Five Mile Reservoir Report

Last Updated: December 5, 2025

Five Mile is a historic dam located in Killingly, Connecticut, along the picturesque Five Mile River.


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Summary

Built in 1855, this masonry dam stands at 16.5 feet tall and has a length of 145 feet, creating a reservoir with a storage capacity of 260 acre-feet. With a drainage area of 77 square miles, the dam has a maximum discharge rate of 3100 cubic feet per second, making it a significant hydroelectric structure in the region.

Managed by a private owner, Five Mile is primarily used for hydroelectric purposes and is regulated by the Federal Energy Regulatory Commission. The dam has a spillway width of 135 feet and is classified as having a significant hazard potential. Despite its age, the dam's condition assessment is not available, highlighting the need for continued monitoring and maintenance to ensure its safety and longevity in the face of changing climate conditions.

Overall, Five Mile represents a blend of historical significance and modern utility, serving as both a key hydroelectric resource and a potential risk management challenge. Its location along the Five Mile River adds to its scenic charm, while its role in energy production underscores the importance of balancing water resource utilization with environmental stewardship in the context of climate change.

Year Completed

1855

Dam Length

145

Dam Height

16.5

River Or Stream

Five Mile River

Primary Dam Type

Masonry

Surface Area

65

Drainage Area

77

Nid Storage

260

Hazard Potential

Significant

Nid Height

17
       
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.