Flood risk assessment in a coastal lagoon under present and future scenarios: Ria de Aveiro case study

Floods are one of the major threats to low-lying coastal lagoons, affecting people, socio-economic activities and ecosystem services. This work proposes a methodology to assess present and future flood hazard and risk in west-boundary low-lying coastal lagoons, using the Ria de Aveiro (Portugal) as case study. A multidisciplinary approach supported on Source–Pathway–Receptor–Consequence model combined with a GIS-based multi-criteria analysis was developed and applied. This comprised the following steps: (1) definition of present and future climate scenarios associated with oceanic, fluvial and combined events, combining sea levels and river discharges for different return periods; (2) characterization of flooding pathway through hydrodynamic modelling; (3) assessment of flood hazard combining flood depth and probability from hydrodynamic simulations; (4) assessment of flood risk calculating the adverse consequences on assets exposed to flood hazard. Results highlight that endangered regions are strongly dependent on the floods origin: oceanic floods threaten settlements and economic activities located along the margins of the lagoon main channels as well as habitats in the lagoon central area; fluvial floods endanger the river’s mouth adjacent areas causing damage in restricted settlements, economic activities and farmland habitats; the combined floods also threaten the margins adjacent to the transition zones. For future scenarios, it is predicted the flood risk increase/decrease for oceanic/fluvial events, as a consequence of mean sea level rise/river discharges reduction predicted for the region. Finally, this work demonstrated the value of the methodology proposed and its potential for flood risk analysis, supporting the decision-making process underlying the flood risk management.