Evaluation of coastal vulnerability to flooding: comparison of two different methodologies adopted by the Emilia-Romagna region (Italy)

Abstract

Abstract. This paper aims at presenting and comparing two methodologies adopted by the Emilia-Romagna region, northern Italy, to evaluate coastal vulnerability and to produce hazard and risk maps for coastal floods, in the framework of the EU Floods Directive. The first approach was adopted before the directive had been issued. Three scenarios of damage were designed (1-, 10-, 100-year return periods), produced by the concurrent occurrence of a storm, high surge levels and high-water spring tidal levels. Wave heights were used to calculate run-up values along 187 equally spaced profiles, and these were added to the tidal and atmospheric water level contributions. The result is a list of 10 vulnerability typologies. To satisfy the requirements of the directive, the Geological, Seismic and Soil Service (SGSS) recently implemented a different methodology that considers three scenarios (10-, 100-and > 100-year return periods) in terms of wave setup (not including run-up) plus the contribution of surge levels as well as the occurrence of high-water springs. The flooded area extension is determined by a series of computations that are part of a model built into ArcGIS ® . The model uses as input a high-resolution lidar DEM that is then processed using a least-path cost analysis. Inundation maps are then overlapped with land use maps to produce risk maps. The qualitative validation and the comparison between the two methods are also presented, showing a positive agreement.

Validation of the coastal storm risk assessment framework along the Emilia-Romagna coast

“…bathtub) along profile lines could work in areas were the back barrier topography increases monotonically landwards. In low-lying areas, like the RER coastline, the bathtub approach leads to the overestimation of the flooding extension, as claimed by Gesch (2009), Murdukhayeva et al (2013 and Perini et al (2016). It is suggested to use bi-dimensional flood maps for CRAF Phase 1, whenever they are available.…”

“…Two main hazards are considered: inundation and erosion. The inundation hazard was taken into account on the basis of the data already available at the regional level, produced for the Floods Directive (2007/60/EC) by SGSS, and on the method described in the paper by Perini et al (2016) that will be presented hereafter. The methodology followed to analyse the erosion hazard is along the lines of the general methods described in Viavattene et al (2017) and will be briefly described in the next paragraphs.…”

“…The tool was calibrated and the maps were validated considering historical information on past and more recent flooding events for which the inundation extension was available. More details can be found in the paper by Perini et al (2016). The polygons provided by SGSS ; grid 5 in their Fig.…”

“…1) is particularly exposed to erosion and inundation hazards (Armaroli et al, 2012;Perini et al, 2016) because of its low-lying nature and high coastal urbanization. Consequently, there is an increasing demand for effective methodologies to properly evaluate coastal risk, which in the RISC-KIT project was defined as the probability of a hazard and its impacts (consequences) (Viavattene et al, 2015).…”

Flood protection structure detection with Lidar: examples on French Mediterranean rivers and coastal areas

“…Indeed as noted by Perini et al [3], to compute hydraulic models on large area the resolution of DTM is often lowered, which leads to a reduction of the accuracy of flood maps despite a more realistic hydraulic computation.…”