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« April 2017 »
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Slope Units Delineation


The software r.slopeunits requires a DEM, an optional raster layer showing alluvial plains, and the following user-defined parameters :

  • the initial flow accumulation area threshold (t in square meters),

  • the reduction factor r (integer, >1), that is used to calculate, iteratively, new values for the flow accumulation area threshold (t = t-t/r). Values larger than 5 are recommended.

  • the minimum surface area for the slope-units (a in square meters),

  • the minimum circular variance of terrain aspect within a slope-units (c, varies between 0 and 1, where 0 means no variance, i.e. cells dip in the same direction, and 1 means maximum variance)

  • the maximum surface area for the slope-units (maxarea, in square meters, optional),

  • threshold area value for the cleaning procedures (cleansize, in square meters, used to remove very small slope units that may occur give some geomorphological conditions)





We provide a compressed location for GRASS GIS 7.0 that can be used to test the code.



GRASS GIS 7.0, Python, Bash


Installation and run

The software have been tested on a Ubuntu 14.04 LTS server but should run on a generic GNU/Linux machine.

The two files provided must be copied inside the “scripts” folder of the GRASS GIS installation directory. The must be set executable. A typical approach, for the installation, is:

#open a bash shell

#move to the download folder, e.g.

cd /home/$USER/Downloads


#move the files

mv r.slopeunits /usr/lib/grass70/scripts

mv /usr/lib/grass70/scripts


#give execution rights

chmod ugo+x /usr/lib/grass70/scripts/r.slopeunits

chmod ugo+x /usr/lib/grass70/scripts/


#Run GRASS GIS, move in the location containing the digital elevation model type and:

r.slopeunits --help

#to see the options. The minimal command line to obtain a slope-units delineation is

r.slopeunits demmap=[dem] slumap=[output_SU_map] thresh=[t, square meters] circularvariance=[c] areamin=[a, square meters] reductionfactor=[r, r>2] maxiteration=[max number of iterations]

#see M. Alvioli, I. Marchesini, P. Reichenbach, M. Rossi, F. Fiorucci, F. Ardizzone, F. Guzzetti

#(2015) for explanations and additional options.


#please address comments, questions and gux fixes rquests to: ivan.marchesini[AT];