Learn more about floods

Rivers in Flood

Flooding occurs when rivers overflow their banks, Flooding on the Lachlan Riverinundating surrounding low lying land.

Using rainfall and flood gauges, the Bureau of Meteorology can often predict the expected arrival time and the depth of floodwater and flood warnings can often provide advance notice to areas and communities.

In places where the land is relatively steep and close to the source of a river, such as coastal NSW, flooding can arrive relatively quickly. Water also flows faster in steeper catchments. The depth of floodwater in these locations can be great and in some coastal rivers, water can rise 10-20 metres above their normal level.

In places where the land is relatively flat and you are further away from the source of the river, such as inland NSW floods may take many days, weeks, or even months to arrive. Large areas can often be flooded and people and animals can be isolated for many weeks.

Flooding can place lives at risk. It is important to be prepared for flooding. The NSW SES has developed FloodSafe Guides to assist people to prepare for flooding.

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Flash Floods

flash flooding in MarrickvilleFlash flooding is a rapid rise in water over a short period of time. It does not usually last more than a few hours. Flash flooding can follow heavy rainfall, so it is important to know the natural indicators for possible flash flooding.

Low-lying areas (under bridges or around culverts, drains, creeks and causeways) can be more susceptible to flash flooding. These are often dangerous places to be if it floods.

Water associated with flash flooding can also move quickly over land in either natural depressions or along roadways and parkland.

Floodwater can place lives at risk. It can be several metres deep, rise quickly and move fast.

When flash flooding is likely, leaving low-lying homes and businesses (evacuation) well before flash flooding begins is the best action to take, but only if it is safe to do so. If you are trapped by rising floodwater, seek refuge in the highest part of a sturdy building. Stay there and call '000' (triple zero) if you need rescue.

Flash floods can place lives at risk. It is important to be prepared for flooding. The NSW SES has developed a Flash FloodSafe Guide to assist people to prepare.

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Dam Failure

Although dam failures are rare, their effects can be significant. In New South Wales dam safety is monitored and some dams have early warning systems for communities that lie downstream of the dam and close to the dam.

Should dam failure occur, significant downstream flooding with potentially swift flowing water and high amounts of debris can occur.

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Storm Surge

Sea levels can be elevated above the highest high tide of the year due to the action of tropical and mid-latitude cyclones.

Under tropical and mid-latitude cyclones locally low pressure can cause sea levels to rise as there is less air pressing down on the sea. This is a particular problem with tropical cyclones where atmospheric pressures can be very low.

Persistent very strong onshore winds can result in localised sea-level rises and potentially flooding low lying coastal areas.

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Tsunami such as the Indian Ocean Tsunami of 2004 can flood significant areas of low lying coastal areas with sea water. Flooding affects not only coastal areas but may extend along estuaries and coastal lakes and rivers some distance from the ocean. Flooding caused by tsunami may carry very large amounts of debris.

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