Engineers find support at Qld flood inquiry

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Hydrology expert, Mark Babister, has told the Queensland flood inquiry that a greater release of water from the Wivenhoe Dam would have lessened the impact of last year’s flood event, but would also have been unjustifiably risky. The extraordinary sittings of the inquiry are investigating allegations that the extent of the January flood event could have been reduced.

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ASHLEY HALL: An expert in hydrology has backed the performance of the four dam engineers at the centre of the Queensland flood inquiry.

Mark Babister was asked by the commission to examine two strategies that involved releasing much more water from the dam at an earlier stage in the flood to see if it would have lessened the impact of the disaster.

Matt Wordsworth is at the inquiry and he joins me now.

Matt, what did Mr Babister conclude?

MATT WORDSWORTH: Ashley, that a greater release would have lowered the flood peak that came later in the week but it would have been unjustifiably risky. Now if you can allow me to get just a touch technical here, it all comes down to this date of January 8th. I keep mentioning this date but it is the really important one.

On that day these four flood engineers were releasing 1000 cubic metres of water per second out of the dam. So Mr Babister was asked to go back and try modelling 3,500 cubic mets and 4,000 cubic mets to see whether that would have had an effect, and it did.

It would have dropped the flood peak that happened in Brisbane City on Thursday by 60 centimetres but, and this is the big but, he says although hindsight indicates it would have been a better flood mitigation result, it would have been unjustifiably risky using the information available at the time.

One of the reasons is that the rainfall forecast that these guys were using were wrong. The rain forecasters were predicting 40 millimetres of rain on that Saturday the 8th but they got double that and then the next day the forecast was for 50 millimetres and they got triple that.

So Mr Babister says you’d be ramping up the release system limit where you know that those releases are going to cause urban damage in Brisbane and it just wouldn’t have been responsible based on the evidence that you had at hand.

ASHLEY HALL: So if the engineers have got the backing of the experts, why then is there still this allegation that they breached the dam operating manual?

MATT WORDSWORTH: Yeah, well this allegation stems from the absence of the notes that they should have been taking while they were busy doing all of this flood mitigation hydrology modelling and releasing. The manual states that you step through four levels, W1, W2, W3 and then the big daddy W4 means that you are just saving the dam, forget everything else because the wall is going to collapse.

You are supposed to tick off when you are in each strategy because each strategy has pre-defined objectives. The first one is just to protect the local rural landholders just downstream from the dam and then W2 and W3 is protecting Brisbane.

What they didn’t do was record when they were going through these levels and then when they wrote the report, they’d come back and gone okay well we were releasing this number of cubic mets so we must have been in this particular strategy and that is where the allegation of writing a fictitious report has come from and that is something that I think is still going to be a problem for these engineers but we’ll find that out when the final report comes out on March 16th.

ASHLEY HALL: What impact then does today’s evidence have on the threat of a class action by flood victims?

MATT WORDSWORTH: Yeah, this is something that a couple of big law firms are going to have to look very closely at because if you have got a hydrologist of 25 years experience from a flood consultancy saying that the engineers released an appropriate amount of water with the information they had at hand, then it is going to be hard for them to prove that there was any extra damage to these flood victims downstream.

If you breached the manual, that is what they are going to be looking at. That could be a trigger for some sort of negligence but then the damage payout is the big one that they are going to have to overcome.

They say they are going to absorb the report over weeks and months, then they’ll decide whether to launch this class action.

ASHLEY HALL: Alright, thanks very much Matt. Matt Wordsworth at the Queensland flood inquiry.

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