Iverson Retention Dam Reservoir Report
Nearby: Eliasson (Petroleum) Ivy #3
Last Updated: December 5, 2025
Located in Mosby, Montana, the Iverson Retention Dam stands as a vital flood risk reduction structure managed by the Bureau of Land Management.
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Summary
Constructed in 1968, this gravity dam holds back the waters of the Flatwillow Creek and Musselshell River, providing a storage capacity of 66.42 acre-feet and covering a surface area of 11.07 acres. With a hydraulic height of 19 feet and a structural height of 22 feet, the dam plays a crucial role in safeguarding the surrounding Petroleum County from potential flooding events.
Despite its importance, the Iverson Retention Dam is currently rated as being in poor condition, highlighting the need for maintenance and upgrades to ensure its continued effectiveness. With a low hazard potential but a very high risk assessment rating, the dam's inspection frequency of every 5 years underscores the ongoing monitoring and management efforts required to mitigate any potential safety concerns. As a federal structure under the jurisdiction of the Bureau of Land Management, the Iverson Retention Dam serves as a key example of the intersection between water resource management, climate resilience, and infrastructure maintenance in the face of evolving environmental challenges.
Year Completed |
1968 |
Dam Length |
306 |
River Or Stream |
FLATWILLOW CK./MUSSELSHELL RIV |
Primary Dam Type |
Gravity |
Surface Area |
11.07 |
Hydraulic Height |
19 |
Nid Storage |
66.42 |
Structural Height |
22 |
Hazard Potential |
Low |
Foundations |
Unlisted/Unknown |
Nid Height |
22 |
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.
Iverson Retention Dam