|usage = spillway|
|Specific waterway usage allowing the controlled release of water from a waterbody (reservoir, canal, river)|
|Used on these elements|
|Tools for this tag|
A structure which allows the release of water 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 remains dangerous since it can be expected at any time.
Spillways may be in regular use or designed only to be used in emergencies.
How to Map
- Smaller spillways, or those parts which are within the dam structure, can be drawn as a way and tagged with waterway=canal + usage=spillway.
- Larger ones can be drawn as an area and tagged with waterway=riverbank + usage=spillway.
The spillway should connect to the water body which it drains and to the downstream outlet.
The material=* of the spillway should be added. The recent near collapse of the Oroville Dam was in part precipitated because the emergency spillway was largely earth.
Wikipedia mentions different types of spillways, use spillway:type=* to describe these.
- man_made=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 stations.