Lecture 13 Engineering a Roman Aqueduct

Understanding Greek and Roman Technology: From the Catapult to the Pantheon

Dr Stephen Ressler (2013)

Film Review

Ressler uses a scale model to demonstrate how an aqueduct relies on gravity and a slight downward gradient (averaging between 0.15 and 0.3% to produce a continuous flow of water. Allowing water to flow too fast eroded the aqueduct’s concrete channels. By the 3rd century AD, Rome was served by 11 aqueducts, delivering 300 million gallons of water per day.* A few of them carried river water, which tasted so foul it was only suitable for irrigation.

In drilling springs to source their aqueducts, Roman engineers chose a hillside where vegetation (eg bull rush and ivy) suggesting the aquifer (water table) was close to the surface. After installing a settling tank (to remove silt, sand and other debris) between the spring and the aqueduct, they used a corobate to measure gradient and develop a terrain profile.

The aqueduct itself was a concrete trough coated with a a lime and crushed brick mortar polished to a glass-like finish. This was covered by a concrete vault (interrupted with regular inspection shafts) to reduce evaporation and keep out foreign matter.

Wherever possibly they routed the aqueduct through underground trenches.

Where the gradient had to be raised (to achieve continuous flow) six feet or less, they used a solid stone or brick faced embankment called a substractio.

If it was between 6 and 70 feet, their used either a bridge or an inverted siphon made up of multiple parallel pipes.

Where it had to be raised 70 feet or more they used two or three tiered arcades to support the water channel. The use of multiple tiers shortened the arches and made them less susceptible to buckling. They only used tunneling as a lost resort. The longest Roman tunnel, 1.4 miles long, was built in 312 BC.

*New York City didn’t achieve this capacity until the 20th century.

Film can be viewed free with a library card on Kanopy.

https://www.kanopy.com/en/pukeariki/watch/video/146678/146704