Milner Dam-Middle Reservoir Report

Last Updated: December 13, 2025

Milner Dam-Middle, located in Twin Falls, Idaho along the Snake River, is a rockfill dam with a height of 80 feet and a storage capacity of 39,000 acre-feet.


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Summary

Originally completed in 1905, the dam serves primarily for irrigation purposes but also supports hydroelectric power generation and recreational activities. With a significant hazard potential and a very high risk assessment rating, Milner Dam-Middle is regulated by the Federal Energy Regulatory Commission and inspected regularly to ensure safety and compliance with state regulations enforced by the Idaho Department of Water Resources.

Managed by a private owner, Milner Dam-Middle underwent rehabilitation in 1992 by Morrison Knudsen, with the original construction designer unknown. The dam features a controlled spillway with a width of 667 feet and five Tainter (radial) outlet gates. The surrounding area encompasses a surface area of 4,000 acres and a drainage area of 17,180 square miles. Recognized for its critical role in water resource management, Milner Dam-Middle plays a vital part in sustaining agriculture and supporting local communities in the region.

As a key structure in the water infrastructure system, Milner Dam-Middle plays a crucial role in maintaining water supply reliability and supporting the local economy. With its historic significance and ongoing importance in water resource management, the dam serves as a focal point for water resource and climate enthusiasts interested in understanding the intersection of water management, infrastructure development, and environmental stewardship in the region.

Year Completed

1905

Dam Length

404

Dam Height

80

River Or Stream

Snake River

Primary Dam Type

Rockfill

Surface Area

4000

Hydraulic Height

75.5

Drainage Area

17180

Nid Storage

39000

Structural Height

80

Outlet Gates

Tainter (radial) - 5

Hazard Potential

Significant

Nid Height

80
       
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.