A Case Study on the Effect of Rear-Side Porosity of a Vertical Breakwater on Wave Propagation and Spectral Energy Distribution within the Harbor

This study experimentally investigated the effects of rear-side profile changes of a vertical breakwater on wave propagation characteristics inside a harbor, using Gayeok Harbor located on the west coast of Korea as the study site. The breakwater cross-sections were classified into a non-porous type (p = 0%) and a porous type with a porosity of 40% (p = 40%). Wave incidence angle, wave steepness, and offset distance were selected as the main parameters. Wave propagation characteristics were quantitatively evaluated using wave height ratios and spectrum-based energy ratios. The results show that the mean wave height ratio decreased from 0.48 (p=0%) to 0.41 (p=40%), indicating an additional reduction of approximately 15% due to the porous structure. Spectral analysis revealed that peak and high-frequency components were significantly attenuated under the porous condition, whereas low-frequency components tended to remain relatively persistent. Analysis of the infragravity (IG) band indicated localized amplification near the breakwater corner; however, no clear amplification was observed in the inner harbor region. These findings suggest that while porous structures are effective in reducing short-period wave energy, their capability to control long-period components is limited.