Recent Experience in Analysis and Design of Perforated Vertical Breakwaters

Two case studies are presented on perforated (porous) breakwaters that have been analyzed, designed, and constructed at Port facilities in the United States and Korea. Motivation for the design and installation of these structures was driven by challenging soil conditions as well as a desire to modify wave reflection/transmission characteristics of the structure and the site. This paper discusses the analysis, numerical modeling, physical modeling, design, construction and post-project monitoring performed for these two perforated breakwaters. Case study #1 describes the Coast Guard and Cruise Terminal Pier at Busan, South Korea that was designed to provide moored vessels with protection from swells and wind-waves with periods ranging from 7 to 15 seconds in a depth of 12 meters. The foundation material at the breakwater location is deep, soft silts and clays. The engineering analysis included development and verification of a 1-D wave transmission/reflection model which predicted reflection and transmission within single and multi-wall (up to 3 walls) perforated breakwater systems; 2-DV physical modeling of wave transmission, wave reflection, and wave forces; and 2-D numerical wave refraction-diffraction-transmission-reflection modeling. The final breakwater cross-sectional configuration was a perforated 3-wall system with varying wall spacing and wall porosity. Transmission and reflection coefficients from the physical model satisfied the project design criteria. Case study #2 describes the breakwater and fill containment structure at the Middle Harbor Enhancement Area, Port of Oakland, CA (USA). The breakwater was constructed to contain fill from the Port of Oakland's 50-ft Dredging Project that was placed in order to create eelgrass habitat. The breakwater was designed to block storm wave energy, with porosity incorporated in order to minimize reflection effects from wind-waves and wakes. The design analysis was conducted using empirical and 2-D wave refraction-diffraction-transmission-reflection modeling techniques. The perforated wall breakwater was constructed in 2004. A post-project monitoring program was completed to verify the performance of the breakwater and the design engineering tools that were used during the design process. The monitoring program includes two non-directional pressure gauges and corresponding digital video images collected remotely via wi-fi dish over the internet. Field data were processed and analyzed, and show that the analysis techniques were valid and that the breakwater design meets the wave reflection design criteria.