[Tagging] waterway=wadi problem

[John F. Eldredge]

I would recommend expanding the definition of "intermittent streams" to 
include not only streams that have a regular, seasonal water flow but also 
streams in desert areas that exist only when a rare storm comes along. The 
topography is the same, the tendency of water to run downhill is the same, 
only the frequency of rainfall is different.

-- 
John F. Eldredge -- john at jfeldredge.com
"Darkness cannot drive out darkness; only light can do that. Hate cannot 
drive out hate; only love can do that." -- Martin Luther King, Jr.



On January 15, 2015 3:13:38 AM Christoph Hormann <chris_hormann at gmx.de> wrote:

> On Thursday 15 January 2015, johnw wrote:
> >
> > A wadi is a place where flash floods occur. It is not an intermittent
> > river - it isn’t really seasonally wet, and doesn’t provide any real
> > expectation that water will be present (except deep underground) -
> > because they are located in places where rain itself is unexpected
> > for most of the year.
>
> Well - that would be a useful concept of a wadi but it has two problems:
>
> * current use of the tag is very different from that, you can see that
> quite well when you look at the taginfo map:
>
> https://taginfo.openstreetmap.org/tags/waterway=wadi#map
>
> the uses in Europe for example are probably almost always seasonal.
>
> * sporadic waterflow is very difficult to determine for the mapper.
> This is especially true for northern Africa where climate got a lot
> drier in the last few thousand years and as a result there are many
> permanently dry valleys that still look like being formed by waterflow
> but that have not seen significant waterflow in the last hundred years.
>
> My suggestion would probably be to stop rendering waterway=wadi in a way
> implying waterflow, encourage mappers to use intermittent/seasonal
> where this is known and reserve waterway=wadi - despite the then
> misleading key - for valleys where waterflow is unknown.
>
> --
> Christoph Hormann
> http://www.imagico.de/
>
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