Assessing the historical residual flood-risk evolution over large floodable areas: dependence of the results on the 2D hydrodynamic numerical model

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Francesca Carisi, Alessio Domeneghetti, Attilio Castellarin

Wednesday 1 july 2015

12:48 - 12:51h at South America (level 0)

Themes: (T) Flood risk management and adaptation, (ST) Flood risk assessment, Poster pitches

Parallel session: Poster pitches: 9J. FloodRisk - Assessment

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This study investigates the evolution of the flood risk along the middle-lower reach of the River Po (length ~350 km, Northern Italy). The analysis starts from the common perception that, due to a combination of different causes, the flood risk is dramatically increasing in Europe and in other areas of the world, which is supported by the steadily increasing economic flood losses recorded worldwide. We refer in particular to the residual flood-risk and we consider an inundation scenario simulated by means of a simplified quasi-two-dimensional (quasi-2D) hydrodynamic model that reproduces the hydraulic behavior of a large floodable area outside the main embankment system of the Po river (named “C-Buffer”) for an exceptional flood event with a 500-year return period; then we perform a detailed flood risk assessment for different land-use scenarios and population dynamics that have been observed for the C-Buffer over the last five decades. The detailed flood-risk assessment refers separately to four hydraulic compartments located within the C-Buffer, which according to the study inundation scenario are flooded during the exceptional event. In particular, the analyses use flood-damage curves proposed in the literature coupled with a reproduction of the inundation dynamics simulated by two fully two-dimensional (2D) hydrodynamic models based on 2D shallow water Saint-Venant equations: Hec-Ras 5.0 and Telemac-2D. The former model has been recently released and enables users to perform combined one_dimensional (1D) and 2D unsteady_flow simulations (i.e. combining 1D reaches and storage areas with 2D flow areas schematized with finite-volume method), while the latter is a widely employed and well known 2D finite-element scheme. The comparison enabled us to assess how recent land-use changes affected the residual risk in the study area and, indirectly, to quantify the dependence of flood-risk assessments on the considered 2D model, i.e. Telemac-2D and the new Hec-Ras 5.0.