Mashapaug Pond Dam #1 South Reservoir Report

Last Updated: December 6, 2025

Mashapaug Pond Dam #1 South, located in Union, Connecticut, is a state-owned concrete dam completed in 1900 with a primary purpose of recreation.


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Summary

The dam stands at a height of 6 feet and has a length of 60 feet, creating a reservoir with a storage capacity of 5,860 acre-feet and a surface area of 273 acres. The dam regulates Bigelow Brook, with a drainage area of 4.68 square miles, and can discharge up to 200 cubic feet per second through a spillway that is 25 feet wide.

Despite being assessed as in fair condition during its last inspection in May 2015, Mashapaug Pond Dam #1 South has been classified as having a significant hazard potential. The dam is subject to regular state regulation, inspection, and enforcement by the Connecticut Department of Energy and Environmental Protection (DEEP). While the dam has not been modified in recent years, its Emergency Action Plan (EAP) was last revised in December 1995, raising questions about its current readiness for emergencies. With a history dating back over a century, this dam plays a crucial role in providing recreational opportunities while also posing potential risks that must be carefully managed and monitored.

Year Completed

1900

Dam Length

60

Dam Height

6

River Or Stream

BIGELOW BROOK

Primary Dam Type

Concrete

Surface Area

273

Drainage Area

4.68

Nid Storage

5860

Hazard Potential

Significant

Nid Height

6
       
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.