Numerical investigation on the effectiveness of pile row in local sand trapping and beach protection

As novel coastal structures, pile row structures, such as breakwaters, have received increasing attention owing to their advantages in coastal protection and coastal landscape improvement. In this study, a nonlinear sediment model is developed based on OpenFOAM® to explore the effect of the pile row structure on the evolution of sandy beaches by waves. Its robustness was proved by published data related to two typical cases, that is, a pure sandy beach and a single pile on a sandy beach. Subsequently, the beach evolution and pile row with varied pile spaces S/D (the D is the pile diameter and S indicates the space between adjacent piles) on the beach were modeled. In addition, a long-term simulation was performed. The results revealed that the backrush-induced beach scour was larger than that induced by the uprush during wave propagation along sandy beaches. Sandy beach morphology changes because of the construction of the pile row structure by adjusting the wave motion, and local vortices and their evolution did not exhibit a simple linear relation following the variation in S/D . The local scour decreased with the increase in S/D when the S/D was less than 1.6, but it increased on the seaside of the piles and both side faces, except the leeside for S/D increased from 1.6 to 1.8. Meanwhile, in the nearshore zone, the pile row structure was effective in trapping beach sand, and its effectiveness was more remarkable as the S/D decreased. The findings would be useful in assessing the influence of pile row structures on beach evolution by waves and provide a basis for coastal protection engineering.