Gilman Reservoir Report

Last Updated: December 17, 2025

Gilman, also known as Centennial Mill Dam, is a privately owned concrete gravity dam located in Dalton, New Hampshire.


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Summary

Built in 1898, this historic structure stands at a height of 38.3 feet with a length of 319 feet, serving primarily for hydroelectric purposes on the Connecticut River. The dam has a storage capacity of 705 acre-feet and a maximum discharge rate of 3538 cubic feet per second.

Managed by the Federal Energy Regulatory Commission (FERC), Gilman is subject to regular state inspections and enforcement to ensure its safety and compliance. Despite a low hazard potential, the dam poses a very high risk due to its age and structural condition assessment being unavailable. Emergency action plans are in place, with a last revision date in January 2018, although detailed risk management measures are not specified in the data. In the event of an emergency, contact information and inundation maps are crucial for effective response and mitigation efforts. Water resource and climate enthusiasts will find Gilman to be a fascinating piece of infrastructure with a rich history and complex risk profile in the realm of dam safety and management.

Year Completed

1898

Dam Length

319

Dam Height

38.3

River Or Stream

Connecticut River

Primary Dam Type

Concrete

Surface Area

130

Drainage Area

1514

Nid Storage

705

Outlet Gates

Flap - 1, Other Controlled - 2

Hazard Potential

Low

Foundations

Rock

Nid Height

38
       
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.