Managing local coastal inundation risk using real-time forecasts and artificial dune placements

Abstract

Uncertainty in the behaviour of future storm events and extreme water levels means that the introduction of Early Warning Systems for coastal inundation risk at vulnerable local sites becomes increasing paramount. In this study the coupled hydro-morphodynamic model XBeach is used at two sites along the Emilia-Romagna coastline in northern Italy to predict coastal inundation risk in the presence of coastal structures and temporary artificial dunes. These dunes are typically formed by beach scraping and are used on this coastline to protect beach-front infrastructure during the winter period. Coastal inundation risk is defined by the cross-shore distance between the seaward edge of the building and the time-varying waterline predicted by XBeach. A series of synthetic storm events as well as a real-world scenario that caused dune failure at one of the sites are tested. Comparisons between XBeach results and the Van Der Meer empirical formula for wave transmission behind offshore structures show a very strong agreement, while the real-world scenario indicates promising model prediction performance of dune failure at least one day in advance. A new model tool known as DuneMaker is developed that modifies XBeach model grids to simulate the impacts of scraped/placed artificial dunes of varying size, shape and configuration. The use of this tool is demonstrated on the same model test runs, where it is shown that improved dune design can reduce the predicted coastal inundation risk at critical points of vulnerability identified by the model.