Colstrip Diversion Dam Reservoir Report
Last Updated: December 5, 2025
Colstrip Diversion Dam, located in Rosebud County, Montana, serves as a vital structure along the TR-East Fork Armells Creek.
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Summary
This earth dam, standing at a height of 44 feet and stretching 535 feet in length, was completed in 1976 and plays a crucial role in water resource management in the region. With a storage capacity of 260 acre-feet and a maximum discharge of 940 cubic feet per second, the dam ensures water supply for various purposes, including irrigation and flood control.
Managed by a public utility, Colstrip Diversion Dam is subject to state regulation and inspection by the Montana Department of Environmental Quality. Despite its high hazard potential, the dam's condition has been assessed as satisfactory, with the last inspection conducted in July 2014. The dam's emergency action plan is yet to be prepared, highlighting the need for proactive risk management measures and updated emergency response protocols. As climate change impacts water resources, the importance of maintaining and improving infrastructure like Colstrip Diversion Dam becomes increasingly crucial for sustainable water management in the region.
With its strategic location and significant storage capacity, Colstrip Diversion Dam stands as a key asset in water resource management in Montana. As climate variability and extreme weather events pose challenges to water security, ensuring the safety and effectiveness of structures like this dam is essential for continued access to water for various uses. As efforts to mitigate climate change intensify, the resilience and adaptability of infrastructure like Colstrip Diversion Dam will be essential in safeguarding water resources for future generations.
Year Completed |
1976 |
Dam Length |
535 |
Dam Height |
44 |
River Or Stream |
TR-EAST FORK ARMMELLS CREEK |
Primary Dam Type |
Earth |
Surface Area |
21 |
Hydraulic Height |
44 |
Drainage Area |
0.43 |
Nid Storage |
260 |
Hazard Potential |
High |
Nid Height |
44 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
Dam Data Reference
Condition Assessment
SatisfactoryNo 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
HighDams 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.
Colstrip Diversion Dam