Late Quaternary environmental evolution of the Como urban area (Northern Italy): A multidisciplinary tool for risk management and urban planning

The historical center of Como (Northern Italy) is prone to lake flooding and subsidence, due to the presence of unconsolidated silty sediments with poor mechanical properties. The sedimentary basin beneath the town contains over 180 m thickness of Late-Quaternary lacustrine, palustrine and alluvial deposits. The landscape evolution and the present-day environmental setting of the Como area have been reconstructed based on (i)more than 250 core logs and related geotechnical tests, (ii) detailed stratigraphic, sedimentological, paleobotanical and geotechnical analysis of several key boreholes, (iii) multi-year hydrogeological monitoring, (iv) estimation of subsidence rates and (v)integration of geomorphology, archeological findings and historical documents. Based on our environmental analysis, we derived an integrated geological and geomorphological model of the latest Pleistocene to Holocene local landscape evolution. This model was used to help design an engineering facility to mitigate flood hazards in the Como urban area. In 2012, we carried out investigations during a re-evaluation of the design parameters for the flood mitigation project at the Como lake-shore. The new campaign included seven boreholes, many in situ and laboratory tests, and four 14C dates. We found an organic silty unit, historical in age, with bad mechanical properties that was critical in the design of the flood mitigation project. We also obtained index properties for static and dynamic conditions, necessary for robust engineering planning. The results were used to update the project and better define future executive phases. Although the importance of acquiring independent experimental data is often overlooked, they can significantly improve the reliability of engineered systems, as demonstrated by the Como town case history.