Donley Reservoir (Rosebud) Reservoir Report
Nearby: T L Johnson #5 T L Johnson #1
Last Updated: December 7, 2025
Donley Reservoir, also known as Donley Dam, is a private-owned water resource located in Rosebud County, Montana.
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Summary
Built in 1930 by the USDA NRCS, this earth dam stands at a height of 38 feet and has a storage capacity of 654 acre-feet. The primary purpose of the reservoir is for fire protection, stock, and as a small fish pond. It is regulated by the Montana Department of Natural Resources and Conservation (DNRC) and has a low hazard potential rating.
Situated on Larson Coulee, Donley Reservoir spans a drainage area of 4.38 square miles and has a maximum discharge of 3500 cubic feet per second. The uncontrolled spillway at the dam is 300 feet wide, ensuring safe water release during periods of high inflow. Despite being not rated in terms of condition assessment, the reservoir has a moderate risk assessment rating of 3, indicating a need for ongoing risk management measures. Donley Reservoir serves as a crucial water source for the local community and plays a vital role in maintaining water supply for various uses in the region.
Year Completed |
1930 |
Dam Length |
400 |
Dam Height |
38 |
River Or Stream |
LARSON COULEE |
Primary Dam Type |
Earth |
Hydraulic Height |
38 |
Drainage Area |
4.38 |
Nid Storage |
654 |
Hazard Potential |
Low |
Nid Height |
38 |
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.
Donley Reservoir (Rosebud)