Flood Risk Assessment in Ria de Aveiro Under Present and Future Scenarios

摘要

Floods are a major threat to coastal regions, affecting millions of people, socioeconomic activities and natural ecosystems. Ria de Aveiro is a coastal lagoon, particularly threatened by floods, facing permanent changes motivated by both natural and anthropogenic factors. Consequently, the main aim of this study is to assess flood risk for floods of oceanic, fluvial and combined origin in Ria de Aveiro under present and future scenarios. This study also aims to propose and evaluate the effectiveness of structural measures on flood risk mitigation. These goals were achieved by applying the methodology Source - Pathway - Receptor, which is a multidisciplinary approach that comprised the following steps: 1) characterization of flooding drivers (oceanic and fluvial) through statistical analysis; 2) implementation, calibration and application of hydro/morphodynamic models to identify the flooding pathway and the flood extent; 3) assessment of flood damage by identifying the socio-economic and ecological assets exposed to flood hazard and determining flood risk by combining the probability and the adverse effects of flood events on assets. In addition, the effectiveness of flood barriers and changes in the lagoon central area geometry on flood risk mitigation was assessed. Results highlight that oceanic floods are consequence of signifcant sea levels induced by storm surge events (>0.4 m) and high tidal levels (>3.3 m), which increased in the last decades due to the general lagoon deepening motivated by dredging activities. These morphological changes increased the tidal prism, the tidal currents and the flood extent, increasing the threat to floods of oceanic origin. These endanger settlements and economic activities (mainly, agriculture, industry and commerce) located along the lagoon main channels margins as well as habitats in the lagoon central area. Floods of fluvial origin occur during adverse weather conditions, and endanger the rivers mouth adjacent regions causing damage in restricted settlements, economic activities (almost only agriculture) and farmland habitats. Besides the areas dominated by oceanic and fluvial forcing, the events of combined origin also affect the margins adjacent to the transition zones, once the flood water drainage is hindered by high sea levels. Although the uncertainties associated to the influence of anthropogenic actions on the lagoon geomorphology, it is predicted an/a increase/decrease of flood risk for events of oceanic/fluvial origin under future scenarios, as consequence of mean sea level rise/river discharges reduction predicted for the region. Finally, this work demonstrated the potential of hydrodynamic modelling for simulate the effectiveness of structural measures on flood risk mitigation, and consequently in supporting the decision making process underlying the flood risk management.