Mascoma Lake Dam Reservoir Report

Last Updated: December 13, 2025

Mascoma Lake Dam, located in Lebanon, New Hampshire, is a concrete structure with a buttress core type that was completed in 1881.


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Summary

The dam stands at a height of 18 feet and stretches for 575 feet, creating a reservoir with a maximum storage capacity of 18,300 acre-feet. The primary purpose of the dam is for recreation, and it is regulated by the NHDES Dam Bureau.

Despite its historical significance, Mascoma Lake Dam is currently rated as having a high hazard potential and a poor condition assessment. The last inspection in October 2020 revealed the need for improvements, with the dam being labeled as a moderate risk (3). With a drainage area of 153 square miles and a maximum discharge capacity of 17,255 cubic feet per second, ensuring the structural integrity and safety of the dam is crucial for the surrounding community and the environment.

As water resource and climate enthusiasts, it is important to monitor the maintenance and potential risks associated with Mascoma Lake Dam. With its significant storage capacity and location on the Mascoma River, the dam plays a vital role in the local ecosystem and recreational activities. Continued inspections, risk assessments, and potential management measures will be essential to safeguarding this important infrastructure for future generations.

Year Completed

1881

Dam Length

575

Dam Height

18

River Or Stream

MASCOMA RIVER

Primary Dam Type

Concrete

Surface Area

1155

Drainage Area

153

Nid Storage

18300

Hazard Potential

High

Foundations

Unlisted/Unknown

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.