Sentinel Detention Dam Reservoir Report
Last Updated: December 5, 2025
Sentinel Detention Dam, located in Phillips County, Montana, is a federal-owned structure managed by the Bureau of Land Management.
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Summary
Completed in 1969, this gravity dam primarily serves the purposes of fire protection, stock, and small fish pond management. With a height of 33 feet and a hydraulic height of 28 feet, the dam has a storage capacity of 256.5 acre-feet and a surface area of 29.6 acres.
The dam is situated on CK CK./MISSOURI RIVER, under the jurisdiction of the Omaha District of the U.S. Army Corps of Engineers. Despite its uncontrolled spillway type and low hazard potential, the dam's condition is assessed as fair, with a moderate risk level. The last inspection in October 2017 revealed the need for ongoing monitoring and maintenance to ensure its effectiveness in protecting the surrounding area from potential flooding events.
With a designated emergency action plan, the Sentinel Detention Dam is equipped to respond to any unforeseen events, although there is room for improvement in meeting guidelines and updating emergency contacts. As a crucial component of water resource management in the region, the dam plays a vital role in safeguarding against the impacts of climate change and ensuring water availability for various uses in the area.
Year Completed |
1969 |
Dam Length |
491 |
River Or Stream |
CK CK./MISSOURI RIVER |
Primary Dam Type |
Gravity |
Surface Area |
29.6 |
Hydraulic Height |
28 |
Drainage Area |
1.4 |
Nid Storage |
256.5 |
Structural Height |
33 |
Hazard Potential |
Low |
Foundations |
Unlisted/Unknown |
Nid Height |
33 |
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.
Sentinel Detention Dam