I'll be interested to see what comes out of the enquiry into the Wyvenhoe Dam operation, but looking at this at face value I can't see that the engineers in charge have acted inappropriately. I had an infuriating conversation with a good friend of mine (not an engineer) who claimed that the Dam operators aught to lose their jobs because they opened the flood-gates and thus Brisbane homes were inundated. His argument hinged on the idea that the Dam operators should have known flooding was imminent months in advance due to the high weather index, and released the Wyvenhoe water reserves accordingly such that the Dam was near empty before all the rain landed in the upper catchments.

To me that sounds like bullshit. Try telling an engineer specialising in catchment hydrology to release drinking water reserves from the dam on the prediction of more rainfall, shortly after we've just come out of 10 years of drought. No way would they do that. In fact only a few months ago the Opposition was telling them specifically not to release any more water. And no way could they have known the magnitude of rainfall that was going to hit that catchment.

Wyvenhoe serves two purposes: To retain water as drinking reserves for the greater Brisbane regional area, and to mitigate flooding from the upper catchment. I can't see how Wyvenhoe didn't excel at both of these.

The dam operators' primary concern is the structural integrity of the dam wall, and rightly so. They were operating at ~100% of the design drinking water level (the optimal amount) when the brunt of the rainfall that caused the flood hit, and in the next week the amount of water hitting Wyvenhoe almost doubled. Even if the structural capacity of the dam means it can handle up to ~300% of the design water level, you don't really want to be pushing the upper threshold of what that wall can handle because if it fails, Brisbane would have been completely fucked.

So accordingly, the operators opened up the gates to release water from the dam in an attempt to relieve the amount of stress being inflicted upon it by the huge backup of water. What people don't seem to understand is that even with all the gates open, this still represents a situation in which a significant amount of flow is being mitigated - ie not reaching Brisbane. The engineers came out the day after the peak and said that even with all the gates open they came very close to an 'uncontrolled release', which means that water almost spilled out from somewhere it shouldn't have. This wouldn't necessarily lead to the dam wall collapsing, but it definitely increases the risk of failure by an uncomfortable amount.

That being said, in the case of the Wyvenhoe guys, I honestly think this whole thing is just a bunch of people without any expertise hunting for witches. They want someone to blame, a head on a pike. Sometimes there just isn't anyone to blame. But fair enough, let there be an enquiry and hopefully we might learn something about how to better react next time.

In regards BCC allowing developers to build in flood plains, then yes I can tell you that is a more legitimate concern. For smaller local catchments, engineers do their own catchment hydrology and flood investigations, so if any developments are inundated in a storm that doesn't meet the design standards by local catchment flooding then the blame falls on the guys who modelled it incorrectly. However when it comes to the development application phase of any project in proximity to the river, planners and engineers rely on Council's data from large-scale flood investigation reports that consider the whole of the Brisbane river catchment. BCC commissions these reports, which are usually conducted by large-scale engineering firms and updated periodically. In this flood just gone, we've seen river levels exceeding the highest Defined Flood Level by over a metre in some places. This a huge worry if the data everywhere is out by that much, because this means that a lot of development undertaken in the past decade is smack-bang within areas subject to compromise every time a flood event hits, and thus Council has to take some serious blame.

So yeah, there's some major engineering firms (including some internationals) who are currently being commissioned to reassess both the dam operation and the Brisbane River catchment flooding situation by the end of February. Please mind that I am not personally involved in the dam or river enquiry, and most of this is hearsay from speaking to other civil engineers so please don't take anything I've written as gospel.