Nature-based Solutions (NbS) are increasingly recognized as effective measures for mitigating flood risks and enhancing climate change adaptation. However, evaluating their efficacy in delivering flood risk reduction ecosystem service (FRR-ESS) is usually limited by reliance on qualitative, expert-based “quick-scan” scoring methods. While already challenging for present-day evaluations, this limitation becomes even more significant when addressing future climate scenarios, introducing deep uncertainties in the evaluation. The present study introduces a model-based framework to quantify FRR-ESS provided by coastal NbS, which integrates expert-based assessments with quantitative results from an eco-hydro-morphodynamic numerical model. The model enables a comparative evaluation of individual and combined effects of NbS following a Building Blocks approach. By integrating habitat map change prediction in the evaluation, NbS flood reduction response to present and future storm scenarios (i.e. wave climate and sea level rise) are investigated. The methodology is applied to a Mediterranean coastal lagoon in Sicily (Italy), and can be easily adapted to diverse coastal ecosystems. Our findings underscore the significant role of coastal habitats in reducing flood risk and highlight the importance of integrating physically-based modelling into FRR-ESS evaluation. This approach provides a robust and flexible tool for policymakers and stakeholders to make informed decisions that support both ecological sustainability and disaster risk reduction.

In the present work, an experimental investigation on the hydrodynamics of shoaling waves superposed on a steady orthogonal current is carried out. An experimental campaign in a wave tank has been performed, with waves and current interacting at a right angle over a sloping planar beach. Velocity data have been gathered during the experiments in order to investigate mean, phase and turbulent flow. A detailed preliminary analysis of the time- and space-variability of the experiments is presented. Results show that a complex interaction between waves and current occurs as the wave shoals, in terms of sheer production, momentum transfer and turbulent mixing. Superposition of waves determines a shear increase at the bottom due to an enhanced turbulence mixing, nonetheless as depth decreases and the current velocity consequently increases, shoaling waves may be less efficient in enhancing shear at the bottom. Moreover, the superposition of waves determines the current to oscillate around its mean velocity value. Nevertheless, as wave shoals and simultaneously current velocity increases with decreasing depth, waves and current oscillatory motion experience a phase lag, as a response of the larger momentum of the current to the changing of the shoaling waves acceleration distribution along the wave phase. Moreover, the turbulent bursting events of the combined flow in proximity of the bed have been investigated by means of quadrant analysis, showing an increase of the turbulent ejections and sweeps due to the superposition of the shoaling waves.