Spencer Reservoir Report

Last Updated: January 11, 2026

Spencer Dam, located in Grangeville, Idaho, is a privately owned structure regulated by the Idaho Department of Water Resources for irrigation purposes.


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Summary

The dam is situated on an unnamed stream and Threemile Creek and was completed in 1954. With a height of 15.4 feet and a storage capacity of 25 acre-feet, the dam serves as a significant asset for water resource management in the area.

Despite its age, Spencer Dam is rated in fair condition with a significant hazard potential, prompting regular inspections every four years to ensure its structural integrity. The dam features an uncontrolled spillway and no outlet gates, making it crucial for proper maintenance and risk management measures. The risk assessment for Spencer Dam is moderate, highlighting the importance of proactive strategies to address any potential issues and ensure the safety of the surrounding community.

Managed by a private entity, Spencer Dam plays a vital role in supporting irrigation activities in the region. With its stone core and earth dam type, the structure represents a blend of traditional engineering practices and modern regulatory standards enforced by the state. As water resource and climate enthusiasts, monitoring and maintaining Spencer Dam is essential to safeguarding its operational efficiency and minimizing the risk of any potential hazards in the future.

Year Completed

1954

Dam Length

650

Dam Height

15.4

River Or Stream

UNNAMED STREAM THREEMILE CREEK

Surface Area

4.7

Hydraulic Height

13.1

Drainage Area

0.2

Nid Storage

25

Outlet Gates

None

Hazard Potential

Significant

Foundations

Rock, Soil

Nid Height

15
       
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.
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