Petrolia Reservoir Report
Nearby: Hassett #1 Hassett #2
Last Updated: December 6, 2025
Petrolia, located in Petroleum County, Montana, is home to a vital irrigation dam known for its impressive height of 76 feet and storage capacity of 14,170 acre-feet.
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Summary
Completed in 1951, this earth dam on the South Fork Flatwillow Creek serves the primary purpose of irrigation, supporting agriculture in the region. With a drainage area of 612 square miles and a maximum discharge capacity of 10,200 cubic feet per second, Petrolia Dam plays a crucial role in water resource management in the area.
Managed by the local government and regulated by the Montana Department of Natural Resources and Conservation (DNRC), Petrolia Dam is subject to regular inspections to ensure its safety and functionality. The dam, with a hazard potential rated as high, has a satisfactory condition assessment as of January 2021. Despite its moderate risk level, the dam has a comprehensive emergency action plan in place to address any potential threats and ensure the safety of downstream communities. With its strategic location and significant storage capacity, Petrolia Dam continues to be a key asset for water resource management in the region.
In the event of an emergency or high-water event, Petrolia Dam's uncontrolled spillway and slide outlet gates are designed to handle excess water flow and mitigate potential risks. With Congressman Greg Gianforte representing the area, the dam's operations and safety measures are closely monitored to uphold environmental and public safety standards. As a critical infrastructure for irrigation and water supply, Petrolia Dam stands as a testament to effective water resource management and climate resilience efforts in Montana's rural landscape.
Year Completed |
1951 |
Dam Length |
3635 |
Dam Height |
76 |
River Or Stream |
SOUTH FORK FLATWILLOW CREEK |
Primary Dam Type |
Earth |
Surface Area |
515 |
Hydraulic Height |
59 |
Drainage Area |
612 |
Nid Storage |
14170 |
Outlet Gates |
Slide (sluice gate) |
Hazard Potential |
High |
Foundations |
Rock, Soil |
Nid Height |
76 |
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.
Petrolia