Brisbane's devastating 2011 flood would have been no more than a minor event had four dam engineers done their jobs competently, lawyers for the victims will argue in a class action.
Approximately 4500 flood victims will seek compensation which could amount to hundreds of millions of dollars in the claim, which was filed at the NSW Supreme Court by Maurice Blackburn Lawyers.
At least $5 million has been spent putting the claim together, including expert reports alleging the dams were operated in a negligent way.
The claim alleges engineers at the Wivenhoe and Somerset dams repeatedly failed to follow their own guidelines throughout December 2010 and January 2011 with both dams above their maximum water supply levels during that period.
During the period in question, and despite forecasts from the Bureau of Meteorology of "heavy and prolonged" rainfall, engineers are accused of failing to heed warnings, ensuring the resulting flood was a far greater disaster than it needed to be.
"When our hydrology expert looked at it using what would have happened had the dams been managed competently, the overwhelming majority of properties would not have been inundated," Maurice Blackburn principal Damian Scattini told reporters.
"Of the remainder? They would have had much less inundation than they did.
"This is a flood that did not need to happen. We would not be sitting here talking about the 2011 flood had the dams been managed properly."
Queensland's long-running flood inquiry had already found in 2012 that Wivenhoe's dam manual was not properly followed on the weekend leading up to the flood peak.
The inquiry's findings also resulted in dam engineers John Tibaldi, Rob Ayre and Terry Malone being referred to the Crime and Misconduct Commission to examine whether they lied under oath and covered their tracks about the strategies they adopted.
The CMC found no evidence of collusion but Bentham IMF Australia executive director John Walker, whose company is funding the claim, said the firm's investigation was far broader than the CMC's.
"The CMC looked at conduct in and around the period of the flood, in the four or five days before the flood event that caused the damage in Brisbane," Mr Walker said.
"It's the evidence that will be put before the court that the negligence goes back to the first of December.
"That there was a flood event, as defined by the manual, going back to the first of December."
Mr Scattini said claimants came from over 100 suburbs in Brisbane and Ipswich, from "fat cats" living on the Brisbane river to families still forced to live in caravans following the flood.
Homeowner Bill Proud paid $80,000 to fix his flood-ravaged house in the Brisbane suburb of Yeronga and says he doesn't think he would have had any problems if the dams had been properly managed.
"If it was in some way not human error I would understand it," Mr Proud told ABC Radio.
"I thought the people running the dam were incompetent."
The claim has been filed against Seqwater, Sunwater and the state of Queensland and had to be lodged in NSW as Queensland has no class action regime.
Queensland Premier Campbell Newman and Sunwater are both refusing to comment as the matter is before the courts.
Seqwater CEO Peter Dennis said in a statement on Tuesday afternoon that the court process would show the firm's actions reduced the impact of the flood.
"Seqwater has never wavered from its belief that our engineers did an extraordinary job in the most difficult and demanding of circumstances," he said.
Mr Dennis added that two major rain events, generating the equivalent of a 1974 flood, occurred across Wivenhoe and Somerset dams less than 30 hours apart.
The Queensland Floods Commission of Inquiry made no finding of negligence against Seqwater, he said.
It's expected the claim could take at least a year to reach the trial phase.
