Anchor South Dam Reservoir Report

Last Updated: December 5, 2025

Anchor South Dam, located in Twin Bridges, Montana, is a privately owned structure primarily used for irrigation purposes.


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Summary

Built in 1904, this earth dam stands at a height of 11 feet and has a maximum storage capacity of 510 acre-feet. The dam spans 113 feet in length and controls the flow of Birch Creek, providing water for agricultural activities in the area.

With a high hazard potential and a moderate risk assessment rating, Anchor South Dam is regulated and inspected by the Montana Department of Natural Resources and Conservation. The dam's spillway, with a width of 6 feet, is uncontrolled, and the outlet gates are also unregulated. Despite its age, the dam's condition remains unrated, emphasizing the importance of regular inspections and maintenance to ensure its structural integrity and the safety of downstream communities.

As a vital water resource infrastructure in Beaverhead County, Anchor South Dam plays a crucial role in supporting the local agricultural economy. Its strategic location and historical significance make it a notable landmark in the area, highlighting the intersection of water resource management and climate resilience. With proper oversight and risk management measures in place, Anchor South Dam continues to serve as a cornerstone of irrigation infrastructure in Montana.

Year Completed

1904

Dam Length

113

Dam Height

11

River Or Stream

TR-BIRCH CREEK

Primary Dam Type

Earth

Surface Area

34

Hydraulic Height

8

Drainage Area

3

Nid Storage

510

Structural Height

11

Outlet Gates

Uncontrolled

Hazard Potential

High

Nid Height

11
       
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.