What is Manning’s ‘n’ value?
The first comprehensive testing program to accurately determine roughness coefficients (n value) was conducted at the University of Iowa in 1924 on pipes that would be classified today as poor quality from both pipe surface and joints. Since that time, many pipe manufacturers and researchers have dramatically improved their hydraulic n values. This is particularly true of pipes and joints that were not available when the University of Iowa report was first published. Today, HDPE pipe manufacturers use a benchmark n value that is much lower than steel, aluminum, or concrete pipe, thus creating better flow-rates.
