Evaluation of XBeach predictions for a real-time warning system in Emilia-Romagna, Northern Italy

The ability to predict coastal hazards several days in advance is a valuable tool for coastal managers to carry out necessary hazard-reduction measures. The project MICORE aims to develop an early-warning system of coastal hazards at nine distinct sites across Europe using a train of numerical models from the prediction of forcing parameters to the localized hydro/morphodynamics. A vital component of this project is the evaluation of morphology predictions of storm erosion, using the recently-developed XBeach model. In this study, XBeach predictions of two storms events on the Emilia-Romagna coastline in Northern Italy are assessed against measured beach response. This site is unique in that as well as consisting of relatively pristine natural areas, it also contains a series of offshore breakwaters protecting urban settlements and hence represents the first time XBeach has been run in such a setting. 1DH model runs at a natural section of the site predict the relatively minor dune erosion relatively well, with best results obtained by increasing the critical avalanching slope below water. For the section with offshore breakwaters, a 1DH model is found to be inappropriate due to the unreasonable increase in water levels modeled in lee of the structures. Water levels are observed to reduce significantly when running the model in 2DH, where return flow currents through the gaps in breakwaters are also included