<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">
  
    
    
  
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    <br>
    <div>On 02/13/2015 08:48 PM, Thomas Adams
      wrote:<br>
    </div>
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      <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>
              Tel.: <a href="tel:%2B49%20331%20288%202821" value="+493312882821" target="_blank">+49 331 288 2821</a><br>
              Fax: <a href="tel:%2B49%20331%20288%201570" value="+493312881570" target="_blank">+49 331 288 1570</a><br>
              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>
              Telegrafenberg, 14473 Potsdam<br>
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              PGP Public Key: <a href="http://bit.ly/13d9Sca" target="_blank">http://bit.ly/13d9Sca</a><br>
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