Nuuanu Dam No. 4

About Nuuanu Dam No. 4

The primary purpose of Nuuanu Dam No. 4 is flood risk reduction. The dam is designed to control downstream flooding by temporarily storing excess water during storms and releasing it at a controlled rate. The dam is owned by Honolulu Board Of Water Supply (local government). It impounds the Nuuanu Stream near Honolulu.

The dam stands 73 feet tall and stretches 2,120 feet across, creates a reservoir covering 25 acres, has a maximum storage capacity of 3,600 acre-feet, and collects water from a drainage area of 1 square miles. Completed in 1910, the structure is over a century old.

This dam carries a high hazard potential classification, which means that a failure or uncontrolled release of water would likely cause loss of human life. This classification reflects the consequences of failure, not the likelihood — it indicates that people live or work in the area downstream. Its condition is rated fair — the dam has minor deficiencies that are being addressed or do not pose an immediate safety threat. An emergency action plan is in place for this dam. The most recent inspection on record was 04/04/2024.

At 73 feet, this dam is taller than 97% of all dams in the United States.

Living Downstream

If you live or work downstream of this dam, consider taking these steps: learn your local evacuation routes, check whether your county emergency management office has a dam failure inundation map, and sign up for local emergency alerts. The Hawaii dam safety program can provide more specific information about emergency planning for this structure.

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