Numerical modelling framework for assessing dune effectiveness against coastal inundation

Abstract. Coastal inundation threatens both economic assets and human lives, yet accurate flood mapping remains limited by gaps in data availability and model capabilities. In this study, we enhanced the LISFLOOD-FP model to simulate coastal floods by incorporating wave setup, swash dynamics, and interactions with protective infrastructure such as temporary dunes. We applied this approach to Cesenatico, Italy, where seasonal dunes serve as winter coastal defenses, analyzing two contrasting storm events with observational data for validation: the 2015 Saint Agatha Storm, which breached the dunes causing extensive inland flooding, and the 2022 Denise Storm, where intact dunes successfully prevented inundation. Our results demonstrate that dunes effectively mitigate flooding when intact, but failure of even small sections can trigger widespread inundation, highlighting the critical need for optimized design. This work advances the development of coastal digital twins by introducing a computationally efficient representation of essential physical processes – swash-related erosion of dune stability and swash contribution to flood volumes through an overwash efficiency parameter – enabling practical risk assessment and infrastructure planning in vulnerable coastal regions.