Hazen-Williams Headloss in a Water Main
Mediumwater distributionheadlosshazen-williams
A 300 mm diameter ductile iron water main 1,200 m long has a Hazen-Williams coefficient C = 130 and carries 0.10 m3/s. The friction headloss over this length is most nearly:
- A3.1 m
- B5.4 m
- C7.7 m
- D12.0 m
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Answer: C. 7.7 m
Area A = πD²/4 = π(0.30)²/4 = 0.0707 m², so V = Q/A = 0.10/0.0707 = 1.42 m/s. The hydraulic radius of a full circular pipe is Rh = D/4 = 0.075 m. Rearranging the SI Hazen-Williams form V = 0.849 C Rh0.63 S0.54 for the slope gives S = 0.00643, and hf = SL = 0.00643 × 1,200 ≈ 7.7 m. A common slip is using D rather than D/4 for the hydraulic radius, which understates the loss.
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