# Chézy, Antoine de

## Contents

## Photograph[edit]

## Dates[edit]

Antoine de Chézy 1 September 1718 (Châlons-en-Champagne) – 5 October 1798 (Paris)

## Biography[edit]

Antoine de Chézy was a French hydraulics engineer. He studied and later taught in a local parochial school and entered at the age of 30 the new federal school in Paris which was later named the Ecole des Ponts et Chaussées. He obtained his degree from the Ecole and joined the Corps des Ponts et Chussées back in his birthplace at Châlons. Perronet, the first director of the Ecole, brought him back to Paris to be the head of the inspectorate of bridges and roads. In 1771 he advanced to Inspector Général and in 1782 to Director of the Ecole des Ponts et Chaussées. In 1790, during the French Revolution, he retired and lived in poor conditions until helped by one of his former students, the Baron Gaspard de Prony (1755-1839). In 1797 he returned as Director for one more year before his death. His son was the orientalist Antoine-Léonard de Chézy.

## Hydrological Achievements[edit]

In 1768 the Paris authorities commissioned Perronet and Chezy to investigate and design a new water supply system using the River Yvette which lay at a higher level and some distance from the city. It fell to Chezy to determine the cross-section of the canal and calculate the discharge. Since he could find nothing in the literature on the subject, he undertook his own investigation submitting his recommendations to Perronet in the form of a report. This report is lost but the files of the Ponts et Chaussées still contain his original manuscript. He sought a relationship between velocity and cross-sectional geometry and slope, establishing the Chézy formula, which first introduced the hydraulic radius (area / wetted perimeter) as a length scale. He noted:

"...it is evident that the velocity due to gravity, which acts continuously,.....is only uniform when it (the water) no longer accelerates, and gravity does not cease to accelerate except when its action upon the water is equal to the resistance caused by the boundary of the channel; ...but the resistance is as the square of the velocity because of the number and force of the particles colliding in a given time; it is also as the part of the perimeter of the section of the flow which touches the boundaries of the channel.”

The coefficient of proportionality in the formula is known as the Chézy roughness coefficient. Pony, his successor at the Ecole, published both the Chézy formula and his own more complex formula that involved by linear and quadratic velocity terms but Chézy's original report was only published a century later by Herschel in 1897. A formula effectively the same as Chézy's was proposed independently in Germany by Johann Albert Eytelwein (1764-1848).

## Reference Material[edit]

Source: Wikipedia page on Antoine de Chézy

Source: Hager, W., 2003, Hydraulicians in Europe 1800 - 2000, Volume 1, CRC Press.

Source: Sellin, R, WATER-RELATED EDUCATION, TRAINING AND TECHNOLOGY TRANSFER - Biographies of Eminent Water Resources Personalities, UNESCO Encyclopaedia of Life Support Systems