[GRASS-user] Stream extraction from pseudo-elevation map using r.watershed

[Johannes Radinger]

Hi,

I tried something that was working at least several months ago, but somehow
r.watershed has changed. What I am trying to do is to extract a stream
network from a pseudo elevation map. This pseudo elevation map is created
by getting the distance of each stream cell from to outlet in upstream
direction (using r.cost). In addition, the streams are buffered (3 cells
wide) with cells of a value that is much greater than the actual stream
value. This map has several features: 1) The cell values for the stream are
certainly decreasing in downstream direction (=elevation is decreasing) 2)
The stream is carved into a valley (important at river junctions where two
streams meet). So this should actually meet the requirements for
r.watershed (at least it was working some time ago) to extract the stream
and get the drainage directions (e.g. for other tools like r.stream.order
etc.).

Now, when I try to run r.watershed (GRASS7.1) I get following warning
several times:
WARNING: MFD: cumulative proportion of flow distribution not 1.0 but
         -0.000000

Although I get a drainage map as output, no output is created for the
extracted stream network. I am wondering what changed and why and if this
is a bug in r.watershed or if I need to change settings differently.

Attached you can find the pseudo elevation map as geotiff to try it
yourself!

The command I am using is:
r.watershed -m --o  elevation="pseudo_elevation" drainage="drainage_test"
stream="stream_test" threshold=3

My system:
GRASS version: 7.1.svn

GRASS SVN revision: 65534

Build date: 2015-07-02

Build platform: i686-pc-linux-gnu

GDAL: 1.10.0

PROJ.4: 4.8.0

GEOS: 3.4.2

SQLite: 3.7.9

Python: 2.7.3

wxPython: 2.9.4.1

Any ideas or suggestions?

Best regards,
Johannes
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