flow map in r.watershed

[margherita]

Hi list!

In the documentation of r.watershed (grass 6.4) I found that it's
possible to use the following (optional) input map:

flow
Input map: amount of overland flow per cell. This map indicates the
amount of overland flow units that each cell will contribute to the
watershed basin model. Overland flow units represent the amount of
overland flow each cell contributes to surface flow. If omitted, a value
of one (1) is assumed. The algorithm is D8 flow accumulation.

How is it possible to obtain  this map,  starting  from  a  DEM?

Thank you
 

--
Ing. Margherita Di Leo
Ph.D. Student
Methods and Technologies for Environmental Monitoring
Department of Environmental Engineering and Physics (DIFA)

University of Basilicata
Campus Macchia Romana
85100 - Potenza
Italy

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E-mail: dileomargherita AT gmail DOT com
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[achim]

Hi Margharita,

if you just have the information of an DEM its not necessary in nearly
all cases. So just omit if you have no further information.

It could be interesting if you are interested in very huge regions (like
continental/long N-S distance) and you have raster cells of very
different sizes.

achim

Margherita Di Leo schrieb:

> Hi list!
>
> In the documentation of r.watershed (grass 6.4) I found that it's
> possible to use the following (optional) input map:
>
> flow
> Input map: amount of overland flow per cell. This map indicates the
> amount of overland flow units that each cell will contribute to the
> watershed basin model. Overland flow units represent the amount of
> overland flow each cell contributes to surface flow. If omitted, a value
> of one (1) is assumed. The algorithm is D8 flow accumulation.
>
> How is it possible to obtain  this map,  starting  from  a  DEM?
>
> Thank you
>
>

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