Nuuanu Reservoir No. 1

About Nuuanu Reservoir No. 1

The primary purpose of Nuuanu Reservoir No. 1 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).

The dam stands 34 feet tall and stretches 588 feet across, creates a reservoir covering 6 acres, has a maximum storage capacity of 63 acre-feet, and collects water from a drainage area of 0 square miles. Completed in 1905, 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 poor, meaning the dam has recognized safety deficiencies that require remediation to address risks. An emergency action plan is in place for this dam. The most recent inspection on record was 04/04/2024.

At 34 feet, this dam is taller than 80% of dams nationwide.

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.

Search for dams near your address to see all dams in your area with hazard classifications and safety data.