Deriving a catchment boundary in GRASS

[J.M. Ruiz]

> 
> 
> Can anyone tell me if it's possible in GRASS to simply derive a catchment 
> boundary. All we want to do is to point to a point on a river and for the 
> system to derive the catchment to that point.
> 
> I've tried the 'r.watershed' function, but it doesn't seem to work with 
> the spearfish test data - although I think it's more likely that I'm not 
> using it correctly.
> 
> I'm thinking of creating a new function, which will mean the users will 
> only have to point at a spot on the screen, in a similar way to 'd.where' 
> and the system will go on to 
> i) derive the catchment boundary and
> ii) calculate various stats (catchment area, percentage of various raster 
> maps, e.g. soils, potential evaporation, etc., in the derived catchment 
> area)
> 
> Anyone done this and/or could point me at the code ?
> 
> Any help much appreciated
> Thanks,
> 
> Steve C.
> 
> 


Hello Steve,

I have found r.water.outlet manual, which was created Chuck.

Here it is:


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r.water.outlet <main> GRASS Reference Manual<main> r.water.outlet



NAME
     r.water.outlet - Watershed basin creation program.
     (GRASS Raster Program)

SYNOPSIS
     r.water.outlet
     r.water.outlet help
     r.water.outlet drainage=name basin=name easting=value
          northing=value

DESCRIPTION
     r.water.outlet generates a watershed basin from a drainage
     direction map (from r.watershed or r.water.aspect) and a set
     of coordinates representing the outlet point of watershed.

OPTIONS
     drainage
          Input map: drainage direction.  Indicates the "aspect"
          for each cell.  Multiplying positive values by 45 will
          give the direction in degrees that the surface runoff
          will travel from that cell.  The value -1 indicates
          that the cell is a depression area.  Other negative
          values indicate that surface runoff is leaving the
          boundaries of the current geographic region.  The
          absolute value of these negative cells indicates the
          direction of flow.  This map is generated from either
          r.watershed or r.water.aspect.

     basin
          Output map: Values of one (1) indicate the watershed
          basin.  Values of zero are not in the watershed basin.

     easting
          Input value: Easting value of outlet point.

     northing
          Input value: Northing value of outlet point.

NOTES
     In the context of this program, a watershed basin is the
     region upstream of an outlet point.  Thus, if the user
     chooses an outlet point on a hill slope, the resulting map
     will be a thin silver of land representing the overland
     slope uphill of the point.

     It is usually a good idea for the user to "find" the stream
     channel of the desired basin.  If the user runs
     r.water.accum, r.water.swale with a small swale threshold,
     and d.where on the resulting map, the user can pinpoint the
     exact location of the outlet point with ease.





GRASS 4.1                U.S. Army CERL                         1






r.water.outlet <main> GRASS Reference Manual<main> r.water.outlet



SEE ALSO
     r.watershed, r.water.aspect, r.water.accum, r.water.swale,
     r.water.basin, d.where

AUTHOR
     Charles Ehlschlaeger, U.S. Army Construction Engineering
     Research Laboratory


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Two days ago i received a mail from Chuck and he told me i could get this 
program from zorro.cecer.army.mil.

I think this program can be useful for your current work



-------------------------------------------------
Juan M. Ruiz
Centro de Estudios Hidrograficos (CEDEX)
Paseo Bajo de la Virgen del Puerto 3, planta 3
28005 Madrid, SPAIN

Telephone: 335.79.51
Fax: 335.79.22
e-mail: jruiz at gea.cedex.es
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