Hawaii's Coastal Highways

by Dr Panos Prevedouros, PhD, Fix Oahu, February 19, 2016

Sea level rise and extreme weather events can wash out portion of coastal highways.  This has happened several times on Oahu and many other locations.  With increasing population and traffic volume, the temporary loss of lanes or entire roadway cross sections becomes a major threat to public health and safety, let alone a threat to daily life and long term economy. Coastal roadway segments must be made more resilient to weather effects and reliable for operations regardless of storm surges.

As I outlined in a report that was the top story on Hawaii News Now (on Feb. 17, 2016) "Long-term solution for erosion along Kamehameha Highway won't come cheap", in general terms, the solution may come in three options, each one more suitable to various coastal highway segments (i.e., not one size fits all.)

1. Maintain the location of the current highway and elevate it by, say, 10 ft. This is a land protection option similar to those in low lying countries such as The Netherlands.
2. Relocate the highway several hundred feet inland and at a higher elevation.
3. Keep the highway largely as is and add jetties, lagoons and breakwaters to widen the coastline and isolate the highway from the forces of the ocean.

The first option requires no transportation work, but it has tremendous impacts by separating the community from the coast and a host of drainage issues. However, this "walling" option may be necessary for the effective protection of property and lives along specific sections, and at locations were current and other ocean forces make the deployment of option 3 impractical.

The second option attempts to develop a new highway in mostly agricultural, Hawaiian homestead or pristine nature areas, all of which are likely to generate insurmountable community and environmental impacts. However, there may be short segments where this option is economical and the impacts are small or moderate. For example a re-alignment of Kam. Hwy. away from Turtle Bay has been outlined in Hawaii DOT plans. Also for this option, the highway may be elevated which minimizes the disruption to lands underneath but it increases costs and reduces accessibility. Low height elevated segments may be necessary for wetland protection.

The third option, jetties and artificial ponds, is the most attractive because it protects the highway and communities, substantially reduces beach erosion and at some places adds beach or ocean recreation space. Its downside is some destruction of marine environment but some of this may be offset by the creation of traditional Hawaiian fishponds. This option also has the potential to be combined with wave action or high/low tide power generation by devices at key locations of the ponds (i.e., tidal power plants). An approximation of the proposed ponds is the lagoons at Ko'olina pictured below.