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