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The Hazen-Williams head loss equation is as follows:

 

where:

 

H = head loss (m or ft) in pipe

L = length of pipe (m or ft)

d = diameter of pipe (m or ft)

Q = flow rate in the pipe (m3/s or cfs)

C = Hazen-Williams roughness coefficient

 

 

The Hazen-Williams coefficient C varies from about 150 for smooth pipes, to about 70 for very rough pipes. Appendix C lists typical values of C for different pipe materials.