How is cohesion used in RAMMS::Avalanche?

Answer:

Since Version 1.6.20 the basic Voellmy equation has been modified to include cohesion, see equation below, where C is the cohesion of the flowing material. Unlike a standard Mohr-Coulomb type relation this formula ensures that S→0 when both N→0 and U→0. It increases the shear stress and therefore causes the avalanche or debris flow to stop earlier, depending on the value of C.

This formula has been established using chute experiments with flowing snow (Platzer et al., 2007a and Platzer et al., 2007b). Snow has different cohesive properties depending on snow temperature. Wet snow avalanches have higher cohesion values; dry snow avalanches have lower cohesion values. Cohesion can help reduce spurious numerical diffusion in runout zones, providing a clearer delineation of the deposition zone. Cohesion values (unit Pascal) may be entered in the Mu/Xi tab of the Run Simulation window.

Recommended values may be found in the following:

• Dry snow: 0 – 100 Pa

• Wet snow: 100 – 300 Pa

Please use cohesion values with care!