A preliminary method for the evaluation of the landslides volume at a regional scale

Dealing with the evaluation of the risk connected to the formation of
landslide dams at regional scale, it is important to estimate the volume of the
depleted material that can reach the riverbed. This information, combined with
other elements (river dimensions, valley width, landslide velocity, etc.) allows making
predictions on the possibility of river blockage. One of the problems of this approach
is the lack of data concerning the shape and position of the sliding surface; this does
not permit us to estimate the volume of the landslide material. The IFFI (Inventario
dei Fenomeni Franosi in Italia, i.e. Landslide Inventory in Italy) project furnishes
information, at different levels of precision, on nearly totality of the landslides
existing in Italy. The first level of the IFFI (compiled for all slides) does not contain
information on the depth of the sliding surface but contains data regarding the type
and the activity of the slope movement. Along with this information the IFFI project
also furnishes vector maps containing the boundary of each landslide and the main
sliding direction. This paper describes the implementation of an algorithm aimed to
define, with an adequate approximation, the 3D geometry of the sliding surface of
rotational slides for which, on the basis of geologic maps available at regional scale,
some geotechnical parameters can be known or estimated. The work also required
the creation of a computer code useful for the 3D analysis of slope stability (3D safety
factor) using the simplified Janbu method. All computer code has been created on
a GNU-Linux OS and using shell scripting, based on GRASS GIS and R statistical
software.