County Line Dam Reservoir Report

Last Updated: December 5, 2025

County Line Dam, located in Custer, South Dakota, is a privately owned Earth dam built in 1945 on a tributary of the Cheyenne River.


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Summary

Standing at a height of 26 feet with a length of 950 feet, the dam has a storage capacity of 780 acre-feet, with a normal storage level of 660 acre-feet. Although not rated for its condition, the dam has a low hazard potential and is regulated by the South Dakota Department of Environment and Natural Resources.

Situated in a picturesque location, County Line Dam serves as a vital water resource for the surrounding area, providing irrigation for agriculture and supporting wildlife habitats. Despite its age, the dam continues to play a crucial role in managing water flow and ensuring water security in the region. With its close proximity to the Omaha District of the US Army Corps of Engineers, the dam is subject to regular inspection and enforcement to maintain its operational integrity.

As a significant infrastructure project in the region, County Line Dam represents a historical landmark that showcases the intersection of water resource management and climate resilience. With its strategic location and impact on the local ecosystem, the dam stands as a testament to the importance of sustainable water management practices in the face of changing climate conditions. Enthusiasts and experts alike can appreciate the role of County Line Dam in safeguarding water resources and adapting to the challenges of a shifting climate landscape.

Year Completed

1945

Dam Length

950

Dam Height

26

River Or Stream

TRIBUTARY CHEYENNE RIVER

Primary Dam Type

Earth

Hydraulic Height

26

Nid Storage

780

Hazard Potential

Low

Nid Height

26
       
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.