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Floods occur when water covers land, which is normally dry. They may result from prolonged or very heavy rainfall, severe thunderstorms, monsoonal (wet season) rains in the tropics, or tropical cyclones. People who live near rivers or in low-lying coastal areas live with the greatest threat of floods.

Right: Flooding in suburban Cairns 1999. ¹

Common Types of Flooding in Australia

Slow-Onset Floods
Flooding of rivers in the vast flat areas of Queensland may last for one or more 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 towns.

Rapid on-set Floods
Flooding can occur more quickly in the mountain headwater areas of the larger rivers as well as in the rivers draining to the coast. These floods are generally much more damaging and can pose a greater risk of loss of life and property. This is because there is generally much less time to take preventative action, and the flow of water is more dangerous.

Above: Small stream turns into a raging river within minutes in Atherton. ¹

Flash Floods
Flash flooding results from relatively short, intense bursts of rainfall, often from thunderstorms. It can occur in almost 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. This type of flood can also result in significant property damage and social disruption.

Right: City council vehicle carried away in Redlynch. ¹

Flood Warnings

Minor Flooding
Minor flooding causes inconvenience such as closure of minor local roads and low bridges.

Moderate Flooding
Low lying areas will be inundated requiring removal of stock, equipment and evacuation of isolated homes. Main traffic bridges may be covered.

Major Flooding
Higher areas will be inundated with isolation of towns and properties, causing extensive damage.

Local Flooding
Where intense rain can be expected to cause high run-off in restricted areas, but doesn't cause significant rises in main streams.

Significant River Rises
This term is used when river rises are expected but it is not certain what flood levels will be exceeded in main streams. This term will be used by the Bureau of Meteorology to alert landholders of the need to remove pumps and irrigation equipment from waterways and plan for stock removal.

Above right: Wharf Street, Cairns. ²

1. Photo courtesy of Cairns Post
2. Photo courtesy of Courier Mail