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Less flow from Roman aqueduct.

ANCIENT ROME WAS A CITY DEPENDENT ON IMPORTED water. Beginning in 312 BCE, the city built a series of aqueducts to supply water from the surrounding region to support a population that would reach as high as a million by the beginning of the imperial period.

But for their size and the degree of documentation, there's no agreement on how much water the aqueducts conveyed. A study published in June in the Journal of Archaeological Sciences examined the buildup of limestone deposits in the flow channel of one aqueduct supplying Rome and determined that final flow reaching the city was significantly smaller than had been previously estimated.

The researchers from the University of Illinois, Urbana-Champaign, looked at a surviving portion of the Anio Novus aqueduct, which was finished in 52 CE. This expansion of the Roman water system tapped into the somewhat muddy Aniene River more than 50 miles east of the city and delivered it to a large cistern that mixed together water from several sources for distribution across the city. The aqueduct was likely still in service during the reign of the last emperor of the Western Roman Empire in the fifth century.

How much water this or any other aqueduct could carry in ancient times has been disputed. According to the geologist Duncan Keenan-Jones, lead author of the study, and his colleagues, a CE 97 account from Roman water commissioner Sextus Julius Frontinus is riddled with discrepancies and did not account for flow velocity, relying instead on a simple cross section of the water held in the aqueduct in the channels.

To get a better estimate the researchers examined a surviving section of the aqueduct and measured the residue of travertine limestone that remained in the channel. They then modeled how that limestone would have coated the walls of the channel while the aqueduct was operational, and how much water must have flowed over the centuries to have left that much travertine behind.

According to the model, the aqueduct was almost always full of water. But the shallow slope of the aqueduct caused the flow rate to be much less than previously estimated, and the gradual constriction of the channel due to the mineral buildup would have cut the flow rate even further. If the Anio Novus aqueduct as constructed could have provided as much as 3.2 cubic meters a second, by the time the water stopped flowing the rate was down to just 1A cubic meters, or about 370 gallons.

What's more, the authors write, even a small coating of travertine on the aqueduct wall could have cut the flow rate by as much as 25 percent.

If other parts of the Roman water system suffered from similar mineral buildup, the gradual reduction in water supply would have put pressure on the city's large population. Even if it took German barbarians to finally kill the empire, the city already may have been slowly dying of thirst.

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Title Annotation:TECH BUZZ
Publication:Mechanical Engineering-CIME
Geographic Code:4EUIT
Date:Aug 1, 2015
Words:491
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