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Floods
Floods occur when water covers land that is normally dry.
They may result from prolonged or very heavy rainfall or severe thunderstorms. Less common causes include snowmelt, dam failure, storm surge and tsunami (seismic sea waves) which both involve rapid seawater flooding.
Who is threatened by floods?
People who live near rivers or in low-lying areas live with the greatest threat of floods. Periods of heavy rain, not necessarily in their area, can lead to rises in the water level of streams and rivers to a point where channels can no longer hold the volume of water. Alternatively, for some coastal dwellers, there is the threat from the sea.
Common types of flooding in Australia
Slow-Onset Floods
Flooding of rivers in the vast flat areas of central and western New South Wales and Queensland, as well as parts of Western Australia, may last for weeks, or even months on some occasions. Floods in these areas can lead to major losses of livestock and damage to crops, as well as extensive damage to rural towns and road and rail links.
Rapid-Onset Floods
Flooding can occur more quickly in the mountain headwater areas of large rivers, as well as in the rivers draining to the coast. In these areas, the rivers are steeper and flow more quickly, with flooding sometimes only lasting for one or two days. These floods can be potentially much more damaging and can pose a greater risk to loss of life and property. This is because there is generally much less time to take preventative action, and a faster, more dangerous flow of water. This type of flooding can affect most of our major towns and cities.
Flash Floods
Flash flooding results from relatively short, intense bursts of rainfall, often from thunderstorms. It can occur almost in all parts of Australia and poses the greatest threat of loss of life. People are often swept away after entering floodwaters on foot or in vehicles.
These floods can also result in significant property damage and major social disruption. They are a serious problem in urban areas where drainage systems are often unable to cope.
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