FAQs

Flood models do not provide detailed information on the extent of potential inundation to physical structures such as homes, sheds and garages. This is because Council does not hold information on floor levels of all properties across the region. Buildings would need to be individually surveyed against the flood model data to determine this level of detail. A property identified as ‘at risk’ means it sits within the area mapped as being affected by water in a modelled flood event.

The nature of the property (slope, structures, drainage, gardens etc.), recent catchment conditions, and the type of flood will determine the presence or depth of floodwater across the property.

Yes. All mapping undertaken by council is subject to ongoing review. As these reviews take place, it is likely that changes to the mapping will occur, particularly as new flood study information or ground topography information become available. However, this is not expected to occur very often – usually only about every three to five years. This is the likely frequency at which the mapping may be amended.

You can purchase a Flood Report that is specific to your property through Council’s Customer Service Centre. The flood report summarises flood information for your property to inform and supplement the application of the Council’s planning scheme Flood Hazard overlay code, floodplain planning provisions, and the applicable flood planning levels.

The flood studies found that flood behaviour in the region can be complex and vary significantly between locations, depending on topography, infrastructure and rainfall pattern. Past flooding was caused by high-intensity local rain creating runoff in backyards and streets, and the overflowing of creeks and the Fitzroy River. These types of flooding can occur separately or together and therefore have varying impacts on properties. Your property may be subject to one or a combination of flooding types.

Local Catchment flooding can be referred to as creek flooding, overland flow flooding or a combination of both.

Creek flooding happens when intense rain falls over a creek catchment. Run-off from houses and streets also contributes to creek flooding. The combination of heavy rainfall, run-off and the existing water in the creek causes creek levels to rise.

Overland flow is run-off that travels over the land during heavy rainfall events. Overland flow can be unpredictable because it is affected by localised rainfall and urban features such as stormwater pipes, roads, fences, walls and other structures. The actual depth and impact of overland flow varies depending on local conditions but it generally occurs quickly.  

The AEP stands for ‘Annual Exceedance Probability’, which is a measure of the rarity of a flood event. Average Exceedance Probability (AEP) is used to explain the chance of a flood of a given size (or larger) occurring in any one year, usually expressed as a percentage. 

The 1 percent AEP flood event is a level of flooding that has a one percent (one in 100) chance of being equalled or exceeded in any given year. This means such a flood event could occur at any time (i.e. it could occur this year or in the next couple of years, and on one or multiple occasions, or not occur at all for many decades) but it only has a one percent chance of doing so in any given year. 

It is important to note that, despite it being a commonly used term, there is no such flood as a ‘one hundred year flood’. All floods are different. While we don’t know when or how the next flood will occur, we can estimate the likelihood (probability or chances) of a certain size flood at a given location during a given period of time. The equivalent of a 1-in-100 year flood is the 1% AEP flood which has a 1% chance in any one year to see a flood of this size or greater occur. The 1% AEP event should not be interpreted as only occurring once in 100 years.

Hazard refers to the source of potential harm or a situation with a potential to cause loss. Flood hazard (in which flooding is the source of potential harm and can cause damage to the community) refers to the potential loss of life, injury and economic loss that can be caused by future flood events. The degree of flood hazard varies with the severity of flooding and location in the floodplain, and is affected by flood behaviour. Flood hazard is characterised by the velocity and depth, rate-of-rise and the timeframe from rainfall to flooding, as well as the interaction of these factors with the topography of the floodplain. The faster or the deeper the water, the greater the hazard. Council’s studies have adopted the national Australian Rainfall and Runoff’s hazard criteria which uses six categories for classifying flood hazard from Low to Extreme.

The updated and new flood modelling has resulted in the comprehensive identification of flood hazard across the catchments, irrespective of whether the flood hazard is a result of creek flow or overland flow.  This includes identification of areas which may be subject to low, medium, high, and extreme hazard due to overland flow which has the potential to cause risk to life, and property damage. Council administers land use planning provisions in floodplain areas based on whether a development is located in Planning Area 1 or Planning Area 2. Flood hazard is a key determinant for classifying flood prone land into Planning Area 1 and Planning Area 2

Application of Flood Hazard Criteria for delineating Planning Area 1 and Planning Area 2

Hydraulic hazard classification plays an important role in informing floodplain risk management in an area.  Council’s previous hazard classification which was included in earlier flood mapping was based on the Queensland Reconstruction Authority hazard classification which delineated flood hazard across 4 categories: Low Flood Hazard, Significant Flood Hazard, High Flood Hazard, and Extreme Flood Hazard.

As part of the flood study updates, a decision was made to adopt the National Best Practice Guideline Australian Rainfall and Runoff(ARR)’s  flood hazard classification, which divides hazard into six categories (H1 to H6), and provides greater clarity on the hazard levels for a person or property exposed to floodwaters. The ARR classification takes into account additional criteria that may impact the prevailing risk including the size of the flood, rate of rise, duration of flooding, effective warning time, flood awareness, effective flood access, evacuation problems, and type of development. Figure 1 and Table 1 (below) show the revised Flood Hazard categorisation:

Figure 1- Proposed General Flood Hazard vulnerability curves (adapted from Australian Rainfall and Runoff 2019)

Table 1: ARR 2019 Hazard Classification Descriptions

Table 2 below provides a summary of how the Australian Rainfall and Runoff hazard categories have been communicated for the proposed Flood Mapping:

Table 2:  Proposed Flood Hazard categorisation for Flood Planning Areas

Planning Area 1 is identified as red on the map. It means flooding is very likely and there may be very deep and/or very fast moving water. This area is considered a ‘high and extreme hazard’ area.

What does it mean for Development?

Any new development will be subject to the highest development assessment requirements.

No new buildings or structures to locate in this area.  

No additional lots to be created.

Any replacement, alterations or extensions to an existing building will have to be constructed in accordance with the Queensland Development Code – Construction of buildings in flood hazard areas, such as meeting minimum floor levels.

Planning Area 2 is identified as blue on the map. It means flooding is likely and there may be shallow and/or slow moving water. This area is considered a ‘low-medium hazard’ area. 

New development may be allowed as long as it is located and designed to minimise the impacts of flooding.  

New buildings that can mitigate flood impacts by being constructed in accordance with the ‘Queensland Development Code – Construction of buildings in flood hazard areas’ provisions (such as meeting minimum finished floor heights) are allowed.

No. Your property may still be subject to low flood hazard (H1), which is characterised by flood waters with velocities of less than 2 metres per second (2m/s), and flood depths of less than 300mm (0.3m) in the defined flood event (1%AEP). Council’s flood hazard mapping shows the full extent of the flood hazard for the defined flood event (1%AEP), including the H1 hazard flood extents. The Planning Area 1 and 2 maps do not show the full extent of flood hazard for the defined flood event, but rather, only the flood hazard that falls within H2 to H6 (i.e., medium to extreme) flood hazard categories, as these flood hazard categories trigger specific floodplain planning restrictions depending on whether the hazard corresponds to Planning Area 1 or Planning Area 2.  It is recommended that residents familiarise themselves with the flood hazard mapping for their property and locality. Being aware of the full extent of flood hazard for your property will enable you to understand what may happen during times of flood and heavy rain, and to also consider necessary precautions (such as finished floor levels, and siting of proposed extensions or new buildings and sheds) when planning for any future development.

If you live near a creek, river, major storm water drain or in a low-lying area, you may be at risk from flooding, even if you have not experienced it personally. The modelling and associated mapping provides an indication of flooding from river, creek or stormwater flows during various modelled rainfall events across the riverine, creek, and local catchment areas within the region. Some of the flood studies have also taken into account actual historic events and anecdotal flood data collated from previous events in the region. It is always possible that flooding may affect an area of the region not currently indicated as being at risk of flooding in the mapping.

Nevertheless, even if your property is not directly affected by flooding it is beneficial for you to understand the flooding impacts for your locality and immediate surroundings. Having this broader understanding of potential flood behaviour is important as it will allow you to take relevant precautions to protect yourself, loved ones and property. For example, viewing the flood mapping for your locality can be helpful to understand potential access issues and if your property might become isolated (not necessarily flooded) so that you are able to evacuate safely (if required).

It must be noted that Flood risk is only one of the factors affecting home insurance premiums. Premiums also consider other risk factors such as building type, building age, security and vulnerability to other natural hazards such as cyclones, bushfire, storms, earthquakes etc.

Most insurance companies already use their own flood mapping to determine premiums relating to flood risk. The insurance industry uses a range of flood maps and studies provided from a number of local, state, Commonwealth and private sources in setting the insurance premiums for properties.  These studies may not be to the same level of detail as Council studies as they do not have information as accurate as Council (e.g. survey levels). If accurate mapping is not available, the industry makes assumptions about the flood risk, and may use alternative methods for estimating risks that may not be reflective of the actual site conditions. For instance, if historical or out-dated flood data is used, new flood mitigation infrastructure or changes in infill development (for example) may not have been considered. This may result in applying higher premiums than is necessary, as the risk is unknown resulting in a high flood risk factored into the premium.

Insurers, due to solvency regulation and need for business sustainability, tend to be more conservative in their assessment of the risk as they need to compensate for the uncertainty. Most insurance companies base their insurance premium prices on the individual site.  Council shares its flood mapping with the Insurance Council of Australia, to ensure that insurance companies have access to reliable flood information. Detailed flood mapping can have a positive impact on insurance for some people as it provides more specific information about a property’s flood risk and allows for more accurate pricing.

For more information on how insurers determine flood risk, please refer to https://insurancecouncil.com.au/resource/flood-insurance-explained/

If you are concerned that your insurer may not be accurately accounting for flooding on your property, we encourage you to familiarise yourself with Council’s flood mapping and discuss your concerns with your insurer or alternatively, seek quotes from other insurance companies. 

No. The aggressive removal of vegetation in the riparian areas of the creeks and the Fitzroy river would cause much greater erosion of the banks, which could lead to bank slumping and result in a reduction of the channel capacity  for effective flow conveyance during storms and flood events. The effect of vegetation overgrowth has been assessed as part of sensitivity scenarios in the flood modelling, and its effects on flood levels have been found to be marginal. Council is working to implement  better riparian management which seeks to achieve a balance between vegetation removal to promote better drainage, whilst retaining enough vegetation to ensure that the integrity and stability of the creek banks is not compromised.

Significant rain at the top of a hill will flow over the land, and concentrate in low lying gullies, channels, roads and surface depressions. Most of Council’s updated and new flood studies have taken this into account and as such, your property may be shown as having overland flow.  The speed and depth of overland floodwater may still be significant enough to cause damage, and your home could also become isolated with access roads cut by rising flood waters. It is important to be aware of this for your safety and well being, particularly if rainfall occurs for a significant period of time.