Computational fluid dynamics investigation of wave interactions with damaged coastal cliffs

• Velocity field analysis reveals multiple vulnerability modes, including exposure, infiltration, and erosion, dependent on the cliff geometry. • Under the highest wave condition, the submerged notch reduces runup by ∼ 10% but increases wetting duration ( ∼ 70%) and contact exposure ( ∼ 60%). • A partially submerged notch reduces runup by ∼ 44% but generates intense jets near the cliff, with horizontal velocities up to 15 m/s under extreme waves. • A 2.0 m solitary wave aligns with the notch gap, producing a resonance-like jet exceeding 6 m/s and surpassing velocities from a 1 m higher wave. • Horizontal velocity near the back wall depends on notch submergence, with narrower ranges for partially submerged cases and wider ranges for submerged cases. Numerous studies have documented that increasingly intense weather and climate events are amplifying marine wave activity. However, complex links between oceanic storms and coastal environments require further investigation to assess risk and develop effective mitigation strategies. Although past works have focused on various coastal structures, this study investigates extreme wave impacts on a Mediterranean Sea cliff containing cultural heritage sites. Advanced two-dimensional computational fluid dynamics models were developed for a range of solitary wave heights and cliff geometries. Unlike previous studies, the work herein considers a key natural feature, namely basal notch, caused by progressive cliff damage under the wave action. Three cliff types are considered: an undamaged cliff, one with a submerged and one with a partially submerged notch. The hydrodynamic interactions of waves with cliffs are investigated both qualitatively and quantitatively, focusing on flow patterns, wave runup and cliff exposure. The CFD results reveal that partial damage, i.e., notch, generally reduces the maximum wave runup but increases the water retention time on cliffs, especially in the submerged notch case. For the largest wave, the submerged notch reduces maximum runup by 10% but increases retention time by 70%, increasing internal weakening probability. Additionally, although the horizontal velocity of water along undamaged cliffs is negligible (-0.006 to 0.004 m/s), the presence of a notch can amplify it to about -6 to 4 m/s under a 2.0m wave, potentially altering the flow patterns and the dominant damage mechanism. Overall, the study highlights cliff geometry as a critical factor in wave vulnerability.