[GRASS-user] Watershed crossovers

[Michael Barton]

Lyle,

It sounds like what you want is to identify least cost paths between two watersheds. The relevant commands in GRASS are r.walk (assuming that you'd like to calculate anisotropic LCP's) and r.drain. These are found under raster/terrain analysis in the menus.

Run r.walk from a hypothetical start point (you'll want to read the manual first if you are unfamiliar with cost surfaces and LCP analysis) making sure to create a movement directions map. Then run r.drain, identifying a hypothetical end point and inputting the movement directions map.

This should give you the LCP between your starting and ending points (i.e., in adjacent watersheds). These are not necessarily deer trails, but represent the route requiring the least energy to cross from one watershed to the next.

Michael
____________________
C. Michael Barton
Director, Center for Social Dynamics & Complexity 
Professor of Anthropology, School of Human Evolution & Social Change
Arizona State University

voice: 	480-965-6262 (SHESC), 480-727-9746 (CSDC)
fax:          480-965-7671 (SHESC),  480-727-0709 (CSDC)
www: http://www.public.asu.edu/~cmbarton, http://csdc.asu.edu




On Sep 5, 2011, at 12:57 AM, <grass-user-request at lists.osgeo.org> <grass-user-request at lists.osgeo.org> wrote:

> Date: Sun, 4 Sep 2011 21:40:41 -0400
> From: "Lyle E. Browning" <lebrowning at att.net>
> Subject: [GRASS-user] Watershed crossovers
> To: GRASS user list <grass-user at lists.osgeo.org>
> Message-ID: <A619EA14-649A-4B35-A5E8-E5F9D8EC6E4E at att.net>
> Content-Type: text/plain; charset=us-ascii
> 
> Perhaps an odd request, but as an archaeologist, I am looking at crossover's from one watershed to another. Typically these involve starting at a stream in one watershed, following a game trail up a ravine to a ridge and then down into a similar ravine into another watershed. Optimal foraging strategy by whitetail deer is the issue. These animals have used these trails for literally thousands of years with hunters on tongues of land overlooking both streams and the ravines, resulting in archaeological sites adjacent to the game trails but not on other tongues of land that aren't as easy to traverse as the optimal trails. These trails are the least physically taxing and shortest distances from one watershed to another. For whatever reason, deer use these trails daily, despite modern development, roadways and the like as impediments. These game trails also explain why of four identical tongues of land, 2 saddling the ravine will have sites and the 2 not saddling the ravine will
> 
>  not.
> 
> Is there a way in GRASS to isolate these?
> 
> Thanks in advance,
> 
> Lyle Browning, RPA