Mcnab Dam Reservoir Report
Nearby: Barnard (Valley) Pippen
Last Updated: January 11, 2026
Mcnab Dam, located in Valley, Montana, is a gravity dam with a hydraulic height of 33 feet and a structural height of 39 feet.
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Summary
Built in 2003 by the Bureau of Land Management, the dam has a storage capacity of 172.25 acre-feet and covers a surface area of 10.6 acres. With a controlled spillway type, the dam has a spillway width of 2 feet and is classified as having a low hazard potential.
Despite its low hazard potential, the condition assessment of Mcnab Dam is considered unsatisfactory, signaling potential risks that need to be addressed. The last inspection date was in August 2016, with an inspection frequency of every 5 years. The dam's risk assessment is classified as very high, highlighting the importance of implementing risk management measures to ensure the safety and integrity of the structure.
As an important water resource in Montana, Mcnab Dam serves as a vital infrastructure for water storage and management. With its unique design and construction by the Bureau of Land Management, the dam plays a crucial role in regulating water flow and providing flood control measures in the region. Climate and water resource enthusiasts can appreciate the significance of Mcnab Dam in sustaining the local ecosystem and supporting water-related activities in the area.
Year Completed |
2003 |
Dam Length |
396 |
Primary Dam Type |
Gravity |
Surface Area |
10.6 |
Hydraulic Height |
33 |
Nid Storage |
172.25 |
Structural Height |
39 |
Hazard Potential |
Low |
Foundations |
Unlisted/Unknown |
Nid Height |
39 |
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.
Mcnab Dam