StormFlood Engineering

A deep dive into flood risk for property development in Brisbane

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Property Development Flooding

When subdividing a property subject to flooding, consideration has to be provided for the type of flooding, the severity and the risks to property and people, which can alter the requirements and outcomes. There is no one size fits all approach, and every subdivision is on a case-by-case basis, as the location of the property can have any one of the flood sources be the peak event.

The Creek/Waterway and Overland Flow Paths are considered higher risk (given the shorter emergency response times) and higher frequency flood events in comparison to peak Coastal hazard or Brisbane River events.

 If you were to be 100% compliant, the following needs to be achieved:

*to find some of the above flood levels, you can use the FloodWise Property reports.

Generally, new lots need to have some level of flood immunity (and majorly flood-free for residential properties) and be designed to allow appropriate flood emergency management strategies to be adopted, for the more uncommon events in mind.

Overall if the new lots create additional risk to human life or burden to emergency services, they may not be supported for Development.

Each case is unique, and a Registered Professional Engineer of Queensland (RPEQ) specialising in hydraulics/flood engineering should be appointed for advice and guidance on potential outcomes.

What about River flooding events?

Each property is case-by-case, however, residential properties are much more constrained for development when the site is majorly affected by the Brisbane River flood extent (and with fair cause, given the damage from the 2011 floods). Some filling is allowed within the Brisbane River Flood overlays which can sometimes make it easier to provide flood-free lots/access, but it would be assessed on a site-by-site basis.

You can refer to the above table also which shows what flood-free level is required.

However, where flood resilient levels are not able to be achieved in Commercial/Industrial properties, there may be potential for flood emergency management approaches.

Can I fill my block to make it comply with the flood requirements?

In most scenarios, especially Residential developments, the two options may be to fill or to develop a raised building. However, in any case, impacts need to be assessed, to ensure you do not create additional adverse impacts to your neighbours. All council Planning Schemes require that no additional nuisance is created as a result of your development to surrounding properties.

Driveways may need to provide trafficable access out of the development, depending on the circumstances and practicality. Generally, developments where higher-risk flood events occur, do require consideration for evacuation via a trafficable vehicle access point.

Some councils have additional requirements, such as Brisbane City Council – which requires the driveway not to be inundated by the more frequent 10yr ARI Flood Event (10% AEP).

When a property is subject to flooding, any future development will generally need to comply with habitable and non-habitable levels, to achieve approval, the requirements for a residential dwelling have been shown below for example:

The levels and flood immunity requirements can also differ depending on the types of internal structures within the development.

Regardless, there is almost always a solution available, and therefore it is highly beneficial to get advice early on in the development approval phase from an RPEQ Flood/Hydraulic Engineer.