The Manning formula, known also as the Gauckler–Manning formula, or Gauckler–Manning–Strickler formula in Europe, is an empirical formula

Empirical relationship

In science, an empirical relationship is one based solely on observation rather than theory. An empirical relationship requires only confirmatory data irrespective of theoretical basis. Sometimes theoretical explanations for what were initially empirical relationships are found, in which case the...

 for open channel flow

Open channel flow

Open-Channel Flow, a branch of Hydraulics, is a type of liquid flow within a conduit with a free surface, known as a channel. The other type of flow within a conduit is pipe flow. These two types of flow are similar in many ways, but differ in one important respect; the free surface...

, or free-surface flow driven by gravity. It was first presented by the French engineer Philippe Gauckler in 1867, and later re-developed by the Irish

Irish people

The Irish people are an ethnic group who originate in Ireland, an island in northwestern Europe. Ireland has been populated for around 9,000 years , with the Irish people's earliest ancestors recorded having legends of being descended from groups such as the Nemedians, Fomorians, Fir Bolg, Tuatha...

 engineer

Engineer

An engineer is a professional practitioner of engineering, concerned with applying scientific knowledge, mathematics and ingenuity to develop solutions for technical problems. Engineers design materials, structures, machines and systems while considering the limitations imposed by practicality,...

 Robert Manning

Robert Manning (engineer)

Robert Manning was an Irish engineer. He is known for creation of the Manning formula.Manning was born in Normandy, France, in 1816, a year after the battle of Waterloo, in which his father had taken part. He died in 1897...

 in 1890.

The Gauckler–Manning formula states:


where:

The discharge

Discharge (hydrology)

In hydrology, discharge is the volume rate of water flow, including any suspended solids , dissolved chemical species and/or biologic material , which is transported through a given cross-sectional area...

 formula, Q = A V, can be used to manipulate Gauckler–Manning's equation by substitution for V.