Hazen-Williams Equation
Fluid Mechanics · FE Reference Handbook section
Core formulas for this FE topic
Definitions, applicability, units, assumptions and worked examples for each relation.
Worked exam-style examples
The four ways this section is written on the real exam — thoughts first, then equations, then substitution.
the Hazen-Williams equation for a water distribution pipeline Given Hazen-Williams coefficient (C_HW) = 116.0; hydraulic radius (R_H) = 0.2100 m; slope of energy grade line (S) = 0.0161 m/m, determine the velocity (V) in m/s.
Given
Find
velocity (V), in m/s
Start with the thinking
- The governing relation printed in this handbook section is Hazen-Williams equation.
- Everything except V is given, so isolate V symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The Hazen-Williams equation estimates flow velocity in a pipeline given its roughness coefficient and slope.
Figure 1 — schematic for Hazen-Williams equation — solve for velocity — Hazen-Williams Equation
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange the relation so that V stands alone on the left-hand side.
Step 3 — List the givens: Hazen-Williams coefficient (C_HW) = 116.0, hydraulic radius (R_H) = 0.2100 m, slope of energy grade line (S) = 0.0161 m/m.
Step 4 — Substitute the given values into the rearranged relation.
Step 5 — Evaluate:
Step 6 — Check: returning V = 3.9632 m/s to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 7.9265 — kept a factor of two that cancels in the correct rearrangement.
- 1.9816 — dropped that same factor in the other direction.
- 4.3596 — rounded an intermediate value before the final step.
Reference: FE Handbook — Hazen-Williams Equation
the Hazen-Williams equation applied to a ductile-iron pipe Given hydraulic radius (R_H) = 0.1800 m; slope of energy grade line (S) = 0.0153 m/m; velocity (V) = 2.4000 m/s, determine the Hazen-Williams coefficient (C_HW).
Given
Find
Hazen-Williams coefficient (C_HW)
Start with the thinking
- The governing relation printed in this handbook section is Hazen-Williams equation.
- Everything except C_HW is given, so isolate C_HW symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The Hazen-Williams equation estimates flow velocity in a pipeline given its roughness coefficient and slope.
Figure 2 — schematic for Hazen-Williams equation — solve for Hazen-Williams coefficient — Hazen-Williams Equation (2)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange the relation so that C_HW stands alone on the left-hand side.
Step 3 — List the givens: hydraulic radius (R_H) = 0.1800 m, slope of energy grade line (S) = 0.0153 m/m, velocity (V) = 2.4000 m/s.
Step 4 — Substitute the given values into the rearranged relation.
Step 5 — Evaluate:
Step 6 — Check: returning C_HW = 79.5698 to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 159.1 — kept a factor of two that cancels in the correct rearrangement.
- 39.7849 — dropped that same factor in the other direction.
- 87.5268 — rounded an intermediate value before the final step.
Reference: FE Handbook — Hazen-Williams Equation
the Hazen-Williams equation to size a municipal pipe Given Hazen-Williams coefficient (C_HW) = 97.0000; hydraulic radius (R_H) = 0.2500 m; slope of energy grade line (S) = 0.0197 m/m, determine the velocity (V) in m/s.
Given
Find
velocity (V), in m/s
Start with the thinking
- The governing relation printed in this handbook section is Hazen-Williams equation.
- Everything except V is given, so isolate V symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The Hazen-Williams equation estimates flow velocity in a pipeline given its roughness coefficient and slope.
Figure 3 — schematic for Hazen-Williams equation — solve for velocity (case 2) — Hazen-Williams Equation (3)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange the relation so that V stands alone on the left-hand side.
Step 3 — List the givens: Hazen-Williams coefficient (C_HW) = 97.0000, hydraulic radius (R_H) = 0.2500 m, slope of energy grade line (S) = 0.0197 m/m.
Step 4 — Substitute the given values into the rearranged relation.
Step 5 — Evaluate:
Step 6 — Check: returning V = 4.1247 m/s to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 8.2494 — kept a factor of two that cancels in the correct rearrangement.
- 2.0624 — dropped that same factor in the other direction.
- 4.5372 — rounded an intermediate value before the final step.
Reference: FE Handbook — Hazen-Williams Equation
the Hazen-Williams equation for a water distribution pipeline Given hydraulic radius (R_H) = 0.0300 m; slope of energy grade line (S) = 0.0181 m/m; velocity (V) = 0.8000 m/s, determine the Hazen-Williams coefficient (C_HW).
Given
Find
Hazen-Williams coefficient (C_HW)
Start with the thinking
- The governing relation printed in this handbook section is Hazen-Williams equation.
- Everything except C_HW is given, so isolate C_HW symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The Hazen-Williams equation estimates flow velocity in a pipeline given its roughness coefficient and slope.
Figure 4 — schematic for Hazen-Williams equation — solve for Hazen-Williams coefficient (case 2) — Hazen-Williams Equation (4)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange the relation so that C_HW stands alone on the left-hand side.
Step 3 — List the givens: hydraulic radius (R_H) = 0.0300 m, slope of energy grade line (S) = 0.0181 m/m, velocity (V) = 0.8000 m/s.
Step 4 — Substitute the given values into the rearranged relation.
Step 5 — Evaluate:
Step 6 — Check: returning C_HW = 74.8944 to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 149.8 — kept a factor of two that cancels in the correct rearrangement.
- 37.4472 — dropped that same factor in the other direction.
- 82.3839 — rounded an intermediate value before the final step.
Reference: FE Handbook — Hazen-Williams Equation
the Hazen-Williams equation applied to a ductile-iron pipe Given Hazen-Williams coefficient (C_HW) = 139.0; hydraulic radius (R_H) = 0.1200 m; slope of energy grade line (S) = 0.0021 m/m, determine the velocity (V) in m/s.
Given
Find
velocity (V), in m/s
Start with the thinking
- The governing relation printed in this handbook section is Hazen-Williams equation.
- Everything except V is given, so isolate V symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The Hazen-Williams equation estimates flow velocity in a pipeline given its roughness coefficient and slope.
Figure 5 — schematic for Hazen-Williams equation — solve for velocity (case 3) — Hazen-Williams Equation (5)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange the relation so that V stands alone on the left-hand side.
Step 3 — List the givens: Hazen-Williams coefficient (C_HW) = 139.0, hydraulic radius (R_H) = 0.1200 m, slope of energy grade line (S) = 0.0021 m/m.
Step 4 — Substitute the given values into the rearranged relation.
Step 5 — Evaluate:
Step 6 — Check: returning V = 1.1112 m/s to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 2.2225 — kept a factor of two that cancels in the correct rearrangement.
- 0.5556 — dropped that same factor in the other direction.
- 1.2224 — rounded an intermediate value before the final step.
Reference: FE Handbook — Hazen-Williams Equation
the Hazen-Williams equation to size a municipal pipe Given hydraulic radius (R_H) = 0.1900 m; slope of energy grade line (S) = 0.0113 m/m; velocity (V) = 0.5500 m/s, determine the Hazen-Williams coefficient (C_HW).
Given
Find
Hazen-Williams coefficient (C_HW)
Start with the thinking
- The governing relation printed in this handbook section is Hazen-Williams equation.
- Everything except C_HW is given, so isolate C_HW symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The Hazen-Williams equation estimates flow velocity in a pipeline given its roughness coefficient and slope.
Figure 6 — schematic for Hazen-Williams equation — solve for Hazen-Williams coefficient (case 3) — Hazen-Williams Equation (6)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange the relation so that C_HW stands alone on the left-hand side.
Step 3 — List the givens: hydraulic radius (R_H) = 0.1900 m, slope of energy grade line (S) = 0.0113 m/m, velocity (V) = 0.5500 m/s.
Step 4 — Substitute the given values into the rearranged relation.
Step 5 — Evaluate:
Step 6 — Check: returning C_HW = 20.7576 to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 41.5153 — kept a factor of two that cancels in the correct rearrangement.
- 10.3788 — dropped that same factor in the other direction.
- 22.8334 — rounded an intermediate value before the final step.
Reference: FE Handbook — Hazen-Williams Equation
the Hazen-Williams equation for a water distribution pipeline Given Hazen-Williams coefficient (C_HW) = 126.0; hydraulic radius (R_H) = 0.1800 m; slope of energy grade line (S) = 0.0112 m/m, determine the velocity (V) in m/s.
Given
Find
velocity (V), in m/s
Start with the thinking
- The governing relation printed in this handbook section is Hazen-Williams equation.
- Everything except V is given, so isolate V symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The Hazen-Williams equation estimates flow velocity in a pipeline given its roughness coefficient and slope.
Figure 7 — schematic for Hazen-Williams equation — solve for velocity (case 4) — Hazen-Williams Equation (7)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange the relation so that V stands alone on the left-hand side.
Step 3 — List the givens: Hazen-Williams coefficient (C_HW) = 126.0, hydraulic radius (R_H) = 0.1800 m, slope of energy grade line (S) = 0.0112 m/m.
Step 4 — Substitute the given values into the rearranged relation.
Step 5 — Evaluate:
Step 6 — Check: returning V = 3.2113 m/s to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 6.4226 — kept a factor of two that cancels in the correct rearrangement.
- 1.6056 — dropped that same factor in the other direction.
- 3.5324 — rounded an intermediate value before the final step.
Reference: FE Handbook — Hazen-Williams Equation
the Hazen-Williams equation applied to a ductile-iron pipe Given hydraulic radius (R_H) = 0.2900 m; slope of energy grade line (S) = 0.0098 m/m; velocity (V) = 1.3500 m/s, determine the Hazen-Williams coefficient (C_HW).
Given
Find
Hazen-Williams coefficient (C_HW)
Start with the thinking
- The governing relation printed in this handbook section is Hazen-Williams equation.
- Everything except C_HW is given, so isolate C_HW symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The Hazen-Williams equation estimates flow velocity in a pipeline given its roughness coefficient and slope.
Figure 8 — schematic for Hazen-Williams equation — solve for Hazen-Williams coefficient (case 4) — Hazen-Williams Equation (8)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange the relation so that C_HW stands alone on the left-hand side.
Step 3 — List the givens: hydraulic radius (R_H) = 0.2900 m, slope of energy grade line (S) = 0.0098 m/m, velocity (V) = 1.3500 m/s.
Step 4 — Substitute the given values into the rearranged relation.
Step 5 — Evaluate:
Step 6 — Check: returning C_HW = 42.1554 to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 84.3108 — kept a factor of two that cancels in the correct rearrangement.
- 21.0777 — dropped that same factor in the other direction.
- 46.3709 — rounded an intermediate value before the final step.
Reference: FE Handbook — Hazen-Williams Equation
the Hazen-Williams equation to size a municipal pipe Given Hazen-Williams coefficient (C_HW) = 116.0; hydraulic radius (R_H) = 0.0300 m; slope of energy grade line (S) = 0.0122 m/m, determine the velocity (V) in m/s.
Given
Find
velocity (V), in m/s
Start with the thinking
- The governing relation printed in this handbook section is Hazen-Williams equation.
- Everything except V is given, so isolate V symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The Hazen-Williams equation estimates flow velocity in a pipeline given its roughness coefficient and slope.
Figure 9 — schematic for Hazen-Williams equation — solve for velocity (case 5) — Hazen-Williams Equation (9)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange the relation so that V stands alone on the left-hand side.
Step 3 — List the givens: Hazen-Williams coefficient (C_HW) = 116.0, hydraulic radius (R_H) = 0.0300 m, slope of energy grade line (S) = 0.0122 m/m.
Step 4 — Substitute the given values into the rearranged relation.
Step 5 — Evaluate:
Step 6 — Check: returning V = 1.0014 m/s to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 2.0027 — kept a factor of two that cancels in the correct rearrangement.
- 0.5007 — dropped that same factor in the other direction.
- 1.1015 — rounded an intermediate value before the final step.
Reference: FE Handbook — Hazen-Williams Equation
the Hazen-Williams equation for a water distribution pipeline Given hydraulic radius (R_H) = 0.1800 m; slope of energy grade line (S) = 0.0045 m/m; velocity (V) = 0.7000 m/s, determine the Hazen-Williams coefficient (C_HW).
Given
Find
Hazen-Williams coefficient (C_HW)
Start with the thinking
- The governing relation printed in this handbook section is Hazen-Williams equation.
- Everything except C_HW is given, so isolate C_HW symbolically first — never rearrange after the numbers are in.
- Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
- The Hazen-Williams equation estimates flow velocity in a pipeline given its roughness coefficient and slope.
Figure 10 — schematic for Hazen-Williams equation — solve for Hazen-Williams coefficient (case 5) — Hazen-Williams Equation (10)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange the relation so that C_HW stands alone on the left-hand side.
Step 3 — List the givens: hydraulic radius (R_H) = 0.1800 m, slope of energy grade line (S) = 0.0045 m/m, velocity (V) = 0.7000 m/s.
Step 4 — Substitute the given values into the rearranged relation.
Step 5 — Evaluate:
Step 6 — Check: returning C_HW = 44.9401 to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 89.8802 — kept a factor of two that cancels in the correct rearrangement.
- 22.4700 — dropped that same factor in the other direction.
- 49.4341 — rounded an intermediate value before the final step.
Reference: FE Handbook — Hazen-Williams Equation