Legion Lake Dam Reservoir Report

Last Updated: December 5, 2025

Legion Lake Dam, located in Custer, South Dakota, is a state-regulated earth dam along Galena Creek with a height of 38 feet and a length of 207 feet.


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Summary

Completed in 1934, the dam has a storage capacity of 198 acre-feet and a maximum discharge rate of 5944 cubic feet per second. The dam is owned and managed by the state, with inspections conducted regularly to ensure its safety and regulatory compliance.

Despite being rated as having a high hazard potential, Legion Lake Dam is currently in fair condition according to its last assessment in November 2020. The dam's Emergency Action Plan (EAP) was last revised in January 2010, with updates needed to meet current guidelines. While no inundation maps or risk assessments have been prepared, the dam continues to serve its primary purpose of water resource management effectively within the region.

An important structure within the Omaha District, Legion Lake Dam stands as a crucial asset for managing water resources in the area. With its historical significance dating back to the early 20th century, the dam plays a vital role in ensuring the safety and sustainability of the surrounding community, highlighting the importance of ongoing maintenance and risk management measures to protect both the dam and the environment it serves.

Year Completed

1934

Dam Length

207

Dam Height

38

River Or Stream

GALENA CREEK

Primary Dam Type

Earth

Hydraulic Height

38

Drainage Area

2

Nid Storage

198

Hazard Potential

High

Nid Height

38
       
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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.