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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 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 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 } .
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 dimensionless Shields Diagram, in combination with the Shields formula is now unanimously accepted for initiation of sediment motion in rivers. Much work was done on river sediment transport formulae in the second half of the 20th century and that work should be used preferably to Hjulström's curve. [3]
Bed material load transport (C) is a function of all the above parameters, i.e.: C = f (b , y , BF, Q , Sf , τ b, τ c, d , σ , Gs , ν) Knowledge of sediment transport is important to such endeavors as river restoration, ecosystem protection, navigation, and infrastructure management.
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.
Bed load sediment in the thalweg of Campbell Creek in Alaska. The term bed load or bedload describes particles in a flowing fluid (usually water) that are transported along the stream bed. Bed load is complementary to suspended load and wash load. Bed load moves by rolling, sliding, and/or saltating (hopping).