watershed surface area

[Eric G . Miller]

There's a r.surf.area (at least in 5.0), but it has a couple problems
which I'm working on.  Doesn't consider NULL area properly (it's
included) and only works with CELL rasters.  I hope to get this fixed-up
for the upcoming release of GRASS 5.0 (stable).

On Mon, Oct 16, 2000 at 11:23:49PM -0700, David Finlayson wrote:
> 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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