[GRASS-user] r.watershed : "minimum size of exterior watershed basin"

[Markus Metz]

On Thu, Oct 25, 2012 at 1:11 PM, laurent celati
<lcelati at latitude-geosystems.com> wrote:
> Hello,
>
> Thanks for your reply. Yesterday i tested Grass via SextanteFORQgis. There
> was a bog during the process and i had a error message.
>
> This morning i have tested Grass via Qgis and it's works well. I have 2
> questions :
>
>
> 1/With Grass r.watershed i have to enter this following parameter : "minimum
> size of exterior watershed basin" (without unit value). What criteria
> determines the value to be enter? How to know this value ?

The unit is number of grid cells. A reasonable value depends on your
question and the required detail. It helps often to first calculate
flow accumulation, then visually inspect the result to figure out a
reasonable value, or look where ground control points are located.

>
> In my case, i 'm using SRTM 90m as DEM raster input.
>
>
> 2/According to you, what is the better tool  between r.watershed or Taudem
> "StreamReach and watershed" ?

I could not find "StreamReach and watershed" in the TauDEM
documentation on command line functions[0]. I did find something in
the online documentation. It seems to me that the equivalent of
Taudem's "StreamReach and watershed" is r.stream.extract followed by
r.stream.order. I would expect the results to be nearly identical if
the input data are the same. Note that TauDEM's "StreamReach and
watershed" can not use the output of r.watershed as input, but
r.stream.extract can use pretty much any input, also data generated
with TauDEM.

Markus M

[0] http://hydrology.usu.edu/taudem/taudem5.0/TauDEM5CommandLineGuide.pdf
>
> Thank you in advance.
>
>
>
> --
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