Effect of Size Gradation on Transport of Sediment Mixtures

Abstract

Total bed-material load computations for nonuniform sediment mixtures were evaluated for the commonly used Engelund and Hansen, Ackers and White, and Yang transport formulas. The results of sediment transport computations indicate considerable scatter is in bed-material load transport relations for nonuniform sediment mixtures. The analysis demonstrates that a single fixed size, such as D35 or D50, cannot reflect the presence of various size fractions on the transport of nonuniform sediment mixtures. A size gradation compensation factor incorporates the effect that the size distribution has on the transport of sediment mixtures. The size gradation compensation factor, Kg, which is a function of the geometric standard deviation, σg, of the bed material and the flow conditions, in conjunction with the D50 of the bed material yields an equivalent representative diameter, De. By including De in the Engelund and Hansen, Ackers and White, and Yang formulas, the agreement between computed and measured bed-materi...