Types of floods

The most common type of flood in Australia happens when a river overflows its natural banks. There are two main types of such floods, slow-onset floods and rapid-onset floods. Slow-onset floods usually occur on inland rivers such as those found in central and western New South Wales, central and western Queensland and parts of Western Australia. As their name suggests, these floods take at least a week to develop and can persist for months. As heavy rain falls, the river is unable to accommodate the extra water. This causes the river to overflow its banks. Slow-onset floods can result in damage to crops, livestock, rail lines, roads and property.

Rapid-onset floods occur more quickly, but they can be more catastrophic since there is less warning than with slow-onset floods. Rapid-onset floods occur on rivers found in coastal areas and the mountain headwaters of major rivers. Since these rivers drain more quickly than slow-moving inland rivers, flooding happens more quickly, over the course of a couple of days.

Flash floods occur when extremely heavy precipitation due to intense storms is more than local drainage systems, either natural or man-made, can accommodate. These floods occur with little or no warning, and as a result, often cause loss of life. Flash floods are an increasing problem in cities, which have inefficient drainage. 

Example of a Flash Flood