Re: [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  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 mailto:dustm...@gmail.com>>
> > 于2021年3月30日周二 上午8:06写道：
> >
> > Got it, thanks everyone~
> > Ming
> >
> > Micha Silver mailto:tsvi...@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@lists.osgeo.org 
> > > 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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Re: [GRASS-user] r.watershed identify inland watershed

[Micha Silver]

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 mailto:dustm...@gmail.com>> 
于2021年3月30日周二 上午8:06写道：


Got it, thanks everyone~
Ming

Micha Silver mailto:tsvi...@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@lists.osgeo.org 
> 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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Re: [GRASS-user] r.watershed identify inland watershed

[Veronica Andreo]

Dear Ming,

To avoid that your suggestion gets lost in emails, please fill in a
*feature request* issue with all details here:
https://github.com/OSGeo/grass/issues/new/choose

Best,
Vero


El vie, 2 abr 2021 a las 16:37, ming han () escribió:

> 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 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  于2021年3月30日周二 上午8:06写道：
>
>> Got it, thanks everyone~
>> Ming
>>
>> Micha Silver  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@lists.osgeo.org
>>> > https://lists.osgeo.org/mailman/listinfo/grass-user
>>>
>>> --
>>> Micha Silver
>>> Ben Gurion Univ.
>>> Sde Boker, Remote Sensing Lab
>>> cell: +972-523-665918
>>>
>>> ___
> grass-user mailing list
> grass-user@lists.osgeo.org
> https://lists.osgeo.org/mailman/listinfo/grass-user
>
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