Reduction of extreme wave overtopping on low - crested seawalls by crown walls

Extreme waves occur in coastal areas globally, often accompanied by rising water levels, potentially causing significant overtopping of seawalls and posing serious threats to seawalls and associated infrastructure. This study investigates the effectiveness of crown walls in mitigating wave overtopping on low-crested seawalls under extreme wave conditions through experimental tests and OpenFOAM simulations. Two crown-wall configurations, i.e., rectangular and arc-shaped, are studied, focusing on examining the overtopping process, overtopping volume and wave-induced forces on crown walls. Results show that arc-shaped walls reduce wave overtopping by up to 99.3 % via redirecting wave flows seaward, although they are subjected to larger wave impact forces. Parametric studies about the arc angle and height of the arc-shaped crown wall are conducted. Results suggest that the crown wall with a 70°–80° arc angle achieves the optimal balance between reducing wave overtopping and constraining wave loads on the crown wall. Besides, as the non-dimensional height of the arc-shaped crown wall, i.e., hw/hs, increases from 0.133 to 0.311, the reduction in overtopping and the maximum wave load on the seawall reach a balance when hw/hs = 0.267. These findings provide guidance for designing crown wall geometry and height in coastal defense applications.