Incipient motion and bed load transport of non-uniform sediment

This study explores characteristics of incipient motion and transport of non-uniform sediments analytically and experimentally. A review of published studies on non-uniform sediment transport is first submitted for better understand the state-of-the-art in this area of research. A new formula to calculate the critical shear stress and another to predict frictional bed load transport rate of non-uniform bed materials has been proposed with the aid of experiments. A modification of Wu et al.'s formula to calculate the critical shear stress of incipient motion of non-uniform was proposed. After that, a new formula to calculate the critical shear stress of individual fractions of non-uniform sediment was established, considering factors of grain size and gradation of bed materials and the different threshold of incipient motion for uniform sediment with various diameters. A new fractional non-uniform sediment bed load transport formula based on energy balance theory was proposed. A wide range of laboratory and field data agree well with this theoretical equation. Good agreement is achieved with the newly proposed formula for uniform sediment.