Petranek Reservoir Report
Last Updated: December 5, 2025
Petranek, located in Fergus County, Montana, is a privately owned earth dam constructed in 1938 by the USDA NRCS for fire protection, stock, and small fish pond purposes.
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Summary
With a height of 24 feet and a hydraulic height of 20 feet, Petranek has a storage capacity of 109 acre-feet and serves the TR-FARGO COULEE river system. The dam spans 528 feet in length and has a spillway width of 40 feet, with a maximum discharge capacity of 200 cubic feet per second.
Despite being categorized as having a low hazard potential and a moderate risk assessment rating, Petranek is not currently assigned a condition assessment and does not have an emergency action plan in place. The dam is under the state jurisdiction of Montana, regulated by the DNRC, and subject to state permitting, inspection, and enforcement. While the structure has not been modified in recent years, its overall condition remains unrated, highlighting the need for further evaluation and risk management measures to ensure the safety and functionality of this vital water resource infrastructure.
Year Completed |
1938 |
Dam Length |
528 |
Dam Height |
24 |
River Or Stream |
TR-FARGO COULEE |
Primary Dam Type |
Earth |
Hydraulic Height |
20 |
Drainage Area |
0.78 |
Nid Storage |
109 |
Hazard Potential |
Low |
Nid Height |
24 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
Missouri River Near Landusky Mt
|
9100cfs |
Judith River Nr Mouth
|
368cfs |
Peoples Creek Near Hays Mt
|
4cfs |
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.
Petranek