Roman Aqueducts: Hydrology versus Hydraulics !?

Roman aqueducts supplied water to cities for public baths and toilets in addition to public fountains (HODGE 1992, FABRE et al. 2000). They were long subterranean conduits, following contour lines. Numerous aqueducts were used for centuries and some are still in use (e.g. Carthage, Mons). Their construction was a huge task, often performed by the army under the guidance of military hydraulic engineers. Their cost was extra-ordinary considering the real flow rate (less than 400 l/s) : i.e., about 1 to 3 million sesterces per kilometre on average (FEVRIER 1979, LEVEAU 1991). Today this would represent about 20 to 60 million US$ per km. For comparison, the construction of the Tarong water pipeline (Australia, 70 km long, Q = 0.9 m3/s) costed about 100,000 US$ per km in 1994. Despite superb ruins, little is known of the hydraulic engineering of the Roman aqueducts. What was the flow rate? How did they operate? How were they designed? In this note, it is argued that the hydraulics of the aqueducts was limited by their catchment hydrology. Four aqueduct systems are discussed and the results demonstrate severe hydrological limitations during dry periods, implying for some form of dynamic regulation