Thomson Dam No 3 Reservoir Report

Last Updated: December 5, 2025

Thomson Dam No 3, located in Thomson, Minnesota, is a gravity dam completed in 1907 with a primary purpose of hydroelectric power generation.


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Summary

The dam is part of a series of structures including Nos 2-3/4, 3, 3a, 4, and 4a, with a total of 13 associated structures. Managed by the Minnesota Department of Natural Resources, the dam is regulated at both the state and federal levels, with inspections conducted by the Federal Energy Regulatory Commission.

With a height of 38 feet and a length of 1322 feet, Thomson Dam No 3 has a maximum storage capacity of 4352 acre-feet and a normal storage capacity of 4352 acre-feet. The dam, situated on the St. Louis River, has a controlled spillway and a high hazard potential, requiring regular inspections and risk assessments. Despite the lack of available condition assessment data, the dam's emergency action plan was last revised in 2009, indicating preparedness for potential emergencies.

Overall, Thomson Dam No 3 is a significant infrastructure for hydroelectric power generation in Minnesota, showcasing a blend of historical significance and modern regulatory compliance. As climate change continues to impact water resources, the dam's role in managing water flow and generating clean energy becomes even more vital, underlining the importance of regular maintenance and risk management measures to ensure the safety and efficiency of the structure.

Year Completed

1907

Dam Length

1322

Dam Height

38

River Or Stream

St Louis River

Surface Area

375

Hydraulic Height

38

Nid Storage

4352

Structural Height

38

Hazard Potential

High

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.