Tag:usage=spillway
 usage = spillway
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| Description |
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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 |
| Used on these elements |
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| Requires |
| Useful combination |
Status: approved
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| Tools for this tag |
An artificial structure channeling water released from a water body, either under controlled circumstances or as a means of ensuring that water levels do not overflow 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=canal for common guidelines on how to map canals.
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 damsnatural=water+water=reservoir- Water area impounded behind.power=plant+plant: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 dischargehazard=*
Examples
| Photo | Location | Tagging | Note |
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Canada |
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Robert Bourassa spillway with Floodgate at the top - Capacity of 16,280 cubic meter / second |
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Wales |
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Llyn Brianne spillway |
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Ethiopia |
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Gerd Dam spillway |
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USA |
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Crystal Dam ogee style spillway |
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Canada |
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Caniapiscau Duplanter spillway |
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USA |
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Hope Mills Dam spillway |
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Iraq |
Think about adding |
Dukan Dam spillway |
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UK |
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The spillway is on the left, an usual concrete canal to drain overflow water. The Archimedes' screw isn't part of the overflow management and shouln't be considered as part of the spillway. See man_made=archimedes_screw
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