Phased adaptation of enhanced flood protection from sea level rise along linear infrastructure in Honolulu, Hawaii

The City and County of Honolulu Department of Planning and Permitting (DPP), WCIT Architecture and Arup collaborated to create a flood resilient linear promenade along the Kapālama Canal, Honolulu, Hawai‘i to mitigate critical sea level rise (SLR) effects. The canal is a 100-year storm flood control measure that is tidally influenced. The project incorporates green infrastructure, erosion control measures, bank stabilization, and dredging to improve capacity and water quality in the canal. This paper describes the analysis, proposed solutions and the resiliency design for the project.

For the analysis, a 1-dimensional HEC-RAS (US Army Corps of Engineers) model was developed to evaluate the effects of the proposed design and the impact of SLR on the canal capacity and design flood elevations (DFE) in the canal. The DPP Civil Engineering Branch recommended designing the project to accommodate 3.2 feet of SLR by 2050 with specific upgrade considerations made for 6 feet of SLR by 2100. To accommodate SLR, and in anticipation of a future revision by the Federal Emergency Management Agency (FEMA) of the floodplain maps for the surrounding area, the project includes enhanced flood protection along the length of the canal. The DFE and freeboard requirements to set the elevation of the flood protection and promenade infrastructure, such as pedestrian bridges were developed. Additionally, a conceptual resiliency design exercise was undertaken to develop viable flood protection solutions that aligned with the project goals of enhancing waterfront connections and providing a community amenity to encourage development in the area. To maintain the architectural vision of the project, the flood protection is aesthetically designed as watertight planter boxes or terraced steps, enhancing the community space. The adaptable design includes a continuous line of defense including permanent and deployable flood protection measures.

The staged implementation approach for flood protection that is adaptable to changing tidal and storm conditions from climate change and incorporates community use, allows for a design that does not disrupt the connection between the promenade, surrounding infrastructure and proximity to the canal.

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