watershed surface area

[David Finlayson]

I'd be suprised if one of the watershed models doesn't
provide this, but you should be able to get it easily
enough for any point on your DEM by computing the
slope of each cell with r.slope.aspect and storing
that in a slope_grid. Then use the following formula
in r.mapcalc (I think this will work):

area_grid = ewres()* nsres()/cos(slope_grid)

This gives you the surface area of each cell. Next use
this grid as the flow grid in r.watershed and create
the accumulation grid which should tally up the _true_
contributing area of each cell in your DEM.  Use masks
if you are only interested in a sub-basin.

--- Rado Bonk <rado at cosmos.dsc.unomaha.edu> wrote:
> Hi GRASSusers,
> Is there a way to compute watershed surface area in
> GRASS? In
> mountain regions it differs a lot from that of
> planimetric area.
> 	
> 	-Rado Bonk
> 
> Rado Bonk
> Geography and Geology
> UNO, Nebraska, 68182-0199,
> rado at cosmos.unomaha.edu
> 


=====
--
David Finlayson
david_finlayson at yahoo.com
University of Washington 
Box 351310 
Seattle, WA   98195 - 1310

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