Erosion and deposition, characterized by motion and rest phases of the particles.

Exceeding the "critical" state, characterized by the (marginal) or shear stress τ or also by the critical flow rate V_crit, results in the beginning of the fluid and sediment transport. The shear stress τ can also be referred to as erosion shear stress.

The opposite shear stress brings the moving particles to an idle sate, and is defined by Kreuter ≥ 0,7 * τ, [Bollr89]. This shear stress is referred to as deposition shear stress.