[GRASS-user] Problem with half basins becoming fragmented using r.watershed

[Daniel Victoria]

Not sure what's going on since I've not seen this before. But have you
tried different threshold values?

On Fri, Jul 13, 2018 at 2:06 PM Erin Hanan <ejhanan at gmail.com> wrote:

> Hello,
>
> I am new to the list; please let me know if my question should be
> formatted differently.
>
> I have been running r.watershed on a large (>400 km2) basin using a 10 m
> resolution dem. I am finding that it produces some half basins that are
> either fragmented or very small (i.e., just a few pixels). This seems to
> happen mostly in areas bordering the stream, though I do sometimes get half
> basins that are also not connected to the stream. I'm attaching a zoomed in
> screen shot that illustrates some very strange sliver and fragmented basins
> that are bordering larger, more appropriately delineated half basins. In
> this case, the inappropriate basins all border the stream.
>
> I have tried running r.watershed using GRASS6.4 and GRASS7. I have also
> tried using SFD, MFD with a range of convergence values, and the -4 flag.
> These options produced different half basin delineations, but the problem
> with sliver basins and basin fragments has not gone away.
>
> I also checked the dem values for the inappropriate half basins, and they
> are very similar to the values for neighboring normal basins. So at this
> point, I'm not sure how to fix the problem. Any advice from the GRASS
> community would be greatly appreciated.
>
> Thank you,
>
> Erin
> _______________________________________________
> grass-user mailing list
> grass-user at lists.osgeo.org
> https://lists.osgeo.org/mailman/listinfo/grass-user
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/grass-user/attachments/20180713/eb33c768/attachment.html>