Flood classifications
Emergency services and flood management authorities classify flooding as minor, moderate or major at key river height gauging stations.
Classification levels at each station are decided by local community and state or territory emergency services. The classification is defined by impacts of the water level.
Minor flooding
If the water level reaches the minor flood level, it causes inconvenience. Low-lying areas next to water courses are inundated. Minor roads may be closed and low-level bridges submerged.
In urban areas flooding may affect some backyards and buildings below floor level, and bicycle and pedestrian paths. In rural areas, livestock and equipment may need to be removed.
Moderate flooding
If the water level reaches the moderate flood level, a bigger area is under water.
Main traffic routes may be affected. Some buildings may be affected above floor level. Evacuation may be required. In rural areas, removal of livestock is necessary.
Major flooding
If the water level reaches the major flood level, large areas are under water.
Many buildings may be affected above floor level. Properties and towns are likely to be isolated and major rail and traffic routes closed.
Evacuation may be required. Utility services such as power may be affected.
Video: Understanding flood classifications
Riverine floods typically occur 6 or more hours after heavy rainfall. In Australia, we have 3 riverine flood classifications: minor, moderate and major.
Minor flooding refers to inundation of low-lying areas next to watercourses. Minor roads may be closed and low-level bridges submerged. In urban areas inundation may affect some backyards and buildings below the floor level as well as bicycle and pedestrian paths.
For moderate flooding the area of inundation is more substantial. Main traffic routes may be covered and some buildings may be affected above floor level. Evacuation of flood affected areas and removal of stock may be required.
Finally, major flooding can be very dangerous and may result in extensive inundation of rural and urban areas. Properties and towns are likely to be isolated and major traffic routes and rail routes are likely to be closed. Evacuation of people from flood affected areas may be required and utility services may be impacted.
The Bureau produces warnings and advice to local communities who are experiencing, or are at risk of experiencing riverine flooding.
Flood Watches provide early advice of a developing situation that may lead to flooding. While Flood Warnings are issued when floods are likely to occur or are already occurring.
Sometimes short bursts of heavy rainfall can lead to rapid onset flooding, known as flash flooding. When this is likely to occur, the Bureau will issue a severe weather warning for heavy rain that may lead to flash flooding.
Current flood watches and warnings, as well as severe weather warnings can be found on our warnings page or the BOM weather app. You can also access rainfall and river level data for around 3,500 locations across Australia.
Sadly, fatalities are common around flood waters. Just 15 cm of water is enough to make your car float. So remember, the best way for you to stay safe is to stay out of flood water and follow advice from local emergency services.
River heights
You'll see these terms used to describe river heights in our Flood Warnings. River heights are measured in metres.
Observed river height
This is the depth of water at a river height measuring gauge.
In most cases, observed river height is measured relative to a local reference point. For example, a typical river height might be 'the South Esk River at Llewellyn in Tasmania, is at 1.60 metres'.
In many tidal areas and a few inland areas, river levels are expressed in metres above sea level or Australian Height Datum (AHD).
Peak river height
This is the highest river height observed during a flood event at the specified site. Our river conditions information includes observed river heights.
This chart shows the level of Sevens Creek at Euroa during a flood in October 2022. The highest water level (peak river height) was observed to be 5.61 m at 2:30 am on Friday 14 October 2022.
Predicted river height
This is the height to which the river is predicted to rise at the gauge referred to in the Flood Warning.
The actual depth of floodwater will vary across the floodplain. Local councils, emergency services and landowners use the predicted river height to determine which areas are likely to flood. They use their knowledge of past flood events and estimates from flood studies to assess this.
The accuracy of river height predictions depends on various factors, including the type of flood forecasting model and its input data. Predicted river heights are provided in updated warnings as more information becomes available.