Effectiveness of nature-based solutions for coastal inundation: towards a digital twin for coastal management

Coastal inundation poses a significant threat to economic assets and human lives. A growing trend in coastal hazard protection management is the transition from traditional "gray" infrastructure to Nature-Based Solutions (NBS), which offer sustainable and adaptive alternatives. Accurate modeling of coastal flooding and interactions with NBS is vital but remains challenging due to limited data and modeling uncertainties. In this study, we evaluated the LISFLOOD-FP model ability to simulate coastal flooding, comparing its performance with observed flood maps and a fully hydrodynamic model in the Gulf of Manfredonia. Furthermore, we enhanced the model’s functionality by incorporating wave contributions to inundation, considering wave setup and swash, and their interactions with protective features such as temporary dunes, including potential erosion and structural failures. These advancements were applied to the Emilia-Romagna coastline in Italy, focusing on Cesenatico and Rimini towns, where seasonal dunes are constructed each winter as temporary coastal defenses. Two storm events were analyzed: The Saint Agatha storm in 2015, which led to dune failure and flooding, and Denise storm in 2022, where intact dunes effectively mitigated flooding. Results showed that the improved model could realistically simulate flood dynamics and capture the protective role of dunes, particularly in 2022. However, the study highlights the importance of correctly sizing these protections and emphasizes the critical impact of data uncertainty. The lack of high-resolution topographic data, especially for temporary dunes, introduces significant variability into model outputs. Small discrepancies in dune height can determine whether dunes fail or withstand storm events, thus affecting the reliability of flood predictions. This issue is compounded by a scarcity of observational flood maps, which limits validation efforts. The advancements represent an important step towards creating a digital twin of coastal NBS protection, providing a robust framework to support coastal management activities.