Floods in Australia
Flooding is among Australia's most deadly natural disasters – but it's also important for agriculture and the life cycle of many plants and animals.
A flood is when a normally dry area is covered in water. There are many ways this can happen and many types of flooding – but all are dangerous.
If you live or travel through a flood prone area, it's important to understand when to prepare and how severe the flood is likely to be.
In this section, explore:
- the natural process of flooding, types of floods, what causes floods in Australia and how we predict them
- flood classifications and river height information used in Australian flood warnings
- why we warn Australians about floods and our flood warning services
- what you can do to prepare for floods.
Some floods near the coast are due to storm tides and storm surge. Learn more about types of tides, including storm surge, on our Tides and sea level page.
For assistance during a flood, contact your state or territory's emergency services – view our Emergency contacts page.
Video: Understanding floods
Put simply, a flood is when a normally dry area is covered in water. There are many ways this can occur and many types of flooding.
Riverine flooding is perhaps the most common in Australia. Rivers are formed over thousands of years, they carry excess water from the land to the lowest point possible, often the sea.
The two main contributors to riverine flooding are heavy rainfall and the land's capacity to absorb water. The land is a lot like your kitchen sponge, there is a limit to how much water it can soak up.
Once the land is saturated, water flows across the land and into our river systems. However, river systems have a maximum capacity to carry water, if this capacity is exceeded, the water will eventually rise higher than its banks, and flow out into the low-lying areas adjacent to streams and rivers.
How quickly a river responds to rainfall and how long that flooding lasts can vary significantly. In flat inland regions, floods may spread thousands of kilometres, and last for weeks to even months. In the mountain and coastal regions, flooding is often less extensive and of shorter duration, but with higher flow velocities.
Likewise, flash flooding happens very quickly, and for that reason is the most dangerous type of flooding. They can occur in any part of Australia but can be a particularly serious problem in urban areas, where the drainage system may not cope.
Flash floods are of short duration, within six hours of intense bursts of rain. The rain falls so quickly that it can't soak into the ground, or drain away through normal channels. It can cause roads to become rivers, and turn normally safe areas to raging torrents within minutes.
In some coastal communities, storm surge can be a dangerous cause of flooding. It can occur when an intense low-pressure system, or a tropical cyclone, crosses the coast, raising sea levels, that can swamp low-lying areas up to a kilometre inland.
The effect of storm surge can be further intensified by exceptionally high tides, often referred to as a king tide These can be caused by the local topography, and the positions of the Earth, and the moon relative to the Sun.
A less common cause of flooding in Australia, is snowmelt, when rapidly warming conditions cause snow to melt quickly into the river system.
While we often associate flooding with damage, disaster and loss, flooding is a natural process that can bring benefits. Floods fill billabongs and wetlands, replenishing water bodies and contributing to the life cycle of many plants and animals. Floodwater also carries valuable nutrients and minerals important for agriculture.
However, flooding is the second most deadly natural disaster in Australia, and all types of flooding can be dangerous.
To find out more about floods, watch our Understanding Flood Classifications video, and visit the Bureau website.
Improving Australia's flood warning network
We're delivering a 10-year program to acquire and upgrade flood warning infrastructure. The National Flood Warning Infrastructure Network (FWIN) Program focusses on critical catchments in each state and territory. Learn about Flood warning network upgrades.
Know your weather. Know your risk.
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