Apthorp Reservoir Report

Last Updated: December 16, 2025

Apthorp is a privately owned concrete dam located in Littleton, New Hampshire, along the Ammonoosuc River.


°F

°F

mph

Wind

%

Humidity

Summary

Completed in 1936, this hydroelectric dam stands at 24 feet high and spans 235 feet in length, with a storage capacity of 210 acre-feet. With a significant hazard potential and moderate risk assessment rating, Apthorp is regulated by the NHDES Dam Bureau and inspected by the Federal Energy Regulatory Commission.

The dam features an uncontrolled spillway with a width of 180 feet and two slide gates for outlet control. It has a maximum discharge capacity of 14,800 cubic feet per second, serving the primary purpose of hydroelectric power generation. Despite its age, the condition assessment of Apthorp is currently not available, with the last inspection conducted in September 2020. The emergency action plan was last revised in July 2019, indicating a commitment to safety and risk management measures.

Located in Grafton County, New Hampshire, Apthorp is a key infrastructure for water resource management in the region. With its historical significance and continued operation for hydroelectric power generation, this dam plays a crucial role in supporting the local economy and contributing to the sustainable use of water resources in the area. Climate and water resource enthusiasts will find Apthorp's unique design and functionality an intriguing subject for further study and appreciation of its impact on the surrounding environment.

Year Completed

1936

Dam Length

235

Dam Height

24

River Or Stream

Ammonoosuc River

Primary Dam Type

Concrete

Surface Area

20

Drainage Area

205

Nid Storage

210

Outlet Gates

Slide (sluice gate) - 2

Hazard Potential

Significant

Nid Height

24
       
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.