Man-induced changes in urban geomorphology: the historic centre of Bologna (Italy)

Abstract

The city of Bologna has been continuously inhabited for about three thousand years, though there have been phases of retreat and subsequent reoccupation. The urbanisation works over the years modified the territory on which the inhabited centre rose up. In particular, a continual accumulation of rubble determined the raising of the original level that Bologna was built on. Reconstruction of the city’s present day morphology was made possible through the gathering of spot elevations from largescale maps and the subsequent creation of a digital elevation model. From this reconstruction, it was possible to obtain a first morphological representation which highlights the presence of an extensive alluvial fan and a raised area of chiefly artificial origin. Using in situ archaeological finds, dating from the Iron Age to the Roman period, it was possible to reconstruct the old ground level in a part of the present historic centre of the city. Comparison between the old and actual ground levels permitted identification of the areas in which anthropic intervention most significantly altered the morphology. In particular it seemed clear how in the parts where settlement was continuous for almost three thousand years, the surface was raised on average more than two and a half metres, with peaks reaching more than four metres. Where urbanisation works underwent prolonged interruptions, the ancient surface is usually at a depth of less than two metres and locally is very close to the actual ground level.