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
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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@gea.cedex.es
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