Tide-surge interaction in Ria de Aveiro lagoon and its influence in local inundation patterns

Abstract

Several problems related with coastal flooding depend on tidal levels, rise in sea level induced by meteorological effects and their nonlinear interaction. The latter is particularly meaningful in coastal lagoons and estuaries since it is strongly dependent on shallow water processes. This work aims to understand the role of tide-surge interaction in local inundation patterns of Ria de Aveiro lagoon and thus provides crucial information for future flood risk management strategies. The methodology adopted comprised two fundamental steps: 1) examine sea level data collected at lagoon inlet between 1976 and 2017 to infer a statistical evaluation of tidal state data to identify the storm surge occurrence; 2) perform a set of numerical simulations using an implementation of Delft3D hydrodynamic model to evaluate the model performance for tidal and storm surge propagation and to investigate tide-surge interactions. Results from the statistical analysis suggest that storm surge climate is best characterized when considering a threshold of two standard deviations and a duration of an event greater than 6 h. It was also found a tendency for storm surge events to occur most frequently on the falling tide. Model results showed that the improved grid and bathymetry resolution enabled a more accurate propagation of tide and storm surge compared with previous applications. In the assessment of flooded area sensitivity to tide-surge interaction there was a tendency for an amplification of maximum residual levels and nonlinearities from lagoon mouth towards the upper reaches of the longer lagoon channel, which led to a higher flooding risk of adjacent margins to these areas.