flood risk and flood map information

What do these flood maps show?

What is riverine and flash flooding?

What is a 1% Annual Exceedance Probability flood?

What is the likelihood of a flood occurring in Canberra?

Why have you produced these maps?

How were the maps developed?

Has the risk of floods occurring always been the same?

How will flooding affect my block?

What will this mean for my insurance?

Will this impact the value of my house?

What does the government do to manage flood risk in the ACT?

What help is available for people who live or have businesses in flood zones?

What effect will climate change have in Canberra?

What kind of warning system is in place in Canberra?

What can I do on my property to prevent flooding?

Who do I call about preparing for a storm or flood?

My yard floods when it rains but I am not near a major waterway or creek.

My stormwater drain overflows in every big storm. How do I get it fixed?

My stormwater drain is blocked. Who do I call?


Q. What do these flood maps show?

A.

These maps show the extent of riverine flooding in Canberra that would be expected during a 1% Annual Exceedance Probability (AEP) flood* in the city’s main catchments.

  • The flood maps have been developed to national standards.
  • The maps show areas likely to be flooded from named watercourses, such as rivers and creeks, including creeks that are now largely used as stormwater drains, such as Yarralumla Creek and Sullivan’s Creek.
  • The maps show the predicted:
    • extent of flooding – how far flood waters will reach
    • depth of flooding – how deep the water will be at different places
    • hazard ranking – this is linked to the speed of flow and depth of the water, and gives an indication of how dangerous the water will be. However, all flood waters are dangerous.
  • The flood maps cannot predict the effect of blocked drains or other damage to infrastructure that may block streamflow or divert water away from the stormwater channels.

1% AEP floods are related to riverine flooding only, where waterways rise up and burst their banks, not to flooding from other sources such as intense local rainfall.

The flood studies that informed these maps provide the most comprehensive review of flood data ever undertaken in Canberra.

*For a definition of 1% AEP flood, please see question What is a 1% Annual Exceedance Probability flood?

Q. What is riverine and flash flooding?

A.

Riverine flooding:

  • A riverine flood is defined as the covering of normally dry land by water that has escaped from the normal confines of a watercourse. It occurs when heavy rainfall finds its way down rivers, causing water levels to rise and overflow their banks,inundating surrounding low-lying land.
  • In Canberra, our watercourses include the Molonglo River and several major creeks. Many of the city’s concrete stormwater drains were once natural creeks, and therefore may be susceptible to riverine flooding.
  • Riverine flooding may occur suddenly due to intense rainfall over a short period, or more gradually as rain falling high in the catchment accumulates and makes its way downstream. In Canberra, the former scenario is more likely.

Flash flooding:

  • Flash flooding is localised flooding that occurs when heavy rain cannot drain away quicker than it falls. A flash flood is defined by the speed of flooding, not the source or location of flooding.Flash flooding is typically caused by short duration storms over a localised area or catchment. While flash flooding may occur in rivers and creeks, it can happen anywhere if rainfall is intense enough. A riverine flood may also be a flash flood.

Q. What is a 1% Annual Exceedance Probability flood?

A.

A 1% Annual Exceedance Probability (AEP) flood is a flood which has a 1% chance of occurring in any year. This means that if you experienced a 1% AEP flood last year, the chance of experiencing a similar flood this year is still 1%.It used to be known as 1 in 100 year flood, but this term is misleading as it suggests such a flood will only occur once every 100 years.Canberra has had two floods at or greater than 1% AEP since records have been kept: in 1971 in the Yarralumla Creek catchment; and in 2018 in the Sullivan’s Creek and Woolshed Creek catchments.

  • The 1% flood extents are calculated using computer modelling, incorporating historical data and a range of evidence-based assumptions relating to factors such as climate, rainfall, and catchment condition. It is our ‘best estimate’ based on the data that is currently available. The amount and intensity of rain needed to produce a 1% flood is unique for every location.
  • More detailed information about the 1% AEP flood calculation can be found at the Bureau of Meteorology website.
  • Floods greater than the 1% AEP are possible; some parts of the Sullivan’s Creek catchment experienced higher levels of flooding than a 1% AEP flood in February 2018.

Q. What is the likelihood of a flood occurring in Canberra?

A.

Riverine flooding in Canberra is unlikely. However, it is prudent to understand the potential risk and plan accordingly.

  • The areas at risk of riverine flooding are small and the expected depth of flooding in these areas is relatively low compared to flood-impacted urban areas in other states and territories.
  • Canberra planning takes into account the need to develop areas above the 1% AEP flood level*. This has been the case for planning for new urban development since the 1970s (however, the 1% AEP flood level may have changed since that time due to factors such as climate change, land-use change in terms of increased development and updated modelling assumptions).
  • The local stormwater system is designed to cope with the 1% AEP storm flows as they were understood at the time of construction.
  • While the new flood models predict the path and extent of the revised 1% AEP, it cannot predict the extent of flooding from other sources, such as intense rainfall and damaged infrastructure.

*please see question What is a 1% Annual Exceedance Probability flood?

Q. Why have you produced these maps?

A.

Along with other jurisdictions in Australia, the ACT is moving toward national best practice in flood risk management. This is the most comprehensive review of Canberra’s catchments and their associated flood risk to date.

  • Flood studies such as these highlight risk areas and help the Government improve planning and residents to better prepare for and respond to floods.
  • The maps help Emergency Services prepare for major storm events and inform the public of potential flooding hazards.
  • The maps will guide long-term planning for new suburbs and the re-design of established suburbs.
  • Funding for the development of the maps was received under an Australian Government grant from the Natural Disaster Resilience Program.

Q. How were the maps developed?

A.

The maps were developed from flood studies of Canberra’s eight main catchments. These studies were undertaken over the course of the last decade for a variety of purposes.

  • Updated data sets and improved hydrological information were added to the existing flood models for each catchment to provide the updated flood maps for the 1% AEP.
  • Each of the flood studies and associated models were reviewed by independent flood mapping experts to determine both their relevancy and accuracy in relation to current industry standard.

Q. Has the risk of floods occurring always been the same?

A.

The extent and depth of the 1% AEP flood will change over time as we experience changes in the catchment (e.g. more built development), changing climatic conditions, and have access to improved hydrological data (rainfall, run-off and streamflow). This means that the 1% AEP flood today may affect different areas from the predicted 1% AEP 50 years ago.

  • Urban physical changes that can influence flood risk include an increase in hard surfaces associated with new roads, footpaths and urban infill, and reduced vegetation cover.
  • Climate change is predicted to lead to more intense storms in the Canberra region, potentially increasing the chances of flash flooding.

Q. How will flooding affect my block?

A.

To see if a1% AEP riverine flooding is likely to affect your block, please go to the Actmapi website. The map will show you if your property is likely to be affected, how deep the water is likely to be and what the flood hazard around you may be .

Q. What will this mean for my insurance?

A.

The Insurance Council of Australia (ICA) has advised that flood risk is calculated on a block-by-block basis. Premiums are set by individual insurance providers and may be adjusted on the basis of this revised mapping, which shows individual blocks.

  • The 1% AEP flood maps will help the industry better assess risk and set more accurate premiums.
  • The ICA advises that in other jurisdictions, premiums generally decreased for homes at less risk when the insurance providers received better information on riverine flood risk.
  • The ICA recommends that residents and property owners contact their individual insurer to assess and review their situation regarding flood risk highlighted by the revised maps and find a policy or insurer that meets their needs.
  • For more detailed queries, callers can call the ICA hotline on 1800 734 621.

Q. Will this impact the value of my house?

A.

Property prices are determined by a variety of factors. The Insurance Council of Australia indicates there is no direct evidence that the release of information from flood risk maps has a long-term impact on market valuation, but it is recommended that residents speak to their insurers and seek expert advice so that individual circumstances can be taken into account.

Q. What does the government do to manage flood risk in the ACT?

A.

The Government is committed to improving the city’s resilience to flooding.

  • Planning and development in the ACT has historically sought to avoid building below the 1% AEP flood line as it is understood at the time.
  • The ACT Government is following the national best practice guidelines for flood mitigation and is currently in stage 3:
    • Stage 1 – data collection including collation of existing studies and current modelling information.
    • Stage 2 – flood study to define nature and extent of flood risk.
    • Stage 3 – flood management options study to determine mitigation options from an economic, social and ecological perspective.
    • Stage 4 – flood management plan to define preferred options following stakeholder consultation.
    • Stage 5 – implementation of plan including budget bids and mitigation works.
  • A high-level flood management options study has been completed and the Government is now working on reviewing and prioritising potential mitigation works.
  • The ACT Territory Plan has provisions that seek to mitigate the impact of development on high flows and run-off.
  • The Territory Plan Waterways General Code (2007) incorporates the principles of water sensitive urban design (WSUD), which aim to mitigate stormwater run-off, reducing the rate and volume of water coming from developments.
  • Retarding basins, on-site detention and retention ponds, swales, raingardens and porous paving are some measures used in the ACT to help manage the flow of stormwater in an urban environment.
  • The ACT Government provides comprehensive community engagement through the ACTSES to assist home owners prepare properties for flood and stay safe during floods.

Q. What help is available for people who live or have businesses in flood zones?

A.

The Emergency Services Agency, the Environment, Planning and Sustainable Development Directorate and the Insurance Council of Australia will hold information sessions to provide the community with an opportunity to better understand their individual flood risk, learn more about flood safety and preparedness and to ask questions about the new flood maps.

  • You can make a direct flood enquiry to Access Canberra.
  • Phone 13 22 81 and select the appropriate option.

You can see more information and details on assistance by visiting:

Q. What effect will climate change have in Canberra?

A.

Research** indicates that there is the potential for more flash flooding events in the future.

  • As the climate continues to change, the Canberra region can expect:
    • storms to be more intense and more localised
    • a decline in spring rainfall and more rain in summer
    • major storms to follow a spell of long, hot weather.
  • The intensity of the storms could create the conditions that lead to 1% EAP flooding and other damage.

**Research is based on data from the NSW and ACT Regional Climate Model (NARCliM) and the Commonwealth and Scientific Industry Research Organisation (CSIRO) /Bureau of Meteorology (BOM) “Climate Change in Australia – Projections for Australia’s Natural Resource Management Regions”.

Q. What kind of warning system is in place in Canberra?

A.

Severe storm weather and flood warnings are available at:

Q. What can I do on my property to prevent flooding?

A.

Please see information on protecting your property at Transport Canberra and City Services.

Some works may require development approval. Please check with the Planning and Land Authority.

For more information about preparing for or responding to floods, please visit ACT Emergency Services Agency.

Q. Who do I call about preparing for a storm or flood?

A.

The ACT Emergency Services Agency website provides information on preparing for a storm or flood and recovery after the event.

Q. My yard floods when it rains but I am not near a major waterway or creek.

A.

This is not riverine flooding and therefore may not show on the updated flood maps. It is most likely caused by water flowing across your property during a major storm event that exceeds the capacity of the local drainage.

For more information, visit Transport Canberra and City Services.

Your flood insurance should cover any damage caused.

Q. My stormwater drain overflows in every big storm. How do I get it fixed?

A.

See more information about stormwater at Access Canberra

Please let Fix My Street know

or call Access Canberra on 13 22 81

Q. My stormwater drain is blocked. Who do I call?

A.

See more information about stormwater at Access Canberra

Please let Fix My Street know

or call Access Canberra on 13 22 81