Big Casino Creek Dam Reservoir Report

Last Updated: December 5, 2025

Big Casino Creek Dam, located in Lewistown, Montana, was completed in 1976 and is owned by the local government.


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Summary

Designed by the USDA NRCS, this earth dam stands at a height of 68 feet and has a structural height of 80 feet, providing irrigation for the surrounding area along Big Casino Creek. With a maximum storage capacity of 2063 acre-feet and a normal storage capacity of 124 acre-feet, the dam serves multiple purposes including flood risk reduction, irrigation, and recreation.

The dam has a spillway width of 350 feet and is classified as having a high hazard potential, although its condition assessment is satisfactory. The last inspection was conducted in June 2020, with a frequency of every 5 years. The risk assessment for Big Casino Creek Dam is moderate, with a DSAC assigned date yet to be determined. This crucial infrastructure plays a vital role in water resource management in the region, ensuring a sustainable water supply for agricultural and recreational activities.

Despite being uncontrolled, the outlet gates and spillway of Big Casino Creek Dam effectively manage the flow of water, with a maximum discharge capacity of 16,000 cubic feet per second. The dam is regulated by the DNRC and falls under the jurisdiction of the state of Montana. With its strategic location and vital functions, Big Casino Creek Dam is a key component in the management of water resources and climate resilience in Fergus County, Montana.

Year Completed

1976

Dam Length

1056

Dam Height

68

River Or Stream

BIG CASINO CREEK

Primary Dam Type

Earth

Surface Area

72

Hydraulic Height

68

Drainage Area

19.82

Nid Storage

2063

Structural Height

80

Outlet Gates

Uncontrolled

Hazard Potential

High

Foundations

Rock, Soil

Nid Height

80
       
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.