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Kuliouou Stream Flood Risk Management

The Kuliouou Stream Flood Risk Management project feasibility study is evaluating reducing the risk of flooding in the Kuliouou Stream area.  There is an existing federal flood control project, originally constructed under Section 205 of the Flood Control Act of 1962 (Public Law 87-874), in the lower portion of the stream.  The federal portion of the project was originally constructed in 1970, with an agreement between the Honolulu District, U.S. Army Corps of the Engineers (POH) and the City and County of Honolulu (CCH).  Later, developers expanded the residential development above the existing federal project, including the construction of a debris basin and a rectangular channel at the upstream end of the project, tying into the federal channel.

During the heavy rainfall on 31 December 1987, the Kuliouou Stream floodwaters reached very high velocities that caused $2.1M in damages to the existing federal flood control channel and severely damaged private and public property in the residential community.  The 1987 flood has highlighted the need to evaluate how changes in the drainage basin may have increased flood risk. 

The current feasibility study is evaluating possible attenuation and non-structural flood mitigation measures.  The study is being sponsored by CCH.  The Feasibility Cost Sharing Agreement was executed in July 2008.  The current plan includes providing flood mitigation along Kuliouou Stream.

Concerns of increased suspended sediments due to stream channelization were raised by the local environmental group, Malama Maunalua.  The community was concerned with sediment loads from the stream emptying into Maunalua Bay.  The Kuliouou Stream basin has approximately 330 homes in the 500-year flood plain.  US Army Corps of Engineers Agency Technical Review was conducted in 2017 and an effort to update the hydraulic and hydrological modeling was completed and discovered additional design must be included to address overtopping.  The economic BCR of this additional design was discovered to be negative thus the PDT will schedule a meeting with the sponsor to seek concurrence.

The last Public Law 84-99 Continuing Eligibility Inspection of the existing project was conducted on 20 September 2016, for which the project condition was rated as “unacceptable,” and the project status was rated as “inactive.”  The project has been inactive since FY09.