Hydrologist questions flood modelling used for Brisbane dam

By on 24 May, 2011
Hydrologist Mark Babister has called into question the hydrology models used by engineers who were releasing water from Brisbane's Wivenhoe Dam during January's floods.
Mr Babister’s report has recommended authorities reconsider the strategy for managing the dam during flooding, as well as the modelling they base their decisions on.
The strategy in question, known as W4, puts the structural safety of the dam before the flooding of urban properties. Mr Babister suggests that authorities should insert another strategy before W4 to make the escalation of releases more gradual, and should also consider how forecast rain can be factored into the calculations.
Mr Babister claims that “the releases from Wivenhoe Dam were the major component of the flood peak in the Brisbane River” and that the flood waters would have been lower had water been released from Wivenhoe Dam in the days leading up to the January floods.
However, Mr Babister said it was also possible the earlier escalation of flows might have increased flood levels at Ipswich. He also conceded he had done no modelling to back his assertions that the majority of water in Brisbane came from Wivenhoe Dam.
At the Queensland Floods Commission on Wednesday, Mr Babister suggested that engineers should be using hydrodynamic models when floods are escalating, because they were more robust than other methods.
"When it gets to complex decisions where you need to make hard calls you might go to the hydrodynamic model," he said.
Dam engineer Robert Ayres has told the inquiry such a model was not available in the flood operations centre, where the dam engineers worked, but was available at the Seqwater office.
It wasn't used at the peak of January's flood because of the effort needed to run it, he said.
But Babister claimed there were now hydrodynamic models in use around the world that only take around one minute to run.
Three independent reviews have found that the dam releases were in accordance with the flood manual.

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