[GRASS-user] Longest flow path

[stephen sefick]

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 at 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=longest
>>
>> the 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
>
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-- 
Stephen Sefick
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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