[GRASS-user] understanding r.watershed

[M S]

In short, r.watershed, without depression input,  will route water in and
*up* and out of depressions in the terrain to illustrate the complete
downward path.  This is why no DEM filling is necessary.  By entering in
known (substantial and impactful) depressions, the water does not route out
of it.

The known depressions are especially useful when delineating sink-watersheds
or internally drained, but can play a role in depressions where water doesnt
flow out of the depression.

Mark

On Thu, Jan 29, 2009 at 10:12 AM, Georg Kaspar <georg at geofs.de> wrote:

> Hi,
> when providing a binary depression layer for r.watershed, areas around
> those depressions will be left out in the resulting basin map. Are
> those areas the watersheds of the given depressions?
> According to Markus Neteler's book "Open Source GIS", r.watershed
> "does not require filling of depressions in DEM prior to it's
> application [...]". What will be the difference if I use a
> depressionless DEM (with/without binary depression layer)?
> Thank's for your help. I'm new to this field so please excuse any
> missing base knowledge!
> Best regards,
> Georg Kaspar
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