New flood mapping for the Logan and Albert rivers south of Brisbane has been released six months after floods swamped more than 250 homes in Logan.
Logan City Council commissioned an updated hydrological model for the rivers and Slacks and Scrubby creeks catchments in 2019, and released the upgraded predictions for individual properties on Monday.
The updated maps were based on a hydrological model developed by engineering company WRM Water and Environment, which was accepted by the council in May.
The new mapping considers a weather event with a 1 per cent chance of happening, or a one-in-100 chance, in any year.
Mayor Darren Power said clearly understanding flood risk would "better protect our community", as Queensland faced a third La Nina season in a row.
"In some areas the level of flood risk will increase because of our improved understanding of flooding and updated data and modelling," Mr Power said.
"It could mean that some homes, businesses or parcels of land may have a higher flood risk than previously considered."
He said that included people who had never experienced a major flood event.
"We are having conversations with those residents to keep them informed and they will also receive letters from council," he said.
Details on how many properties had their flood levels altered in the new modelling were not immediately available from the council.
Flood damage
There were 263 Logan homes flooded across low-lying suburbs including Waterford, Chambers Flat, Beenleigh and Bethania in February and March.
Between 420 and 880 millimetres of rain fell into the Logan and Albert River catchments in a week.
Power was cut to thousands of homes and access to the suburb of Yarrabilba was temporarily blocked.
The Logan River at Maclean Bridge peaked well above the major flood level of 16 metres on February 28, reaching 20.5 metres, according to Logan council, which was below the 2017 level of 23.97 metres.
Mr Power said the council had an obligation to provide detailed information to residents about flood risk as climate change altered the region's weather.
"It's important for people to understand that more extreme weather events will occur and we need to be prepared," he said.
"This requires an evidence-based approach to guide future development and decisions in flood-affected areas of our city."
'Shock' update
Waterford West resident Briana Kalkman said she wanted the council to review the updated mapping after it predicted her home of two years, which previously had no flood overlay, could be inundated.
"The main reason we purchased [our property] was it didn't go under in the 1974 floods, where it has been deemed as the highest flood level," she said.
"We've now found that with this new flood mapping, our property completely goes under."
Ms Kalkman said most of her neighbours were unaffected by the updated mapping but others on her street were in the same situation.
She said she was concerned that the value of her property, which was previously owned by her grandparents, would plummet while insurance would go up.
"It's just going to make insurance unaffordable, not only for us but also for many others in our area," she said.
"I know that the property has never flooded … and even talking to my next-door neighbours when we purchased the property they said, 'no, you're fine'.
"It's definitely a shock and not a nice thing to see."
Ms Kalkman said she had contacted the council to ask for more details on how the flood mapping had been developed and why her property's flood prediction had changed so drastically.
The council is still developing updated flood modelling for eight other creeks across the region, five of which will be published in mid-2023.
Flood mapping for priority development areas, however, such as Yarrabilba and Flagstone, are the responsibility of the state government.
Moreton Bay and Ipswich City councils are updating their flood mapping following the 2022 floods.
