ALA WAI FLOOD RISK MANAGEMENT PROJECT

BY DINO BUCHANAN, Honolulu District

The proposed $345 million congressionally authorized Ala Wai Flood Risk Management project is the largest civil works project in the history of the Honolulu District. The project will take approximately five years to design and construct.

A high risk of flooding exists within the Ala Wai watershed due to aging and undersized flood conveyance infrastructure. Based on the peak flows computed for the flood risk feasibility study, it is estimated the Ala Wai Canal has the capacity to contain about a 20 percent annual chance exceedance (ACE) flood before overtopping the banks. The risk of flooding is exacerbated by the flashy nature of the streams in the watershed, with heavy rains flowing downstream extremely quickly due to steep topography and relatively short stream systems. The U.S. Army Corps of Engineers (USACE) estimates a major flood in the watershed could damage 3,000 structures and cost more than $1.14 billion.

Honolulu District’s Ala Wai Flood Risk Management Project Manager Jeff Herzog explains the Ala Wai watershed drainage complexities to Mary Frances Repko (center), staff director, Senate Committee on Environment and Public Works, and other congressional staff delegates at the east end of the Ala Wai Canal.

Photo by Dino W. Buchanan, U.S. Army Corps of Engineers Honolulu District

The Ala Wai Canal Flood Risk Management Project completed the feasibility stage in December 2017 when the USACE chief of engineers submitted his report to Congress. The Record of Decision for the Environmental Impact Statement was signed by the Assistant Secretary of the Army for Civil Works in September 2018 and was transmitted to the state of Hawaii for adoption. The project was funded for construction by the Bipartisan Budget Act of 2018 under the Long-term Disaster Recovery Investment Program with an authorized cost of $345,076,000. The program allows for single-phase design and construction, as well as a deferred payment option to expedite funding and execution of projects.

Project Manager Jeff Herzog (second from right) explains some of the natural and cultural sensitivities for the proposed retention basin in the Waiakeakua Stream area to state, city, and county of Honolulu officials and USACE enterprise personnel from the Seattle and New Orleans districts, as part of the three-day Ala Wai Watershed Flood Mitigation Design Charrette.

Photo By Dino W. Buchanan, U.S. Army Corps of Engineers Honolulu District

The Honolulu District is negotiating project partnership with the state of Hawaii and the city and county of Honolulu. The team is currently in the early stages of exploration and survey to refine data gathered during the feasibility phase and develop the feasibility designs into full designs. Currently, the state of Hawaii has pledged the $125 million nonfederal cost share for the project, once the city and county of Honolulu sign the project partnership agreement (anticipated in late 2019).

To maintain control of a project of this magnitude, USACE has systems of checks and balances in place that include a three tiered governance structure, including not only the local Corps of Engineers, but nonfederal partner(s), contractors, USACE enterprise, and national-level leadership. There are regularly scheduled meetings and reviews at several levels to ensure that the project remains on schedule, within scope, and on budget. After construction is complete, the project will be entered into a Federal Rehabilitation and Inspection Program, commonly referred to as PL 84-99.

The Ala Wai watershed encompasses 19 square miles and extends from the ridge of the Ko’olau Mountains to the near-shore waters of M mala Bay. It includes Makiki, M noa, and P lolo streams, which flow to the Ala Wai Canal, a 2-mile-long, man-made waterway constructed during the 1920s to drain extensive coastal wetlands. This construction and subsequent draining allowed the development of the Waikiki District.