Gilman Mill Reservoir Report

Last Updated: December 20, 2025

Gilman Mill in Penobscot, Maine, is a privately owned hydroelectric dam on Blackman Stream, completed in 1963.


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Summary

Standing at 15 feet tall and 250 feet long, this concrete dam serves a primary purpose of generating hydroelectric power. With a storage capacity of 86 acre-feet and a normal storage of 52 acre-feet, Gilman Mill plays a crucial role in water resource management in the area.

Despite being classified as having a low hazard potential, Gilman Mill is subject to state regulation, permitting, inspection, and enforcement by the Maine Emergency Management Agency. The dam has not been rated for its condition assessment, with the last inspection conducted in April 2011. With a spillway width of 40 feet, Gilman Mill is equipped to handle water discharge effectively, contributing to flood control measures in the region.

Located in the New England District, Gilman Mill's operational efficiency and structural integrity are vital for sustainable water resource management and climate resilience. As a key player in the local hydroelectric infrastructure, this dam serves as a reminder of the intersection between water resources, climate adaptation, and renewable energy generation in Maine.

Year Completed

1963

Dam Length

250

Dam Height

15

River Or Stream

Blackman Stream

Primary Dam Type

Concrete

Surface Area

20

Hydraulic Height

15

Nid Storage

86

Structural Height

15

Hazard Potential

Low

Nid Height

15
       
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.