Jan 12, 2022 · First use the Hazen-Williams equation to find the velocity of the fluid: v = k × C × R 0.63 × S 0.54.In this equation, k is either 0.489 for metric or 1.318 if using imperial units, C is the roughness coefficient of the pipe material, R is the hydraulic radius (cross-sectional area divided by perimeter), and S is the slope of the pipe.