Carrying-Sediment Capacity for Non-uniform Sediment

This chapter presents the in-depth theoretical analysis for carrying-sediment capacity, which is one of the most important topics for sediment transport that lacks thorough illustrations of the mechanisms and strict theoretical expressions in previous researches. The main contents include: (1) Based on the authors’ study on the theory for the sediment exchange intensities in the bed layer, and the single-step parameters a set of more than twenty equations are derived for the carrying-sediment capacity for strong equilibrium transport of non-uniform suspended load. Under this condition, the size distribution of sediment concentration is determined by the gradation of bed material, or vice versa. The mechanisms, parameters, and expressions of these equations are completely different from the results in the past. (2) The impact of the turbulent bursting on the incipient suspension period is obtained. (3) The newly derived formulae for carrying-sediment capacity show good agreement with the data collected in flume experiments and in natural streams, without any parameters that need to be calibrated. It is also proved that the total carrying-sediment capacity determined with the summation based on the bed material gradation is the same as that determined with the summation based on the size distribution of suspended load. This solves a past dispute about which size distribution should be used in the summation in order to determine the total carrying-sediment capacity for non-uniform sediment mixture. (4) This newly derived formula shows that the carrying-sediment capacity is not only a function of V3/(ghω). It is also impacted by the sediment grain size, the shear velocity u*, and the water depth. This new formula can be applied to more general conditions than the existing formulas. (5) This newly derived formula can be used to encapsulate, within certain ranges, some formulas that are generally used, and to illustrate the advantages and limitations of these formulas.