[GRASS-user] Question about r.watershed and flow accumulation grid

[Thomas Adams]

Micha,

No, after looking at what's going-on in more detail, I think the DEM is too
coarse (even at 90m), so the flow direction and accumulation is
mis-directed in one critical area of the watershed. I tried using r.carve,
but it is taking forever — after 15 minutes, no advancement of the progress
bar…

I did not want to have to do this for my testing, but I'll probably try at
3 or 10 meter — lots of pixels for my basin! The problem, in general, for
me is that I want to apply my techniques at international locations where I
probably won't have the benefit of higher resolution DEMs, so I need to
develop something a bit more robust…

Cheers!
Tom

On Fri, Feb 13, 2015 at 1:15 PM, Micha Silver <micha at arava.co.il> wrote:

>
> On 02/13/2015 08:48 PM, Thomas Adams wrote:
>
> Stefan,
>
>  A fair question; since I know the stream topology from personal
> experience it is clear that there should be no break in the stream network
> and the flow accumulation grid should reflect that. I am seeing the flow
> accumulation values break at a point where they should continue to
> accumulate downstream.
>
>
> Are these breaks possibly caused by null pixels in the DEM?
>
>  Tom
>
> On Fri, Feb 13, 2015 at 11:43 AM, Stefan Lüdtke <sluedtke at gfz-potsdam.de>
> wrote:
>
>> -----BEGIN PGP SIGNED MESSAGE-----
>> Hash: SHA1
>>
>> Hi Tom,
>>
>> just out of curiosity, what do you mean by "break in the flow
>> accumulation"?
>>
>> Cheers,
>>
>> Stefan
>>
>> On 02/13/2015 07:12 PM, Thomas Adams wrote:
>> > Hello all!
>> >
>> > I'm making use of the flow accumulation grid in GRASS 6.4.5
>> > generated from r.watershed using the SFD (D8) flow algorithm. The
>> > DEM has a 250m spatial resolution. What I'm getting is a break in
>> > the flow accumulation in a few locations which is causing me
>> > serious problems with subsequent processing (with help from some
>> > here, I have put together some scripting to generate a pixel
>> > connectivity file for a distributed hydrologic model).
>> >
>> > Besides going to a higher resolution DEM, are there any thoughts as
>> > to how I can eliminate these flow accumulation breaks?
>> >
>> > Thank you, Tom
>> >
>> > --
>> >
>> >
>> >
>>  > _______________________________________________ grass-user mailing
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>> >
>>
>> - --
>> Stefan Lüdtke
>>
>> Section 5.4-  Hydrology
>> Tel.: +49 331 288 2821
>> Fax: +49 331 288 1570
>> Email: sluedtke at gfz-potsdam.de
>>
>> Helmholtz-Zentrum Potsdam
>> Deutsches GeoForschungsZentrum GFZ
>> (GFZ German Research Centre for Geoscience)
>> Stiftung des öff. Rechts Land Brandenburg
>> Telegrafenberg, 14473 Potsdam
>> - -------------------
>>
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>
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