ENGINEERING RESILIENCE
bathymetric surveys were conducted along the breakwater and surround- ing seabed. The surveys identified two particularly important character- istics: a steep offshore shelf that varies in width along the structure and the extensive relic debris field surrounding the breakwater. The engineering team also needed to understand the size and distribution of the existing armor stone. To accom- plish this, Baird used its proprietary “Stone ID” software, which analyzes high resolution imagery to estimate individual stone sizes. The informa- tion provided a detailed picture of the armor material on the above and below water portions of the structure, includ- ing the relic debris field. Understanding the existing stone sizes was important not only for design purposes, but also for con- struction planning and determin- ing the equipment types and sizes/ capacities required for the work. The team also undertook detailed num- erical wave modelling. Rather than relying solely on the offshore design wave conditions specified in the pro- ject requirements, the team analyzed long-term wind and storm records to understand how waves travel across the offshore shelf, break and trans- form before interacting with the structure. The resulting wave analysis became a fundamental input to the new repair design. From massive stone to interlock- ing concrete armor units The engineering team considered two repair concepts: continuing to use large quarried armor stone or adopting a more robust concrete armor unit. The decision was ultimately made to use Accropode TM units. Each Accropode TM is approximately 16 cubic meters in size and weighs about 42 tons — roughly equivalent to the weight of 17 Toyota 4Runners.
Courtesy of W.F. Baird
The above schematic highlights repairs made to the Glass Breakwater over time in response to successive typhoons.
Further repairs followed in 1987 and 1997, while concrete cubes were added to the roundhead and a short section of the trunk in 2013. Today, remnants of these different generations of repairs can still be seen along the structure, with older, mostly broken, dolos units and newer concrete cubes sitting alongside the original armor stone. Collectively, the repairs succeeded in keeping the breakwater functional, but they also created a new challenge. “Each intervention essentially bought us some time,” Treflik-Body said, “but the structure now needs a comprehensive repair strategy to unify and strengthen it against Guam’s severe wave climate.”
Repeated stone replenishment and erosion has created a submerged “relic debris field” on the seabed in front of the breakwater. The structure foot- print has progressively expanded sea- ward, accumulating loose material well beyond its original footprint. The result is a breakwater that is much lar- ger than when originally constructed, but not necessarily stronger. Understanding the breakwater as it exists today Before developing the new repair design, Baird’s team undertook an extensive investigation of the existing structure. High-resolution topographic and
Courtesy of W.F. Baird
Design concept for the breakwater repair.
Courtesy of W.F. Baird
40 — PACIFIC PORTS — October 2026
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