Sediment Transport in Smooth Fixed Bed Channels

Incipient motion of discrete particles resting on a fixed smooth channel bed is investigated in different conveyance shapes. The results are compared with incipient motion studies in conveyances with movable beds. Higher critical velocities and shear stresses are obtained for smooth rectangular channels than for circular ones, but a single equation for all tested conveyance shapes is derived. The experimental results suggest that for normal sand as well as gravel much lower values of critical velocities are needed to avoid deposition than usually adopted in sewer design. An analysis of the sediment transport parameter φ and flow parameter ψ results in a relationship enabling the computation of sediment concentration Cv for any conveyance for sediment transport as bed load without tendency for deposition. The results are again compared with similar functions for conveyances with movable beds.