[GRASS-user] r.water.outlet map does not display

GRASS GRASS user
1

   Using r.watershed specifying the input DEM and a name for the drainage map
I can view the drainage map. When I follow this command with r.water.outlet
specifying the drainage map as input, 'watershed' as the output map name,
and the coordinates of the designated outlet, no map is displayable.

   Could this be due to the very flat nature of the terrain?

Rich

2

Hello,

You should make sure that the point you give to r.water.outlet is
located on a main stream. The accumulation map from r.watershed is
useful for this task.
If you're not doing so, you might end up with a tiny watershed.

Regards,
Laurent

2017-03-06 16:50 GMT-06:00 Rich Shepard <rshepard@appl-ecosys.com>:

  Using r.watershed specifying the input DEM and a name for the drainage map
I can view the drainage map. When I follow this command with r.water.outlet
specifying the drainage map as input, 'watershed' as the output map name,
and the coordinates of the designated outlet, no map is displayable.

  Could this be due to the very flat nature of the terrain?

Rich
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3

On Mon, 6 Mar 2017, Laurent C. wrote:

You should make sure that the point you give to r.water.outlet is located
on a main stream. The accumulation map from r.watershed is useful for this
task. If you're not doing so, you might end up with a tiny watershed.

Laurent,

   There are no streams in this area, only a couple of ditches.

Rich

4

Yes. The watershed computed via r.water.outlet may be only a single pixel in size, if your outlet point is not located on a stream. Better use r.watershed.

···

Am 06.03.2017 11:50 PM schrieb “Rich Shepard” <rshepard@appl-ecosys.com>:

Using r.watershed specifying the input DEM and a name for the drainage map
I can view the drainage map. When I follow this command with r.water.outlet
specifying the drainage map as input, ‘watershed’ as the output map name,
and the coordinates of the designated outlet, no map is displayable.

Could this be due to the very flat nature of the terrain?

Rich

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grass-user@lists.osgeo.org
https://lists.osgeo.org/mailman/listinfo/grass-user

5

On Tue, 7 Mar 2017, Sören Gebbert wrote:

Yes. The watershed computed via r.water.outlet may be only a single pixel
in size, if your outlet point is not located on a stream. Better use
r.watershed.

Sören,

   I ran r.watershed first. But, since there are no streams present no map
was produced.

   Because I could not create the mask using r.watershed and r.water.outlet I
manually digitized (in the map display window) a smaller area, converted
that to a raster map, then used that for the mask. Itzi is now happy and
running much faster than before.

Thanks,

Rich