Common Misconceptions about Flooding

It won’t flood during a drought 

Record flooding can happen at any time.  Australia has one of the most variable rainfalls in the world and experiences both severe floods and droughts.  Significant flooding can occur in the middle of a drought without the drought breaking.  For example during the record drought from 1998 to the present day, record rainfall and flooding has occurred in the Melbourne suburb of Fairfield (December 2003), the Qld Gold Coast (June 2005), Greater Melbourne (Feb 2005), SA Flinders Ranges (January 2007), NSW Central Coast (June 2007), Vic Gippsland (June 2007), Qld Sunshine Coast (August 2007).  Further record flooding is possible anywhere in Australia during a drought.

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This property has never flooded

Floods bigger than those we have experienced are inevitable.  We have less than 200 years of flood records in Australia.  While there may be no memory or record of your property flooding it does not mean that the land has not flooded in past centuries nor that it won’t flood in coming years.  Extensive rainfall records for south east Australia, catchment topographic data and sophisticated computer models can now be used to accurately predict the possible extent of flooding for the full range of possible floods.

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I am on a hill so I can’t flood

Hills are not always free of floods. This can happen in two ways.

  • Creeks and Rivers can rise several metres when they flood and land that we think could be high and dry ends up well under water.
  • When water is running down the hill to the creek or river it will find the easiest path to follow. When pipes or kerb and guttering cannot handle all the water in a severe storm, the water will find its own path, even when properties are located on hills.
  • In addition to the above, even if your property is not flooded, you may be isolated by floodwaters and you may not be able to leave or enter your property safely until floodwaters have subsided.

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I am not near a creek or a river

Water finds its way in unexpected places. This can happen in two ways.

  • When creeks and rivers burst their banks the water can spread several hundred metres (even kilometres).
  • When water is running down the hill to the creek or river it will find the easiest path to follow.  When pipes or kerb and guttering cannot handle all the water in a severe storm the water will find its own path, even when properties are located on hills.

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I am above the flood level

Floods can go higher than we plan for.  In Victoria, the minimum floor level for buildings that are at risk of flooding are arbitrarily set at least 300 millimetres above the 100-year flood level. In some areas, higher freeboards are applied depending on uncertainties and the nature of the floodplain. Floods can go higher than the 100-year flood level.  In Australia, the flood planning level is usually defined by the 100-year flood.  This is not a flood which happens once every 100 hundred years but one which has a 1 in 100 or 1% chance of occurring in each and every year. In a 70 year lifetime there is a 50/50 chance of a 1 in 100 flood being exceeded at any location.

To find out more about setting floor levels in known floodplain areas consult your floodplain management authority (CMA or MW).

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I won’t be here in 100 years

Extreme floods can happen at any time.  In Australia new buildings are usually built above the 100-year flood level.  This is not a flood which happens once every 100 hundred years but one which has a 1 in 100 or 1% chance of occurring in each and every year.  In a 70 year lifetime there is a 50/50 chance of a 1 in 100 flood being exceeded at any location.  Two such floods can occur one after the other as happened in Kempsey NSW in 1949 and 1950.  In 2007 alone rainfall exceeding the 1 in 100 event occurred in Flinders Ranges SA, Campbelltown NSW, Newcastle NSW, Macalister River Vic, Sunshine Coast QLD.

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We are protected by levees 

Levees provide limited protection.  It is not practical to build levees high enough to keep out all floods.  Every levee has a chance of being overtopped by floodwaters.  When a levee overtops the water rises very quickly in the areas which the levee was protecting. Many have been built by individuals privately and may not be properly maintained. Failures of levees occur regularly and can worsen flooding in areas directly behind the failed levee than would occur naturally.

Page Last Updated: Friday 16 July, 2010