Experimental analysis of the effect of bed-load movement on flow hydraulic characteristics

Abstract

In this study, the effect of bed-load movement on mean flow characteristics was evaluated in two rigid rectangular flumes. The experiments consisted of creating flow conditions carrying sediments with mean diameters of D50 ¼ 0.5, 0.6, and 2.84 mm over both smooth and rough beds. Various sediment concentrations were injected at the upstream end of the flume at non-deposit injection rates to study the effect of various concentrations on flow resistance. The effect of sediment movement on flow resistance was examined by comparing the results with those of clear-water flows (without sediment injection on both smooth and rough beds). The results showed that the sediment transport at maximum injection rate may increase the friction factor up to 50% and 58% in the smooth bed, and up to about 75% and 80% in the rough bed with mean diameter of 0.5 and 0.6 mm. In addition, for D50 ¼ 2.84 mm, the friction factor decreased in the smooth bed and increased up to 50% in the rough bed. In general, it can be concluded that bed-load transport can be increased by the flow friction factor. The results also showed that bed-loads may decrease the average velocity and increase shear velocity with extraction of momentum from the flow, and both the mentioned factors may increase the flow friction factor. Raising the bed-load concentration in the flow may increase the elevation of the friction factor, approaching a constant value after reaching the aggregation threshold and generation of bed-forms.