HazenWilliams Equation
HazenWilliams equation is an empirical formula used in civil engineering and fluid dynamics to calculate the flow rate of water in a pressurized pipe or conduit. It is commonly employed to estimate the flow of water through pipes for various applications, such as water distribution systems, municipal water supply, and plumbing design. It's important to note that the HazenWilliams equation is primarily used for water flow calculations in relatively simple systems where the flow is pressurized and steady. It is less accurate for situations with turbulent flow or nonwater fluids. For such cases, more complex equations like the DarcyWeisbach equation or computational fluid dynamics simulations are often used.
HazenWilliams Equation 

\( v = k \; C \; r_h^{0.63} \; S^ {0.54} \) (HazenWilliams Equation) \( C = v \;/\; k \; r_h^{0.63} \; S^ {0.54} \) \( r_h = \left( v \;/\; k \; C \; S^{0.54} \right)^{ \frac{1}{0.63} } \) \( S = \left( v\;/\; k \; C \; r_h^{0.63} \right)^{ \frac{1}{0.54} } \) 

Solve for v
Solve for C
Solve for rh
Solve for S


Symbol  English  Metric 
\( v \) = mean flow velocity (flow rate)  \(ft\;/\;sec\)  \(m\;/\;s\) 
\( k \) = conversion factor (1.318 English units) (0.849 Metric units)  \(dimensionless\)  \( dimensionless \) 
\( C \) = HazenWilliams roughness coefficient  \(dimensionless\)  \( dimensionless \) 
\( r_h \) = hydraulic radius  \(in\)  \(mm\) 
\( S \) = slope of energy grade line (head loss per unit of pipe \(\frac{h_l}{l}\))  \(ft\)  \(m\) 