Hi all
Can anyone suggest a way for me to determine the longest flow path in
a catchment? I have several hundred to do, so I'd like a way to
automate it if possible.
Regards
David
David Townshend pisze:
Hi all
Can anyone suggest a way for me to determine the longest flow path in
a catchment? I have several hundred to do, so I'd like a way to
automate it if possible.Regards
David
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grass-user@lists.osgeo.org
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r.watershed elevation=elev drainage=dirs streams=stream treshold=<some value>
r.stream.order streams=streams dirs=dirs hack=longest
the stream with order 1 will be the longest streams of the catchment
J.
On Tue, 3 Aug 2010, Jarek Jasiewicz wrote:
r.watershed elevation=elev drainage=dirs streams=stream treshold=<some value>
r.stream.order streams=streams dirs=dirs hack=longestthe stream with order 1 will be the longest streams of the catchment
Jarek,
Please correct me if I'm wrong, but I don't believe this answers David's
question. Using both the Horton and Strahler systems of calculating stream
order, order 1 is the headwater reach. However, a drainage basin does not
have each stream length from origin to outlet the same length.
I believe that what David asked is how to calculate the longest path from
the top of first order streams to the basin outlet.
Thinking about this now, I can see that looping across all streams from
headwaters to outlet, and presenting those in a table (with some indication
of which path has which length) would be highly useful. One could calculate
average stream length and other descriptive statistics that could be
cleverly applied to questions of runoff, flooding, and habitats
(particularly if incorporated with gradient measures and a few other basin
attributes).
You research guys could work on this; us applied folks need to focus on
billable work. 
Rich
To add on to Rich's comments. I will gladly suggest things that would
be helpful to applied stream ecologists that could be used by a great
many folks. I will help in any way. I am finding that I need to
write a fair amount of shell script to extract the things that I am
interested in. I may just be a dunce, however.
my two cents,
Stephen Sefick
On Tue, Aug 3, 2010 at 8:22 AM, Rich Shepard <rshepard@appl-ecosys.com> wrote:
On Tue, 3 Aug 2010, Jarek Jasiewicz wrote:
r.watershed elevation=elev drainage=dirs streams=stream treshold=<some
value>
r.stream.order streams=streams dirs=dirs hack=longestthe stream with order 1 will be the longest streams of the catchment
Jarek,
Please correct me if I'm wrong, but I don't believe this answers David's
question. Using both the Horton and Strahler systems of calculating stream
order, order 1 is the headwater reach. However, a drainage basin does not
have each stream length from origin to outlet the same length.I believe that what David asked is how to calculate the longest path from
the top of first order streams to the basin outlet.Thinking about this now, I can see that looping across all streams from
headwaters to outlet, and presenting those in a table (with some indication
of which path has which length) would be highly useful. One could calculate
average stream length and other descriptive statistics that could be
cleverly applied to questions of runoff, flooding, and habitats
(particularly if incorporated with gradient measures and a few other basin
attributes).You research guys could work on this; us applied folks need to focus on
billable work.Rich
_______________________________________________
grass-user mailing list
grass-user@lists.osgeo.org
http://lists.osgeo.org/mailman/listinfo/grass-user
--
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.
\-K\. Mullis
I realized this later... I didn't mean to come off as a jerk if I
did. I am in everyone's debt who has written or otherwise contributed
to all free software projects. Thank you to all of those named and
un-named.
Stephen
On Tue, Aug 3, 2010 at 8:32 AM, stephen sefick <ssefick@gmail.com> wrote:
To add on to Rich's comments. I will gladly suggest things that would
be helpful to applied stream ecologists that could be used by a great
many folks. I will help in any way. I am finding that I need to
write a fair amount of shell script to extract the things that I am
interested in. I may just be a dunce, however.
my two cents,Stephen Sefick
On Tue, Aug 3, 2010 at 8:22 AM, Rich Shepard <rshepard@appl-ecosys.com> wrote:
On Tue, 3 Aug 2010, Jarek Jasiewicz wrote:
r.watershed elevation=elev drainage=dirs streams=stream treshold=<some
value>
r.stream.order streams=streams dirs=dirs hack=longestthe stream with order 1 will be the longest streams of the catchment
Jarek,
Please correct me if I'm wrong, but I don't believe this answers David's
question. Using both the Horton and Strahler systems of calculating stream
order, order 1 is the headwater reach. However, a drainage basin does not
have each stream length from origin to outlet the same length.I believe that what David asked is how to calculate the longest path from
the top of first order streams to the basin outlet.Thinking about this now, I can see that looping across all streams from
headwaters to outlet, and presenting those in a table (with some indication
of which path has which length) would be highly useful. One could calculate
average stream length and other descriptive statistics that could be
cleverly applied to questions of runoff, flooding, and habitats
(particularly if incorporated with gradient measures and a few other basin
attributes).You research guys could work on this; us applied folks need to focus on
billable work.Rich
_______________________________________________
grass-user mailing list
grass-user@lists.osgeo.org
http://lists.osgeo.org/mailman/listinfo/grass-user--
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.\-K\. Mullis
--
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.
\-K\. Mullis
Rich Shepard pisze:
On Tue, 3 Aug 2010, Jarek Jasiewicz wrote:
r.watershed elevation=elev drainage=dirs streams=stream treshold=<some value>
r.stream.order streams=streams dirs=dirs hack=longestthe stream with order 1 will be the longest streams of the catchment
Jarek,
Please correct me if I'm wrong, but I don't believe this answers David's
question.
yes this is correct answer. I suggest hack ordering not horton or strahler. Hack ordering ascribe first order to the longest stream in the catchement, second order to its tributaries etc. see more in documentation.
If you need more options also you can use:
r.stream.order streams=streams dirs=dirs hack=longest table=ordering
it will create table which has several attributes including longest length from head (cumlength) for every segment and distance to outlet (distance) where all segments has its more downstream cell distance to the outlet. Also see documentation.
On Tue, 3 Aug 2010, Jarek Jasiewicz wrote:
yes this is correct answer. I suggest hack ordering not horton or strahler. Hack ordering ascribe first order to the longest stream in the catchement, second order to its tributaries etc. see more in documentation.
Jarek,
Thanks for the information. I never used Hack's law or stream order. Then
again, my work hasn't involved such attributes since the mid-1980s.
Rich