Manning’s Equation, Its Derivation, and Its Purpose

For water resource engineers, Manning’s equation is almost ubiquitous. But what does it do?

The equation was first developed by French engineer Philippe Gaspard Gauckler in 1867, but it was fully developed by Robert Manning in 1890. This equation was created to estimate the average velocity of water flowing in an open channel in areas where it cannot be accurately measured. This equation relies on several factors, including the roughness coefficient of the pipe, the slope of the water surface, and the channel’s geometry. As a result, an engineer can easily estimate velocity in a pipe.

This is important for water resource engineers for one reason: self-cleaning. In wastewater and stormwater pipes, it is difficult for pipes to be cleaned after they have been constructed. That is why the pipe has to have its liquid flow at a fast enough velocity in order for the pipe to clean itself.

In water resource engineering, engineers have to be mindful of this equation in order to create an effective pipe system. If a system does not clean itself, it leaves lots of room for clogging, and will hurt vital waterways in the area it is constructed.