Big John M
Key Takeaway
Big John M is classified as low hazard in Montana. It was completed in 1972 and is 54 years old. Its primary use is irrigation.
Physical Details
| Dam Height | 52 ft (taller than 97% in MT) |
| Dam Length | 210 ft |
| Dam Type | Earth |
| Max Storage | 1.0K acre-ft |
| Normal Storage | 281 acre-ft |
| Drainage Area | 1 sq mi |
| Max Discharge | 2,250 cfs |
| Year Completed | 1972 (54 years old) |
| NID ID | MT03096 |
Safety Information
No probable loss of human life and low economic/environmental losses expected.
Hazard potential describes downstream consequences of failure, not the dam's current condition. What does this mean?
Ownership
CJ/MARALYN MONTGOMERY
Private
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Low Hazard 22 ftFrequently Asked Questions
What is the hazard classification of Big John M?
Big John M is classified as Low Hazard. No probable loss of human life and low economic/environmental losses expected. This classification refers to the potential downstream consequences of a failure, not the dam's current structural condition.
Who owns and operates Big John M?
Big John M is owned by CJ/MARALYN MONTGOMERY (Private). The owner is responsible for maintenance, inspections, and compliance with dam safety regulations.
When was Big John M built?
Big John M was completed in 1972, making it 54 years old. Many U.S. dams were built between the 1930s and 1970s during a period of major infrastructure investment.
What is the primary purpose of Big John M?
Big John M serves the following purposes: Irrigation. Many dams in the U.S. are multi-purpose, supporting flood control, water supply, recreation, and other uses.
How tall is Big John M?
Big John M has a dam height of 52 ft. Dam height is measured from the natural streambed at the downstream toe to the top of the dam, and may differ from the visible height.