Poquonnock Reservoir Dam Reservoir Report

Last Updated: December 5, 2025

The Poquonnock Reservoir Dam, also known as Groton Reservoir, is a vital water supply structure located in Groton, Connecticut.


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Summary

Built in 1901, this masonry dam stands at a height of 17.5 feet and has a storage capacity of 1,660 acre-feet, serving the community with a normal storage capacity of 921 acre-feet. The dam is situated on the Great Brook river and is regulated by the Connecticut Department of Energy and Environmental Protection (DEEP).

With a surface area of 139 acres and a drainage area of 15.9 square miles, the Poquonnock Reservoir Dam plays a crucial role in managing water resources in the region. The dam has a high hazard potential but is currently in satisfactory condition, as per the last assessment conducted in January 2018. It is inspected every two years to ensure its structural integrity and overall safety for the surrounding area.

Despite not having a spillway type specified, the dam has a spillway width of 209 feet and a maximum discharge capacity of 1,160 cubic feet per second. The primary purpose of the Poquonnock Reservoir Dam is water supply, and it continues to fulfill this role effectively for the residents of Groton and beyond. As a key component of the local water infrastructure, the dam's importance in managing water resources and ensuring water supply reliability cannot be overstated.

Year Completed

1901

Dam Length

290

Dam Height

17.5

River Or Stream

GREAT BROOK

Primary Dam Type

Masonry

Surface Area

139

Drainage Area

15.9

Nid Storage

1660

Hazard Potential

High

Nid Height

18
       
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.