Thompson Falls - Main Channel Dam Reservoir Report

Reservoir Report

Montana

Nearby: Thompson Falls - Dry Channel Dam Thompson Falls - Intake Dam B

Last Updated: December 24, 2025

Thompson Falls - Main Channel Dam, located in Sanders, Montana, is a historic gravity dam completed in 1915 on the Clark Fork River.

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Summary

With a height of 50 feet and a length of over 1000 feet, the dam serves primarily for hydroelectric purposes, generating power from the flowing waters of the river. The dam has a normal storage capacity of 14,970 acre-feet and a maximum discharge rate of 175,000 cubic feet per second, making it a vital structure for water resource management in the area.

Owned privately, the Thompson Falls Dam is regulated by the Federal Energy Regulatory Commission and is inspected by the same agency. The dam's spillway type is controlled, with a width of 913 feet, and it is equipped with outlet gates for water control. Despite its low hazard potential, the dam is recognized for its very high risk assessment due to its age and structural integrity concerns, requiring ongoing risk management measures to ensure its continued safety and functionality. The dam is not state-regulated, inspected, or permitted, highlighting the significant federal oversight in its operation and maintenance.

The Thompson Falls - Main Channel Dam stands as a significant landmark in the region, providing hydroelectric power and water resource management for the surrounding area. With a rich history dating back over a century, the dam's engineering marvel continues to serve its primary purpose effectively while facing challenges related to its age and risk assessment. As a vital component of the Clark Fork River system, the dam's operation and maintenance remain crucial for ensuring sustainable water management and climate resilience in the face of changing environmental conditions.

Year Completed	1915
Dam Length	1016.33
Dam Height	50
River Or Stream	Clark Fork River, Pend Oreille
Primary Dam Type	Gravity
Surface Area	1580
Hydraulic Height	50
Drainage Area	21113
Nid Storage	24450
Structural Height	54
Outlet Gates	Other Controlled - 33, Tainter (radial) - 2
Hazard Potential	Low
Nid Height	54

Explore Interactive Map

THOMPSON FALLS - MAIN CHANNEL DAM

Reservoir Report • Water Levels • Weather Forecast

December 24, 2025

Year_Completed	1915
Dam_Length	1016.33
Dam_Height	50
River_Or_Stream	Clark Fork River, Pend Oreille
Primary_Dam_Type	Gravity
Surface_Area	1580
Hydraulic_Height	50
Drainage_Area	21113
Nid_Storage	24450
Structural_Height	54
Outlet_Gates	Other Controlled - 33, Tainter (radial) - 2
Hazard_Potential	Low
Nid_Height	54

Seasonal Comparison

Weather Forecast

Nearby Streamflow Levels

Prospect Creek At Thompson Falls Mt 560.0cfs	560cfs
Thompson River Near Thompson Falls Mt 765.0cfs	765cfs
St. Regis River Near St. Regis 1210.0cfs	1210cfs
Clark Fork At St. Regis Mt 9520.0cfs	9520cfs
Clark Fork Near Plains Mt 24900.0cfs	24900cfs
Canyon Creek Ab Mouth At Wallace 80.8cfs	81cfs

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.