The Australian Government introduced a standard definition of flood for certain insurance policies. For this purpose, a flood is defined as:
The covering of normally dry land by water that has escaped or been released from the normal confines of: any lake, or any river, creek or other natural watercourse, whether or not altered or modified; or any reservoir, canal, or dam.
Floods can bring welcome relief for people and ecosystems suffering from prolonged drought, but also are estimated to be the most costly natural disaster in Australia.
Why do floods occur?
Flooding occurs most commonly from heavy rainfall when natural watercourses do not have the capacity to carry excess water. However, floods are not always caused by heavy rainfall. In coastal areas, water inundation can be caused by a storm surge as a result of a tropical cyclone, a tsunami or a high tide coinciding with higher than normal river levels. If a dam fails, triggered for example by an earthquake, the downstream area will flood, even in dry weather conditions.
Other factors which can contribute to flooding include:
- volume, spatial distribution, intensity and duration of rainfall over a catchment
- the capacity of the watercourse or stream network to carry runoff
- catchment and weather conditions before rainfall
- ground cover
- tidal influences.
The average annual cost of floods is $32 Bilion (measured in American dollars). Since the year 2000 floods have cost the U.S economy an estimated $850 bilion.
How does a flood event occur?
Global flood events are on the rise
Would you know what to do when disaster strikes?