Technical Blog

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John Houle: Senior Technical Consultant, PVC Pipe Industry

John Houle holds a Master’s Degree in Civil Engineering from the University of Missouri and an MBA from the University of Oregon. He has more than 25 years of experience in the plastic pipe industry in applications engineering, market development, forensic analysis, technical writing, and standards development.

Manning's "n" for PVC Gravity Sewer Pipe

Posted By John Houle on Jan 12, 2017

“Conservative” design is taught continually to all engineers during college and throughout their employment. I think we can all agree that this is a good idea – we don’t want engineers to cut corners and cause potential problems.

However, sometimes the conservative designer refuses to take advantage of the engineering properties of the materials being designed. The result is over-conservative design that may not effectively use limited capital resources.

A case in point is hydraulic design of sewer pipe. Traditionally, engineers used a hydraulic factor called “Manning’s n” equal to 0.013. The advent of PVC sewer pipe in the 1960s made a smooth-walled pipe available with Manning’s n value of 0.009 (the lower the number, the better the flow.)

Fast-forward fifty years from the mid-60s to now and you will find that many engineers still use n = 0.013 for all sewer pipe materials! The result: more funds spent on larger pipes, on deeper excavations, and on more pump stations. For my Tech Brief on this subject, click here.