stephen sefick pisze:
What is good guidance for where to set the threshold? I am in the
coastal plain, but In the very upper part ~10 miles from the piedmont,
so it is not terribly low gradient (I am going to quantify this "not
terribly low gradient" soon). I don't see the -b flag for r.watershed
6.4svn checkout (probably a week ago) in the man pages. I said
realistic because you can set the threshold to 1 for a 1m res dem.
There are lines that don't even look like streams all over the place.
Is it possible to extract streams with the landscape (Mongomery) as a
guide for the threshold?
the rule for Montgomery is described in literature cited in
r.stream.extract help. Look into this.
In general, Montomery's assumptions take into account annual
precipitation versus slope gradient * SCA (specific catchment area). It
is not a problem if you have 1m dem, because in that one specific
situation SCA = accumulation, so you can use a threshold = 200, as
suggested by Montogmery and Dietrich for Appalachian. But it is not
possible to say which value is best.
I want to be able to do this so all of the
stream ordering is done on a consistent stream network among
watersheds. If this is not possible then I will use a threshold and
use this for all stream network extraction on all of the other dems
that I need to process so they are all comparable. I appologize if
this doesn't make sense, but I will explain in greater detail if I
need to.
kindest regards,
Stephen Sefick
On Thu, Aug 5, 2010 at 9:35 AM, Jarek Jasiewicz <jar...@amu.edu.pl> wrote:
stephen sefick pisze:
I would like to use the Montgomery method to extract streams (exp~2
from the paper). What should the threshold value be? And in general
what should the threshold value be? I am working in the southeastern
coastal plain (USA), which is characterized by low gradient (if this
helps).
for flat areas Montgomery's method is not a good option. Generally that
method was created and tested on areas with gradient > 5%.
I am using 1m resolution LIDAR data. I would like to extract
the most realistic map of streams that I can.
Chmmm... what you mean realistic? Maybe use existing stream network will be
the best solution?
For coastal plains where is no real vallyes the r.watershed's treeshold with
-b option seems to be best option
I am also trying to
track down the inttermitance perminance threshold. Any guidance would
be greatly appreciated.
SWAT (soil water assessment tool) but not for GRASSS.
kindest regards,
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