Dense flow model (FL-1D)

Avalanche flow is described by two scalar fields A(x,t) and Q(x,t). The first field A(x,t) represents the cross sectional flow area at x and time t and the second field Q(x, t) gives the average snow discharge along the mountain profile (Bartelt et al., 1999). A Voellmy-fluid flow law is applied that assumes no shear strain-rates in the avalanche flow plug.

FL-1D is a quasi one-dimensional, hydraulics-based, depth-averaged continuum model. It tracks the motion of the avalanche (velocities, snow heights, pressures) from initiation to runout. The model is based on several important assumptions:

  1. Flowing snow is modelled as a fluid continuum of mean constant flow density.
  2. The flow width is known.
  3. A clearly defined top flow surface exists.
  4. The flow height is the average flow height across the section, i.e. the flow height is level over the flow width.
  5. The vertical pressure distribution is hydrostatic. Centripetal pressures which modify the hydrostatic pressure distribution are not accounted for.
  6. Flow velocity and depth is unsteady and non-uniform.
  7. The avalanche mass is constant and no entrainment processes are modelled.