Nepaug East Dike Reservoir Report

Last Updated: December 10, 2025

Nepaug East Dike, also known as Nepaug Reservoir, is a concrete dam located in Collinsville, Connecticut.


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Summary

Built in 1916, this structure serves a primary purpose of water supply, with a storage capacity of 40,540 acre-feet and a normal storage level of 29,300 acre-feet. The dam stands at a height of 30 feet and spans a length of 700 feet, creating a reservoir with a surface area of 850 acres and draining a watershed area of 31.9 square miles.

Managed by the Connecticut Department of Energy and Environmental Protection (DEEP), Nepaug East Dike is a critical infrastructure for water resource management in the region. The dam has a high hazard potential and is inspected every two years to ensure its satisfactory condition and compliance with regulatory standards. Its associated structures include CT00370 and CT00370S02, with the last inspection conducted in August 2019.

Located on the Nepaug River, Nepaug East Dike plays a vital role in supplying water to the surrounding communities while also mitigating flood risks and ensuring water resource sustainability. As a key component of Connecticut's water infrastructure, this dam exemplifies the importance of proactive management and maintenance to safeguard both water resources and the environment in the face of changing climate conditions.

Year Completed

1916

Dam Length

700

Dam Height

30

River Or Stream

NEPAUG RIVER

Primary Dam Type

Concrete

Surface Area

850

Drainage Area

31.9

Nid Storage

40540

Outlet Gates

Valve

Hazard Potential

High

Foundations

Unlisted/Unknown

Nid Height

30
       
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.