Does the density play a role in my simulations?

I made several different calculations, but the results differ only with the height of the released snow; the density doesn’t count. Did I make any mistake while modeling, or it doesen’t play a role?

Answer:

The RAMMS model (Avalanche and Debrisflow) uses depth-averaged mass and momentum conservation equations, particularly the Voellmy–Salm (VS) model. These are formulated under the assumption of a constant flow density.

“…we model as an incompressible continuum of mean constant density …”

The key point is that:

Density appears in both sides of the momentum equations (inertia and frictional terms). When these equations are written in terms of depth-averaged quantities, and the density is assumed to be constant across space and time, it can be factored out and canceled from both sides of the equations. The equations govern how the flow evolves over time, but crucially, it’s expressed in terms of velocity and height, not mass, and the density is implicitly removed.

What this means for engineers:

• When using RAMMS (Avalanche and Debrisflow), the flow density won’t affect the outcomes like runout, flowheight or velocity directly.
• The density (e.g., 300 kg/m³ for avalanches) only plays a role in output variables like impact pressure — not in the internal dynamics.