Ninth Street Reservoir Report

Last Updated: December 5, 2025

Ninth Street Dam in Alpena, Michigan, is a historic gravity dam completed in 1910 primarily for hydroelectric power generation and recreation purposes.


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Summary

The dam stands at 24 feet in height and spans 503 feet in length, with a storage capacity of 6,000 acre-feet and a drainage area of 1,275 square miles. Situated on the Thunder Bay River, the dam's uncontrolled spillway has a width of 84 feet and can discharge up to 20,600 cubic feet per second.

Managed by the Federal Energy Regulatory Commission, Ninth Street Dam has a high hazard potential due to its age and condition, with a moderate risk assessment rating. Despite its critical importance for water resource management and energy production in the region, the dam's condition assessment is currently listed as "Not Available". Emergency action plans are in place, with the last revision in December 2020, to ensure a prompt response in case of any unforeseen events.

As a key infrastructure for both water resource management and energy production, Ninth Street Dam plays a vital role in the local community. With its historical significance and ongoing operational challenges, maintaining the dam's safety and functionality is crucial for ensuring the sustainable management of the Thunder Bay River watershed and the continued provision of hydroelectric power to the region.

Year Completed

1910

Dam Length

503

Dam Height

24

River Or Stream

Thunder Bay

Primary Dam Type

Gravity

Surface Area

700

Drainage Area

1275

Nid Storage

6000

Outlet Gates

Tainter (radial) - 7

Hazard Potential

High

Foundations

Rock

Nid Height

24
       
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.