Answer:
Since Version 1.6.20 the basic Voellmy equation has been modified to include yield stress (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 real scale experiments with debris flows in Illgraben (VS). Yield stress can help reduce spurious numerical diffusion in runout zones, providing a clearer delineation of the deposition zone. Yield stress (cohesion) values (unit Pascal) may be entered in the Mu/Xi tab of the Run Simulation window.
Please use cohesion values with care!
