Several failures of recurved concrete crownwalls have been observed in recent years. This work aims to get a better insight within the processes underlying the loading phase of these structures due to non-breaking wave impulsive loading conditions and to identify the dominant failure modes. The investigation is carried out through an offline one-way coupling of computational fluid dynamics (CFD) generated wave pressure time series and a time-varying structural Finite Element Analysis. The recent failure of the Civitavecchia (Italy) recurved parapet is adopted as an explanatory case study. Modal analysis aimed to identify the main modal parameters such as natural frequencies, modal masses and modal shapes is firstly performed to comprehensively describe the dynamic response of the investigated structure. Following, the CFD generated pressure field time-series is applied to linear and non-linear finite element model, the developed maximum stresses and the development of cracks are properly captured in both models. Three non-linear analyses are performed in order to investigate the performance of the crownwall concrete class. Starting with higher quality concrete class, it is decreased until the formation of cracks is reached under the action of the same regular wave condition. It is indeed shown that the concrete quality plays a dominant role for the survivability of the structure, even allowing the design of a recurved concrete parapet without reinforcing steel bars.

Flood protection by coastal vegetated systems depends on the persistence of vegetation structures, but it is currently impossible to predict vegetation survival during extreme storms. Using the largest artificially generated waves in the world, we here quantified the persistence of tidal marsh vegetation by measuring stem breakage of winter-state vegetation (3 species and mimics) during extreme storms with up to 2.0 m significant wave height, 4 m water level and 8 s peak period waves. Vegetation persistence was unexpectedly high, with on average only 30% biomass loss. Stiff stems which were unable to sway under waves were most frequently broken, so the storm left behind a more flexible and resilient post-storm canopy. We derived a generic diagram to predict biomass loss of global vegetation species across increasing storm intensities, allowing prediction of marsh vegetation survival under extreme storm events – a critical next step towards reducing the uncertainty hampering the implementation of nature-based flood protection strategies.