Calculating incipient velocity of non-uniform sediment through stress analysis

The incipient motion of sediment particles is one of the most essential features in sediment dynamics. The inherent mechanism of sediment initial motion, the influences of flow and sediment factors are studied for non-uniform sediment particles. A theory of sediment incipient motion is completed by introducing the concepts of instantaneous velocity of flow, criterion of incipient motion, relative exposure degree of particles on river bed, and additional mass force. A non-dimensional formula for calculating the critical shear stress of non-uniform sediment is derived using a model with the sediment particles rolling along the riverbed. This formula contains several coefficients correlated with flow pulsation and relative exposure degree, and proves to be reasonable by comparison with theoretical solutions and measurements.