Ruby Dam Reservoir Report
Last Updated: December 5, 2025
Ruby Dam, located in Alder, Montana, on the Ruby River, is a state-regulated irrigation dam completed in 1938.
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Summary
Owned by the state of Montana, this earth dam stands at a height of 111 feet and has a length of 846 feet, providing a storage capacity of 56,355 acre-feet. With a spillway width of 125 feet, the dam has a maximum discharge of 36,000 cubic feet per second, serving the primary purpose of irrigation. The dam is under the regulatory jurisdiction of the Montana Department of Natural Resources and Conservation (DNRC) and is inspected regularly to ensure its structural integrity.
Despite being classified as having a high hazard potential, Ruby Dam is in satisfactory condition as per its last assessment in June 2018. With a drainage area of 595 square miles and a surface area of 970 acres, the dam plays a crucial role in water resource management in the region. Its risk assessment is categorized as moderate, and emergency action plans are in place to address any potential threats. With a rich history dating back to its construction in the late 1930s, Ruby Dam continues to be a vital component of the water infrastructure in Madison County, Montana.
Year Completed |
1938 |
Dam Length |
846 |
Dam Height |
111 |
River Or Stream |
RUBY RIVER |
Primary Dam Type |
Earth |
Surface Area |
970 |
Hydraulic Height |
111 |
Drainage Area |
595 |
Nid Storage |
56355 |
Hazard Potential |
High |
Foundations |
Rock |
Nid Height |
111 |
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.
Ruby Dam