Motion of Contact‐Load Particles at High Shear Stress

For rivers in flood and beaches under wave attack, the shear stress at the top of the stationary granular bed can set up a sheared layer of contact‐load (bed‐load) particles. This type of motion also occurs in pressurized ponduits, where more accurate observations can be obtained. For high shear stress (Y>0.8) the shear layer has a thickness of several grain diameters. Experimentation and analysis demonstrated that mobile beds at high shear stress obey neither the smooth‐boundary nor the rough‐boundary law, but follow a different friction relation of their own, which does not depend on particle size. This analysis has now been significantly extended using a curvilinear concentration profile based on previous experiments. This profile is now applied to the evaluation of boundary friction and the transport rate of contact‐load solids. The present analysis provides the theoretical background to explain both existing experimental results and new data presented here.