South Fork Detention Dam Reservoir Report

Last Updated: December 5, 2025

South Fork Detention Dam, located in Custer, Idaho, is a gravity dam primarily owned and managed by the Bureau of Land Management for flood risk reduction in the Bradshaw Basin area.


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Summary

The dam stands at a structural height of 31 feet, with a hydraulic height of 26 feet, and a length of 340 feet. It has a storage capacity of 30 acre-feet, with a normal storage of 24 acre-feet, covering a surface area of 24 acres and draining a 3.9 square mile watershed.

Although the dam has a low hazard potential and is considered to be in moderate risk condition, it has not been rated for its condition assessment. The last inspection was conducted in July 2012, with an inspection frequency of 5 years. The spillway type is uncontrolled with a width of 2 feet, and the maximum discharge capacity is 220 cubic feet per second. Despite its relatively small size and limited functionality, South Fork Detention Dam plays a crucial role in mitigating flood risks in the region and protecting the surrounding rural ranch community.

Overall, South Fork Detention Dam serves as a vital infrastructure for flood control in the Bradshaw Basin, with the Bureau of Land Management overseeing its operation, maintenance, and regulatory compliance. While its risk assessment indicates moderate concerns, the dam's low hazard potential suggests that it poses minimal threat to downstream areas. With its strategic location and purposeful design, South Fork Detention Dam stands as a testament to efficient water resource management and climate adaptation efforts in Idaho.

Dam Length

340

River Or Stream

BRADSHAW BASIN

Primary Dam Type

Gravity

Surface Area

24

Hydraulic Height

26

Drainage Area

3.9

Nid Storage

30

Structural Height

31

Hazard Potential

Low

Foundations

Unlisted/Unknown

Nid Height

31
       
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.