Gaining knowLedge of Overtopping RIsk for urbanized coastal Areas

Hazards in coastal regions are expected to increase because of the sea level rise and increased storminess induced by the climate change. These will lead to significant changes in the coastal wave driven processes and increase the threats for coastal communities, as dramatically shown during the last decades by the growing number of extra-tropical cyclones that led to more frequent and disastrous flooding events. In the meantime, population in coastal areas is expected to grow into the future, especially in low-lying and urbanized coastal zones. Major economic damages and loss of life are caused by waves that overtop and breach the coastal defences. 

Will urban coastal areas withstand the sea level rise and flood events in the near future? Which is the risk associated with it and how to mitigate it?

Under the complexity of the coastal environment and the changing wave forcing, it is mandatory to deepen the understanding of the physics governing wave overtopping phenomena, representing the major cause of flooding in coastal areas, in order to guide the upgrade of existing coastal defences toward low-impact but cost-effective solutions.

Despite the large literature on wave overtopping, important knowledge gaps still exist when relating coastal safety to individual overtopping events: physics needs better modelling to lead to more accurate and physically based assessment methods. The relationship between individual overtopping flow properties (velocity, depth, volumes, discharges) and coastal safety requires further and deep analysis and must include second-order effects (e.g. infra-gravity waves).

The present project aims to establish a novel methodology for safety assessment in urbanized coastal areas, applying focused wave group methods in experimental modelling facilities. The reduction in consumption time of the wave generation provided by this methodology allows analysing the flooding patterns under numerous scenarios, considering also those driven by the changing climate. The proposed research will identify at least two different case studies in Spain, characterised by different wave forcing, tidal regimes and urban coastal layouts. The first case study will be identified along the Atlantic Ocean or the Cantabrian Sea, characterised by meso-macro tidal regimes, shallow and gentle sandy foreshores. In such a context, second order effects, namely, infra-gravity waves are expected to play a major role in wave overtopping and flooding. The second case study will be selected in the Mediterranean Sea, a micro-tidal environment with steeper foreshores, pocket beaches and deeper water conditions, where coastal towns present typical urban narrow beaches followed by promenades with intense recreational use.

The project relies on experimental modelling, carried out in small-scale and large scale wave flumes, and employs a novel data-driven regression technique to attain a parametric optimisation of focused wave group generation for laboratory practices and analysis of extreme overtopping events on coastal defences. Tests in the large-scale facility will help to quantify and correct scale effects associated with individual overtopping events and to validate the methodology proposed at small-scale.