Hebgen Dam Reservoir Report

Last Updated: December 5, 2025

Hebgen Dam, located in Ennis, Montana, is a captivating structure with a primary purpose of generating hydroelectric power.


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Summary

Completed in 1915, this earth dam stands at a height of 88 feet and has a structural height of 120 feet, with a reservoir capacity of 525,620 acre-feet. The dam also serves purposes such as flood risk reduction, recreation, and water supply for the surrounding area.

With a drainage area of 905 square miles and a maximum discharge capacity of 4,400 cubic feet per second, Hebgen Dam plays a crucial role in managing water resources in the region. The dam features a controlled spillway with a width of 47 feet and slide gates for outlet control. Despite its high hazard potential, the dam is inspected regularly by the Federal Energy Regulatory Commission to ensure its safety and reliability.

Surrounded by the scenic beauty of the Madison River and serving as a source of renewable energy, Hebgen Dam stands as a symbol of efficient water resource management and sustainable energy generation. Its strategic location and design make it a vital piece of infrastructure that contributes to the overall well-being of the community while preserving the natural environment.

Year Completed

1915

Dam Length

721

Dam Height

88

River Or Stream

Madison River

Primary Dam Type

Earth

Surface Area

13000

Hydraulic Height

75

Drainage Area

905

Nid Storage

525620

Structural Height

120

Outlet Gates

Slide (sluice gate) - 4

Hazard Potential

High

Nid Height

120
       
Seasonal Comparison

Weather Forecast

Dam Data Reference

Condition Assessment

Satisfactory
No 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

High
Dams 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.