GIS-based study of land subsidence in the city of Bologna

Geographic information systems (GIS) are very powerful tools capable of performing spatial analyses over large amounts of the territory representing large amounts of data. They consist of hardware, software, and human activities that facilitate collection, analysis, and storage of data, in different forms, related to the features of the territory. In the present chapter, the potential of the GIS tool is explored in a study of the effects of subsidence that occurred during the previous decades in the city of Bologna, where a valuable historic and cultural heritage made up of an intricate system of old masonry buildings, churches and monuments, is exposed and at risk. Data from previous geological, hydrogeological and geotechnical studies was collected and georeferenced. Then, topographical investigations and periodic records of the groundwater level in the network wells were superposed to establish a relation between causes and effects. The analysis reveals the spatial and temporal distribution of settlements in the city center and in the surrounding area. The evolution of the subsidence phenomenon has been possible, and the use of GIS has revealed the role of different factors and their mutual correlation. By combining all information, it can be seen that the area is severely affected by the distribution of total and differential settlements and that a particularly critical situation emerges in the city center. Additionally, the causes of the phenomenon could be established with great precision, enabling the identification of appropriate countermeasures.