Wave Transmission Over Reefs and Physical Modelling of COPED Units, Rarotonga, Cook Islands

Client: Coastal Environmental International
Year: 2006
Project Reference: 05104
WRL Technical Reports: Flume Testing of COPED Breakwater Units Fronting Rarotonga Airport, Cook Islands (2007/26); Flume Testing of COPED Breakwater Units Fronting New Zealand High Commission Houses, Nikao, Rarotonga, Cook Islands (2006/36)

The Cook Islands are located in the south-western Pacific in an area subject to tropical cyclones, especially during El Niño patterns. Although the coral fringing reefs provide good protection to the foreshore during typical wave conditions, recent cyclonic waves have caused substantial damage to beachfront buildings due to wave runup and inundation.

WRL was involved in the design and testing of a series of breakwaters for the protection of different sites in the Cook Islands using COPED units. COPED (Coastal Protection and Environmental Development) are coreless precast concrete units invented and developed in the Cook Islands which can be used in a number of configurations to form breakwaters, revetments and vertical walls. The COPED breakwaters were tested by WRL in the 1 m wave flume using both regular and irregular wave heights to reproduce in-situ cyclonic extreme wave conditions. The COPED hydraulic performance was quantified by measuring wave reduction with Ultra-sonic sensors mounted on the leeward side of the breakwater. Hydraulic uplift loads on the units caused by wave impacts were recorded using load cells installed on the units.

2D physical modelling of the COPED breakwaters allowed optimisation of the design, by measuring the wave reduction obtained with different configurations. Uplift forces measurement due to wave impacts were collected for detailed structural design.