Riverine and flash flooding information for communities and properties on the Tyenna River and its tributaries

DRAFT – Please email any comments to ses@ses.tas.gov.au

Much of Westerway township is prone to flooding, as is the lower part of Mount Field National Park.  There are some private properties along the river upstream of Westerway that can become flooded.

Heavy rain in the Tyenna River catchment can also flood Gordon River Road, isolating many properties.

Agricultural areas and the picnic area at Mount Field National Park can be impacted by more common heavy rain events in the Tyenna catchment. The entrance to the National Park may be closed.

Areas around Ellendale may also become isolated due to flooding around the Ellendale Road intersection with Gordon River Road if there is also flooding along the Derwent River. If there is widespread rain around the Derwent River catchment, all areas around the Tyenna River may become isolated for possibly a few days.

The maps show the likely areas to be flooded in a rain event that has a 2%, 1% and 0.5% chance of happening any year (% Annual Exceedance Probability). Events with a 2% chance of happening any year can have major impacts around Westerway, inundating homes, other buildings and roads, and isolating many properties.  You are likely to experience this level of flooding at least once in your lifetime.  Tasmanians need to be prepared for levels of flooding most people may not have experienced.

The Tyenna River is fast flowing, and so flood waters are likely to be hazardous. Flood waters are likely to drop quickly once rain stops falling in the catchment.

Are you at risk of flood?

The area most recently had moderate flooding in July 2016, when the lower part of Mount Field National Park was flooded.  Westerway experienced major flooding in March 1931 and May 1948. This impacted buildings, the highway and the railway line. Such levels of flooding are likely to happen again. It is important to be prepared for flooding events that may not have happened within most people’s living memory.

What should I do?

• Check the map opposite to see whether your home or business is likely to be at risk of flooding during a flood.
• Prepare a Home Emergency Plan, including whether you need to evacuate in advance of a flood, where you will go and what you need to take.
• If you have a business in the area, you should have a plan that covers flooding.  Business Tasmania can help– see www.business.tas.gov.au/manage_a_business/ 
• If you need to evacuate or return home during a flood, make sure your route is safe.
• Asses your home or business and know what you need to do to prepare it to minimise possible damage from water inundation.

Floods like the one shown on the map, or worse, will occur again. No two floods are the same.

If you live in a low-lying area or near a watercourse, your house may flood. Even if your home is safe, you may need to detour around flooded areas or your road access may be cut. Never drive into or enter flood waters. Roads and bridges may be washed out or unsafe. Avoid travel during floods.

Knowing what to do can save your life and help protect your property. Having a Home Emergency Plan is one of the best ways to prepare. Decide on weather and rainfall triggers for when to act.

Bureau of Meteorology Forecasts, Warnings, and Observations

The Tyenna River can rise quickly after rainfall and so there can be little warning of flooding.  There is a river gauge on the river at Newbury (between Maydena and National Park) – see http://www.bom.gov.au/tas/flood/rain_river.shtml . There are no Bureau of Meteorology formal minor, moderate and major riverine flood warnings issued for the Tyenna River.  The short river length between Newbury and Westerway means there would not be enough warning time. 

Rainfall levels across the catchment during heavy rain events can give less accurate but more timely warning of possible flooding along the Tyenna River. Go to www.bom.gov.au/tas/ . Rainfall gauges in or near the catchment include:

• Tim O’Shea
• Meuller Ridge
• Maydena
• Newbury
• Mt Field National Park (Weir Road)

Whenever heavy rain is expected in an area that may lead to flooding, the Bureau issues

• Severe Weather Warning, and/or
• Thunderstorm Warning for heavy rainfall that may lead to flash flooding.

The time between the warning and heavy rain falling can vary from an hour to 24 hours or more. It is best to act on the warnings from the Bureau of Meteorology rather than wait for local flooding alerts.

The Mt Koonya Radar is useful to see when and where heavy rainfall is falling and is available on the BOM Weather app and website.

Download BOM Weather app and set your location to receive push notifications of warnings (more details at www.bom.gov.au/app/) .

Listen to ABC 936AM or go to tasalert.com for warnings.

Understand the warnings and key information

Keep aware of what is happening around you. Check forecasts, observations and warnings regularly.

• TasALERT.com
• your local ABC radio station or
• the Bureau of Meteorology’s website.

	Advice (Yellow): an incident has started. There is no immediate danger. Stay up to date in case the situation changes.
	Watch and Act (Orange): There is a heightened level of threat. Conditions are changing and you need to start taking action now to protect you and your family
	Emergency Warning (Red): An Emergency Warning is the highest level of warning. You may be in danger and need to take action immediately. Any delay now puts your life at risk.
	Community update (Blue): Specific information and updates for affected communities regarding a particular event or incident.
	Incident (White): an incident is the initial occurrence of an event before it becomes an emergency warning. As soon as an incident is reported, TasALERT published basic information including the type and location of incident.

Flood levels around the Tyenna River

While no two floods are the same, the following describes what is likely to happen if there is flooding around the area. Even if your property is not flooded, you need to think about access.

The rainfall amounts that might cause such an event are examples. Other levels of rainfall can cause flooding depending on

• where the rain falls
• how heavy the rain is
• how long the rain lasts, and
• how wet the ground is beforehand.

Melting snow can also contribute to flooding.

Minor flooding

• Water spills over riverbanks and covers nearby low-lying areas.  Agricultural and horticultural land on river flats may be at risk.  Livestock should be moved from these areas.
• There may be some flooding of low-level roadways along minor roadways and driveways.
• Some low-lying properties may have flooding around buildings below floor level, particularly properties on the river side in Westerway.
• There may be some areas of the Mount Field National Park picnic grounds inundated.

Moderate flooding

• There is more extended and deeper flooding of agricultural land along the river flats with some stock losses if not moved. There may be damage to fences and equipment such as pumps.
• Flooding may reach above floor heights of some low-lying houses and other buildings particularly on the river side of the Gordon River Road through Westerway.
• Some properties above low-lying bridges may become isolated.
• There is more extended flooding at Mount Field National Park picnic grounds and surrounding low lying areas. The road into the National Park may become inundated.

Major flooding

Widespread heavy rainfall across the catchment that has a 2% chance or less of happening can cause major flooding, particularly around Westerway and the lower part of Mount Field National Park.  This level of rainfall might be for example around:

• 53mm over 6 hours
• 73mm over 12 hours
• 101 mm over 24 hours
• 132mm over 48 hours

Note the level of flooding can depend on many factors, such as how wet the catchment is beforehand.  Major flooding may also start happening in less severe rain events. Impacts can include the following.

• Several areas of the Gordon River Road will become flooded and impassable, particularly through Westerway and upstream.  The Gordon River Road intersection with Ellendale Road is likely to be flooded. Areas upstream of Westerway are likely to become isolated, particularly if the Styx River is also in flood.
• Many properties in Westerway township may become flooded, including parts of the Primary School, the shop/ service station and other local businesses. Residents would need to evacuate, most likely to New Norfolk. There may not be enough time for sandbagging.
• Many river crossings will be impassable due to flooding or become hazardous. This can isolate areas upstream. High velocity flood waters can damage bridges and wash out roadways.
• Other low-lying properties on the river side of Gordon River Road. may be flooded above floor level.  It may be necessary to evacuate some dwellings.
• There is likely to be significant crop loss and stock loss unless the stock are moved to higher ground.
• There will be some flooding of land near the river around Maydena.  Properties to the north of the river may become isolated.
• Flooding in the Tyenna River may happen at the same time as more widespread flooding in the Derwent River catchment.  This may close roads between Westerway and New Norfolk, Ouse and other townships.

Go to tasalerts.com or listen to ABC local radio for detailed up to date information and advice during heavy rainfall events.

Know your risk, get ready, reduce risk where you can, connect with others, stay alert and act safe.

Before a flood

1. Know your risk

Flooding often happens in Tasmania and can cause widespread and significant damage. In the past 200 years there have been 78 flood related deaths in Tasmania. This guide is to help you understand flood risk in your area.

2. Prepare your household

Have an emergency plan that covers storms and floods

Thinking about what you would do in a storm or flood means you are more prepared and everyone is safer. Have an emergency plan that everyone in your household understands. There are checklists to help you think through your plan – see the SES website or Red Cross Rediplan.
Check your plan regularly and test it by everyone in the household thinking through a flooding scenario that may affect your household.

Prepare an Emergency Kit

Regularly test batteries in radios and torches.

3. Reduce your risk from flooding where you can

• Think about storms, flooding and other hazards when buying, maintaining or developing property.
• Trim or remove trees and branches overhanging your home, business or near powerlines on your property.
• Keep your gutters and drains clear.

4. Connect with others

Know your neighbours and get involved in your community.  A connected community is a safer and more resilient community in an emergency and can help everyone recover better afterwards. Check that family and neighbours are safe and aware of what’s happening.

See for example the Huon Valley Good Neighbour project.

During

5. Keep up to date

Keep aware of what is happening around you. Check forecasts, observations and warnings regularly. 

• TasALERT 
• your local ABC radio station or
• the Bureau of Meteorology’s website.

6. Act Safe

• Supervise children.
• Prepare for possible power, water or internet outages.
• Check your emergency kit is ready to go.
• Keep clear of flooded areas such as drains. NEVER walk, play, ride or drive in floodwater. You can’t always see what is under the water or how deep or fast-moving the water is. It is easy to be swept away and drown in as little as 20cm of fast-moving water. Flood water can be dangerous.

When your home may be flooded

• Put household items up high to minimise possible damage.
• Turn off the electricity and gas if it is safe to do so. 
• A great way to stop sewerage flowing back into your home is to place sandbags inside plastic bags and use them to block toilets and cover drains and sinks.
• Leave while you can get out safely.

If you need to evacuate

• Follow the advice from SES / Tasmania Police.  
• Take your emergency kit. 
• Go to friends or family in a safer place or an evacuation centre. 
• Let others know where you have gone.

Look after your animals

You are responsible for your animals in an emergency. If you have pets and other animals it will take you longer to evacuate in a flood or other emergency. Move livestock from flood prone areas well before flood waters may rise.  For more information see

• RSPCA’s guidance on preparing for animals in an emergency
• Huon Valley Council’s advice on preparing an emergency pet plan
• the Primary producer farm flood readiness toolkit.

Avoid travelling during storms and after storms

• Do not go sightseeing. Sightseers delay emergency services and cause accidents.
• Watch out for hazards such as
  • water over roads
  • damaged powerlines
  • landslides
  • damaged roads
  • falling trees or roofing iron.
• Never drive through flood waters. Most deaths and rescues in floods are from people driving through flood waters.
• Drive slowly and turn your headlights on roads not affected by flood waters.

After

• Keep listening for ABC Local Radio updates, road re-openings, community meetings, etc.
• If you left your home, do not return home until SES or Tasmania Police tell you it is safe to do so.
• Be aware of road hazards, such as mud or debris on the road, damaged roads/bridges and crews working on clean-up and repairs.

If your home has been damaged

• Stay at ground level while checking for damage. Be careful of fallen trees, broken glass, loose roofing or other hazards.
• Wear strong boots, gloves and protective clothes. 
• Use a torch, never use matches or candles inside flood affected buildings. 
• Boil all drinking water until you are told the tap water is safe again.
• Do not turn on it is tested by a licensed electrician or gas fitter for safety.
• If your home is damaged and you need to stay somewhere else, take your emergency kit and pets with you
• Take photos of any damage if safe for you to do so and contact your insurance company.
• Supervise children.
• Check neighbours are okay.

For further information go to www.ses.tas.gov.au

Staying informed and further information

Current warnings (TasAlerts) alerts.tas.gov.au

Bureau of Meteorology (BoM)

Emergency Broadcasters ABC 936AM

TASSES Social Media

• facebook.com/sestasmania
• twitter.com/sestasmania

Preparing for Flood Emergencies ses.tas.gov.au/plan-prepare/flood 

Derwent Valley Council  derwentvalley.tas.gov.au   6261 8500

National Relay Service (NRS) relayservice.gov.au

Disclaimer

The maps show potential flooding risks from consistent levels of rainfall across catchments, such as a 1% Annual Exceedance Probability (AEP).  In flooding events, rainfall is likely to be more inconsistent across a catchment, so these flood maps should be considered indicative only.  The mapped areas of flood risk show higher probability of inundation. Other areas have lower probability of flooding, but in severe and rare events (rarer than 1%AEP), other lower areas may be also at risk of inundation.

The information in this guide is current at the date of publication. While every effort has been taken to ensure the validity and accuracy of the data presented, the State Emergency Service does not take responsibility for data error or omission. Please see the standard Tasmanian Government’s Copyright and Disclaimer Statement for more details.