Tag:usage=spillway
 usage = spillway
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Specific waterway usage allowing the controlled release of water from a waterbody (reservoir, canal, river) 
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| Group: man made |
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Status: approved
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An artificial structure channelling water released from a water body, either under controlled circumstances or as a means of ensuring that water levels do not overtop and destroy containing structures (dams, levees). Spillways will normally be free of water but remain dangerous since water can be expected at any time.
Spillways may be in regular use or designed only to be used in emergencies.
How to map
See waterway=river for common guidelines on how to map waterways.
All spillways can be drawn as ways 
and tagged with waterway=canal + usage=spillway.
Larger spillways can be completed with an area 
and tagged with natural=water + water=canal + usage=spillway.
As any waterway, spillways should connect to the water body which it drains and to the downstream outlet.
The material=* of the spillway should be added.
Wikipedia mentions different types of spillways, use spillway:type=* to describe these.
Related tags
- waterway=dam - Spillways will most usually be mapped in association with dams
- natural=water + water=reservoir - Water area impounded behind.
- power=generator + generator:source=hydro - A spillway is often associated with hydropower power plants.
- emergency=siren + siren:purpose=flood – a siren that warns a downstream area of an impending discharge
- hazard=*