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Flooding Information

While average annual rainfall is lower in Sorell than for much of Tasmania, high intensity and short duration rainfall events can cause local flooding issues particularly when tides are high or the ground is so saturated that it cannot absorb any further rainfall.  

Your property maybe at risk of flood damage if:

  • You are near a waterway, including naturally occurring ephemeral waterways that are usually dry.
  • Your property is in a natural depression, including behind a coastal dune strip.
  • Your property slopes up into surrounding farmland or natural bushland.
  • Your property is in a low-lying area near the coast or a waterway.
  • Your property is located at the bottom of a hill with adjoining developed properties above.

Before a flood:

  • Model and map flood risk.
  • Statutory planning in flood risk areas.
  • Undertake stormwater pit and grate inspections prior to a major rainfall event.

During a flood:

  • Keep the pipe system clear of blockages.
  • Ensure the main natural drains are kept free of debris as much as possible.
  • Respond to customer requests about blockages with the existing infrastructure.

After a flood:

  • Clear debris from waterways, roadways, and parks.
  • Repair damaged assets.

Whilst Council does all it can within available resources to ensure the drainage/stormwater infrastructure for which Council is responsible is efficiently and effectively maintained and continuously improved, it should be noted that it is not unusual for drainage and storm water infrastructure to reach capacity very quickly during significant rain events.

Keep up to date on current storm and flood warnings and information.

Property owners should do everything practicable to ensure drainage and stormwater infrastructure within their properties is kept clear of debris.  It is important that all these overland drainage paths are well maintained and kept free from obstructions including fencing and other structures.

It is important for property owners in flood prone areas to have an emergency/flood plan in place to prepare for such an event, including ensuring the safety of animals and stock where practicable.

The State Emergency Service has useful advice on its website https://www.ses.tas.gov.au/be-ready-storms-floods/.

Council engaged Entura consulting to undertake detailed flood studies in urban areas. These flood studies have adopted the approach recommended by national guidelines for flood modelling in Australia.

Computer models have been set up using historical flood events, which allows council to estimate the extent of urban flooding for a range of different rainfall events. This includes several scenarios including a 5% and 1% AEP flood and other flood scenarios related to climate change.

The flood mapping on council’s website shows the 1% AEP flood, including an allowance for climate change. This is the storm event which is used by council to implement town planning and building controls, as well as plan for the safety of the public.

In non-urban parts of Sorell flood risk mapping is available through the State Emergency Services (SES) Tasmanian strategic flood map which can be viewed on listmap and https://www.ses.tas.gov.au/floodmaps/

The next section explains what a 1% AEP and 5% AEP storm mean.

AEP stands 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 likelihood of a storm event occurring in any given year and is usually expressed as a percentage (%). A 1% AEP storm event has a one percent chance of occurring in any given year. This expression has replaced the use of the old terminology of a one in 100-year storm event. Likewise, a 5% AEP storm event has a five percent chance of occurring in any given year.

The lower the percentage (%), the less likely an event is to occur. Very extreme rainfall events have a low chance of occurring in any given year, whereas less extreme events are more frequent and more likely.

Flood mapping included on council’s website is based on the 1% AEP storm event and includes an allowance for climate change. Rainfall is predicted to be heavier as a result of climate change, which means that flooding may also be more frequent and more severe. This possible increase in rainfall has been considered in council’s flood mapping.

Council’s flood studies considered a range of different scenarios, including the impact of sea level rise and change in rainfall intensity caused by climate change. Council always uses the most up-to-date climate change predictions and acknowledges that this may change in the future as more information becomes available.
The flood maps provided on the council website include an allowance for climate change and sea level rise.

Council recommends that you contact your insurer to make sure that you have adequate flood insurance for your property. Council is working on prioritising projects to mitigate the impact of future flood events. Increasing our understanding of existing and future flood risks allows for improved planning to better prepare for and manage these events into the future.

Flood mapping is available on council’s website and listmap.

The flood mapping shows the likely effects of the 1% AEP flood, including an allowance for climate change. This is the storm event which is used by council to implement town planning and building controls, as well as plan for the safety of the public.

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 an extreme event, with a one percent chance of occurring in any year, and may not have occurred in your location while you have lived in the area.

Council is collecting information and developing an understanding of flooding within the municipality. Therefore, we may not have known that your property was in a flood zone when you purchased your property. Council can provide advice to any property owners and buyers about whether a property is subject to flooding. If you are concerned, please contact council.

Please note that a Land Information Certificate (also called a Section 337 Certificate) for a property does not currently provide information about flooding.

If you need assistance during a flood event, call your local State Emergency Service (SES) on 132 500 or triple zero (000) in life threatening situations.

Underground stormwater infrastructure in Tasmania is typically designed for a 5% AEP flood event. This is considered to provide a reasonable level of protection from flooding at a cost which is sustainable to the community.

In the event of a more severe storm, where the capacity of the underground system is exceeded, overland flow can be expected to occur. In contemporary design, it is best practice to allow for additional capacity in the road reserve, or through easements on private land, for overland flooding to occur without damage to infrastructure and property.

However, older infrastructure was built at a time when there were different design standards, different climate and a lower level of urbanisation. As a result, parts of council’s stormwater drainage network may reach capacity for weather events that happen more often than the 5% AEP and overland flow paths for flooding, once the system capacity is exceeded, may not have been provided for.

Council is continuously working on upgrading its stormwater drainage network to meet the expected level of service.

Please report any concerns about blocked council stormwater drains to council’s customer service team on (03) 6217 9500. Property owners are responsible for making sure that private stormwater systems are properly connected to council’s stormwater system. If you think there is a blockage in one of the drainage pipes on your property, you should contact a licensed plumber to investigate.

The Bureau of Meteorology has a PDF on what to do before, during and after a flood.

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 websites:

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