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). I am using 1m resolution LIDAR data. I would like to extract
the most realistic map of streams that I can. I am also trying to
track down the inttermitance perminance threshold. Any guidance would
be greatly appreciated.
kindest regards,
--
Stephen Sefick
____________________________________
| Auburn University |
| Department of Biological Sciences |
| 331 Funchess Hall |
| Auburn, Alabama |
| 36849 |
|___________________________________|
| sas0025@auburn.edu |
| http://www.auburn.edu/~sas0025 |
|___________________________________|
Let's not spend our time and resources thinking about things that are
so little or so large that all they really do for us is puff us up and
make us feel like gods. We are mammals, and have not exhausted the
annoying little problems of being mammals.
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.
kindest regards,
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? 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 <jarekj@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.
kindest regards,
--
Stephen Sefick
____________________________________
| Auburn University |
| Department of Biological Sciences |
| 331 Funchess Hall |
| Auburn, Alabama |
| 36849 |
|___________________________________|
| sas0025@auburn.edu |
| http://www.auburn.edu/~sas0025 |
|___________________________________|
Let's not spend our time and resources thinking about things that are
so little or so large that all they really do for us is puff us up and
make us feel like gods. We are mammals, and have not exhausted the
annoying little problems of being mammals.
What is good guidance for where to set the threshold?
Try using some already existing data for mapped streams, such as the
national hydrography dataset. You can adjust the threshold of the
accumulation until your modeled output is close to already mapped
features.
I don't see the -b flag for r.watershed
6.4svn checkout (probably a week ago) in the man pages.
I think the -b option starts in version 7 (?)
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.
Threshold relates to the accumulation of upgradient cells. Its
usually a larger number in the thousands to 10s of thousands (at least
from my data/experience).
Is it possible to extract streams with the landscape (Mongomery) as a
guide for the threshold?
Try without altering the montgomery exponent and see how well it
matches known features.
Mark
On Thu, Aug 5, 2010 at 9:35 AM, Jarek Jasiewicz <jarekj@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.
kindest regards,
--
Stephen Sefick
____________________________________
| Auburn University |
| Department of Biological Sciences |
| 331 Funchess Hall |
| Auburn, Alabama |
| 36849 |
|___________________________________|
| sas0025@auburn.edu |
| http://www.auburn.edu/~sas0025 |
|___________________________________|
Let's not spend our time and resources thinking about things that are
so little or so large that all they really do for us is puff us up and
make us feel like gods. We are mammals, and have not exhausted the
annoying little problems of being mammals.
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 <jarekj@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.
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). I am using 1m resolution LIDAR data. I would like to extract
the most realistic map of streams that I can.
There is no universally recommended threshold, the threshold value
depends on how much detail you want. Reference stream maps are often
digitized on a certain scale, showing a more or less detailed stream
network. A threshold value of 1 (cell) doesn't make sense because then
streams will be everywhere. As a general rule of thumb, standard
deviation of the absolute flow accumulation values seems to be a
useful value and should in general provide accurate stream locations.
This general rule of thumb considers what detail can be extracted from
a given DEM, and not where real stream heads are located. I guess that
real stream heads can only be extracted from very high res DEMs.
Channel tracing is not that much of a problem, independent of the
threshold used, the extracted streams should match real streams.
The challenge is the proper determination of stream heads (channel
initiation), which can only be done with ancillary data like
precipitation and soil infiltration rate. It also depends on whether
permanent streams should be extracted or permanent plus temporary
(e.g. seasonal) or permanent plus temporary plus ephemeral (existing
only after heavy rainfall).
The -b option in grass 7.0 (beauty flat areas) applies to flat areas
only, and as the name says, beautifies flat areas. Stream locations
might or might not be more accurate with the -b option. The -b option
applies to flat areas in the DEM, i.e. zero slope and zero tangential
and profile curvature. Coastal plains are not flat areas in this sense
because there should still be slight variation in elevation. The flat
areas targeted with the -b option are lakes, broad rivers and sea.
These areas might need to be flattened in the DEM anyway, depending on
the source DEM, in order to get realistic flow accumulation and stream
networks.