Reconstruction and Analysis of the Po River Inundation of 1951

Flood inundation models have become essential tools in flood risk management, being used also in the analysis of historical flood events, which is often needed for a reliable assessment of the potential flood hazard. This study aims at reconstructing the 1951 inundation of the Polesine Region, Italy. The 1951 flooding was a mayor natural catastrophe that caused a large inundated area (1080 km2) and produced devastating social consequences. The reconstruction of the 1951 hydraulic conditions is based on partial knowledge of discharges and water stages at the Pontelagoscuro gauging station (downstream of the 1951 levee breach) using extrapolation of the rating curves beyond the measurement range. This is, even today, something open to uncertainty. We applied a decoupled hybrid approach to the hydraulic modeling: a 1D model is used to simulate the flow into the river and to compute the flow through the levee breach; this result is then adopted as the inflow condition for a 2D model application on the inundated area. A good agreement between the patterns of the observed and reconstructed inundation areas was found, and the timing of the inundation was also found to be close to the information derived from the historical chronicles. The results of the flood inundation modelling exercise provide two practical insight: (i) obstacles in the floodplains increased the flooded area by 40% and prolonged the time to reach the sea from 5 to 15 days, (ii) the peak discharge of the event was overestimated by up to 20