Size Distribution for Carrying-Sediment Capacity and Effective Bed Material Gradation

For strong equilibrium sediment transport, it is sufficient to only use the bed material gradation and the size distribution of suspended load to describe the non-uniform suspended load transport. However, for non-equilibrium condition, it is necessary to introduce the size distribution for carrying-sediment capacity and the effective bed material gradation. Until now there is no study on this topic presented except two size distributions under equilibrium transport condition. This chapter presents the pioneering and systematic study by the authors for these subjects. The main contents of this chapter are as follows: (1) Based on the analysis of some typical cases for non-equilibrium transport of non-uniform sediment, the size distribution for carrying-sediment capacity and the effective bed material gradation are introduced, and the necessity of introducing these size distributions is discussed; (2) Ten properties of the size distribution for carrying-sediment capacity are illustrated and verified theoretically. They represent the theoretical meaning of this size distribution. (3) General expressions are developed for the carrying-sediment capacity, its size distribution, and the effective bed material gradation at a given channel section. These expressions cover the cases with sediment inflow all or partially changing to carrying-sediment capacity and with the bed material all or partially suspendable during a scour or deposition of non-uniform sediment; (4) The size distribution for carrying-sediment capacity and the effective bed material gradation are thoroughly investigated using new approaches with the water volume percentage and the sediment exchange on the bed; (5) The mechanisms and simplified expressions for the size distribution for the carrying-sediment capacity, the effective bed material gradation, and the size distribution of suspended load are investigated for the cases of massive scour and of massive deposition. These expressions will simplify their applications; (6) The size distribution for carrying-sediment capacity and the effective bed material gradation are determined for the exit section of a relatively long reach with significant scour or deposition; (7) Some special cases of sediment transport are thoroughly analyzed and explained with the application the size distribution for carrying-sediment capacity. This indicates that the concept and the expression for the size distribution for carrying-sediment capacity are consistent with the reality.