Union Street Reservoir Report
Last Updated: December 19, 2025
Union Street in West Peterborough, New Hampshire, is home to a historic concrete gravity dam that was completed in 1916 for hydroelectric purposes on Nubanusit Brook.
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Summary
This dam, with a height of 15 feet and a length of 101 feet, has a storage capacity of 9 acre-feet and serves a drainage area of 44 square miles. With a spillway width of 75 feet and a maximum discharge of 3500 cubic feet per second, the dam is regulated by the NHDES Dam Bureau and the Federal Energy Regulatory Commission.
The dam at Union Street poses a significant hazard potential and has a moderate risk assessment rating of 3. While the condition assessment is not available, the dam is inspected every two years, with the last inspection conducted in September 2018. The emergency action plan was last revised in December 2018, ensuring that proper risk management measures are in place. The dam's operation and maintenance are overseen by private owners, highlighting the importance of ongoing monitoring and compliance with regulatory agencies to ensure the safety and sustainability of this vital water resource in Hillsborough County.
Year Completed |
1916 |
Dam Length |
101 |
Dam Height |
15 |
River Or Stream |
Nubanusit Brook |
Primary Dam Type |
Concrete |
Surface Area |
1 |
Drainage Area |
44 |
Nid Storage |
9 |
Outlet Gates |
Slide (sluice gate) - 1 |
Hazard Potential |
Significant |
Nid Height |
15 |
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.
Union Street
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