Debris flow hazard modelling at medium (regional) scale has been subject
of various studies in recent years. In this study, hazard zonation
was carried out, incorporating information about debris flow initiation
probability (spatial and temporal), and the delimitation of the potential
runout areas. Debris flow hazard zonation was carried out in the
area of the Consortium of Mountain Municipalities of Valtellina di
Tirano (Central Alps, Italy). The complexity of the phenomenon, the
scale of the study, the variability of local conditioning factors,
and the lacking data limited the use of process-based models for
the runout zone delimitation. Firstly, a map of hazard initiation
probabilities was prepared for the study area, based on the available
susceptibility zoning information, and the analysis of two sets of
aerial photographs for the temporal probability estimation. Afterwards,
the hazard initiation map was used as one of the inputs for an empirical
GIS-based model (Flow-R), developed at the University of Lausanne
(Switzerland). An estimation of the debris flow magnitude was neglected
as the main aim of the analysis was to prepare a debris flow hazard
map at medium scale. A digital elevation model, with a 10 m resolution,
was used together with landuse, geology and debris flow hazard initiation
maps as inputs of the Flow-R model to restrict potential areas within
each hazard initiation probability class to locations where debris
flows are most likely to initiate. Afterwards, runout areas were
calculated using multiple flow direction and energy based algorithms.
Maximum probable runout zones were calibrated using documented past
events and aerial photographs. Finally, two debris flow hazard maps
were prepared. The first simply delimits five hazard zones, while
the second incorporates the information about debris flow spreading
direction probabilities, showing areas more likely to be affected
by future debris flows. Limitations of the modelling arise mainly
from the models applied and analysis scale, which are neglecting
local controlling factors of debris flow hazard. The presented approach
of debris flow hazard analysis, associating automatic detection of
the source areas and a simple assessment of the debris flow spreading,
provided results for consequent hazard and risk studies. However,
for the validation and transferability of the parameters and results
to other study areas, more testing is needed.