Whaley #11 Dam Reservoir Report
Nearby: Whaley #13 Gearhart #15
Last Updated: December 8, 2025
Whaley #11 Dam, located in Rosebud, Montana, is a gravity dam with a height of 26 feet and a hydraulic height of 21 feet.
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Summary
It was built by the Bureau of Land Management and is situated on Rattlesnake Creek. The dam has a storage capacity of 150.1 acre-feet, with a normal storage level of 134.98 acre-feet and a surface area of 25.7 acres.
Despite its low hazard potential, the dam is currently in poor condition, with a risk assessment rating of moderate. The last inspection was conducted in September 2018, and the dam is scheduled for inspection every 5 years. Whaley #11 Dam is classified as uncontrolled spillway type and has a spillway width of 2 feet. The primary purpose of the dam is not specified, but it serves as a vital water resource for the region.
With its historical significance as a federal structure and its role in water management on Rattlesnake Creek, Whaley #11 Dam is a key feature for water resource and climate enthusiasts. The dam's condition assessment and risk level highlight the importance of ongoing maintenance and monitoring to ensure the safety and efficiency of this essential infrastructure for the surrounding community.
Dam Length |
487 |
River Or Stream |
RATTLESNAKE CREEK |
Primary Dam Type |
Gravity |
Surface Area |
25.7 |
Hydraulic Height |
21 |
Drainage Area |
2.3 |
Nid Storage |
150.1 |
Structural Height |
26 |
Hazard Potential |
Low |
Foundations |
Unlisted/Unknown |
Nid Height |
26 |
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.
Whaley #11 Dam