Monadnock Reservoir Report

Last Updated: December 19, 2025

Monadnock is a private hydroelectric dam located in Bennington, New Hampshire, along the Contoocook River.


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Summary

Built in 1923, this concrete structure stands at a height of 22 feet and stretches 500 feet in length. With a storage capacity of 240 acre-feet and a drainage area of 190 square miles, Monadnock serves the dual purposes of hydroelectric power generation and water supply.

Managed by the Federal Energy Regulatory Commission, Monadnock has a low hazard potential and a moderate risk assessment rating. The dam features an uncontrolled spillway with a width of 165 feet and is equipped with a single slide (sluice gate) outlet gate. While the condition assessment is not available, the dam is inspected every three years, with the last inspection conducted in June 2017. Despite its age, Monadnock continues to operate within regulatory guidelines, showcasing its importance in water resource management and climate resilience efforts in the region.

Overall, Monadnock stands as a significant infrastructure contributing to the sustainable utilization of water resources in New Hampshire. With its historical significance, operational efficiency, and regulatory compliance, this hydroelectric dam serves as a vital component in the state's efforts to balance energy generation and water supply needs while mitigating climate-related risks. As enthusiasts in water resource and climate management, Monadnock's role in supporting the region's environmental sustainability efforts is both fascinating and commendable.

Year Completed

1923

Dam Length

500

Dam Height

22

River Or Stream

Contoocook River

Primary Dam Type

Concrete

Surface Area

4

Drainage Area

190

Nid Storage

240

Outlet Gates

Slide (sluice gate) - 1

Hazard Potential

Low

Nid Height

22
       
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.