The risk of Brisbane flooding as it did in 1974, grows higher as rain continues to fall on south-east Queensland.
Over the Australia Day weekend in 1974, the Brisbane River broke its banks and inundated the city, killing 14 people and flooding almost 6000 homes.
The ABC reports the flood followed months of rain which had filled rivers in the south-east. After Cyclone Wanda brought heavy rain across the region, these rivers were pushed over the limit, leading to the worst floods of the century.
The pattern now seems to be repeating itself. Swollen creeks and rivers are flooding towns, causing pockets of isolation across south-east Queensland.
The Brisbane River is on flood alert and residents already are being offered sandbags.
Professor Roger Stone from the University of Southern Queensland says the La Nina weather pattern, which is currently pushing monsoonal conditions over parts of Australia, is the same as the one experienced in the lead-up to the 1974 floods.
"It's the same type of pattern in the Pacific Ocean. That was one of the major La Ninas," he said.
"We had a similar pattern in 1954 and '55 and also back in 1893 and we've had a few slightly less intense patterns in the meantime - 1988, 2008 and a few intervening years that aren't quite as strong as this."
Professor Stone says this pattern means the risk Brisbane will experience another flood like that in 1974 is eight times higher.
"I know looking at the work we do for the water authorities and other agencies, instead of the risk being about 5% in any year, this year it's about 30% - 40%," he said.
"So the risk is certainly increased. It's not guaranteed, but as with many agencies and insurance agencies and water resource folk working on risk management, we know that the risk is substantially increased in a year like this."
Dam defence
The Wivenhoe Dam was built in the aftermath of 1974 as Brisbane's defence against another major flood.
But even this may not be enough to prevent a disaster downstream.
SEQ Water has been releasing 170,000 megalitres of water from the dam per day in preparation for flooding.
Many creeks in Brisbane's suburban areas are prone to flash flooding and Professor Stone says the weather conditions will test the city's planning.
He says the success of the Wivenhoe Dam will depend on the type of weather pattern experienced.
"It depends exactly how the rain falls and where it falls and which sort of catchments areas are involved," he said.
"It might help in certain circumstances, but it depends exactly on the nature of the rainfall event or the rainfall events because the one we have at the moment may not be the last one - we could have more of these types of events over the next couple of months."
Not over yet
The weather pattern began last May and when parts of northern Victoria and southern New South Wales were flooded by intense rain.
Professor Stone says there is still a way to go before the risk of flooding from La Nina passes.
"These types of systems tend to start in May-June of any year and last until the following autumn, so the climate year tends to run autumn to autumn," he said.
"You'd expect the main hope for this to start to break down to be in about three months, so we still have a long way to go yet."
And Professor Stone says we are yet to see the tropical cyclones usually spawned out of the Coral Sea during these kinds of weather patterns.
"Queensland still has a long way to go, and in fact this also applies to parts of New South Wales and to northern Australia," he said.
"There's still a fair way to go before we see the breakdown of the underlying cause of the whole problem.
"Sometimes they can go through to a second year, so when we get closer to May-June we'll have a better idea if this will continue on or whether it will do what we hope it will do and start to break down."
