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On 19/04/2012 01:48, Rich Shepard wrote:
<blockquote
cite="mid:alpine.LNX.2.00.1204181543020.24382@salmo.appl-ecosys.com"
type="cite"> The attached pdf shows the basin map output by
r.watershed based on a 10m
<br>
DEM and a threshold of 150000. The NHD level 6 subbasins are
outlined in
<br>
black and the 1:24K NHD streams are in blue.
<br>
<br>
The small white areas at the bottom left and center right appear
to be
<br>
external to defined sub-basins. But I don't know how to interpret
the larger
<br>
white areas with streams in them (center and top). The top margin
is an
<br>
international boundary so I can understand not being able to
completely
<br>
define sub-basins across that boundary since the DEM doesn't reach
that far
<br>
north, but it's not consistently white.
<br>
<br>
</blockquote>
<br>
Using the 10m DEM (I suppose your regions settings are the same?)
then each pixel is 100 sq.m. So a threshold of 150000 would
delineate watersheds of a minimum 15,000,000 sqm = 15 sq km. Does
that seem to be what you're getting? If so, then white areas are
small catchments that are hydrologically separated from the larger
basins, and thus don't "belong" to any of the NHD larger basins. The
streams in those smaller catchments flow off the map into some other
large basin that doesn't appear in the NHD group.<br>
<br>
I'm not sure if this helps any. What do you see as a problem?<br>
<br>
<blockquote
cite="mid:alpine.LNX.2.00.1204181543020.24382@salmo.appl-ecosys.com"
type="cite"> Please help me interpret the white areas with vector
streams.
<br>
<br>
TIA,
<br>
<br>
Rich
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</blockquote>
<p><br>
</p>
<br>
<pre class="moz-signature" cols="72">--
Micha Silver
052-3665918
</pre>
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