Protecting heritage cities from pluvial flooding: the Santa Croce district in Florence

In the study, we investigate the hazard related to pluvial flood to which the cultural heritage located in the most vulnerable areas of Santa Croce district (Florence, Italy) is exposed. This area is threatened by different sources of flood hazard: river flooding since it lies next to the Arno River; surcharging and overflowing of one of the main sewer conduits of the city, the Chiesi sewer pipe (named as the designer engineer Flaminio Chiesi); surface runoff flowing from the upper basin to the river. The comprehensive hazard assessment is carried out exploiting a 1D/2D dual drainage model so to simulate the interactions between all hydraulic phenomena occurring both on the surface and underground. Different scenarios are designed and simulated to evaluate each possible concatenation of events or failures. The hydraulic model is implemented at a multi-scale resolution including: the high-resolution digital surface model of the city and the Arno River, the public sewer network, and the internal Rainwater Drainage System (RDS) of the historical buildings. Detailed historical research and field surveys have been conducted for drawing the forgotten technical design of the internal RDS of the National Central Library of Florence. The hydraulic model allows highlighting the critical nodes within the drainage network and identifying which areas are more exposed and where to focus the rescue efforts in case of extreme events. Hence, the results may also help site and city managers to increase the emergency plans efficiency. Moreover, the purpose of the study is to propose suitable technical and functional solutions for protecting and decreasing the vulnerability of the cultural heritage in a context where planning structural defence works are hardly compatible with the historical urban texture.