Hawaii is taking an innovative approach to protecting its coastal highways from erosion and rising seas.
A consortium of research and community organizations has developed a system to protect these vulnerable roadways while also supporting native marine life using a hybrid reef system, according to a press release from Hawaii Department of Transportation.
The hybrid reef system incorporates engineered reef structures with living coral to “reduce wave energy, strengthen shorelines and improve coastal resilience.”
The Kalaeloa Hybrid Reef is a living breakwater consisting of “60 engineered, porous concrete reef mimicking structures” that “dissipate wave energy while allowing water to flow through the reef.” Attached coral settlement modules will support the recruitment and growth of native coral, while specially developed biomaterials will repel competing algae and accelerate coral growth.
During large-scale wave-flume tests, model breakwaters were found to reduce incoming wave energy by more than 80% and remained stable during extreme conditions.
The Hawaii Institute of Marine Biology 3D-printed ceramic modules featuring small, spiral shaped shelters called “helix recesses.” The modules were shown to yield an 80-fold increase in baby coral settlement and up to a 50-fold increase in survival rates compared to flat surfaces. These crevices will help kickstart the living reef.
The reef system will be deployed at a degraded area of Kalaeloa Harbor with a hard rock bottom. Work will begin with the careful removal of coral fragments and preservation of coral on growing tables near the project site. This will be followed by the installation of the reef structures, attachment of live coral fragments to the structures and continued scientific monitoring to evaluate their performance, the press release states.
Makai Ocean Engineering developed a shallow-water catamaran to minimize disruption to the surrounding marine environment and eliminate the need for heavy crane barges. The structures will be anchored using a novel rotary micropiling system, significantly reducing the anchoring footprint and sound pollution compared with traditional pile drivers, according to the press release.
The system was developed over four years by Defense Advanced Research Projects Agency (DARPA) as part of its Reefense Program, along with the University of Hawaii, Makai Engineering, Kuleana Coral Restoration and other project partners. HDOT will take ownership of the structures following deployment.
Once deployed, the system will serve as a living laboratory for the emerging field of nature-based coastal engineering which combines engineered infrastructure with natural ecosystems.
Hawaii’s Green Fee program will fund the first year of monitoring and maintenance. Long-term monitoring will be conducted by the newly formed Kalaeloa Hybrid Reef Monitoring Hui, a partnership of researchers, agency representatives, community organizations and cultural practitioners that will “assess the reef’s environmental, engineering and cultural impacts,” the press release states.
Findings will be shared with regulators, engineers and coastal managers to support future shoreline projects in Hawaii and elsewhere.
Sources: HDOT
