# Trivial Water and Sewer Fun Stuff

Robert Manning was an Irish engineer. He is known for creation of the Manning formula.

Manning and his mother moved to Waterford, Ireland, in 1826 after the death of his father, where he eventually worked as an accountant for his uncle, John Stephans, from 1834 through 1845. The first phase of Manning's career as a civil engineer came in 1846 when he was drafted into the Arterial Drainage Division of the Irish Office of Public Works due to an expansion of this office during the Irish famine years.

Initially a clerk, accountant, and draftsman, he was eventually appointed later that year as an assistant engineer to Samuel Roberts in his first year. Upon Roberts' transfer in 1848, Manning was appointed as District Engineer on the Ardee and Glyde works , a position he held until 1855. From 1855 to 1869, Manning was employed by the Marquis of Downshire, during which time he conducted surveys of estates in Ireland, oversaw construction of the Dundrum Bay Harbor, and designed a water supply system for the city of Belfast. After the Marquis’ death in 1869, Manning was not reappointed to the position, so he returned to the Office of Public Works in 1869 as Assistant to the Chief Engineer.

In October 1869 Manning was appointed Second Engineer in the Office of Public Works and on April 1, 1874 was appointed Chief Engineer a position he held until his retirement in 1891. As Chief Engineer, he was in charge of all engineering works for the department, and was responsible for numerous harbor, navigation, arterial drainage, and sewerage projects, including work at the five Royal harbors, nearly 200 fishery piers and harbors, of which he designed and constructed upwards of 100, and improvement works on the River Shannon.

During the 1860s, Manning studied the classical 19th century experiments on open channel flow where he carried out extensive scientific studies on aspects of rainfall, river volumes and water runoff and ventured into new areas of theory and practice. This resulted in his classic paper in 1889 entitled “On the flow of water in open channels and pipes” published in Transactions of the Institution of Civil Engineers of Ireland. In the end, this paper became the primary reference for his work and the source of Manning's monomial equation.

It is interesting to note that Manning received no formal training in fluid mechanics or engineering and would have likely remained an accountant/ clerk had it not been for the Irish famine.

In an 1895 paper, Manning describes how he "devoured" the Traite d‘Hydraulique of d'Aubisson des Voisons as a newly appointed District Engineer in 1848 in order to teach himself hydraulics.

Manning compared and evaluated seven best known formulas of the time: Du Buat (1786), Eyelwein (1814), Weisbach (1845), St. Venant (1851), Neville (1860), Darcy and Bazin (1865), and Ganguillet and Kutter (1869). During this period, Manning devoted considerable effort to the development of a simple, dimensionally homogeneous formula for open-channel flow. He calculated velocities obtained from each formula. Then found the mean value of the seven velocities and developed a formula that best fit the data. On December 4, 1889, at the age of 73, Manning first proposed his formula to the Institution of Civil Engineers of Ireland.

When trying to understand the applicability and limitations of any analytical tool, the user must understand the context in which it was developed and the use for which it was intended.

Robert Manning in his Presidential Address to the Institution of Civil Engineers of Ireland:

“And now a few words, again addressed to the younger members, with regard to the use of formulae. I very much fear that if I were to illustrate any observations I have to make with chalk on the black-board, a dozen note-books would be taken out, the formula copied without investigation, probably to my discredit, and eventually worked to death. It should be remembered that a formula is only a short memorandum (put in a shape fit for ready use) of the result arrived at after a patient consideration of the facts and principles upon which it is founded, and to use it without investigation is the merest empiricism.”

The application of the Manning equation presumes that a measure of resistance (e.g. the value of n) is known or can be accurately estimated. Considerable research focused on developing good resistance coefficients to bed material size or type of bed form. Thus, for fixed beds and alluvial channels in which resistance is due primarily to grain resistance, reasonable estimates can be made using any number of techniques. Guidance for estimating resistance coefficients when vegetation, boulders, or other large resistance elements are present is much more elusive.

Manning did not like his own equation for two reasons:

- It was difficult in those days to determine the cube root of a number and then square it to arrive at a number to the 2/3 power.
- The equation was dimensionally incorrect, and so to obtain dimensional correctness he developed the following equation:

Manning described this equation as "entirely empirical" and suggested that this better approach should be used. In his 1895 paper, Manning did not include the earlier equation, but rather suggested the latter as the appropriate formula and named it after himself.