[Imports] UN Mappers import of UNSOS waterways in Somalia
osm at imagico.de
Wed Apr 8 22:33:56 UTC 2020
On Wednesday 08 April 2020, Arne Kimmig via Imports wrote:
> - how can we distinguish a 'drainage shaped landscape' from a stream?
Reliably only through local knowledge or through imagery depicting
actual waterflow. There are occasionally good indications of recent
waterflow even in dry situation images - like a recently newly built
river crossing of a road next to an old and destroyed one. Bridges or
culverts are also a clear indicator.
> Actually, what do you mean with this term? - same question for
> 'fossil river'. Is that something like a dry valley?
As mentioned throughout subtropical Africa - both in the north and in
the south - there are a lot of valleys evidently shaped by water that
have not seen any more recent surface water flow.
On images you can sometimes see that for example from visible artificial
or natural structures of significant age that would not withstand
or dunes across the riverbed:
In most cases however this is very hard to reliably see (the problem of
proving a negative - what i mentioned in my reply to Rafael) -
especially in relatively flat areas like much of Somalia where
scrubland covers much of what could be useful hints.
Famous example of a fossile river is the Molopo River in South Africa
where it is generally said that it has not carried water over its whole
length for at least a hundred years:
I could imagine that this similarly applies today to the Lagh Dera:
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