Flood

Flooding can happen anywhere, at any time, and can be caused by more than just rain. Even if you don't live near a river or creek, different types of flooding may still happen in your area from other causes.

On this page:
  • Riverine flooding

In riverine flooding, relatively high water levels overtop the natural or artificial banks of a stream or river. The nature of riverine flooding can vary significantly in terms of cause, timing and depth between different locations. Coastal rivers with short, steep headwaters often have floods that rise and recede quickly. Inland floods with low gradients have floods that move slowly down the river, sometimes lasting for several months.

  • Flash flooding

Flash flooding occurs when soil absorption, runoff or drainage cannot adequately disperse intense rainfall, and is usually caused by slow-moving thunderstorms. Flash floods are generally defined as developing in six hours or less from rainfall to the onset of flooding.

  • Dam failure

Although dam failures are rare, their effects can be significant. In Victoria dam safety is monitored, and warning arrangements are in place to warn downstream residents of potential dam failure threats. Should dam failure occur, significant downstream flooding can involve potentially swift flowing water and high amounts of debris.

  • Storm surge

Storm surge occurs when sea levels are elevated above the usual tidal limit due to the action of intense low pressure systems over the open ocean. The low pressure causes sea level to rise as there is less air pressing down on the sea. Combined with gale force onshore winds, this can lead to flooding of low-lying coastal land.

Bureau of Meteorology warnings

 

  • Warnings are issued by the Bureau of Meteorology (BoM) to tell people about possible flooding.

  • Flood Watch means there is a developing weather pattern that might cause floods in one or two days.

  • Flood Warning means flooding is about to happen or is already happening. There are minor, moderate and major flood warnings. 

 

minor flood
A Minor Flood Warning means floodwater can:

 

  • Reach the top of the river banks.

  • Come up through drains in nearby streets.

  • Cover low-lying areas including riverside camping areas.

  • Affect some low-lying caravan parks.

  • Cover minor roads, tracks and low level bridges.

  • Spread across land or go into buildings on some properties and farms.

 

moderate flood warning
A Moderate Flood Warning means floodwater can:

 

  • Spill over river banks and spread across low-lying areas.

  • Start to threaten buildings, roads, rail, power and other developments.

  • Require evacuation in some areas.

  • Cover main roads.

 

Major flood
A Major Flood Warning means floodwater can:

 

  • Cause widespread flooding.

  • Threaten more houses and businesses.

  • Cause properties and whole areas to be isolated by water.

  • Disrupt major roads and transport routes.

  • Require many evacuations.

 

 

Severe Thunderstorm Warnings 

Thunderstorms are classified as severe when there is potential to cause significant localised damage through wind gusts, large hail, tornadoes or flash flooding. Severe Thunderstorm Warnings are issued to the community by BoM.

 

Severe Weather Warnings 

These warnings are issued to the community by BoM when severe weather is expected that is not directly related to severe thunderstorms or bushfires. Examples of severe weather include damaging winds and flash flooding.

Flash flooding happens quickly. Residents should listen out for warnings with flash flooding and remember that flash flooding:

  • Occurs so fast that it is difficult to provide a detailed warning. Often it arrives without warning.

  • Results from heavy rainfall during short severe storms.