Triple Seven No.1 Reservoir Report

Last Updated: December 5, 2025

Triple Seven No.1 is a privately owned earth dam located in Custer, South Dakota, along the TR-CHEYENNE river.


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Summary

Built in 1947, this dam stands at a height of 18 feet and has a storage capacity of 115 acre-feet, with a normal storage level of 67 acre-feet. The dam has a low hazard potential and its condition assessment is currently listed as "Not Rated".

Managed by the South Dakota Department of Environment and Natural Resources (DENR), Triple Seven No.1 is regulated, permitted, inspected, and enforced by the state. Despite its age, the dam has not been modified over the years and has not undergone a recent inspection. With a maximum discharge capacity of 2835 cubic feet per second, the dam does not have an emergency action plan (EAP) in place at this time.

Triple Seven No.1 serves as an important structure for water resource management in the area, providing storage for irrigation and other purposes. With its historical significance and continued functionality, this dam is a key piece of infrastructure in the region for both water resource and climate enthusiasts to appreciate and monitor.

Year Completed

1947

Dam Length

900

Dam Height

18

River Or Stream

TR-CHEYENNE

Primary Dam Type

Earth

Hydraulic Height

18

Nid Storage

115

Hazard Potential

Low

Nid Height

18
       
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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.