Effect of Sediment Density on Bed‐Load Transport

Experiments on transport by water of synthetic lightweight sediments of specific gravities, $1.0<s<2.5\text{,}$ and uniform grain size, $D=3.5\mathrm{mm}\text{,}$ are described. The results confirm the dimensional reasoning that the volumetric specific sediment transport rate, $q_s\text{,}$ is proportional to a simple power relation of the quotient, shear velocity/grain fall velocity $(V*/w)\text{.}$ The sediment transport rate, $q_s\text{,}$ is found to be proportional to the sixth power of the shear velocity, $V*\text{,}$ and inversely proportional to the fifth power of the grain fall velocity, w. An empirical formula based on the dimensional reasoning and the results above is found to be equivalent to the Einstein‐Brown bed load formula. A comparison of the experimental data with the predictions of several common bed load formulas shows the behavior of these formulas with lightweight sediments. The Einstein‐Brown formula and a modified version of Smart's formula provide good predictions.