STRADA
Avalanche safety
personnel often face the problem of whether to close a road, train or a ski
slope. Those decisions are often very difficult to make, as they demand
forecasting of meteorological conditions and corresponding snow cover
characteristics as well as their influence on avalanche dynamics and
prospective run-out distances.
Present avalanche
mitigation methods do not directly associate snow cover properties with
avalanche dynamics and, as a result, no specific decision making tools exist. The STRADA project was
founded in 2010 to fill this gap and to develop strategies to adapt and enhance
the management of natural risks to climate change in Switzerland and Italy.
This project is part of the Programme of Collaboration in European cross-border
zones, Italy/Switzerland 2007/2013.
The project aims to develop a procedure to
automatically detect potential release zones and to estimate run-out distances
of frequent snow avalanches by taking into account the effect of snow cover
properties both in the release and flowing zones.
Photo: P. Caviezel, TBA GR. The avalanche Val Raschitsch cross the Engadin street (2002)
Assessing the effect of snow cover on location and
extension of release zones
Existing
mathematical algorithms for automatic definition of avalanche release zones
mainly focus on terrain parameters such as slope and curvature. While these
algorithms may work correctly for the definition of extreme avalanches release
zones, they work poorly on a smaller scale where snow distribution and the
influence of the wind on the snow deposition play a major role in the
definition of the release area extension.
In the project
STRADA, in order to improve the efficiency of these algorithms we aim to link
the release areas of frequent avalanches to both terrain and snow cover
distribution. We investigate how snow cover changes topography, and in
particular terrain roughness and how terrain smoothing may influence location
and extension of avalanche release zones. To this aim, the snow-cover distribution is first characterized at
different test sites by performing terrestrial and airborne laser scanning at
regular time intervals during the winter seasons. Measurements are especially
performed before and after an avalanche release to precisely characterize the
avalanche release area. In a second phase, data are analyzed to quantify terrain
smoothing and understand the relevant scales important for avalanche formation.
Finally, the results are integrated into a new algorithm to
identify potential release areas, combining terrain and snow cover parameters.
Assessing the effect of snow cover on avalanche
dynamics
A second task of
the project STRADA deals with the understanding on how snow cover affects
avalanche mobility and thus the run-out distance. As avalanches move downward
they erode the underlying snow cover. Depending on the erosion depth, layers
with various characteristics are entrained. The average temperature of the entrained snow, its density
and its water content have a major influence on the avalanche mobility by
giving origin to highly fluidized layers as in the case of cold and light snow
or dense granular layers as in the case of warmer and more cohesive snow.
To assess the influence of different
snow typologies on avalanche dynamics many measurements
were made at the experimental sites Vallée de la
Sionne (Valais, Switzerland) and others occasional sites: mass, speed,
flow regimes and runout distances of numerous avalanches were recorded. The
corresponding snow cover characteristics were directly measured in the field or
indirectly determined using the numerical model SNOWPACK
and Alpine3D. This allows to link observed
avalanche dynamics measurements with the prevailing snow cover conditions and
identify the controlling variables, e.g. snow temperature.
These new findings will help to enhance a new generation of
numerical avalanche dynamics models like RAMMS which can take into account both
entrainment of snow and influence of snow temperature on avalanche dynamics and it will finally be possible to
calculate avalanche scenarios which link average snow cover conditions to
expected avalanche location and mobility.
This pioneering
approach opens new possibilities in the field of management of roads and ski
resorts, but also for numerous other applications where a more realistic
knowledge of real time causes and effects is needed.
In
this project we work in collaboration with: Kanton Graubünden, Amt für Wald Graubünden,
Naturgefahren; Canton du Valais, Service des forêts et du
paysage (SFP), section des dangers naturels; Regione autonoma Val d’Aosta, Dipartimento difesa del suolo e risorse idriche; Regione Lombardia, Agenzia Regionale per la Protezione dell’Ambiente; Arpa Piemonte, Agenzia Regionale per la
Protezione Ambientale.
Contact persons:
