Thorson Group North Reservoir Report

Last Updated: December 5, 2025

Thorson Group North, located in Houston, Minnesota, is a state-regulated earth dam designed by the USDA NRCS with a primary purpose of flood risk reduction.


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Summary

Completed in 1963, this dam stands at 30 feet high and spans 440 feet in length, with a storage capacity of 45 acre-feet. The structure is situated along the Root River South Fork-TR and falls under the jurisdiction of the MNDNR EWR for permitting, inspection, and enforcement.

With a significant hazard potential and a satisfactory condition assessment as of 2015, the Thorson Group North dam plays a crucial role in mitigating flood risks in the area. The spillway, with a width of 125 feet, is uncontrolled, and the structure has uncontrolled outlet gates. The dam's risk assessment is moderate, with a notable discharge capacity of 800 cubic feet per second. Regular inspections are conducted every 4 years, with the most recent inspection carried out in May 2019.

Overall, Thorson Group North serves as a vital infrastructure for flood protection in Minnesota, showcasing the collaborative efforts between state agencies and the USDA NRCS in managing water resources and climate challenges. As a key component in the region's flood risk reduction strategy, this earth dam underscores the importance of proactive maintenance and regulatory oversight to ensure the safety and resilience of water infrastructure systems.

Year Completed

1963

Dam Length

440

Dam Height

28

River Or Stream

ROOT RIVER S FORK-TR

Primary Dam Type

Earth

Drainage Area

0.8

Nid Storage

45

Structural Height

30

Outlet Gates

Uncontrolled

Hazard Potential

Significant

Foundations

Unlisted/Unknown

Nid Height

30
       
Seasonal Comparison

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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.