the rivers and dams in the area: