Three-dimensional hydraulic characterisation of the Arno River in Florence

Rivers in historical cities, such as the Arno River in Florence, are typically characterised by unique complex‐shaped hydraulic structures (such as bridges and weirs). The flow interaction with these structures can lead to a fully 3D flow field which cannot be properly investigated with commonly employed 1D, and even 2D, hydraulic models. Nowadays, 3D computational fluid dynamics (CFD) tools can be successfully used in river management context. Florence is characterised by a high risk of flooding and the disastrous consequences of such events being greatly increased due to its inestimable artistic heritage. The main cause of flooding is the limited hydraulic conveyance capacity of the Arno River in Florence due to several complex hydraulic structures along the reach. The present work represents the first 3D hydraulic model of the Arno River in the urban reach of Florence. The geometric model was created using the 3D bed topography of the river surveyed in 2015. The hydraulic model was calibrated and validated using discharge and water stage field data measured in 2016. The 3D model can be used as a more realistic tool for exploring mitigation solutions for the reduction of hydraulic risk.