Mansfield Hollow Dam - Dike C Reservoir Report

Last Updated: December 6, 2025

Mansfield Hollow Dam - Dike C, also known as Mansfield Hollow Lake, is a gravity dam located in Willimantic, Connecticut, along the Nachaug River.


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Summary

Completed in 1952 by the US Army Corps of Engineers, the dam serves as a crucial flood risk reduction structure with a height of 78 feet and a storage capacity of 76,000 acre-feet. The dam's primary purpose is to mitigate flooding in the region, with a maximum discharge capacity of 106,500 cubic feet per second.

Managed by the US Army Corps of Engineers, Mansfield Hollow Dam - Dike C is classified as having a high hazard potential, requiring regular inspections and risk assessments. The dam's risk management measures include continuous monitoring, prioritized maintenance activities, and collaboration with local emergency managers to ensure preparedness for potential dam-related emergencies. Despite the inherent risks associated with dams, USACE works diligently to address flood risks and maintain the structural integrity of the dam to protect surrounding communities.

As part of its risk management strategy, the US Army Corps of Engineers at Mansfield Hollow Dam - Dike C emphasizes the importance of public engagement, emergency preparedness, and ongoing maintenance to minimize the impact of severe weather events and potential flood incidents. Through the development of emergency action plans, regular inspections, and coordinated efforts with local authorities, the dam continues to play a vital role in safeguarding the region against flood risks while ensuring the safety and well-being of nearby residents.

Year Completed

1952

Dam Length

14050

Dam Height

78

River Or Stream

NACHAUG RIVER

Primary Dam Type

Gravity

Surface Area

450

Hydraulic Height

74

Drainage Area

159

Nid Storage

76000

Structural Height

78

Hazard Potential

High

Nid Height

78
       
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.
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