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 <[email protected] <mailto:[email protected]>>
于2021年3月30日周二 上午8:06写道：
Got it, thanks everyone~
Ming
Micha Silver <[email protected] <mailto:[email protected]>>
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
>
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--
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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