Geografic-Information-System/raster/r.water.outlet/r.water.outlet.html

<h2>DESCRIPTION</h2>

<em>r.water.outlet</em> generates a watershed basin from a drainage
direction map and a set of coordinates representing the outlet point
of watershed.

<p>
Input drainage direction map indicates the &quot;aspect&quot; 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 raster map is generated from
<em><a href="r.watershed.html">r.watershed</a></em>.

<p>
Output raster map values of one (1) indicate the watershed
basin. Values of zero (0) are not in the watershed basin.

<h2>NOTES</h2>

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.

<h2>EXAMPLE</h2>

A watershed in
the <a href="http://grass.osgeo.org/download/sample-data/">North
Carolina sample dataset</a> region:

<div class="code"><pre>
g.region raster=elev_lid792_1m -p
# the watershed outlet position should be placed on a stream (from
# accumulation map):
r.watershed elev_lid792_1m threshold=5000 accumulation=accum_5K drainage=draindir_5K basin=basin_5K
r.water.outlet input=draindir_5K output=basin_A30 coordinates=638740.423248,220271.519225

d.mon wx0
d.rast map=accum_5K
d.rast map=basin_A30

# overlay with transparency
r.colors map=basin_A30 color=grey
d.his h=accum_5K i=basin_A30

# report outlet size in ha
r.report map=basin_A30 units=h
</pre></div>

<p>
<center>
<img src="r_water_outlet.png" border=0><br>
<i>Figure: Watershed draped over flow accumulation</i>
</center>

<h2>SEE ALSO</h2>

<em>
<a href="d.where.html">d.where</a>,
<a href="r.basins.fill.html">r.basins.fill</a>,
<a href="r.watershed.html">r.watershed</a>,
<a href="r.topidx.html">r.topidx</a>
</em>

<h2>AUTHOR</h2>

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

<p>
<i>Last changed: $Date$</i>