Horsethief Reservoir Report

Last Updated: December 19, 2025

Horsethief is a state-owned dam located in the Payette River region of Idaho, specifically in Valley County.


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Summary

Constructed in 1967, this earth dam with a stone core stands at a height of 52.6 feet and has a storage capacity of 4900 acre-feet. The dam serves multiple purposes and is regulated by the Idaho Department of Water Resources, with regular inspections and enforcement measures in place to ensure its safety and functionality.

The dam's spillway, which is uncontrolled, has a width of 17 feet and is designed to handle a maximum discharge of 310 cubic feet per second. Horsethief Dam is considered to have a significant hazard potential, but its overall condition is assessed as fair. Emergency action plans are in place, although details on their preparation and adherence to guidelines are not specified in the data. The risk assessment for the dam is moderate, with a designated risk level of 3, indicating a need for ongoing monitoring and management measures to mitigate potential hazards.

Horsethief Dam, situated along Horsethief Creek and Big Creek, plays a crucial role in water resource management in the region. With its strategic location and storage capacity, the dam contributes to irrigation, flood control, and water supply needs. Enthusiasts interested in water resources and climate will find Horsethief a captivating case study of dam infrastructure in Idaho, highlighting the importance of regulatory oversight, maintenance, and risk assessment in ensuring the safety and sustainability of water resource systems.

Year Completed

1967

Dam Length

220

Dam Height

52.6

River Or Stream

HORSETHIEF CREEK BIG CREEK

Surface Area

185

Hydraulic Height

47.5

Drainage Area

8.3

Nid Storage

4900

Outlet Gates

Slide (sluice gate)

Hazard Potential

Significant

Foundations

Rock, Soil

Nid Height

53
       
Seasonal Comparison

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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.