Analysis of coastal flooding hazard in low lying areas of the Northern Adriatic Sea

This note presents a method for producing coastal flooding hazard maps and its application to Lido delle Nazioni (Ferrara, Italy), a low-lying area of the Northern Adriatic sea protected by emerged barriers and a dike. The application is not part of a supported investigation but a mere example, the site being selected since a detailed altimetry was available, even though no specific information on dune resistance could be obtained. Some simplifying assumption are therefore made, the most strict being that flooding is only induced by overtopping, i.e. in the absence of dune breaching. MIKE21 flexible mesh tool is used for simulating several flooding scenarios induced by different combinations of waves and tide. By interpolating simulation results, a level II analysis based on the First Order Reliability Method (FORM) is used to produce maps giving the annual probability that flood level exceeds a given threshold. For instance, the most exposed urbanised areas have an yearly probability of 0.2% that flooding exceeds 1.0 m (0.01% that flooding exceeds 2.0 m). Hazard maps, usually evaluated by engineers, are the first step required to produce quantitative risk maps, for which also socio-economic expertise is needed.