Comparison of Powder snow avalanche simulation Models (RAMMS and SamosAT) based on reference events in Switzerland

740-744

Artikel aus einem Buch

200204855

ISSW2018 - Special Topic: Model chains and simulation ; P8.6 (2018) , 740-744
ISSW2018: international snow science workshop: a merging of theory and practice - Abstracts ; P8.6 (2018) 

ABSTRACT: In this paper, we compare two advanced avalanche dynamics simulation tools: SamosAT
and RAMMS. Both tools apply similar depth-averaged approaches to model the avalanche core, including
cohesive extensions to the classical Voellmy flow rheology. However, they apply vastly different approaches
to model the formation and motion of the powder cloud. The extended RAMMS model considers streamwise
variations of avalanche flow density that are coupled to the statistical configuration of the snow particles.
Expansions and contractions of the particle configurations define the mass and energy fluxes driving the
formation of the powder cloud. SamosAT assumes mass transfer into the powder cloud proportional to
the shear stress acting on the dense flow surface and models the powder cloud as a three-dimensional, twophase
flow of ice-particles and air. RAMMS adopts a two-phase depth-average approach for the powder cloud
leading to dramatic reduction in calculation times. However, information over the height of the cloud is lost.
In RAMMS snow entrainment is considered as a collisional-thermomechanical process that amplifies random
mechanical energy fluxes that enhance the configurational energy of the core and therefore the formation
and strength of the powder cloud. Also in SamosAT entrainment can be included in various ways through
the dense flow layer, or directly into the powder cloud, taking into account threshold values of particle-Froude
numbers. However, in the standard operational setting entrainment is currently not activated. We apply
both simulation tools to three well-documented reference events from Switzerland. We compare not only the
predicted process area, but also peak velocities and impact pressures. Both simularities and differences in
the simulation results exist.
Keywords: powder snow avalanche, SamosAT, RAMMS, snowcover, entrainment, case studies.