Queensland dam engineers were concerned before the 2011 floods that they could suffer a "major embarrassment" if they released water and then dire rainfall predictions didn't eventuate, a Sydney court has heard.
A class-action suit is underway in the NSW Supreme Court on behalf of more than 6000 flood victims almost seven years after the disaster.
At the core of the case is whether flood engineers breached the Wivenhoe Dam manual and acted negligently in not taking into account rainfall predictions before major releases became necessary in mid-January 2011.
On Tuesday, the court heard dam engineer John Tibaldi raised the risk of unnecessary water releases in an email written in early December 2010.
He said there was “never any certainty” about the amount of rain predicted to fall in a dam catchment, citing an example from November 2010 when the weather bureau predicted between 25 and 50 millimetres of rain in the Wivenhoe Dam catchment, west of Brisbane, but only 10mm ended up falling.
“Pre-release of anticipated floodwater based on forecast could result in major embarrassment,” the email said.
Julian Sexton SC for the plaintiffs said it demonstrated potential embarrassment was of concern to the engineers.
“Major embarrassment is not one of the objectives in the flood manual, nor is concern about media reporting or public relations,” he told the court.
The court also heard a 2006 discussion paper by engineers engaged by Seqwater explored a possible change to Wivenhoe’s gate operations to factor in forecasts.
Under the heading “possibility of an early release”, that document warned: “If significant rainfall is forecast and does not eventuate, the results could include adverse media reporting and public relations”.
Seqwater could be seen to be “wasting water”, the paper said.
Mr Sexton said water supply concerns were “particularly pressing” in 2011 despite the Bureau of Meteorology’s October 2010 seasonal outlook predicting a wetter-than-normal wet season.
In addition, the Sunshine State had just experienced its wettest Spring and wettest December.
The Wivenhoe and Somerset Dams were also able to meet Brisbane’s water supply requirements for a minimum of seven years, Mr Sexton said.
“It was unreasonable, having regard to those factors, to consider that ensuring the dams never went below supply level outweighed protecting urban Brisbane from extensive damage,” he told the court.
Seqwater insists its engineers will be vindicated because they did the very best they could in extremely challenging circumstances.
Seqwater chief executive Donna Gregory says the operation of dams “significantly mitigated the flood”.
Maurice Blackburn class action principal Rebecca Gilsenan on Tuesday cited expert evidence that water releases from Wivenhoe Dam would have been halved if rainfall predictions were factored in and the dam manual followed.
“For a large portion of people, that meant no flooding,” she told reporters outside court.
“For the rest of the people it meant flooding, albeit to a lesser degree.”
The action, which is being heard before NSW Justice Robert Beech-Jones, because Queensland did not have a class-action regime at the time the case was filed, continues on Wednesday.