Alton Power Dam Reservoir Report

Last Updated: December 15, 2025

The Alton Power Dam, also known as the Wentworth Dam, is a concrete buttress dam located in Alton, New Hampshire on the Merrymeeting River.


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Summary

Completed in 1923, the dam primarily serves a recreational purpose, offering activities such as boating and fishing for visitors. With a height of 16 feet and a length of 190 feet, the dam has a storage capacity of 3392 acre-feet and a maximum discharge of 3900 cubic feet per second.

Despite its recreational value, the Alton Power Dam has a high hazard potential and is currently in poor condition according to a 2016 assessment. The dam is regulated by the NHDES Dam Bureau, with state permitting, inspection, and enforcement in place to ensure its safety. With a risk assessment rating of moderate, efforts to manage and mitigate potential risks associated with the dam are ongoing, though further improvements may be necessary to enhance its safety and stability for the surrounding community and environment.

In light of its historical significance and potential risks, the Alton Power Dam stands as a focal point for water resource and climate enthusiasts, highlighting the importance of maintaining and managing aging infrastructure to ensure the safety and sustainability of our water resources. As discussions continue regarding the dam's future and potential upgrades, it remains a critical structure in the region, balancing both recreational and safety considerations in the face of evolving climate challenges.

Year Completed

1923

Dam Length

190

Dam Height

16

River Or Stream

MERRYMEETING RIVER

Primary Dam Type

Concrete

Surface Area

719

Drainage Area

35.4

Nid Storage

3392

Hazard Potential

High

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.