Rocky Gorge Upper Reservoir Report
Nearby: South Berwick South Berwick
Last Updated: December 18, 2025
Rocky Gorge Upper in South Berwick, Maine, is a privately owned hydroelectric dam completed in 1900, standing at a height of 10 feet and a length of 140 feet.
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Summary
With a maximum storage capacity of 141 acre-feet, this concrete gravity dam sits on the Great Works River, with a drainage area of 85.5 square miles. The dam's spillway type is uncontrolled, with a width of 100 feet, and a maximum discharge capacity of 6600 cubic feet per second.
Despite its age, Rocky Gorge Upper has a low hazard potential and a moderate risk assessment rating of 3, as determined by the Federal Energy Regulatory Commission. While the dam has not undergone a recent condition assessment, it has a scheduled inspection frequency of 3 years, with the last inspection conducted in July 2019. The emergency action plan for the dam was last revised in January 2016, ensuring that the necessary protocols are in place in case of any unforeseen events.
With its strategic location and historical significance in the region, Rocky Gorge Upper serves as an essential component of Maine's water resource infrastructure, providing clean hydroelectric power while managing water flow and storage. As a well-maintained and regulated structure under the oversight of federal agencies, the dam continues to play a crucial role in both energy production and environmental stewardship in the area.
Year Completed |
1900 |
Dam Length |
140 |
Dam Height |
10 |
River Or Stream |
Great Works River |
Primary Dam Type |
Concrete |
Surface Area |
43 |
Drainage Area |
85.5 |
Nid Storage |
141 |
Hazard Potential |
Low |
Nid Height |
10 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
Dam Data Reference
Condition Assessment
SatisfactoryNo 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
HighDams 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.
Rocky Gorge Upper
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