Particle size hydraulic radius

Instead of considering the largest particle diameter that can pass through a given void space, the hydrodynamic pore size may be used for predicting the hydromechanics of non-woven geotextiles. If the void is assumed to be equivalent to a circular flow channel, then the hydrodynamic pore size may be defined by its hydraulic radius, Rh, where ... 

Equation (95) has been found to provide a good estimation of permeability for packed beds of voidage between 0.26 and 0.80. Carman (1956) also found that if the hydraulic radius was used to replace the particle radius in Eq. (95), the equation was also good for mixtures of different particle sizes. The hydraulic radius for a bed of spherical particles can be ealeulated from... 

On a note of caution, the design engineer should not apply data from small to large flumes. The change of the hydraulic radius and the ratio of particle size to depth of flow affect the magnitude of the slope of the launder. 

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