on . Posted in Fluid Dynamics

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.

$$r_h = ( v \;/\; C \; 1.318 \; m^{0.54} )^{1 / 0.63}$$     (Hazen-Williams Hydraulic Radius)

$$v = C \; 1.318 \; r_h^{0.63} \; m^{0.54}$$

$$C = v \;/\; 1.318 \; r_h^{0.63} \; m^{0.54}$$

$$m = ( v \;/\; C \; 1.318 \; r_h^{0.63} )^{1 / 0.54}$$

### Solve for rh

 flow velocity, v Hazen-Williams coefficient, C hydraulic grade line, m

### Solve for C

$$r_h$$ = hydraulic radius $$ft$$ $$m$$
$$v$$ = mean flow velocity $$ft \;/\; sec$$ $$m \;/\; s$$
$$C$$ = Hazen-Williams coefficient, see below for values $$dimensionless$$
$$m$$ = hydraulic grade line slope $$dimensionless$$