Maui Reservoir 20 Reservoir Report

Last Updated: December 19, 2025

Maui Reservoir 20, also known as Hc&S Reservoir 20, is a privately owned water storage facility located in Haliimaile, Maui, Hawaii.


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Summary

Built in 1913, this Earth-type dam stands at a height of 42 feet and has a maximum storage capacity of 164.8 acre-feet. The reservoir primarily serves the purpose of irrigation, being fed by an irrigation ditch.

Despite its historical significance and essential role in supporting agricultural activities in the region, Maui Reservoir 20 poses a high hazard potential due to its poor condition assessment. With a moderate risk rating, there is a pressing need for maintenance and risk management measures to ensure the safety and functionality of this critical water resource infrastructure. The last inspection in August 2020 revealed the dam's deteriorating state, emphasizing the urgency for rehabilitation and emergency preparedness.

As a key component of Hawaii's water resource infrastructure, Maui Reservoir 20 requires attention and investment to address its aging infrastructure and mitigate potential hazards. With state regulation and inspection in place, stakeholders must collaborate to safeguard this vital reservoir for sustainable water management and climate resilience in Maui County.

Year Completed

1913

Dam Length

1320

Dam Height

42

River Or Stream

FED BY IRRIGATION DITCH

Primary Dam Type

Earth

Surface Area

10.2

Hydraulic Height

35

Drainage Area

0.09

Nid Storage

164.8

Structural Height

37

Hazard Potential

High

Foundations

Unlisted/Unknown

Nid Height

42
       
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.