<div dir="ltr">Micha,<div><br></div><div>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…</div><div><br></div><div>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…</div><div><br></div><div>Cheers!</div><div>Tom</div><div class="gmail_extra"><br><div class="gmail_quote">On Fri, Feb 13, 2015 at 1:15 PM, Micha Silver <span dir="ltr"><<a href="mailto:micha@arava.co.il" target="_blank">micha@arava.co.il</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div style="direction:ltr" bgcolor="#FFFFFF" text="#000000"><span class="">
<br>
<div>On 02/13/2015 08:48 PM, Thomas Adams
wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">Stefan,
<div><br>
</div>
<div>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.</div>
<div><br>
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<br></span>
Are these breaks possibly caused by null pixels in the DEM? <br>
<br>
<blockquote type="cite"><div><div class="h5">
<div dir="ltr">
<div>Tom</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Fri, Feb 13, 2015 at 11:43 AM,
Stefan Lüdtke <span dir="ltr"><<a href="mailto:sluedtke@gfz-potsdam.de" target="_blank">sluedtke@gfz-potsdam.de</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">-----BEGIN
PGP SIGNED MESSAGE-----<br>
Hash: SHA1<br>
<br>
Hi Tom,<br>
<br>
just out of curiosity, what do you mean by "break in the
flow<br>
accumulation"?<br>
<br>
Cheers,<br>
<br>
Stefan<br>
<div>
<div><br>
On 02/13/2015 07:12 PM, Thomas Adams wrote:<br>
> Hello all!<br>
><br>
> I'm making use of the flow accumulation grid in
GRASS 6.4.5<br>
> generated from r.watershed using the SFD (D8)
flow algorithm. The<br>
> DEM has a 250m spatial resolution. What I'm
getting is a break in<br>
> the flow accumulation in a few locations which is
causing me<br>
> serious problems with subsequent processing (with
help from some<br>
> here, I have put together some scripting to
generate a pixel<br>
> connectivity file for a distributed hydrologic
model).<br>
><br>
> Besides going to a higher resolution DEM, are
there any thoughts as<br>
> to how I can eliminate these flow accumulation
breaks?<br>
><br>
> Thank you, Tom<br>
><br>
> --<br>
><br>
><br>
><br>
</div>
</div>
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<br>
- --<br>
Stefan Lüdtke<br>
<br>
Section 5.4- Hydrology<br>
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Email: <a href="mailto:sluedtke@gfz-potsdam.de" target="_blank">sluedtke@gfz-potsdam.de</a><br>
<br>
Helmholtz-Zentrum Potsdam<br>
Deutsches GeoForschungsZentrum GFZ<br>
(GFZ German Research Centre for Geoscience)<br>
Stiftung des öff. Rechts Land Brandenburg<br>
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