[GRASS-user] r.watershed identify inland watershed

[ming han]

Hi Micha

    I understand what you mean. But it requires another step to
manually identify depressions from these pre-conditioned DEM.

Cheers
Ming


Micha Silver <tsvibar at gmail.com> 于2021年4月3日周六 下午12:43写道：

>
> On 4/2/21 5:37 PM, ming han wrote:
> > Maybe I am the only one who has this demand. Following is just a
> > recommendation to GRASS r.watershed function.
> > Maybe it is worth having an option to avoid r.watershed overcome
> > depressions.
> > The reasons are 1) there are many hydrologically pre condition DEM
> > data available globally, such as:HydroSHEDS, MERIT
> >                             2) the depression in these DEM are real
> > depressions, overcome these depressions will make the entire drainage
> > system
>
>
> Regarding Hydrosheds, the documentation[1] in section 3.4 explains how
> they overcame the problem of sinks. They performed a regular "fill
> sinks" operation on areas that were SRTM artifacts. True natural
> depressions were identified manually, then another manual procedure of
> carving rivers was done to force flow thru these depressions and produce
> hydrologically correct streams and basins. So pre-conditioning to
> overcome depressions is not a magic bullet...
>
>
> In my opinion, the best results are obtained when true depressions
> (pits, salt playas or karst regions) are identified, and set to NULL in
> the elevation raster. That will allow r.watershed to stop routing at
> those locations, and produce correct stream and basin layers.
>
>
> [1]https://hydrosheds.org/images/inpages/HydroSHEDS_TechDoc_v1_2.pdf
>
>
> > incorrectly.
> >
> > I understand GRASS has other functions to solve this problem, but just
> > a user recommendation. I use GRASS a lot.
> >
> > Thanks
> > Ming
> >
> > ming han <dustming at gmail.com <mailto:dustming at gmail.com>>
> > 于2021年3月30日周二 上午8:06写道：
> >
> >     Got it, thanks everyone~
> >     Ming
> >
> >     Micha Silver <tsvibar at gmail.com <mailto:tsvibar at gmail.com>>
> >     于2021年3月29日周一 下午2:40写道：
> >
> >         Hello:
> >
> >         You might try `r.param.scale`, or even better `r.geomorphons`
> >         modules to
> >         identify geomorphology features, then filter out all pixels
> >         identified
> >         as pits.
> >
> >
> >         r.watershed is purposely designed to overcome depressions, and
> >         find flow
> >         routing thru these spots. So I don't think you can use that
> >         module to
> >         identify depressions.
> >
> >
> >         On 3/27/21 8:49 PM, ming han wrote:
> >         > Hi  Everyone
> >         >
> >         >      When I do watershed delineation using r.watershed for
> >         great salt
> >         > lake watershed. I found r.watershed always tried to assign
> >         an outlet
> >         > for a great salt lake, which does actually not exist because
> >         it is an
> >         > inland lake and the great salt lake has no watershed outlet
> >         at all.
> >         >
> >         >       I noticed that there is a depression option. But is
> >         there any
> >         > way that  r.watershed can automatically identify depressions
> >         while
> >         > defining flow accumulation and stream network?
> >         >
> >         > Thanks
> >         > Ming
> >         >
> >         > _______________________________________________
> >         > grass-user mailing list
> >         > grass-user at lists.osgeo.org <mailto:grass-user at lists.osgeo.org>
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> >         <https://lists.osgeo.org/mailman/listinfo/grass-user>
> >
> >         --
> >         Micha Silver
> >         Ben Gurion Univ.
> >         Sde Boker, Remote Sensing Lab
> >         cell: +972-523-665918
> >
> --
> Micha Silver
> Ben Gurion Univ.
> Sde Boker, Remote Sensing Lab
> cell: +972-523-665918
>
>
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