Analysis of the vulnerability of the lagoon levees of the Po Delta to coastal flooding in a changing climate

This study analyses the coastal flooding hazard of the Po River Delta (Italy) area and develops a credible strategy for adaptation to climate change. The Po Delta, located in the north-western Adriatic Sea, is a peculiar coastal environment of great ecological and productive importance. The inland area is protected by different lines of levees, some of which are situated along river branches and others along the perimeters of the lagoons. Following the 1966 extreme storm event, the levees were raised and reinforced. Now, the predicted sea level rise and the subsidence affecting the area pose new warnings that require the possible upgrading of the levees surrounding the lagoons. Extensive field measurements and surveys are available and have been used to classify the 84 km long lagoonal levees. A set of numerical wave and surge results allows the overtopping and overflow discharges to be calculated with analytical tools to highlight the critical stretches along the defence. By 2070, considering the worst IPCC SSP5-8.5 scenario and a typical subsidence rate (6 ÷ 10 mm/y), it is found that ∼36 km of levees require mitigation measures to face the future projections and ∼15 km of them are associated with high level of hazard. The most vulnerable area is the Scardovari lagoon in the southern part of the Delta. The adaptation strategy includes raising the crest of the levees, improving the armour layer and, eventually, constructing low-crested structures or other wave attenuation options within the lagoons.