[GRASS-user] elevation values of watershed basins
dylan.beaudette at gmail.com
Mon Feb 5 16:51:32 EST 2007
On Monday 05 February 2007 02:19, Hamish wrote:
> temiz wrote:
> > As I see, you are a soil scientist, so you will understand me better.
> I'm not, but maybe there is are ideas from other fields which can help-
> > The logic of my question is based on finding slopes' length as
> > landslide susceptibility parameter ( I accept slope is waterhed
> > area).
> Perhaps the concept of "fetch"? "The unobstructed region of the ocean
> over which the wind blows to generate waves." The idea is the longer the
> fetch, the greater height waves can grow. Your slope length seems like a
> direct analogy, of sorts. Perhaps there are some fetch calculation
> algorithms which may be applicable?
This is a good analogy for the dynamics of hillslopes: longer slope length per
unit of water = greater potential for erosion. Landslides would of course be
a bit more complex, but could follow a similar cascade-of-events type system:
like an avalanche in the snow.
> run r.watershed and get a basin and half-basin maps, r.to.vect,
> then isolate half basin borders not matching basin borders.
> This gives anti-ridges (obtain ridges with "r.param.scale par=feature").
> The anti-ridges will be the landslide path? (I guess ridges of flow
> accum river map will be the same thing?)
> then use the river paths as a MASK and maybe r.cost with slope as cost
> layer to see which basin (river) has the biggest cumulative slope?
> shooting in the dark,
Those are some interesting shots, and definitely something to try. Slope
length (RUSLE) and 'contributing upslope area' (a couple of definitions of
this are out there see  for some definitions).
1. Wilson, J.P. & Gallant, J.C. Terrain Analysis : Principles and Applications
Soils and Biogeochemistry Graduate Group
University of California at Davis
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