CFD investigation of wave runup on coastal cliffs for impact assessment on cultural heritage

Wave runup plays a pivotal role in shaping the stability of coastal cliffs, as it generates hydrodynamic pressures that can compromise their structural integrity over time. These cliffs, especially those near cultural heritage (CH) sites, are vital natural structures that indirectly safeguard invaluable assets. Their destabilization, however, poses significant risks, necessitating a comprehensive understanding of the underlying processes that threaten their stability. Despite growing interest in coastal hazard assessments, there remains a paucity of quantitative studies focused on the interplay between wave runup dynamics and the structural characteristics of cliffs. Addressing this gap is essential for improving risk assessment methodologies and developing effective mitigation strategies.

Field measurements conducted in the Horizon Europe project TRIQUETRA revealed that coastal cliffs rarely conform to idealized vertical geometries. Instead, they often exhibit structural irregularities, such as varying inclinations or pre-existing damage like notches, which can exacerbate their exposure to wave-induced pressures. These variations are critical in determining the wave runup and consequently the exposed height of the cliff, which affects its stability. In this study, computational fluid dynamics (CFD) simulations using the Volume of Fluid (VOF) method were employed to model wave-cliff interactions. The analysis focused on the influence of geometric configurations and structural irregularities on the maximum wave runup and the  hydrodynamic pressure distributions, with particular attention to the behavior of steeply inclined cliffs and notched formations. The results demonstrate that wave runup is significantly amplified on near-vertical cliffs, with this effect becoming more pronounced under larger wave conditions. Conversely, notches reduce overall wave runup as their height increases, redistributing hydrodynamic forces along the cliff face and altering the pressure patterns. These findings highlight the intricate relationship between wave dynamics and structural variations, emphasizing the need for site-specific analyses when assessing cliff vulnerabilities.

By advancing the understanding of wave-cliff interactions, this research provides a valuable contribution to coastal hazard studies, offering new insights into the mechanisms driving cliff instability. The outcomes underscore the importance of integrating advanced CFD tools into risk assessments, enabling the design of targeted mitigation strategies to protect coastal regions and preserve the structural integrity of cliffs that play a critical role in safeguarding nearby CH sites.

Acknowledgments: This work is based on procedures and tasks implemented within the project “Toolbox for assessing and mitigating Climate Change risks and natural hazards threatening cultural heritage—TRIQUETRA”, which is a Project funded by the EU HE research and innovation program under GA No. 101094818.