[Tagging] Wadi vs intermittent stream?

[Richard Z.]

On Sat, Aug 23, 2014 at 02:52:41PM -0700, Tod Fitch wrote:

> So which is the preferred tagging?
> 
> If waterway=wadi then I have some OSM editing to do but at least the renderer should be easy. If waterway=stream, intermittent=yes then I need to get some changes done by the project who's rendering database I am using.
> 

Wadi is something different than a wash. While not easy to state
objectively, some hints are

* wash tends to be shorter and steeper, they often run out in 
  alluvial fans as soon as they get into flat areas. Some collect
  into intermittent rivers though.
* the wash-valley form  will be merely a deepening from erosion
  and often quite young and quickly changing ( in the order of 
  decades or hundreds of years )
* when a wash is dry there is no water flow close underneath the
  surface

* wadi will be longer, perhaps 10km or much more
* the valley is older, has gone through several geological stages 
  of riverbed formation
* even in dry seasons there will be often underground water,
  places with swamps or pools and distinct vegetation.

Richard