Abstract: In the aim of exploring the physical mechanisms and critical probability of sediment’s incipient motion, the incipient motion is regarded as a critical phenomenon and is compared with continuous phase transition. Two-dimensional Ising model and renormalization group model as well as algorithm of sediment are established based on the principle and method of critical phenomena, continuous phase transition and renormalization group. By comprehensive analysis, a critical probability of sediment’s incipient motion is obtained (the threshold is about 0.42) which is approximate with the results of experiments and observations. In association with sediment movement mechanics and fractal dynamics, the physical mechanism of bed surface starting is discussed. The results show that the integral incipient motion of bed surface have similar physical mechanism with fractal growth DLA group. It gives a physical interpretation to the integral incipient motion of bed surface with a threshold less than 0.5.

Key words: incipient motion of sediment, phase transition, Ising model, renormalization group, threshold, incipient motion of bed surface