Bed load

Bed load is sediment transported along a fluid-flow boundary by rolling, sliding, or brief hops. Its grains remain in frequent contact with the bed, unlike suspended sediment.

Shields parameter: A dimensionless measure comparing fluid shear stress on a bed grain with the submerged weight resisting its motion. It predicts when flow is strong enough to initiate grain movement.
Sediment transport: The movement of particulate material by fluids, gravity, or other agents. Bed load is one mode within the broader movement of sediment.
Bed-load transport equation: A formula estimating the rate of sediment movement along a bed from flow and grain properties. These equations turn bed-load mechanics into predicted transport rates.
Bedform: A patterned sediment feature, such as a ripple or dune, formed on a bed by fluid flow. Bed-load grains build and migrate the ripples and dunes that reshape a channel bed.
Critical shear stress: The minimum boundary shear stress required to initiate motion of sediment grains under specified conditions. Bed load begins when flow overcomes this threshold for bed grains.
Suspended load: Sediment carried within a fluid column for substantial periods by turbulent mixing. Unlike bed load, its grains remain aloft rather than moving in frequent bed contact.
Meyer-Peter–Müller equation: An empirical equation for estimating bed-load transport in steady, uniform flow. It is a classic quantitative relation between excess shear stress and transport rate.
Dune (fluid mechanics): A sediment ridge with a gentle upstream slope and steep downstream lee face formed beneath flowing fluid. Bed-load transport moves sediment over dunes and controls their migration.
Incipient motion: The onset of sediment-grain movement under fluid flow. It marks the transition from a stable bed to active bed-load transport.
Wash load: Fine sediment transported in suspension without significant exchange with the local streambed. It contrasts with bed load, which is supplied by and interacts with the bed.

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