Effect of Bed-Load Movement on Flow Friction Factor

The effect of bed-load movement on the friction factor of pipe flow and open-channel flow was studied experimentally. The measured results for flows without bed-load movement for both of these flows compares well with the theoretical relationships. The experimental data associated with the pipe flow are hydraulically smooth, whereas that with the open-channel flow is hydraulically rough. The flows were in the fully developed turbulent region. The data show that bed-load movement increases the flow friction factor. The increment depends on the volumetric concentration of the bed load and the size of the particle, and is attributed to the additional energy consumption associated with the collision of sediment particles, as well as the horizontal particle acceleration-induced momentum extraction from the flow. An empirical equation is fitted to the experimental data from which the friction factor associated with bed-load movement can be obtained for a given bed-load concentration and particle size.