Brisbane Flood Maps: Assess Flood Impacts Before Buying

Buying Property in Brisbane’s Flood-Prone Areas

Brisbane, the “River City,” is also a city exposed to flood risk.

Brisbane is a city built along the banks of the Brisbane River, earning its nickname as the “River City.” But with this riverside location comes exposure to flood risk. This article focuses on how to use Brisbane flood maps to assess potential flood impacts before purchasing a home or an investment property.

Brisbane’s History of Major Flood Events and Their Impacts

Brisbane has experienced many significant flood events over the past two centuries. Back in February 1893, the first big river flooding event occurred where water levels were recorded at 8.35 meters above the low tide level in the Brisbane CBD, the second highest flood event ever recorded at the City gauge. This event was termed the Great Flood and that month was then referred to as Black February. The flooding was caused by a huge rain event associated with a tropical cyclone. This caused the Brisbane River banks to burst and the water flooded into the surrounding areas. This flood resulted in 11 deaths and about 190 people were hospitalized.

Fast forward to January 1974 and Brisbane city experienced the largest flood to affect the city in the twentieth century. Once again, this was caused by a cyclone where 642 millimetres of rain fell within the space of 36 hours and the river system simply could not cope.

At that time, the water levels peaked at 6.6 meters at the City gauge, but because development was a lot more advanced than it was back in 1893, 8,500 homes were completely inundated with floodwaters on this occasion. Brisbane was an inland sea during this flood event and 14 people lost their lives as a result, mostly in the inner city suburbs.

Off the back of these flood events, the Wivenhoe Dam was constructed to provide flood mitigation control for the City. This is located about 80km by road from the Brisbane CBD. Residents in Brisbane became more optimistic that Brisbane would never flood again and development was fast tracked throughout the city. No one thought that a river flooding event would impact our lives, or our homes again.

Then in 2011, the flood that was never meant to happen happened. After days of rain, the Wivenhoe Dam was over its capacity and the flood gates had to be opened to release some of the water. Brisbane was in for a shock.

On 11 January 2011, the Brisbane River broke its banks and by 13 January 2011, the river was raging. This time 20,000 residential homes were affected by flood waters across 94 suburbs throughout the city. It was the flood that was never meant to happen, but it highlighted the fact that our River City may never be immune from future flood events. For ongoing updates on how flood risks and other market factors are impacting property values, check out our Brisbane Monthly Market Updates.

Steps to Assess Flood Impact Using Brisbane Flood Maps

Understanding how to assess the flood risk associated with a property is therefore important when you are looking to buy a property in Brisbane. A buyers agent services in Brisbane can help you navigate this process, ensuring that you make informed decisions. Here are some steps you can follow that will help you to assess this risk.

Step 1 – Access the Brisbane City Council Flood Awareness Map

The Brisbane City Council provides predictions for the potential for flood risk for most properties around the City. You can access flood information online via the Brisbane City Council website. You will be required to select:

I am … a resident/visitor / business and then

I want to … search the Flood Awareness Map.

See the image below which will show you these options.

Then enter the property address in the search bar.

You will then see the property on a the Brisbane flood map with a Flooding Overview provided as per below.

You will then see the property on a Brisbane flood map with a Flooding Overview provided as per below.

For a more detailed report on the property itself, including the contours of the site and the relative flood levels, you can click on the Technical FloodWise Property Report button at the bottom of the Flooding Overview.

This search will provide one of four types of reports, depending on the property and its relative risk in relation to flood.

Step 2 – Generate a FloodWise Property Report

First Report Type – No Known Flood Impact

The first type of Report is issued when there is no known FLOOD impact across a site. You will see this note on Page 1 of the FloodWise Report if this applies to your property search.

Obviously, this is the best possible outcome as it means the property is not going to be impacted at all by any type of flooding event.

Second Report Type – Flood and Development Flags

The second type of report provides a warning that the property has Flood and Planning Development Flags, but there will be no visible graphs. The alert on Page 3 of the FloodWise Report will look like this.

This usually means that the property is impacted by either overland flow flooding or coastal hazard flooding. Brisbane City Council does not have publicly available information on the overland flow modelling. Whilst we can get an understanding of the overland flow pathways, we don’t have details and the onus is on a buyer to engage a hydraulics engineer to complete an assessment to ascertain what that impact actually is. For development, this becomes much more important compared with just buying a residential site.

Third Report Type – Incomplete Flood Data

The third type of report might be produced when there is a known flood impact, but the information is incomplete. There will be a graph on the first page of the report that looks something like this.

This usually happens when historical data for a site is incomplete or not available so further investigation is always recommended. Sometimes a block of land is too large for the council to have complete clarity of what the flood impact is likely to be at every point on the site and therefore the minimum habitable floor level is sometimes not noted on the report.

Fourth Report Type – Known Flood Impact and Floor Level Data

The fourth and final type of report is produced when there is a known flood impact and sufficient information in the council’s database to determine the minimum habitable floor level. The graph on this report looks something like this.

You can see in this example, there is a dotted line that shows the minimum habitable floor level. This is the most comprehensive report out of all of the possible options.

Understanding FloodWise Report Data and Graphs

Now let’s look at how to interpret the rest of the information in these reports.

Reading the Ground Levels (Green Line)

The green line on the right-hand side of the FloodWise Report graph represents the property’s ground levels or contours, measured in meters (mAHD) using the Australian Height Datum.
A level of 0.0 AHD equals sea level. Suburbs closer to the bay in Brisbane will naturally show lower readings than elevated suburbs further inland.

Interpreting the Flood Probability Bars

The bars on the left-hand side of the report represent the annual probability of a flood event occurring. These bars also show the magnitude of the associated risk for any flood event.

A higher AEP percentage (i.e., more likely to flood) correlates with a lower flood level.
Conversely, a lower AEP (i.e., less likely to flood) typically means a higher flood level.

Historical Flood Data and Defined Flood Levels

Some FloodWise Reports include additional data showing the recorded 2011 flood levels and the Defined Flood Level (DFL). This is the standard used to measure Brisbane River flooding, which is 3.7m AHD at the City Gauge and a river flow of 6,800m³/s.

Comparing Flood Levels to Ground Levels

If the flood probability bars on the left are higher than the ground level (green line), it indicates that water is likely to cover parts or all of the site during a flood.
You can estimate potential flood depth by comparing these two points.

Council Requirements and Flood Level Benchmarks

For new builds or renovations, Brisbane City Council uses the 1% AEP level as a key benchmark:

Non-habitable areas: 300mm above the 1% AEP
Habitable areas: 500mm above the 1% AEP

For existing dwellings that may not already achieve flood immunity, comparing the actual floor level to ground level can determine expected inundation during major floods.

Special Considerations for Creek, Waterway, and Overland Flow Flooding

If a property ALSO falls within a Creek/Waterway Flooding overlay Category 1, 2 or 3 OR in a mapped overland flow path, you may also need to account for an undercroft area in the event you are looking to complete any future renovation works. This can get quite complex, and we recommend if this applies to seek help from professionals such as architects, certifiers, and town planners.

Technical Summary in the FloodWise Property Report

Page 2 of the FloodWise Property Report provides a technical summary used mainly by builders and architects.
If you already understand the main graph data from Page 1, you generally will not need to interpret the advanced technical details.

Conclusion: Why Brisbane Flood Maps Matter When Buying Property

Checking the FloodWise Report and Brisbane flood maps is a crucial step in property due diligence. Understanding how to interpret these reports helps buyers make informed decisions and ensures compliance with council requirements for flood-prone properties. If you need assistance, feel free to contact Streamline Property Buyers Agents for expert guidance.

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How to Assess Brisbane Flood Maps and Understand Their Impacts