How to read a QLD flood model report: a checklist

A published flood model gives four numbers for a property in a given event: modelled flood depth, flow velocity, depth times velocity hazard, and the flood level in metres AHD. Read them in that order and against the right event, and you can tell how a property floods, not just whether it sits inside an overlay. This checklist walks through it for a Queensland property, whether the model comes from Brisbane City Council, the Gold Coast, Sunshine Coast, Toowoomba or a state study.

A flood model is not the same as a planning flood overlay. The overlay is a zoning line that triggers assessment rules. The model is the hydraulic run behind it, or a separate study, and it carries the actual depths and levels. If you have only ever seen the overlay, reading the mapping like a planner is a useful companion to this.

Stage 1: Confirm what model you are reading

• Check the source and date. Note whether the model is a council study (for example a Brisbane creek catchment study) or a state model. An older model may predate recent catchment works or the 2022 floods.
• Check the flood type. Riverine, creek and overland flow behave differently. Brisbane River backwater, a Bremer River event at Ipswich, and local overland flow in a Toowoomba gully are separate models with separate numbers.
• Confirm the event. Every number is tied to a probability. Read the AEP (annual exceedance probability, the chance the event is reached or beaten in any year) or the older ARI (average recurrence interval).
• Note present-day versus future-climate. Many Queensland models now publish a climate-change run with a rainfall increase and, on the coast, a sea level rise allowance. These give a higher level than the present-day run.

Term	Meaning
1% AEP	1 percent chance in any year, the "1 in 100"
2% AEP	2 percent chance, the "1 in 50"
5% AEP	5 percent chance, the "1 in 20"
Defined Flood Level (DFL)	The level councils set floor heights against, often the 1% AEP plus freeboard

Stage 2: Read the four numbers for your event

• Modelled flood depth. Metres of water over the ground at that point. A depth of 0.1 m and a depth of 1.5 m are both "flooded" but mean very different things for a build.
• Flow velocity. Metres per second. Low velocity is nuisance water; higher velocity carries debris and scours foundations.
• Depth times velocity hazard. The two combined, usually as a hazard classification (H1 through to H6 under the national guidance). It tells you whether the flow is safe to stand in, unsafe for vehicles, or unsafe for buildings.
• Flood level in metres AHD. The water surface elevation, not the depth. This is the number you compare to a floor level and to the ground level at the property.
• Compare the flood level to the ground. Flood level minus ground level equals the depth over that spot. Confirm the two match, because a single property can sit part above and part below the modelled surface.

Stage 3: Turn the numbers into floor level and insurance answers

• Find the required floor level. Queensland councils set a habitable floor level against a defined flood level plus freeboard (a safety margin, often around half a metre). The 1% AEP flood level plus freeboard is the usual target for a new habitable floor.
• Check freeboard is added, not assumed. The model gives the flood level. The freeboard sits on top and comes from the local planning scheme, so read both.
• Use the future-climate level for a long-lived build. A slab you pour today should clear the future run, not just the present-day one. On the Gold Coast and Sunshine Coast that includes a sea level rise component.
• Take the numbers to your insurer. Insurers price on modelled depth over floor level, not on the overlay. A property that floods to 1.2 m over the ground but has a floor 1.5 m above that ground is a different conversation from one at ground level.
• Separate the flood model from the flood certificate. A council flood certificate or flood search confirms the planning status and may quote a level. The model is the underlying data and gives the full range of events. You often want both.

Stage 4: Check disclosure and coverage before you rely on it

• Read the seller's Form 2 disclosure. Queensland's seller disclosure regime uses Form 2, which flags certain matters but does not hand you the modelled depths. Treat it as a starting point, not the flood assessment.
• Confirm a model actually reaches the property. Modelling is published catchment by catchment. Not every Queensland address sits inside a published model, and a gap in coverage is not the same as no flood risk.
• Cross-check with ground elevation. Where a model exists, compare its flood level to the site's elevation. The flood source versus elevation check explains why one without the other can mislead.
• Do not treat the model as site-specific engineering. It scopes the risk and sets floor-level expectations. A hydraulic assessment for a specific development still needs an engineer.

To see the published depths, velocities and levels for a Queensland address in one place, check whether a flood model covers the address, or if you want the wider planning and overlay picture, get a Property Report instead.

LayeredGeo's Flood Model Report collects every published flood model that reaches a property in the areas we hold across Queensland, New South Wales, the ACT and Tasmania, with modelled depth, velocity and flood level for each event.

About this article. Published by LayeredGeo. It is general information about how property and ground conditions are assessed in Australia, not engineering, planning, legal or financial advice, and it is not specific to any property. Check anything that matters against the source dataset or a suitably qualified professional before you rely on it. If you spot something wrong, tell us at hello@layeredgeo.com.au and we will fix it.

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