[Tagging] waterway=wadi problem

[Christoph Hormann]

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/