Hazen-Williams Hydraulic Radius

Hazen-Williams hydraulic radius is a term used in the Hazen-Williams equation for calculating the flow of water in a pipe.  The hydraulic radius is a measure of the effective cross-sectional area available for flow relative to the wetted perimeter of the pipe.  It's worth noting that the Hazen-Williams equation is an empirical formula and, while widely used for its simplicity, it may not provide the same level of accuracy as more complex hydraulic models in certain situations.

 

Hazen-Williams Hydraulic Radius formula
\( r_h  =  (  v \;/\; C \; 1.318  \;  m^{0.54} )^{1 / 0.63}   \)     (Hazen-Williams Hydraulic Radius) \( v =  C \; 1.318  \; r_h^{0.63}  \; m^{0.54}   \) \( C =  v \;/\; 1.318 \; r_h^{0.63}  \; m^{0.54} \) \( m  =  (  v \;/\; C \; 1.318  \;  r_h^{0.63}  )^{1 / 0.54}   \)
Symbol	English	Metric
\( r_h \) = Hydraulic Radius	\( ft \)	\( m \)
\( v \) = Mean Flow Velocity	\(ft \;/\; sec\)	\(m \;/\; s\)
\( C \) = Hazen-Williams Coefficient, see below for Values	\( dimensionless \)	\(dimensionless\)
\( m \) = Hydraulic Grade Line Slope	\( dimensionless \)	\(dimensionless\)