High‐resolution (Pixe) Analyses of Carbonate Deposits in a Roman Aqueduct (Fréjus, Se France): Implications for the Study of Palaeohydrological Variability and Water Resources Management in Southern Gaul During the Roman Period*

Abstract

Urban water was supplied to the Roman city of Forum Julii (Fréjus, southeastern France) for at least 200 years by a 39.4 km long aqueduct, operating in ad 50. Two perennial springs were successively collected, the Foux and the Siagnole, located at the outlet of Triassic and Jurassic karstic reservoirs, respectively. In this study, we performed high‐resolution PIXE (Particle‐Induced X‐ray Emission) measurements of Ca, Si, Fe and Sr concentrations on selected cross‐sections of laminated carbonate sampled along the sidewalls, before and after the connection of the two collection channels. Seasonal variations of water composition, suspended sediment load and discharge are recorded by alternating clear and dark layers, and can be traced by their Sr and Fe contents. On the basis of an annual bimodal high‐discharge regime for the two karstic reservoirs, the concentration measurements allow the derivation of a chronological record (117.5 years) of water supply and maintenance activities for a part of the operational period of the aqueduct. The water level in the channel was mainly controlled by the extent of carbonate deposition and by dredging, repair and maintenance operations rather than by the past hydrological regime of the two springs.

Laminated carbonate deposits in Roman aqueducts: Origin, processes and implications

“…Adolphe () and Guendon & Vaudour () found evidence for microbiological activity in calcareous sinter and claimed that this may have influenced the formation of the micritic laminae. These micritic laminae are enriched in Fe, Si and Al, possibly due to the presence of clay minerals (Rodier et al ., ; Guendon et al ., ; Carlut et al ., ; Bobée et al ., ). Guendon et al .…”

“…() published some spot δ 18 O analyses for the Fréjus aqueduct (southern France) showing a very similar range for different lamina couplets. Trace‐element data of calcareous sinter deposits were successfully applied to determine the provenance of water for the aqueducts of Fréjus and Pompeii, both of which were fed by more than one source (Ohlig, ; Guendon et al ., ; Bobée et al ., ). Finally, a number of previous studies tried to use calcareous sinter deposits in aqueducts to obtain information on palaeoseismicity (Meghraoui et al ., ; Volant et al ., ; Galli et al ., ; Sbeinati et al ., ).…”

The valens aqueduct of constantinople: hydrology and hydraulics

“…Whilst there have been some studies on the possible water-carrying capacity of Roman aqueducts (for example Keenan-Jones et al (2015); Motta et al (2017) previously cited). A few, including Bobée et al (2011) and Keenan-Jones (2013) have considered the amount of water available to flow into the aqueducts at various seasons, including some consideration of possible variations between ancient and modern times. Given the size and complexity of the Valens aqueduct catchment, the amount of water obtainable, or in modern terms, the hydrology of the catchment, must have been a serious consideration for its Roman designers.…”

X-ray Spectrometry

“…As a typical example of PIXE application in the research field of geochemistry, the laminated carbonate deposited on the side walls of Roman aqueducts was measured by PIXE . It was found that the thick and clear laminae of the carbonate layers were enriched with Sr, while Fe and Si were depleted in the thin and dark laminae.…”