A multidisciplinary approach for the study of an ancient drainage tunnel: preliminary results

A multidisciplinary approach is being used to investigate an ancient draining tunnel, about 70 m long, built in the roman age, used to supply drinkable water to the city of Spellum (now Spello, Central Italy). The surface geological and structural information of the site were integrated with the data acquired by Ground Penetrating Radar (GPR) extending surficial observations to the subsurface. In the surveyed area the outcrops are made up by the marly Scaglia Variegata and carbonatic Scaglia Rossa Formations, belonging to the Umbria Sequence. As it is well known, the GPR is a non-destructive geophysical tool that provides several advantages over other methods as it can provide continuous, high-resolution data allowing rapid field surveys where the required investigation depth is up to 20 m depth; however in the presence of freactured rocks, water and artificial manufacts many problems are still open. The initial acquisition of structural and stratigraphic measurements on the studied area allowed to plan and set up the radar survey to improve the following phase of interpretation of the geophysical data. The combined analysis of structural, stratigraphic and geophysical data allowed to map at high resolution the underground stratigraphic sequence around the drainage tunnel. It was also possible to detect the water table, and its spatial relationship with the tunnel. The results of this study, in spite of being still in an embryonic state, indicate that the approach can give interesting results: it will define with good details the geologic setting of the site and the local infiltration pattern, in order to provide all the necessary information to protect the historical resource.