Jim Detention Dam Reservoir Report
Last Updated: December 20, 2025
Jim Detention Dam, located in Montana, is a federal-owned gravity dam primarily designed for flood risk reduction along Willow Creek and the Milk River.
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Summary
Completed in 1964 by the Bureau of Land Management, this structure stands at 19 feet tall with a hydraulic height of 14 feet, offering a storage capacity of 1380 acre-feet. With a surface area of 163 acres and a drainage area of 25.5 square miles, the dam serves as a crucial asset in mitigating potential flood hazards in the region.
Despite being classified as low hazard potential, Jim Detention Dam undergoes regular inspections by the Bureau of Land Management, with the last assessment conducted in October 2017. The dam is deemed to be in satisfactory condition, ensuring its operational readiness in case of emergencies. Although the structure has not been modified since its completion, its spillway type is uncontrolled with a width of 6 feet. With a moderate risk assessment rating, the dam is equipped with risk management measures to address any potential issues that may arise.
For water resource and climate enthusiasts, Jim Detention Dam presents an intriguing case study of a federal-owned gravity dam serving a critical flood risk reduction purpose in Montana. Its strategic location and design elements underscore the importance of sustainable water management practices in safeguarding communities and natural habitats from potential water-related disasters. The dam's operational history and risk assessment provide valuable insights into the ongoing efforts to maintain and enhance its resilience in the face of changing environmental conditions.
Year Completed |
1964 |
Dam Length |
1150 |
River Or Stream |
WILLOW CK./MILK RIVER |
Primary Dam Type |
Gravity |
Surface Area |
163 |
Hydraulic Height |
14 |
Drainage Area |
25.5 |
Nid Storage |
1380 |
Structural Height |
19 |
Hazard Potential |
Low |
Foundations |
Unlisted/Unknown |
Nid Height |
19 |
Seasonal Comparison
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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.
Jim Detention Dam