Lebanon Water Treatment Intake Dam Reservoir Report

Last Updated: December 13, 2025

The Lebanon Water Treatment Intake Dam, located on the Mascoma River in Grafton County, New Hampshire, serves as a crucial water supply structure for the city of Lebanon.


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Summary

Built in 1934, this concrete dam stands at a height of 16 feet and has a length of 140 feet, providing a storage capacity of 3.7 billion gallons of water. With a significant hazard potential but a satisfactory condition assessment, the dam is regulated, inspected, and enforced by the NHDES Dam Bureau to ensure its safety and functionality.

Despite its age, the Lebanon Water Treatment Intake Dam continues to play a vital role in water resource management, with a normal storage capacity of 0.92 billion gallons and a drainage area of 169 square miles. The dam's uncontrolled spillway, with a width of 93 feet, is designed to handle a maximum discharge of 5314 cubic feet per second to prevent potential flooding. The risk assessment for this structure is moderate, and appropriate risk management measures are in place to address any potential issues that may arise.

As a key component of Lebanon's water infrastructure, the Lebanon Water Treatment Intake Dam is essential for providing clean and safe drinking water to the local community. With regular inspections, a robust emergency action plan, and adherence to state regulatory standards, this dam exemplifies the importance of proper maintenance and management of water resources in the face of changing climate conditions.

Year Completed

1934

Dam Length

140

Dam Height

16

River Or Stream

MASCOMA RIVER

Primary Dam Type

Concrete

Surface Area

0.4

Drainage Area

169

Nid Storage

3.7

Hazard Potential

Significant

Foundations

Unlisted/Unknown

Nid Height

16
       
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.