The discharge of the pipelines supplying public fountains in Roman Pompeii

•The supply of a Roman small lacus fountain is estimated for Pompeii examples.•New data on Roman pipes’ roughness is defined through experimental work.•The discharge of a Roman pipeline can be calculated through a graphical method.•Figures obtaines for the flowrate supplied correspond to those previously estimated from the geometry of the basins’overflow channels. The public fountains of the ancient Roman town of Pompeii were supplied through pipelines descending from the nearby water towers. The water discharge was determined by the height of the water towers as well as the hydraulic features of the pipes, including the average diameter and the internal surface roughness. In the present study the possible connections between each fountain and the nearby water towers are assessed. Based on available elevation data and measurements taken in various survey campaigns, a range is defined for the pipeline hydraulic slope. The discharge of the pipelines is estimated through a graphical method, which can conveniently be applied by scholars of non-technical background; values of the diameter between those of the ancient Roman digitus and denaria, and values of the hydraulic absolute roughness ks between 0.1 and 0.5 mm are considered. For 47 connections of fountains to water towers, the discharge is calculated to be between 0.1 and 2.5 l/s. The original height of the towers 12 and 13, not reconstructed after the 62–63 CE earthquake, is estimated as close to 6 m. The values of discharge in the pipelines generally confirm the figures obtained in 2021 by Monteleone et al., in a study on the discharge of the Pompeian fountains overflow channels.