The Significance of Entrainment on Debris Flow Modelling: The Case of Hunnedalen, Norway

This paper studies the influence of entrainment on the runout behavior of a documented debris flow, in Hunnedalen (Norway), happened on 2nd June 2016. The steepness of the channel and the availability of sediments along the flow path caused the debris flow to grow from approximately 2000 m3 to approximately 19000 m3. This paper aims to back calculate this event, using a Voellmy rheology implemented in RAMMS:DF and including a debris flow entrainment model. Voellmy rheological parameters (friction coefficient μ and turbulence coefficient ξ) are back-calculated using the default parameters of the entrainment model in RAMMS:DF. The back-calculation aims to replicate available field data such as: the deposit shape and the total entrained volume. It is also shown how the total eroded volume is strongly affected by the choice of μ and ξ. Finally, the entrainment parameters are varied from their default value to understand their influence on entrainment magnitude.