Patillas Dam Reservoir Report

Last Updated: December 12, 2025

Located in Patillas, Puerto Rico, the Patillas Dam stands as a vital structure harnessing the power of the Grande de Patillas River for hydroelectricity and irrigation purposes.


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Summary

Built in 1976 by the Puerto Rico Electric Power Authority, this concrete dam boasts a height of 127 feet and a length of 1067 feet, with a storage capacity of 17,073 acre-feet and a maximum discharge of 79,000 cubic feet per second.

Despite its strategic importance, the Patillas Dam has been rated with a high hazard potential and poor condition assessment, signaling the need for urgent maintenance and risk management measures. With a very high risk level assigned and a history of poor condition, the dam poses a significant challenge for regulatory agencies like PREPA to ensure its safety and functionality. In light of these concerns, efforts to enhance emergency preparedness, conduct regular inspections, and implement necessary repairs are crucial to safeguard the surrounding communities and water resources.

Year Completed

1976

Dam Length

1067

Dam Height

127

River Or Stream

GRANDE DE PATILLAS RIVER

Primary Dam Type

Concrete

Surface Area

367

Hydraulic Height

118

Drainage Area

25.2

Nid Storage

17073

Structural Height

127

Outlet Gates

Tainter (radial), Vertical Lift

Hazard Potential

High

Foundations

Rock

Nid Height

127
       
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.