Upper Unionville Reservoir Dam Reservoir Report

Last Updated: December 10, 2025

The Upper Unionville Reservoir Dam, located in Unionville, Connecticut, is a historic masonry dam completed in 1909 for the primary purpose of recreation.


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Summary

The dam, standing at 23 feet high and 220 feet long, creates a reservoir with a storage capacity of 18 acre-feet and a surface area of 1.5 acres. The dam is situated on Hawley Brook and is regulated by the Connecticut Department of Energy and Environmental Protection (DEEP), with state permitting, inspection, and enforcement in place to ensure its safety and compliance with regulations.

Despite its age, the Upper Unionville Reservoir Dam is assessed to be in fair condition, with significant hazard potential. The dam has a spillway width of 35 feet and a maximum discharge capacity of 100 cubic feet per second. Regular inspections are conducted, with the last assessment taking place in September 2019. While the dam serves as a recreational area for the community, its condition and risk potential are closely monitored to ensure the safety of residents and visitors. Climate and water resource enthusiasts can appreciate the historical significance and environmental importance of this dam in the Hartford County area.

Year Completed

1909

Dam Length

220

Dam Height

23

River Or Stream

HAWLEY BROOK

Primary Dam Type

Masonry

Surface Area

1.5

Drainage Area

0.9

Nid Storage

18

Hazard Potential

Significant

Nid Height

23
       
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.