What is a Flood?

A simple definition of flooding is water where it is not wanted. Another, more comprehensive definition of a flood is:

A general and temporary condition of partial or complete inundation of normally dry land areas from overflow of inland or tidal waters from the unusual and rapid accumulation or runoff of surface waters from any source.

In November 2011, the Australian Government introduced a standard definition of flood for certain insurance policies. The announcement was part of the Government's response to the recommendations in the Natural Disaster Insurance Review report.

The standard definition will apply when an insurer offers flood cover for a home building, home contents, small business or strata title insurance policy. 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 have both positive and negative impacts. They 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.

Every year in Australia, floods cause millions of dollars damage to buildings and critical infrastructure, such as roads and railways as well as to agricultural land and crops. They also disrupt business and can affect the health of communities. Between 1967 and 2005, the average direct annual cost of flooding has been estimated at A$377 million (Bureau of Infrastructure, Transport and Regional Economics analysis of the Emergency Management Australia database).

The losses due to flooding vary widely from year to year and are dependent on a number of factors such as the severity of a flood and its location. The most costly year for floods was 1974, when events resulted in a total cost of A$2.9 billion (Bureau of Transport and Regional Economics, 2001).

Talking about Floods

The use of consistent terminology is important for improving the quality and consistency of flood information. Geoscience Australia uses the following flood related terms when talking about floods and flood research.