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Vague state planning policy gives councils too much leeway when drawing up flood maps, leading to drastically different interpretations across Australia’s most highly populated disaster-prone area, multiple experts have warned.
Respected flood engineer Adam Berry, who provides flood modelling for councils through his consultancy Synergy Solutions, said the Queensland government’s language is confusing and leaves too much to interpretation in the state’s south-east.
He said the problems arise around two things: the severity of the floods councils choose to model for planning maps, and how much they think climate change will impact future floods.
“When we’re generating the maps, we’re doing flood modelling in the background,” Berry said.
“It’s based on mathematics and physics, so technically, it should be pretty similar across the board.
“Where the variation comes in across councils is what [they] do with this modelling.”
Under the State Planning Policy, which dictates how councils build their own planning schemes, councils must map for a series of potential floods, large and small, using a “defined flood event” – usually a 1 in 100 chance of occurring every year – as the basis.
That system, known as the annual exceedance probability (AEP), is the most common way councils express various potential floods to residents.
Most south-east Queensland councils choose something in this range for their flood maps:
- Highly likely: 1 in 20 chance of happening per year.
- Likely: 1 in 100 chance of happening per year.
- Low likelihood: 1 in 500 chance of happening per year.
- Very low likelihood: 1 in 2000 chance of happening per year.
But these maps are not always the same as those used for development applications. For example, the Gold Coast shows all of these possible flood scenarios on its online portal, but when it comes to development, it’s still running off the 2016 City Plan, which is only based on the “1 in 100” probability.
Another example – one that played out very publicly – was recent maps released for Logan, the flood-prone council area that’s home to some 400,000 people.
The State Planning Policy states councils should “consider the widest range of flood events possible” when assessing risk, including the worst-case scenario.
This “probable maximum flood”, or PMF, is generally a 1 in 1,000,000 event, or, as one engineer described it, Armageddon. This is generally considered helpful for disaster planning but not for development.
Logan City Council included that worst-case scenario in its publicly available planning material, leading to thousands of homes and properties being considered at-risk on the flood map.
Uproar ensued, and an independent review recommended the council walk back the extent of floods that impact planning decisions to a 1 in 2000 chance of occurring per year, which is in line with the majority of south-east Queensland councils.
“When the flood maps were commissioned, the inclusion of extreme flood scenarios was required under the State Planning Policy,” Mayor Jon Raven said after the review.
Following the debacle, Raven met with Deputy Premier Jarrod Bleijie, who also serves as the state’s planning minister, twice to ask him to clarify the planning policy, which is currently being reviewed.
“I met with Deputy Premier Jarrod Bleijie on May 28 and June 16 to discuss reducing our flood map overlays back to the 1 per cent AEP for our planning scheme, which would remove over 25,000 properties from the overlay,” Raven said this week.
“We want to see a more practical approach to flood mapping, especially as the State Planning Policy is being reviewed.”
Similarly vague language about how councils should prepare for flood risks when climate change is factored in can be found in the policy.
“Consider how to address climate change, particularly if existing available flood studies do not include climate change risk factors,” it says.
Berry said unclear language such as this led to inconsistencies between councils.
“That’s why you see across neighbouring councils, there will be different climate change projections that are modelled and used in land-use planning,” he said.
The policy suggests councils should consult Geoscience Australia’s rainfall and run-off guidelines, which were updated in late 2024 to include substantially worse scenarios that predict more rain falling in shorter amounts of time.
Ipswich, which updated its maps in 2025, said it was now working to incorporate the advice of the latest climate change updates.
In Brisbane, a council spokesperson said it had been using a “middle-range” prediction for flood mapping since 2018.
Will Prentice, the national technical director of Floodplain Management Australia, the peak body for flood-risk practitioners, said the state should step in and provide clarity for councils when it comes to both the level of floods they should map for and the severity of climate change to consider.
“The important thing to understand is our climate is changing, and how floods behave today will be very different from how floods will behave over the life of a home or infrastructure that is built today,” he said.
Bleijie’s office did not provide comment before deadline.
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