DESCRIPTION
r.hydrodem applies hydrological conditioning (sink removal) to
a required input elevation map. If the conditioned elevation
map is going to be used as input elevation for r.watershed,
only small sinks should be removed and the amount of modifications
restricted with the mod option. For other modules such as
r.terraflow or third-party software, full sink removal is
recommended.
OPTIONS
- input
- Input map, required: Digital elevation model to be corrected. Gaps
in the elevation map that are located within the area of interest should
be filled beforehand, e.g. with r.fillnulls or
r.resamp.bspline, to avoid distortions.
- output
- Output map, required: Hydrologically conditioned digital elevation
model. By default, only minor modifications are done and not all sinks
are removed.
- size
- All sinks of up to size cells will be removed.
Default is 4, if in doubt, decrease and not increase.
- mod
- All sinks will be removed that require not more than mod
cells to be modifed. Often, rather large sinks can be removed by
carving through only few cells. Default is 4, if in doubt, increase
and not decrease.
- -a
- Not recommended if input for r.watershed is generated.
With the -a flag set, all sinks will be removed using an impact
reduction approach based on Lindsay & Creed (2005). The output will be a
depression-less digital elevation model, suitable for e.g.
r.terraflow or other hydrological analyses that require a
depression-less DEM as input.
NOTES
This module is designed for r.watershed with the purpose to
slightly denoise a DEM prior to analysis. First, all one-cell peaks and
pits are removed, then the actual hydrological corrections are applied.
In most cases, the removal of one-cell extrema could already be
sufficient to improve r.watershed results in difficult terrain,
particularly nearly flat areas.
The impact reduction algorithm used by r.hydrodem is based on
Lindsay & Creed (2005), with some additional checks for
hydrological consistency. With complete sink removal, results of
r.terraflow are very similar to results of r.watershed.
r.hydrodem uses the same method to determine drainage directions
like r.watershed.
REFERENCES
Lindsay, J. B., and Creed, I. F. 2005. Removal of artifact depressions
from digital elevation models: towards a minimum impact approach.
Hydrological Processes 19, 3113-3126.
DOI: 10.1002/hyp.5835
SEE ALSO
r.watershed,
r.terraflow,
r.fill.dir,
r.fillnulls,
r.resamp.bspline
AUTHOR
Markus Metz
Last changed: $Date$