Closed Conduit Hydraulics - Hazen Williams Equation

Hazen-Williams can be used to determine the flow characteristics in closed conduits (pipe systems).

For Velocity

S = slope, in decimal form. This is equivalent to

R = hydraulic radius,

C = Roughness Coefficient, get this from a table (available in both the AIO and CERM)

For Head Loss

To derive these  has been substituted for S.


The Hazen-Williams equation is similar to the Darcy-Weisbach equation, but it is only used for turbulent flow.

When to use Hazen-Williams

  1. You are only given C
  2. You prefer it and are sure the flow is turbulent (Reynolds number (Re) > 4000)
  3. You are directly told to (from the examples it looks like several problem prompts do this)

When to NOT use Hazen-Williams

  1. The flow is NOT turbulent (Re < 2100)
  2. You are given . If you are given a friction factor use Darcy-Weisbach

About Conrad

I am a Civil Engineer. I work in San Diego and am preparing to take the PE Exam. I am interested in surfing, business, travelling, and spending time with my wife. Thanks!

Posted in Water and Environmental Breadth and tagged , , , , , . Bookmark the permalink. Leave a Comment.

Leave a Reply

Your email address will not be published. Required fields are marked *