Upper Dam Reservoir Report

Last Updated: December 19, 2025

Upper Dam, located in Errol, Maine, along the Rapid River, is a hydroelectric dam completed in 1883.


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Summary

With a height of 25 feet and a length of 1500 feet, the dam has a storage capacity of 192,039 acre-feet and serves as a controlled spillway with a width of 200 feet. The dam is primarily regulated by the Federal Energy Regulatory Commission and has a high hazard potential due to its age and condition.

This historic dam, constructed with buttress, earth, and rockfill materials, plays a crucial role in providing hydroelectric power to the region. The dam's controlled spillway and outlet gates, including slide and tainter gates, help manage the flow of water and ensure the safety of the surrounding areas. Despite its age, the dam has a very high risk assessment rating, indicating the need for continued monitoring and maintenance to prevent potential hazards.

As a key infrastructure for water resource and climate enthusiasts, Upper Dam serves as a reminder of the importance of sustainable energy solutions and the need to balance environmental impact with energy production. With its rich history and significant storage and discharge capabilities, the dam represents a vital piece of Maine's hydroelectric infrastructure and underscores the ongoing challenges of managing aging dams in a changing climate.

Year Completed

1883

Dam Length

1500

Dam Height

25

River Or Stream

Rapid River

Surface Area

15741

Drainage Area

382

Nid Storage

192039

Outlet Gates

Slide (sluice gate) - 2, Tainter (radial) - 1

Hazard Potential

High

Foundations

Soil

Nid Height

25
       
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.