Australasian Coasts and Ports Conference, 2025, Adelaide
As sea levels rise and coastal hazard exposure increases, the vulnerability of coastal infrastructure along our coastlines is also increasing resulting in greater demand for coastal armouring. At the same time, existing aging structures are deteriorating and quarried rock, which has historically been the primary source of coastal armouring, is becoming more difficult to obtain in the quality and size required to provide adequate long-term protection.
Concrete armour units have been used as an alternative to rock armour since the 1950s. Earlier armour units such as cubes relied on similar characteristics as rock to achieve stability under wave loading – primarily mass and were placed two layers thick. Over time, many different armour unit configurations have evolved including higher interlocking units, random and pattern placement, double and single layer. The primary driver for adopting concrete armour units has typically been the limited availability of rock at sufficient size to provide stability in the design wave climate. However, there are several other key considerations that influence the selection of armour type.
In this paper we examine rock armour and concrete armour units from a design, logistics, economic, environmental and sustainability, construction, and maintenance perspective using multiple recent case studies throughout New Zealand and the Pacific. We find that the key driver influencing rocks vs blocks is rock supply cost and programme rather than primarily design conditions. We also discuss the key drivers influencing the selection of concrete armour unit type including stability, constructability, seabed form, seismic performance, local contractor skill, licence fees and material efficiency.
