Upper Helemano Reservoir Reservoir Report

Last Updated: December 19, 2025

Upper Helemano Reservoir, located in Waialua, Hawaii, is a privately owned water resource crucial for irrigation purposes.


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Summary

Built in 1912, this Earth dam stands at a height of 46 feet, with a storage capacity of 700 acre-feet and a surface area of 17 acres. The reservoir is fed by the TR-POAMOHO STREAM and serves as a vital source of water for agricultural activities in the region.

Despite its historical significance, Upper Helemano Reservoir is facing challenges in terms of its condition assessment, with a poor rating and high hazard potential. The dam's last inspection in May 2018 highlighted the need for improvements, with a moderate risk assessment score of 3. While there are concerns about its structural integrity, the reservoir continues to play a key role in water management in Honolulu, Hawaii.

As water resource and climate enthusiasts continue to monitor the impact of climate change on water sources, the Upper Helemano Reservoir serves as a reminder of the importance of sustainable water management practices. With its rich history and critical role in irrigation, efforts to improve the dam's condition and mitigate potential risks are essential to ensure the continued availability of water for agricultural needs in the region.

Year Completed

1912

Dam Length

530

Dam Height

46

River Or Stream

TR-POAMOHO STREAM

Primary Dam Type

Earth

Surface Area

17

Hydraulic Height

46

Drainage Area

0.45

Nid Storage

700

Structural Height

51

Hazard Potential

High

Foundations

Unlisted/Unknown

Nid Height

51
       
Seasonal Comparison

Weather Forecast

Dam Data Reference

Condition Assessment

Satisfactory
No existing or potential dam safety deficiencies are recognized. Acceptable performance is expected under all loading conditions (static, hydrologic, seismic) in accordance with the minimum applicable state or federal regulatory criteria or tolerable risk guidelines.
Fair
No existing dam safety deficiencies are recognized for normal operating conditions. Rare or extreme hydrologic and/or seismic events may result in a dam safety deficiency. Risk may be in the range to take further action. Note: Rare or extreme event is defined by the regulatory agency based on their minimum
Poor A dam safety deficiency is recognized for normal operating conditions which may realistically occur. Remedial action is necessary. POOR may also be used when uncertainties exist as to critical analysis parameters which identify a potential dam safety deficiency. Investigations and studies are necessary.
Unsatisfactory
A dam safety deficiency is recognized that requires immediate or emergency remedial action for problem resolution.
Not Rated
The dam has not been inspected, is not under state or federal jurisdiction, or has been inspected but, for whatever reason, has not been rated.
Not Available
Dams for which the condition assessment is restricted to approved government users.

Hazard Potential Classification

High
Dams assigned the high hazard potential classification are those where failure or mis-operation will probably cause loss of human life.
Significant
Dams assigned the significant hazard potential classification are those dams where failure or mis-operation results in no probable loss of human life but can cause economic loss, environment damage, disruption of lifeline facilities, or impact other concerns. Significant hazard potential classification dams are often located in predominantly rural or agricultural areas but could be in areas with population and significant infrastructure.
Low
Dams assigned the low hazard potential classification are those where failure or mis-operation results in no probable loss of human life and low economic and/or environmental losses. Losses are principally limited to the owner's property.
Undetermined
Dams for which a downstream hazard potential has not been designated or is not provided.
Not Available
Dams for which the downstream hazard potential is restricted to approved government users.