<p>Extreme events can cause damage to coastal defences resulting in overtopping, breaching, or their total destruction. The resulting flood can impact the population and assets, causing short- to long-term losses to the economy. Two examples of extreme coastal storms are the Katrina Hurricane (2005) in the USA, and the Xynthia storm (2010), in France. The Northern Adriatic Sea is often impacted by coastal storms, impacting residential and commercial areas. The region of Emilia-Romagna (Italy) is so often affected that it is common practice to create an artificial dune on the beach during winter to protect the properties.<br />On 22 November 2022, a coastal storm developed in the Northern Adriatic Sea, impacting the coasts of Veneto and Emilia-Romagna Italian regions. This storm, coming from ESE, was characterised by non-extreme waves, but coincided with spring tides, producing an extreme surge, reaching a total water level of 1.48 m above MSL, recorded for the first time by tide gauge at Porto Garibaldi (Comacchio), which corresponds to a return period greater than 100 years. The Saint Agatha storm that hit the same areas in 2015, reached a TWL of 1.2 m at the same location. The event of November 2022, caused damages on the coast, erosion of beaches, artificial and natural dunes, damage to coastal infrastructures, and flooding of residential buildings and local business activities.&#160;<br />While this storm represented a success for the MOSE, which succeeded in protecting the lagoon of Venice against one of the most hazardous events of the last decades, its effects on the Ferrara coasts were, in some cases, devastating. The most affected area was the Lido di Volano (Comacchio), where the extreme event caused a dike breach in the inner part of the Po di Volano mouth, leading to the recurring flooding of the town, due to the high spring tides that followed the storm. Indeed, the breach remained open for several days after the event. The event required the heavy involvement of first responders.<br />The site was surveyed on 23 and 25 November 2022. The research team measured flood extension and flood markers with the use of DGPS and aerial images, while UAV aerial surveys were implemented on the emerged beach to assess the morphologic impacts.<br />The flood associated with the extreme event was simulated using a hydrodynamic model (LISFLOOD-FP) to verify the causes and evolution of the flood event. The model was set up using topo-bathymetric data from 2019, water levels from the tide gauge of Porto Garibaldi. &#160;A thorough calibration was implemented using the fieldwork data. The model was used to simulate scenarios considering different dike-breach configurations and/or forcing it with other recent events (e.g. Saint Agatha, 2015).&#160;<br />The model was able to properly simulate the flooding event of November 2022. The tested scenarios highlighted the role of the magnitude of the event and the effects that a breaching dike can have on the associated areas. This is a contribution to the ECFAS project (EU H2020 GA 101004211).</p>
Abstract. Coastal flooding is recognized as one of the most devastating natural disasters, resulting in significant economic losses. Therefore, hazard assessment is crucial to support preparedness and response to such disasters. Toward this, flood map databases and catalogues are essential for the analysis of flood scenarios, and furthermore can be integrated into disaster risk reduction studies. In this study and in the context of the ECFAS project (GA 101004211), which aimed to propose a European Copernicus Coastal Flood Awareness System, a catalogue of flood maps was produced. The flood maps were generated from flood models developed with LISFLOOD-FP for defined coastal sectors along the entire European coastline. For each coastal sector, fifteen synthetic scenarios were defined focusing on high-frequency events specific to the local area. These scenarios were constructed based on three distinct storm durations and five different Total Water Level (TWL) peaks incorporating tide, mean sea level, surge and wave set-up components. The flood model method was extensively validated against twelve test cases for which observed data were collated using satellite-derived flood maps and in situ flood markers. Half of the test-cases well represented the flooding with hit scores higher than 80 %. The synthetic scenario approach was assessed by comparing flood maps from real events and their closest identified scenarios, producing a good agreement and global skill scores higher than 70 %. Using the catalogue, flood scenarios across Europe were assessed, and the biggest flooding occurred in well-known low-lying areas. In addition, different sensitivities to the increase of the duration and TWL peak were noted. The storm duration impacts a few limited flood prone areas such as the Dutch coast for which the flooded area increases more than twice between a 12 h and 36 h storm scenarios. The influence of the TWL peak is more global, especially along the Mediterranean coast for which the relative difference between a 2- and 20-year return period storm is around 80 %. Finally, at a European scale, the expansion of flood areas in relation to increases in TWL (Total Water Level) peaks demonstrated both positive and negative correlations with the presence of urban and wetland areas, respectively. This observation supports the concept of storm flood mitigation by wetlands.
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