Big Timber #21 Reservoir Report
Nearby: Montana #17 Sun Coulee
Last Updated: December 6, 2025
Big Timber #21, also known as Big Timber Dam, is a privately owned structure located in Mosby, Montana.
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Summary
Built in 1944 by the USDA NRCS, this earth dam stands at a height of 18 feet and has a length of 1000 feet, providing essential fire protection and serving as a stock or small fish pond. With a storage capacity of 60 acre-feet and a drainage area of 1.72 square miles, the dam has a low hazard potential and a moderate risk assessment rating.
Managed by the DNRC, Big Timber #21 is equipped with an uncontrolled spillway with a width of 100 feet and a maximum discharge capacity of 1100 cubic feet per second. While its condition assessment is currently not rated, the dam undergoes regular state inspections and enforcement to ensure its integrity and safety. With its primary purpose of fire protection and water resource management, this dam plays a crucial role in the local ecosystem and landscape, contributing to the overall sustainability and resilience of the surrounding area.
For water resource and climate enthusiasts, Big Timber #21 offers a fascinating glimpse into the intersection of human infrastructure and natural ecosystems. As a key feature of Fords Creek Offstream, this dam not only provides vital water storage for fire protection and agricultural purposes but also serves as a habitat for small fish populations. With its location in Rosebud County, Montana, and its association with the Omaha District of the USACE, Big Timber #21 exemplifies the importance of sustainable water management practices in mitigating climate risks and promoting environmental stewardship.
Year Completed |
1944 |
Dam Length |
1000 |
Dam Height |
18 |
River Or Stream |
FORDS CREEK OFFSTREAM |
Primary Dam Type |
Earth |
Hydraulic Height |
18 |
Drainage Area |
1.72 |
Nid Storage |
60 |
Hazard Potential |
Low |
Nid Height |
18 |
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.
Big Timber #21