W = weight of particle, lb f and 

 L = lift force, lb f 



Free Stream Velocity 



Figure 1. Forces on a particle in unidirectional flows 



The value for 4> is typically assumed to be equal to the angle of repose of the 

 grains. For sand, this value is typically taken between 30 and 35 deg**. 

 The lift force L is typically not considered in the analysis because it is 

 inherently included in turbulent fluctuations. The forces W and D can be 

 written as 



*~ C ^ (1 sediment fluid) 



(2) 



and 



D = C, d 2 t r 



(3) 



where 



7 = specific weight, lb f /ft 3 



C x = "shape" coefficient 



C 2 = drag coefficient 



t = boundary shear stress, lb f /ft z 



Combination of Equations 2 and 3 yields an expression for the shear stress 

 given by 



C, 



x =— tan 4> d (y sedimeat -f tluid ) (4) 



Rearranging Equation 4 to obtain r in dimensionless form results in 



A table of factors for converting non-SI units of measurement to SI 

 (metric) units is presented on page 5. 



