Modelling wet snow avalanche flow with a temperature dependent Coulomb friction function. In

ABSTRACT: We present a model to describe the motion of wet snow avalanches. This model is used to simulate a well-documented wet snow avalanche event in Switzerland. We begin by identifying the physical processes which are most affected by snow temperature and moisture, including meltwater lubrication at the sliding surface and the cohesive, plastic interactions between wet snow granules. We then introduce two conservation equations for internal heat energy and advective water transport into the governing differential equations describing avalanche motion. Different physical mechanisms (dissipative energy fluxes) contribute to the rise in temperature within the avalanche. Meltwater can be produced depending on the temperature of the flowing snow, which is strongly related to the tempera-ture of the entrained snowcover. We then identify how temperature and moisture affect different con-stitutive relationships: (1) we modify the basal friction to account for water at the sliding surface, (2) we increase the dissipation of turbulent kinetic energy to account for the moisture controlled, plastic inter-actions between granules and (3) to model wet snow surges and levee formation we include a cohe-sion term in the basal shear stress. Because the temperature varies in the stream-wise and lateral flow directions different deposition structures result. Melting can occur in different flow regions, including the tail of the avalanche. This helps explain wet snow avalanche pile-ups. Even though the flow re-mains laminar and slug-like, we find that wet snow avalanche runout distances can be large due to the meltwater lubrication observed in the study cases