These frequently asked questions aim to provide a better understanding of the flood studies Council has been conducting.
They explain what the flood mapping is, what they tell us, how they are carried out and definitions of the terms used.
Why is Council undertaking flood risk mapping?
Flooding can cause significant damage to property and infrastructure and pose a risk to life. All Councils in Tasmania are required by law to work towards identifying the land in their areas which has the potential to be affected by flooding. This helps Councils to guide urban development, identify potential mitigation options and improvements to stormwater infrastructure, protect property and keep the public safe.
Three of the finalised flood studies to date covers the key areas identified in Council’s Climate Change Plan: Kingston Beach, Snug and Adventure Bay (Captain Cook Creek catchment).
The storm event in May 2018 had devastating impacts within the Whitewater Creek (including Kingston CBD) and the Blackmans Bay area. State funded grants allowed Council to undertake flood risk mapping for Whitewater Creek and to develop catchment resilience programs for Kingston CBD and Blackmans Bay.
What are the flood risk maps and what do they tell us?
The flood risk maps demonstrate the extent of predicted inundation and the resulting hazard levels (discussed below). This information will help Council to:
- Accurately communicate the existing and future flood risk of affected communities.
- Develop mitigation strategies to either reduce the magnitude or the impact of future flood event for the safety of the public.
- Implement appropriate planning controls to guide future development.
How was the flood risk mapping undertaken? How do we know they are accurate?
To identify flood risk areas, a computer model is set up based on current best practice and available information at the time of the study.
The output from the model, such as flood levels, is verified and compared against a historic storm event. When the model is considered to produce a good representation of the same historic event, it can be used to estimate the extent of inundation for a range of flood events. This includes flood scenarios for current year and climate change predictions.
What does a 1 per cent (%) AEP and 5% AEP mean?
AEP stand for Annual Exceedance Probability. This is a term used to describe the intensity of a storm event, and the associated flood that it causes. It is used in flood studies to model the effects of different types of storm events.
The AEP is the probability or likelihood of a storm event occurring in any given year. It is usually expressed as a percentage.
A 1% AEP storm event has a 1% chance of occurring in any given year. This expression has replaced the use of the old terminology of a 1 in 100-year storm event.
Likewise, a 5% AEP storm event has a 5% chance of occurring in any given year and is likely to occur once every 20 years.
The lower the percentage, the more intense the rain and associated flood event.
What does the term ‘flood hazard’ mean and what do different flood hazard categories indicate?
Floods create hazardous conditions which can result in damage to property or even loss of life.
The level of flood hazard is estimated by the depth and speed of water, or a combination of the two, when there is a flood at a specific location. Flood hazards are categorised from H1 to H6, where H1 is considered generally safe and H6 is extremely hazardous. The categories describe flood conditions as follows:
- ‘H1’ hazard means the area is generally safe for people, vehicles and buildings;
- ‘H2’ hazard means the area is unsafe for small vehicles;
- ‘H3’ hazard means unsafe for vehicles, children and the elderly;
- ‘H4’ hazard means unsafe for people and vehicles;
- ‘H5’ hazard means unsafe for vehicles and people. All buildings vulnerable to structural damage. Some less robust building types vulnerable to failure; and
- ‘H6’ hazard means unsafe for vehicles and people. All building types considered vulnerable to failure.
How do I know what the flood hazard level at my property is?
The flood hazard levels for all properties within the study areas are available on Council’s website.
If my house is in a high-risk flood zone, is there anything I can do now? What will Council do about it?
We recommend that you contact your insurer to make sure you have adequate flood insurance for your property.
Defining the flood hazard within the municipality is the first step to build a more flood resilient community.
Council is working on prioritising projects to mitigate the impact of future flood events or reducing the magnitude of them where possible. Having identified the existing and future flood hazard provides Council with the opportunity to manage them as best as possible.
Has Climate Change been considered?
Council’s flood studies consider a range of different scenarios, including the impact of sea level rise and change in rainfall intensities caused by climate change. Council always uses the most up to date climate change predictions and acknowledge that this may change in the future as more information is made available.
I have been living in my house for many years and it has never flooded. Why is Council now saying that my property is subjected to flooding?
Council’s mapping represents current and future flood RISK at your property and does not consider WHEN and HOW a future flood event will occur. Floods do not occur in a regular pattern. There may be long periods where there are no floods, followed by short periods with several floods.
A 1% AEP flood is considered as an extreme (and rare) event and may not have occurred in your location while you have lived in the area.
I wasn’t told my house was in a flood zone when I bought it. Why did not Council have this information before?
Council is collecting information and developing an understanding of flooding within the municipality and may not have known that your property was in a flood zone when you purchased your property.
We can provide advice to any property owners and buyers about whether a property is subjected to flooding and encourage you to get in touch with us if you are concerned.
Will Council’s stormwater pipe protect me from flooding?
The current design standards for stormwater drainage system is to cater for runoff from storm events up to and including a 5% AEP. This is the level of service expected by Council.
However, older infrastructure was built at a time with different design standards, different climate and a lower level of urbanisation. As such, parts of Council’s stormwater drainage network may reach capacity for events more frequent than the 5% AEP. Council is continuously working on upgrading its stormwater drainage network to meet the expected level of service.
For major storm events, such as the 1% AEP, the capacity of Council’s stormwater drainage network is expected to be exceeded as the intensity of the rainfall is higher than the design standard. During these events, stormwater runoff will discharge as overland flow and flooding may occur.
What is Council’s role in managing flood risk?
Council has many different roles to play in relation to flood management. These include:
- Developing and implementing local flood management plans to reduce the adverse impacts of flooding to acceptable levels.
- Incorporating flood mapping and controls into the local planning schemes to manage land use and development (buildings, works and subdivisions) within flood prone areas.
- Managing local community infrastructure, by building, owning, and maintaining it.
- Implementing and maintaining local flood early warning systems for Kingston Beach and Adventure Bay.
- Supporting, developing and resourcing the implementation of flood response plans.
- Providing for the conservation of significant natural resources and environmental values.
If my house floods who do I call for help?
If you need assistance during a flood event, call your local State Emergency Service (SES) on 132 500 or triple-0 (000) in life threatening situations.
What is next and what is Council doing about the flooding issue?
Council will continue to develop flood maps for urban and identified flood risk areas in the municipality and will make these available to the general community.
The flood information will be used by Council to prioritise upgrades to our stormwater infrastructure, guide the planning of new and future developments and to develop and implement flood management plans as required.
Council is currently working on updating its Flood Early Warning System which will provide information to Authorities including Council, SES and Police.
Where can I get more information?
You can find the completed studies on our Flood Studies page.
- The Bureau of Meteorology provides information on what to do before, during and after a flood here: http://www.bom.gov.au/water/floods/document/What_todo_floods.pdf
They also provide information in relation to their Flood Warning Service on their website here:
Additional information on what you can do to manage and prepare for a flood situation is found on the State Emergency Services and the Tas Alert Services following the links below:
You are always welcome to contact Council’s Customer Service team on (03) 6211 8200 should you have any concerns regarding flooding or stormwater within the municipality.