A Brisbane couple has recounted the incredible scenes they witnessed in the city’s 1974 flood; 40 years on they are once again recovering from disaster.

It was an abnormally wet summer when Cyclone Wanda crossed the Queensland coast 40 years ago today.

Wanda made landfall near Maryborough, about 250km north of Brisbane, as a relatively weak system, but at the time no one realised it was about to unleash the flood of the century on the state’s capital.

In the five days that followed the cyclone’s landfall on January 24, 1974, almost a metre of rain fell in the Brisbane area, and Ron and Patricia Goeldner were sitting ducks.

On January 25 all those years ago, the couple huddled on their second-floor balcony in Yeronga and gasped at what came into view as they trained a torch on the churning Brisbane River.

Through the rain and dark they snatched glimpses of yachts and caravans tumbling in the current.

Aside from the days of pelting rain, there’d been no proper warnings about just how far the river would rise.

The Goeldners’ only realised the danger they were in when it was too late to save their most treasured possessions, including their children’s baby photos.

By 5pm the next day, Australia Day, the river broke its banks at Yeronga and took just two hours to rise the 30 metres towards the Goeldners’ home.

Ron flung his five-year-old son over one shoulder, his three-year-old daughter over the other, and tucked their cat under his arm.

Patricia followed with the budgie and a packet of Weet-Bix.

They waded through waist-deep water to their back neighbour’s house where they were soon joined by 16 other soaked and bewildered neighbours.

“It just broke the bank and was on us, we had no warning,” Patricia tells AAP.

When morning came, the river had risen further. Only their roof and a few tree tops could be seen above the boiling, muddy torrent.

By the time the water receded four days later, 14 people were dead and 300 injured, 6000 homes flooded in Brisbane and Ipswich to the west, 56 homes were completely destroyed – three of them in the Goeldners’ street.

The flood had swallowed vast swathes of the city, with the river rising to a peak of 5.45 metres – about one-metre higher than Brisbane’s 2011 flood disaster.

The 1974 event was the catalyst for the construction of the Wivenhoe Dam, 80km upstream from Brisbane. Finished a decade later, it was intended to mitigate future severe floods and prevent smaller ones.

The dam was designed to reduce the level of a 1974-scale flood by two metres. But it didn’t.

When the 2011 flood hit Brisbane, it delivered another disaster for the Goeldner family. They had no insurance because they’d believed Wivenhoe would save them.

Water again swept through their home, albeit at a lower level than in 1974.

Property values have since plummeted and a recent assessment of the Goeldners’ home wiped $340,000 off its value.

While Patricia is at peace with the 1974 “freak of nature” flood, she becomes tense when talking about the 2011 disaster, which she insists was avoidable.

She is one of 2500 flood victims who’ve signed up for a class action aimed at achieving a $1 billion-plus damages payout from the state over the 2011 event.

“We’ve always been told it wouldn’t happen again because of Wivenhoe,” Patricia says. “They’ve got to be held accountable.”

Litigation funder IMF Australia and Maurice Blackburn lawyers will argue Wivenhoe’s engineers should have released more water, earlier, to reduce the peak.

They will also question why the dam’s flood centre was shut and monitored from home between January 2 and 6, despite the unfolding disaster.

Their modelling suggests that had the dam been properly operated, about 85 per cent of properties would have been spared flooding, and the rest would have escaped with less damage.

“This was a flood that didn’t have to happen,” Damian Scattini from Maurice Blackburn tells AAP.

A wide-ranging inquiry into the 2011 flood, and a subsequent Crime and Misconduct Commission investigation, found the four engineers who operated the dam didn’t follow the manual.

But it cleared them of colluding to cover up their mistakes.

However, the dam’s manual was described as a dog’s breakfast and is being rewritten.

As a precaution, the dam will also be reduced to 75 per cent of capacity when extremely wet summers are forecast, and the Brisbane City Council is also improving its storm water systems to help protect 15 low-lying areas.

The class action is expected to be filed in March, and that can’t come soon enough for the Goeldners.

It took them 18 years to financially recover from the 1974 flood. Their recovery from 2011 flood is a work in progress.