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Ala Wai Canal

The Ala Wai watershed encompasses approximately 19 square miles. The Ala Wai Canal is a two-mile-long man-made waterway constructed in the 1920's to drain extensive wetlands in order to allow development of the Waikiki area on the island of Oahu. The Canal has overtopped and previously flooded Waikiki during both November 1965 and December 1967 storms and during the passage of Hurricane Iniki in 1992. An October 2004 storm flooded Manoa Valley and a March 2005 storm flooded Makiki. The October 2004 storm, estimated to be a 25-year event, caused $85 million in damages including the loss of irreplaceable documents in the University of Hawaii’s library. Modeling efforts indicate that a 100-year event would result in damages to more than 3,000 structures in the watershed with total damages of about $1.14 billion.

The Ala Wai Canal Project is in the feasibility phase. The feasibility study is investigating and evaluating solutions flood damage problems throughout the entire Ala Wai watershed (Manoa, Palolo, and Makiki drainages, including Waikiki and surrounding areas). The recommended plan would reduce flood risks by improving the flood warning system, and constructing six in-stream debris and detention basins in the upper reaches of Makiki, Mānoa and Pālolo streams, one standalone debris catchment feature, three multi-purpose detention areas in open spaces through the developed watershed, and concrete floodwalls averaging 4 feet high along one or both sides of approximately 1.9 miles of the Ala Wai Canal (including two pump stations). Potential adverse impacts include those related to biological resources (aquatic habitat), cultural resources, recreation, and visual resources; however, measures to avoid, minimize, and mitigate these impacts have been incorporated to the extent practicable. Although some degree of impact would occur, project analyses have not identified significant, unavoidable adverse impacts that would remain after implementation of proposed mitigation measures. Unavoidable environmental impacts to aquatic habitat would be fully compensated for by eliminating migratory passage barriers at two in-stream structures in Mānoa Stream to improve connectivity for native aquatic fauna. The estimated total project first cost of the recommended plan is $306,095,000. The benefit-cost ratio is approximately 3.68 to 1.

The feasibility phase will conclude with the signing of the report of the Chief of Engineers. Pending final review of the Feasibility Report and Environmental Impact Statement, the Chief of Engineers report is anticipated to be signed by 30 August 2017.

Instructions on submitting comments during the final Feasibility Report and Environmental Impact Statement (through 25 June 2017) can be found in the Notice of Availability: Notice of Availability

The Chief of Engineers' response to the independent panel's peer review report is currently under development, and will be posted and distributed within 10 days of completion and signature.

To see the independent panel's peer review report click on: Ala Wai Canal Independent External Peer Review

To see a copy of the draft report of the Chief of Engineers, click on: Ala Wai Chiefs Report

To see the final Feasibility Report / Environmental Impact Statement, click on: Final Feasibility Report / Environmental Impact Statement

To see the Appendices to the Final Feasibility Report, click on:  

Appendix A Hydrology and Hydraulic Analysis
                   And Engineering Design
Appendix B Economics
Appendix C Real Estate
Appendix D Cost Engineering
Appendix E Environmental And Regulatory
Appendix F Cultural Resources
Appendix G Public And Agency Involvement
Appendix H Value Engineering Study
Appendix I   Design Drawings