DESCRIPTION

The intersection between the topographic profile and the line starting from the point of detachment with a certain angle to the horizontal line defines the point of maximum propagation (Evans and Hungr, 1993; Jaboyedoff and Labiouse, 2003). The angle of inclination and the line of propagation are defined as zenith angle and shadow zone. This script defines rockfall zones from a digital elevation model (DEM) and vector layer containing starting point or points.

Energy line used for the cone method from the top or the bottom of a cliff (shadow angle), according to various authors (Image from Jaboyedoff and Labiouse, 2003)

INPUT

Digital Elevation Model = name

Name of elevation raster map

Starting points = name

Name of vector map containing rockfall source area. It can be one point or more.

Shadow angle = integer

Angle of inclination that defines the propagation zone. It's calculated from an horizontal plane starting from source point: highest values determine a lowest propagation.

Reduction value = double

Reduction moltiplicator for velocity. Default value is 0.9

Number of boulders = integer

For each starting point can be generated other random points used in the computations. By default points are located in a radius from the starting point equal to: (cell size * number of boulders)/2. Insert 1 for use only the original starting point or points. Note that a high number of boulders can make excessively long the calculation times.

Rock mass = double

Value of rock mass (Kg)

Output prefix = string

Name of prefix used for output raster maps

Buffer distance = integer

This value define the radius for randomly generatin boulders starting from starting point. It's in the option dialog window.

OUTPUT

r.droka generates 5 raster maps and a vector map. The names of all output maps start with the prefix defined by the parameter prefix followed by name of map

• prefix_propagation: raster map rapresenting the area of propagation. If are used multiple source points, each pixel show the percentage of passage (%)
• prefix_vel_max: maximum rock-fall translational velocities (m/sec)
• prefix_vel_med: medium rock-fall translational velocities (m/sec)
• prefix_vel_max: medium kinetic energy (kJ)
• prefix_en_max: maximum kinetic energy (kJ)
• prefix_starting: vector map of starting points

REFERENCES

FILIPELLO A., GIULIANI A., MANDRONE G. (2010) - Rock Slopes Failure Susceptibility Analysis: From Remote Sensing Measurements to Geographic Information System Raster Modules. American Journal of Environmental Sciences 6 (6): 489-494, 2010 ISSN 1553-345X 2010 Science Publications.

JABOYEDOFF M., LABIOUSE V. (2003) - Preliminary assessment of rockfall hazard based on GIS Data. Proceeding of the 10th ISRM Congress, South African Inst. Min. Met., Johannesburg, pp: 575-578

EVANS, S.G., HUNGR O. (1993). The assessment of rock fall hazard at the base of the talus slope. Can. Geotech. J., 30: 620-636. DOI: 10.1139/t93-054

SEE ALSO

AUTHORS

Andrea Filipello, University of Turin, Italy

Daniele Strigaro, University of Milan, Italy