Shields parameter

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 nondimensionalization of a shear stress, and is typically denoted \(\tau_\ast\) or \(\theta\). It is given by:

\[\tau_\ast = \theta = \frac{\tau}{(\rho_s-\rho) g D},\]

where:

\(\tau\)	is a dimensional shear stress;
\(\rho_s\)	is the density of the sediment;
\(\rho\)	is the density of the fluid;
\(g\)	is acceleration due to gravity;
\(D\)	is a characteristic particle diameter of the sediment.

Physical meaning

By multiplying the top and bottom of the Shields parameter by D², you can see that it is proportional to the ratio of fluid force on the particle to the weight of the particle.

External links

• Southard, John. "Chapter 9 – Threshold of movement". Lecture notes – Special topics: An introduction to fluid motions, sediment transport, and current-generated sedimentary structures. MIT Open Courseware. http://ocw.mit.edu/courses/earth-atmospheric-and-planetary-sciences/12-090-special-topics-an-introduction-to-fluid-motions-sediment-transport-and-current-generated-sedimentary-structures-fall-2006/lecture-notes/ch9.pdf. Retrieved 2011-01-31.

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