[Tagging] Spillways

Mark Wagner mark+osm at carnildo.com
Wed Mar 22 05:25:23 UTC 2017

On Wed, 22 Mar 2017 10:44:17 +0900
John Willis <johnw at mac.com> wrote:

> How do you tag an emergency spillway? 
> I am tagging a giant flood control reservoir in my region. The “lake”
> is surrounded by giant man-made embankments on all sides, surrounded
> by an additional  set of embankments, with gates to let the water
> out. There is no dam per se, because there is ~200 km of this
> man-made 10-20m tall earthen embankment (levee) around the entire
> river system - it is part of that. 
> When this levee system fails uncontrollably (like it did downstream
> from me in 2015), it is really bad.
> https://www.youtube.com/watch?v=Hfs3OeqiqRk
> <https://www.youtube.com/watch?v=Hfs3OeqiqRk> 
> This reservoir system catches water during a typhoon from a smaller
> river, then releases it slowly after the peak flooding into the
> larger river. this reduces the chance of flooding further
> downstream.  
> However, it has 2 sets of emergency spillways (each about 1Km long)
> to let water out of both sets of embankments, so where it “fails" can
> be controlled. it is 5 m lower than rest of the embankments
> surrounding the reservoirs. These were recently added. 
> I made a polygon on one such spillway.
> https://www.openstreetmap.org/way/481898093#map=14/36.2115/139.6880
> <https://www.openstreetmap.org/way/481898093#map=14/36.2115/139.6880> .
> the heart-shaped lake is the reservoir, and most of the surrounding
> green areas are part of the flood control basin made by the second
> set of levees. 
> These *emergency* spillways are considered safety features of most
> large water control projects - if the human-controlled gates o the
> normal spillway jam shut, the emergency spillways will keep the
> dam/embankments from being over-topped in unexpected places. I know
> these are a major mappable feature of large dams, but they are not
> mentioned on the Dam wiki page. Maybe I am looking at it wrong. 
> As these are not a weir, nor a normal path for water to go, I
> wouldn’t tag them as a weir nor as a object normally associated with
> a waterway line running through it. 
> is there an existing tag or another name for these features that I
> don’t know of? How do I tag these emergency spillways (and heck -
> these huge levee embankments!) correctly? 

For what it's worth, Oroville Dam
(https://www.openstreetmap.org/#map=17/39.54412/-121.49263) currently
has its emergency spillway tagged as a weir.


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