75 per cent
This post, written in the immediate aftermath of the floods (and the subject of some controversy) is looking pretty good in the light of the recent decision to release water from Wivenhoe Dam, with a target of 75 per cent.
Having had some time for reflection, the obvious modification to my initial position is that we shouldn’t have a fixed target, but rather should take account of the seasonal pattern of rainfall and, to the extent that this is possible, of the El Nino/La Nina/SO cycle. One way to do this would be to set targets for the beginning and end of the wet season, designed to be consistent with expected rainfall and usage for the wet and dry seasons. As I mentioned in my previous post, the flexibility associated with desal and recycling plants and the Water Grid would make this kind of management much easier than in the past.
Looking back at the controversy this post aroused, it’s clear that it was due in part to the involvement of The Australian and the anti-science lobby on climate change, which, for reasons that remain obscure to me, decided to run with the line that early release of water from Wivenhoe Dam would have greatly reduced the severity of the floods. It’s interesting to find that being in partial agreement with the Oz is even worse than being attacked by them. The Oz presentation of news on the dam management policy, as on all issues where it decides to push a line, was so selective and skewed that it even relatively simple issues, like the proportion of floodwater that came from the Bremer river, became hopelessly confused.
So, to clarify, both my original post and this one refer to policy options for the future, which might be adopted in the light of the floods, and of the likelihood of more extreme climate events in the future. With perfect hindsight, and discretion unfettered by a rulebook, managers would certainly have made different decisions in the days leading up to the flood. But what is really needed is a long-term change to the management procedures that set 100 per cent of water supply capacity as a fixed target. IIRC, the only calls for such a change in the leadup to this wet season were from those objecting to the release of water, and implicitly calling for a higher target.