South Fork Detention Dam Reservoir Report

Last Updated: December 6, 2025

South Fork Detention Dam, located in Glendive, Montana, is a gravity dam built in 1964 by the Bureau of Land Management for fire protection, stock, and small fish pond purposes.


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Summary

With a structural height of 28 feet and a hydraulic height of 22 feet, this dam serves as a crucial resource for the surrounding area, providing a storage capacity of 520 acre-feet and covering a surface area of 41.09 acres. Situated on Cherry Creek and the Yellowstone River, the dam plays a key role in water management and protection for the region.

Despite its importance, South Fork Detention Dam has been assessed as having poor condition, with a low hazard potential but a moderate risk rating. The dam features an uncontrolled spillway and has a history of infrequent inspections, with the last one conducted in July 2020. While the dam has not been modified in recent years, there is a need for improved risk management measures to ensure its continued safety and functionality. With its federal ownership and oversight by the Bureau of Land Management, South Fork Detention Dam represents a significant water resource for the community, deserving of attention and maintenance to address its current condition and potential risks.

Year Completed

1964

Dam Length

730

River Or Stream

CHERRY CK./YELLOWSTONE RIVER

Primary Dam Type

Gravity

Surface Area

41.09

Hydraulic Height

22

Nid Storage

520

Structural Height

28

Hazard Potential

Low

Foundations

Unlisted/Unknown

Nid Height

28
       
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.