Hillman Reservoir Report

Last Updated: December 5, 2025

Located in Montmorency County, Michigan, Hillman is a hydroelectric dam on the Thunder Bay River that was completed in 1895.


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Summary

With a dam height of 16 feet and a length of 128 feet, Hillman serves multiple purposes including hydroelectric power generation and recreation. The dam has a storage capacity of 500 acre-feet and covers a surface area of 160 acres, with a maximum discharge of 2100 cubic feet per second.

Managed by the Federal Energy Regulatory Commission, Hillman has a low hazard potential and a moderate risk assessment rating. It features an uncontrolled spillway with a width of 45 feet and three slide (sluice gate) outlet gates. While the condition assessment is currently not available, the dam undergoes inspections every three years to ensure its safety and integrity. In the event of an emergency, an Emergency Action Plan (EAP) is in place, last revised in December 2019.

Hillman Dam represents a blend of historical significance and modern-day functionality, contributing to water resource management and renewable energy generation in the region. Its presence on the Thunder Bay River not only provides economic benefits through hydroelectric power production but also offers recreational opportunities for visitors. As climate change continues to impact water resources, the maintenance and monitoring of dams like Hillman become crucial for sustainable water management and climate resilience efforts.

Year Completed

1895

Dam Length

128

Dam Height

16

River Or Stream

Thunder Bay

Surface Area

160

Drainage Area

249

Nid Storage

500

Outlet Gates

Slide (sluice gate) - 3

Hazard Potential

Low

Foundations

Soil

Nid Height

16
       
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.