Why Council Updated the Flood Mapping
Gympie’s relationship with the Mary River goes back further than most towns in Queensland. Major floods have affected the region in 1893, 1955, 1974, 1999, 2013 and again in 2022, when the river peaked at 22.96 metres — the second-highest level ever recorded locally.
Following recent flood events and updated modelling, Gympie Regional Council introduced a new flood mapping standard known as the Future Climate 1% AEP, now used as the Defined Flood Event.
The revised mapping incorporates more detailed terrain information, updated hydraulic modelling and infrastructure such as bridges and culverts, providing a more accurate representation of flood behaviour across the region.
As a result, some properties that were previously outside the mapped flood hazard area may now be affected by updated planning and building requirements.
What This Means for Your Finished Floor Level
If your property falls within the updated flood hazard area, a new habitable building — and some major renovations — may need to be constructed to a minimum finished floor level.
For affected properties, the minimum finished floor level is calculated as:
Finished Floor Level = Defined Flood Level + 300mm freeboard
The defined flood level is the modelled flood height for the property. The additional 300mm freeboard provides a safety margin above that level and is required under Queensland Development Code MP3.5.
For properties on the Cooloola Coast, including Tin Can Bay, Cooloola Cove and Rainbow Beach, the calculation may instead be based on the adopted storm tide level for the area.
These requirements generally apply to new dwellings, major renovations and certain commercial works. Existing approved homes are not retrospectively required to comply with the updated finished floor level requirements.
How Do You Know If Your Block Is Affected?
Council’s online mapping system provides a useful starting point. You can check the “Building Regulations 2021 Flood Resolutions” layer to view:
- The defined flood event boundary
- Habitable floor level requirements for Cooloola Coast properties
This mapping helps identify whether your property may be affected, but it does not provide the precise ground levels needed to design a compliant building.
Why You Need a Survey, Not Just a Map
While Council’s mapping is an important planning tool, it does not replace a detailed land survey. Before a dwelling can be designed or approved, accurate site levels must be established to determine the required finished floor height.
A contour and detail survey provides this information by measuring the existing ground levels across the property. The survey data allows your designer, builder and certifier to compare the site levels with Council’s defined flood level and establish the correct finished floor height.
The survey information can then be used to:
- Confirm whether the proposed dwelling location sits above or below the required finished floor level
- Design footings, retaining walls and site cut or fill to the correct height
- Provide certifiers with the flood level information required for approval
- Support discussions with Council where flood levels vary across a larger property
On larger rural properties, flood levels may vary across different areas of the same lot. In these situations, a detailed survey can help identify the most suitable building location and may support a more practical building platform.
A Few Things Worth Knowing
Insurance Considerations
Many insurers reference flood mapping, claims history and building characteristics when assessing flood risk. Once you understand your property’s flood classification, it may be worth discussing any potential insurance implications with your insurer.
Existing Homes
The updated mapping generally applies to new dwellings, major renovations and certain commercial developments. Existing approved homes are not retrospectively required to meet the new finished floor level requirements.
Property Values
Council has advised that flood risk is only one of many factors that may influence property value. The purpose of the updated mapping is to improve planning, resilience and building safety rather than determine property valuations.
Planning to Build in Gympie? Start With a Survey
If you are planning to build in the Gympie region, understanding your site’s flood requirements early can save time, cost and design changes later.
A contour and detail survey provides the accurate information needed for designers, builders and certifiers to establish compliant finished floor levels before construction begins.
Colston Surveyors has been assisting property owners throughout Gympie and the Sunshine Coast since 1988. Whether you are building on a residential allotment or a large rural property, our experienced surveyors can provide the site information needed to move your project forward with confidence.
Contact us to discuss a flood level or topographical survey for your Gympie project, or learn more about our topographical surveys and specialised survey services.