Thomson Dam No 11 Reservoir Report

Last Updated: December 5, 2025

Thomson Dam No 11, also known as Nos 11, 11-1/2, and Upper Gate House, is a key structure located in Thomson, Minnesota, along the St.


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Summary

Louis River. Built in 1907 for hydroelectric purposes, this gravity dam stands at 17 feet tall and stretches 365 feet in length, with a storage capacity of 4352 acre-feet. Owned and regulated by the Minnesota Department of Natural Resources, this dam is inspected regularly to ensure its safety and functionality, with the Federal Energy Regulatory Commission overseeing its operation.

With a high hazard potential due to its location and design, Thomson Dam No 11 plays a crucial role in managing water resources and generating hydroelectric power in the region. Its controlled spillway and associated structures support its function for flood control, recreation, and water storage. The dam's risk assessment indicates a very high level of risk, highlighting the importance of ongoing monitoring, maintenance, and emergency preparedness to safeguard the surrounding community and environment.

Thomson Dam No 11 serves as a historic and vital infrastructure for water resource management and climate resilience in Carlton County, Minnesota. As part of the larger St. Paul District of the US Army Corps of Engineers, this dam exemplifies the collaboration between state and federal agencies to ensure the safety, sustainability, and efficiency of water infrastructure for the benefit of both people and the environment.

Year Completed

1907

Dam Length

365

Dam Height

17

River Or Stream

St Louis River

Surface Area

375

Hydraulic Height

17

Nid Storage

4352

Structural Height

17

Hazard Potential

High

Nid Height

17
       
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.