Flood mitigation is critical in Honolulu reducing risk for 65,000 residents and an additional 200,000 transient daily visitors

100 Resilient Cities: Assessment of the Ala Wai Flood Mitigation Project

An estimated 3,000 structures in Honolulu are at flood risk due to a one percent probable storm—a 100-year event—with potential damages exceeding $1 billion. The City and County of Honolulu (CCH), State of Hawaii, and the U.S. Army Corps of Engineers (USACE) Honolulu District are currently reviewing design features and negotiating terms of the partnership for the construction of the Ala Wai Watershed Flood Mitigation Project.

The City and County of Honolulu (CCH) retained Stantec to review proposed USACE feasibility study level designs and provide general support services, including helping to identify opportunities for place-making and green infrastructure. Our team worked closely with the CCH Department of Design and Construction to produce multiple alternatives for the design and location of canal areas, walls and levees, and park areas. Our designs also considered the incorporation of ongoing complete streets planning alongside CCH goals for multi-modal transport. Concepts were provided for greening and increased safety for middle and upper watershed features. We also provided alternative conceptual designs to increase normal and higher frequency flood flows.

Our conceptual alternative designs and adjustments could reduce the risk to approximately 65,000 residents and an additional 200,000 transient daily visitors.