Introduction

The studies on the non-equilibrium transport of non-uniform suspended load are reviewed. The comments focused on progress and problems in five areas, namely the vertically two-dimensional non-equilibrium sediment transport and bottom boundary condition; 1-D non-equilibrium sediment transport; size distribution for carrying-sediment capacity under equilibrium condition; size distribution for carrying-sediment capacity and effective bed material gradation for non-equilibrium sediment transport and sediment saturation recovery coefficient. Due to the complexities of sediment transport, individual and semi-empirical studies were typically conducted for specific problems without a systematic approach and sufficient theoretical basis. Lacking of generality the study results is difficult to apply to engineering practice. In view of the problems in the study of non-equilibrium sediment transport, this chapter summarizes the progress made by the authors in this respect, including the establishment of the bottom boundary conditions of the suspended load diffusion equation on the basis of statistical theory of sediment transport and the statistical theory of sediment exchange, the introduction of the carrying-sediment capacity and its size distribution, the effective bed material gradation and the theoretical expression of the saturation recovery coefficient, so as to establish a complete equation system for non-equilibrium transport of non-uniform suspended load. Then a series of long-term sediment problems are studied. For example, bed material coarsening, bed material and wash load following the same transport law, the multi-value of carrying-sediment capacity and the mechanism of long-distance scouring downstream the dam site.