Roman Aqueduct Flow Estimation Using Geomatic Measurement

Abstract

The aqueducts built by the ancient Romans are among the most impressive evidence of their engineering skills. The water inside the aqueducts was transported for kilometers, exploiting only the slight but constant differences in altitude throughout the route. To keep the differences in height constant, the aqueducts could proceed underground or aboveground on well-known arched structures that supported lead, ceramic or stone pipes. In order to reconstruct the characteristics of these structures, it is necessary to carry out an accurate survey of the orthometric heights, and therefore the most suitable technology is geometric levelling. In this case, however, it is not applicable, and therefore here we propose an alternative methodology. The final goal of this work was to estimate the flow of some sectors of these aqueducts preserved in the area south of the city of Rome. This has two main purposes: The first is to reconstruct the flow rate of these aqueducts for historical studies; the second is to check how much the orthometric heights have changed over the centuries, in order to reconstruct the movements from a geophysical and geodynamic point of view. The latter analysis will be developed in a following phase of this research. For this purpose, a high-precision geomatic survey was carried out in the area under study, partly retracing a survey already carried out in 1917 whose purpose and methodologies are not known. The area has been affected by a gradual subsidence over centuries, including since 1917. The observed sections of the aqueducts showed average inclinations, slightly lower than the 2 per thousand that is reported in the literature for similar aqueducts. The measurements carried out allowed the flow rate of the two specific aqueducts to be estimated more accurately, both as they were originally and in the presence of deposits that have accumulated during the years of use of the aqueducts. The reconstruction of the initial geometry will later be used as a reference to estimate how much the geodynamic deformations of the area have deformed the aqueducts themselves.

Technical observations about a possible new portion of the Aqua Iulia Roman aqueduct in the municipality of Ciampino (Italy).

“…However, as it seems clear from the figure 2 they were also used as pivot points to determine aqueduct path: a significative change in direction of the latter can be indeed observed at each of them. The slope is much greater than the usual slope for the aqueducts over the arches (in opere arcuate) which varies between 0.1% and 0.2% (Alimonti et al, 2018;Alimonti et al, 2021;Corbellini et al, 1917). This difference might be due to the different in strength between the artificial structures (the arches) and the underground portions: the latter can obviously support greater pressures.…”

Ancient landscape reconstruction using archive data from the Pontine Plain (Italy): the Caprolace lagoon case study

“…Generally, a good agreement is observed, even higher than expected, considering the accuracy of about 1.8 metres assumed for the cartography and that of 0.4 metres declared for the laser scanning. In figure 3 it is possible to observe the contribution of the proper correction of the altimetry due to the different datum used then and now (42cm added to the IGM DEM; Alimonti et al, 2021). After the correction, the area where virtually no difference could be observed and the values were close to 0 becomes much larger.…”

“…Unfortunately, detailed information on the IGM map datum cannot be conclusively ascertained (Mori, 1922). We then use the planimetric (Baiocchi and Lelo, 2010) and the altimetric (Alimonti et al, 2021) information used in some contemporary maps of the area of Rome. The cartography has been reprojected in the currently used datum (EPSG:7792; EPSG, 2021) and then interpolated in QGIS using an algorithm based on the TIN networks that allow estimating the terrain even in flat areas.…”