APIA PORT BREAKWATER RECONSTRUCTION

Abstract

Samoa is located in the South Pacific Ocean, about halfway between Hawaii and New Zealand. The first wharf at Apia (185m long) was constructed in 1966 and a 100m long breakwater with 8t Dolos armor units was constructed in 1988-89 to provide shelter. Following large cyclones in the early 1990s, the breakwater was rehabilitated in 1996 with larger 20t Dolos armor units. In 2003 a solid concrete crown wall added to the breakwater to mitigate wave transmission into the harbor. There is limited toe and scour protection and multiple units have broken legs, cracks and rust stains from corroding steel reinforcement. The design intent of the breakwater upgrading project is to improve resilience to extreme climatic and natural disaster events. Reconstructing the breakwater with a higher crest, larger roundhead, new concrete armor units, toe support and a scour apron was selected as the most appropriate option to meet the design criteria. Physical modelling was undertaken to verify and optimize the design. Wave calibration indicated good correlation with numerical modelling and showed that for offshore wave heights of ~11.5m and greater the near structure wave height is depth limited (Hs ~9.1m). The physical model testing indicated that the existing 20t Dolos units on the rear slope are unstable under the 1percent AEP event as the base units have limited rock toe support. Further model testing was undertaken using 16m3 Xblocs on the leeside which was successful and detailed design was completed accordingly.