Hazen-Williams equation:

It was developed for water flow in larger pipes (D≥5 cm, approximately 2 in.) within a moderate range of water velocity (V≤3 m/s, approximately 10 ft/s). Hazen-Williams equation, originally developed for the British measurement system, has been written in the form

Module 16 Lesson 26 HazenWilliams Equation

S= slope of the energy grade line, or the head loss per unit length of the pipe (S=hf/L)

Rh = the hydraulic radius, defined as the water cross sectional area (A) divided by wetted perimeter (P). For a circular pipe, with A=πD2/4 and P=πD, the hydraulic radius is

Module 16 Lesson 26 1.1 HazenWilliams Equation

CHW= Hazen-Williams coefficient. The values of CHW for commonly used water-carrying conduits are given in Table 1.2.

The Hazen-Williams equation in SI units is written in the form of

Module 16 Lesson 26 1.2 HazenWilliams Equation

Velocity in m/s and Rh is in meters

Module 16 Lesson 26 1.3 HazenWilliams Equation

Manning’s Equation

Manning equation has been used extensively open channel designs. It is also quite commonly used for pipe flows. The Manning equation may be expressed in the following form:

 Module 16 Lesson 26 1.1 MANNING’S EQUATION

n= Manning’s coefficient of roughness. Typical values of n for water flow in common pipe materials is given in Table 1.3

In British units, the Manning equation is written as

Module 16 Lesson 26 1.2 MANNING’S EQUATION

Where V is units of ft/s.

Module 16 Lesson 26 Table. MANNING’S EQUATION

Last modified: Tuesday, 8 October 2013, 9:53 AM