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The Shields parameter, also called the Shields criterion or Shields number, is a nondimensional number used to calculate the initiation of motion of sediment in a fluid flow. It is a dimensionalization of a shear stress , and is typically denoted ψ {\displaystyle \psi } or θ {\displaystyle \theta } .
Sediment transport is the movement of solid particles , typically due to a combination of gravity acting on the sediment, and the movement of the fluid in which the sediment is entrained.
The stability of granular material in flow can be determined by the Shields formula or the Izbash formula. The first is more suitable for fine grain material (such as sand and gravel), while the Izbash formula is more suitable for larger stone. The Shields formula was developed by Albert F. Shields (1908-1974). In fact, the Shields method ...
The Exner equation describes conservation of mass between sediment in the bed of a channel and sediment that is being transported. [1] It states that bed elevation increases (the bed aggrades) proportionally to the amount of sediment that drops out of transport, and conversely decreases (the bed degrades) proportionally to the amount of sediment that becomes entrained by the flow.
The concentration of suspended sediment with depth goes as the power of the negative Rouse number. It also is used to determine how the particles will move in the fluid. The required Rouse numbers for transport as bed load , suspended load , and wash load , are given below.
The Hjulström curve, named after Filip Hjulström (1902–1982), is a graph used by hydrologists and geologists to determine whether a river will erode, transport, or deposit sediment. It was originally published in his doctoral thesis "Studies of the morphological activity of rivers as illustrated by the river Fyris .
Original Shields diagram, 1936. Albert Frank Shields (June 26, 1908 – July 1, 1974) [1] [2] was an American mechanical engineer who is best known for his derivation of the formula for determining the beginning of movement of sand and gravel in currents (incipient motion).
Transport of sediment in a channel; Shear velocity also helps in thinking about the rate of shear and dispersion in a flow. Shear velocity scales well to rates of dispersion and bedload sediment transport. A general rule is that the shear velocity is between 5% and 10% of the mean flow velocity.