Thelma #1 Reservoir Report

Last Updated: December 5, 2025

Thelma #1 is a privately owned Earth dam located in Emigrant, Montana, along the TR-Yellowstone River.


°F

°F

mph

Wind

%

Humidity

Summary

Designed by the USDA NRCS and completed in 1962, this dam primarily serves the purpose of irrigation and has a storage capacity of 106 acre-feet. With a low hazard potential and a height of 19 feet, Thelma #1 plays a crucial role in water resource management in the area.

Managed by the DNRC and regulated by the state of Montana, Thelma #1 is subject to regular inspections and enforcement to ensure its safety and functionality. Although its condition is currently not rated, the dam has not undergone any modifications and continues to operate within its design parameters. With a maximum discharge of 120 cubic feet per second, Thelma #1 remains a vital piece of infrastructure for the surrounding agricultural community.

As a key component of the irrigation system in Park County, Thelma #1 provides essential water resources for local farmers and ranchers. Its location along the Yellowstone River and its storage capacity make it a valuable asset for mitigating drought and ensuring a reliable water supply for the region. Climate and water resource enthusiasts can appreciate the role that Thelma #1 plays in sustainable water management practices in Montana.

Year Completed

1962

Dam Length

211

Dam Height

19

River Or Stream

TR-YELLOWSTONE RIVER

Primary Dam Type

Earth

Hydraulic Height

19

Nid Storage

106

Hazard Potential

Low

Nid Height

19
       
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.