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Public-images-osm logo.svg flood_prone
Whether or not the feature is likely to flood after very heavy rain. Show/edit corresponding data item.
Group: hazards
Used on these elements
may be used on nodesmay be used on waysmay be used on areas (and multipolygon relations)should not be used on relations (except multipolygon relations)
Useful combination
See also
Status: in use

An area or way, that is prone to flooding. This is mostly applicable to roads that go under water after heavy rains. Flooded roadways are often very dangerous to cross and many people die each year as a result.

The default value is flood_prone=no and should not be used

A [W] floodplain is an area around a waterway where it could break its banks and flood the surrounding area. A [W] floodway is a crossing along a waterway or floodplain.

Other than floodways, this tag is typically used only on short stretches of major highways, such as in low-lying tunnels, low-lying passages under bridges, and low-lying roads near bodies of water that overflow easily. Depending on the situation, it is rare and generally undesirable to apply it to large sets of adjacent local urban streets.

Mapping waterway crossings

To map a simple floodway crossing that does not have a bridge-like structure. Apply a tunnel=culvert tag to the waterway, and put flood_prone=yes on the intersecting highway.

Waterway Floodway Crossing.png

Mapping flood prone bridges

For a flood prone bridge, you should ensure a bridge=* tag is on the relevant highway and add flood_prone=yes. Nothing really needs to be done to the waterway since the bridge is a structure above the waterway.

Flood Prone Bridge.png

Mapping flood prone highways

If the area is surrounded by flood plains or is otherwise at risk of flooding. You should apply a flood_prone=yes to the exact part of the way that is likely to go underwater. However, if you don't this information precisely, you can also tag flood_prone=yes on a single node.

Flood Prone Area.png

General situation


Photos were taken south of Barellan, in the Mirrool Creek floodplain.


The above photos are of the Gwydir highway east of Moree

Rendering and possible usages

Flood prone areas don't have water across them 99.9% of the time, so there isn't any perceived benefit in rendering these areas most of the time.

However, the information can help routing software to avoid potentially hazardous crossings after heavy rain.

Furthermore, some Emergency services may find it useful to have their own flood mapping that highlights these and similar tags.

Similar tag ideas

  • It might be useful to tag the markers that indicate depth of water when flooded, although similar markers can be found along river banks and tidal water areas
  • It might be useful to tag how often flooding gets or covers a certain area, eg once in 100 years.

See also